Damage Mechanisms Affecting Fixed Equipment in the Refining Industry

Damage Mechanisms Affecting 

Fixed Equipment in the 

Refining Industry 

影响炼油行业固定设备的 

损伤机理 

2013 年内部培训

Charlie Chong/ Fion Zhang 

中国固有领土 : 钓鱼岛

印度支那不就是 “Indo-China” 吗 ?, 中华人民共和国不就是 “People Republic of China”. 这 “China” 或 

“ 支那 ” 不是歧视字眼 .“ 支那 ” 是个威震四方的大国 , 以前郑和下西洋的 “ 支那 “ 这是闻之丧胆字眼 , 现在 

我们也不渐渐变成 ” 强大支那 ” 了吗 ?. 小的时候 (40 年前 ), 友族 , 善意的叫我 “ 中华人 ”, 我很善意的告诉 

他 , 我叫 “ 支那人 ”, 虽然我只是东南亚华裔 , 但我永远以 “ 支那 -China" 引以为荣 . 我爱中国 , 我爱 "China" 

我爱 " 支那 ". 

http://news.ifeng.com/world/detail_2014_03/20/34944726_0.shtml 

中国固有领土 : 钓鱼岛 

Charlie Chong/ Fion Zhang

影响炼油行业固定设备的 

损伤机理 -2013 年内部培训 

http://www.smt.sandvik.com/en/search/?q=stress+corrosion+cracking

Speaker: Fion Zhang 

2013/7/4

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For API 510 ICP - API RP 571, Damage mechanisms Affecting Fixed 

equipment in the Refining Industry ATTN: Examination questions will be based on 

the following sections only: 

Par. 3. – Definitions (included as a frame of reference only) 

4.2.3 – Temper Embrittlement 

4.2.7 – Brittle Fracture 

4.2.9 – Thermal Fatigue 

4.2.14 – Erosion/Erosion-Corrosion 

4.2.16 – Mechanical Failure 

4.3.2 – Atmospheric Corrosion 

4.3.3 – Corrosion Under Insulation (CUI) 

4.3.4 – Cooling Water Corrosion 

4.3.5 – Boiler Water Condensate Corrosion 

4.3.10 – Caustic Corrosion 

4.4.2 – Sulfidation 

4.5.1 – Chloride Stress Corrosion Cracking (Cl-SCC) 

4.5.2 – Corrosion Fatigue 

4.5.3 – Caustic Stress Corrosion Cracking (Caustic Embrittlement) 

5.1.2.3 – Wet H2S Damage (Blistering / HIC/ SOHIC/ SSC) 

5.1.3.1 – High Temperature Hydrogen Attack (HTHA)

For API 570 ICP - API RP 571, Damage mechanisms Affecting Fixed 

equipment in the Refining Industry ATTN: Examination questions will be based on 

the following sections only: 

Par. 3 – Definitions (included as a frame of reference only) 



4.2.14 – Erosion/Erosion Corrosion 

4.2.16 – Mechanical Fatigue 

4.2.17 – Vibration-Induced Fatigue 

4.3.1 – Galvanic Corrosion 




4.3.7 – Flue Gas Dew Point Corrosion 

4.3.8 – Microbiological Induced Corrosion (MIC) 

4.3.9 – Soil Corrosion 



4.5.3 – Caustic Stress corrosion Cracking (Caustic Embrittlement) 

5.1.3.1 – High Temperature Hydrogen Attack (HTTA)

BODY OF KNOWLEDGE 

API-510 PRESSURE VESSEL INSPECTOR 

CERTIFICATION EXAMINATION 

August 2010 (Replaces January 2009)

API RP 571, Damage Mechanisms Affecting Fixed equipment in the Refining Industry 

ATTN: API 510 Test questions will be based on the following mechanisms only: 

Par. 3. - Definitions (included as a frame of reference only) 

1. 4.2.3 – Temper Embrittlement 

2. 4.2.7 – Brittle Fracture 

3. 4.2.9 – Thermal Fatigue 

4. 4.2.14 – Erosion/Erosion-Corrosion 

5. 4.2.16 – Mechanical Failure 

6. 4.3.2 – Atmospheric Corrosion 

7. 4.3.3 – Corrosion Under Insulation (CUI) 

8. 4.3.4 – Cooling Water Corrosion 

9. 4.3.5 – Boiler Water Condensate Corrosion 

10. 4.3.10 – Caustic Corrosion 

11. 4.4.2 – Sulfidation 

12. 4.5.1 – Chloride Stress Corrosion Cracking (Cl-SCC) 

13. 4.5.2 – Corrosion Fatigue 

14. 4.5.3 – Caustic Stress Corrosion Cracking (Caustic Embrittlement) 

15. 5.1.2.3 – Wet H2S Damage (Blistering/HIC/SOHIC/SCC) 

16. 5.1.3.1 – High Temperature Hydrogen Attack (HTHA)

BODY OF KNOWLEDGE 

API-570 AUTHORIZED PIPING INSPECTOR 

CERTIFICATION EXAMINATION 

August 2010 (Replaces June 2007)

API RP 571, Damage mechanisms Affecting Fixed equipment in the Refining Industry 

ATTN: API 570 Examination questions will be based on the following sections only: 

Par. 3 – Definitions (included as a frame of reference only) 

1. 4.2.7 – Brittle Fracture 

2. 4.2.9 – Thermal Fatigue 

3. 4.2.14 – Erosion/Erosion Corrosion 

4. 4.2.16 – Mechanical Fatigue 

5. 4.2.17 – Vibration-Induced Fatigue 

6. 4.3.1 – Galvanic Corrosion 

7. 4.3.2 – Atmospheric Corrosion 

8. 4.3.3 – Corrosion Under Insulation (CUI) 

9. 4.3.5 – Boiler Water Condensate Corrosion 

10. 4.3.7 – Flue Gas Dew Point Corrosion 

11. 4.3.8 – Microbiological Induced Corrosion (MIC) 

12. 4.3.9 – Soil Corrosion 

13. 4.4.2 – Sulfidation 

14. 4.5.1 – Chloride Stress Corrosion Cracking (Cl-SCC) 

15. 4.5.3 – Caustic Stress corrosion Cracking (Caustic Embrittlement)

2013- API570 Examination 

Par. 3 – Definitions 















4.5.3 – Caustic Stress corrosion Cracking 

5.1.3.1 – High Temperature Hydrogen Attack (HTTA) 

2013-API510 Examination 

Par. 3. - Definitions 














4.5.3 – Caustic Stress Corrosion Cracking 

5.1.2.3 – Wet H2S Damage (Blister/HIC/SOHIC/SCC) 


Mechanical and Metallurgical Failure Mechanisms 

机械和冶金失效机理 

Graphitisation 石墨化 

800 o F for C Steel 

Plain carbon steel 

875 o F for C ½ Mo Steel 

C- ½ Mo 

Spheroidisation 碳化物球状 

850 o F ~ 1400 o F 

Low alloy steel up to 9% Cr 

API510 

Tempered Embrittlement 

650 o F~ 1070 o F 

2 ¼ Cr-1Mo low alloy steel, 3Cr- 

回火脆性 

1Mo (lesser extent), & HSLA Cr- 

Mo-V rotor steels 

Strain Aging 延伸时效 

Intermediate temperature 

Pre-1980’s C-steels with a large 

grain size and C- ½ Mo 

885 o F embrittlement 脆性 

600 o F~ 1000 o F 

300, 400 & Duplex SS containing 

ferrite phases 

Sigma-Phase 

1000 o F~ 1700 o F 


Embrittlement 


σ 相脆化 

API510 

Brittle Fracture 

Below DTBTT 

C, C- ½ Mo, 400 SS

Creep & stress rupture 

700 o F ~ 1000 o F 

All metals and alloys 

蠕变和应力断裂 

API510 

Thermal fatigues 

Operating temperature 

All materials of construction 

Short Term Overheating – 

>1000 o F 

All fired heater tube materials and 

Stress Rupture 

common materials of construction 

短期过热 – 应力破裂 

Steam Blanketing 蒸汽遮盖 

>1000 o F 

Carbon steel and low alloy steels 

Dissimilar Metal Weld (DMW) 


Carbon steel / 300 SS junction 

Cracking 

Thermal Shock 温度突然变 

Cold liquid impinge on hot 

All metals and alloys. 

surface 

Flue-gas dew-point 

H 2 

SO 4 

-280 o F (138 o C), 

CS, low alloy and 300 SS 

corrosion 

HCL-130 o F (54 o C). 

CUI 

10 o F (–12 0 C) and 350 o F 

C-Steel and low alloy steel 

(175 o C) 

140 o F (60 o C) and 400 o F 

austenitic stainless steels and 

(205 o C) 

duplex stainless steels

High Temperature Corrosion [>400 o F (204 o C)] 

Oxidation 

CS - >1000 o F (538 o C) 


氧化 

300SS- >1500 o F (816 o C). 

API510 

Sulfidation 

Iron based alloy 500 o F (260 o C). 


硫腐蚀 

Others ? 

Carburization 

>1100 o F (593 o C) 


渗碳 

Decarburization 

? 

CS and low alloy steel 

脱碳 

Metal dusting 

900 o F ~1500 o F(482 o C~ 816 o C) 


金属尘化 

Fuel ash corrosion 

> 700 o F(371 o C), varies with melting 


燃料灰腐蚀 

point of salts formed. 

Nitriding 

>600 o F (316 o C) 

Carbon steels, low alloy steels, 300 

渗氮 

Series SS and 400 Series SS

今日课程 : 

0900~1130hrs 

第一篇 : 第一章至第三章 - 大纲与定义 

第二篇 : 第四章 - 一般损伤机制 - 所有行业 

1300~1700hrs 

第三篇 : 第五章 - 炼油行业损坏机理 

第四篇 : Q&A 问与答

FOREWORD 前言 

The overall purpose of this document is to present information 

on equipment damage mechanisms in a set format to assist the 

reader in applying the information in the inspection and 

assessment of equipment from a safety and reliability standpoint. 

本文件的总体目标 

从安全性和可靠性的角度 , 用预设的文件格式 , 提供设备损坏机理 

信息 , 以协助读者应用此信息协助设备的 (1) 检查和 (2) 评估 .

这份文件反映了行业信息 , 但它不是一个强制性的标准或规范 . 这作业指导 

“Recommended practice 571” 是作为 API 检验规范如 API 510, API 570, 

API 653 和执行基于风险的检验 API 580/API 581 提供有用的信息 

本出版物中包含的综合指导 , 考虑的事项有 : 

• 可能会影响工艺设备的损伤机理实用信息 , 

• 设备上 , 有关可以预测到的损伤类型和损害程度 , 

• 如何从这些知识帮助选择正确的选择检验方法来 

发现 / 鉴定与检测尺寸 .

This publication contains guidance for the combined considerations of: 

• Practical information on damage mechanisms that can affect 

process equipment, 影响设备损坏机理的实用信息 , 

• Assistance regarding the type and extent of damage that can be 

expected, and 协助确定设备潜在的损伤类别与损伤程度 , 

• How this knowledge can be applied to the selection of effective 

inspection methods to detect size and characterize damage. 

通过上述的知识确定如何选用真确的探测方法来对损伤定型与定量 .

值得留意的是此文件 API571 没提到 : 材料选择作为损坏机理的防范 . 同样 

的是 , 在 ASME B31.3 300(6) Compatibility of materials with the service 

and hazards from instability of contained fluids are not within the scope 

of this Code. See para. F323. 材料的兼容性对因所含流体 ( 媒介 ) 不稳定造 

成的危害 , 不在本规范范围内 .

Table of contents 目录 

1.0 Introduction and scope 简介及范围 

2.0 References 参考 

3.0 Definition of terms and abbreviations 

定义 , 术语和缩略语 

4.0 General damage mechanisms – all industries 

一般损伤机制 - 所有行业 

5.0 Refining industry damage mechanisms 

炼油行业损坏机理 

Appendix a – technical inquiries 

附录 A - 技术咨询

SECTION 1.0 

Introduction and scope 

简介及范围

1.1 Introduction 序言 

ASME 和 API 加压设备的设计规范和标准 - 提供设计 , 制造 , 检验和测试 “ 新的 ” 压力 

容器 , 管道系统和储罐的规则 . 这些规范不解决设备在服务期间设备的老化 , 腐蚀 , 

损坏等的考虑 . 这 RP 主要针对在役设备上述信息 . 

在执行适用性评价 (FFS), 基于风险的检验 (RBI), 也提供需要的信息 . 因为 : 

• 进行 FFS/ API RP 579- FFS 评估第一步是确定 (1) 缺陷类型和 (2) 损坏的原因 . 

• 基于风险的检验 (RBI) 第一个步骤也是正确的识别系统设备损伤机理或其他形 

式的恶化原因 .

当进行 FFS/RBI 评估时也作为重点 : 

• 观察到的或预测的损坏的原因 

• 未来进一步损坏的可能性和损坏程度 

化工设施的材料 / 环境条件相互作用非常多样化 . 许多不同的处理单元各有其 

自身的进取过程 , 媒介组合 , 不同的温度 / 压力条件这些不确定因素带给 FFS/RBI 

评估带来一些难度 .

当设备观察到的缺陷时 , 这缺陷可能是 : 

• 使用前新建造 , 本来缺陷 , 

• 在职服务导致的后来缺陷 . 

在役服务导致的后来缺陷原因有 : 

• 设计不足的因素 -( 包括材料的选择和缺乏设计详细考虑 ) 

• 设备运行中的腐蚀性的环境 / 条件引起 -( 正常的服务或瞬态期间 )

In general, the following types of damage are encountered in 

petrochemical equipment: 化工设备一般损伤类型 

1. General and local metal loss due to corrosion and/or erosion, 

由于腐蚀和 / 或侵蚀均匀与局部金属减薄 

2. Surface connected cracking, 表面连接开裂 

3. Subsurface cracking, 内表面开裂 

4. Microfissuring/microvoid formation, 微裂纹 / 微孔形成 

5. Metallurgical changes. 金相变化

基于外观或形态 , 损伤分类

SECTION 4.0 

GENERAL DAMAGE MECHANISMS – ALL INDUSTRIES 


4.2 Mechanical and Metallurgical Failure Mechanisms. 机械和冶金失效机制 

4.3 Uniform or Localized Loss of Thickness. 均衡或局部厚度亏损 

4.4 High Temperature Corrosion [400°F (204°C)]. 高温腐蚀 

4.5 Environment Assisted Cracking. 环境辅助开裂 

SECTION 5.0 

REFINING INDUSTRY DAMAGE MECHANISMS 

炼油工业的损伤机制 

5.1.1 Uniform or Localized Loss in Thickness Phenomena 

均匀或局部现象损失厚度 

5.1.2 Environment-Assisted Cracking 环境辅助开裂 

基于引发因素 , 损伤分类

General and local metal loss/ 均匀与局部减薄

General and local metal loss/ 

均匀与局部减薄




Surface connected cracking













SCC or fatigue cracks 

nucleate at stress 

concentration points 

SCC cracks have 

highly branch 

Corrosion fatigue cracks 

have little branching 


subsurface cracking





Microfissuring/microvoid formation

Microfissuring/microvoid formation 

http://www.aws.org/wj/supplement/WJ_1985_04_s91.pdf

Microfissuring/microvoid formation 

http://www.aws.org/wj/supplement/WJ_1985_04_s91.pdf

Metallurgical changes





Each of these general types of damage may be caused by a single or 

multiple damage mechanisms. In addition, each of the damage 

mechanisms occurs under very specific combinations of materials, 

process environments, and operating conditions. 

每个损伤 , 可能是由一个或多个损坏机理造成 . 每一个损伤机制有非常具 

体的 (1) 材料 (2) 过程环境和 (3) 操作条件 , 的组合下发生 .

1.2 Scope 范围 

This recommended practice provides general guidance as to the most likely 

damage mechanisms affecting common alloys used in the refining and 

petrochemical industry and is intended to introduce the concepts of serviceinduced 

deterioration and failure modes. These guidelines provide 

information that can be utilized by plant inspection personnel to assist in 

identifying likely causes of damage; to assist with the development of 

inspection strategies; to help identify monitoring programs to ensure 

equipment integrity. 此规范对石油化工行业常用材料在役损蚀与失效最可能的 

损坏机理一般指导 . 协助检验人员识别可能导致伤害的原因 , 从而确定检测策略 , 

以确保设备的完整性 . 

The summary provided for each damage mechanism provides the 

fundamental information required for an FFS assessment performed in 

accordance with API 579-1/ASME FFS-1 or an RBI study performed in 

accordance with API RP 580. 每个损伤机理的总结作为提供 RBI/FFS 评估所需 

的基本信息 .

API571, 此规范对石油化工行业常用材料在役损蚀与失效最可 

能的损坏机理一般指导 . 协助检验人员识别可能导致伤害的原 

因 , 从而确定检测策略 , 以确保设备的完整性 .

1.3 Organization and Use 格式和使用 

The information for each damage mechanism is provided in a set 

format as shown below. This recommended practice format facilitates 

use of the information in the development of inspection programs, FFS 

assessment and RBI applications. 

为了协助 (1) 检验计划的开发 / (2) FFS 使用性评估 (3) RBI 基于风险分析 

检验的运用 , 个别的损坏机理的信息提供的格式如下 :

a) Description of Damage – a basic description of the damage mechanism. 

损伤机理的基本描述 

b) Affected Materials – a list of the materials prone to the damage 

mechanism. 受影响的材料 

c) Critical Factors – a list of factors that affect the damage mechanism (i.e. 

rate of damage). 破坏机理的影响因素列表 

d) Affected Units or Equipment – a list of the affected equipment and/or 

units where the damage mechanism commonly occurs is provided. 

受影响的单元或设备 

e) Appearance or Morphology of Damage – a description of the damage 

mechanism, with pictures in some cases, to assist with recognition of the 

damage. 外观或损伤形态学 .

f) Prevention / Mitigation – methods to prevent and/or mitigate 

damage. 预防 / 缓解 

g) Inspection and Monitoring – recommendations for NDE for detecting 

and sizing the flaw types associated with the damage mechanism. 

检查和监测 

h) Related Mechanisms – a discussion of related damage mechanisms. 

相关的损伤机理讨论 

i) References – a list of references that provide background and other 

pertinent information. 参考 .

Damage mechanisms that are common to a variety of industries including 

refining and petrochemical, pulp and paper, and fossil utility are covered in 

Section 4.0. 通用炼油化工 , 纸浆和纸张 , 以及石化设施 - 损坏机理信息 

Damage mechanisms that are specific to the refining and petrochemical 

industries are covered in Section 5. 专门针对炼油和石化工业 - 损坏机理信息 

In addition, process flow diagrams are provided in 5.2 to assist the user in 

determining primary locations where some of the significant damage 

mechanisms are commonly found. 5.2 提供了一些工艺流程图主要的单元常见 

的一些重大损害机理 .

• 提供损伤机理作为定性定量的信息 

• 提供损伤机理作为 FFS/RBI 评估有用的信息 

• 提供损伤机理作为 API510/ 570/ 653 在职设备检验有用的信息 

• 损伤机理可以分为 5 大类型 

• 设备损伤发现可能是源于新建或在职服务导致 .

SECTION 2.0 

REFERENCES 

2.1 Standards 

2.2 Other References

2.1 Standards 

API 

• API 530 Pressure Vessel Inspection Code 

• Std. 530 Calculation of Heater Tube Thickness in Petroleum Refineries 

• RP 579 Fitness-For-Service 

• Publ. 581 Risk-Based Inspection - Base Resource Document 

• Std. 660 Shell and Tube Heat Exchangers for General Refinery Service 

• RP 751 Safe Operation of Hydrofluoric Acid Alkylation Units 

• RP 932-B Design, Materials, Fabrication, Operation and Inspection 

Guidelines for Corrosion Control in Hydroprocessing Reactor Effluent Air 

Cooler (REAC) Systems 

• RP 934 Materials and Fabrication Requirements for 2-1/4 Cr-1Mo & 3Cr- 

1Mo Steel Heavy Wall Pressure Vessels for High Temperature, High 

Pressure Service 

• RP 941 Steels for Hydrogen Service at Elevated Temperatures and 

Pressures in Petroleum Refineries and Petrochemical Plants 

• RP 945 Avoiding Environmental Cracking in Amine Units

ASM 

• Metals Handbook Volume 1, Properties and Selection: Iron, Steels, and 

High-Performance Alloys; 

• Volume 13, Corrosion in Petroleum Refining and Petrochemical Operations; 

• Volume 11, Failure Analysis and Prevention 

ASME 

• Boiler and Pressure Vessel Code Section III, Division I, Rules for 

Construction of Nuclear Power Plant Components; Section VIII, Division I, 

Pressure Vessels. 

ASTM 

• MNL41 Corrosion in the Petrochemical Industry 

• STP1428 Thermo-mechanical Fatigue Behavior of Materials 

BSI 

• BSI 7910 Guidance on Methods for Assessing the Acceptability of Flaws in 

Fusion Welded Structures 

MPC 

• Report FS-26 Fitness-For Service Evaluation Procedures for Operating 

Pressure Vessels, Tanks and Piping in Refinery and Chemical Service

NACE 

• Std. MR 0103 Materials Resistant to Sulfide Stress Cracking in Corrosive 

Petroleum Refining Environments” 

• RP 0169 Standard Recommended Practice: Control of External Corrosion on 

Underground or Submerged Metallic Piping Systems 

• RP 0170 Protection of Austenitic Stainless Steels and Other Austenitic Alloys from 

Polythionic Acid Stress Corrosion Cracking during Shutdown of Refinery 

Equipment 

• RP 0198 The Control of Corrosion Under Thermal Insulation, and Fireproofing – A 

Systems Approach 

• RP 0294 Design, Fabrication, and Inspection of Tanks for the Storage of 

Concentrated Sulfuric Acid and Oleum at Ambient Temperatures 

• RP 0296 Guidelines for Detection, Repair and Mitigation of Cracking of Existing 

Petroleum Refinery Pressure Vessels in Wet H 2 

S Environments 

• RP 0472 Methods and Controls to Prevent in-Service Environmental Cracking of 

Carbon Steel Weldments in Corrosive Petroleum Refining Environments 

• Publ. 5A151 Materials of Construction for Handling Sulfuric Acid 

• Publ. 5A171 Materials for Receiving, Handling, and Storing Hydrofluoric Acid 

• Publ. 8X194 Materials and Fabrication

WRC 

• Bulletin 32 Graphitization of Steel in Petroleum Refining Equipment and 

the Effect of Graphitization of Steel on Stress-Rupture Properties 

• Bulletin 275 The Use of Quenched and Tempered 2-1/4Cr-1Mo Steel for 

Thick Wall Reactor Vessels in Petroleum Refinery Processes: An 

Interpretive Review of 25 Years of Research and Application 

• Bulletin 350 Design Criteria for Dissimilar Metal Welds 

• Bulletin 409 Fundamental Studies Of The Metallurgical Causes And 

Mitigation Of Reheat Cracking In 1¼Cr-½Mo And 2¼Cr-1Mo Steels 

• Bulletin 418 The Effect of Crack Depth (a) and Crack-Depth to Width Ratio 

(a/W) on the Fracture Toughness of A533-B Steel 

• Bulletin 452 Recommended Practices for Local Heating of Welds in 

Pressure Vessels

2.2 Other References 

A list of publications that offer background and other information pertinent 

to the damage mechanism is provided in the section covering each 

damage mechanism.

SECTION 3.0 

DEFINITION OF TERMS AND 

ABBREVIATIONS 

3.1 Terms 

3.2 Symbols and Abbreviations

3.1 Terms 

3.1.1 Austenitic 奥氏体 – a term that refers to a type of metallurgical structure 

(austenite) normally found in 300 Series stainless steels and nickel base alloys. 

3.1.2 Austenitic stainless steels 奥氏体系不锈钢 – the 300 Series stainless steels 

including Types 304, 304L, 304H, 309, 310, 316, 316L, 316H, 321, 321H, 347, 

and 347H. The “L” and “H” suffixes refer to controlled ranges of low and high 

carbon content, respectively. These alloys are characterized by an austenitic 

structure. 

3.1.3 Carbon steel 碳素钢 – steels that do not have alloying elements intentionally 

added. However, there may be small amounts of elements permitted by 

specifications such as SA516 and SA106, for example that can affect corrosion 

resistance, hardness after welding, and toughness. Elements which may be found 

in small quantities include Cr, Ni, Mo, Cu, S, Si, P, Al, V and B.

3.1.4 Di-ethanolamine 二乙醇胺 (DEA) – used in amine treating to remove 

H2S and CO2 from hydrocarbon streams. 

3.1.5 Duplex stainless steel 双相不锈钢 – a family of stainless steels that contain 

a mixed austenitic-ferritic structure including Alloy 2205, 2304, and 2507. The 

welds of 300 series stainless steels may also exhibit a duplex structure. 

3.1.6 Ferritic 铁素体 – a term that refers to a type of metallurgical structure 

(ferrite) normally found in carbon and low alloy steels and many 400 series 

stainless steels. 

3.1.7 Ferritic stainless steels 铁素体不锈钢 – include Types 405, 409, 430, 442, 

and 446. 

3.1.8 Heat Affected Zone (HAZ) – the portion of the base metal adjacent to a 

weld which has not been melted, but whose metallurgical microstructure and 

mechanical properties have been changed by the heat of welding, sometimes 

with undesirable effects.

Add Nickel 

Add Nickel 

0% Nickel-Ferrite 

铁素体 

5% Nickel-Duplex 

双相 ( 铁素 / 奥氏体 ) 

>8% Nickel-Austenite 

奥氏体

The 1949 Schaeffler diagram



http://www.intechopen.com/books/environmental-and-industrial-corrosion-practical-and-theoreticalaspects/corrosion-behaviour-of-cold-deformed-austenitic-alloys

3.1.9 Hydrogen Induced Cracking (HIC) 氢致开裂 – describes stepwise internal 

cracks that connect adjacent hydrogen blisters on different planes in the metal, or 

to the metal surface. No externally applied stress is needed for the formation of 

HIC. The development of internal cracks (sometimes referred to as blister cracks) 

tends to link with other cracks by a transgranular plastic shear mechanism 

because of internal pressure resulting from the accumulation of hydrogen. The 

link-up of these cracks on different planes in steels has been referred to as 

stepwise cracking to characterize the nature of the crack appearance. 

3.1.10 Low alloy steel 低合金结构钢 – a family of steels containing up to 9% 

chromium and other alloying additions for high temperature strength and creep 

resistance. The materials include C-0.5Mo, Mn-0.5Mo, 1Cr-0.5Mo, 1.25 Cr-0.5Mo, 

2.25Cr-1.0Mo, 5Cr-0.5Mo, and 9Cr-1Mo. These are considered ferritic steels.

3.1.11 Martensitic 马氏体 – a term that refers to a type of metallurgical 

structure (martensite) normally found in some 400 series stainless steel. 

Heat treatment and or welding followed by rapid cooling 

can produce this structure in carbon and low alloy steels.

3.1.12 Martensitic stainless steel – include Types 410, 410S, 416, 420, 440A, 

440B, and 440C. 

3.1.13 Methyldiethanolamine (MDEA) – used in amine treating to remove H 2 S 

and CO 2 from hydrocarbon streams. 

3.1.14 Monoethanolamine (MEA) – used in amine treating to remove H 2 S and 

CO 2 from hydrocarbon streams. 

3.1.15 Nickel base alloy– a family of alloys containing nickel as a major 

alloying element ( Ni>30% ) including Alloys 200, 400, K-500, 800, 800H, 825, 

600, 600H, 617, 625, 718, X-750, and C276.

3.1.16 Stress oriented hydrogen induced cracking (SOHIC) 应力导向氢致开裂 – 

describes an array of cracks, aligned nearly perpendicular to the stress, that are 

formed by the link-up of small HIC cracks in steel. Tensile strength (residual or 

applied) is required to produce SOHIC. SOHIC is commonly observed in the base 

metal adjacent to the Heat Affected Zone (HAZ) of a weld, oriented in the throughthickness 

direction. SOHIC may also be produced in susceptible steels at other 

high stress points, such as from the tip of the mechanical cracks and defects, or 

from the interaction among HIC on different planes in the steel. 

3.1.17 Stainless steel 不锈钢 – there are four categories of stainless steels that are 

characterized by their metallurgical structure at room temperature: austenitic, 

ferritic, martensitic and duplex. These alloys have varying amounts of chromium 

and other alloying elements that give them resistance to oxidation, sulfidation and 

other forms of corrosion depending on the alloy content.

3.2 Symbols and Abbreviations 

3.2.1 ACFM – alternating current magnetic flux leakage testing. 

3.2.2 AE – acoustic emission. 

3.2.3 AET – acoustic emission testing. 

3.2.4 AGO – atmospheric gas oil. 

3.2.5 AUBT – automated ultrasonic backscatter testing. 

3.2.6 BFW – boiler feed water. 

3.2.7 C 2 

– chemical symbol referring to ethane or ethylene. 

3.2.8 C 3 

– chemical symbol referring to propane or propylene. 

3.2.9 C 4 

– chemical symbol referring to butane or butylenes. 

3.2.10 Cat – catalyst or catalytic. 

3.2.11 CDU – crude distillation unit. 

3.2.12 CH 4 

– methane. 

3.2.13 CO – carbon monoxide. 

3.2.14 CO 2 

– carbon dioxide. 

3.2.15 CVN – charpy v-notch.

3.2.16 CW – cooling water. 

3.2.17 DIB – deisobutanizer. 

3.2.18 DNB – Departure from Nucleate Boiling. 

3.2.19 DEA – diethanolamine, used in amine treating to 

remove H 2 

S and CO 2 

from hydrocarbon streams. 

3.2.20 EC – eddy current, test method applies primarily to nonferromagnetic 

materials. 

3.2.21 FCC – fluid catalytic cracker. 

3.2.22 FMR – field metallographic replication. 

3.2.23 H 2 

– hydrogen. 

3.2.24 H 2 

O – also known as water. 

3.2.25 H 2 

S – hydrogen sulfide, a poisonous gas. 

3.2.26 HAZ – Heat Affected Zone 

3.2.27 HB – Brinnell hardness numbe 

3.2.28 HCO – heavy cycle oil. 

3.2.29 HCGO – heavy coker gas oil. 

3.2.30 HIC – Hydrogen Induced Cracking 

571-3 


3.2.31 HP – high pressure. 

3.2.32 HPS – high pressure separator. 

3.2.33 HVGO – heavy vacuum gas oil. 

3.2.34 HSLA – high strength low alloy. 

3.2.35 HSAS – heat stable amine salts. 

3.2.36 IC4 – chemical symbol referring isobutane. 

3.2.37 IP – intermediate pressure. 

3.2.38 IRIS – internal rotating inspection system. 

3.2.39 K.O. – knock out, as in K.O. Drum. 

3.2.40 LCGO – light coker gas oil. 

3.2.41 LCO – light cycle oil. 

3.2.42 LP – low pressure. 

3.2.43 LPS – low pressure separator. 

3.2.44 LVGO – light vacuum gas oil. 

3.2.45 MDEA – methyldiethanolamine. 

3.2.46 MEA – monoethanolamine. 

3.2.47 mpy – mils per year. 

3.2.48 MT – magnetic particle testing

3.2.49 NAC – naphthenic acid corrosion. 

3.2.50 NH 4 

HS – ammonium bisulfide. 

3.2.51 PMI – positive materials identification. 

3.2.52 PFD – process flow diagram. 

3.2.53 PT – liquid penetrant testing. 

3.2.54 RFEC – remote field eddy current testing. 

3.2.55 RT – radiographic testing. 

3.2.56 SCC – stress corrosion cracking. 

3.2.57 SOHIC – Stress Oriented Hydrogen Induced Cracking 

3.2.58 SS: – Stainless Steel. 

3.2.59 SW – sour water. 

3.2.60 SWS – sour water stripper. 

3.2.61 SWUT – shear wave ultrasonic testing. 

3.2.62 Ti – titanium. 

3.2.63 UT – ultrasonic testing. 

3.2.64 VDU – vacuum distillation unit. 

3.2.65 VT – visual inspection. 

3.2.66 WFMT – wet fluorescent magnetic particle testing.

SECTION 4.0 

GENERAL DAMAGE 

MECHANISMS – ALL 

INDUSTRIES 

一般损伤机制 - 所有行业

4.1 General 大纲 

4.2 Mechanical and Metallurgical Failure Mechanisms. 机械和冶金失效机制 

4.3 Uniform or Localized Loss of Thickness. 均衡或局部厚度亏损 

4.4 High Temperature Corrosion [400°F (204°C)]. 高温腐蚀 

4.5 Environment Assisted Cracking. 环境辅助开裂



GENERAL DAMAGE MECHANISMS 

– ALL INDUSTRIES 


GENERAL DAMAGE MECHANISMS – ALL 

INDUSTRIES 




美国德克萨斯化肥厂爆炸 , 死亡人数攀升至 35 人




INDUSTRIES 




INDUSTRIES 




INDUSTRIES 




INDUSTRIES 

http://edition.cnn.com/2013/04/18/us/texas-explosion/ 




INDUSTRIES 



INDUSTRIES 一般损伤机制 - 所有行业


INDUSTRIES 一般损伤机制 - 所有行业 . 

API 571 人为的把损伤机理分类为 4 种作为学习 ; 

1. 机械和冶金失效机理 , 

2. 均衡或局部厚度亏损 . 

3. 高温腐蚀 , 

4. 环境辅助开裂

4.2 Mechanical & 

Metallurgical Failure 

Mechanisms 

机械和冶金失效机理

4.3 Uniform or Localized Loss of Thickness 

均衡或局部厚度亏损

4.4 High 

Temperature 

Corrosion 高温腐蚀

4.5 Environment Assisted 

Cracking 环境辅助开裂

4.2 Mechanical & 

Metallurgical Failure 

Mechanisms 

机械和冶金失效机制

4.2 Mechanical and Metallurgical Failure Mechanisms 

4.2.1 Graphitization. 

4.2.2 Softening (Spheroidization). 

4.2.3 Temper Embrittlement. 

4.2.4 Strain Aging. 

4.2.5 885°F (475°C) Embrittlement. 

4.2.6 Sigma Phase Embrittlement . 

4.2.7 Brittle Fracture. 

4.2.8 Creep and Stress Rupture. 

4.2.9 Thermal Fatigue . 

4.2.10 Short Term Overheating – Stress Rupture. 

4.2.11 Steam Blanketing. 

4.2.12 Dissimilar Metal Weld (DMW) Cracking. 

4.2.13 Thermal Shock. 

4.2.14 Erosion/Erosion – Corrosion. 

4.2.15 Cavitation. 

4.2.16 Mechanical Fatigue. 

4.2.17 Vibration-Induced Fatigue. 

4.2.18 Refractory Degradation. 

4.2.19 Reheat Cracking. 

4.2.20 GOX-Enhanced Ignition & Combustion

2013- API570 Examination 

Par. 3 – Definitions 















4.5.3 – Caustic Stress corrosion Cracking 

5.1.3.1 – High Temperature Hydrogen Attack (HTTA) 

2013-API510 Examination 

Par. 3. - Definitions 














4.5.3 – Caustic Stress Corrosion Cracking 

5.1.2.3 – Wet H2S Damage (Blister/HIC/SOHIC/SCC) 


Exam 

Damage Mechanism 

Temperatures 

Affected materials 

Graphitisation 

800°F~1100°F for C Steel 


875°F for C ½ Mo Steel 

C, C ½ Mo 

Spheroidisation 

850 °F ~ 1400 °F 


510 

Tempered 

650 °F~ 1070 °F 


Embrittlement 

1Mo (lesser extent), & HSLA Cr- 

Mo-V rotor steels 

Strain Aging 


Pre-1980’s C-steels with a large 

grain size and C- ½ Mo 

885°F embrittlement 

600 °F~ 1000 °F 



Sigma-Phase 

1000 °F~ 1700 °F 

Ferritic, austenitic & duplex SS. 

Embrittlement 

Sigma forms most rapidly from the 

ferrite phase that exists in 300 Series 

SS and duplex SS weld deposits. It can 

also form in the 300 Series SS base 

metal (austenite phase) but usually 

more slowly.

Exam 


Temperatures 


510/570 


Below DTBTT 

C, C- ½ Mo, 400 SS 


700 °F ~ 1000 °F 


510/570 



All materials of construction 

Short Term 

>1000 °F 

All fired heater tube materials 

Overheating – Stress 

and common materials of 

Rupture 

construction 

Steam Blanketing 

>1000 °F 

Carbon steel and low alloy 

steels 

Dissimilar Metal Weld 


Carbon steel / 300 SS 

(DMW) Cracking 

junction 

Thermal Shock 

Cold liquid impinge on hot 

All metals and alloys. 

surface

Exam 


Temperatures 


570/510 

Erosion/Erosion 

Service temperature 

All 

Corrosion 

Cavitation 


All 

570/510 

Mechanical fatigue 


All 

570 

Vibration-Induced 


All 

Fatigue 

Refractory 


All 

Degradation 

Reheat Cracking 


CS, 300SS, Ni Based 

GOX enhances 


All 

combustion

4.2.1 Graphitization 

石墨化 

( 不是 API510/570 考试项 )

Prolong Exposure 

800°F ~ 1100°F for C Steel 

>875°F for C ½ Mo Steel

4.2.1 Graphitization 石墨化 

4.2.1.1 Description of Damage 

a) Graphitization is a change in the microstructure of certain carbon steels 

and 0.5Mo steels after long-term operation in the 800°F to 1100°F (427°C 

to 593°C) range that may cause a loss in strength, ductility, and/or creep 

resistance. 在 800°F 1100°F 长期运行后 

b) At elevated temperatures, the carbide phases in these steels are unstable 

and may decompose into graphite nodules. This decomposition is known 

as graphitization. 碳钢 /C - ½ Mo 钢 , 在长期受到高温度影响 , 钢中碳化物相 

变得不稳定 , 从而分解成石墨结节 

4.2.1.2 Affected Materials 

Some grades of carbon steel and 0.5Mo steels. ( 普通碳钢 /0.5 钼钢 )

碳钢 /C - ½ Mo 钢 , 在长期受到高温度影响 , 钢 

中碳化物相变得不稳定 , 从而分解成石墨结节

Graphitization Location: 

Areas with tubes containing carbon steel and C-Mo. Most likely in the 

weld heat-affected zones and high residual stress areas. 

易受影响区 : 碳钢或 C- ½ Mo 普通碳钢 , 焊接热影响区和高残余应力区

Probable cause: 

Prolonged exposure to above 800°F (425°C) for carbon steels and greater than 

875°F (470°C) for the carbon- ½ molybdenum alloys. In graphitized boiler 

components, the nucleation of graphite likely starts by the precipitation of 

“carbon” from super-saturated ferrite, an aging phenomenon. This nucleation is 

enhanced by strain, in effect a strain aging. The preferential formation of 

graphite within the heat-affected zone is dependent on the balance of the 

structure being nearly strain free. Thus the “more unstable” heat-affected zone 

microstructure will decompose into ferrite and graphite before the annealed 

ferrite and pearlite of the normalized structure will. If the base metal is coldworked, 

the annealing of the weld will slow the nucleation of graphite, and the 

strained tube will graphitize before the heat-affected zone. 

在长时间的高温影响下 , 蝶状珠光体 ( 碳化铁 ) 首先转化为粒状珠光体 , 然后碳从超饱 

和的碳化铁析出 , 晶核形成石墨与周边缺碳纯铁素体 .

4.2.1.3 Critical Factors 

a) The most important factors that affect graphitization are the chemistry, 

stress, temperature, and time of exposure. 

b) In general, graphitization is not commonly observed. Some steels are much 

more susceptible to graphitization than others, but exactly what causes 

some steels to graphitize while others are resistant is not well understood. It 

was originally thought that silicon and aluminum content played a major 

role but it has been shown that they have negligible influence on 

graphitization. 

c) Graphitization has been found in low alloy C-Mo steels with up to 1% Mo. 

The addition of about 0.7% chromium has been found to eliminate 


d) Temperature has an important effect on the rate of graphitization. Below 

800°F (427°C), the rate is extremely slow. The rate increases with 

increasing temperature.

e) There are two general types of graphitization. 

First is random graphitization in which the graphite nodules are 

distributed randomly throughout the steel. While this type of 

graphitization may lower the room-temperature tensile strength, it 

does not usually lower the creep resistance.

f) The second and more damaging type of graphitization results in chains 

or local planes of concentrated graphite nodules. 

• Weld heat-affected zone graphitization is most frequently found in the 

heat-affected zone adjacent to welds in a narrow band, is called 

“eyebrow,” graphitization. 

• Non-weld graphitization is a form of localized graphitization that 

sometimes occurs along planes of localized yielding in steel. It also 

occurs in a chain-like manner in regions that have experienced significant 

plastic deformation as a result of cold working operations or bending.

Weld heat affected zone graphitization 

is most frequently found in the heat-affected zone adjacent to welds in a 

narrow band, corresponding to the low temperature edge of the heat affected 

zone. In multi-pass welded butt joints, these zones overlap each other, 

covering the entire cross-section. Graphite nodules can form at the low 

temperature edge of these heat affected zones, resulting in a band of weak 

graphite extending across the section. Because of its appearance, this graphite 

formation within heat affected zones is called “eyebrow” graphitization. 

Type 2: HAZ graphite nodules

eyebrow! 

Type2 Graphitization 

焊缝热影响区石墨化现象

eyebrow! Graphitization

eyebrow! Type 2 Graphitization 

焊缝热影响区现象 

太厉害了 , 别人的肖像变成他家的版权了 ..NMD

Non-weld graphitization is a form of localized graphitization that sometimes 

occurs along planes of localized yielding in steel. It also occurs in a chain-like 

manner in regions that have experienced significant plastic deformation as a 

result of cold working operations or bending. 

显著地塑性变形区域 , 石墨化可能以链状方式形成 . 

Type 2: Non 

Weld Chains or 

local planes of 

concentrated 

graphite nodules

4.2.1.4 Affected Units or Equipment 

a) Primarily hot-wall piping and equipment in the FCC, catalytic reforming and 

coker units. 

b) Bainitic grades are less susceptible than coarse pearlitic grades. 

c) Few failures directly attributable to graphitization have been reported in the 

refining industry. However, graphitization has been found where failure 

resulted primarily from other causes. 

d) Several serious cases of graphitization have occurred in the reactors and 

piping of fluid catalytic cracking units, as well as with carbon steel furnace 

tubes in a thermal cracking unit and the failure of seal welds at the bottom 

tube sheet of a vertical waste heat boiler in a fluid catalytic cracker. A 

graphitization failure was reported in the long seam weld of a C 0.5Mo 

catalytic reformer reactor/inter-heater line.

e) Where concentrated eyebrow graphitization occurs along heat-affected 

zones, the creep rupture strength may be drastically lowered. Slight to 

moderate amounts of graphite along the heat-affected zones do not appear 

to significantly lower room or high-temperature properties. 

f) Graphitization seldom occurs on boiling surface tubing but did occur in low 

alloy C-0.5Mo tubes and headers during the 1940’s. Economizer tubing, 

steam piping and other equipment that operates in the range of 

temperatures of 850°F to 1025°F (441°C to 552°C) is more likely to suffer 

graphitization.

4.2.1.5 Appearance or Morphology of Damage 

1. Damage due to graphitization is not visible or readily apparent and can only 

be observed by metallographic examination (Figure 4-1 and Figure 4-2). 

2. Advanced stages of damage related to loss in creep strength may include 

micro-fissuring / microvoid formation, subsurface cracking or surface 

connected cracking. 

0.5μm

Figure 4-1 – High magnification photomicrograph of metallographic sample showing 

graphite nodules. Compare to normal microstructure shown in Figure 4-2.

Figure 4-2 – High magnification photomicrograph of metallographic 

sample showing typical ferrite-pearlite structure of carbon steel.

4.2.1.6 Prevention / Mitigation 预防 / 缓解 

Graphitization can be prevented by using chromium containing low alloy steels 

for long-term operation above 800°F (427°C). 

The addition of about 0.7% chromium has been found to eliminate 


0.7% chromium 以消除石墨化 .

4.2.1.7 Inspection and Monitoring 

a) Evidence of graphitization is most effectively evaluated through removal 

of full thickness samples for examination using metallographic 

techniques. Damage may occur mid-wall so that field replicas may be 

inadequate. 

b) Advanced stages of damage related to loss in strength include surface 

breaking cracks or creep deformation that may be difficult to detect. 

4.2.1.8 Related Mechanisms 

Spheroidization (see 4.2.2) and graphitization are competing mechanisms 

that occur at overlapping temperature ranges. Spheroidization tends to 

occur preferentially above 1025°F (551°C), while graphitization 

predominates below this temperature.

Spheroidization (see 4.2.2) and graphitization are competing mechanisms that 

occur at overlapping temperature ranges. Spheroidization tends to occur 

preferentially above 1025°F (551°C), while graphitization predominates below 

this temperature. 

Graphitization can be prevented by using chromium containing low alloy steels 

for long-term operation above 800°F (427°C). 

Affected Materials: Some grades of carbon steel and 0.5Mo steels. 

Graphitization has been found in low alloy C-Mo steels with up to 1% Mo. The 

addition of about 0.7% chromium has been found to eliminate graphitization.

Creep Type: Microvoid formation & jointing of ligament between voids

Typical ferrite-pearlite structure of carbon steel.

Typical ferrite-pearlite structure of carbon steel.

Typical martensitic structure of carbon steel.

Figure 13: Lower bainite generated by 

isothermal transformation of 52100 steel at 

230C for 10h 

http://www.msm.cam.ac.uk/phase-trans/2011/Bearings/index.htm l

Random graphitization

Random graphitization

Chain graphitization 

http://davidnfrench.com/Graphitization.html

Graphitization of A Cast Iron Main

800°F

石墨化 , 学习重点 : 

1. 高温现象 : 800°F to 1100°F 

2. 受影响材料 : 碳钢 ( 不包括低合金钢 ), ½ Mo 钢 

3. 损伤模式 : (1) 无规则石墨化 ( 仅仅影响室温抗拉 ) 与 (2) HAZ/ 平面石墨化 

( 较为严厉 , 影响室温抗拉高温蠕变性能 ) 

4. 注意项 : ½ Mo 钢 , 抗拒性较强 , 敏感温度为 875°F 高于碳钢 800°F 

5. 添加 0.7%Cr 有效阻止石墨化 . 

6. 不是 API 510/570 考试学习项 . 

http://www.chasealloys.co.uk/steel/alloying-elements-in-steel/#chromium

4.2.2 Carbide Spheroidization 

碳化物球化 

( 不是 API510/570 考试项 )

Spheroidization 

Prolong Exposure 

850°F ~ 1400°F

4.2.2 Softening (Spheroidization) 碳化物球化 


Spheroidization is a change in the microstructure of steels after exposure in the 

850°F to 1400°F (440°C to 760°C) range, where the carbide phases 碳化物 in 

carbon steels are unstable and may agglomerate from their normal plate-like 

form to a spheroidal form, or from small, finely dispersed carbides in low alloy 

steels like 1Cr-0.5Mo to large agglomerated carbides. Spheroidization may 

cause a loss in strength and/or creep resistance. 


All commonly used grades of carbon steel and low alloy steels including C- 

0.5Mo, 1Cr-0.5Mo,1.25Cr-0.5Mo, 2.25Cr-1Mo, 3Cr -1Mo, 5Cr-0.5Mo, and 9Cr- 

1Mo steels. 

高温现象 : 在长期高温下 , 细分散或板状碳化物形成球状形式 . 

涵盖了普通碳钢 , 0.5Mo 钢 , 低合金钢 ,

Figure 9: The microstructures near the OD 

surface were mostly decarburized. The 

remaining carbides were highly spheroidized 

and agglomerated along the ferrite grain 

boundaries. The microstructure 90° from 

the rupture and at the tube end is 

shown.(Nital etch, Mag. 500X) 

Figure 10: The microstructures near the ID 

surface consisted of partially and highly 

spheroidized and agglomerated carbides 

along the ferrite grain boundaries. The 

microstructure 90° from the rupture and at 

the tube end is shown. (Nital etch, Mag. 500X) 

http://www.met-tech.com/short-term-overheat-rupture-of-t11-superheater-tube.html

Differences 

• Softening (Spheroidization), at prolong exposure to high temperature 

carbide phases in carbon steels are unstable and may agglomerate 

from their normal plate-like form to a spheroidal form, or from small, 

finely dispersed carbides in low alloy steels like 1Cr-0.5Mo to large 

agglomerated carbides. 在长期高温工作下 , 低合金碳钢 , 碳化物相变得 

不稳定 , 导致正常板状形式凝聚成一个球状形式 . 

• Graphitisation, the carbide phases in carbon/Molydenum steels are 

unstable and may decompose into graphite nodules. 在高温长期工作 

下 , 普通碳钢 /0.5 钼钢中的化物相变得不稳定 , 这碳化物分解成石墨结节 . 

影响的材料差别为 ; 

(1) 普通碳钢 / 受石墨化影响 

(2) 低合金含铬钼高强度 , 高温钢受碳化物球化

Spheroidization 球化 

in physical metallurgy, a process 

consisting in the transition of 

excess-phase crystals into a 

globular (spheroidal) form. The 

transition occurs at relatively high 

temperatures and is associated with 

a decrease in the interfacial energy 

高温下界面的能量减少 . Of particular 

importance is the spheroidization of 

the cementite plates contained in 

pearlite. In this process, the lamellar 

pearlite is converted into granular 

pearlite 片状珠光体转变为粒状珠光 

体 . As a result, the hardness and the 

strength of the metal are 

significantly decreased, but the 

ductility is increased.

Carbide Spheroidization 碳化物球化 

Figure 1. Corroded sheath 

exterior (0.85X Original 

Magnification) 

Figure 2. Etched sample of 

a section of non-corroded 

material (200X Original 

Magnification with Nital 

Etch)

http://www.matter.org.uk/steelmatter/forming/4_5.html

• Graphitisation and spheroidization both were 

high temperature phenomenon. 石墨化与球化都 

是材料高温效应 

• Graphitisation affect normal carbon steel. It is a 

break down of carbides into ferrite and free 

graphite (carbon) nodules. 石墨化是高温下 , 碳化 

物分解为铁素体和游离石墨 / 碳 . 

• Spheroidization affect Cr-Mo low carbon steel up 

to 9%Cr. It is a agglomeration of carbides 

forming spheroidal carbides. 球化是高温下 , 界面 

的能量减少导致片状珠光体转变为粒状珠光体

Spheroidization affect Cr-Mo low carbon steel up to 9% Cr. It is a 

agglomeration of carbides forming spheroidal carbides 影响达 9%Cr 低合金 

碳钢 , 高温下界面的能量减少 , 片状珠光体转变为粒状珠光体 ( 片状碳化物集聚 

形成球状碳化物 ). 

含 9% Chromium 碳化物球化影响范围 .

• Residual stress & cold works accelerated graphitization. 残余应 

力和冷工程加速石墨化 . 

• For spheroidisation coarse-grained steels are more resistant 

than fine-grained. Fine grained silicon-killed steels are more 

resistant than aluminum killed. 

• 粗粒度的钢比细粒度更抗拒碳化物球化 . 

• 细晶硅镇静钢比铝镇静更抗拒碳化物球化 .

Susceptibility to Spheroidization 球化易感性 

• Annealed steels 退火钢材 are more resistant to spheroidization than 

normalized steels. 

• Coarse-grained steels 粗粒度钢材 are more resistant than fine-grained. 

• Fine grained silicon-killed steels are more resistant than aluminum-killed. 

• The loss in strength 强度损失 may be as high as about 30% but failure is not 

likely to occur except under very high applied stresses.

Exam 

DM 

Temperatures 


NO 





C, C ½ Mo 

• Some grades of carbon steel and 0.5Mo steels. 

NO 

Spheroidisation 

850°F ~ 1400°F 

Low alloy steel up to 9% Cr. 

•All commonly used grades of carbon steel and low alloy steels including C-0.5Mo, 

1Cr-0.5Mo,1.25Cr-0.5Mo, 2.25Cr-1Mo, 3Cr-1Mo, 5Cr-0.5Mo, and 9Cr-1Mo steels. 

Spheroidization (see 4.2.2) and graphitization are competing mechanisms that occur at 

overlapping temperature ranges. Spheroidization tends to occur preferentially above 1025°F 

(551°C), while graphitization predominates below this temperature. 

Discussion: Graphitization occurs on some carbon steel and 0.5Mo steels only.

Spheroidization is a change in the microstructure of steels after 

exposure in the 850°F to 1400°F (440°C to 760°C) range, 

where the carbide phases in carbon steels are unstable and may 

agglomerate from their normal plate-like form to a spheroidal form. 

碳化物球化学习重点 : 

1. 高温现象 –850°F to 1400°F, 

2. 原理 : 低合金碳钢 , 高温下界面的能量减少 , 片状珠光体转变为粒状珠光 

体 ( 片状碳化物集聚形成球状碳化物 ), 

3. 受影响材质 : 涵盖了普通碳钢 , 0.5Mo 钢 , 低合金钢至 9Cr1Mo 钢 , 

4. 粗粒度的钢比细粒度更抗拒碳化物球化 , 

5. 细晶硅镇静钢比铝镇静更抗拒碳化物球化 , 

6. 不同于石墨化 , 碳化物还是碳化物只不过高温下聚集成为球状 , 

7. 非 API 510/570 考试题非 API 510/570 考试题

4.2.3 Temper Embrittlement 

回火脆化 

API510-Exam

650 o F~ 1070 o F 

API510-Exam

API510-Exam 

Graphitization 

石墨化 

Spheroidization 碳 

化物球化 

Tempered 

Embrittlement 

回火脆化 



850°F ~ 1400°F 

650°F~ 1070°F 

Plain carbon steel / 0.5Mo 

Steel 

0.5Mo Steel, Low alloy steel 

up to 9 % Cr 

2 ¼ Cr-1Mo low alloy steel, 

3Cr-1Mo (lesser extent), & 

HSLA Cr-Mo-V rotor steels

API510-Exam 

4.2.3 Temper Embrittlement 回火脆化 


Temper embrittlement is the reduction in toughness due to a metallurgical 

change that can occur in some low alloy steels as a result of long term 

exposure in the temperature range of about 650°F to 1100°F (343°C to 

593°C) . This change causes an upward shift in the ductile-to-brittle transition 

temperature as measured by Charpy impact testing. Although the loss of 

toughness is not evident at operating temperature, equipment that is temper 

embrittled may be susceptible to brittle fracture during start-up and shutdown. 

2¼ Cr-1Mo ~ 3Cr-1Mo 量低合金钢在 650°F to 1100°F 工作下 , 导致受影响材质 , 

韧脆转变温度向上移位 . 工作状态下 , 设备不会受到此损伤机理任何影响 , 但在 

关机 , 重启时的低温下 , 材料会因回火脆性的损伤机理导致产生设备受压母材脆 

裂 .

API510-Exam 

Temper embrittlement is the reduction in toughness due to a metallurgical 

change that can occur in some low alloy steels as a result of long term 

exposure in the temperature range of about 650°F to 1100°F (343°C to 

593°C) . 2¼ Cr-1Mo~ 3Cr-1Mo 钢材在 650°F to 1100°F 工作下 , 导致受影响材质 , 

韧脆转变温度向上移位 .

API510-Exam 


a) Primarily 2 ¼ Cr-1Mo (P5A) low alloy steel, 3Cr-1Mo (P5A) (to a lesser 

extent), and the high-strength low alloy Cr-Mo-V (P5C) rotor steels. 

b) Older generation 2 ¼ Cr-1Mo materials manufactured prior to 1972 may be 

particularly susceptible. Some high strength low alloy steels are also 

susceptible. 

c) The C- ½ Mo (P3) and 1 ¼ Cr- ½ Mo (P4) alloy steels are not significantly 

affected by temper embrittlement. However, other high temperature 

damage mechanisms promote metallurgical changes that can alter the 

toughness or high temperature ductility of these materials. 

主要是对 2¼ Cr-1Mo~ 3Cr-1Mo 低合金钢 , Cr-Mo-V 轴钢受影响 .

API510-Exam 

Temper 

Embrittlement 

回火脆性易感性 

Primarily 2.25Cr-1Mo low 

alloy steel. and the highstrength 

low alloy Cr-Mo-V 

rotor steels. 

3Cr-1Mo 

(to a lesser extent) 

The C-0.5Mo, 1Cr- 

0.5Mo and 1.25Cr- 

0.5Mo alloy steels are 

not significantly 

affected.

[Embrittlement temperature 650°F~1070°F] 

API510-Exam


API510-Exam


API510-Exam

韧脆转变温度 

API510-Exam

韧脆转变温度向上移位 

API510-Exam

API510-Exam 

脆性转变温度向上移位 . 另 

个特征是回火脆化 , 不会对 

脆性转变点上搁架冲击功有 

任何影响 .

API510-Exam 

SEM fractographs of 

tempered embrittled 

material show 

primarily intergranular 

cracking due to 

impurity segregation at 

grain boundaries 

材料的回火脆化 , 主要 

是由于晶界杂质偏聚 

导致是沿晶开裂

http://www.twi.co.uk/news-events/bulletin/archive/1999/januaryfebruary/welding-and-fabrication-of-high-temperature-components-foradvanced-power-plant-part-1/ 

API510-Exam

API510-Exam 

4.2.3.3 Critical Factors 关键因素 

a) Alloy steel composition, thermal history, metal temperature and exposure 

time are critical factors. 受热历史 , 金属温度和受感时间是关键因素 

b) Susceptibility to temper embrittlement is largely determined by the 

presence of the alloying elements manganese and silicon, and the tramp 

elements phosphorus, tin, antimony, and arsenic. The strength level and 

heat treatment/fabrication history should also be considered. 回火脆化敏感 

性很大程度上决定于锰 / 硅与杂元素 ( 磷 / 锡 / 锑和砷 ) 含量 . 

c) Temper embrittlement of 2.25Cr-1Mo steels develops more quickly at 

900°F (482°C) than in the 800°F to 850°F (427°C to 440°C) range, but the 

damage is more severe after long-term exposure at 850°F (440°C). 高温下 

易感性较大 , 但在低温下伤害较为严重 .

API510-Exam 

d) Some embrittlement can occur during fabrication heat treatments, but most 

of the damage occurs over many years of service in the embrittling 

temperature range. 有的损伤是因建造热处理引发 , 但一般上大多数受感于长 

期在敏感温度下操作引发的 . 

e) This form of damage will significantly reduce the structural integrity of a 

component containing a crack-like flaw. An evaluation of the materials 

toughness may be required depending on the flaw type, the severity of the 

environment, and the operating conditions, particularly in hydrogen service. 

含裂纹状缺陷的部件会减弱结构完整性 . 特别是氢服务设备 , 应在考虑缺陷的 

类型 , 处理工艺的严峻性与操作条件 , 进行材料的韧性评估 .

API510-Exam 


a) Temper embrittlement occurs in a variety of process units after long term 

exposure to temperatures above 650°F (343°C). It should be noted that 

there have been very few industry failures related directly to temper 

embrittlement. 

b) Equipment susceptible to temper embrittlement is most often found in 

hydroprocessing units, particularly reactors, hot feed/effluent exchanger 

components, and hot HP separators. Other units with the potential for 

temper embrittlement include catalytic reforming units (reactors and 

exchangers), FCC reactors, coker and visbreaking units. 

c) Welds in these alloys are often more susceptible than the base metal and 

should be evaluated. 

受影响的设备主要是用于高温处理单元 , 例如加氢装置 , 催化重整装置 , 催化裂 

化反应器 , 炼焦器 , 减粘裂化单元 , 等 . 焊接部位受感性比母材强 , 这位应当作为 

评估考虑部位 .

API510-Exam 

http://www.twi-global.com/technical-knowledge/job-knowledge/defectsimperfections-in-welds-reheat-cracking-048/ 

http://en.wikipedia.org/wiki/Welding_defect

API510-Exam

API510-Exam 


a) Temper embrittlement is a metallurgical change that is not readily apparent 

and can be confirmed through impact testing. Damage due to temper 

embrittlement may result in catastrophic brittle fracture. 

外观变化不明显 , 需要通过冲击试验证实 . 

b) Temper embrittlement can be identified by an upward shift in the ductile-tobrittle 

transition temperature measured in a Charpy V-notch impact test, as 

compared to the non-embrittled or de-embrittled material (Figure 4-5). 

Another important characteristic of temper embrittlement is that there is no 

effect on the upper shelf energy. 夏比 V 型缺口冲击试验证实韧性 - 脆性转变 

温度向上移位 . 另个特征是回火脆化 , 不会对脆性转变点上搁架冲击功有任何 

影响 . 

c) SEM fractographs of severely temper embrittled material show primarily 

intergranular cracking due to impurity segregation at grain boundaries. 

主要为晶间开裂

API510-Exam

Intergranular Cracking 

API510-Exam

Intergranular 

Cracking 

API510-Exam 

Metal surface 

Cr 5 

C 2 

/ Cr 3 

C 2 

precipitated 

Low Cr grain 

boundary 

Crack initiation & 

growth 

Progressive crack

API510-Exam 

Embrittlement Mechanism 

Tensile stress 

Cr depleted grain 

boundary 

PPT as 

Cr 5 C 2 /Cr 3 C 2 

Grain 

Boundary 

Grain boundary 

decohesion- 

Crack initiation pt.

API510-Exam 

4.2.3.6 Prevention / Mitigation 

a) Existing Materials 

1. Temper embrittlement cannot be prevented if the material contains critical 

levels of the embrittling impurity elements and is exposed in the embrittling 

temperature range. 

2. To minimize the possibility of brittle fracture during startup and shutdown, 

many refiners use a pressurization sequence to limit system pressure to 

about 25 percent of the maximum design pressure for temperatures below a 

Minimum Pressurization Temperature (MPT). Note that MPT is not a single 

point but rather a pressure temperature envelope which defines safe 

operating conditions to minimize the likelihood of brittle fracture.

API510-Exam 

3. MPT’s generally range from 350°F (171°C) for the earliest, most highly 

temper embrittled steels, down to 125°F (52°C) or lower for newer, temper 

embrittlement resistant steels (as required to also minimize effects of 

hydrogen embrittlement). 

4. If weld repairs are required, the effects of temper embrittlement can be 

temporarily reversed (de-embrittled) by heating at 1150°F (620°C) 

[compared: embrittlement temperature 650°F~1070°F] for two hours per inch 

of thickness, and rapidly cooling to room temperature. It is important to note 

that re-embrittlement will occur over time if the material is re-exposed to the 

embrittling temperature range.

API510-Exam 

Existing Material: De-embrittlement treatment. 

Heating at 1150°F (620°C) 

[compared: embrittlement 

temperature 650°F~1070°F 

(343°C to 593°C) ] for two 

hours per inch of thickness, 

and rapidly cooling to room 

temperature.

) New Materials 

API510-Exam 

The best way to minimize the likelihood and extent of temper embrittlement is to 

limit the acceptance levels of manganese, silicon, phosphorus, tin, antimony, 

and arsenic in the base metal and welding consumables. In addition, 

strength levels and PWHT procedures should be specified and carefully 

controlled. 最好的缓解方法是控制母材 / 焊材的锰 , 硅 , 磷 , 锡 , 锑 , 砷的成分 . 

Acceptance Level of Mn, Si, P, Sn, Sb, As.

API510-Exam 

Susceptibility to temper embrittlement 

A common way to minimize temper embrittlement is to limit the "J*" Factor for 

base metal and the "X" Factor for weld metal, based on material composition as 

follows: 

J* = (Si + Mn) x (P + Sn) x 104 {elements in wt%} 

X = (10P + 5Sb + 4Sn + As)/100 {elements in ppm}

API510-Exam 

Typical J* and X factors used for 2.25 Cr steel are a maximum of 100 and 15, 

respectively. Studies have also shown that limiting the (P + Sn) to less than 0.01% is 

sufficient to minimize temper embrittlement because (Si + Mn) control the rate of 


J* : 100 Max. (Base metal) 

X 

: 15 Max. (Weld metal)

API510-Exam 


a) a) A common method of monitoring is to install blocks of original heats of 

the alloy steel material inside the reactor. Samples are periodically removed 

from these blocks for impact testing to monitor/establish the ductile-brittle 

transition temperature. The test blocks should be strategically located near 

the top and bottom of the reactor to make sure that the test material is 

exposed to both inlet and outlet conditions. 

b) Process conditions should be monitored to ensure that a proper 

pressurization sequence is followed to help prevent brittle fracture due to 

temper embrittlement. 


Not applicable.

Figure 4-5 – Plot of 

CVN toughness as a 

function of 

temperature showing a 

shift in the 40-ft-lb 

transition temperature. 

API510-Exam

API510-Exam

API510-Exam 

Temper embrittlement is inherent in many steels and can be characterized 

by reduced impact toughness. The state of temper embrittlement has practically no 

effect on other mechanical properties at room temperature. Figure 1 shows 

schematically the effect of temperature on impact toughness of alloy steel which is 

strongly liable to temper embrittlement. Many alloy steels have two temperature 

intervals of temper embrittlement. For instance, irreversible temper brittleness may 

appear within the interval of 250-400°C and reversible temper brittleness, within 

450°C-650°C. 

http://www.keytometals.com/Articles/Art102.htm

API510-Exam 

irreversible temper 

brittleness may appear 

within the interval of 

250-400°C 

reversible temper brittleness, 

within 450°C-650°C.

API510-Exam 

Metallurgy of Mo in alloy steel & iron 

Temper embrittlement may occur when steels are slowly cooled after tempering 

through the temperature range between 450 and 550°C. This is due to the 

segregation of impurities such as phosphorus, arsenic, antimony and tin on the 

grain boundaries. The molybdenum atom is very large relative to other alloying 

elements and impurities. It effectively impedes the migration of those elements 

and thereby provides resistance to temper embrittlement. 

http://www.imoa.info/molybdenum_uses/moly_grade_alloy_steels_irons/tempering.php 

Other/ 其他阅读 

Other reference: http://www.twi.co.uk/technical-knowledge/faqs/material-faqs/faq-what-is-temperembrittlement-and-how-can-it-be-controlled/

回火脆化学习重点 : 

1. 高温现象 : 650°F to 1100°F, 

2. 原理 : 材料的回火脆化 , 主要是由于晶界杂质偏聚导致是沿晶开裂 

3. 受影响材质 :, 2.25Cr1Mo ~ 3Cr1Mo 低合金钢与轴钢 , 不涵盖普通碳钢 , 

4. 最好的缓解方法是控制母材 / 焊材的锰 , 硅 , 磷 , 锡 , 锑 , 砷的成分 , 

5. 其他缓解方法 : 控制材料强度 (?) 与热处理受感温度 , 

6. 这种脆化现象不能在高于受感温度热处理逆转恢复 . 

7. 除了低温冲击功 , 不影响其他高低温机械性能 .

4.2.4 Strain Aging 

时效伸张 

( 不是 API510/570 考试项 )

Intermediate 

temperature





800°F for C Steel 


850 o F ~ 1400 o F 

650°F~ 1070°F 



Plain carbon + Low alloy steel 

up to 9% Cr 


1Mo (lesser extent), & HSLA 

Cr-Mo-V rotor steels 

pre-1980’s carbon steels with a 

large grain size and C-0.5 Mo 

885 o F embrittlement 

600°F~ 1000°F 

受影响的材质是那些老工艺的炼钢方法的普通碳钢与 

0.5Mo 钢 – 含有高成分的关键杂质元素与粗晶粒 . 

300, 400 & Duplex SS 

containing ferrite phases

4.2.4 Strain Aging 伸张时效 


Strain aging is a form of damage found mostly in older vintage carbon 

steels and C-0.5 Mo low alloy steels under the combined effects of 

deformation and aging at an intermediate temperature. This results in an 

increase in hardness and strength with a reduction in ductility and 

toughness. 


Mostly older (pre-1980’s) carbon steels with a large grain size and C-0.5 

Mo low alloy steel. 

When susceptible materials are plastically deformed and exposed to 

intermediate temperatures, the zone of deformed material may become 

hardened and less ductile. 

一般上受影响的是 1980 年或更早前的碳钢 ( 特别是大粒径 / C- ½ Mo), 当这些 

敏感的材料 , 经过塑性变形和接触中间温度作业时 , 这变形材料区可能变硬 

和延展性与韧性降低。

http://link.springer.com/article/10.1007%2Fs11668-006-5014-3#page-1 

http://link.springer.com/article/10.1007%2FBF02715166#page-1 

http://matperso.mines-paristech.fr/Donnees/data03/386-belotteau09.pdf 

Most of the effects of cold work on 

the strength and ductility of 

structural steels can be eliminated 

by thermal treatment, such as 

stress relieving, normalizing, or 

annealing. However, such 

treatment is not often necessary. 

伸张时效对强度和韧性的影响能以 

热处理逆转恢复 .

韧性减低 / 抗拉曾强

拉 

力 

AISC- Guide to Design Criteria for Bolted and Riveted Joints

拉 

力 

AISC- Guide to Design Criteria for Bolted and Riveted Joints


a) Steel composition and manufacturing process determine steel susceptibility. 

b) Steels manufactured by the Bessemer or open hearth process contain 

higher levels of critical impurity elements than newer steels manufactured 

by the Basic Oxygen Furnace (BOF) process. 

c) In general, steels made by BOF and fully killed with aluminum will not be 

susceptible. The effect is found in rimmed and capped steels with higher 

levels of nitrogen and carbon, but not in the modern fully killed carbon 

steels manufactured to a fine grain practice. 

受感性强材质 : 

• 含有高成分的关键杂质元素的转炉或平炉炼钢法 ( 老炼钢法 ), 

• 含大量的氢与碳元素的压盖钢 / 半镇静钢 / 沸腾钢 

不受影响材质 : 

• 碱性氧气转炉炼钢法 , 铝镇静钢 , 细晶粒实践钢 .

d) Strain aging effects are observed in materials that have been cold worked 

and placed into service at intermediate temperatures without stress 

relieving. 冷加工件 ( 无热处理 ) 用于中等温度服务 . 

e) Strain aging is a major concern for equipment that contains cracks. If 

susceptible materials are plastically deformed and exposed to intermediate 

temperatures, the zone of deformed material may become hardened and 

less ductile. This phenomenon has been associated with several vessels 

that have failed by brittle fracture. 塑性变材料当接触到中等温度时 , 变形的 

区域会变硬与减少韧性 , 如这材料带裂缝时会导致设备脆性断裂 . 

f) The pressurization sequence versus temperature is a critical issue to 

prevent brittle fracture of susceptible materials. 加压顺序与温度是预防时效 

伸张开裂的关键方法 . 

g) Strain aging can also occur when welding in the vicinity of cracks and 

notches in a susceptible material. 焊接加热也会加剧带裂纹的受感材料 .

Bessemer Process

Bessemer Process

Bessemer Process

Bessemer Process

Open hearth Process

Open hearth Process

Open hearth Process

Open hearth Process 平炉炼钢法

Basic Oxygen Process 

碱性氧气转炉炼钢法

Basic Oxygen Process

Basic Oxygen Process

Metallurgy for Dummies 

http://metallurgyfordummies.com/steelmaking-technology/

Capped Steel 半镇静钢 , 加盖钢 : 

• It has characteristics similar to those of rimmed steels but to a degree 

intermediate between those of rimmed and semi-killed steels. 

• A deoxidizer may be added to effect a controlled running action when 

the steel is cast. the gas entrapped during solidification is in excess of 

that needed to counteract normal shrinkage, resulting in a tendency for 

the steel to rise in the mould. 

• The capping operation caused the steel to solidify faster, thereby 

limiting the time of gas evolution, and prevents the formation of an 

excessive number of gas voids within the ingot. 

• Capped steel is generally cast in bottle-top moulds using a heavy metal 

cap. 

• Capped steel may also be cast in open-top moulds, by adding aluminum 

or ferro-silicon on the top of molten steel, to cause the steel on the 

surface to lie quietly and solidify rapidly.

4) Rimmed Steel 沸腾钢 , 不脱氧钢 : 

• In rimmed steel, the aim is to produce a clean surface low in carbon 

content. Rimmed steel is also known as drawing quality steel. 

• The typical structure results for a marked gas evolution during solidification 

of outer rim. 

• They exhibit greatest difference in chemical composition across sections 

and from top to bottom of the ingot. 

• They have an outer rim that is lower in carbon, phosphorus, and sulphur 

than the average composition of the whole ingot and an inner portion or 

core that is higher the average in those elements. 

• In rimming, the steel is partially deoxidized. Carbon content is less than 

0.25% and manganese content is less than 0.6%. 

• They do not retain any significant percentage of highly oxidizable elements 

such as Aluminum, silicon or titanium. 

• A wide variety of steels for deep drawing is made by the rimming process, 

especially where ease of forming and surface finish are major 

considerations. 

• These steel are, therefore ideal for rolling, large number of applications, 

and is adapted to cold-bending, cold-forming and cold header applications.

应变时效学习重点 : 

1. 中等温度现象 –?°F to ?°F, 

2. 受感材质 : 含有高成分的关键杂质元素的转炉或平炉炼钢法 , 未经过热处 

理冷加工件 . 粗晶粒钢 . 

3. 受感设备 : 高厚度非热处理受感材质设备 . 

4. 碱性氧气转炉炼钢法 , 铝镇静钢 , 细晶粒实践钢不受影响 . 

5. 蓝脆性为别名 . 

6. 非 API 510/570 考试题非 API 510/570 考试题

4.2.5 885°F (475°C) embrittlement 

885°F 脆化 - 铁素体不锈钢 / 双相钢 

( 不是 API510/570 考试项 )

885°F (475°C) embrittlement 

600°F~ 1000°F






800°F for C Steel 


850 o F ~ 1400 o F 

650°F~ 1070°F 


600°F~ 1000°F 


Plain carbon + Low alloy steel 

up to 9% Cr 


1Mo (lesser extent), & HSLA 

Cr-Mo-V rotor steels 

pre-1980’s carbon steels with a 

large grain size and C-0.5 Mo 

300*, 400 & Duplex SS 

containing ferrite phases 

受影响的材质 : 含铁素土的不锈钢 . 

* 锻与铸件奥氏体不锈钢 .

4.2.5 885°F (475°C) Embrittlement 


• 885°F (475°C) embrittlement is a loss in toughness due to a metallurgical 

change that can occur in stainless steel containing a ferrite phase, as a 

result of exposure in the temperature range 600°F~1000°F (316°C to 

540°C). 


a) 400 Series SS- ferritic & martensitic 

(e.g., 405, 409, 410, 410S, 430, and 446). 

b) Duplex stainless steels such as Alloys 2205, 2304, and 2507. 

c) Wrought and cast 300 Series SS containing ferrite, particularly welds and 

weld overlay. 

高温现象 : 600°F to 1000°F 

含有铁素体相不锈钢 ( 铁素体 / 马氏体 / 双相 / 奥氏体 - 全包含 ) 由于冶金的变化韧 

性的损失现象 .

885°F (475°C) embrittlement 

Embrittlement of stainless steels containing ferrite phase upon extended 

exposure to temperatures between 730°F and 930°F (400°C and 510°C ). 

This type of embrittlement is caused by fine, chromium-rich precipitates that 

segregate at grain boundaries: time at temperature directly influences the 

amount of segregation. Grain-boundary segregation of the chromium-rich 

precipitates increases strength and hardness, decreases ductility and 

toughness, and changes corrosion resistance. This type of embrittlement 

can be reversed by heating above the precipitation range. 

885°F 脆化 , 这种类型的脆化是由于富含铬的析出物在晶界处偏析出 . 晶界偏析 

的富含铬的析出增加强度和硬度 , 降低塑性和韧性和耐腐蚀变化 ( 减弱 ). 这种脆 

化现象能在高于析出温度热处理逆转恢复 . 

http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&LN=CN&NM=102

• Most refining companies limit the use of ferritic stainless steels to nonpressure 

boundary applications because of this damage mechanism. 

• 885°F embrittlement is a metallurgical change that is not readily apparent 

with metallography but can be confirmed through bend or impact testing 

(Figure 4-6).

• The existence of 885°F embrittlement can be identified by an increase in 

hardness in affected areas. Failure during bend testing or impact testing of 

samples removed from service is the most positive indicator of 885°F 


• 885°F embrittlement is reversible by heat treatment to dissolve precipitates, 

followed by rapid cooling. The de-embrittling heat treatment temperature is 

typically 1100°F (593°C) or higher and may not be practical for many 

equipment items. If the de-embrittled component is exposed to the same 

service conditions it will re-embrittle faster than it did initially.


a) The alloy composition, particularly chromium content, amount of ferrite 

phase, and operating temperature are critical factors. 

铬 , 铁素体相的数量和操作温度 

b) Increasing amounts of ferrite phase increase susceptibility to damage 

when operating in the high temperature range of concern. A dramatic 

increase in the ductile-to-brittle transition temperature will occur. 

越来越多的铁素体相的增加损伤的易感性 ( 韧脆转变温度显著提高 ) 

c) A primary consideration is operating time at temperature within the critical 

temperature range. Damage is cumulative and results from the 

precipitation of an embrittling intermetallic phase that occurs most readily 

at approximately 885°F (475°C). Additional time is required to reach 

maximum embrittlement at temperatures above or below 885°F (475°C). 

For example, many thousands of hours may be required to cause 

embrittlement at 600°F (316°C). 损伤是因在受感温度操作时 , 金属间项 

(intermetallic phase) 的溢出 / 沉淀在晶间导致的 .

d) Since 885°F embrittlement can occur in a relatively short period of time, it 

is often assumed that susceptible materials that have been exposed to 

temperatures in the 700°F to 1000°F (371°C to 538°C) range are affected. 

受感温度一般上定义为 700°F 至 1000°F 之间 

e) The effect on toughness is not pronounced at the operating temperature, 

but is significant at lower temperatures experienced during plant 

shutdowns, startups or upsets. 对韧性的影响体现在较低于操作温度例如在 

停机 , 启动和颠覆状态时 . 

f) Embrittlement can result from tempering at higher temperatures or by 

holding within or cooling through the transformation range. 

在受感温度回火热处理或当冷却时在受感 ( 转变 ) 温度停留会导致 885°F 脆化 .

Fig. 2—Microstructure of solution-annealed 304LN stainless steel

Fig. 3—Oxalic acid etched microstructures of 304LN stainless steel sensitized for (a) 

1 h, (b) 25 h, (c) 50 h, and (d) 100 h.


a) Impact or bend testing of samples removed from service is the most positive 

indicator of a problem. 

b) Most cases of embrittlement are found in the form of cracking during 

turnarounds, or during startup or shutdown when the material is below about 

200°F (93°C) and the effects of embrittlement are most detrimental. 

c) An increase in hardness is another method of evaluating 885°F 

embrittlement.

Impact energy and brinell hardness as function of time exposure qt 475°C 

475 o C Embrittlement in a Duplex Stainless Steel UNS S31803

475 o C Embrittlement in a Duplex Stainless Steel UNS S31803 

http://www.scielo.br/scielo.php?pid=S1516-14392001000400003&script=sci_arttext

http://www.sciencedirect.com/science/article/pii/S0921509309000197

• 885°F (475°C) Embrittlement of stainless steels in alloys containing 

a ferrite phase (Ferritic/Martensitic/Duplex stainless steel and ferrite 

phases in austenitic stainless steel e.g. weld areas) 影响材质 : 含铁素 

体的不锈钢 

• Grain-boundary segregation of the chromium-rich precipitates 

increases strength and hardness, decreases ductility and toughness, 

and changes corrosion resistance (lower). 含富铬金属间 

(intermetallic) 在晶间溢出导致脆化 . 

• This type of embrittlement can be reversed by heating above the 

precipitation range. 可以通过加热逆转恢复 

• Impact testing/bend test & hardness testing used to evaluate 

susceptibility. 冲击试验 , 弯曲试验 , 硬度试验作为易感性的评估 . 

• Restrict the used of ferritic steel to non-pressure boundary application. 

限制铁素体不锈钢用于非受压用途 .

4.2.6 Sigma-Phase Embrittlement 

“ 西格玛 ” 相脆化 

( 不是 API510/570 考试项 )

Sigma-Phase Embrittlement 

1000 o F~1700 o F


Sigma phase embrittlement 

600°F~ 1000°F 

1000°F~ 1700°F 

300*, 400 & Duplex SS 

containing ferrite phase 

300, 400 & Duplex SS 

containing ferrite phases 

受影响的材质 : 含铁素体的不锈钢 , 

* 锻与铸件奥氏体不锈钢

4.2.6 Sigma Phase Embrittlement 


Formation of a metallurgical phase known as sigma phase can result in a loss 

of fracture toughness in some stainless steels as a result of high 

temperature exposure. 


a) 300 Series SS wrought metals, weld metal, and castings. Cast 300 Series 

SS including the HK and HP alloys are especially susceptible to sigma 

formation because of their high (10-40%) ferrite content. 

b) The 400 Series SS and other ferritic and martensitic SS with 17% Cr or 

more are also susceptible (e.g., Types 430 and 440). 

c) Duplex stainless steels. 

受影响的材质 : 铁素体不锈钢 , 含铁素体的马氏体 , 奥氏体不锈钢和双相不锈钢 . 

脆化原因 : 在受感温度下 , 西格玛相形成 , 在铁素体项析出导致脆化 . 

http://www.hindawi.com/journals/isrn.metallurgy/2012/732471/

Sigma-Phase Embrittlement 西格玛相脆化 

Description: Embrittlement of iron-chromium alloys caused by precipitation 

at grain boundaries of the hard, brittle intermetallic sigma phase σ during 

long periods of exposure to temperatures between approximately 565 o C and 

980 o C (1050 o F and 1800 o F). Sigma phase embrittlement results in severe 

loss in toughness and ductility and can make the embrittled material 

structure susceptible to intergranular corrosion. 

在长时间暴露在温度约 565 o C ~ 980 o C (1050 o F ~ 1800 o F) 之间 , 硬而脆的金 

属间化合物 (σ 相 ) 在铁素体晶界处析出 , σ 相脆化导致的韧性和延展性严重损失 

与导致易受晶间腐蚀 . 

http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&LN=CN&NM=102


a) Alloy composition, time and temperature are the critical factors. 

化学成分 , 时间 , 温度都是关键因素 . 

b) In susceptible alloys, the primary factor that affects sigma phase 

formation is the time of exposure at elevated temperature. 易感材料 ; 时间 

与经历温度为主要因素 . 

c) Sigma phase occurs in ferritic (Fe-Cr), martensitic (Fe-Cr), austenitic (Fe- 

Cr-Ni) and duplex stainless steels when exposed to temperatures in the 

range of 1000°F to 1700°F (538°C to 927°C). Embrittlement can result by 

holding within or cooling through the transformation range. 铁素体 , 马氏体 , 

奥氏体 , 双相钢 , 当停留或冷却途径 1000°F to 1700°F 温度时 , 产生 σ 相析出 . 

d) Sigma forms most rapidly from the ferrite phase that exists in 300 Series 

SS and duplex SS weld deposits. It can also form in the 300 Series SS 

base metal (austenite phase) but usually more slowly. σ 相以较快的速度 

在铁素体相析出 , 但也会在奥氏体项较慢的速度析出 .

e) The 300 Series SS can exhibit about 10% to 15% sigma phase. Cast 

austenitic stainless steels can develop considerably more sigma. 

σ 相在奥氏体不锈钢以 10%~15% 表现出来 , 铸件可能还高 . 

f) Formation of sigma phase in austenitic stainless steels can also occur in a 

few hours, as evidenced by the known tendency for sigma to form if an 

austenitic stainless steel is subjected to a post weld heat treatment at 

1275°F (690°C). 

σ 相在奥氏体的析出只需几个小时 , 这脆化趋向可以从 1275°F 焊接热处理后 , 

出现 σ 相的到证明 . 

g) The tensile and yield strength of sigmatized stainless steels increases 

slightly compared with solution annealed material. This increase in 

strength is accompanied by a reduction in ductility (measured by percent 

elongation and reduction in area) and a slight increase in hardness. 

σ 相脆化后 , 抗拉强度 . 硬度相比固溶退火材料略有增加 , 同时 , 延展性与韧性 

减少 .

Σ(σ)phase 

in austenitic 

matrix 

http://www.intecho 

pen.com/books/met 

allurgy-advancesin-materials-andprocesses/homogeni 

zation-heattreatment-toreduce-the-failureof-heat-resistantsteel-castings

Σ(σ)phase 

in austenitic 

matrix

h) Stainless steels with sigma can normally withstand normal operating 

stresses, but upon cooling to temperatures below about 500°F (260°C) 

may show a complete lack of fracture toughness as measured in a Charpy 

impact test. Laboratory tests of embrittled weld metal have shown a 

complete lack of fracture toughness below 1000°F (538°C) 

一般上材料在正常操作温度时不受西格玛相脆化影响 , 但是当材料温度降至 

500°F 材料完全缺乏韧性 ( 实验室导致完全缺乏韧性的温度可能高至 1000°F). 

i) The metallurgical change is actually the precipitation of a hard, brittle 

intermetallic compound that can also render the material more susceptible 

to intergranular corrosion. The precipitation rate increases with increasing 

chromium and molybdenum content. 缺乏韧性是因硬脆性金属间化合物沉 

淀在晶间 . 随着铬和钼含量提高 , 沉淀率相应加速 .

σ 相脆化 - 缺乏韧性是因硬脆性金属间 (intermetallic-sigma phase) 化合物沉淀 

在晶间 . 随着铬和钼含量提高 , 沉淀率相应加速 . 

Cr% & Mo% 

铬和钼含量增加 

The precipitation 

rate increases 

σ 相析出增加


a) Common examples include stainless steel cyclones, piping ductwork and 

valves in high temperature FCC (fluidized catalytic cracking )Regenerator 

service. 

b) 300 Series SS weld overlays and tube-to-tubesheets attachment welds can 

be embrittled during PWHT treatment of the underlying CrMo base metal. 

c) Stainless steel heater tubes are susceptible and can be embrittled.

FCC (fluidized catalytic cracking ) 

Regenerator service

FCC (fluidized catalytic 

cracking ) 

Regenerator service


Regenerator service 

http://www.phxequip.com/plant.73/fluid-catalytic-cracker-unit.aspx


Regenerator service


Regenerator service

Stainless steel heater tubes

Stainless steel heater tubes

tube-to-tubesheets attachment




4.2.6.5 Appearance or Morphology of Damage 损伤外观形态 

a) Sigma phase embrittlement is a metallurgical change that is not readily 

apparent, and can only be confirmed through metallographic examination 

and impact testing. (Tables 4-1 and 4-2) 外观上不能体现损伤 , 只能依靠金相 

分析和冲击试验 

b) Damage due to sigma phase embrittlement appears in the form of cracking, 

particularly at welds or in areas of high restraint. σ 相脆化一般上以开裂的形 

态出现特别是在焊缝与高抑制区域 . 

c) Tests performed on sigmatized 300 Series SS (304H) samples from FCC 

regenerator internals have shown that even with 10% sigma formation, the 

Charpy impact toughness was 39 ft-lbs (53 J) at 1200°F (649°C). 

材料 : 304H 

敏化度 : 10%σ 相 

温度 / 冲击功 : 649°C / 53J

设备 : 催化裂化再生器 

材料 : 304H 

敏化度 : 10%σ 相 

温度 / 冲击功 : 649°C / 53J 

新材料的机械性能 : 

SPECIFICATION FOR HEAT-RESISTING 

CHROMIUM AND CHROMIUM-NICKEL STAINLESS 

STEEL PLATE, SHEET, AND STRIP FOR 

PRESSURE VESSELS 

ASTM SA-240

SPECIFICATION FOR HEAT-RESISTING CHROMIUM AND CHROMIUM-NICKEL STAINLESS STEEL PLATE, 

SHEET, AND STRIP FOR PRESSURE VESSELS ASTM SA-240

d) For the 10% sigmatized specimen, the values ranged from 0% ductility at 

room temperature to 100% at 1200°F (649°C). Thus, although the impact 

toughness is reduced at high temperature, the specimens broke in a 

100% ductile fashion, indicating that the wrought material is still suitable 

at operating temperatures. See Figures 4-7 to 4-11. 敏化材料的室温延展 

性或许降至为零 . 但在 1200°F 材料的延展性可能不受任何的影响 . 

e) Cast austenitic stainless steels typically have high ferrite/sigma content 

(up to 40%) and may have very poor high temperature ductility. 铸造奥氏 

体不锈钢敏化都可能高至 40% 的 σ 相 , 这导致很差的高温塑性 / 延展性 .

Evaluation of Sigma Phase Embrittlement of a Stainless Steel 

304H Fluid Catalyst Cracking Unit Regenerator Cyclone 不锈钢 

304H 催化裂化再生旋风器 σ 相脆化评价 . 

Authors: Ali Y. Al-Kawaie and Abdelhak Kermad 

ABSTRACT 

Testing was performed on a 304H stainless steel sample removed from a Fluid Catalyst Cracking 

Unit (FCCU) regenerator cyclone after 25 years of service to check for sigma phase formation. 

Sigma phase is a nonmagnetic inter-metallic phase composed mainly of iron and chromium (Fe- 

Cr), which forms in ferritic and austenitic stainless steels during exposure at the temperature 

range 1,050 °F to 1,800 °F (560 °C to 980 °C), causing loss of ductility and toughness. Cracking 

may also occur if the component was impact-loaded or excessively stressed during shutdown or 

maintenance work. This article discusses the effect of sigma phase embrittlement on the FCCU 

regenerator cyclone after extended high temperature service. 

http://www.saudiaramco.com/content/dam/Publications/Journa 

l%20of%20Technology/Spring2011/Art%2012%20- 

%20JOT%20Internet.pdf

Table 2. Impact testing (Test Method: ASTM E23) 

Table 3. Micro-hardness 

testing. Test load: 200 g, 

Calibration Block Hardness: 

256 + 10 HV, Measured 

Hardness of the calibration 

block: 258 VHN.

Fig. 1. Cyclone 

sample, as received.

Fig. 2. Micrograph 

showing carburized 

layer at the outer (top) 

surface, 100x (As 

received).

Note: solution annealing at 1,066 °C for four hours, followed by a water 

quench before testing. 


showing the 

microstructure at the 

outer (top) surface, 

100x (Heat treaded).


showing sigma 

formation at the center 

of the sample. 

Estimated volume 

fraction 7%, 100x (As 

received).






center of the heat 

treated sample, 100x 

(Heat treated).


showing sigma phase 

at the inner (bottom) 

surface of the original 

sample, 100x (As 

received).






inner surface of the 

heat treated sample, 

100x (Heat treated).

Fig. 8a. SEM fractography showing the brittle fracture surface (Top - As received)

Fig. 8b. SEM fractography showing the ductile fracture (Bottom - Heat treated) of the 

impact tested samples.


a) The best way to prevent sigma phase embrittlement is to use alloys that are 

resistant to sigma formation or to avoid exposing the material to the 

embrittling range. 最好的预防方法是不用易敏材料与避免使材料暴露在脆化 

温度范围作业 ( 这牵涉到设定合适的 IOW) 

b) The lack of fracture ductility at room temperature indicates that care should 

be taken to avoid application of high stresses to sigmatized materials during 

shutdown, as a brittle fracture could result. 室温断裂韧性不足是 σ 相脆化损 

伤机理的特点 . 这显著地影响设备在启动 , 关断与瞬态状态的使用 ; 在设备处于 

低温状态时避免设备受到高应力 ( 设备随着温度提高增加设备受压 ).* 

c) The 300 Series SS can be de-sigmatized by solution annealing at 1950°F 

(1066°C) for four hours followed by a water quench. However, this is not 

practical for most equipment. σ 相脆化损伤可以可以通过加热逆转恢复 ( 温度 

1950°F 固溶退火 ). 然而这往往并不是在役设备实用的修护方案 . 

Note* 注意设备压力试验时可能导致低温脆裂的危险 .

d) Sigma phase in welds can be minimized by controlling ferrite in the range of 5% to 

9% for Type 347 and somewhat less ferrite for Type 304. The weld metal ferrite 

content should be limited to the stated maximum to minimize sigma formation 

during service or fabrication, and must meet the stated minimum in order to 

minimize hot short cracking during welding. 奥氏体不锈钢铁素体含量的控制用 

于减少 σ 相脆化的形成 . 

e) For stainless steel weld overlay clad Cr-Mo components, the exposure time to 

PWHT temperatures should be limited wherever possible. 铬钼覆盖层焊后热处理 

尽量减少暴露时间 .

What causes knife-line attack? 

For stabilized stainless steels and alloys, carbon 

is bonded with stabilizers (TiC or NbC) and no 

weld decay occurs in the heat affected zone 

during welding. In the event of a subsequent heat 

treatment or welding (above 1200 o C), however, 

first the TiC / NbC may dissociated into free Ti, 

Nb and C, on cooling precipitation of chromium 

carbide Cr 23 C 6 is possible and this leaves the 

narrow band adjacent to the fusion line 

susceptible to intergranular corrosion. 

What causes weld decay? As in the case of intergranular corrosion, grain boundary precipitation, notably 

chromium carbides in non-stabilized stainless steels, is a well recognized and accepted mechanism of weld 

decay. In this case, the precipitation of chromium carbides is induced by the welding operation when the 

heat affected zone (HAZ) experiences a particular temperature range (550 o C~850 o C). The precipitation of 

chromium carbides consumed the alloying element - chromium from a narrow band along the grain 

boundary and this makes the zone anodic to the unaffected grains. The chromium depleted zone becomes the 

preferential path for corrosion attack or crack propagation if under tensile stress.

Anodic site

4.2.6.7 Inspection and Monitoring 检验与监测 

a) Physical testing of samples removed from service is the most positive 

indicator of a problem. 设备采样机械试验时最好的方法确认损伤机制 . 

b) Most cases of embrittlement are found in the form of cracking in both 

wrought and cast (welded) metals during turnarounds, or during startup or 

shutdown when the material is below about 500°F (260°C) and the effects 

of embrittlement are most pronounced. σ 相脆化开裂失效模式一般出现于设 

备温度处于低于 500°F (260°C) 状态例如当设备周转 , 启动 , 关断时 . 

4.2.6.8 Related Mechanisms 相关机制 

Not applicable. 不适用

Figure 10: Shaeffler diagram showing the embrittlement region of theσphase [33]. 

http://www.hindawi.com/journals/isrn.metallurgy/2012/732471/

http://www.metalconsult.com/failure-analysis-furnace-tubes.html



http://www.metallograf.de/start-eng.htm?/untersuchungen-eng/sigmaphase/sigmaphase.htm

http://www.industrialheating.com/articles/90371-sigma-phase-embrittlement 

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1517-70762009000300017

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1517-70762009000300017

Table 4: Chemical composition of ferrite austenite and sigma phases at 900 o C

Polishing markings

Improperly etched specimen showing little or no sign of sigma phase

NaOH etched

Oxalic acid etched- 

Duplex SS

Sigma-phase embrittlement 

• 高温现象 :1000 o F~1700 o F 

• 影响材质 : 铁铬合金 

• 原理 :σ 相脆化损伤机理 : 是当铁铬合金暴露在高温下 , 硬 , 脆性的 σ 相金属间 

化合物晶界沉淀引起的脆性现象 . 

• 解决方法 : σ 相脆化损伤可以可以通过加热逆转恢复 ( 温度 1950°F 固溶退火 ). 

然而这往往并不是在役设备实用的修护方案 . 

• 非 API 510/570 考试项

4.2.7 Brittle Fracture 

脆性破裂 

API 510/570 考试学习科目 

API510/570-Exam


Below DTBTT 

DTBT: Ductile to brittle 

transition temperature. 

API510/570-Exam

No shear lip, little micro void coalescence, little deformation 

API510/570-Exam

API510/570-Exam 

4.2.7 Brittle Fracture 脆性断裂 

4.2.7.1 Description of Damage 损伤描述 

Brittle fracture is the sudden rapid fracture under stress (residual or applied) 

where the material exhibits little or no evidence of ductility or plastic 

deformation. 脆性断裂 - 在应力 ( 残余或应用 ) 作用下突然快速断裂 . 材料表现出很 

少的延展性 , 塑性变形 . 

4.2.7.2 Affected Materials 受影响材质 

Carbon steels and low alloy steels are of prime concern, particularly older 

steels. 400 Series SS are also susceptible. 受影响的材质有 ; 碳钢 , 低合金钢与 

铁素体 / 马氏体不锈钢 

Affected Materials Ferritic/Martensitic STEELS 只对铁素体 / 马氏体钢材影响



a) When the critical combination of three factors is reached, brittle fracture can 

occur: 

1. The materials’ fracture toughness (resistance to crack like flaws) as 

measured in a Charpy impact test; 断裂韧性 

2. The size, shape and stress concentration effect of a flaw; 

应力的形状与大小 

3. The amount of residual and applied stresses on the flaw. 

残余或外加应力 

b) Susceptibility to brittle fracture may be increased by the presence of 

embrittling phases. 晶体脆化相存在会增加脆裂易感性 

c) Steel cleanliness and grain size have a significant influence on toughness 

and resistance to brittle fracture. 钢的纯净度和晶粒大小显著地影响材料韧性 

和断裂抗拒能力 .


d) Thicker material sections also have a lower resistance to brittle fracture 

due to higher constraint which increases triaxial stresses at the crack tip. 

较厚的材料因更高的应力约束 , 增加了在裂纹尖端的三轴应力 ; 导致较低的断 

裂阻力 

d) In most cases, brittle fracture occurs only at temperatures below the 

Charpy impact transition temperature (or ductile-to-brittle transition 

temperature), the point at which the toughness of the material drops off 

sharply. 一般上脆裂发生在低于韧脆转变温度 .


Definition of Brittle Fracture 脆性断裂定义 

a steel member may experience a brittle fracture. Three basic factors contribute to a 

brittle-cleavage type of fracture. They are; 

• a triaxial state of stress, 

• a low temperature, and 

• a high strain rate or rapid rate of loading. 

All these factors need not be present. Crack often propagates by cleavage – 

breaking of atomic bonds along specific crystallographic planes (cleavage planes), 

propagate rapidly without further increase in applied stress (applied or residual) 

with little indication of plastic deformation. 

In contrast, a ductile fracture occurs mainly by shear, usually preceded by 

considerable plastic deformation.

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Figure 7: The fracture examination using a SEM on C1 and C2 revealed features 

typical of transgranular fracture (left and middle) and signatures of intergranular 

cracking (left and right). The presence of both intergranular and transgranular features 

indicates a mixed-mode fracture morphology. 

http://www.drillingcontractor.org/tubular-fracturing-pinpointing-the-cause-14544


In Case 2 from Oklahoma, the pin connection twisted off while making up 

the pin connection of a saver sub. 

http://www.drillingcontractor.org/tubular-fracturing-pinpointing-the-cause-14544

Figure 4: The fracture on the Case 1 sub showed a grainy texture and “chevron 

marks” that point toward the initiation site, which is typical morphology for brittle 

cracking 

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Figure 5: The fracture 

on C3 exhibited a 

small fatigue region 

that was followed by 

brittle fracture. The 

fracture surface had a 

grainy appearance 

and presented a 

minuscule shear lip, 

which is also typical 

of a brittle fracture


Various stages during ductile fracture 韧性断裂 are schematically shown in above figure. 

(a) Necking, 缩颈 

(b) Cavity formation (microvoid), 微孔形成 

(c) Cavity coalescence to form a crack (microvoid coalescence), 微孔的聚结 

(d) Crack propagation, 裂缝蔓延 

(e) Fracture (shear fracture). 断裂 ( 剪切断裂 )

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Brittle fracture of a shaft caused by a 

small fatigue crack close to the keyway. 

The fatigue would be expected to start 

at the keyway root but actually began at 

a surface defect. 

http://www.surescreen.com/scientifics/library-of-failures.php

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http://www.wermac.org/misc/pressuretestingfailure2.html 

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4.2.7.4 Affected Units or Equipment 受影响的单元或设备 

a) Equipment manufactured to the ASME Boiler and Pressure Vessel Code, 

Section VIII, Division 1, prior to the December 1987 Addenda, were made 

with limited restrictions on notch toughness for vessels operating at cold 

temperatures. However, this does not mean that all vessels fabricated prior 

to this date will be subject to brittle fracture. Many designers specified 

supplemental impact tests on equipment that was intended to be in cold 

service. 

ASME 锅炉和压力容器规范 1987 年 12 月前 , 因为对低温操作设备缺乏材料韧性 

要求的限制 , 这些设备可能有脆裂的隐患 . 然而虽然不是规范要求 , 有的设计会因 

设备低温操作 , 对材质附加低温冲击要求 . 

b) Equipment made to the same code after this date were subject to 

the requirements of UCS 66 (impact exemption curves). 

引用 ASME VIII DIV1 UCS 66 对材料冲击要求宽松条款的设备 .


c) Most processes run at elevated temperature so the main concern is for brittle 

fracture during startup, shutdown, or hydrotest/tightness testing. Thick wall 

equipment on any unit should be considered. 在设备因周转 , 启动 , 停机时低温 

状态 

d) Brittle fracture can also occur during an auto-refrigeration event in units 

processing light hydrocarbons such as methane, ethane/ethylene, 

propane/propylene, or butane. This includes alkylation units, olefin units and 

polymer plants (polyethylene and polypropylene). Storage bullets/spheres for 

light hydrocarbons may also be susceptible. 蒸发自动冷却服务 . 

e) Brittle fracture can occur during ambient temperature hydrotesting due to 

high stresses and low toughness at the testing temperature. 室温试压时

UCS-66 MATERIALS. 

ASME VIII Div.1- Charlie Chong/ Fion Zhang 

UCS-66

The main material property that API 510 / ASME VIII is concerned 

with is that of resistance to brittle fracture. The fundamental issue is 

therefore whether a material is suitable for the minimum design metal 

temperature (MDMT design ) for which a vessel is designed. This topic is 

covered by clause UCS-66 of ASME VIII. 


UCS-66

Steps: 

1. UG-20 for exemption on impact testing. 

2. UCS-66. 

• Identified material Group A,B,C,D. 

• Figure UCS-66 to determine the allowable MDMT. 

• Figure UCS-66.1 to determine the reduction in MDMT based on 

coincident ratio. 

3. UCS-68(c) to determine on further reduction in MDMT. 


UCS-66

Figure UCS 66.1 Coincident Ratio 

The Coincident Ratio is based on a vessel’s extra thickness due to its 

design calculations which were based on its Maximum Temperature. 

Meaning that; As metal’s temperature increases its strength decreases, 

hotter means weaker, therefore the allowable stress is decreased during 

calculations resulting in vessel that requires thicker walls when hot 

than when it is operating at its coldest temperature, the MDMT. 

This ratio takes credit for the extra wall thickness that is present, but 

not needed to resist pressure at the MDMT. The following graphic will 

help. Usually when there is a drop in temperature there is also a drop 

in the pressure. The two operating conditions are calculated and the 

Ratio is determined. This Ratio is given on the exam and you need 

only use the table to apply this rule. 


UCS-66

How to use FIG. UCS-66 & FIG. UCS-66.1 to 

determine allowable impact test value 

(MDMT allowable ) 


UCS-66

Steps: 

1. Determine material group. 

2. Determine MDMT allowable on 

the graph. 

3. If Design MDMT higher than 

MDMT allowable , no test requires. 

4. If MDMT allowable is higher than 

design MDMT goto FIG. UCS- 

66.1 


UCS-66


UCS-66

Steps: 

5. If the coincident ratio is 0.70 

reduction of 30 o F from the 

MDMT allowable . The revised 

MDMT’ allowable = 59 o F. 

6. If the revised MDMT’ 

allowable is higher than the 

design MDMT, check on 

item 7. 

7. If material is P1, UCS-68(c) 

If postweld heat treating is 

performed when it is not 

otherwise a requirement of 

this Division, a reduction of 

30 o F. The resulting MDMT 

allowable may be colder than - 

55 o F. 


UCS-66

Once the MDMT allowable had been ascertained, further reductions are 

possible by within -55ºF capping with exception 

1. Low coincident stress ratio 

2. postweld heat treating is performed when it is not otherwise a requirement 

of this Division on P1 materials. 

-55 o F 


UCS-66

UCS-66 (b2) For minimum design metal temperatures colder than -55ºF (- 

48ºC), impact testing is required for all materials, except as allowed in (b)(3) 

below and in UCS-68(c). 

UCS-66 (b3) When the minimum design metal temperature is colder than - 

55ºF (-48ºC) and no colder than -155ºF (-105ºC), and the coincident ratio 

defined in Fig. UCS-66.1 is less than or equal to 0.35, impact testing is not 

required. 


UCS-66

UCS-66 (b2) For minimum design metal temperatures colder than -55ºF (- 

48ºC), impact testing is required for all materials, except as allowed in (b)(3) 

below and in UCS-68(c). 

UCS-68(c) If postweld heat treating is performed when it is not otherwise a 

requirement of this Division, a 30ºF (17ºC) reduction in impact testing 

exemption temperature may be given to the minimum permissible 

temperature from Fig. UCS-66 for P-No. 1 materials. The resulting 

exemption temperature may be colder than -55ºF (-48ºC). 


UCS-66



a) Cracks will typically be straight, non-branching, and largely devoid of any 

associated plastic deformation (no shear lip or localized necking around 

the crack) (Figure 4-6 to Figure 4-7). 

宏观 : 直 , 不分枝 , 并在很大程度上没有任何相关的塑性变形 . 

b) Microscopically, the fracture surface will be composed largely of cleavage, 

with limited intergranular cracking and very little microvoid coalescence. 

微观 : 主要为分裂 ( 少量的沿晶开裂 ?) 与非常小的微孔聚合

API510/570-Exam

Crack propagation (cleavage) in brittle materials occurs through planar 

sectioning of the atomic bonds between the atoms at the crack tip. 

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a) For new equipment, brittle fracture is best prevented by using materials 

specifically designed for low temperature operation including upset and autorefrigeration 

events. Materials with controlled chemical composition, special heat 

treatment and impact test verification may be required. Refer to UCS 66 in 

Section VIII of the ASME BPV Code. 低温设备选材合适冲击要求材料 

b) Brittle fracture is an “event” driven damage mechanism. For existing materials, 

where the right combination of stress, material toughness and flaw size govern the 

probability of the event, an engineering study can be performed in accordance 

with API 579-1/ASME FFS-1 , Section 3, Level 1 or 2. 脆裂为 “ 事件 ” 驱动的损 

伤机制 ( 因素 : 应力 , 韧性和裂纹尺寸 ) 应用 FFS-1 适用性分析 , 评估设备完整性 . 

c) Preventative measures to minimize the potential for brittle fracture in existing 

equipment are limited to controlling the operating conditions (pressure, 

temperature), minimizing pressure at ambient temperatures during startup and 

shutdown, and periodic inspection at high stress locations. 维持 IOW 操作参数 , 

周转期间启动 , 关断设备受压与温度控制与在高应力区的定期检查 .


d) Some reduction in the likelihood of a brittle fracture may be achieved by: 

缓解行动有 ; 

1. Performing a post weld heat treatment (PWHT) on the vessel if it was not 

originally done during manufacturing; or if the vessel has been weld 

repaired/modified while in service without the subsequent PWHT. 焊后热 

处理 

2. Perform a “warm” pre-stress hydrotest followed by a lower temperature 

hydrotest to extend the Minimum Safe Operating Temperature (MSOT) 

envelope. 周转期间水压试验 / 温度控制 .



a) Inspection is not normally used to mitigate brittle fracture. 检验不能用来缓 

解脆性开裂 

b) Susceptible vessels should be inspected for pre-existing flaws/defects. 易 

感容器的存在缺陷的监测


4.2.7.8 Related Mechanisms 相关机理 

Temper embrittlement (see 4.2.3), strain age embrittlement (see 4.2.4), 885 o F 

(475 o C) embrittlement (see4.2.5), titanium hydriding (see 5.1.3.2) and sigma 

embrittlement (see 4.2.6). 

脆性破裂作为形态定义时 , 上述损坏机理 , 破断形态可以归类为 ” 脆性破裂 ” 

Temper embrittlement

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Ductile fracture (non creep type)

Microvoid due to plastid yielding & ductile 

fracture (non creep type)

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Further reading: 

http://www.sut.ac.th/engineering/metal/pdf/MechMet/14_Brittle%20fracture%20and%20impact%20testing.pdf 

http://lecture.civilengineeringx.com/structural-analysis/structural-steel/brittle-fracture/ 

http://www.keytometals.com/articles/art136.htm 

http://people.virginia.edu/~lz2n/mse209/Chapter8.pdf 

http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&LN=CN&NM=136 

http://www.techtransfer.com/resources/wiki/entry/3645/



• 低温现象 : 室温 / 低于 400 o F, 

• 影响材质 : 铁素体 / 马氏体钢 , 

• 焊后热处理作为预防与缓解方法 , 

• 周转期间设备处于低温状态时的受压控制 (MSOT), 

• 应用 FFS-1 合适性分析 , 评估带缺陷的设备可用性 , 

• 导致脆性开裂的因素有 ; (1) 低韧性铁素体钢材 , (2) 服务导致脆化 , 例如 ; 回火 

脆化 , 应变时效脆性 ,885 o F 脆化 , 钛氢化 , 西格玛的脆化 .

4.2.8 Creep & Stress Rupture 

蠕变和应力断裂 

非 API 510/570 考试科目

Creep & Stress 

Rupture 

700 o F ~ 1000 o F






Sigma-Phase 

Embrittlement 





850 o F ~ 1400 o F 

650 o F~ 1070 o F 

Intermediate 

temperature 

600 o F~ 1000 o F 

1000 o F~ 1700 o F 

Below DTBTT 

700 o F ~ 1000 o F 


C- ½ Mo 


2 ¼ Cr-1Mo low alloy steel, 3Cr-1Mo (lesser 

extent), & HSLA Cr-Mo-V rotor steels 

Pre-1980’s C-steels with large grain size and C- ½ 

Mo 

300, 400 & Duplex SS containing ferrite phases 


C, C- ½ Mo, 400 SS 

All metals and alloys

4.2.8 Creep and Stress Rupture 蠕变和应力开裂 

4.2.8.1 Description of Damage 描述 

a) At high temperatures, metal components can slowly and continuously 

deform under load below the yield stress. This time dependent deformation 

of stressed components is known as creep. 

b) Deformation leads to damage that may eventually lead to a rupture. 

在高温和载荷低于屈服应力下 , 金属部件缓慢 , 持续下的变形 . 这变形导致损伤 , 

最终可能破裂 . 

4.2.8.2 Affected Materials 受影响的材料 

All metals and alloys. 所有的金属和合金。

http://www.ejsong.com/mdme/me 

mmods/MEM30007A/properties/Pr 

operties.html

4.2.8.3 Critical Factors 蠕变和应力断裂关键因素 

a) The rate of creep deformation is a function of the material, load, and 

temperature. The rate of damage (strain rate) is sensitive to both load and 

temperature. Generally, an increase of about 25°F (12°C) or an increase of 

15% on stress can cut the remaining life in half or more, depending on the 

alloy. 

影响蠕变的因素 : (1) 材质易感性 , (2) 负载和 (3) 温度 , 例子 : 25°F(12°C) 或 15% 

应力增加一般上导致使用寿面减半 . 

b) Table 4-3 lists threshold temperatures above which creep damage is a 

concern. If the metal temperature exceeds these values, then creep damage 

and creep cracking can occur. 

表 4-3 列出不同材料的易感温度

c) The level of creep damage is a function of the material and the coincident 

temperature/stress level at which the creep deformation occurs. 蠕变破坏依 

赖温度与应力的组合影响 . 

d) The life of metal components becomes nearly infinite at temperatures below 

the threshold limit (Table 4-3) even at the high stresses near a crack tip. 

低于易感温度时 , 甚至在高应力的使用下 , 材料几乎是无限的不受蠕变的影响 . 

e) The appearance of creep damage with little or no apparent deformation is 

often mistakenly referred to as creep embrittlement, but usually indicates 

that the material has low creep ductility. 不是所有的蠕变失效具有明显的外表 

变形 . 低延展性蠕变在外观上不容易被识别 .

f) Low creep ductility is: 低延展性蠕变 

1) More severe for higher tensile strength materials and welds. 高强材料 

2) More prevalent at the lower temperatures in the creep range, or low 

stresses in the upper creep range. 普遍于 (1) 蠕变低温度范围或 (2) 低应 

力高温度范围 . 

3) More likely in a coarse-grained material than a fine-grained material. 

粗晶材料 

4) Not evidenced by a deterioration of ambient temperature properties. 

低温机械性能不显著地退化 . 

5) Promoted by certain carbide types in some CrMo steels. 

某些碳化物促进破坏 

g) Increased stress due to loss in thickness from corrosion will reduce time to 

failure. 腐蚀厚度损失加剧蠕变破坏

不是所有的蠕变失效具有明显的外表变形 ! 

低延展性蠕变 

Is all creep failure associated with apparent deformation? 

The appearance of creep damage with little or no apparent deformation is 

often mistakenly referred to as creep embrittlement, but usually indicates that 

the material has low creep ductility. 经常被误称蠕变脆化其实是低延展性蠕变

4.2.8.4 Affected Units or Equipment 受影响的设备 

a) Creep damage is found in high temperature equipment operating above 

the creep range. Heater tubes in fired heaters are especially susceptible 

as well as tube supports, hangers and other furnace internals. 一切高温设 

备 , 特别是加热器的加热管 , 管支架 , 吊架和炉内附件等 . 

b) Piping and equipment, such as hot-wall catalytic reforming reactors and 

furnace tubes, hydrogen reforming furnace tubes, hot wall FCC reactors, 

FCC main fractionator and regenerator internals all operate in or near the 

creep range. 催化裂化反应器的管道 , 罐壁 , 氢转化炉炉管 , 炉管等 .

c) Low creep ductility failures have occurred in weld heat-affected zones 

(HAZ) at nozzles and other high stress areas on catalytic reformer 

reactors. Cracking has also been found at long seam welds in some high 

temperature piping and in reactors on catalytic reformers. 

催化重整反应器焊缝与热影响区 

d) Welds joining dissimilar materials (ferritic to austenitic welds) may suffer 

creep related damage at high temperatures due to differential thermal 

expansion stresses. 异种材料的焊接接合 ( 例如 : 铁素体 / 奥氏体 ) 经历因热膨 

胀差异导致的应力与高温蠕变 .

4.2.8.6 Prevention / Mitigation 预防与缓解 

a) There is little that inspectors or operators can do to prevent this damage 

once a susceptible material has been placed into creep service, other 

than to minimize the metal temperature, particularly with fired heater tubes. 

Avoiding stress concentrators is important during design and fabrication. 

(1) 温度控制与 (2) 设计时避免应力集中点 . 

b) Low creep ductility can be minimized by the careful selection of chemistry 

for low alloy materials. Higher post weld heat treatment temperatures may 

help minimize creep cracking of materials with low creep ductility such as 

1.25Cr-0.5Mo. 

低合金钢的低延性蠕变 ; (1) 通过焊后热处理 , (2) 材料化学成分控制 .

c) Creep damage is not reversible. Once damage or cracking is detected 

much of the life of the component has been used up and typically the 

options are to repair or replace the damaged component. Higher PWHT in 

some cases can produce a more creep ductile material with longer life. 蠕 

变损伤是不可逆转 

1. Equipment – Repair of creep damaged catalytic reformer reactor nozzles 

has been successfully accomplished by grinding out the affected area 

(making sure all the damaged metal is removed), re-welding and careful 

blend grinding to help minimize stress concentration. PWHT temperatures 

must be carefully selected and may require a higher PWHT than originally 

specified. 

催化重整反应器管口修护例子 : (1) 磨出受影响的区域 , (2) 修补焊接填充 , (3) 

打磨平滑减少应力集中 , (4) 高于原设计的焊后热处理 .

c2 Fired Heater Tubes 炉管 

• Alloys with improved creep resistance may be required for longer life. 

改进的抗蠕变性合金管 

• Heaters should be designed and operated to minimize hot spots and 

localized overheating (Figure 4-19). 

减少热点和局部过热 

• Visual inspection followed by thickness measurements and or strap 

readings may be required to assess remaining life of heater tubes in 

accordance with API 579-1/ASME FFS-1. 

目视 , 捆扎法 ( 测量外径变化 ) 以识别受影响的管道 . 运用合适性分析法 FFS, 评 

估受影响的管道是否能继续的使用 . 

• Minimizing process side fouling/deposits and fire side deposits/scaling 

can maximize tube life. 

减少工艺侧的污垢 / 堆积 , 火侧的堆积 / 氧化皮加厚


a) Creep damage with the associated microvoid formation, fissuring and 

dimensional changes is not effectively found by any one inspection 

technique. A combination of techniques (UT, RT, EC, dimensional 

measurements and replication) should be employed. Destructive sampling 

and metallographic examination are used to confirm damage. 蠕变体现为 

微孔 , 裂隙与尺寸变化 . 当个无损探伤方法或许不容易探测到蠕变破坏 . 综合 

考虑运用多种探伤方法与晶相模塑法 (in-situ replication) 或切片晶相微观观 

察 . 

b) For pressure vessels, inspection should focus on welds of CrMo alloys 

operating in the creep range. The 1 Cr-0.5Mo and 1.25Cr-0.5Mo materials 

are particularly prone to low creep ductility. Most inspections are 

performed visually and followed by PT or WFMT on several-year intervals. 

Angle beam (shear wave) UT can also be employed, although the early 

stages of creep damage are very difficult to detect. Initial fabrication flaws 

should be mapped and documented for future reference. 铬钼材质特别是 

焊缝区域是检验关注点 . 多数的检验步骤为 ; (1) 外观目视 (2) PT/WFMT (2+) 

斜束剪切波 UT. ( 提防建造缺陷导致误判 )

c) Fired heater tubes should be inspected for evidence of overheating, 

corrosion, and erosion as follows: 炉管检验 

1. Tubes should be VT examined for bulging, blistering, cracking, 

sagging and bowing. 目视观察 ; 鼓 , 起泡 , 开裂和弯曲与垂落 . 

2. Wall thickness measurements of selected heater tubes should be 

made where wall losses are most likely to occur. 厚度检测 

3. Tubes should be examined for evidence of diametric growth (creep) 

with a strap or go/no go gauge, and in limited cases by metallography 

on in place replicas or tube samples. However, metallography on the 

OD of a component may not provide a clear indication of subsurface 

damage. 检测外径变化 ( 上下限制测量规 ), 现场晶相模塑法 (replica) 

4. Retirement criteria based on diametric growth and loss of wall 

thickness is highly dependent on the tube material and the specific 

operating conditions. 基于直径生长和损失的壁厚的报废准则很大程度 

上依赖于管材与具体操作条件 .

4.2.8.8 Related Mechanisms 相关机理 

a) Creep damage that occurs as a result of exposure to very high 

temperatures is described in 4.2.10. (Overheating stress rupture 过热的应 

力破裂 ) 

b) Reheat cracking (see 4.2.19) is a related mechanism found in heavy wall 

equipment. 再热裂纹 - 厚壁的设备发现的相关机理

Figure 4-17 – Pinched 

Alloy 800H pigtail 

opened up creep 

fissures on the surface.

Figure 4-18 – Creep rupture of an HK40 heater tube.

a 

b 

Figure 4-19 – Creep Failure of 310 SS Heater Tube Guide Bolt after approximately 7 

years service at 1400°F (760°C). a.) Cross-section at 10X, as-polished.

a 

b 

Figure 4-19 – Creep Failure of 310 SS Heater Tube Guide Bolt after approximately 7 years service 

at 1400°F (760°C). b) Voids and intergranular separation characteristic of long term creep, 100X, 

etched.

蠕变和应力开裂学习重点 : 

1. 温度 : 高温 , 

2. 原理 : 在高温和载荷低于屈服应力下 , 金属部件缓慢 , 持续下的变形 . 这变 

形导致损伤 , 最终可能破裂 . 

3. 易感材质 : 全部工程材料 . 

4. 易感设备 : 一切高温设备 , 特别是加热器的加热管 , 内构件 . 

5. 非 API 510/570 考试题非 API 510/570 考试题

4.2.9 Thermal Fatigue 

热疲劳 

API510/570-Exam

Thermal Fatigue 

Operating Temp. 

API510/570-Exam







Sigma-Phase 

Embrittlement 






850 o F ~ 1400 o F 

650 o F~ 1070 o F 

Intermediate 

temperature 

600 o F~ 1000 o F 

1000 o F~ 1700 o F 

Below DTBTT 

700 o F ~ 1000 o F 

Operating temp. 


C- ½ Mo 


2 ¼ Cr-1Mo low alloy steel, 3Cr-1Mo (lesser 

extent), & HSLA Cr-Mo-V rotor steels 

Pre-1980’s C-steels with large grain size and C- ½ 

Mo 



C, C- ½ Mo, 400 SS 


All metals and alloys


4.2.9 Thermal Fatigue 热疲劳 


Thermal fatigue is the result of cyclic stresses caused by variations in 

temperature. Damage is in the form of cracking that may occur anywhere in a 

metallic component where relative movement or differential expansion is 

constrained, particularly under repeated thermal cycling. 

热疲劳开裂是由温度变化引起循环应力引起的开裂 . 

4.2.9.2 Affected Materials 受影响的材料 

All materials of construction. 所有施工材料



a) Key factors affecting thermal fatigue are the magnitude of the temperature 

swing and the frequency (number of cycles). 温度摆动的幅度和频率 

b) Time to failure is a function of the magnitude of the stress and the number of 

cycles and decreases with increasing stress and increasing cycles. 故障时间 

有赖于 (1) 温度摆动的幅度 (2) 频率 (3) 应力的大小 

c) Startup and shutdown of equipment increase the susceptibility to thermal 

fatigue. There is no set limit on temperature swings; however, as a practical 

rule, cracking may be suspected if the temperature swings exceeds about 

200°F (93°C). 周转 / 启动 / 停机增加热疲劳的易感性 . 作为一个实际的规则大于 

200°F 摆动幅度作为热疲劳损伤怀疑点 .


d) Damage is also promoted by rapid changes in surface temperature that 

result in a thermal gradient through the thickness or along the length of a 

component. For example: cold water on a hot tube (thermal shock); rigid 

attachments and a smaller temperature differential; inflexibility to 

accommodate differential expansion. 促进因素 : 沿着管道长度或厚度的温度偏 

差 , 自由膨胀阻碍 ( 缺少弹性的设计 ) 

e) Notches (such as the toe of a weld) and sharp corners (such as the 

intersection of a nozzle with a vessel shell) and other stress concentrations 

may serve as initiation sites. 缺口 - 焊趾处 , 尖锐点 ( 应力集中点 ).



a) Examples include the mix points of hot and cold streams such as hydrogen 

mix points in hydroprocessing units 加氢装置 , and locations where 

condensate comes in contact with steam systems, such as de-superheating 

or attemporating equipment 减温装置 (Figures 4-20 and 4-23). 不同温度流体 

混合点 . 

b) Thermal fatigue cracking has been a major problem in coke drum shells. 

Thermal fatigue can also occur on coke drum skirts where stresses are 

promoted by a variation in temperature between the drum and skirt (Figure 

4–21 and Figure 4–22). 焦炭鼓裙边与塔壁 . ( 考试题 ) 

c) In steam generating equipment, the most common locations are at rigid 

attachments between neighboring tubes in the superheater and reheater. 

Slip spacers designed to accommodate relative movement may become 

frozen and act as a rigid attachment when plugged with fly ash. 

蒸汽发生装置 ( 过热器和再热器管路 )

Figure 4-20 – Thermal fatigue cracks on the inside of a heavy wall SS pipe downstream of a 

cooler H2 injection into a hot hydrocarbon line. 

API510/570-Exam

Figure 4-21 – Bulging in a skirt of a coke drum. 

API510/570-Exam

Figure 4-22 –Thermal fatigue cracking associated with 

bulged skirt shown in Figure 4-21. 

API510/570-Exam

Figure 4-23 – Thermal fatigue of 304L stainless at mix point in the BFW preheater 

bypass line around the high temperature shift effluent exchanger in a hydrogen 

reformer. The delta T is 325°F (181°C) at an 8 inch bypass line tying into a 14 inch 

line, 3 yrs after startup. 

API510/570-Exam


Figure 4-24 – In a carbon steel sample, metallographic section through a thermal fatigue crack 

indicates origin at the toe of an attachment weld. Mag. 50X, etched.


Figure 4-25 – Older cracks fill with oxide, may stop and restart (note jog part way along the 

crack), and do not necessarily require a change in section thickness to initiate the crack. Mag. 

100X, etched.


d) Tubes in the high temperature superheater or reheater that penetrate 

through the cooler water-wall tubes may crack at the header connection if 

the tube is not sufficiently flexible. These cracks are most common at the 

end where the expansion of the header relative to the water-wall will be 

greatest. 穿过水冷冷却器壁的过热器 , 再热器管路 . 

d) Steam actuated soot blowers may cause thermal fatigue damage if the first 

steam exiting the soot blower nozzle contains condensate. Rapid cooling of 

the tube by the liquid water will promote this form of damage. Similarly, 

water lancing or water cannon use on water-wall tubes may have the same 

effect. (1) 蒸汽驱动的吹灰器接触冷凝液的热管路 , (2) 其他接触冷凝液的热管 

路服务 .

API510/570-Exam

http://www.slashgear.com/bill-gates-helping-china-build-super-safenuclear-reactor-08200894/ 

API510/570-Exam


4.2.9.5 Appearance or Morphology of Damage 破坏外观形貌 

a) Thermal fatigue cracks usually initiate on the surface of the component. 

They are generally wide and often filled with oxides due to elevated 

temperature exposure. Cracks may occur as single or multiple cracks. 

表面发起点 , 开裂表面氧化 , 裂缝可能为单个或多个裂纹延伸 . 

b) Thermal fatigue cracks propagate transverse to the stress and they are 

usually dagger-shaped, transgranular, and oxide filled (Figure 4-24 and 4- 

25). However, cracking may be axial or circumferential, or both, at the same 

location. 应力方向横向开裂 , 穿晶 , 氧化 , 刀纹状 (?), 开裂方向为 ; 轴向或圆周向 

或并存 .


c) In steam generating equipment, cracks usually follow the toe of the fillet 

weld, as the change in section thickness creates a stress raiser. Cracks 

often start at the end of an attachment lug and if there is a bending moment 

as a result of the constraint, they will develop into circumferential cracks into 

the tube. 在蒸汽发生装置 , 通常开裂起点在焊道应力集中点 , 周圆的延伸 . 

d) Water in soot blowers may lead to a crazing pattern. The predominant 

cracks will be circumferential and the minor cracks will be axial. (Figure 4- 

26 to 4-27). 水助吹灰器的裂纹一般上体现为纹状 .


Figure 4-27 – Photomicrograph of the failed 

superheated steam outlet shown in Figure 4-26. 

Etched. 

Figure 4-26 – Metallographic cross-section of a superheated 

steam outlet that failed from thermal fatigue. Unetched.



a) Thermal fatigue is best prevented through design and operation to 

minimize thermal stresses and thermal cycling. Several methods of 

prevention apply depending on the application. 

1. Designs that incorporate reduction of stress concentrators, blend grinding 

of weld profiles, and smooth transitions should be used. 减少应力集中 , 焊 

缝节点疲劳处理 , 圆滑过渡 . 

2. Controlled rates of heating and cooling during startup and shutdown of 

equipment can lower stresses. 周转 ( 开机 , 关机 ) 控制加热和冷却速率 . 

3. Differential thermal expansion between adjoining components of dissimilar 

materials should be considered. 设计阶段考虑异种材料之间的差热膨胀 .


b) Designs should incorporate sufficient flexibility to accommodate differential 

expansion. 设计时考虑具有足够的灵活性 

1. In steam generating equipment, slip spacers should slip and rigid 

attachments should be avoided. 滑动垫片 . 

2. Drain lines should be provided on soot-blowers to prevent condensate in 

the first portion of the soot blowing cycle. 吹灰器安装排水线避免冷凝液聚集 . 

3. In some cases, a liner or sleeve may be installed to prevent a colder liquid 

from contacting the hotter pressure boundary wall 安装衬垫或套用于防止 

冷液体接触热的压力边界墙


4.2.9.7 Inspection and Monitoring 检查和监督 

a) Since cracking is usually surface connected, visual examination, MT and 

PT are effective methods of inspection. 由于裂缝通常是表面连接 MT/PT 是 

有效的检查方法 . 

b) External SWUT inspection can be used for non-intrusive inspection for 

internal cracking and where reinforcing pads prevent nozzle examination. 

切波角度超声可以用于非侵入性检查 , 例如 : 被补强板妨碍的容器 / 管口区域 . 

c) Heavy wall reactor internal attachment welds can be inspected using 

specialized ultrasonic techniques. 厚壁反应器内部连接焊缝运用切波角度超 

声探测法 

4.2.9.8 Related Mechanisms 相关机制 

Corrosion fatigue (see 4.5.2) and dissimilar metal weld cracking (see 4.2.12). 

腐蚀疲劳 , 异种金属焊缝开裂 .

API510/570-Exam

API510/570-Exam

API510/570-Exam

API510/570-Exam


571-4 


API510/570-Exam

API510/570-Exam

API510/570-Exam

API510/570-Exam

API510/570-Exam

热疲劳学习重点 : 

a) 易感温度 : 高温 

b) 原理 : 热疲劳开裂是由温度变化引起循环应力引起的开裂 , 

c) 易感材质 : 一切工程材料 , 

d) 易感设备 : 蒸汽发生装置 , 蒸汽驱动的吹灰器等 , 高温设备 , 

e) API 510/570 考试题 .

4.2.10 Short Term Overheating Stress Rupture 

短期过热应力开裂 

非 API 510/570 考试题

Short Term 

Overheating Stress Rupture 

Local over-heating.

4.2.10 Short Term Overheating – Stress Rupture 


Permanent deformation occurring at relatively low stress levels as a result of 

localized overheating. This usually results in bulging and eventually failure 

by stress rupture. 

4.2.10.2 Affected Materials 影响材质 

All fired heater tube materials and common materials of construction. 

一切建造材料


a) Temperature, time and stress are critical factors. 温度 , 时间 , 应力 

a) Usually due to flame impingement or local overheating. 火焰冲击或局部过热 

b) Time to failure will increase as internal pressures or loading decrease. 

However, bulging and distortion can be significant at low stresses, as 

temperatures increase. 失效时间随着内部压力或负载减少增长 . 

c) Local overheating above the design temperature. 局部过热 

d) Loss in thickness due to corrosion will reduce time to failure by increasing 

the stress. 由于腐蚀厚度损失增加易感性 .

4.2.10.4 Affected Units or Equipment 受影响的单元或设备 

a) All boiler and fired heater tubes are susceptible. 所有锅炉和加热炉管 

b) Furnaces with coking tendencies such as crude, vacuum, heavy oil 

hydroprocessing and coker units are often fired harder to maintain heater 

outlet temperatures and are more susceptible to localized overheating. 焦 

化倾向的设备 

c) Hydroprocessing reactors may be susceptible to localized overheating of 

reactor beds due to inadequate hydrogen quench or flow mal-distribution. 

氢反应器 - 易受局部过热加反应器床 

d) Refractory lined equipment in the FCC, sulfur plant and other units may 

suffer localized overheating due to refractory damage and/or excessive 

firing. 催化裂化 , 硫磺厂与其他可能遭受局部过热的耐火材料衬里的设备 .

4.2.10.5 Appearance or Morphology of Damage 破坏外观形貌 

a) Damage is typically characterized by localized deformation or bulging on 

the order of 3% to 10% or more, depending on the alloy, temperature and 

stress level. 损坏的典型特征是局部变形或膨胀 (3%~10% 或更多 ) 

b) Ruptures are characterized by open “fishmouth” failures and are usually 

accompanied by thinning at the fracture surface (Figure 4-28 to 4-31). 

破裂的特点是在变薄断裂面 “ 鱼嘴 ” 形象的开裂的特征 .


a) Minimize localized temperature excursions. 减少局部温度漂移 

b) Fired heaters require proper burner management and fouling/deposit 

control to minimize hot spots and localized overheating. 火焰加热器需要适 

当的燃烧器管理 / 污垢和沉积控制以减少局部过热 . 

c) Utilize burners which produce a more diffuse flame pattern. 

d) In hydroprocessing equipment, install and maintain bed thermocouples in 

reactors and minimize the likelihood of hot spots through proper design 

and operation. 

e) Maintain refractory in serviceable condition in refractory lined equipment.

短期过热应力开裂学习重点 : 


b) 原理 : 热疲劳开裂是由温度变化引起循环应力引起的开裂 , 


d) 易感设备 : 蒸汽发生装置 , 蒸汽驱动的吹灰器等 , 高温设备 , 

e) 非 API 510/570 考试题 .

4.2.11 Steam Blanketing 

蒸汽封

Steam Blanketing 

Local over-heating.

4.2.11 Steam Blanketing 


The operation of steam generating equipment is a balance between the heat 

flow from the combustion of the fuel and the generation of steam within the 

waterwall or generating tube. The flow of heat energy through the wall of the 

tube results in the formation of discrete steam bubbles (nucleate boiling) on 

the ID surface. The moving fluid sweeps the bubbles away. When the heat 

flow balance is disturbed, individual bubbles join to form a steam blanket, a 

condition known as Departure From Nucleate Boiling (DNB). Once a steam 

blanket forms, tube rupture can occur rapidly, as a result of short term 

overheating, usually within a few minutes. 


Carbon steel and low alloy steels.

individual bubbles join to form a steam blanket, a condition known as 

Departure From Nucleate Boiling (DNB).

individual bubbles join to form a steam blanket, a condition known as 

Departure From Nucleate Boiling (DNB).

Heat transfer and mass transfer during nucleate boiling has a significant effect on the 

heat transfer rate. This heat transfer process helps quickly and efficiently to carry 

away the energy created at the heat transfer surface and is therefore sometimes 

desirable - for example in nuclear power plants, where liquid is used as a coolant. 

The effects of nucleate boiling take place at two locations: 

• the liquid-wall interface 

• the bubble-liquid interface 

http://en.wikipedia.org/wiki/Nucleate_boiling


a) Heat flux and fluid flow are critical factors. 

b) Flame impingement from misdirected or damaged burners can provide a 

heat flux greater than the steam generating tube can accommodate. 

c) On the water side, anything that restricts fluid flow (for example, pinhole 

leaks lower in the steam circuit or dented tubes from slag falls) will reduce 

fluid flow and can lead to DNB conditions. 

d) Failure occurs as a result of the hoop stress in the tube from the internal 

steam pressure at the elevated temperature.


All steam-generating units including fired boilers, waste heat exchangers in 

sulfur plants, hydrogen reformers and FCC units. Failures can occur in 

superheaters and reheaters during start-up when condensate blocks steam flow.


a) These short-term, high-temperature failures always show an open burst 

with the fracture edges drawn to a near knife-edge (Figure 4-32). 

b) The microstructure will always show severe elongation of the grain 

structure due to the plastic deformation that occurs at the time of failure. 

Figure 4-32 – Short-term high-temperature failures from DNB are wideopen 

bursts with the failure lips drawn to a near knife edge. They are ductile 

ruptures. Mag. 25X.


a) When a DNB condition has developed, tube rupture will quickly follow. 

Proper burner management should be practiced to minimize flame 

impingement. 

b) Proper BFW treatment can help prevent some conditions that can lead to 

restricted fluid flow. 

c) Tubes should be visually inspected for bulging. 


Burners should be properly maintained to prevent flame impingement.

Causes of Caustic Cracking 

Caustic is a boiler water additive. It is added to preserve the thin film of iron oxide to protect the boiler from corrosion. The 

following are the causes of concentration of caustics: 

1. Small bubbles of steam nucleated at the metal surface in minute concentrations of solids in the boiler water would be 

deposited on the metal surface. As the solids are formed they are simultaneously removed from the metal surface by 

water which re-dissolves them. However, when the rate of bubble formation exceeds the rate of dissolution of the solids, 

concentration of caustics would begin to increase. 

2. The deposits of solids shield the metal from the back water. Steam forms under the deposits and escapes leaving behind a 

caustic residue. 

3. Caustic also concentrates by evaporation if a water line exists. 

Mechanism 

Concentrated caustic dissolves the protective magnetite oxides 

http://faculty.kfupm.edu.sa/ME/hussaini/Corrosion%20Engineering/04.10.01.htm

蒸汽封学习重点 : 


b) 原理 : 当热流量平衡被打破 , 单个气泡的加入形成蒸汽毛毯 , 一种被称 

为偏离泡核沸腾 , 

c) 易感材质 : 碳钢和低合金钢 , 

d) 易感设备 : 所有蒸汽发电机组包括锅炉 , 硫磺厂余热换热器 , 制氢转化炉和 

催化裂化装置 , 

e) 预防 / 缓解 : 锅炉热管理 ( 火焰 , 锅炉水管理 ), 锅炉管目视检验 . 

f) 非 API 510/570 考试题 .

4.2.12 Dissimilar Weld Cracking 

异种钢焊接开裂

4.2.12 Dissimilar Metal Weld (DMW) Cracking 


Cracking of dissimilar metal welds occurs in the ferritic (carbon steel or low 

alloy steel) side of a weld between an austenitic (300 Series SS) and a ferritic 

material operating at high temperature. 


The most common are ferritic materials such as carbon steel and low alloy 

steels that are welded to the austenitic stainless steels as well as any 

material combinations that have widely differing thermal expansion 

coefficients.


a) Important factors include the type of filler metal used to join the materials, 

heating and cooling rate, metal temperature, time at temperature, weld 

geometry and thermal cycling. 

b) Cracking can occur because of the different coefficients of thermal 

expansion between ferritic and austenitic (e.g. 300 Series stainless steel 

or nickel-base alloys) which differ by about 25 to 30% or more. At high 

operating temperatures, the differences in thermal expansion leads to 

high stress at the heat-affected zone on the ferritic side (Table 4-4). 

c) As the operating temperature increases, differential thermal expansion 

between the metals results in increasing stress at the weldment, 

particularly if a 300 Series SS weld metal is used. Ferritic/austenitic joints 

can generate significant thermal expansion/thermal fatigue stresses at 

temperatures greater than 510°F (260°C).

Table 4-4: Coefficients of Thermal Expansion for Common Materials

510°F 

Ferritic/austenitic joints can 

generate significant thermal 

expansion/thermal fatigue 

stresses at temperatures 

greater than 510°F (260°C).

d) Thermal cycling aggravates the problem. Stresses during start up and shut 

down can be significant. 

e) Stresses acting on the weldment are significantly higher when an austenitic 

stainless steel filler metal is used. A nickel base filler metal has a 

coefficient of thermal expansion that is closer to carbon steel, resulting in 

significantly lower stress at elevated temperatures. 

f) For dissimilar welds that operate at elevated temperatures, the problem is 

aggravated by the diffusion of carbon out of the heat-affected zone of the 

ferritic material and into the weld metal. The loss of carbon reduces the 

creep strength of the ferritic material heat-affected zone, thereby increasing 

the cracking probability (Figure 4-35). The temperature at which carbon 

diffusion becomes a concern is above 800°F to 950°F (427°C to 510°C) for 

carbon steels and low alloy steels, respectively.

Austenitic Steel 

Ferritic Steel 

Creep void due to loss of 

Carbon at HAZ 

Figure 4-35 – High magnification photomicrograph of a DMW joining a 

ferritic alloy (SA213 T-22) used in high temperature service. Creep 

cracks (black specks) can be observed in the ferritic alloy heat-affected 

zones. Mag. 50X, etched.

g) Dissimilar metal welds on a ferritic steel that are made with a 300 Series SS 

weld metal or a nickel based filler metal result in a narrow region (mixed 

zone) of high hardness at the toe of the weld, near the fusion line on the 

ferritic steel side. These high hardness zones render the material 

susceptible to various forms of environmental cracking such as sulfide stress 

cracking or hydrogen stress cracking (Figures 4-36 and 4-37). PWHT of the 

weldment will not prevent environmental cracking if the weld is exposed to 

wet H 2 S conditions.(?) 

h) DMW’s for high temperature service in hydrogen environments must be 

carefully designed and inspected to prevent hydrogen disbonding (Figures 

4-38 to 4-41).

Environmental Cracking 

– Ambient service 

Figure 4-36 – Weld detail used to join a carbon steel elbow (bottom) to a weld overlaid 

pipe section (top) in high pressure wet H 2 

S service. Sulfide stress cracking (SSC) occurred 

along the toe of the weld (arrow), in a narrow zone of high hardness.

Environmental Cracking 

– Ambient service 

Figure 4-37 – High magnification photomicrograph of SSC in pipe section shown in 

Figure 4-36.

High temperature service 

Blister 

Figure 4-38 – Failure of DMW joining 1.25Cr-0.5Mo to Alloy 800H in a Hydro-dealkylation 

(HAD) Reactor Effluent Exchanger. Crack propagation due to stresses driven at high 

temperature of 875°F (468°C) and a hydrogen partial pressure of 280 psig (1.93 MPa).


Blister 

Figure 4-39 – High magnification photomicrograph of the crack in Figure 4-38 showing 

blistering and disbondment along the weld fusion line interface.


Figure 4-40 – High magnification photomicrograph of the crack shown above in Figure 4-39. 

Plastic deformation of the grain structure can be found at the vicinity of the blister.


Figure 4-41 – Failure of nickel alloy DMW joining HP40 (Nb modified) tube to 1.25Cr-0.5Mo 

flange in a Steam Methane Reformer due to cold hydrogen disbonding of the buttering layer. 

Process temperature 914°-941°F (490o to 505°C), Pressure (2.14 MPA), H2 content 10-20% 

(off-gas).

i) In environments that promote liquid ash corrosion, weld cracking problems 

may be accelerated by stress-assisted corrosion. The ferritic heat-affected 

zone will preferentially corrode due to the large thermal strain. The results 

are long, narrow, oxide wedges that parallel the fusion line of the weld 

(Figure 4-42). 

j) Poor geometry of the weld, excessive undercut, and other stress 

intensification factors will promote crack formation.

Intergranular liquid metal 

embrittlement (coal ash 

corrosion) 

Figure 4-42 – When both liquid phase coal ash corrosion and a DMW exists, stress assisted 

corrosion of the 2.25 Cr-1Mo heat-affected zone may occur. Note that there is a lack of creep 

damage at the crack tip. Mag. 25X, etched.


a) Dissimilar metal welds are utilized in special applications in refineries and 

other process plants. 

b) Examples of DMW’s include: 

• Welds used to join clad pipe in locations such as transitions in 

hydroprocessing reactor outlet piping from overlaid low alloy CrMo nozzles 

or piping to solid 300 Series stainless steel pipe. 

• Hydroprocessing exchanger inlet and outlet piping. 

• Alloy transitions inside fired heaters (e.g. 9Cr to 317L in a crude furnace) 

• Hydrogen reformer furnace 1.25 Cr inlet pigtails to Alloy 800 sockolets or 

weldolets on Hydrogen reformer tubes 

• Hydrogen reformer furnace Alloy 800 outlet cones to CS or 1.25 Cr 

refractory lined transfer lines.

• Alloy transitions inside fired heaters (e.g. 9Cr to 317L in a crude or 

vacuum furnace) 

• Welds joining clad pipe sections to themselves or to unclad carbon or 

low alloy steel pipe (e.g. Alloy C276 clad CS piping in crude unit 

overhead system) 

• Nickel base alloy welds joining socket weld valves in 5 and 9 Cr piping 

systems 

• 300 series SS weld overlay in numerous refinery reactors and pressure 

vessels 

• Similar DMWs have been used in FCCU reactors and regenerator 

vessels and in Coker Units. 

c) All superheaters and reheaters that have welds between ferritic 

materials (1.25Cr-0.5Mo and 2.25Cr-1Mo) and the austenitic materials 

(300 Series SS, 304H, 321H and 347H).


a) In most cases, the cracks form at the toe of the weld in the heat-affected 

zone of the ferritic material (Figure 4-36 to Figure 4-42). 

b) Welds joining tubes are the most common problem area, but support lugs 

or attachments of cast or wrought 300 Series SS to 400 Series SS are 

also affected.


a) For high temperature applications, nickel base filler metals which have a 

coefficient of thermal expansion closer to carbon steel and low alloy steels 

may dramatically increase the life of the joint, because of the significant 

reduction in thermal stress acting on the steel (ferritic) side of the joint. 

Refer to API 577 and API 582 for additional information on filler metal 

selection, welding procedures and weld inspection. 

b) If 300 Series SS welding electrodes are used, the dissimilar metal weld 

should be located in a low temperature region. 

c) Consider buttering the ferritic side of the joint with the SS or nickel base 

filler metal and perform PWHT prior to completing the DMW to minimize the 

hardness of the mixed weld zone in order to minimize susceptibility to 

environmental cracking. See Figure 4-34 and 4-35.(Figure 4-33 and 4-34) 

d) On buttered joints, the thickness of the weld metal should be a minimum of 

0.25 inch (6.35 mm) after the bevel is machined. Figure 4-35.(Figure 4-34)

Figure 4-33 – Two primary DMW 

configurations. 

a ) Ferritic steel pipe (left) welded to 

clad or weld overlaid pipe (right) 

b) Solid Stainless steel pipe (left) 

welded to clad or weld overlaid pipe 

(right)

Figure 4-34 – Schematic of typical weld detail used to join a solid stainless steel pipe to a clad or 

weld overlaid pipe. The sequence is: 1) Butter the weld bevel on the ferritic steel side, 2) Perform 

PWHT of the ferritic side prior to making dissimilar weld, 3) Complete the dissimilar weld using 

alloy filler metal, 4) Do not PWHT the completed dissimilar weld.

e) In steam generating equipment, the weld at the high temperature end 

should be made in the penthouse or header enclosure, out of the heat 

transfer zone. 

f) For high temperature installations, consider Installing a pup piece that has 

an intermediate thermal expansion coefficient between the two materials 

to be joined.


a) The following elements should be considered for non-destructive 

examination of critical dissimilar butt welds before they are put into 

service: 

• 100% PT after buttering and completion 

• 100% UT on butter layer after PWHT (check bonding) 

•100% RT 

• 100% UT – recordable 

•PMI 

b) For dissimilar welds in fired heater tubes, RT and UT shear wave 

inspection should be performed. 

c) Environmental cracking will also result in surface breaking cracks initiating 

on the ID surface exposed to the corrosive environment, which can be 

detected using WFMT or external SWUT methods.


Thermal fatigue (see 4.2.9), corrosion fatigue (see 4.5.2), creep (see 4.2.8), 

and sulfide stress cracking 

(see 5.1.2.3.)

异种钢焊接开裂学习重点 : 

a) 易感温度 : 室温与高温两种 

b) 原理 : (1) 室温感应 - 铁素体混合区高强度导致环境开裂与氢裂 , (2) 高温 

感应 - 铁素体热影响区脱碳导致高温强度降低与蠕变强度 . 

c) 易感材质 : 铁素体 / 奥氏体异种焊接 , 

d) 非 API510/570 考试题

4.2.13 Thermal Shock 

热冲击

4.2.13 Thermal Shock 温度突变 


A form of thermal fatigue cracking – thermal shock – can occur when high and 

non-uniform thermal stresses develop over a relatively short time in a piece of 

equipment due to differential expansion or contraction. If the thermal 

expansion/contraction is restrained, stresses above the yield strength of the 

material can result. Thermal shock usually occurs when a colder liquid contacts 

a warmer metal surface. 

当的液体接触一个高温的金属表面时 , 在很短的时间 , 高和非均匀的热应力发生 . 

如果热膨胀 / 收缩受到抑制 , 可能会导致材料的屈服强度以上的应力 . 


All metals and alloys.


a) The magnitude of the temperature differential and the coefficient of 

thermal expansion of the material determine the magnitude of the stress. 

b) Cyclic stresses generated by temperature cycling of the material may 

initiate fatigue cracks. 

c) Stainless steels have higher coefficients of thermal expansion than 

carbon and alloy steels or nickel base alloys and are more likely to see 

higher stresses. 

d) High temperature exposure during a fire. 

e) Temperature changes that can result from water quenching as a result of 

rain deluges.

f) Fracture is related to constraint on a component that prevents the 

component from expanding or contracting with a change in temperature. 

g) Cracking in cast components such as valves may initiate at casting flaws on 

the ID and progress through the thickness. 

h) Thick sections can develop high thermal gradients.


a) FCC, cokers, catalytic reforming and high severity hydroprocessing units 

are high temperature units where thermal shock is possible. 

b) High temperature piping and equipment in any unit can be affected. 

c) Materials that have lost ductility, such as CrMo equipment (temper 

embrittlement) are particularly susceptible to thermal shock. 

d) Equipment subjected to accelerated cooling procedures to minimize 

shutdown time.


Surface initiating cracks may also appear as “craze” cracks. 


a) Prevent interruptions in the flow of high temperature lines. 

b) Design to minimize severe restraint. 

c) Install thermal sleeves to prevent liquid impingement on the pressure 

boundary components. 

d) Minimize rain or fire water deluge situations. 

e) Review hot/cold injection points for potential thermal shock.


a) This type of damage is highly localized and difficult to locate. 

b) PT and MT can be used to confirm cracking. 


Thermal fatigue (see 4.2.9).

高温突变学习重点 : 


b) 原理 : 当冷液体接触高温的金属表面时 , 高和非均匀的热应力发生 . 在热膨 

胀 / 收缩受到抑制下形成屈服强度以上的应力 , 导致材料开裂 . 


d) 易感设备 : 高温设备 , 

e) 非 API 510/570 考试题

4.2.14 Erosion/ Erosion Corrosion 

冲刷腐蚀 

API510/570-Exam


4.2.14 Erosion/Erosion – Corrosion 冲蚀 / 冲蚀 - 腐蚀 


a) Erosion is the accelerated mechanical removal of surface material as a 

result of relative movement between, or impact from solids, liquids, vapor or 

any combination thereof. 

b) Erosion-corrosion is a description for the damage that occurs when 

corrosion contributes to erosion by removing protective films or scales, or by 

exposing the metal surface to further corrosion under the combined action 

of erosion and corrosion. 

• 冲蚀 - 当材料表面 ( 固体 , 液体 , 气体或它们的任何组合 ) 之间的相对运动 / 撞击 

的影响而加速材料表面机械去除 . 

• 冲蚀 - 腐蚀 - 腐蚀导致侵金属表面保护膜 / 氧化皮的丢失 , 冲蚀机表面去除 , 冲蚀 - 

腐蚀的协作效应加深便面损坏 . 


All metals, alloys and refractory.



a) In most cases, corrosion plays some role so that pure erosion (sometimes 

referred to as abrasive wear) is rare. It is critical to consider the role that 

corrosion contributes. 

b) Metal loss rates depend on the velocity and concentration of impacting 

medium (i.e., particles, liquids, droplets, slurries, two-phase flow), the size 

and hardness of impacting particles, the hardness and corrosion resistance 

of material subject to erosion, and the angle of impact. 

c) Softer alloys such as copper and aluminum alloys that are easily worn from 

mechanical damage may be subject to severe metal loss under high velocity 

conditions. 

d) Although increasing hardness of the metal substrate is a common approach 

to minimize damage, it is not always a good indicator of improved resistance 

to erosion, particularly where corrosion plays a significant role.


e) For each environment-material combination, there is often a threshold 

velocity above which impacting objects may produce metal loss. Increasing 

velocities above this threshold result in an increase in metal loss rates as 

shown in Table 4-5. This table illustrates the relative susceptibility of a 

variety of metals and alloys to erosion/corrosion by seawater at different 

velocities. 

f) The size, shape, density and hardness of the impacting medium affect the 

metal loss rate. 

g) Increasing the corrosivity of the environment may reduce the stability of 

protective surface films and increase the susceptibility to metal loss. Metal 

may be removed from the surface as dissolved ions, or as solid corrosion 

products which are mechanically swept from the metal surface. 

h) Factors which contribute to an increase in corrosivity of the environment, 

such as temperature, pH, etc., can increase susceptibility to metal loss.



a) All types of equipment exposed to moving fluids and/or catalyst are subject 

to erosion and erosion corrosion. This includes piping systems, particularly 

the bends, elbows, tees and reducers; piping systems downstream of 

letdown valves and block valves; pumps; blowers; propellers; impellers; 

agitators; agitated vessels; heat exchanger tubing; measuring device 

orifices; turbine blades; nozzles; ducts and vapor lines; scrapers; cutters; 

and wear plates. 

b) Erosion can be caused by gas borne catalyst particles or by particles 

carried by a liquid such as a slurry. In refineries, this form of damage occurs 

as a result of catalyst movement in FCC reactor/regenerator systems in 

catalyst handling equipment (valves, cyclones, piping, reactors) and slurry 

piping (Figure 4-43); coke handling equipment in both delayed and fluidized 

bed cokers (Figure 4-44); and as wear on pumps (Figure 4-45), 

compressors and other rotating equipment.


c) Hydroprocessing reactor effluent piping may be subject to erosion-corrosion 

by ammonium bisulfide. The metal loss is dependent on several factors 

including the ammonium bisulfide concentration, velocity and alloy corrosion 

resistance. 

d) Crude and vacuum unit piping and vessels exposed to naphthenic acids in 

some crude oils may suffer severe erosion-corrosion metal loss depending 

on the temperature, velocity, sulfur content and TAN level.



a) Erosion and erosion-corrosion are characterized by a localized loss in 

thickness in the form of pits, grooves, gullies, waves, rounded holes and 

valleys. These losses often exhibit a directional pattern. 

b) Failures can occur in a relatively short time.



a) Improvements in design involve changes in shape, geometry and materials 

selection. Some examples are: increasing the pipe diameter to decrease 

velocity; streamlining bends to reduce impingement; increasing the wall 

thickness; and using replaceable impingement baffles. 

b) Improved resistance to erosion is usually achieved through increasing 

substrate hardness using harder alloys, hardfacing or surface-hardening 

treatments. Erosion resistant refractories in cyclones and slide valves have 

been very successful.


c) Erosion-corrosion is best mitigated by using more corrosion-resistant alloys 

and/or altering the process environment to reduce corrosivity, for example, 

deaeration, condensate injection or the addition of inhibitors. Resistance is 

generally not improved through increasing substrate hardness alone. 

d) Heat exchangers utilize impingement plates and occasionally tube ferrules 

to minimize erosion problems. 

e) Higher molybdenum containing alloys are used for improved resistance to 

naphthenic acid corrosion.



a) Visual examination of suspected or troublesome areas, as well as UT 

checks or RT can be used to detect the extent of metal loss. 

b) Specialized corrosion coupons and on-line corrosion monitoring electrical 

resistance probes have been used in some applications. 

c) IR scans are used to detect refractory loss on stream. 


Specialized terminology has been developed for various forms of erosion and 

erosion-corrosion in specific environments and/or services. This terminology 

includes cavitation, liquid impingement erosion, fretting and other similar 

terms.

Figure 4-43 – Erosion Corrosion of a 1.25Cr 300 # valve flange on an FCC 

Catalyst withdrawal line. 

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Figure 4-44 – Erosion of a 9Cr-1Mo coker heater return bend. 

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Figure 4-45 – Erosion-Corrosion of is ASTM A48 Class 30 

Cast Iron Impeller in recycle water pump. 

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定义 : 

Corrosion 腐蚀 – 化学现象 

Erosion 冲蚀 - 机械现象 

Erosion- corrosion 冲蚀 - 腐蚀 - 化学与机械组合现象 

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金属可能从表面以 (1) 溶解离子腐蚀或作为 (2) 固体机械扫冲蚀 

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Flow Direction

Flow Direction 

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Impingement 

point 


Flow Direction

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冲蚀 / 冲蚀 - 腐蚀学习重点 : 

a) 易感温度 : 操作温度 , 

b) 原理 : 设备溶液流动 ( 液体 , 气体 , 固体或其组合 ) 导致机械磨损与通过保护 

性氧化膜机械去除加剧表面腐蚀 . 


d) 易感设备 : , 

e) API 510/570 考试题 .

4.2.15 Cavitation 

气穴现象

4.2.15 Cavitation 


• 当液体受压波动 , 在压力的快速变化时 , 小气空会在低压区域产生 , 这无数 

小气泡形成 , 瞬间在高压区域崩溃 . 上述的崩溃的气泡产生严重的局部冲击 

力 , 可导致金属损失的侵蚀现象 , 这叫做气穴现象 . 

a) Cavitation is a form of erosion caused by the formation and instantaneous 

collapse of innumerable tiny vapor bubbles. 

b) The collapsing bubbles exert severe localized impact forces that can 

result in metal loss referred to as cavitation damage. 

c) The bubbles may contain the vapor phase of the liquid, air or other gas 

entrained in the liquid medium. 


• Most common materials of construction including copper and brass, cast 

iron, carbon steel, low alloy steels, 300 Series SS, 400 Series SS and 

nickel base alloys.


a) In a pump, the difference between the actual pressure or head of the liquid 

available (measured on the suction side) and the vapor pressure of that liquid 

is called the Net Positive Suction Head (NPSH) available. The minimum 

head required to prevent cavitation with a given liquid at a given flow rate is 

called the net positive suction head required. Inadequate NPSH can result in 

cavitation. 

b) Temperatures approaching the boiling point of the liquid are more likely to 

result in bubble formation than lower temperature operation. 

c) The presence of solid or abrasive particles is not required for cavitation 

damage but will accelerate the damage.


a) Cavitation is most often observed in pump casings, pump impellers (low 

pressure side) and in piping downstream of orifices or control valves. 

b) Damage can also be found in restricted-flow passages or other areas 

where turbulent flow is subjected to rapid pressure changes within a 

localized region. Examples of affected equipment include heat exchanger 

tubes, venturis, seals and impellers. 


Cavitation damage generally looks like sharp-edged pitting but may also have 

a gouged appearance in rotational components. However, damage occurs 

only in localized low-pressure zones (see Figure 4-46, Figure 4-47 to 

Figure 4-49).


a) Resistance to cavitation damage in a specific environment may not be 

significantly improved by a material change. A mechanical modification, 

design or operating change is usually required. 

b) Cavitation is best prevented by avoiding conditions that allow the 

absolute pressure to fall below the vapor pressure of the liquid or by 

changing the material properties. 

Examples include: 

1. Streamline the flow path to reduce turbulence. 

2. Decrease fluid velocities. 

3. Remove entrained air. 

4. Increase the suction pressure of pumps. 

5. Alter the fluid properties, perhaps by adding additives. 

6. Use hard surfacing or hardfacing. 

7. Use of harder and/or more corrosion resistant alloys.

c) Attack is accelerated by the mechanical disruption of protective films at the 

liquid-solid interface (such as a protective corrosion scale or passive films). 

Therefore, changing to a more corrosion resistant and/or higher hardness 

material may not improve cavitation resistance. Excessively hard materials 

may not be suitable if they lack the toughness required to withstand the high 

local pressures and impact (shear loads) of the collapsing bubbles.


a) Cavitating pumps may sound like pebbles are being thrashed around inside. 

a) Techniques include limited monitoring of fluid properties as well as acoustic 

monitoring of turbulent areas to detect characteristic sound frequencies. 

a) Visual examination of suspected areas, as well as external UT and RT can 

be used to monitor for loss in thickness. 


Liquid impingement or erosion (see 4.2.14).

气穴腐蚀学习重点 : 

a) 易感温度 : 操作温度 

b) 原理 : 当液体受压波动 , 在压力的快速变化时 , 小气空会在低压区域产生 , 

这无数小气泡形成 , 瞬间在高压区域崩溃 . 上述的崩溃的气泡产生严重的 

局部冲击力 , 可导致金属损失的侵蚀现象 , 这叫做气穴现象 . 


d) 易感设备 : 泵 , 限流通道或其他湍流流动设备与管道 . 

e) 预防 / 缓解 : 更改设计以减少湍流 , 提高泵的吸入压力 , 改变流体的性质如 

通过加入添加剂 , 增加材料硬度等 . 

f) 非 API 510/570 考试题 .

4.2.16 Mechanical Fatigue 

机械疲劳 

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4.2.16 Mechanical Fatigue 机械疲劳 


a) Fatigue cracking is a mechanical form of degradation that occurs when a 

component is exposed to cyclical stresses for an extended period, often 

resulting in sudden, unexpected failure. 长期的循环应力造成破坏 . 

b) These stresses can arise from either (1) mechanical loading or (2) thermal 

cycling and are typically well below the yield strength of the material. 

通常低于屈服强度的机械载荷或循环热应力 


• All engineering alloys are subject to fatigue cracking although the stress 

levels and number of cycles necessary to cause failure vary by material.



Geometry, stress level, number of cycles, and material properties (strength, hardness, 

microstructure) are the predominant factors in determining the fatigue resistance of a 

component. 

a) Design: Fatigue cracks usually initiate on the surface at notches or stress raisers under 

cyclic loading. For this reason, design of a component is the most important factor in 

determining a component’s resistance to fatigue cracking. Several common surface 

features can lead to the initiation of fatigue cracks as they can act as stress 

concentrations. Some of these common features are: 

1. Mechanical notches (sharp corners or groves); 

2. Key holes on drive shafts of rotating equipment; 

3. Weld joint, flaws and/or mismatches; 

4. Quench nozzle areas; 

5. Tool markings; 

6. Grinding marks; 

7. Lips on drilled holes; 

8. Thread root notches; 

9. Corrosion.


b) Metallurgical Issues and Microstructure 

1. For some materials such as titanium, carbon steel and low alloy steel, the number of 

cycles to fatigue fracture decreases with stress amplitude until an endurance limit 

reached. Below this stress endurance limit, fatigue cracking will not occur, 

regardless of the number of cycles. 

2. For alloys with endurance limits, there is a correlation between Ultimate Tensile 

Strength (UTS) and the minimum stress amplitude necessary to initiate fatigue 

cracking. The ratio of endurance limit over UTS is typically between 0.4 and 0.5. 

Materials like austenitic stainless steels and aluminum that do not have an endurance 

limit will have a fatigue limit defined by the number of cycles at a given stress 

amplitude. 

3. Inclusions found in metal can have an accelerating effect on fatigue cracking. This is 

of importance when dealing with older, “dirty” steels or weldments, as these often 

have inclusions and discontinuities that can degrade fatigue resistance. 

4. Heat treatment can have a significant effect on the toughness and hence fatigue 

resistance of a metal. In general, finer grained microstructures tend to perform better 

than coarse grained. Heat treatments such as quenching and tempering, can improve 

fatigue resistance of carbon and low alloy steels.


For alloys with endurance limits, there is a correlation between Ultimate 

Tensile Strength (UTS) and the minimum stress amplitude necessary to 

initiate fatigue cracking. The ratio of endurance limit over UTS is typically 

between 0.4 and 0.5. Materials like austenitic stainless steels and aluminum 

that do not have an endurance limit will have a fatigue limit defined by the 

number of cycles at a given stress amplitude. 

疲劳极限合金 : 引发疲劳开裂最小应力振幅和材料抗拉强度存在相关性 , 这通 

常在 0.4 和 0.5UTS 之间 . 

奥氏体不锈钢和铝材料 , 没有引发疲劳开裂极限的最小应力振幅 .

API510/570-Exam


c) Carbon Steel and Titanium: These materials exhibit an endurance limit 

below which fatigue cracking will not occur, regardless of the number of 

cycles. 

d) 300 Series SS, 400 Series SS, aluminum and most other non-ferrous alloys: 

1. These alloys have a fatigue characteristic that does not exhibit an 

endurance limit. This means that fatigue fracture can be achieved under 

cyclical loading eventually, regardless of stress amplitude. 

2. Maximum cyclical stress amplitude is determined by relating the stress 

necessary to cause fracture to the desired number of cycles necessary 

in a component’s lifetime. This is typically 10 6 to 10 7 cycles.



a) Thermal Cycling 

1. Equipment that cycles daily in operation such as coke drums. 

2. Equipment that may be auxiliary or on continuous standby but sees intermittent 

service such as auxiliary boiler. 

3. Quench nozzle connections that see significant temperature deltas during operations 

such as water washing systems. 

b) Mechanical Loading 

1. Pressure Swing Absorbers on hydrogen purification units. 

2. Rotating shafts on centrifugal pumps and compressors that have stress concentrations 

due to changes in radii and key ways. 

3. Components such as small diameter piping that may see vibration from adjacent 

equipment and/or wind. For small components, resonance can also produce a cyclical 

load and should be taken into consideration during design and reviewed for potential 

problems after installation. 

4. High pressure drop control valves or steam reducing stations can cause serious 

vibration problems in connected piping.

a) Thermal Cycling 

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b) Mechanical Loading 

Amplitude



a) The signature mark of a fatigue failure is a “clam shell” type fingerprint that 

has concentric rings called “beach marks” emanating from the crack initiation 

site (Figure 4-50 and Figure 4-51). This signature pattern results from the 

“waves” of crack propagation that occur during cycles above the threshold 

loading. These concentric cracks continue to propagate until the crosssectional 

area is reduced to the point where failure due to overload occurs. 

b) Cracks nucleating from a surface stress concentration or defect will typically 

result in a single “clam shell” fingerprint (Figure 4-52 to Figure 4-56). 

c) Cracks resulting from cyclical overstress of a component without significant 

stress concentration will typically result in a fatigue failure with multiple 

points of nucleation and hence multiple “clam shell” fingerprints. These 

multiple nucleation sites are the result of microscopic yielding that occurs 

when the component is momentarily cycled above its yield strength.

Figure 4-50 – Schematic of a fatigue fracture surface showing “beach marks”. 

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Figure 4-51 – Compressor rod fracture surface showing “beach marks” 

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Figure 4-52 – Higher magnification view of figure above showing “beach marks”. 

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Figure 4-53 – Fatigue fracture surface of a carbon steel pipe. 

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Figure 4-54 – Fatigue crack in a 16-inch pipe-to-elbow weld in the fill line of 

crude oil storage tank after 50 years in service. 

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Figure 4-55 – A cross-section through the weld showing the crack location. 

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Figure 4-56 – The surface of the fracture faces of the crack shown in 

Figure 4-54 and Figure 4-55. 

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The signature mark of 

a fatigue failure is a 

“clam shell 蛤壳 ”type 

fingerprint that has 

concentric rings called 

“beach marks” 

emanating from the 

crack initiation site

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http://www.efunda.com/formulae/solid_mechanics/fatigue/fatigue_lowcycle.cfm 

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530.352 Materials Selection 

Lecture #23 Fatigue 

Tuesday 

November 8 th , 2005 

http://www.me.jhu.edu/hemker/MatSel/lectures/23%20Fatigue.ppt 

159

Failure even at low Stresses 

• Failure often occurs even when: 

applied < fracture 

yielding 

and 

applied < 

• 90% of all mechanical failures are 

related to dynamic loading. 

• Dynamic Loading -> > Cyclic Stresses 

160

Examples of Fatigue Failures 

Plastic Tricycle: 

161


Door Stop: 

162


Railway Accidents: 

• Versailles 1842 

• first fatigue problem 

• axial failure 

• Today 

• flaws in 10% of 

rails. 

163

Types of Fatigue 

• Fatigue of uncracked components 

• No pre-cracks; initiation controlled fracture 

• Examples : most small components: pins, gears, 

axles, ... 

• High cycle fatigue 

• fatigue 

• Low cycle fatigue 

< yield ; N f > 10,000 

• fatigue 

> yield ; N f < 10,000 

164

Types of Fatigue: 

Fatigue of cracked structures 

–Pre-cracks exist: propagation 

controls fracture 

–Examples : most large components, 

particularly those containing welds: 

bridges, airplanes, ships, pressure 

vessels, ... 

165

Cyclic Loading 

 

Weight 

+ 

time 

- 

166

Basic Fatigue Terminology: 

+ 

max 

 

0 

- 

mean 

min 

time 

max min 

mean max min 

amplitude max min 

N = number of fatigue cycles 

N f = number of cycles 

to failure 

167

High Cycle Fatigue 

S-N Curves 

• Apply controlled 

applied < ~ 2 / 3 yield 

• Stress is elastic 

on gross scale. 

• Locally the metal 

deforms plastically. 

Stress 

50 

40 

30 

10 

0 

Mild Steel 

Al alloys 

10 5 10 6 10 7 10 8 10 9 

N failure 

Fatigue limit 

168

Low Cycle Fatigue 

• Apply controlled amounts of 

• total = elastic + 

plastic 

total 

• Empirical Observations and Rules 

• Coffin-Manson Law 

• Miner’s s Rule 

169

Coffin-Manson Law 

For low cycle fatigue: 

plastic N failure 

1/2 

= Const. 

log pl 

y = y /E 

~10 4 

log N failure 

170

Miner’s s Rule 

Rule of Accumulative damage: 

N 1 N 2 N 3 

 

N i 

= N 1 

failure @ i 

Fraction of life time @ i 

171

• Crack initiation 

The Fatigue Process 

• early development of damage 

• Stage I crack growth 

• deepening of initial crack on shear planes 

• Stage II crack growth 

• growth of well defined crack on planes normal 

to maximum tensile stress 

• Ultimate Failure 

172

Crack initiation 

Cracks start at: 

• Surfaces 

• Inclusions 

• Existing 

cracks 

Alternate stresses -> slip bands 

-> surface rumpling 

173

Crack Initiation: 

174

Crack Growth 

Striation indicating 

steps in crack 

advancement. 

175

Propagation in Cracked 

Structures 

a o ~ a detectible < a critical 

a o -> a critical = FAILURE !!! 

K = K -K max min 

= (a) 1/2 

da = A K m 

1 

dN 

log da/dN 

threshold 

linear 

Fast fracture 

log K 

176

Real world comparisons: 

log da/dN 

threshold 

linear 

Fast fracture 

log K 

177

Fracture surfaces: 

178

Fracture Surfaces: 

Initiation 

site 

Fatigue 

cracking 

Final fracture 

179


机械疲劳学习重点 : 

a) 易感温度 : 操作温度 , 

b) 原理 : 长期的循环应力造成破坏 . 


d) 易感设备 : 温度循环设备 , 机械振动设备 , 

e) 预防 / 缓解 : 通过设计减少振动与温度循环 . 

f) API 510/570 考试题 .

4.2.17 Vibration Induced Fatigue 

振动疲劳 

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4.2.17 Vibration-Induced Fatigue 振动引起的疲劳 


A form of mechanical fatigue in which cracks are produced as the result of 

dynamic loading due to vibration, water hammer, or unstable fluid flow. 


All engineering materials. 


a) The amplitude and frequency of vibration as well as the fatigue 

resistance of the components are critical factors. 振动的振幅和频率 

b) There is a high likelihood of cracking when the input load is 

synchronous or nearly synchronizes with the natural frequency of the 

component. 共鸣 ( 同步 ) 频率 

c) A lack of or excessive support or stiffening allows vibration and 

possible cracking problems that usually initiate at stress raisers or 

notches. 局部应力集中或缺口

API 570-Exam 


a) Socket welds and small bore piping at or near pumps and compressors that 

are not sufficiently gusseted. 

b) Small bore bypass lines and flow loops around rotating and reciprocating 

equipment. 

c) Small branch connections with unsupported valves or controllers. 

d) Safety relief valves are subject to chatter, premature pop-off, fretting and 

failure to operate properly. 

e) High pressure drop control valves and steam reducing stations. 

f) Heat exchanger tubes may be susceptible to vortex shedding.

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a) Damage is usually in the form of a crack initiating at a point of high stress or 

discontinuity such as a thread or weld joint (Figure 4-57 and Figure 4-58). 

b) A potential warning sign of vibration damage to refractories is the visible 

damage resulting from the failure of the refractory and/or the anchoring 

system. High skin temperatures may result from refractory damage.

API 570-Exam 


a) Vibration-induced fatigue can be eliminated or reduced through design and 

the use of supports and vibration dampening equipment. Material upgrades 

are not usually a solution. 

b) Install gussets or stiffeners on small bore connections. Eliminate 

unnecessary connections and inspect field installations. 

c) Vortex shedding can be minimized at the outlet of control valves and safety 

valves through proper side branch sizing and flow stabilization techniques. 

d) Vibration effects may be shifted when a vibrating section is anchored. 

Special studies may be necessary before anchors or dampeners are 

provided, unless the vibration is eliminated by removing the source.

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a) Look for visible signs of vibration, pipe movement or water hammer. 

b) Check for the audible sounds of vibration emanating from piping 

components such as control valves and fittings. 

c) Conduct visual inspection during transient conditions (such as startups, 

shutdowns, upsets, etc.) for intermittent vibrating conditions. 

d) Measure pipe vibrations using special monitoring equipment. 

e) The use of surface inspection methods (such as PT, MT) can be effective 

in a focused plan. 

f) Check pipe supports and spring hangers on a regular schedule. 

g) Damage to insulation jacketing may indicate excessive vibration. This 

can result in wetting the insulation which will cause corrosion.

API 570-Exam 


Mechanical fatigue (see 4.2.16) and refractory degradation (see 4.2.18).

Figure 4-57 – Vibration induced fatigue of a 1-inch socket weld flange in a 

thermal relief system shortly after startup. 

API 570-Exam

Figure 4-58 – Cross-sectional view of the crack in the socket weld in Figure 4-57. 

API 570-Exam

API 570-Exam

API 570-Exam

振动引起的疲劳学习重点 : 


b) 原理 : 热疲劳开裂是由振动引起循环应力引起的开裂 , 


d) 易感设备 : 小口径管路 , 高压力差管路 , 

e) 预防 / 缓解 : 设计控制 , 振动阻尼装置 , 支撑 , 

f) API 570 考试题 .

4.2.18 Refractory Degradation 

耐火垫退化

4.2.18 Refractory Degradation 耐火材料退化 


Both thermal insulating and erosion resistant refractories are susceptible to 

various forms of mechanical damage (cracking, spalling and erosion) as well 

as corrosion due to oxidation, sulfidation and other high temperature 

mechanisms. 


Refractory materials include insulating ceramic fibers, castables, refractory 

brick and plastic refractories.


a) Refractory selection, design and installation are the keys to minimizing 

damage. 

b) Refractory lined equipment should be designed for erosion, thermal shock 

and thermal expansion. 

c) Dry out schedules, cure times and application procedures should be in 

accordance with the manufacturer’s specifications and the appropriate 

ASTM requirements. 

d) Anchor materials must be compatible with thermal coefficients of expansion 

of the base metal. 

e) Anchors must be resistant to oxidation in high temperature services.

f) Anchors must be resistant to condensing sulfurous acids in heaters and 

flue gas environments. 

g) Refractory type and density must be selected to resist abrasion and erosion 

based on service requirements. 

h) Needles and other fillers must be compatible with the process environment 

composition and temperature.


a) Refractories are extensively used in FCC reactor regenerator vessels, 

piping, cyclones, slide valves and internals; in fluid cokers; in cold shell 

catalytic reforming reactors; and in waste heat boilers and thermal reactors 

in sulfur plants. 

b) Boiler fire boxes and stacks which also use refractory are affected.


a) Refractory may show signs of excessive cracking, spalling or lift-off from 

the substrate, softening or general degradation from exposure to moisture. 

b) Coke deposits may develop behind refractory and promote cracking and 

deterioration. 

c) In erosive services, refractory may be washed away or thinned, exposing 

the anchoring system. (Figure 4-59) 


Proper selection of refractory, anchors and fillers and their proper design and 

installation are the keys to minimizing refractory damage.


a) Conduct visual inspection during shutdowns. 

b) Survey cold-wall equipment onstream using IR to monitor for hot spots to 

help identify refractory damage. 


Oxidation (see 4.4.1), sulfidation (see 4.4.2) and flue gas dew point corrosion 

(see 4.3.7).

Figure 4-59 – Damaged refractory and ferrules.

耐火材料退化学习重点 : 


b) 原理 : 机械或腐蚀引起退化 , 

c) 易感材质 : 耐火材料 , 

d) 易感设备 : 耐火材料设备 , 

e) 预防 / 缓解 : 锚杆材料必须与基体金属的热膨胀系数相兼容 , 锚栓必须耐高 

温氧化 , 

f) 非 API 510/570 考试题 .

4.2.19 Reheat Cracking 

再热裂纹

4.2.19 Reheat Cracking 


由于再次受热产生的应力松弛的金属开裂 

Cracking of a metal due to stress relaxation during Post Weld Heat Treatment 

(PWHT) or in service at elevated temperatures. It is most often observed in 

heavy wall sections. 


Low alloy steels as well as 300 Series SS and nickel base alloys such as 

Alloy 800H. (ferritic & Austenitic) 


Reheat cracking has also been referred to in the literature as “stress relief 

cracking” and “stress relaxation cracking”. 应力松弛开裂

再热裂纹 

Reheat cracking occurs at elevated temperatures when creep ductility is 

insufficient to accommodate the strains required for the relief of 

applied or residual stresses. The grain size has an important influence on 

the high temperature ductility and on the reheat cracking susceptibility. 

A large grain size result in less ductile heat affected zones, making the 

material more susceptible to reheat cracking. 

在升高的温度下 , 再热裂纹发生 ; 当蠕变延性不足以容纳 , 所需的 ” 应用 ” 或 ” 残余 

应力 ” 松弛变化 . 大粒径的晶粒 , 焊接热影响区韧性较差 , 这造成焊接热影响易 

受再热开裂 .


Important parameters include the type of material (chemical composition, 

impurity elements), grain size, residual stresses from fabrication (cold 

working, welding), section thickness (which controls restraint and stress 

state), notches and stress concentrators, weld metal and base metal 

strength, welding and heat treating conditions. From the various theories 

of reheat cracking for both 300 Series SS and low alloy steels, cracking 

features are as follows: 

a) Reheat cracking requires the presence of high stresses and is therefore 

more likely to occur in thicker sections and higher strength materials. 

b) Reheat cracking occurs at elevated temperatures when creep ductility is 

insufficient to accommodate the strains required for the relief of applied or 

residual stresses. 蠕变延性不足以适应 (1) 应用或 (2) 残余应力缓减 , 所需的 

伸张 .

c) In the first half of 2008, numerous cases of reheat cracking occurred 

during 2 ¼ Cr-1 Mo-V reactor fabrication. The cracks were in weld metal 

only, transverse to the welding direction, and in only SAW welds. It was 

traced to a contaminant in the welding flux. 

d) Reheat cracking can either occur during PWHT or in service at high 

temperature. In both cases, cracks are intergranular and show little or no 

evidence of deformation. 

e) Fine intragranular precipitate particles make the grains stronger than the 

grain boundaries and force the creep deformation to occur at the grain 

boundaries. 

f) Stress relief and stabilization heat treatment of 300 Series SS for 

maximizing chloride SCC and PTASCC resistance can cause reheat 

cracking problems, particularly in thicker sections.

http://www.hydrocarbonprocessing.com/Article/27 

64339/How-to-fabricate-reactors-for-severeservice.html

https://etd.ohiolink.edu/ap/0?0:APPLICATION_PROCESS%3DDOWNLOAD_ET 

D_SUB_DOC_ACCNUM:::F1501_ID:osu1188419315%2Cinline

http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld017.htm


a) Reheat cracking is most likely to occur in heavy wall vessels in areas of 

high restraint including nozzle welds and heavy wall piping. 

b) HSLA steels are very susceptible to reheat cracking. 


a) Reheat cracking is intergranular and can be surface breaking or embedded 

depending on the state of stress and geometry. It is most frequently 

observed in coarse-grained sections of a weld heat affected zone. 

b) In many cases, cracks are confined to the heat-affected zone, initiate at 

some type of stress concentration, and may act as an initiation site for 

fatigue. Figure 4-60 to 4-63.

Figure 4-60 – Samples removed from a cracked 12-inch NPS 321SS 

elbow in hot recycle H2 line that operated at 985°F in hydrocracker.

Figure 4-61 – Crack at weld from SS321 elbow shown in the Figure 4-60.

Figure 4-62 – Cross-section through the weldment showing the crack in Figure 4-61.

Figure 4-63 – 

Photomicrographs of the 

weldment area.


a) Joint configurations in heavy wall sections should be designed to minimize 

restraint during welding and PWHT. Adequate preheat must also be applied. 

b) The grain size has an important influence on the high temperature ductility and 

on the reheat cracking susceptibility. A large grain size results in less ductile 

heat-affected zones, making the material more susceptible to reheat cracking. 

c) Metallurgical notches arising from the welding operation are frequently the 

cause of heat-affected zone cracking (at the boundary between the weld and 

the heat-affected zone). 

d) In design and fabrication, it is advisable to avoid sharp changes in cross 

section, such as short radius fillets or undercuts that can give rise to stress 

concentrations. Long-seam welds are particularly susceptible to mismatch 

caused by fitup problems.

e) For 2 ¼ Cr-1 Mo-V SAW weld materials, prequalification screening tests for 

reheat cracking such as high temperature (650 o C) Gleeble tensile tests 

should be considered. 

f) For Alloy 800H, the risk of in-service cracking can be reduced by using base 

metal and matching weld metal with Al+Ti 540 o C, the material may need to be 

purchased with a thermal stabilization heat treatment, and with PWHT of 

welds and cold worked sections. Welds should be made with matching Alloy 

800H filler material and should be stress relieved. Refer to ASME Section VIII, 

Div. 1 Code in UNF-56(e) for additional information. 

h) For thick-wall SS piping, PWHT should be avoided whenever possible.


a) Surface cracks can be detected with UT and MT examination of carbon 

and low alloy steels 

b) UT and PT examination can be used to detect cracks in 300 Series SS 

and nickel base alloys. 

c) Embedded cracks can only be found through UT examination. 

d) Inspection for reheat cracking in 2 ¼ Cr-1 Mo-V reactors during 

fabrication is typically done with TOFD or manual shear wave UT with 

the demonstration block having defects as small as 3 mm side drilled 

holes 


Reheat cracking has also been referred to in the literature as “stress relief 

cracking” and “stress relaxation cracking”.

http://www.twi-global.com/technical-knowledge/job-knowledge/defectsimperfections-in-welds-reheat-cracking-048/

http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WFAULT/sld017.htm

再热裂纹学习重点 : 


b) 原理 : 蠕变延性不足以适应 (1) 应用或 (2) 残余应力缓减 , 所需的伸张引 

起的开裂 , 

c) 易感材质 : 铁素体 , 奥氏体 , 厚壁钢材 , 

d) 易感设备 : 高温服务 , 厚壁设备 , 

e) 非 API 510/570 考试题 .

4.2.20 GOX-Enhanced Ignition & Combustion 

气化氧 - 增强燃烧

4.2.20 Gaseous Oxygen-Enhanced Ignition and Combustion 

气态氧增强的点火和燃烧 


Many metals are flammable in oxygen and enriched air (>25% oxygen) 

services even at low pressures, whereas they are non-flammable in air. The 

spontaneous ignition or combustion of metallic and nonmetallic components 

can result in fires and explosions in certain oxygen-enriched gaseous 

environments if not properly designed, operated and maintained. Once ignited, 

metals and non-metals burn more vigorously with higher oxygen purity, 

pressure and temperature


a) Carbon steels and low alloy steels are flammable in low pressure oxygen, 

greater than about 15 psig (0.103 MPa). With special precautions, these 

materials are safely used in high pressure oxygen. 

b) Austenitic stainless steels (300 series) have better resistance to low pressure 

oxygen and are generally difficult to ignite at pressures below about 200 psig 

(1.38 MPa). 

c) Copper alloys (with >55% copper) and nickel alloys (with >50% nickel) are 

very fire resistant and are generally considered non-flammable. Because of 

their excellent oxygen “compatibility” they are often selected for impingement 

and turbulent services such as valves and instrumentation (Figure 4-69). 

Alloy 400 is highly resistant.

d) Although widely used for oxygen cylinders and in oxygen manufacturing 

plants, aluminum is usually avoided for flowing oxygen. If ignited it burns 

quickly and with a large energy release. 

e) The easiest materials to ignite are plastics, rubbers, and hydrocarbon 

lubricants and these are minimized in oxygen systems. 

f) Titanium alloys are generally avoided in oxygen and oxygen-enriched 

service because they have low ignition energies and release a large 

amount of energy during combustion. Tests indicate that titanium can 

sustain combustion at oxygen pressure as low as 7 kPa (1 psi) absolute. 

Most industry documents caution against the use of titanium in oxygen 

systems (References 6 and 7). 

Note: These are general guidelines and should not be considered for design.


a) Many factors affect the likelihood of combustion and ignition in oxygen 

services including the system pressure, oxygen content of the stream, 

line velocity, component thickness, design and piping configuration, 

cleanliness and temperature. 

b) The primary concern under high velocity oxygen flow conditions is the 

entrainment of particulate and their subsequent impingement on a 

surface, such as at a pipe bend. Oxygen velocities in carbon steel and 

stainless steel piping should comply with industry limits as shown in 

Reference 1. Allowable velocity is a function of pressure and flow 

condition (direct impingement or non-impingement).

c) The temperature of a material affects its flammability. As temperature 

increases, a lower amount of additional energy is required for ignition and 

sustained combustion. The minimum temperature at which a substance will 

support combustion, under a specific set of conditions is referred to as the 

ignition temperature. Published ignition temperatures for most alloys are 

near the alloy’s melting temperature. However, these are measured in nonflowing 

conditions. Actual systems can suffer ignition and combustion at 

room temperature (and lower) due to particle impact and other mechanisms. 

d) System cleanliness is important for the safe operation of oxygen systems. 

Contamination of with metallic fines or hydrocarbons such as oils and 

greases during construction or maintenance activities can lead to fires 

during subsequent start up of the unit. These materials are easy to ignite 

and can lead to a large fire and breach of the system.

e) Impingement areas such as sharp elbows, tees and valves have a higher 

risk of ignition than straight pipe. Particles in the flowing oxygen can strike 

these areas and cause ignition. Operation of valves and regulators (opening 

/ closing) cause high turbulence and impingement and only components 

selected and cleaned specifically for oxygen service should be used.


a) These guidelines apply to any unit that uses oxygen or enriched air for 

combustion or other process reasons. 

b) Oxygen is sometimes used in sulfur recovery units (SRU) and fluid catalytic 

cracking units (FCCU), Gasification, and Partial Oxidation (POX) units. 

Figures 4-64 to 4-66. 

c) Oxygen piping systems especially valves, regulators, and other impingement 

areas are potentially vulnerable. Non-metals such as those used for seats 

and seals, are easier to ignite than metals (Figure 4-69).


a) In some cases a small component will burn, such as a valve seat, without 

kindling other materials and without any outward sign of fire damage. It is 

noticed when the component is removed because it is not functioning 

properly. Figure 4-67 to 4-68. 

b) Also, external heat damage (glowing pipe or heat tint) is a strong indication 

of an internal fire. This can be caused by accumulation of flammable debris 

at a low point or other location and combustion or smoldering of the debris. 

c) The worst situation is when the pressure envelope is breached because of 

fire. Oxygen fires can cause significant burning of metal components and 

extensive structural damage (Figure 4-68).


Refer to industry recommended guidelines included in the references listed below. 

Some general considerations are as follows: 

a) Oxygen fires are a sudden occurrence and not a progressive degradation or 

weakening of the material. Prevention is best accomplished be keeping 

systems clean, or cleaning them after maintenance or inspections. 

b) Maintain velocity within recommended limits. If practical, avoid velocities that 

are nominally above 100 feet/second (30 m/sec) in gaseous oxygen. 

c) Ensure that replacement components are suitable for oxygen service. 

d) Oxygen systems should be thoroughly cleaned after maintenance. 

e) Minimize lubricants and use only “oxygen compatible” lubricants. 

f) Do not unnecessarily open oxygen systems for visual or other inspections as 

this could introduce contamination.

g) A thorough review is needed before modifying oxygen systems to operate at 

higher pressures, temperatures, or velocities. 

h) Minimize sudden changes in pressure in the system. If high pressure oxygen 

suddenly enters a system initially at low pressure by quick operation of a 

valve, the “dead end” of that system experiences heating from adiabatic 

compression of the oxygen. Adiabatic compression heating can ignite 

plastics and rubbers, but will not ignite metals. Valve seats, seals, nonmetallic 

hoses, etc can be ignited by this mechanism. 

i) Do not use plastic pipe in oxygen piping systems. 

j) Personnel activities near oxygen piping and systems should be minimized 

during start ups.


a) Most commercial oxygen is dry and non-corrosive at normal ambient 

temperatures. Because of the sudden catastrophic ignition of metals under 

certain conditions this type of damage is difficult to inspect for in advance. 

b) Tell-tale signs of a minor fire such as external heat damage, or signs of 

malfunctioning valves or other components containing non-metallic 

components may be indicative of a problem. 

c) Blacklights can be used to check for hydrocarbon contamination. 


Not applicable.

Figure 4-64 – Thermal combustor 

on the front end of a reaction 

furnace on a sulfur recovery unit.

Figure 4-65 – Same as figure above after 

damage due to oxygen combustion resulting 

from oxygen injection into the thermal 

combustor on the front end of the reaction 

furnace.

Figure 4-66 – Same as figure 

above when viewed from a 

different angle.

Figure 4-67 – Photograph of a burned 304 SS elbow. The fire started in an upstream 

stainless steel wire filter (due to particle impact) and the burning filter material 

impacted the elbow and ignited it. Thin stainless steel components (e.g., filter) are much 

more flammable than thicker SS. Thin SS (

Figure 4-68 – Photograph illustrating burn through of a brass pressure gage. 

Brass is generally suitable for oxygen service. However, the gauge was not 

was not intended for oxygen service and was not “oil free”. Hydrocarbon 

contamination, probably from manufacture, caused the fire.

Figure 4-69 – Burn-through of 

a PTFE-lined stainless steel 

hose in high pressure gaseous 

oxygen (GOX) service. Grease 

contamination ignited and 

penetrated the hose.

气化氧 - 增强燃烧学习重点 : 


b) 原理 : 氧气导致燃烧 , 

c) 易感材质 : 铁素体 , 奥氏体 , 其他 , 

d) 易感设备 : 气态氧设备 , 

e) 预防 / 缓解 : 正确材料选择 , 清洁度 , 流速 ( 避免冲击 ), 外来固体 , 

f) 非 API 510/570 考试题 .

Damage Mechanisms Affecting Fixed Equipment in the Refining Industry

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