API Standards for Coiled Tubulars

API Standards for Coiled 

Tubulars 

Roderic K. Stanley, Ph. D, I. Eng. 

SPE 

International Oilfield Services 

Chm: API Resource Group for Coiled Tubing 

Rkstanley@ndeic.com 

SPE-Icota SPE Icota-Aberdeen Aberdeen Nov 05

Coiled Tubulars? 

• Coiled Tubing (CT) - small dia – 4.5-in. ERW 

carbon steel tubing used in numerous ways 

• CT55, CT70, CT80, CT90 (in RP 5C7) 

• Coiled Line Pipe (CLP) –small dia –6.625-in. 

ERW carbon steel tubing used as umbilicals, 

flowlines, etc. 

• X52C, X56C, X60C, X65C, X70C, X80C – 

follow the 5L classifications for line pipe 

• Currently Excludes: Excludes short welded lengths of 

ERW and smls. 


Coiled 

Tubing 

Note.. 

…a cycle here 

A cycle here 

is not….. 

CT and CLP 

CLP 

CLP 

From 

1944 

From 

2000 

Coiled line 

Pipe SPE-Icota SPE Icota-Aberdeen Aberdeen Nov 05

A Little Background….. 


Where we were in 1998……. 

• Resource Gp. Gp. 

for Coiled Tubing formed 1996 

• SPE 46019 “Progress “ Progress Towards API Specifications for 

Coiled Tubing and Pipe” Pipe” 

by Sas-Jaworski 

Sas Jaworski/Stanley /Stanley 

• Working on RP 5C7 – “catch all” RP – one of a kind. 

• Working on Spec 5LCP – Coiled Line Pipe thought to 

be very important 

• Working on Spec 5ST - Coiled Tubing Spec was 

shelved in order to get 5LCP into print. 

• Approved –to to work on RP 5C8 (Care, Maintenance 

and Inspection of Coiled Tubing*) 

* Later changed to “Coiled Tubulars” 


SPE-Icota SPE Icota-Aberdeen Aberdeen Nov 05 

Current API Organization 

And we are in 

here too 

Kinda wild 

here too 

CT CLP 

You are 

here 

The new 

guys on the 

block 

Fun stuff 

here

API representation - today 

• Purchasers: Purchasers Service Companies, Major Oils, 

Pipeliners. 

• Operators: Operators Major Oils 

• Mills: Manufacturers. 

• Consultants: Consultants Welding, Collapse 

• Observers: Observers MMS, DoT, Rosen, Sumitomo 

• Inspection: Inspection Tuboscope, Patterson (RD/Tech), 

Intl. OilFld Svcs 

• API: attend all meetings 


Current Documents - 5C7 

• API RP 5C7 – CT55-90 

only (1996) 

• Tensiles before bending 

• Renewed 2001 

• Remain in force until 

either updated or 

withdrawn 

• Operational sections 

transferred to a 

Committee 6 document on 

well servicing 

• Corrosion and Collapse 

transferred to RP 5C8 


Current Documents – 5LCP (1999) 

• Converted from 5L (41 st Ed) 

• Dropped all mfg except ERW 

• Added Skelp-end Skelp end weld, weld NDE 

not in 5L, 5L 15 min hydro at 

80% SMYS, butt welding to 

API 5L/1104, 5L/1104 tensiles at “mill 

stops”. 

• Charpy tests at customer 

request. 

• Can class CT55-80 CT55 80 as X52C- X52C 

X80C. (No X42C) 

• Up for 5-yr 5 yr review 


In the Works… 

API Spec 5ST 

(Specification for Coiled Tubing) 

• (5LCP pbl conv to CT) 

• Was Voted in 2001 

• Not enough votes 

• “Not tight enough” 

• Put on hold 

• Pressure to re-introduce 

in 2003 

• New chm. found 2005 

• Work to begin now 


API RP 5C8 

(Care, Maintenance, Inspection of Coiled 

Tubulars) 

•Grades up to CT110 

•Mechanicals, inc CSA, defect 

removal definitions 

•Corrosion & Mitigation 

•Butt Welding and its NDE 

•Tube NDE – Visual/Dimensional 

EMI, Prove-Up 

• Assessment of Used CT 

• Collapse from 5C7 into Appendix 

• Defect Pictures in appendix

Why RP 5C8? 

• Repeated and unidentified field 

failures 

• Provide minimum requirements 

for field protection of C-Tubulars 

•Provide field welding procedures 

•Provide field general NDE 

procedures for common EMI 

systems. 

•Provide NDE equipment 

standardization/calibration 

requirements 

•Aim to replace RP 5C7 


OCCURENCES 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

COILED TUBING FAILURES 1987-98 

Corrosion 

Rig Operations 

Manufacturing 

OD wear 

Tensile 

Butt Weld

Pits/cracks 

on OD→ 

Corrosion and 

Mitigation 

Pitting at root of flash 

column, + crack 


Mitigation and Prevention 

• Flushing – high pH 

fluids 

• OD Cleaning and 

coating 

• ID Cleaning and coating 

• Air drying 

• N 2 dry and backfill 

• Relative Humidity of 

flush/backfill 

measurement 

• Dew point measurement 

RH meter 


Tube-Tube Tube Tube Butt Welding…….. 

• Industry welding subcommittee 

formed 

• WPS and PQR contents 

established 

• Manual and Orbital butt 

welds 

• ..not ADB or other exotic 

methods 

• Borrowed material from 

Icota Welding document 

Bonded 

interface 

Amorphous 

Bond in CT 

400μm 



………….and its NDE 

Geometry considerations 

Phased array weld inspection 

16 element linear array Sweep from 40 to 70 degrees

5LCP – voted late 2004 

• changes out for vote 

• Added more ultrasonic 

NDE, esp for butt welds 

• Add X90C grade 

• Provide for torch-cut 

ends 

• Reduce acceptable min. 

wall from 

–12.5%t 12.5%t to –10%t. 10%t. 

Status today…… 

RP 5C8 – Voted late 2004 

• changes out for vote 

• more “shoulds” and no 

“shalls”. 

• Added definitions of “cycle” 

and “critical sour well“ 

(AEUB) 

• Added pictures of common 

defects in an appendix 


Status today..(2) 2) 

5ST 

• Chm. found midyear 

• Cover mfg, grades, 

testing, inspection 

• Include Product 

Service Levels? 


PSLs might include 

•Additional UT of SE weld 

•Additional UT of Butt weld 

•Restricted tensile ranges (for sour 

service) 

•Restricted hardness ranges (same) 

•Additional microhardness 

readings 

• Final NDE Inspection after hydro 

• Longer/higher pressure test

5C8 - Equipment 

Standardization & Calibration 

From RP 5A5……. 

• All equipment calibrated at regular intervals 

• All equipment standardized at regular intervals 

• Reference standards & reference indicators 

maintained. 

• EMI unit, UT Compression wall gauge, UT shear 

wave unit, RT unit, Mag. particle yokes, pit depth 

gauges. 

• All Operators trained, qualified and certified 


Examples - Calibratable 

EMI equipment for full length 

CT inspection – now defunct 


Equipment 

UT Butt weld inspection 

equipment

Tubing 

Assessment 

Table-5C8 Table 5C8 

Classified sections of 

tubulars from TFL and 

NDE, not just either 

one 


What Do You Do When You Find 

• Need to notify 

owner of tubing 

•Check the 

inspection table 

• Use a Fatigue 

model 

•Make assessment 

including fatigue 

model and defect 

size 

an Imperfection? 

•Repair the damage SPE-Icota SPE Icota-Aberdeen Aberdeen Nov 05

5C8 Appendix 


Training and Certification 1 

• All Inspectors qualified and certified….. 

• Use ASNT Scheme (TC-1A or CP-189) 

• 0r PCN Scheme 

• Level 1 

• Level II 

• Level III 

• In EMI, UT, MT, PT, RT 

• Nonlevelled courses in Visual, Dimensional and 

Hardness Testing 


Training and Certification 2 

Inspector should be; 

1. Trained in all inspections used on CT/CLP 

2. T/C to Level II under ASNT or PCN regime 

3. Cognisant of accept/reject/derating criteria 

4. This implies that the Specific part of the certification exams 

should cover knowledge of the equipment used, and the 

accept/reject criteria. 


Typical Training Course 

• Coiled Tubulars 

• Fatigue Models 

• Common defects 

• Effect of defects 

• PT course (G, S, Pr) 

• RT course (G, S, Pr) 

• UT course (G, S, Pr) 

• MT course (G, S, Pr) 

• EMI course (G, S,Pr) 

Outline 

• Visual Inspection 

• Hardness Testing 

• Other, as needed 

Similar to classes 

developed for DS-1 DS 1 

or NS-2 NS 


Collapse in RP 5C8 

• Moved from body of 5C7 to Appendix of 5C8 

• Added disclaimer regarding origin of collapse 

equations for new and used coiled tubing 


Collapse appendix 

•Vast amt of high level work done on 

new/old tubular collapse data 

•New equation developed for API 

5C3/ISO 119400 

•Eliminates 4 equations for Yield 

strength, plastic, transition, and elastic 

collapse regimes 

•Replaced them with one (more 

complex) equation 

•Tamano 4, generalized by Dr. Frans 

Kever ( KGT) 

• Work yet to be defined for 

normalized ERW tubing 


Possible new API RGCT 

Approach….. 

• Obtain results from KGT (2000 data points), which includes 

all data points at higher measured values for concervatism. 

•Use results for more rounded Stress-strain curves 

•Add existing Avakov-Timoshenko correction for Ovality 

•Add existing Avakov correction for coiled tubing usage 

This is the same approach as was used to generate the original 

values in 5C7, but there, the old equations from 5C3 were 

used. Here, we place them with KGT 


Where 

The equations……Collapse 

p c,ult = (p e +p y )/2 – [(p e -p y ) 2 /4 + p e p y H ult ] 1/2 (A1) 

p e =1.08[2E/(1-ν 2 )][(D o /t) -1 (D o /t - 1) -2 ] (A2) 

p y = 2f y [D o /t – 1][D o /t] -2 [1 + 1.5/(D o /t –1)] (A3) 

H ult = 0.071Ov + 0.0022 ec – 0.018 rs (A4) 

And 

D o = actual average diameter, E = Young’s Modulus 

ec = eccentricity in % as (t max -t min )/t av f y = Actual API Yield stress. 

H ult = is a decrement factor Ov = Ovality% as (D o,max -D o,min )/D o,av 

pc,ult = Ultimate collapse str, pe = Collapse str for elastic failure 

py = Collapse str for yield failure, rs = Residual stress 

t = Average wall thickness ν = Poisson’s ratio. 


Collapse Design Equations 

p c,des = (k e p e +k p p y )/2 – [(k e p e -k p p y ) 2 /4 + k e p e k p p y H des ] 1/2 (A5) 

where 

H des = Decrement factor (varies with manufacturing process). 

k e 

= Downrating Factor for elastic collapse 

k p = Downrating Factor for plastic collapse. 

One challenge is to define H for a coiled tubular. Is the 

value for normalized, not hot/cold straightened applicable?

API Standards for Coiled Tubulars

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