Section 6: Selected Applications & Techniques

Section 6: Selected Applications 

& Techniques

Content: Section 6: Selected Applications & Techniques 

6.1: Defects & Discontinuities 

6.2: Rail Inspection 

6.3: Weldments (Welded Joints) 

6.4: Pipe & Tube 

6.5: Echo Dynamic 

6.6: Technique Sheets 

6.7: Material Properties-Elastic Modulus Measurements 

6.8: High Temperature Ultrasonic Testing 

6.9: Thickness Gauging 

6.10: In-Service Inspection 

Continues next page….

6.11: Casting 

6.12: Inspection of bonded Joints 

6.13: Corrosion Monitoring 

6.14: Crack Monitoring 

6.15: Residual Stress Measurements 

6.16: Bond Testing 

Appendix: (Non-exam) 

6.App-1: TOFD Introduction

6.1: Defects & Discontinuities

6.1.1 Casting Defects & Discontinuities

Casting Defects & Discontinuities

Casting Defects & Discontinuities- A Cold Shut is caused when a molten 

metal is poured over solidified metal without fusing.

Casting Defects & Discontinuities – Hot tear or shrinkage crack forms 

when the molten section of unequal thickness solidified and the shrinkage 

stress tear the partially molten apart.


Micro-shrinkage is usually many small subsurface holes that appear at the 

gate of casting / can also occur when molten metal must flow from a thin 

section into thicker section of casting. 

Blow hole are small hole at the surface of the casting caused by gas which 

comes from the mold itself. (wet sand mould forming steam resulting in blowhole) 

Porosity is caused by entrapped gas. It is usually subsurface or surface 

depending on the mold design.


Casting Defects & Discontinuities- Hot Tear

Casting Defects & Discontinuities- Blister

Casting Defects & Discontinuities- Porosity




Casting Defects & Discontinuities - Mismatch

Casting Defects & Discontinuities- Cold Shut

Casting Defects & Discontinuities- Missrun

Casting Defects & Discontinuities- Misrun

Casting Defects & Discontinuities- Blow Hole

Casting Defects & Discontinuities- Gas Porosity


Casting Defects & Discontinuities- Cold Shut

Casting Defects & Discontinuities- Shrinkage Cavity

Casting Defects & Discontinuities- Assorted

6.1.2 Processing Defects & Discontinuities

Processing Defects & Discontinuities

Salute to the Steel Workers!

Processing Defects & Discontinuities- Lamination formed when the 

casting defects are flatten during rolling, forging, extrusion or other 

mechanical working processes.

Processing Defects & Discontinuities- Stringers formed when the billet is 

rolled into shape the casting non metallic inclusions are squeezed into long 

and thinner inclusions.

Processing Defects & Discontinuities- Forging lap is caused by folding of 

metal on the surface, usually when some of the metal is squuaed ot between 

the two dies.

Processing Defects & Discontinuities- Forging burst is a rupture causes 

by forging at improper temperature. The burst may be internal or external.

Processing Defects & Discontinuities

Q9: The preferred method of ultrasonically inspecting a complex-shape 

forging: 

A. Is an automated immersion test of the finished forging using instrument 

containing a calibrated attenuator in conjunction with a C-scan recorder 

B. Combined thorough inspection of the billet prior to forging with a 

careful inspection of the finished part in all areas where shape permit 

C. Is a manual contact test of the finished part 

D. Is an automated immersion test of the billet prior to forging

6.1.3 Welding Defects & Discontinuities

Welding Defects & Discontinuities






Welding Defects & Discontinuities- Incomplete Penetration

Welding Defects & Discontinuities- Slag Inclusion

Welding Defects & Discontinuities- Cluster Porosity

Welding Defects & Discontinuities- Lack of Sidewall Fusion (with Slag 

entrapped)

Welding Defects & Discontinuities- Wagon Track 

(slag inclusion at hot pass)

Welding Defects & Discontinuities- Burn Thru

Welding Defects & Discontinuities- Offset with LOP

Welding Defects & Discontinuities- Excessive Penetration

Welding Defects & Discontinuities- Internal (Root) Under Cut

Welding Defects & Discontinuities- Transverse Crack

Welding Defects & Discontinuities- Tungsten Inclusion

Welding Defects & Discontinuities- Root Pass Porosity

6.1.4 Service Induced Defects & Discontinuities

Service Induced Defects & Discontinuities 

http://failure-analysis.info/2010/05/analyzing-material-fatigue/

Service Induced Defects & Discontinuities- Fatigue Cracks

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 4-26 – Metallographic cross-section of a superheated steam outlet that 

failed from thermal fatigue. Unetched.

Figure 4-36 – Weld detail used to join a carbon steel elbow (bottom) to a weld 

overlaid pipe section (top) in high pressure wet H2S service. Sulfide stress 

cracking (SSC) occurred along the toe of the weld (arrow), in a narrow zone 

of high hardness.

Figure 4-37 – High magnification photomicrograph of SSC in pipe section 

shown in Figure 4-36.

Figure 4-38 – Failure of DMW joining 1.25Cr-0.5Mo to Alloy 800H in a Hydrodealkylation 

(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).

Figure 4-57 – Vibration induced fatigue of a 1-inch socket weld flange in a 

thermal relief system shortly after startup.

Figure 4-58 – Cross-sectional view of the crack in the socket weld in Figure 4- 

57.

Figure 5-1 – Localized amine corrosion at the weld found in piping from 

reboiler to regenerator tower in an MEA unit. Many other similar cases found, 

some going as deep as half thickness. They were originally found and 

mistaken as cracks with shear wave UT inspection.

Figure 5-2 – Hot Lean Amine Corrosion of Carbon Steel:

Figure 5-3 – Preferential weld corrosion in lean amine (Reference 5)

Figure 5-46 – Overhead interstage knockout drum vapor outlet nozzle.

Figure 5-47 – Carbonate cracking adjacent to a weld (Reference 6).

Figure 5-48 – Metallographic sample showing intergranular carbonate 

cracking developed after 6 months service (Reference 6).lean amine 

(Reference 5)

Figure 5-49 – Most cracks originate in base metal but this weldment 

contained a crack that originated at the root and propagated through the weld 

metal. Other cracks appear to have initiated in the HAZ (Reference 7).

6.2: Rail Inspection

Rail Inspection 

One of the major problems that railroads have faced since the earliest days is 

the prevention of service failures in track. As is the case with all modes of 

high-speed travel, failures of an essential component can have serious 

consequences. The North American railroads have been inspecting their 

most costly infrastructure asset, the rail, since the late 1920's. With increased 

traffic at higher speed, and with heavier axle loads in the 1990's, rail 

inspection is more important today than it has ever been. Although the focus 

of the inspection seems like a fairly well-defined piece of steel, the testing 

variables present are significant and make the inspection process challenging. 

Rail inspections were initially performed solely by visual means. Of course, 

visual inspections will only detect external defects and sometimes the subtle 

signs of large internal problems.

The need for a better inspection method became a high priority because of a 

derailment at Manchester, NY in 1911, in which 29 people were killed and 60 

were seriously injured. In the U.S. Bureau of Safety's (now the National 

Transportation Safety Board) investigation of the accident, a broken rail was 

determined to be the cause of the derailment. The bureau established that the 

rail failure was caused by a defect that was entirely internal and probably 

could not have been detected by visual means. The defect was called a 

transverse fissure (example shown on the bottom). The railroads began 

investigating the prevalence of this defect and found transverse fissures were 

widespread.

Transverse Fissure

Transverse Fissure

Transverse Fissure

One of the methods used to inspect rail is ultrasonic inspection. Both 

normal- and angle-beam techniques are used, as are both pulse-echo and 

pitch-catch techniques. The different transducer arrangements offer different 

inspection capabilities. Manual contact testing is done to evaluate small 

sections of rail but the ultrasonic inspection has been automated to allow 

inspection of large amounts of rail. 

Fluid filled wheels or sleds are often used to couple the transducers to the 

rail. Sperry Rail Services, which is one of the companies that perform rail 

inspection, uses Roller Search Units (RSU's) comprising a combination of 

different transducer angles to achieve the best inspection possible. A 

schematic of an RSU is shown below.

Techniques: Wheel Probe

Techniques: Examples of axles with outside bearings of the Deutsche 

Bundesbahn. (a) Of goods truck; (b) axle with roller bearing, bearing ring not 

removed; c same with additional brake disc

Techniques: (c) same with additional brake disc

6.3: Weldments (Welded Joints)

6.3.1: UT of Weldments (Welded Joints) 

The most commonly occurring defects in welded joints are porosity, slag 

inclusions, lack of side-wall fusion, lack of inter-run fusion, lack of root 

penetration, undercutting, and longitudinal or transverse cracks. 

With the exception of single gas pores all the defects listed are usually well 

detectable by ultrasonics. Most applications are on low-alloy construction 

quality steels, however, welds in aluminum can also be tested. Ultrasonic flaw 

detection has long been the preferred method for nondestructive testing in 

welding applications. This safe, accurate, and simple technique has pushed 

ultrasonics to the forefront of inspection technology. 

Ultrasonic weld inspections are typically performed using a straight beam 

transducer in conjunction with an angle beam transducer and wedge. A 

straight beam transducer, producing a longitudinal wave at normal incidence 

into the test piece, is first used to locate any laminations in or near the heataffected 

zone. This is important because an angle beam transducer may not 

be able to provide a return signal from a laminar flaw.

UT of Weldments (Welded Joints) 

F 

s 

0 20 40 60 80 100 

x 

a = s sinß 

a' = a - x 

d' = s cosß 

d = 2T - t' 

a 

a' 

ß = probe angle 

s = sound path 

a = surface distance 

a‘ = reduced surface distance 

d‘ = virtual depth 

d = actual depth 

T = material thickness 

ß 

Work piece with welding 

s 

Lack of fusion 

d

UT Calculator

Flaw Detection- Depth Determination

The second step in the inspection involves using an angle beam transducer 

to inspect the actual weld. Angle beam transducers use the principles of 

refraction and mode conversion to produce refracted shear or longitudinal 

waves in the test material. [Note: Many AWS inspections are performed using 

refracted shear waves. However, material having a large grain structure, such 

as stainless steel may require refracted longitudinal waves for successful 

inspections.] This inspection may include the root, sidewall, crown, and heataffected 

zones of a weld. The process involves scanning the surface of the 

material around the weldment with the transducer. This refracted sound wave 

will bounce off a reflector (discontinuity) in the path of the sound beam. With 

proper angle beam techniques, echoes returned from the weld zone may 

allow the operator to determine the location and type of discontinuity.

T = Plate Thickness 

ϴ = Shear wave angle 

LEG = T/Cos ϴ, V path= 2 x LEG. 

Skip = 2.T Tan ϴ

https://www.mandinasndt.com/index.php?option=com_content&view=article&id=32%253A 

ut-angle-beam-calculator&catid=12%253Atools&Itemid=18 

https://www.nde-ed.org/GeneralResources/Formula/AngleBeamFormula/AngleBeamTrig.htm

Flaw Detection- Triangulations of reflector 

ϴ = Refracted angle T= Thickness LEG1=LEG2= T/Cos ϴ 

V PATH= 2x LEG= 2T/Cos ϴ 

SKIP= 2.T Tan ϴ 

ϴ

Flaw Detection- Triangulations of reflector 

ϴ = Refracted angle T= Thickness Surface Distance= S.Sin ϴ 

Depth= S.Cos ϴ 

ϴ

To determine the proper scanning area for the weld, the inspector must first 

calculate the location of the sound beam in the test material. Using the 

refracted angle, beam index point and material thickness, the V-path and skip 

distance of the sound beam is found. Once they have been calculated, the 

inspector can identify the transducer locations on the surface of the material 

corresponding to the crown, sidewall, and root of the weld.

6.3.2 Weld Scanning

Expert at works

Typical Scanning Patterns: 

Typically the weld should be inspected in the 1 st or 2 nd leg (1 st Skip).

Typically scanning patterns

Weld Scanning

Weld Scanning

Weld Scanning

Weld Scanning

Echo Dynamic- Position of Defects 

Sometimes it will be possible to differentiate between these 2 defects simply 

by plotting their position within the weld zone:

Echo Dynamic- Position of Defects

Plate Weld Scanning

Plate Weld Scanning

Plate Weld Scanning

Plate Weld Scanning

Plate Weld Scanning

Practice Makes Perfect 

52. One of the most apparent characteristics of a discontinuity echo, as 

opposed to a non-relevant indication is: 

(a) Lack of repeatability 

(b) Sharp, distinct signal 

(c) Stable position with fixed transducer position 

(d) High noise level 

58. What useful purpose may be served by maintaining grass on the baseline? 

(a) To estimate casting grain size 

(b) To provide a reference for estimating signal to noise ratio 

(c) To verify adequate coupling to the test piece 

(d) All of the above

Practice Makes Perfect 

62. Which of the following conditions would be most likely to cause strong, 

interfering surface waves? 

(a) High frequency transducers 

(b) Testing on a small diameter surface 

(c) Testing on a flat surface 

(d) Testing on a curved surface with a contoured wedge and transducer

6.4: Pipe & Tube

Pipe & Tube

Pipe & Tube

Experts at work

Pipe Scanning

Pipe Scanning

Pipe Scanning 

48.59 o max 

30 o max

Pipe Scanning

Pipe Scanning

Pipe Scanning- thickness/OD ratio

Pipe Scanning- thickness/OD ratio 

When the t/OD ratio = .2 , t=.2OD, ID=OD-2t= OD-.4OD= .6OD 

ϴ max = Sin -1 (ID/OD), ϴ max = Sin -1 (0.6), ϴ max = 37° Max. 

For the sound path to scans the inner face the maximum shear angle shall be 

37° Max. Therefore 45° /60° /70° probe can not scan the pipe inner face.

Pipe Scanning- Contact Methods



Q: Calculate the maximum shear wave angle and the range for 360° 

revolution scanning when the shear wave angle is 45°. 

Given that the OD=6” Thickness=3/4” 

Answer: 

(a) 

The maximum shear wave angle ϴ = Sin -1 (ID/OD) = Sin -1 (2.25/3) 

ϴ = 48.6° Max. 

(b) ?

Answer part B 

c 

a 

b 

a/Sin A = b/Sin B 

2.25/ Sin 45 = b / Sin B, 3.182= b/ Sin B, 

c = a.Sin B, Sin B= c/a 

3.182= b/c x 2.25, b/c= 1.414

Q35: During immersion testing of pipe or tubing the incident longitudinal wave 

angle must be limited to a narrow range. The reason for the upper limit is: 

(a) To avoid complete reflection of ultrasound from the test piece 

(b) To prevent formation of Rayleigh waves 

(c) To prevent formation of shear waves 

(d) To avoid saturating the test piece with ultrasound

Q35: Which of the following may result in a narrow rod if the beam 

divergence results in a reflection from a side of the test piece before the 

sound wave reaches the back surface: 

A. Multiple indications before the first back reflection 

B. Indications from multiple surface reflections 

C. Conversion from longitudinal mode to shear mode 

D. Loss of front surface indications

6.5: Echo Dynamic

Expert at works

6.5.1 Basic echodynamic pattern of reflectors 

Echo Dynamic of Discontinuity- Non-destructive testing of welds - 

Ultrasonic testing - Characterization of indications in welds; German version 

EN 1713:1998 + A1:2002

Basic echodynamic pattern of reflectors 

C.1 Pattern 1 

Point-like reflector response, figure C.1. At any probe position the A-scan 

show a single sharp echo. As the probe is moved this rises in amplitude 

smoothly to a single maximum before falling smoothly to noise level. 

4 

5 

2 

3 

6 

1 

7

C.1 Pattern 1 Point-like reflector

C.1 Pattern 1 Point-like reflector

C.2 Pattern 2 

Extended (elongated) smooth reflector respond, figure C.2. At any probe 

position the A-scan shows a single sharp echo. When the ultrasound beam is 

moved over the reflector the echo rises smoothly to a plateau and is 

maintained with minor variation in magnitude up to 4 dB, until the beam 

moves off the reflector, when the echo fall smoothly to noise level.

C.2 Pattern 2 

Extended (elongated) smooth reflector

C.2 Pattern 2 

Extended (elongated) smooth reflector

C.2 Pattern 2 

Extended (elongated) smooth reflector 

(figure modified to depict obliquely oriented planar face) 

Extended (elongated) 

smooth reflector-planar 

face obliquely oriented

C.3 Pattern 3 

Extended (elongated) rough reflector response. There are two variants of this 

pattern, depending upon the angle of incident of the probe beam on the 

reflector.

C.3 Pattern 3a 

Extended (elongated) rough reflector response. Near normal incidence, figure 

C.3a At any probe position the A-scan shows a single but rugged echo. As 

the probe moved this may undergo large (>+/- 6dB) random fluctuation in 

amplitude. The fluctuation are caused by reflection from the different facets of 

the reflector and by interference of waves scattered from the groups of facets.


Extended (elongated) rough reflector response.


Extended (elongated) rough reflector response.

C.3 Pattern 3b 

Oblique incidence, travelling echo pattern, figure C.3 b At any probe position, 

the A-scan shows an extended train of signals (subsidiary peaks) within a 

bell-shaped pulse envelope. As the probe is moved each subsidiary peak 

travels through the pulse envelop, rising to its own maximum toward the 

center envelop and then falling. The overall signal may shown large (>+/-6dB) 

random fluctuation in amplitude.


Oblique incidence, travelling echo pattern


Oblique incidence, travelling echo pattern

C.4 Pattern 4 

Multiple reflector respond, figure C.4. At any probe position the A-scan shows 

a cluster of signal which may or may not be well resolved in range. As the 

probe is moved the signals rise and fall at random but the signal from each 

separate reflector element ,if resolved, shows pattern 1 respond.

C.4 Pattern 4 

Multiple reflector respond

C.4 Pattern 4 

Multiple reflector respond

Echodynamic- Change of echo height and echo shape when the direction of 

irradiation is changed. (a) On flat or linear flaw; (b) on rounded flaw

Echodynamic- Differences between the indications of inclusions and cracks, 

drawn schematically and exaggerated for greater clarity. a Inclusions; b flake 

cracks. The echoes of the more distantflaws, because of divergence and 

attenuation of the sound beam, are rather weak

Break Time

Echo Dynamic of Discontinuity- Flaw detection

Echo Dynamic of Discontinuity- Flaw Detection

Echo Dynamic of Discontinuity- Flaw detections

Echo Dynamic of Discontinuity- Improper flaw orientation


Echo Dynamic of Discontinuity- Reflection angle

Echo Dynamic of Discontinuity- Angles of reflection


Echo Dynamic of Discontinuity- Perfect flaw orientation


Echo Dynamic of Discontinuity- Vertical near surface flaw

Echo Dynamic of Discontinuity- Tandem Techniques



Echo Dynamic

Echo Dynamic- Root Concavity

Echo Dynamic

Echo Dynamic

Echo Dynamic

Echo Dynamic

Echo Dynamic 

Crack

Echo Dynamic- Broad indication with low amplitude

Echo Dynamic- Shaper indication and higher amplitude than porosity

Echo Dynamic

Echo Dynamic 

Threadlike defects, point defects and flat planar defects orientated nearnormal 

to the beam axis all produce an echo response which has a single 

peak

Echo Dynamic 

The echo response from a large slag inclusion or a rough crack is likely to 

have multiple peaks:

Echo Dynamic 

In case “a” it will be difficult to determine whether the defect is slag or a crack. 

“Rotational- Swivel” or “orbital” probe movements may help:

Echo Dynamic 

Typical Echo Dynamic Patterns

Echo Dynamic 


Echo Dynamic 


Q. A smooth flat discontinuity whose major plane is not perpendicular to the 

direction of sound propagation may be indicated by: 

A. An echo amplitude comparable in magnitude to the back surface reflection 

B. A complete loss of back surface reflection 

C. An echo amplitude larger in magnitude than the back surface reflection 

D. All of the above

Q183. In immersion testing, irrelevant or false indications caused by 

contoured surfaces are likely to result in a: 

A. Broad base indication 

B. Peaked indication 

C. Hashy signal 

D. Narrow based indication

Q24. During inspection of a parallel sided machined forging using straight 

beam immersion techniques, a diminishing back reflection in a localized 

area in the absence of a defect indication would least likely represent: 

A. A course grain structures 

B. A small non-metallic stringer 

C. A defect oriented at a severe angle to the entry surface 

D. A large inclusion.

Q46. Which best describes a typical display of a crack whose major surface is 

perpendicular to the ultrasound beam? 

A. A broad indication 

B. A sharp indication 

C. A indication will not show due to improper orientation 

D. A broad indication with high amplitude

Q46. A smooth flat discontinuities whose major plane is not perpendicular to 

the direction of sound propagation may be indicated by: 

A. An echo amplitude comparable in magnitude to the back surface reflection 

B. A complete loss of back surface reflection 

C. An echo amplitude larger in magnitude than the back surface reflection 

D. All of the above

6.6: Technique Sheets

Expert at works

Hanger Pin Testing using Shear Wave 

http://www.fhwa.dot.gov/publications/research/infrastructure/structures/04042/index.cfm#toc

Physical Dimension

Physical Dimension

Physical Dimension

Physical Dimension

Reporting: Basic Pin Information

Reporting: Scanning Report – Top of Pin

Reporting: Scanning Report – Bottom of Pin

Mock-Up

Mock-Up

Mock-Up

Mock-Up

Mock-Up

Reporting: Basic Pin Information

Hanger Pin Testing using Shear Wave

Pitch and Catch Methods- Echo Dynamic

Pitch and Catch Methods- Set-up

Pitch and Catch Methods- Echo Dynamic

6.7: Material Properties- 

Elastic Modulus Measurements

6.7.1 Determination of Microstructural Differences 

Ultrasonic methods can be used to determine microstructural differences in 

metals. For this, contact testing with the pulse-echo technique is used. The 

testing can be either the measurement of (1) ultrasonic attenuation or the (2) 

measurement of bulk sound velocity.

6.7.2 The attenuation method 

The attenuation method is based on the decay of multiple echoes from test 

piece surfaces. Once a standard is established, other test pieces can be 

compared to it by comparing the decay of these echoes to an exponential 

curve. This test is especially suited for the microstructural control of 

production parts, in which all that is necessary is to determine whether or not 

the parts conform to a standard. An example of the use of ultrasonic 

attenuation in the determination of differences in microstructure is the control 

of graphite-flake size in gray iron castings, which in turn controls tensile 

strength. In one application, a water-column search unit that produced a 

pulsed beam with a frequency of 2.25 MHz was used to test each casting 

across an area of the casting wall having uniform thickness and parallel front 

and back surfaces.

A test program had been first carried out to determine the maximum size of 

graphite flakes that could be permitted in the casting and still maintain a 

minimum tensile strength of 200 MPa (30 ksi). Then, ultrasonic tests were 

made on sample castings to determine to what intensity level the second 

back reflection was lowered by the attenuation effects of graphite flakes larger 

than permitted. Next, a gate was set on the ultrasonic instrument in the region 

of the second back reflection, and an alarm was set to signal whenever the 

intensity of this reflection was below the allowable level. The testing 

equipment was then integrated into an automatic loading conveyor, where the 

castings were 100% inspected and passed or rejected before any machining 

operation.

6.7.3 Velocity Measurements 

Velocity Measurements When considering the compressional and shear 

wave velocities given in Table 1, there may be small deviations for crystalline 

materials because of elastic anisotropy. This is important and particularly 

evident in copper, brass, and austenitic steels. The following example 

illustrates the variation of sound velocity with changes in the microstructure of 

leaded free-cutting brass.

6.7.4 Elastic Modulus Measurement 

Application: 

Measurement on Young's Modulus and Shear Modulus of Elasticity, and 

Poisson's ratio, in non-dispersive isotropic engineering materials. 

Background: 

1. Young's Modulus of Elasticity is defined as the ratio of stress (force per 

unit area) to corresponding strain (deformation) in a material under tension 

or compression. 

2. Shear Modulus of Elasticity is similar to the ratio of stress to strain in a 

material subjected to shear stress. 

3. Poisson's Ratio is the ratio of transverse strain to corresponding axial 

strain on a material stressed along one axis. 

http://www.olympus-ims.com/en/applications/elastic-modulus-measurement/ 

http://www.olympus-ims.com/en/applications/?347[search][sCategoryId][1166017122]=1166017163&347[search][submit]=Search

Elastic Modulus Measurement – Young’s Modulus & Shear Modulus 

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

Elastic Modulus Measurement- Poisson Ratio

These basic material properties, which are of interest in many manufacturing 

and research applications, can be determined through computations based 

on measured sound velocities and material density. 

Sound velocity can be easily measured using ultrasonic pulse-echo 

techniques with appropriate equipment. The general procedure outlined 

below is valid for any (1) homogeneous, (2) isotropic, (3) non-dispersive 

material (velocity does not change with frequency). 

This includes most common metals, industrial ceramics, and glasses as long 

as cross sectional dimensions are not close to the test frequency wavelength. 

Rigid plastics such as polystyrene and acrylic can also be measured, 

although they are more challenging due to higher sound attenuation. 

Keyword: 

non-dispersive material (velocity does not change with frequency).

Rubber cannot be characterized ultrasonically because of its high dispersion 

and nonlinear elastic properties. Soft plastics similarly exhibit very high 

attenuation in shear mode and as a practical matter usually cannot be tested. 

In the case of anisotropic materials, elastic properties vary with direction, and 

so do longitudinal and/or shear wave sound velocity. Generation of a full 

matrix of elastic moduli in anisotropic specimens typically requires six 

different sets of ultrasonic measurements. 

Porosity or coarse granularity in a material can affect the accuracy of 

ultrasonic modulus measurement since these conditions can cause variations 

in sound velocity based on grain size and orientation or porosity size and 

distribution, independent of material elasticity. 

Keyword: 

anisotropic materials, elastic properties vary with direction

Equipment: 

The velocity measurements for modulus calculation are most commonly 

made with precision thickness gages such as models 38DL PLUS and 45MG 

with Single Element software, or a flaw detector with velocity measurement 

capability such as the EPOCH series instruments. Pulser/receivers such as 

the Model 5072PR or 5077PR can also be used with an oscilloscope or 

waveform digitizer for transit time measurements. 

This test also requires two transducers appropriate to the material being 

tested, for pulse-echo sound velocity measurement in longitudinal and shear 

modes. Commonly used transducers include an M112 or V112 broadband 

longitudinal wave transducer (10 MHz) and a V156 normal incidence shear 

wave transducer (5 MHz). These work well for many common metal and fired 

ceramic samples. Different transducers will be required for very thick, very 

thin, or highly attenuating samples. Some cases may also require use of 

through transmission techniques, with pairs of transducers positioned on 

opposite sides of the part. It is recommended that in all cases the user consult 

Olympus for specific transducer recommendations and assistance with 

instrument setup.

The test sample may be of any geometry that permits clean pulse/echo 

measurement of sound transit time through a section on thickness. Ideally 

this would be a sample at least 0.5 in. (12.5 mm) thick, with smooth 

parallel surfaces and a width or diameter greater than the diameter of the 

transducer being used. Caution must be used when testing narrow 

specimens due to possible edge effects that can affect measured pulse 

transit time. Resolution will be limited when very thin samples are used 

due to the small changes in pulse transit time across short sound paths. 

For that reason we recommend that samples should be at least 0.2 in. (5 

mm) thick, preferably thicker. In all cases the thickness of the test sample 

must be precisely known. 

Keywords: 

1. Caution must be used when testing narrow specimens due to possible 

edge effects that can affect measured pulse transit time. 

2. Resolution will be limited when very thin samples are used due to the 

small changes in pulse transit time across short sound paths.

Testing Procedure: Equipment Used. 

Measure the (1) longitudinal and (2) shear wave sound velocity of the test 

piece using the appropriate transducers and instrument setup. 

The shear wave measurement will require use of a specialized high viscosity 

couplant such as our SWC. A Model 38DL PLUS a 45MG thickness gage 

can provide a direct readout of material velocity based on an entered sample 

thickness, and an EPOCH series flaw detector can measure velocity through 

a velocity calibration procedure. In either case, follow the recommended 

procedure for velocity measurement as described in the instrument's 

operating manual. If using a pulser/receiver, simply record the round-trip 

transit time through an area of known thickness with both longitudinal and 

shear wave transducers, and compute: 

Question: For measurement of shear wave velocity is normal incident 

transverse wave used? (hint by the used of highly viscous couplant 

requirement)

Testing Procedure: Velocity Measurements & Calculations 

Velocity= Distance / ( ½ Round trip traverse time) 

Convert units as necessary to obtain velocities expressed as inches per 

second or centimeters per second. (Time will usually have been measured in 

microseconds, so multiply in/uS or cm/uS by 10 6 to obtain in/S or cm/S.) The 

velocities thus obtained may be inserted into the following equations. 

Poisson Ratio (v) = 

Young’s Modulus = 

Shear Modulus =

Velocity & Equations 

Poisson Ratio (v) = 

Young’s Modulus (E) = 

Shear Modulus (G) = , 

V L , V S 

v 

p 

= Longitudinal and Shear Velocity 

= Poisson ratio 

= Material density

Note on units: If sound velocity is expressed in cm/S and density in g/cm 3 , 

then Young's modulus will be expressed in units of dynes/cm 2 . If English units 

of in/S and lbs/in 3 are used to compute modulus in pounds per square inch 

(PSI), remember the distinction between "pound" as a unit of force versus a 

unit of mass. Since modulus is expressed as a force per unit area, when 

calculating in English units it is necessary to multiply the solution of the above 

equation by a mass/force conversion constant of (1 / Acceleration of Gravity) 

to obtain modulus in PSI. Alternately, if the initial calculation is done in metric 

units, use the conversion factor 1 psi = 6.89 x 104 dynes/cm 2 . Another 

alternative is to enter velocity in in/S, density in g/cm 3, and divide by a 

conversion constant of 1.07 x 104 to obtain modulus in PSI.

6.8: High Temperature Ultrasonic Testing

Experts at work

1.0 Background: 

Although most ultrasonic flaw detection and thickness gauging is performed 

at normal environmental temperatures, there are many situations where it is 

necessary to test a material that is hot. This most commonly happens in 

process industries, where hot metal pipes or tanks must be tested without 

shutting them down for cooling, but also includes manufacturing situations 

involving hot materials, such as extruded plastic pipe or thermally molded 

plastic immediately after fabrication, or testing of metal ingots or castings 

before they have fully cooled. Conventional ultrasonic transducers will 

tolerate temperatures up to approximately 50° C or 125° F. At higher 

temperatures, they will eventually suffer permanent damage due to internal 

disbonding caused by thermal expansion. If the material being tested is hotter 

than approximately 50° C or 125° F, then high temperature transducers and 

special test techniques should be employed. 

http://www.olympus-ims.com/en/applications/high-temperature-ultrasonic-testing/

This application note contains quick reference information regarding selection 

of high temperature transducers and couplants, and important factors 

regarding their use. It covers conventional ultrasonic testing of materials at 

temperatures up to approximately 500°C or 1000°F. In research applications 

involving temperatures higher than that, highly specialized waveguide 

techniques are used. They fall outside the scope of this note. 

Testing Methods used: 

Methods used to increase the useful range for high temperature application 

are: 

■ 

■ 

■ 

Delay Line 

High temperature Couplants 

Testing Techniques & Equipment Requirements

Temperature Limitation: 

Conventional ultrasonic 

transducers 50°C



transducers 50°C



transducers 50°C 

http://amazingunseentravel.blogspot.com/2011_08_28_archive.html



transducers 50°C




http://www.wisdompetals.com/index.php/photos/138-wonder-of-the-world-crescent-lake-in-gopi-deser




http://www.wisdompetals.com/index.php/photos/138-wonder-of-the-world-crescent-lake-in-gopi-deser

敦煌大漠美食 -50 度火锅双塔鱼 

http://www.cc6uu.com/science/article/raiders/2407

High Temperature Conventional UT- 

Good Till & No-More.

2.0 Methods used for H.Temperature Scanning 

2.1 Transducers- H.Temperature Delay Line Material 

Panametrics-NDT high temperature transducers fall into two categories, 

■ 

■ 

dual element transducers and 

delay line transducers. 

In both cases, the delay line material (which is internal in the case of duals) 

serves as thermal insulation between the active transducer element and the 

hot test surface. 

For design reasons, there are no high temperature contact or immersion 

transducers in the standard product line. High temperature duals and delay 

line transducers are available for both thickness gaging and flaw detection 

applications. As with all ultrasonic tests, the best transducer for a given 

application will be determined by specific test requirements, including the 

material, the thickness range, the temperature, and in the case of flaw 

detection, the type and size of the relevant flaws.

(1a) Thickness gaging 

The most common application for high temperature thickness gaging is 

corrosion survey work, the measurement of remaining metal thickness of hot 

pipes and tanks with corrosion gages such as Models 38DL PLUS and 45MG. 

Most of the transducers that are designed for use with Olympus corrosion 

gages are suitable for high temperature use. The commonly used D790 

series transducers can be used on surfaces as hot as 500° C or 930° F. For a 

complete list of available corrosion gauging duals that includes temperature 

specifications, see this link: Corrosion Gage Duals.

For precision thickness gauging applications using the Models 38DL PLUS or 

Model 45MG with Single Element software ,such as hot plastics, any of the 

standard Micro-scan delay line transducers in the M200 series (including 

gage default transducers M202, M206, M207, and M208) can be equipped 

with high temperature delay lines. DLHT-1, -2, and -3 delay lines may be 

used on surfaces up to 260° C or 500° F. DLHT-101, -201, and -301 delay 

lines may be used on surfaces up to 175° C or 350° F. These delay lines are 

listed in the Delay Line Option Chart.

In challenging applications requiring low frequency transducers for increased 

penetration, the Videoscan Replaceable Face Transducers and appropriate 

high temperature delay lines can also be used with 38DL PLUS and 45MG 

thickness gages incorporating the HP (high penetration) software option. 

Custom transducer setups will be required. Standard delay lines for this 

family of transducers can be used in contact with surfaces as hot as 480° C 

or 900° F. For a full list of transducers and delay lines, see this link: 

Replaceable Face Transducers.

(1b) Flaw detection 

As in high temperature thickness gaging applications, high temperature flaw 

detection most commonly uses dual element or delay line transducers. All 

standard Panametrics-NDT flaw detection duals offer high temperature 

capability. Fingertip, Flush Case, and Extended Range duals whose 

frequency is 5 MHz or below may be used up to approximately 425° C or 

800° F, and higher frequency duals (7.5 and 10 MHz) may be used up to 

approximately 175° C or 350° F. For a full list of transducers in this category, 

see this link: Flaw Detection Duals. 

All of the Videoscan Replaceable Face Transducers can be used with 

appropriate high temperature delay lines in flaw detection applications. The 

available delay lines for this family of transducers can be used in contact with 

surfaces as hot as 480° C or 900° F. For a full list of transducers and delay 

lines suitable for various maximum temperatures, see this link: Replaceable 

Face Transducers.

Applications involving thin materials are often best handled by the delay line 

transducers in the V200 series (most commonly the V202, V206, V207, and 

V208), any of which can be equipped with high temperature delay lines. 

DLHT-1, -2, and -3 delay lines may be used on surfaces up to 260° C or 500° 

F. DLHT-101, -201, and -301 delay lines may be used on surfaces up to 175° 

C or 350° F. These transducers and delay lines are listed on the Delay Line 

Transducer List. 

We also offers special high temperature wedges for use with angle beam 

transducers, the ABWHT series for use up to 260° C or 500° F and the 

ABWVHT series for use up to 480° C or 900° F. Detailed information on 

available sizes is available from the Sales Department.

2.2 High Temperature Couplants 

Most common ultrasonic couplants such as propylene glycol, glycerin, and 

ultrasonic gels will quickly vaporize if used on surfaces hotter than 

approximately 100° C or 200° F. Thus, ultrasonic testing at high temperatures 

requires specially formulated couplants that will remain in a stable liquid or 

paste form without boiling off, burning, or releasing toxic fumes. It is important 

to be aware of the specified temperature range for their use, and use them 

only within that range. Poor acoustic performance and/or safety hazards may 

result from using high temperature couplants beyond their intended range. 

At very high temperatures, even specialized high temperature couplants must 

be used quickly since they will tend to dry out or solidify and no longer 

transmit ultrasonic energy. Dried couplant residue should be removed from 

the test surface and the transducer before the next measurement.

Note that normal incidence shear wave coupling is generally not possible at 

elevated temperatures because commercial shear wave couplants will liquify 

and lose the very high viscosity that is necessary for transmission of shear 

waves. 

We offer two types of high temperature couplant: 

■ Couplant E - Ultratherm Recommended for use between 500° and 

970° F (260° to 520° C) 

■ Couplant G - Medium Temperature Couplant Recommended for use at 

temperatures up to 600° F (315° C). 

For a complete list of couplants available from Olympus, along with further 

notes on each, please refer to the application note on Ultrasonic Couplants.

Keyword: 

Note that normal incidence shear wave coupling is generally not possible at 

elevated temperatures because commercial shear wave couplants will liquify 

and lose the very high viscosity that is necessary for transmission of shear 

waves. 

http://www.olympus-ims.com/en/applications/normal-incidence-shear-wave-transducers/ 

http://static5.olympus-ims.com/data/Flash/shear_wave.swf?rev=3970 

http://www.olympus-ims.com/en/ultrasonic-transducers/shear-wave/

2.3 Test Techniques 

The following factors should always be taken into consideration in 

establishing a test procedure for any high temperature application: 

Transducer Time of Contacts 

All standard high temperature transducers are designed with a duty cycle in 

mind. Although the delay line insulates the interior of the transducer, lengthy 

contact with very hot surfaces will cause significant heat buildup, and 

eventually permanent damage to the transducer if the interior temperature 

becomes hot enough. For most dual element and delay line transducers, the 

recommended duty cycle for surface temperatures between approximately 

90° C and 425° C (200° F to 800° F) is no more than ten seconds of contact 

with the hot surface (five seconds is recomended), followed by a minimum of 

one minute of air cooling. Note that this is guideline only; the ratio of contact 

time to cooling time becomes more critical at the upper end of a given 

transducer's specified temperature range.

As a general rule, if the outer case of the transducer becomes too hot to 

comfortably hold with bare fingers, then the interior temperature of the 

transducer is reaching a potentially damaging temperature and the transducer 

must be allowed to cool down before testing continues. 

Some users have employed water cooling to accelerate the cooling process, 

however Olympus publishes no official guidelines for water cooling and its 

appropriateness must be determined by the individual user 

Keyword: 

■ 

■ 

10 second contact follows by 60 second air cooling 

Water cooling is not guarantee by Olympus NDT

Coupling Technique: The combination of transducer duty cycle 

requirements and the tendency of couplants to solidify or boil off at the upper 

end of their usable thickness range requires quick work on the part of the 

operator. Many users have found the best technique to be to apply a drop of 

couplant to the face of the transducer and then press the transducer firmly to 

the test surface, without twisting or grinding it (which can cause transducer 

wear). Any dried couplant residue should be removed from the transducer tip 

between measurements.

2.4 Equipment Functions 

Freeze Function 

Olympus Epoch series flaw detectors and all thickness gages have freeze 

functions that can be used to freeze the displayed waveform and reading. The 

freeze function is very useful in high temperature measurements because it 

allows the operator to capture a reading and quickly remove the transducer 

from the hot surface. With gages, the fast screen update mode should be 

used to help minimize contact time. 

High Gain Boost 

Gain Boost: The 38DL PLUS and 45MG gages have user adjustable gain 

boost functions, as do all Epoch series flaw detectors. Because of the higher 

attenuation levels associated with high temperature measurements, it is often 

useful to increase gain before making measurements.

3.0 High Temperature Testing and Variability 

3.1 Velocity Variation: 

Sound velocity in all materials changes with temperature, slowing down as 

the material heats up. Accurate thickness gaging of hot materials always 

requires velocity recalibration. In steel, this velocity change is approximately 

1% per 55°C or 100°F change in temperature. (The exact value varies 

depending on the alloy.) In plastics and other polymers, this change is much 

greater, and can approach 50% per 55°C or 100°F change in temperature up 

to the melting point. If a temperature/velocity plot for the material is not 

available, then a velocity calibration should be performed on a sample of the 

test material at the actual test temperature. The temperature compensation 

software function in the 38DL PLUS gage can be used to automatically adjust 

velocity for known elevated temperatures based on a programmed 

temperature/velocity constant. 

Keyword: 

■ Velocity change of -1% (minus) per 55°C or 100°F change in temperature 

■ Temperature versus velocity plot

Keyword: 

■ 

■ 

Velocity change of -1% (minus) per 55°C or 100°F change in temperature 

Temperature versus velocity plot

3.2 Zero Recalibration: 

When performing thickness gaging with dual element transducers, remember 

that the zero offset value for a given transducer will change as it heats up due 

to changes in transit time through the delay line. Thus, periodic re-zeroing is 

necessary to maintain measurement accuracy. With Olympus corrosion 

gages this can be quickly and easily done through the gage's auto-zero 

function; simply press the 2nd Function > DO ZERO keys.

3.3 Increased Attenuation: 

Sound attenuation in all materials increases with temperature, and the effect 

is much more pronounced in plastics than in metals or ceramics. In typical 

fine grain carbon steel alloys, attenuation at 5 MHz at room temperature is 

approximately 2 dB per 100 mm one-way sound path (equivalent to a round 

trip path of 50 mm each way). At 500°C or 930°C, attenuation increases to 

approximately 15 dB per 100 mm of sound path. This effect can require use 

of significantly increased instrument gain when testing over long sound paths 

at high temperature, and can also require adjustment to distance/amplitude 

correction (DAC) curves or TVG (Time Varied Gain) programs that were 

established at room temperature. 

Temperature/attenuation effects in polymers are highly material dependent, 

but will be typically be several times greater than the above numbers for steel. 

In particular, long high temperature delay lines that have heated up may 

represent a significant source of total attenuation in a test.

Keyword: 

• In typical fine grain carbon steel alloys, attenuation at 5 MHz at room 

temperature is approximately 2 dB per 100 mm one-way sound path 

(equivalent to a round trip path of 50 mm each way). 

• At 500°C or 930°C, attenuation increases to approximately 15 dB per 100 

mm of sound path.

3.4 Angular Variation in Wedges: 

With any high temperature wedge, sound velocity in the wedge material will 

decrease as it heats up, and thus the refracted angle in metals will increase 

as the wedge heats up. If this is of concern in a given test, refracted angle 

should be verified at actual operating temperature. As a practical matter, 

thermal variations during testing will often make precise determination of the 

actual refracted angle difficult. 

Keyword: 

As a practical matter, thermal variations during testing will often make precise 

determination of the actual refracted angle difficult.

Discussion: An offshore installation of Topside to Jacket Legs, hot 

conventional Ultrasonic Testing at elevated temperature below 500 C was 

proposed. What are the critical information to be reviewed? 

Hints: 

High temperature testing methods used & limitations 

Variability due to high temperature & concerns

6.9: Dimension-Measurement Applications

6.9.1 Dimension-Measurement Applications 

Ultrasonic inspection methods can be used for measurement of metal 

thickness. These same methods can also be used to monitor the deterioration 

of a surface and subsequent thinning of a part due to wear or corrosion and to 

determine the position of a solid object or liquid material in a closed metallic 

cavity.

6.9.2 Thickness measurements 

are made using pulse-echo techniques. Resonance techniques were also 

used in the past, but have become obsolete. The results can be read on an 

oscilloscope screen or on a meter, or they can be printed out. Also, the same 

data signals can be fed through gates to operate sorting or marking devices 

or to sound alarms. Resonance thickness testing was most often applied to 

process control inspection where opposite sides of the test pieces are smooth 

and parallel, such as in the inspection of hollow extrusions, drawn tubes, tube 

bends, flat sheet and plate, or electroplated parts. 

The maximum frequency that can be used for the test determines the 

minimum thickness that can be measured. The maximum thickness that can 

be measured depends on such test conditions as couplant characteristics, 

test frequency, and instrument design and on material type, metallurgical 

condition, and surface roughness.

Pulse-echo thickness gages with a digital readout are widely used for 

thickness measurement. Pulse-echo testing can measure such great 

thickness that it can determine the length of a steel reinforcing rod in a 

concrete structure, provided one end of the rod is accessible for contact by 

the search unit. Although pulse-echo testing is capable of measuring 

considerable thicknesses, near-field effects make the use of pulse-echo 

testing ineffective on very thin materials.

6.9.3 Position measurements 

Position measurements of solid parts or liquid materials in closed metallic 

cavities are usually made with pulse echo type equipment. One technique is 

to look for changes in back reflection intensity as the position of the search 

unit is changed. In one variation of this technique, the oil level in differential 

housings was checked to see if the automated equipment used to put the oil 

in the housing on an-assembly line had malfunctioned. The test developed for 

this application utilized a dual-gated pulse-echo system that employed a 1.6- 

MHz immersion-type search unit with a thin, oil filled rubber gland over its 

face. The search unit was automatically placed against the outside surface of 

the housing just below the proper oil level, as shown in Fig. 60(a).

With oil at the correct level, sufficient beam energy was transmitted across 

the boundary between the housing wall and the oil to attenuate the reflected 

beam so that multiple back reflections were all contained in the first gate (Fig. 

60b). The lack of oil at the correct level allowed the multiple back reflections 

to spill over into the second gate (Fig. 60c). Thus, the test was a fail-safe test 

that signaled "no test" (no signal in the first gate), "go" (signals in the first gate 

only), and "no go" (signals in both gates).

Fig. 60 Method of determining correct oil level in on automobile differential 

housing by use of an ultrasonic pulse-echo system. See text.

In another position measurement system, a set of two contact-type 4-MHz 

search units was utilized in a through transmission pitch-catch arrangement to 

determine the movement of a piston in a hydraulic oil accumulator as both 

precharge nitrogen-gas pressure and standby oil pressure varied (Fig. 61). 

The two search units were placed 180° apart on the outside surface of the 

accumulator wall at a position on the oil side of the piston, as shown in Fig. 

61. 

When a high energy pulse was sent from the transmitting unit, the beam was 

able to travel straight through the oil, and a strong signal was picked up by 

the receiving unit. However, as the search units were moved toward the 

piston (see locations drawn in phantom in Fig. 61), the sloping sides of the 

recess in the piston bottom deflected the beam so that very little signal was 

detected by the receiving unit.

Fig. 61 Setup for determining the position of a piston in a hydraulic oil 

accumulator by use of two contact search units utilizing a through 

transmission arrangement

Q144. A thin sheet may be inspected with the ultrasonic wavw direction 

normal to the surface by observing: 

A. The amplitude of the front surface reflection 

B. The multiple reflection pattern 

C. All front surface reflection 

D. None of the above

6.10: In-Service Inspection

In-Service Inspection 

The methods described above are applied in the course of and immediately 

after the production process and are therefore called production tests. To 

survey highly stressed parts, especially in power plants, repeated tests or inservice 

inspections are becoming more and more important. In these 

inspections any defects identified earlier but not being a cause for rejection 

can be observed for any changes caused by the service conditions. In 

addition service-produced defects must be detected, these being mainly 

cracks caused by thermal shock, fatigue or creep, or by corrosion attack.

In-Service Inspection- Testing for fatigue cracks on crankshafts and 

crankpins. a Without bore; b with bore

In-Service Inspection- Oblique or skewed fatigue cracks on crankpins

In-Service Inspection- (a) Crack test on press columns, pump rods, etc. 

(b) Crack test on thread in the shadow of a sound beam; schematic screen 

picture above

In-Service Inspection- (a) Probe for detecting fatigue cracks in turbine discs 

(design Krautkriimer-Branson) (b) Detection of cracks in riveted turbine 

blades

In-Service Inspection- (a) Testing methods for conical defects in a bolt 

(b) Testing for fatigue cracks in bolts

In-Service Inspection- (a) Cross-section through a leaf spring for railway 

cars with quenching crack showing testing with small angle probe or normal 

probe. The use of surface waves is unfavorable due to roughness 

(b)Testing a helical spring for quenching cracks, using surface waves

6.11: Casting

Casting 

In castings flaw detection is almost exclusively concerned with manufacturing 

defects and only rarely as in-service inspection. Suitable testing techniques 

and the subsequent evaluation of indications in castings is very different from 

the testing of forged and worked material so that the differences must not be 

forgotten or difficulties can occur. In-service inspection, as in the case of 

forgings, depends on the local stresses and the piece geometry so it is not 

necessary to treat it specially in this section.

Casting- Typical casting defects and their detection methods

Casting

Casting- Detection of shrinkage cavities with normal and angle probes

6.12: Bonded Joint

Inspection of Bonded Joints 

If the shape of a joint is favorable, ultrasonic inspection can be used to 

determine the soundness of joints bonded either adhesively or by any of the 

various metallurgical methods, including brazing and soldering. Both pulseecho 

and resonance techniques have been used to evaluate bond quality in 

brazed joints. 

A babbitted sleeve bearing is a typical part having a metallurgical bond that is 

ultrasonically inspected for flaws. The bond between babbitt and backing 

shell is inspected with a straight-beam pulse-echo technique, using a contacttype 

search unit applied to the outside of the steel shell. A small-diameter 

search unit is used to ensure adequate contact with the shell through the 

couplant. Before inspection, the outside of the steel shell and the inside of the 

cast babbitt liner are machined to a maximum surface roughness of 3.20 μm 

(125 μ in.) (but the liner is not machined to final thickness).

During inspection, the oscilloscope screen normally shows three indications: 

the initial pulse, a small echo from the bond line (due to differences in 

acoustical impedance of steel and babbitt), and the back reflection from the 

inside surface of the liner. Regions where the bond line indication is minimum 

are assumed to have an acceptable bond. Where the bond line signal 

increases, the bond is questionable. Where there is no back reflection at all 

from the inside surface of the liner (babbitt), there is no bond. 

Inspection of other types of bonded joints is often done in a manner similar to 

that described above for babbitted bearings. An extensive discussion of the 

ultrasonic inspection of various types of adhesive-bonded joints (including 

two-component lap joints, three component sandwich structures, and 

multiple-component laminated structures) is available in the article "Adhesive- 

Bonded Joints" in this Volume.

6.13: Corrosion Monitoring

Corrosion Monitoring 

Ultrasonic inspection can be used for the in situ monitoring of corrosion by 

measuring the thickness of vessel walls with ultrasonic thickness gages. The 

advantage of this method is that internal corrosion of a vessel can be 

monitored without penetration. 

There are, however, some disadvantages. Serious problems may exist in 

equipment that has a metallurgically bonded internal lining, because it is not 

obvious from which surface the returning signal will originate. A poor surface 

finish, paint, or a vessel at high or low temperature may also complicate the 

use of contact piezoelectric transducers (although this difficulty might be 

addressed by noncontact in situ inspection with an EMA transducer).

Despite these drawbacks, ultrasonic thickness measurements are widely 

used to determine corrosion rates. To obtain a corrosion rate, a series of 

thickness measurements is made over an interval of time, and the metal loss 

per unit time is determined from the measurement samples. Hand-held 

ultrasonic thickness gages are suitable for these measurements and are 

relatively easy to use. 

However, depending on the type of transducer used, the ultrasonic thickness 

method can overestimate metal thicknesses when the remaining thickness is 

under approximately 1.3 mm (0.05 in.). Another corrosion inspection method 

consists of monitoring back-surface roughness with ultrasonic techniques. 

The following example describes an application of this method in the 

monitoring of nuclear waste containers.

6.14: Crack Monitoring

Crack Monitoring 

Laboratory and in-service monitoring of the initiation and propagation of 

cracks that are relatively slow growing (such as fatigue cracks, stress-rupture 

cracks, and stress-corrosion cracks) has been accomplished with ultrasonic 

techniques. An example of the ultrasonic detection of stress-rupture cracks 

resulting from creep in reformer-furnace headers is given in the article 

"Boilers and Pressure Vessels" in this Volume. A relatively new and improved 

approach for monitoring the growth of cracks is done with ultrasonic imaging 

techniques.

Monitoring of fatigue cracks in parts during laboratory tests and while in 

service in the field has been extensively done using ultrasonic techniques. 

Reference 13 describes the use of surface waves to detect the initiation of 

cracks in cylindrical compression-fatigue test pieces having a circumferential 

notch. The surface waves, which were produced by four angle-beam search 

units on the circumference of each test piece, were able to follow the contour 

of the notch and detect the cracks at the notch root. 

Monitoring the crack-growth rate was accomplished by periodically removing 

the cracked test piece from the stressing rig and measuring the crack size by 

straight-beam, pulse-echo immersion inspection. It was found necessary to 

break open some of the cracked test pieces (using impact at low temperature) 

and visually measure the crack to establish an accurate calibration curve of 

indication height versus crack size.

The use of pulse-echo techniques for monitoring fatigue cracks in pressure 

vessels in laboratory tests is described in Ref 14. These techniques use 

several overlapping angle-beam (shear wave) search units, which are glued 

in place to ensure reproducible results as fatigue testing proceeded. The inservice 

monitoring of fatigue cracking of machine components is often 

accomplished without removing the component from its assembly.

For example, 150 mm (6 in.) diam, 8100 mm (320 in.) long shafts used in 

pressure rolls in papermaking machinery developed fatigue cracks in their 

500 mm (20 in.) long threaded end sections after long and severe service. 

These cracks were detected and measured at 3-month intervals, using a 

contact-type straight-beam search unit placed on the end of each shaft, 

without removing the shaft from the machine. 

When the cracks were found to cover over 25% of the cross section of a shaft, 

the shaft was removed and replaced. In another case, fatigue cracking in a 

weld joining components of the shell of a ball mill 4.3 m (14 ft) in diameter by 

9.1 m (30 ft) long was monitored using contact type angle-beam search units. 

The testing was done at 3-month intervals until a crack was detected; then it 

was monitored more frequently. When a crack reached a length of 150 mm (6 

in.), milling was halted and the crack repaired.

6.15: Stress Measurements

Stress Measurements 

With ultrasonic techniques, the velocity of ultrasonic waves in materials can 

be measured and related to stress (Ref 16). These techniques rely on the 

small velocity changes caused by the presence of stress, which is known as 

an acousto-elastic effect. The technique is difficult to apply because of the 

very small changes in velocity with changes in stress and because of the 

difficulty in distinguishing stress effects from material variations (such as 

texture; see Ref 17). However, with the increased ability to time the arrival of 

ultrasonic pulses accurately (±1 ns), the technique has become feasible for a 

few practical applications, such as the measurement of axial loads in steel 

bolts and the measurement of residual stress (Ref 5). 

.

The real limitation of this technique is that in many materials the ultrasonic 

pulse becomes distorted, which can reduce the accuracy of the measurement. 

One way to avoid this problem is to measure the phase difference between 

two-tone bursts by changing the frequency to keep the phase difference 

constant (Ref 5). Small specimens are used in a water bath, and the pulses 

received from the front and back surfaces overlap. The presence of stress 

also rotates the plane of polarization of polarized shear waves, and there is 

some correlation between the angle of rotation and the magnitude of the 

stress. Measurement of this rotation can be used to measure the internal 

stress averaged over the volume of material traversed by the ultrasonic beam.

6.16: Bond Testing

The real limitation of






6.App-1: TOFD Introduction 

NOTE: Not in the exam syllabus or BOK

6.App-1.1 TOFD Basic Theory 

TOFD is usually performed using longitudinal waves as the primary detection 

method. Ultrasonic sensors are placed on each side of the weld. One sensor 

sends the ultrasonic beam into the material and the other sensor receives 

reflected and diffracted ultrasound from anomalies and geometric reflectors.

TOFD provides a wide area of coverage with a single beam by exploiting 

ultrasonic beam spread theory inside the wedge and the inspected material. 

When the beam comes in contact with the tip of a flaw, or crack, diffracted 

energy is cast in all directions. Measuring the time of flight of the diffracted 

beams enables accurate and reliable flaw detection and sizing, even if the 

crack is off-oriented to the initial beam direction. 

During typical TOFD inspections, A-scans are collected and used to create B- 

scan (side view) images of the weld. Analysis is done on the acquisition unit 

or in post-analysis software, positioning cursors to measure the length and 

through-wall height of flaws. 

Keywords: 

■ 

■ 

■ 

■ 

■ 

Tip Diffraction 

Off-oriented to the initial beam direction 

Time of Flight 

A-scan / B-scan 

Post analysis software

6.App-1.2 

Main Benefits of TOFD for Weld Inspection 

• Based on diffraction, so relatively indifferent to weld bevel angles and flaw 

orientation 

• Uses time of arrival of signals received from crack tips for accurate defect 

positioning and sizing 

• Precise sizing capability makes it an ideal flaw monitoring method 

• Quick to set up and perform an inspection, as a single beam offers a large 

area of coverage 

• Rapid scanning with imaging and full data recording 

• Can also be used for corrosion inspections 

• Required equipment is more economical than phased array, due to 

conventional nature (single pulser and receiver) and use of conventional 

probes 

• Highly sensitive to all weld flaw types

TOFD offers rapid weld inspection with excellent flaw detection and sizing 

capacities. The diffraction technique provides critical sizing capability with 

relative indifference to bevel angle or flaw orientation. TOFD can be utilized 

on its own or in conjunction with other NDT techniques.

6.App-1.3 

6.App-1.3.1 The Theory 

More Reading on Time of Flight Diffraction (TOFD) 

Time of flight diffraction (TOFD) detects flaws using the signals diffracted from 

the flaw’s extremities. Two angled compression wave probes are used in 

transmit-receive mode, one each side of the weld. The beam divergence is 

such that the majority of the thickness is inspected, although, for thicker 

components, more than one probe separation may be required. When the 

sound strikes the tip of a crack, this acts as a secondary emitter which 

scatters sound out in all directions, some in the direction of the receiving 

probe. A ‘lateral wave’ travelling at the same velocity as the compression 

waves, travels directly from the transmitter to the receiver. The time difference 

between the lateral wave and the diffracted signal from the flaw 

provides a measure of its distance from the scanned surface. 

If the flaw is large enough in the through wall dimension, it may 

be possible to resolve the tip diffracted signals from its top and 

bottom, thereby allowing the through wall height of the flaw to be 

measured. 

http://www.iteglobal.com/services/advanced-ndt/time-of-flight-diffraction-tofd/

Due to the low amplitude of the diffracted signals, TOFD is usually carried out 

using a preamplifier and hardware designed to improve signal-to-noise 

performance. As the probes are scanned along the weld, the RF A-Scan 

signals are digitised and displayed in the form of a grey-scale image showing 

flaws as alternating white and black fringes. 

Depending on which direction the probes are moved over the component 

surface, it is possible to construct ‘end-view’; (B-scan TOFD) or ‘side-view’ 

(D-scan TOFD) cross-sectional slices. TOFD can also utilise Synthetic 

Aperture focusing or beam modelling software to minimise the effects of 

beam divergence, thereby providing more accurate location and sizing 

information.

TOFD is generally recognised as the most accurate ultrasonic technique for 

measuring the through-wall height of planar flaws that lie perpendicular to the 

surface and as a method for detecting and quantifying crevice corrosion at the 

weld root. At present, national standards for the application of TOFD exist, 

however, no acceptance criteria have been agreed upon. 

The TOFD technique is suited for the detection and sizing of all types of 

embedded flaws, especially those planar in nature. However, the detection of 

small near the scan surface flaws can be more difficult due to the presence of 

the lateral wave response which often occupies several millimeters of the 

depth axis on images.

Tips Diffractions

TOFD 

Transmitter 

Receiver 

Crack 

Back-wall echo 

Diffracted wave from upper end of crack 

Diffracted wave from lower end of crack 

Crack height can be calculate by measuring propagation 

delayed time of diffraction wave 

Diffracted 

wave from 

upper end of 

crack 

Lateral wave 

Diffracted wave from lower end of crack

TOFD

6.App-1.2 Application Examples 

■ 

TOFD for Weld Root Corrosion and Erosion 

For piping and other flow systems, certain conditions exist that lead to 

corrosion and erosion in the weld root and the heat-affected zone (HAZ) of 

the weld. The contributing factors are often metallurgical, chemical, or flow 

related, and the resulting metal loss can lead to failure of the weld/base metal. 

The shape of the corroded or eroded weld or base metal can make ultrasonic 

inspection extremely difficult to apply, thus impeding accurate detection and 

measurement of anomalies. 

The time-of-flight diffraction (TOFD) technique proves to be a valid option for 

evaluating weld root corrosion and erosion, as well as similar conditions such 

as FAC (flow-accelerated corrosion). The goal of any of these inspections is 

to accurately measure the wall thickness, the weld, and the HAZ. The 

unpredictable shape of the remaining material often makes pulse-echo 

ultrasonic inspection ineffective. 

http://www.olympus-ims.com/en/applications/tofd-for-weld-root-corrosion-and-erosion/

TOFD has been used for some time for general weld inspections. It has 

proven to be a rapid and easily deployable method with an excellent capacity 

for sizing. One of the inherent strengths of TOFD for detection and sizing 

purposes is its relative indifference to the orientation of defects because of its 

primary use of diffracted versus reflected energy. 

The TOFD technique utilizes two transducers: a transmitter transducer floods 

the inspected region with sound in the forward direction; on the opposite side 

of the weld, a receiver transducer is positioned to receive diffracted and 

reflected energy from the back wall or from anomalies present in the region. 

Common pulse-echo techniques can be misdirected by the shape of the 

region, resulting in imprecise measurement and assessment.

Figure 5-3 – Preferential weld corrosion in lean amine (Reference 5)

Figure 5-2 – Hot Lean Amine Corrosion of Carbon Steel:

Weld Root Corrosion and Erosion 

Pulse-echo shear wave beam being reflected at an off angle. 

Illustration of diffracted energy reflecting off weld root/HAZ in all directions.

For these types of weld inspections, TOFD is typically performed from three 

positions for each weld: (1) centered on the weld, (2) offset to the left, and (3) 

offset to the right. 

Scanning from these particular positions helps to achieve the best results. 

This method ensures detection of the highest point of material loss, 

determines from which side of the weld the erosion/corrosion indications are 

originating, and eliminates any masking caused by the back wall signal. 

Depending on the instrument, these scans can be run concurrently or in 

separate acquisitions.

TOFD is deployed by scanning the weld with a semiautomatic or fully 

automatic scanner. Scan settings are set to determine scan resolution. The 

resulting data file can be saved indefinitely for review and comparison to 

future scans. After data is acquired, it is analyzed to identify any areas of 

concern, either directly on the instrument or in post-analysis software. Shifts 

in data (time/depth) are measured in order to assess the severity of metal 

loss. The cursors can then be positioned to define areas for depth or 

thickness measurement readings. Weld defects such as porosity, lack of 

fusion, and cracking can also be detected when scanning for corrosion and 

erosion.

Scan of weld with cursor positioned on an uncorroded area; A-scan shows 

good lateral wave and back wall signal with no indications in between.

Scan of weld with cursor positioned on a corroded area; A-scan shows shift in 

time of back wall signal from material loss.

Measurement of good area shows thickness as 7.39 mm; TOFD (m-r) reading 

shows the distance between the positioned cursors.

Measurement of corroded area shows thickness as 5.28 mm; cursors are 

positioned at top of plate (0) and highest point of material loss. In this 

example, there is 2.11 mm of material loss due to corrosion.

6.11.3.3TOFD for Corrosion Measurement Equipment (Typical) 

• OmniScan SX or MX2 (PA or UT models, depending on the number of 

channels desired and if phased array capability is needed). 

• TOFD circumferential scanner (HST-Lite or similar, depending on the 

desired number of probe holders and other application specifics; for 

example, pipe versus plate). 

• TOFD probe and wedges (various frequencies, angles, and materials). 

• Couplant delivery system, WTR-SPRAYER-8L or similar. 

• TomoView Analysis or OmniPC post-analysis software (optional).

6.App-1.3.4 

TOFD Benefits for Corrosion/Erosion Measurement 

• Rapid scanning. 

• Cost effective. 

• Auditable and retrievable permanent data sets. 

• Accurate sizing capability. 

• Excellent detection, even on irregularly shaped areas of metal loss. 

• Fast post-acquisition analysis results. 

• Portable and user-friendly TOFD scanning packages.

TOFD for Weld- TOFD Parallel Scanning

6.App-1.3.5 

Overview on Scanning Direction 

Most typical TOFD inspections are performed with the send and receive 

transducers on opposite sides of the weld and scanning movement parallel to 

the weld axis. The main purpose of this “perpendicular” (defined by beam to 

weld relationship) scanning is to quickly perform weld inspection with the weld 

cap or re-enforcement in place. This technique can give location in the scan 

axis, the indication length, height of indication and flaw characterization 

information. One of the weaknesses of this technique is the lack of index 

positioning (or where between the probes) the indication is located. This 

information is usually obtained with complimentary pulse echo ultrasonics 

when the weld is left in place.

■ 

Perpendicular Scanning 

Scanning direction “parallel” to the weld axis. Beam direction “perpendicular” 

to the weld axis. 

? Carriage movement 

direction 

One of the weaknesses of this technique is the lack of index positioning (or 

where between the probes) the indication is located.

■ 

Parallel TOFD scanning: 

Where the scan direction and beam direction are the same is less used, for 

obvious reasons of not being able to cover the entire length of weld rapidly, 

more complex movement pattern required of scanner mechanisms, and 

complexity of the data output of an entire weld inspected. This technique does 

have advantages when it is possible to be performed.

Typical “Perpendicular” Weld Scanning Setup and Data Collected. Data is 

side view of weld from scan start to scan finish down the weld. Position of 

encoder and scanning direction are highlighted.

Typical “Parallel” Weld Scanning Setup and Data Collected. Data is side view 

of weld from scan start to scan finish across the weld. Position of encoder and 

scanning direction are highlighted.

■ 

Benefit of TOFD Parallel Scanning 

Although perpendicular TOFD scanning down the weld can give highly 

accurate depth measurement, generally speaking a parallel scan will give 

more accurate depth information as well as flaw information, and location in 

the index position in the weld. With perpendicular scanning, no index position 

is possible without multiple offset scans being performed or complimentary 

NDT techniques to position the flaw. In parallel scanning Index position is 

ascertained by locating the minimum time peak, which corresponds to when 

the indication is centered between the two probes. For these reasons this 

technique is often used in critical crack sizing inspections, as well as change 

monitoring, in other words, monitoring a crack or other defect for growth until 

it reaches a critical level at which time it is repaired or replaced. For these 

reasons the technique is often performed on critical components that are 

costly to shut down for repair, often in the Power Generation industry. More 

information is often gathered from the flaw as diffraction occurs across the 

flaw instead of just down the flaw.

6.App-1.3.6 Further Reading- Introduction to Phased Array 

• http://www.olympus-ims.com/en/ndt-tutorials/intro/ut/

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Section 6: Selected Applications & Techniques

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