Category Archives for In-Service Inspection

Shear Wave UT – UT Imaging

UT imaging can be used to obtain two- and three-dimensional pictures of cracks, or other types of flaws, in a pressure vessel component from an automated ultrasonic examination. An ultrasonic transducer (either longitudinal or shear wave) is moved over the … Continue reading

29. April 2018 by Jack
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Shear Wave UT – Time Based Sizing

Time based sizing generally provides greater accuracy for determining depth, especially when the crack is relatively small with respect to the diameter of the transducer. Therefore, time based sizing should be used whenever a fitness-for-service analysis is made to evaluate … Continue reading

29. April 2018 by Jack
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Shear Wave UT – Amplitude Based Sizing

Figure 700-20 illustrates how the depth of a crack is determined using amplitude based sizing techniques. The crack was detected by shear wave UT as shown in Figure 700-19. The occurrence of a relatively high amplitude peak in the oscilloscope … Continue reading

28. April 2018 by Jack
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Shear Wave UT – Crack Sizing

The ability to determine the depth of a crack through the thickness of a vessel shell is a very important attribute of shear wave UT. However, the accuracy of the depth measurements made with UT can vary considerably, depending on … Continue reading

28. April 2018 by Jack
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Shear Wave UT – Crack Detection

Shear wave UT is very useful for detecting cracks that have developed during service. Figure 700-19 illustrates how shear wave UT, calibrated according to Figure 700-18, can be used to detect a crack in the heat affected zone of a … Continue reading

28. April 2018 by Jack
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Shear Wave UT – Calibration

Shear wave UT is calibrated using a test block manufactured from a material similar to the workpiece (i.e., with the same velocity of sound), that has side-drilled holes and a notch on the back surface as shown in Figure 700-18. … Continue reading

28. April 2018 by Jack
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Shear Wave UT

Shear wave UT is used primarily to detect and determine the size of cracks that have developed during service. Forms of deterioration that can result in cracking include mechanical and thermal fatigue, creep, stress-corrosion, and hydrogen attack, among others (see … Continue reading

28. April 2018 by Jack
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Ultrasonic Examination – Hydrogen Blisters

The use of longitudinal wave UT for detecting, locating, and determining the size of hydrogen blisters is illustrated in Figure 700-17. The blisters are internal flaws that have a reflecting surface at a depth from the front surface that is … Continue reading

28. April 2018 by Jack
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Ultrasonic Examination – Remaining Thickness

Figure 700-16 illustrates the use of longitudinal UT for determining the remaining thickness of a corroded shell. If the transducer is placed on a location of the shell component that is not corroded, as depicted by the position of Transducer … Continue reading

28. April 2018 by Jack
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Ultrasonic Examination – Calibration

Calibration of longitudinal wave UT consists of developing a “distance amplitude curve (DAC)” for the instrument and transducer, using test blocks manufactured from a material similar to the workpiece (i.e., with the same velocity of sound). Calibration for determining the … Continue reading

28. April 2018 by Jack
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