Category: In-Service Inspection

Inspection of Spheres

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In general, the practices that apply to pressure vessels also apply to spheres although the techniques may vary. The tall legs necessary to support spheres should be carefully inspected to determine the condition of the fireproofing and the rain seals. Remove cracked or spalled fireproofing and inspect the exposed steel. Earthquake or sway bracing must […]

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Shear Wave UT – Applications and Limitations

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UT is a very efficient NDE method. A large amount of data for evaluating the integrity and reliability of a vessel can be obtained in a relatively short period of time, without requiring extensive preparation of the vessel or interfering with other work in the area. Longitudinal wave UT is applicable for determining the remaining […]

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Shear Wave UT – UT Imaging

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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 vessel’s surface with a scanning fixture. The X-Y coordinates of the transducer locations on the […]

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Shear Wave UT – Time Based Sizing

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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 the integrity and reliability of a vessel. Several variations of time based sizing have been […]

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Shear Wave UT – Amplitude Based Sizing

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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 display at a distance corresponding to the thickness of the shell confirms that the crack […]

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Shear Wave UT – Crack Sizing

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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 the technique used and the skill of the technician. UT crack sizing techniques are classified […]

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Shear Wave UT – Calibration

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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. The test block should have a thickness within 1 inch of the thickness of the […]

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