Final answer:
The correct answer is A) the A-scan display is normally set as an RF display so differences in phase can be seen, which is essential for detecting and sizing defects in the material during weld inspections with TOFD. Option A is correct.
Step-by-step explanation:
When performing weld inspections with Time of Flight Diffraction (TOFD), the statement A) the A-scan display is normally set as an RF display so differences in phase can be seen is the correct answer. TOFD is an advanced nondestructive testing method used to detect flaws in welds.
The RF (radio frequency) A-scan display is preferred because it allows inspectors to visualize changes in the phase and amplitude of the received signals, which are critical for identifying and sizing defects in the material. Discontinuities in the weld can cause phase changes indicative of a flaw's presence.
Option B is not generally preferred because the positive half-wave display might not show all necessary information about phase changes. Option C is incorrect, as the A-scan is not only used for calibration but is also a vital part of the inspection process. Finally, option D is wrong because both shear waves and longitudinal waves can be used in TOFD, depending on specific inspection requirements and the type of material being inspected.