Hire an ASNT qualified nondestructive testing (NDT) firm for this activity. They will have the procedure, calibration standard, and ASNT qualified UT examiners.
The big thing to watch out for with stainless steel is the use of calibration blcosk without welds (not specifically required by some specifications). Shear waves will work fine on the un-welded calibration block but will significantly under-test the weld. This can be readily seen if a welded block is used. All angle beam scans should be done with angle longitudinal waves.
Not all inspection houses have figured this out. Unfortunately, it is not obvious based on the screen display that the weld is being significantly under-tested.
