Tight cracks and lack-of-fusion discontinuities are also difficult to detect with
ultrasonics; however, the threshold limit for the ultrasonic technique is considerably smaller than for radiography. Not infrequently, cracks and similar discontinuities in areas of high comprehensive-residual weld stress are so tight that they are completely invisible to ultrasonics.
Часто трещины и аналогичные несплошности на участках высокого comprehensive - остаточного напряжения шва настолько малы, что не распознаются ультразвуковой техникой.

Здесь может быть опечатка - вместо comprehensive может быть compressive?