The correlation field of the “ultrasonic signal amplitude–lack-of-fusion depth” regression representsa graphic model of estimating the reliability of testing. However, in this case the necessary condition is the requirement that the welded seams must be welded complying with the standard technology. The boundaries corresponding to a standard-permissible flaw hs and an adopted rejection level Arej of the ultrasonic signal amplitude divide the correlation field into four regions corresponding by implication to four squares of the reliability matrix: ns, nu, nα, and nβ.