Error in determining the position of a nominal defect section in the ultrasonic testing of welded joints

Very rigorous technical requirements are usually applied to the quality of welded joints in important metal structures in order to ensure the necessary in-service reliability in the final structure [1]. In the ultrasonic testing of welded joints, measurements are as a rule made not only of the maximum amplitude of the echo signal from a defect but also of the nominal length of the defective section. The accuracy of the determination of the position of nominal defective sections (NDSs) in a weld is of importance in: 1) the periodic testing in use of objects with unremoved defective sections; 2) qualification of specialists at the 2nd or 3rd level [2]; 3) comparison of the results of testing carried out by different operators; 4) inspection control (control of an already tested product) [3].