Reliability of the manual and automatic ultrasonic technique in the detection of pipe weld defects

Abstract

The objective of this work is to evaluate the reliability of the ultrasonic non-destructive testing (NDT) technique, for specific test conditions, using PoD (probability of detection) curves developed by experimental procedures. Two classes of defects, lack of penetration (LP) and lack of fusion (LF), were intentionally inserted in 24 girth weld beads of an API X70 steel pipeline with an outer diameter of 254 mm and wall thickness of 19.05 mm. These welds were inspected using manual and automatic ultrasonic techniques. The automatic ultrasonic inspection was carried out using pulse-echo and TOFD (Time-of-Flight Diffraction) techniques and manual tests were carried out by five qualified inspectors using pulse-echo technique. The bootstrap technique was used in order to obtain a confidence interval for the PoD curves. The results, besides producing real PoD curves, showed the superiority of the automatic techniques over the manual test in the probability of detection of these two classes of defects.