Studying Applicability of TOFD Technique to Inspection of Welded Joints in Polyethylene Pipes

Abstract

Issues of quality control of welded joints in hot-tool butt-welded polyethylene pipelines are considered. It is indicated that the main scope of control currently falls on inspections based on the parameters of welding and on selective mechanical testing of welded joints. Physical nondestructive post-welding testing methods are used little, which is generally not typical for the practice of testing welded joints. The reason for this is the general problem of ultrasonic methods, viz., the low detectability of contracted defects, partially transmitting ultrasound. To ensure the detectability of such defects, we evaluate the possibility of increasing the sensitivity of ultrasonic testing by using the ultrasonic time-of-flight-diffraction (TOFD) technique. It is proposed to use the tip of vertical drillings to simulate defects weakly scattering ultrasound. It is shown that when tuning is performed based on such targets, the inspection sensitivity can be increased by at least 6 dB, i.e., two times or more. In this case, the drilling tip can simulate the upper and lower edges of a planar defect vertically oriented in the section of the weld. The results of experimental studies aimed at revealing multidirectional drills with a diameter of 1 mm in welded seams of polyethylene pipes, including pipes with an additional removable outer layer, are presented. The expediency of gathering statistical data on the identification of real defects in welded butt joints of polyethylene pipes using the considered testing method is shown.