STUDY OF TOFD TECHNOLOGY APPLICABILITY FOR POLYETHYLENE PIPE WELD INSPECTION
The issues of non destructive testing of polyethylene pipelines welds made by butt welding with a heated tool are considered. It is indicated that the main scope of the testing currently falls on the parameters monitoring during the welding process and selective mechanical testing of welded joints. Physical non destructive testing methods after the completion of welding are used seldom, which is generally non typical for the welded joints testing practice. The reason for this is the general problem of ultrasonic testing methods, that consists in the low detectability of contracted flat defects that partially transmit ultrasound. To provide the detectability of such defect type, the possibility of increasing ultrasonic testing sensitivity by using time of flight diffraction (TOFD) is considered. To simulate defects that weakly scatter ultrasound, it is proposed to use the tip of vertical drills. It is shown that when making calibration for such targets, the inspection sensitivity can be increased by at least 6 dB, i.e. 2 times or more. In this case, the drill 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 on detecting multidirectional drills with a diameter of 1 mm in polyethylene pipe welds, including pipes with an additional removable outer layer, are presented. The utility of statistical data set on the identification of real defects in polyethylene pipes welded butt joints using the considered inspection method is shown.