APPLICATION OF ULTRASONIC TESTING TO BUTT-WELDED POLYETHYLENE PIPE JOINTS

Abstract

The paper investigates the specific features and limitations of applying ultrasonic testing (UT) methods to the inspection of butt-welded joints of high-density polyethylene (HDPE) pipes, which are widely used in modern pipeline systems for water supply, gas distribution, and industrial applications. Special attention is paid to the structural and acoustic properties of HDPE that significantly affect ultrasonic wave propagation and complicate reliable defect detection.

Typical welding defects occurring in HDPE butt joints, including lack of fusion, voids, inclusions, and geometrically oriented discontinuities, are analyzed in detail. Current international and industry technical standards are reviewed with respect to the selection of ultrasonic transducer frequencies and inspection techniques, with a focus on phased array ultrasonic testing (PAUT). Based on experimental studies conducted on HDPE pipes with diameters ranging from 600 to 800 mm, a high level of ultrasonic attenuation inherent to polymer materials was confirmed. The results demonstrate that the use of longitudinal ultrasonic waves with a frequency of 2.25 MHz ensures an optimal balance between penetration depth and signal-to-noise ratio.

The study shows that the application of conventional ultrasonic methods, particularly the pulse-echo technique, has limited effectiveness in detecting lack of fusion and other planar or oriented defects in HDPE welds due to signal scattering and strong attenuation. In contrast, the advantages of the time-of-flight diffraction (TOFD) method are substantiated experimentally. TOFD provides enhanced sensitivity to defect tips, stable measurement results, and minimal dependence on defect orientation and surface geometry.

The obtained results confirm the high potential of TOFD as a reliable and cost-effective alternative to phased array ultrasonic techniques for the non-destructive testing of welded joints in HDPE pipes. The findings can be used to improve inspection procedures, optimize testing parameters, and enhance the overall reliability of polymer pipeline systems.