Evaluation of Electrofusion Jointing of Polyethylene Pipes Using Phased Array Ultrasonic Testing and Microstructural Characterization

ABSTRACT The integrity of polyethylene (PE) pipe joints is critical for ensuring the long‐term reliability of pipeline systems. This study develops a method of using phased array ultrasonic testing (PAUT) technique to identify welding defects in the joints of PE pipes. PAUT allows signal focusing and steering at desired angles and can overcome the limitations of the conventional ultrasonic method. The research investigates how varying fusion times at a constant welding voltage of 39.5 V affect weld quality and mechanical performance of PE pipe joints. Key findings indicate that the heat‐treated joints, placed in a drying oven, revealed clear melt fusion zone (MFZ) boundaries, with the distance from the melt zone to the heating wire closely matching the Eigen‐line positions observed in the PAUT results. Cold‐welded joints (100 s) exhibited narrow fusion zones (1.4 mm), while over‐welded joints (300 s) showed excessively wide zones (5.2 mm). Outside the heat‐affected MFZ could be considered another type of welding defect where crystallinity was significantly affected by welding time, decreasing from 67.53% to 57.26% in standard welding, from 61.4% to 55.59% in cold welding, and from 59.35% to 48.52% in over welding. In over‐welded joints, excessive heating led to stress concentration, thermal oxidative degradation, chain scission, and the formation of blow hole defects that most severely impaired mechanical properties. Peel tests confirmed the mechanical integrity of standard‐welded joints, with a maximum peeling force of 2828.52 N, compared to 1806.47 N in cold welding and 1360.76 N in over welding. SEM analysis revealed a uniform size and distribution of crazes in standard‐welded joints, whereas defective joints exhibited irregular and sparsely distributed craze structures.