Accelerated thermal-oxidative aging and degradation mechanism of high-density polyethylene butt-fusion welded joint

High-density polyethylene (HDPE) pipelines are widely used for the transportation of natural gas. The butt-fusion welded joints melt and cool during the welding process, resulting in changes in mechanical properties, molecular chain spatial position microstructure, and functional groups. Herein, we investigate the aging behavior of an HDPE butt-fusion welded joint in accelerated thermal-oxidative aging tests under various temperature gradients. The Vicat softening temperature, oxidation induction time, and infrared spectrum were measured, and the microstructures were observed. The results indicated that the mechanical and chemical properties of the butt-fusion welded joint degraded with incresing aging temperature. Analysis was conducted to identify the molecular chain intersection mechanism in the heat-affected zone and the weld joining mechanism. The findings help understand the aging behavior of HDPE and provide guidelines to reduce the risk caused by butt-fusion welded joint degradation.