Porosity Formation Mechanisms and Their Effects on the Mechanical Properties of High-Density Polyethylene Extrusion Welds

High-density polyethylene (HDPE) has attracted attention as an alternative material for marine structures because of its chemical resistance, processability, and recyclability. However, internal pores formed during extrusion welding can reduce weld quality and mechanical performance. This study investigated pore formation mechanisms in HDPE extrusion welds by considering material throughput, filler wire storage condition, and artificial defect volume fraction. Porosity increased from 0.06% to 0.37% as material throughput increased from 0.96 to 2.00 kg/h and slightly decreased to 0.33% at 2.60 kg/h. Under these process conditions, tensile strength changed within approximately 1.49%, whereas elongation decreased more clearly with increasing porosity. In contrast, residual surface moisture on the filler wire caused severe pore formation and reduced tensile strength by approximately 55.53%. Artificial defect tests also confirmed that increasing internal defect volume directly reduced tensile strength. Overall, controlling material throughput and removing surface moisture are essential for improving HDPE extrusion weld quality.