Study on the Chlorine Resistance of HDPE Pipe to Chlorinated Seawater

High-density polyethylene (HDPE) pipes are widely used for seawater transportation. However, residual chlorine introduced for disinfection purposes can induce oxidative degradation and accelerate material failure. Existing investigations predominantly focus on HDPE aging in chlorinated freshwater, while the degradation mechanism of HDPE subjected to chlorinated seawater remains poorly documented. In this paper, chlorine-resistance tests for HDPE pipes were performed following the ASTM F2263 standard at 90 °C using real seawater with 0.2 ppm free residual chlorine. Micro-morphology, elemental distribution, and tensile properties were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and uniaxial tensile tests. The chlorine-resistance test results revealed that HDPE pipes eventually failed in a brittle-fracture mode after long-term exposure to chlorinated seawater. Numerous axial surface-initiated microcracks formed on the pipe inner wall, while EDS line scan demonstrated that chloride ions hardly diffused into the bulk polymer matrix. Reducing hoop stress by 18% only extended failure lifetime by approximately 6%, indicating a weak linear correlation between hoop stress and failure time under the present chemo-mechanical coupling condition. This study provides experimental references for the safety evaluation of HDPE pipes serving in chlorinated seawater environments.