Failure Analysis of Underground HDPE Pipe for Domestic Water

Within a span of five years between 2016 and 2021 a total of eleven (11) failures were documented for high density polyethylene (HDPE) pipe installed underground to deliver domestic water. The pipes were reported to have a service life in excess of 50 years. The typical pipe failures experienced included splitting of the pipe and/or crushing of the pipe by the weight of the soil. The pipe material was High Performance PE4710 Polyethylene. The HDPE pipes failed as a result of slow crack growth initiated by oxidative degradation at the ID.

Three stages of pipe failure are reported for HDPE material; Stage I failures are ductile and a result of high stresses over short time durations; Stage II failures are non-ductile and manifest as slit type cracks or pin hole cracks; Stage III failures are non-ductile but require a minimum level of oxidative degradation to take place. Oxidation induction time (OIT) measurements demonstrated a clear loss of antioxidants at the ID surface of the pipes. Crack deposits were chemically analyzed by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and exhibited Cl constituents; the Cl compounds assisted the oxidative degradation of the pipes facilitating crack initiation at the ID.