Failure analysis of plastic pipes: case studies of PEX pipes

Failures of plastics used as structural components can be critical, potentially leading to partial or complete system shutdowns. Such failures often arise from system-level deficiencies, service conditions, or intrinsic material vulnerabilities. Therefore, the initial stage of failure analysis must encompass a comprehensive review of the entire system, including installation conditions, operational environment, and loading history, in addition to examination of the failed plastic component itself.

For polymeric materials in particular, geometric configuration and stress distribution are key to identifying probable failure modes and formulating plausible failure mechanisms prior to physico-chemical characterization. Because polymer degradation is often complex, this study discusses these general challenges in polymer failure analysis and introduces cross-linked polyethylene (PEX) pipe as a representative case. Widely adopted in potable water and hydronic systems, PEX has replaced copper and chlorinated poly(vinyl chloride) (CPVC) in many applications, yet remains susceptible to environment-assisted degradation mechanisms that may not be apparent through routine inspection.

This study examines two distinct field failures: one initiated at the external surface and another from the inner surface. By integrating system-level review (visual and microscopic examination) with targeted laboratory characterization including spectroscopy and thermal analysis, we demonstrate how early failure mode identification guides analytical selection process and subsequent interpretation of data. The findings highlight the synergy between macro-scale system assessment and micro-scale laboratory characterization in establishing mechanistic root causes for polymer degradation, providing a structured framework for failure analysis of plastic structural components.