Cyclic fatigue in HDPE sewer mains: comparison of logged data against industry guidelines for asset life estimation

Current Australian industry guidelines (PIPA POP010A) for evaluating cyclic fatigue in high-density polyethylene (HDPE) pressure pipes rely on legacy studies of unplasticised PVC. This study investigates whether these fatigue design parameters are overly conservative for HDPE, which could be driving unnecessary infrastructure costs. Analysing high-resolution field data from pressure loggers on a buried HDPE sewer rising main in South East Queensland, the research assessed transient pressure waves generated by routine pump shutdowns. The observed data indicates that secondary pressure waves in buried HDPE decay approximately 2.5 times faster than the PVC benchmarks used in current standards. Consequently, the cumulative fatigue damage from secondary cycles is significantly lower than currently assumed, with total equivalent cycles measured between 1.23 and 1.28 per event, compared to the guideline assumption of 2. Furthermore, applying a material-appropriate Paris-Erdogan crack growth exponent further reduces the calculated fatigue. These findings demonstrate that HDPE sewer mains experience far less cumulative fatigue than modelled. Recognising this actual behaviour allows engineers to safely specify lower pressure class pipes or extend asset life beyond 100 years, offering significant capital cost savings and reduced carbon emissions.