Distortions From a Simplified Approach to Fatigue Analysis in PVC Pipes

This work examines the extent to which simplifications suggested for fatigue analysis of polyvinyl chloride (PVC) pipes can cause distortion in system evaluation. To this end, fatigue analysis is performed on a hypothetical pipe system using two independent approaches: first, using a recommended method that calculates the fatigue parameters through thorough transient modeling and, second, through a highly simplified but widely used approach arising from direct application of the Joukowsky equation (through Plastics Pipe Institute's program Pipeline Analysis & Calculation Environment). The results show that the simplified approach significantly overestimates the transient loading and tends to devalue the expected fatigue resistance of PVC pipe. This devaluation arises from the fact that the Joukowsky approach, along with several other assumptions, is too conservative and simplified for fatigue analysis. This study concludes that for the PVC pipe systems exposed to significant pressure cycles, fatigue analysis is a required design check, but only a thorough and thoughtful consideration of transient loading can provide accurate and meaningful results.