Wear and Tear: Fatigue Life in PVC Force Mains

Polyvinyl Chloride (PVC) pipe was commercially introduced into the United States public market in the early 1960’s and was quickly adopted by sewer utilities because of its resistance to corrosion. The initial design basis for PVC pipes was based on the results of long term, steady state pressure regression tests (ASTM D 1598) and did not consider the effects of cyclic fatigue pressure; however, it was found that PVC pipe, where frequent opening and closing of valves created transient conditions, was failing prematurely. Researchers discovered that PVC pipe had two distinct lives, one based on steady state conditions and the other based on cyclic conditions. The 2007 version of AWWA C900 incorporates the latest accepted method for designing a PVC pipe system subjected to cyclic pressure loading.This paper outlines the theory, methodology, and results of a fatigue analysis performed on PVC force mains. Prior to the analysis, transient pressure monitoring was performed on the system to understand the operational and surge pressures within the force main and their impact on the structural integrity of the pipes.