Popelar shifting, rate-process method, and brown projections of service life of polyethylene (pe) gas pipe [PE]

Various methods have been proposed and used to estimate the service life of Polyethylene (PE) piping in natural gas distribution. These include the Rate Process Method (RPM), various bi-directional shift functions, including the Popelar Shift Functions (PSF), and the shift functions of Brown and Lu. More recently, Brown has proposed a method for projecting life of a pipe based solely on service conditions and the PE material Slow Crack Growth (SCG) resistance as measured by a standard test, ASTM F1473, the ““PENT”” test. This paper compares the projections made by these methods for early-generation, low-PENT gas distribution pipes. The projections are compared for historical, previously-documented data as well as for new data obtained on samples exhumed after 37 years in service. Of the methods compared, the Popelar Shift Functions appear to provide the most credible projections from the relatively small data sets typically obtainable for in-service pipe populations.