Lifetime prediction for ABS pipes subjected to combined pressure and deflection loading

As part of an investigation into the performance of acrylonitrile-butadiene-styrene (ABS) systems for water transportation, this paper presents a method for predicting the service lifetimes of buried pipes under in-service loading conditions. A linear fracture mechanics approach was used to analyze brittle failure initiating from adventitious flaws located at the bore surface of pipe. Failure criteria were determined using the time-dependent, quasistatic, plane strain fracture toughness of the ABS material, combined with empirical parameters that describe slow, steady crack growth. The expected operating conditions of a buried pipe were then separated into static loading contributions from internal pressure, diametrical deflection and residual stress. Idealized stress intensity factors associated with mode-I crack opening under each of these components were determined using a finite element analysis and superposed to describe the general case in service. The computed nett stress intensity factor was then combined with the previously determined fracture toughness and slow crack growth data in an algorithm to simulate incremental radial crack growth from the pipe bore. Predicted failure times compared well with an experimental model of expected operating conditions, which combined hydrostatic pressure and parallel-plate deflection loading of an internally notched pipe. The prediction method was also used to identify the factors that control the lifetime of a pipe in service. The influence of material visco-elasticity was investigated by simulating variations in fracture toughness and slow crack growth resistance. It was proposed that, in practice, these variations are governed by opposing changes in visco-elasticity. The effect of changing diametrical deflection and residual stress distribution were also simulated, allowing recommendations on pipe manufacture and installation conditions to be made.