Response of a polymer liner passing across a pressure pipeline joint opening under axial ground movements

Abstract

A closed form solution is developed to quantify the stresses that develop in polymer liners installed within pressure pipes, where the liner spans across a joint or ring fracture in the ‘host’ pipeline that is subjected to axial extension as a result of ground movements. The solution considers the zones of slip between liner and host pipe on either side of the joint that is opening. The expression derived indicates that maximum axial liner stress is proportional to the square root of the product of the gap that opens across the joint, liner modulus, internal fluid pressure, coefficient of friction between liner and host pipe, and inverse of liner thickness. Calculations are presented for a typical liner installed within a cast iron water pipe, though research is needed to quantify liner-host pipe friction. Comparisons to finite element calculations demonstrated that the new solution characterises the liner as having higher stiffness than numerical analysis using thick shell elements. Initially the two solutions match, but the new closed form solution becomes more conservative with increasing gap size. FEA was then used to show that temporary reductions in water pressure decrease axial liner stresses significantly.