# Tightness of flange joints for polyethylene pipes

Polyethylene pipelines are commonly used for underground water supply systems. Leaks could occur in flange joints in these pipelines. Analysis of such joints requires detailed material model to take into account time-dependent behaviors of pipe and gasket.

In this work a flange joint is simulated by using an axisymmetric model for quick results. A G-ST profile gasket with steel core is considered to seal the joint. An internal pressure of 10 bar is assumed. The goal of the analysis is to investigate the tightness of the flange joint over 100 years by taking into account the creep of pipe and gasket. This is a challenging problem as it involves multiple nonlinearities: material, geometric and contact between multiple components.

The analysis of flange joint is performed in three steps. In the first step, bolts are tightened and in the second step, a fluid pressure is applied. In the third step,  fluid pressure is held constant for 100 years and viscoelastic effects are analyzed.

Note: This exercise is part of the Solving Non-linear Problems with Abaqus course.

The contour plot of von Mises stresses in assembly. In first figure stress distribution is shown after the bolt tightening and fluid pressure application. In the second figure stress distribution is shown after the creep over 100 years. A linear viscoelastic model has been used to model creep and relaxation in polyethylene. The strain hardening power law creep model has been used to model the nonlinear viscoelastic behavior of EPDM (seal material).

The contour plot of von Mises stresses in pipes. In first figure stress distribution is shown after the bolt tightening and fluid pressure application. In the second figure stress distribution is shown after the creep over 100 years. Vertical forces due to bolt tightening and creep expansion of the pipe cause to bend the joint.

Contact pressure distribution on the surface of gasket before bolt tightening. This is a G-ST profile gasket which has an O-ring profile on the inner diameter.

Contact pressure distribution on the surface of gasket after bolt tightening and fluid pressure application.

Contact pressure distribution on the surface of gasket after creep over 100 years. Considerable difference in distribution of contact pressure can be noticed as compared to the distribution after bolt tightening.

The following animation shows the evolution of axial stresses in pipe and contact pressure distribution on gasket surface.