Effect of internal pressure on the flexural fatigue behaviour of trenchless internal replacement pipe systems

• Developing FE models to investigate fatigue behaviour of pressurised IRP systems. • Evaluation of the effect of design parameters on fatigue behaviour of IRP systems. • Development of analytical expressions to predict the fatigue life of IRP systems. • Generation of fatigue life contour plots under internal pressure and traffic loads. Internal replacement pipe (IRP) systems are a novel trenchless technique that is gaining interest in the rehabilitation of damaged legacy pipelines distributing natural gas. Performance evaluation of IRP systems under repetitive loads transmitted from vehicular traffic is essential to ensure their optimal and safe design. This study conducted numerical simulations to examine the impact of internal pressure on the bending fatigue behaviour of IRP systems that are fully bonded to legacy gas pipes with circumferential discontinuities. Other design parameters include the thickness and modulus of elasticity of IRP and the level of transmitted traffic load. The findings indicate that the operating internal pressure has a greater impact on the longitudinal stresses than the circumferential stresses of IRP when subjected to cyclic bending. The level of internal pressure changes the failure behaviour of IRP under fatigue. Based on the results obtained from extensive parametric simulations, mathematical expressions were formulated to predict the fatigue life of the IRP systems. Contour plots were generated to represent fatigue life response for different combinations of internal pressure levels and transmitted traffic loads.