Analysis of failure modes in pipe-in-pipe repair systems for water and gas pipelines

•Performance Objectives (POs) and associated Failure Mechanisms (FMs) of pipe-in-pipe (PIP) systems were analysed.•Numerical models for detailed understanding of the FMs of PIP systems were developed.•The effect of material and geometric properties on the PIP systems were evaluated.•Design nomographs for PIP systems for different POs were developed.•Analytic hierarchy process (AHP) to rank the POs and associated FMs for PIP systems. Different failure modes should be carefully analyzed to effectively design the pipe-in-pipe (PIP) repair systems to rehabilitate natural gas and water pipelines in place and in service. This study characterizes the failure modes through analytical and numerical modelling of the different performance objectives to have a comprehensive understanding of the overall behavior of PIP systems with a range of thicknesses and elastic moduli. It focused on assessing the structural performance of PIP systems under different load actions including vibration/fatigue due to traffic loads, lateral deformation, cross-section ovalization, axial stresses and thermal deformation, internal pressure, and impact. The results of the analyses showed that the thickness and elastic modulus significantly affect the failure modes of PIP systems. The implemented Analytical Hierarchy Process (AHP) suggested that lateral deformation is the most critical failure mode followed by internal pressure based on global priority as well as both criteria (thickness and elastic modulus) when the design pressure is 200 psi with the cross-section ovalization the least critical failure mode of the PIP systems. The results of this study provide useful predictive modelling techniques and preliminary design tools for PIP systems for new material systems development and/or evaluation of the suitability of the available PIP systems for pipeline repair.