Effects of the legacy pipe ends on the behaviour of pipe-in-pipe repair systems under internal pressure

•The effects of the sharp edge of the legacy pipe opening on the pipe-in-pipe (PIP) systems are investigated.•The effects of design parameters and material properties are evaluated.•High strain material systems and rounding the edge of the host pipe contribute to reducing stress concentration.•Both unbonded and rounded factors are found effective in terms of stress concentration relief. Pipe-in-pipe (PIP) has become an acceptable system for the rehabilitation and repair of natural gas distribution networks. Damaged host pipes usually contain defects such as circumferential cracks which can affect the performance of the PIP systems. Under internal pressure, the PIP system will be in contact with the damaged pipes and may have an adverse effect on its structural performance. This paper investigates the effect of the sharp edge of the legacy pipe opening on the PIP systems under the internal pressure. The effect of several design parameters including the bonding condition of the PIP to the host pipe, the material properties of the PIP system, and the level of sharpness of the host pipe ends are evaluated. The numerical results show that without bonding of the PIP to the host pipe, the stress concentration is minimised as the PIP can deform around the edge of the host pipe. The use of high strain PIP material systems and rounding the edge of the host pipe also contribute to reducing stress concentration. The irregular opening of the legacy pipe represents the practical situation in which both unbonded and rounded factors are found effective in terms of stress concentration relief. The outcomes of this work provide useful information on minimising stress concentrations on PIP systems, which can be effectively utilised in repairing damaged pipes with a circumferential crack under the internal pressure loading.