Evaluation of dynamic behaviour of pipe-in-pipe systems for deepwater J-lay method

The pipe-in-pipe (PIP) system, with good structural resistance and favourable thermal insulation capacity, has been extensively applied in oil and natural gas exploitation in deep waters. In the present paper, a simplified equivalent numerical model of the PIP system for deepwater J-lay operation was developed to evaluate the dynamic response of the outer pipe and the inner pipe under the combined hydrodynamic load and pipelay vessel motion by the software OrcaFlex. The comparison of mechanical responses between the present equivalent model and other available PIP models was performed to verify its reasonability. Considering vessel motion, pipe-soil interaction, wave and current, the dynamic behaviour of the outer and inner pipes was evaluated on aspects of the bending moment, effective tension, equivalent stress and strain. After that, the influences of key geometric parameters on the dynamic behaviour of PIP systems were systematically studied, including the diameter-to-thickness ratios of the outer pipe and inner pipe as well as the core thickness. The findings would provide good guidance for the structural design and the installation analysis of PIP systems using the deepwater J-lay operation.