Development of Earthquake-Resistance Evaluation Method for Composite-Repaired Pipelines Considering Interface Delamination

Abstract Buried gas pipelines play a crucial role in our modern infrastructure, and hence, ensuring both safety and uninterrupted supply by prompt repair in case of damage is a critical need. The composite repair method has been utilized for emergency repairs in pipelines, yet the earthquake resistance of the composite-repaired pipeline remains uncertain. This study aims to evaluate the resistance of pipelines repaired with composite materials against earthquake ground displacement through experiments and finite element analysis incorporating a cohesive zone model. An axial loading test was performed on a test pipe repaired with composite materials. During the experiment, delamination occurred at the interface between the steel pipe and composite repair, leading to internal water leakage. The average local strain in the pipe at the onset of internal water leakage exceeded the strain demand imposed by earthquake ground displacement, indicating the earthquake resistance of the composite-repaired pipeline under the experimental conditions. A finite element analysis utilizing a cohesive zone model was carried out to replicate the experimental delamination. In this analysis, the delamination penetrated earlier than in the experiment, suggesting that the developed analysis method can conservatively evaluate the earthquake resistance of the composite-repaired pipeline. Furthermore, the developed analysis method was applied under conditions differing from the experiment. In all cases, the strain in the pipe exceeded the strain demand from earthquake ground displacement before interface delamination penetrated. These findings lead to the conclusion that the composite-repaired pipeline demonstrated earthquake resistance.