Effect of CFRP Geometry on the Repair Performance of Corroded Steel Pipelines: A Finite Element Study

Carbon fiber-reinforced polymer (CFRP) repair is widely used to rehabilitate corroded steel pipelines; however, the relative influence of CFRP repair geometry on stress reduction remains insufficiently quantified. This study investigated the effects of CFRP thickness and repair length on the hoop stress response of steel pipelines containing circumferentially uniform longitudinal corrosion defects under internal pressure. An axisymmetric finite element model was developed in ABAQUS and verified against an analytical multilayer cylinder solution based on the Lamé thick-cylinder theory. The model was based on an idealized circumferentially uniform corrosion defect, linear elastic material behavior, and perfect bonding between the steel pipe, epoxy filler, and CFRP repair layer. A parametric study was performed by varying the defect depth, defect length, CFRP thickness, and repair length. The results showed that CFRP thickness was the dominant parameter controlling the repair effectiveness. For the deepest defect case, increasing the CFRP thickness ratio from 0.25 to 0.75 increased the hoop stress reduction from approximately 40% to more than 58% for the shorter defect and from approximately 40% to more than 62% for the longer defect case. In contrast, increasing the repair length beyond full defect coverage produced only marginal additional stress reduction. Based on a 10% stress-tolerance criterion relative to the intact pipe response, the required CFRP thickness-to-defect-depth ratio increased with defect severity. These findings support the preliminary CFRP repair sizing by prioritizing repair thickness over excessive repair length.