Fatigue life analysis of API X65 pipelines with longitudinal crack repaired by compressive sleeve

This study evaluates the fatigue behavior of API 5L X65 pipelines containing semi-elliptical longitudinal cracks repaired using compressive sleeve Type A. Although this repair technique is commonly applied to mitigate corrosion and dent defects, its effectiveness in crack-like defects governed by fracture mechanics parameters remains insufficiently quantified. The objective of this work is to assess the reduction in crack driving force induced by sleeve installation and to validate fatigue life predictions through a combined experimental and numerical approach based on elastic–plastic fracture mechanics (EPFM). Five full-scale pipe specimens were tested under cyclic internal pressure, including two non-repaired and three repaired configurations. A finite element model was developed in ABAQUS, and the J-integral was extracted using the contour integral method. Fatigue crack growth was predicted using a ΔJ-based Paris-type formulation. Mesh convergence and contour independence analyses were performed to ensure numerical reliability. Plastic zone estimation indicated that small-scale yielding conditions were not satisfied for deeper cracks (a/t up to 0.7), justifying the adoption of an EPFM framework. Numerical predictions showed good agreement with experimental results, with errors below 9% for non-repaired specimens and below 3.5% for repaired configurations. A sleeve hole was introduced in two repaired specimens to enable stable crack growth and calibration of fatigue parameters under modified residual stress conditions. The intact sleeve configuration exhibited negligible crack propagation after approximately 160,000 cycles, confirming the strong crack-tip shielding effect of the compressive sleeve. For crack depths between 3.57 mm and 5.00 mm (50–70% of wall thickness), ΔJ reductions between 98.66% and 99.41% were obtained compared to the non-repaired condition. Hoop stress redistribution analysis demonstrated significant reduction of near crack-front circumferential stress after sleeve installation. A parametric study showed that reducing repair pressure is more effective in lowering ΔJ than increasing tightening load, highlighting the dominant role of installation stress state in crack-tip shielding. The results confirm that compressive sleeve Type A repair substantially reduces crack driving force and extends fatigue life in pipelines containing longitudinal cracks. • EPFM model validated for cracked API 5L X65 pipelines • Type A sleeve reduced cyclic crack driving force (ΔJ) by up to 99% • Significant fatigue life extension for longitudinal cracks • Repair pressure had greater influence than tightening load • Stress redistribution quantified through hoop stress analysis