Repair process of fillet weld defects in oil and gas branch pipes with composite materials: finite-element modelling and experimental verification

This study developed a GF–CF–GF sandwich composite repair method for superficial defects in the fillet welds of oil and gas pipeline branches, which can effectively prevent galvanic corrosion and provide effective reinforcement. Finite-element analysis (Abaqus) of fillet weld defects of common oil and gas pipelines (main pipe: 323.9 × 12.5 mm; branch pipe: 76 × 5 mm) shows that the defect depth dominated the weld strength, with a repairable critical size of 52 × 1 × 5 mm. The repair adopts cross-winding, with the curing temperature and winding tension set to 35 °C and 12 N, respectively, during curing. The winding area is divided into core and non-core zones with a 150 mm boundary from the defect. The repair layer thickness is 6.4 mm in the core zone and 3.2 mm in the non-core zone. Finally, pressure burst tests confirm that the ultimate pressure of the repaired pipeline reaches 33.9 MPa, exceeding that of normally serving pipelines (32.7 MPa).