Experimental investigation of through-wall hole geometry on pressure resistance in steel pipelines repaired with composite materials

Metallic pipelines exposed to harsh environments, such as high humidity and temperatures, are susceptible to damage. Composite wrapping is a highly effective repair method, and the geometry of defects such as through-wall holes plays a crucial role, especially in irregularly shaped damage. This study experimentally investigates the influence of a through-wall hole on the effectiveness of composite repairs for steel pipelines under hydrostatic pressure. Three plain-woven composite materials—glass, carbon, and a balanced hybrid (each carbon layer is followed by a glass layer)—were evaluated. Results demonstrated that circular defects rehabilitated with glass/epoxy composites withstood 46.6% higher hydrostatic pressures compared to square defects of equal cross-sectional area. Furthermore, carbon fiber composites exhibited superior pressure resistance compared to glass fiber, and increasing the number of composite layers enhanced the overall failure pressure. Conversely, increasing the defect area from 1.44 cm² to 4.3 cm² significantly reduced failure pressure. A Taguchi analysis revealed the primary influence of reinforcing fabric type and layer number on failure pressure, with defect shape also playing a significant role. This study demonstrates that the reduction of stress concentration through a modification of defect shape can significantly increase failure pressure.