Experimental Investigation of Defect Geometry and Composite Type on the Pressure Resistance of Repaired Steel Pipelines

Metallic pipelines exposed to harsh environments, such as high humidity and temperatures, are susceptible to damage. Composite patching is a highly effective repair method, and the geometry of defects plays a crucial role, especially in irregularly shaped damage. This study investigates the influence of defect geometry on the effectiveness of composite repairs for steel pipelines under hydrostatic pressure. Three plain-woven composite materials—glass, carbon, and a hybrid—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 1.4 cm² to 4.33 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.