Finite Element Analysis and Test Verification of Composite Repair Length on Corrosion Defects

Engineered composite repairs are rapidly gaining traction as an alternative pipeline integrity repair method. These repair systems are being used to repair corrosion, erosion, dents, wrinkle bends, mechanical damage, and other anomalies that commonly occur on pipelines. Composites possess many significant advantages when compared to traditional metallic repairs. One of the most critical benefits of composites is that most composite repairs are fabricated on-site by installing an uncured composite that subsequently cures. This cure-in-place approach enables the production of repairs that can conform to complex geometries. Conformability allows for the reinforcement of damaged piping and pressure vessels that were difficult, or impossible, to repair with rigid metallic sleeves. While composites offer improved performance and reduced installation times for complex geometries, the engineering and installation of these repair systems is not as straightforward. Many areas of the methodology used to design composite repair systems are active areas of research. One of the current areas of discussion is the distance a repair must extend past a non-through-wall defect. The current nonmetallic repair standards, ASME PCC-2 Article 4.1 [1] and ISO/TS 24817 [2], suggest that a composite repair should extend a varying length past the defect in each direction, based on either the diameter and thickness of the pipe to be repaired or the stiffness of the composite. For the case of through-wall defects, the design methodology is based on the lap-shear strength of the composite and generally leads to repairs that extend farther beyond the defect when compared with non-through wall repiars. For this damage scenario, the presence of an extended repair area is considered an additional factor of safety. However, for non-leaking external defects, there is some debate as to whether the standard-prescribed, minimum repair length is required. This paper investigates a comparison of the minimum repair length required by ASME PCC-2 Equation 17 versus a shorter overlap length of 2 inches. Finite Element Analysis is used to model the difference in the two repair approaches. The FEA model is then verified by a hydrotest on a full-scale spool repair. Six specimens are machined to 75% wall loss and repaired with an engineered composite solution. The defect design for these repairs is adopted from guidance in ASME PCC-2. After installation of the repair, the pipe spool is then subjected to a hydrotest to 100% SMYS. After the 100% SMYS test, the specimens were ruptured in order to compare the ultimate strengths of the two repair approaches. All test results are compared using appropriate statistical approaches to determine significance (α = 0.05).