Reinforcement of Planar Defects in Low-Frequency ERW Long Seams Using Composite Reinforcing Materials

Abstract

A comprehensive study was conducted to investigate the reinforcement of LF-ERW flaws located in a 16-inch × 0.312-inch (406-mm × 7.93-mm), w.t. Grade X52 ethylene pipeline. The study was prompted by an in-service leak that was discovered in an LF-ERW seam during routine maintenance activities. The investigation was subsequently expanded as a result of the discovery of several additional leaks. An initial failure analysis of the leak location was conducted followed by broader material testing, full-scale testing, and metallurgical analysis of the remaining pipe. The use of composite repair systems as a feasible method of LF-ERW seam reinforcement was also examined. As part of this study, testing was also conducted on 8.625-inch × 0.250-inch. (219-mm × 6.35-mm) pipe material having LF-ERW seams. Test results documented the potential for composite repair systems to provide reinforcement to LF-ERW flaws and crack-like defects. Distinct contrasts were observed between the performance of samples with unreinforced and reinforced notches subjected to cyclic pressure and burst tests. Reinforced samples exhibited improvements in pressure cycle life and significantly increased burst pressure capacities as compared to unreinforced samples. The results of this program demonstrate that, when properly designed and installed, composite materials are an effective means for reinforcing LF-ERW long seam weld flaws and other planar defects. The composite repairs served to ensure that cracks neither form nor propagate during aggressive pressure cycling and burst testing. It should be noted that the testing program was specific to the operating and material conditions associated with a particular ethylene pipeline that is the subject of this paper.