Don’t Crack Up - Composite Repair of SSWC

Composite repairs have been extensively qualified and used to repair external corrosion and dents encountered on pipeline systems. More recently, test programs have explored extending the use of composite repairs to reinforce crack-like indications, including those found in low-frequency electric resistance welded (LF-ERW) pipe. This paper addresses repairing selective seam weld corrosion (SSWC) using composite repair systems, which is yet another extension for composite repairs. Current approved techniques for repair of SSWC include full encirclement steel sleeves and mechanical clamps, however, there can be challenges when repairing out of straight or out of round pipe and they can require large pipe excavations to find a suitable location for in-service welding. Finding a clean in-service welding landing zone becomes more difficult when considering vintage line pipe steel which have a higher probability of laminations. SSWC results in a groove centered on the ERW bondline, which typically has lower toughness than the surrounding pipe. While corrosion is active, the groove remains relatively blunt. Therefore, a SSWC repair must minimize or eliminate the potential for sudden fracture along the seam. The chosen repair should reduce or eliminate the likelihood of crack formation at the stress concentration at the base of the SSWC groove. In this study, fabricated SSWC-like features were reinforced with commercially available composite repair systems on vintage ERW pipe and subjected to cyclic pressure. Results have shown that composites can sufficiently reduce stress to prevent crack formation, providing a permanent repair option. Further corrosion is also mitigated by creating a barrier between the steel pipe and environment.