Effects of Pipe Pressure During Repair Installation on its Relative Performance for Circumferential Defects on Pipelines
Proceedings Publication Date
Dr. Tyler Johnson
Tyler Johnson, Curtis Mokry, Chris Apps, Kalen Jensen, Mark Brimacombe, Peter Chan, Wade Forshner
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While many non-welding technologies focus on repairing axial defects (i.e. hoop reinforcement), the evaluation of these technologies for circumferential defects (i.e. axial reinforcement) has been limited. A multi-phase Joint Industry Project (JIP) was developed with four pipeline operators to address this knowledge gap, and Phase 1 focused on technology identification and relative performance testing. Phase 1 also identified the potential effects of pipe pressure during repair installation on repair performance. This paper focuses on these effects, which were investigated in Phase 2 of the JIP by evaluating three repairs: two composite repairs (a composite fabric pre-impregnated with water-activated resin, and a wet-lay-up of composite fabric and epoxy) and a hybrid repair (steel sleeves adhered to the pipe using epoxy). Each repair was installed on seven NPS 12 pipe specimens that contained pressures generating hoop stresses ranging from 0% to 70% of the pipe’s specified minimum yield strength (SMYS). Each specimen’s pressure was then maintained or pressure cycled to decouple the effects of these real-world operations. For all seven axial tests, the specimen pressure was maintained at 72% SMYS, while the axial tension was slowly increased until the maximum tensile load was reached. Each repair’s performance was defined by the axial stiffness it added to the underlying pipe during elastic loading and into plastic deformation. The results indicated that lower installation pressures generally lead to better repair performance. However, the performance effects depended on the repair, with a 1% to 12% average decrease in axial stiffness between the two lower and two higher installation pressures tested. The hybrid and wet-lay-up composite repairs added more axial stiffness than the pre-impregnated composite repair (36% and 15% on average into plastic loading, respectively), but their performance was more impacted by the pressure cycling (17% and 10% on average into plastic loading, respectively).

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