In-service weld repair by direct deposition: Numerical simulation and experimental validation

Abstract

In-Service Welding is a technological process for which interconnection and repair of pipelines can be made while they are in operation, before making it two main risks need to be assessed: hydrogen cracking and burn-through. Current simulations and validations assess these risks independently, but due to its interdependence these risks need to be assessed in conjunction. A repair method not normally used, but with high potential due to its simplicity and versatility is the direct deposition of weld.In the present research, a fluid-thermo-mechanical coupled simulation and validation were done of an in-service welding repair by direct deposition on a flowing pressurized pipe having an internal defect. The results demonstrated the effectiveness of using this repair method to restore the mechanical strength of pipelines. Surface, sub-surface, and volumetric non-destructive examinations evidenced no cracking immediately to finish the repair and delayed. Temperature tendency curves showed good approximations having a maximum difference of 5.09 % between numerical and experimental. Perimeter deformation along the pipe length between numerical and experimental results displayed a similar behaviour with a significant difference in the numerical values attributed to the lack of input data for weld properties. The structural analysis performed in this study used the approach of the risk of burn-through under internal pressure determined by the occurrence of localized radial bulging. Numerical results indicated no relevant plastic strain occurs. Is strongly recommended that thermal analysis assessments using the actual defect morphology would be performed, not only considering the remaining thickness of the pipe.