L51713 Effective Procedure Variables for Weld onto In-Service Pipelines

The ability of the flowing contents to remove heat from the pipe wall causes welds made onto in-service pipelines to cool at an accelerated rate and makes these welds particularly susceptible to hydrogen cracking. Several approaches exist for qualifying procedures where the thermal conditions produced by the flowing pipeline contents are simulated, allowing the ability of a procedure to produce sound, crack-free welds to be demonstrated.

This report documents the various methods that can be used, under a number of different conditions, for simulating the proper cooling effects that will be experienced when welding on in-service pipelines. Three candidate methods were selected and evaluated based on their simplicity and their ability to produce realistic weld cooling rates. Several field trials were undertaken in conjunction with actual in-service welding operations conducted by PRCI-member companies, and using a flow loop at the GRI Metering Research Facility, to collect weld cooling rate data to establish which procedure qualification conditions are applicable for various actual in-service conditions.Several field trials were undertaken and documented within this report on actual in-service welding operations as well as using a flow loop at the Gas Research Institute (GRI) Metering Research Facility to collect weld cooling rate data to establish which procedure qualification conditions are applicable for various in-service conditions and pipe repairs.