L51660 Development of Simplified Weld Cooling Rate Models for In-Service Gas Pipelines

For some time, the gas transmission industry has been faced with the problem of standardizing guidelines for welding on "in-service" pipelines. Such guidelines would permit the welding engineer to safely and accurately assess field operations either prior to or during welding.

Edison Welding Institute (EWI) and Battelle Memorial Institute (Battelle) separately developed models for predicting hot-tap/repair welding conditions for "in-service" pipelines. EWI researchers developed a field-adaptable technique for "in-service" welding of pipelines that requires actual field measurement of the pipeline's heat-sink capacity. The measured value, in conjunction with extensive experimental field data allows the assessment of acceptable welding procedures to avoid underbead cracking. Battelle researchers devised a different approach to the problem of "in-service" welding. Thermal-analysis computer models were devised that determine acceptable welding parameters to avoid cracking and burnthrough based on heat-transfer equations. Both of the original EWI and Battelle methods were validated through extensive field trials. The result of this work by EWI, Battelle and Kiefner & Associates integrated these two (2) methods into a single "standard" approach suitable for predicting safe welding procedures for welds made on "in-service" pipelines. This report describes the field-adaptable technique, the thermal-analysis models and the validating experimental data. This report further delineates how the EWI and Battelle hot-tap methods were integrated into a new approach to welding on "in-service" pipelines.