Modelling brings toughness improvement to welded natural gas transmission pipelines

Weldability research at OCAS for natural gas transmission pipelines has been valorised for many years to support ArcelorMittal customers. One of the technologies widely used to produce tubes and pipes from strip is high frequency induction (HFI) welding. This welding technology does not require welding consumables, results in a narrow weld zone, and is the most productive method.

OCAS’s technical capabilities in HFI (other than welding itself) allow us to carry out in-depth research – these capabilities were recently extended with numerical modelling of the welding process. A 2-dimensional numerical model, coupled with electromagnetic and thermal physics, has been developed at OCAS to predict the temperature profile of the strip as it passes through the induction welder. Within a collaborative project with one of ArcelorMittal’s most important customers, this model allowed us to review the existing forging practice of the mill and to provide recommendations for implementing a sophisticated forging control during HFI welded pipe production. The customer could achieve a substantial toughness improvement on the welds: Charpy impact toughness of the bond line increased by more than 30% at -20 °C, and the ductileto-brittle transition temperature shifted to a lower temperature. With the current information available, calculation of the thermal profile for upcoming production cases should be possible before the production starts, which will minimise the number of expensive trials that are required to optimise process parameters.