Welding simulation for comparative analysis of steels for main pipelines

Estimation of the weldability of new linepipe steels, based on the traditional carbon equivalent approach has certain shortcomings especially when considering the very low carbon contents in ultra high strength steels (X-80 and above). The I.P. Bardin Institute has developed a new method based on analysis of continuous cooling transformation diagrams and the hardness, microstructure and CTOD properties of samples prepared in the dilatometer. Studies of a broad range of steels using the new method have shown that cold cracking resistant microstructures form over a much larger range of cooling rates when carbon contents are reduced from above 0.10 percent to 0.03 percent. This is attributed to the formation of acicular ferrite/bainite microstructures in the CGHAZ in 0.03 percent carbon steels versus ferrite – pearlite microstructures at more conventional carbon levels >0.10 percent. The SSC performance of the low carbon steels also improves at low carbon levels and bodes well for the new generation of X-80 steels in pipeline service. (AU)