A study of the effect of homopolar pulse welding parameters on microstructure and mechanical properties of carbon steel HSLA linepipe

Homopolar pulse welding (HPW) utilizes the high current, low voltage pulse produced by a homopolar generator to rapidly resistance heat the interface between two components to forging temperature. An upset force is then applied to produce a forge weld at the interface, requiring only a few seconds from initiation of the pulse to completion of the weld. HPW is being investigated as a means to rapidly join API line pipe, having potential for application in deep water offshore pipeline construction requiring the J-lay method. Early HPW welds in API 51, X-52 carbon steel linepipe exhibited full tensile strength but unacceptably low impact toughness. The effects of process parameter variations on microstructure and mechanical properties of the weld zone were experimentally investigated in this study.;Circumferentially uniform homopolar pulse welds were readily produced in API 5L X-52 carbon steel linepipe during this study. Tensile strength was found to be strongly dependent on generator discharge parameters and required a nominal upset displacement for full strength welds to be produced. Weld line microstructure and impact toughness were altered by weld process parameter variations. Weld cooling rate was found to be strongly dependent on electrode location. Homopolar pulse normalizing was found to be a viable means to improve the impact toughness of homopolar pulse welds.