Advances in homopolar welding of API line pipe for deepwater applications

The University of Texas at Austin Center for Electromechanics is conducting a research program, funded by six oil companies, two industrial contractor s, and two government agencies, to study homopolar welding of line pipe for J-Lay applications. In 1995, the third year of the five year research prog ram, the set of weld parameters, those input variables used to control weld performance and quality, was expanded to include joint geometry, with dram atic improvement in the mechanical properties of two HSLA nominal 3-in. lin e pipe materials: X60 and X65. These improvements increased the Charpy V-No tch impact toughness properties to near parent metal values, while maintain ing acceptable strength. After demonstrating repeatable performance with th e new parameters, new research focused on real world effects including tole rancing the parameters and evaluating the effect of poor fit up resulting f rom misalignment and rough and wavy interfaces. During the final:year of th e research program, the pipe welding program has scaled up to 12-in. nomina l line pipe, a seven-fold increase in the Cross-sectional area. The paper w ill cover the basics of homopolar welding (HPW), weld parameters and modifi cations, the effects of these changes on real time process data, mechanical properties, weld upset profile, HPW metallurgy, and the studies of real wo rld effects. Results from HPW of 12-in. pipe will also be presented.