Dissimilar weld joint of ARMCO iron and SS-304L using GTAW orbital welding process

Liquid sodium is selected as coolant for the Prototype Fast Breeder Reactor (PFBR) at Kalpakkam to transfer the heat generated in the reactor core to steam generator to produce high pressure steam. Any leakage of water/steam into sodium at the steam generator, would result in aggressive sodium-water reaction. It is essential to detect this leak at its very beginning and take immediate corrective action. Electro Chemical Hydrogen Meter (ECHM) has been developed at IGCAR for this purpose, for online measurement of hydrogen concentration in sodium circuit for indicating the occurrence of sodium - water reaction. Fabrication of ECHM probe involves dissimilar welding consisting of pipe sleeve (made of SS-304L), and thimble (made of ARMCO Iron). Towards this, many weld trials using orbital GTAW based technique have been carried out between ARMCO Iron and austenitic stainless steel (SS-304l). Weld parameters have been optimized and dissimilar weld joint has been successfully developed between these two materials. Orbital welding process is a specialized welding process in which the arc is rotated mechanically through the circumference around a static workpiece (an object such as a pipe). This process is a computer-controlled process which runs with little intervention from the operator, and it is specifically used for high quality repeatable welding. The butt weld joints were tested using visual examination, dye penetrant test (DPT), helium leak test (HLT) and X-radiography and found to be qualified. Development of dissimilar weld joint between ARMCO Iron and SS-304L using GTAW orbital welding process and the tests carried out to qualify / characterize the joints are described in this paper. (author)