MODIFIED GTAW ORBITAL TUBE-TO-TUBESHEET WELDING TECHNIQUE, AND THE EFFECT OF A COPPER WELD RETAINER DURING WELDING OF ALLOY 825

摘要

Tube-to-tubesheet welds are an essential part of the design of heat exchangers used in power generation, petro-chemical, chemical processing, pharmaceutical, and food processing industries. The tube-to-tubesheet welds are typically produced using gas tungsten arc welding (GTAW) with or without the addition of filler wire, and involve carbon steels and various creep and corrosion resistant alloys. The weld heat input in tube-to-tubesheet welds is an essential parameter that controls the productivity and weld quality, in terms of weld bead geometry and heat affected zone microstructure and properties. A modified GTAW tube-to-tubesheet orbital welding head that utilizes a copper weld retainer is described in this paper. The copper weld retainer provides a heat sink during welding, and supports the molten weld metal. This permits the use of a relatively high heat input, required for a single pass welding with filler wire addition. Furthermore, the copper retainer limits the amount of weld overlap into the tube bore. The application of the modified orbital welding technique, which helped for resolving a suspected liquation cracking problem in Alloy 825 tube to 316L stainless steel tubesheet welds, is presented.