This paper, which won the SAIW Harvey Shacklock in 2017 for its principal author Angel Krustef, was first delivered at the ASME 2017 Pressure Vessels and Piping Conference of July 16-20, 2017 in Hawaii. It details the development of a technique for controlling the heat input during tube-to-tubesheet welding of Alloy 825.
Tube-to-tubesheet welds are an essential part of the design of heat exchangers used in the power generation, petrochemical, 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 productivity and weld quality, in terms of weld bead geometry and heat-affected zone micro- structure and properties.
A modified GTAW tube-to-tubesheet orbital welding head that utilises a cop- per weld retainer is described in this paper. The copper weld retainer provides a heat sink during welding, while supporting 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 a modified orbital welding technique, which helped resolve a suspected liquation cracking problem in Alloy 825 tube to 316L stainless steel tubesheet welds, is presented here.