There are restrictions for in-service welding on carbon steel for external attachments used in alkaline service because cracking can occur with the residual stress contributed by welding when in contact with the process fluid. There is belief that in-service welding could be possible for these situations if the wall thickness is great enough so that the stress field due to welding does not reach the I.D. surface in contact with the process, and PWHT would not be required. The project objective is to determine the minimum wall thickness with different weld heat inputs that could allow external attachment welding in this service.
