Grade 91 pipes and tubes have become a standard material for the design of new and refurbishment of existing Power Plants. Several major failures have been encountered after fabrication of these new steels and are mainly attributable to improper practices. Gas backing and the required PWHT are a time consuming factor. In a collaborative research program, the BWI and Laborelec undertook the challenge to investigate the feasibility of a Cold Weld Repair (CWR) methodology in order to weld repair T91 tubes without the use of gas backing and PWHT. The study so far demonstrated that a repair method based on the selection of an undermatched consumable and a controlled deposition procedure can result in acceptable properties. In this research we would like to investigate the residual stress relaxation in the CWR during in-situ experiment in order to further optimize the welding ability of T91.