Recent Experience With Weld Overlay Repair of Indications in Alloy 182 Butt Welds in Two Operating PWRs

Recent service experience with Alloy 182/82 butt welds in PWR primary piping and its joints with major components has revealed stress corrosion cracking. This mechanism of environmental cracking is known to have long incubation times, so these incidences of cracking have not been numerous to date, but it is becoming increasingly evident that this may not be the case in the future. This paper provides a summary of two recent repairs which were performed as a result of the finding of indications during in-service inspections. The weld overlay repairs followed the guidelines of code case N504, but a number of supplementary requirements were added. In each case, the repair had to be initiated with no warning other than the knowledge that the inspection was underway. The design of the weld overlay repair was done while the repair equipment was being mobilized, and the repair went as planned, with the final inspections showing that the weld overlay was flawless. In each case excellent cooperation between the plant personnel, the engineering designers, the inspectors, and the welders made for an excellent end product. In addition to a review of the processes used for each of the key steps in the repair, a review of lessons learned will be provided, so that operating plants which may face similar issues in the future can benefit from this experience.