Weldability investigation in inner surface repairs of WWER-440 nuclear power plant pressure vessel

The weldability of the base material of WWER-440 reactor pressure vessels, viz. 15Kh2MFA steel, was examined experimentally in relation to the repair of cracks occurring in and beneath the overlays on the inner surfaces of the vessels. During the repair welding without preheating, cold cracks tend to develop in the steel. This tendency is promoted by the presence of the unfavourable martensitic structure associated with a growth of the grain in the overheated heat affected zone. Appreciable embrittlement takes place in this zone in the unannealed state. It is suggested that this embrittlement can be partly eliminated by re-annealing in the optimal temperature cycle with a maximum temperature of about 850 degC. In conventional conditions, hot crackability will not be the limiting factor in the weldability of 15Kh2MFA steel or of the austenitic filler materials examined (EA-400/10 T, C-442, EA-395/9). (Z.M.). 10 figs., 2 tabs