This paper is focused on the problematics of weld joint corrosive degradation in the boiler water environment. The boiler water is commonly used in power industry. The corrosion experiment simulated the boiler water environment during shutdown, when chemicals may be concentrated in the deposits, or as a result of evaporation. The corrosion experiment was performed on heterogeneous weldments made of P265GH//X6CrNiTi18-9 steels in the environment of stagnant boiler water with the addition of NaCl for 53 days. The data showed only minimal weight losses, and small changes in the measured fracture toughness of the welded joint. At the same time, a tendency for a mechanical weakening of the welded joint with the increasing aggressivity of the boiler water environment was observed. The metallographic analysis was performed to describe the nature of corrosive degradation.