Crevice corrosion of hydrogen-charged stainless steel weldments in chloride media

Austenitic stainless steels (for example types 304, 304L, 316 and 316L) are commonly used as cladding materials for pressure vessels and control rod assemblies as well as in the construction of core components in nuclear power plants. Welding is the predominant joining technique in these components. Severe operating conditions in the reactors represented by the combined effect of temperature, pressure, and neutron irradiation lead to degradation in the corrosion resistance and mechanical properties of pressure vessel steels and core components. Several types of corrosion may be encountered, the most common and dangerous being the localized-type attack. Expectedly, welds are the most susceptible sites of such attack. In this investigation, the effect of hydrogen (cathodically charged) on the crevice corrosion of 308L weldments as well as 304L base metal, both in the solution treated condition, was studied. Cathodically charged hydrogen led to the creation of surface cracks (wavy and straight) which notably affected the electrochemical corrosion characteristics. The values of corrosion potential and breakdown potential were shifted into the active direction. The corrosion current values were also markedly increased. The electrochemical findings were supplemented by SEM surface investigation. Despite the fact that both materials suffered from hydrogen charging, 308L weld metal showed a better resistance.