Corrosion of Borated Stainless Steel In Water And Humid Air

Borated stainless steel alloys are candidate neutron absorber materials for criticality control in disposal containers or dry storage canisters. Type 304 borated stainless steels are similar to conventional Type 304 stainless steels except that they contain a boron addition, which imparts a much higher thermal neutron absorption cross section than other austenitic stainless steels. This work investigated the corrosion behavior of borated stainless steel in water and humid air. In this study, Type 304B4 and 304B5 borated stainless steels were exposed to the liquid and vapor phases of simulated groundwater at 60, 75, and 90 °C [140, 167, and 194 °F] for about 3 months. The vapor phase was open to air representing the humid air condition. The posttest specimens were analyzed to determine general corrosion rates and occurrence of localized corrosion. It was found that some specimens exposed to humid air at 75 and 90 °C [167 and 194 °F] suffered pitting corrosion, but pitting corrosion was not observed at 60 °C [140 °F] or from the liquid exposure at 75 and 90 °C [167 and 194 °F]. The pits were circular, and the surface near the pitted area was stained. The maximum pit depth was about 70 μm [2.8 mil]. All the specimens exposed to the liquid phase showed weight gain before acid cleaning of the surface due to scale formation. Most of the specimens exposed to humid air showed weight loss. At all three temperatures, the general corrosion rates of Type 304B4 were less than 80 nm/yr [0.0032 mil/yr] and those of Type 304B5 were less than 600 nm/yr [0.024 mil/yr]. No clear trend was observed regarding the influence of temperature on general corrosion rates of each material. The general corrosion rates of Type 304B5 were higher than those of Type 304B4.