Caustic embrittlement of steel structures in alumina refineries can occur over time where there is a combination of (a) high temperature/caustic conditions, (b) residual or applied stress, and (c) a susceptible material. The only published guidelines, NACE Standard RP0403, take into account the temperature and caustic concentration, but not the level of stress or the exposure time, nor the fact that Bayer liquors contain chemical species other than caustic soda. As such, Standard RP0403 should be seen as a departure point, to be complemented by additional industry-specific information.
The paper is the result of ongoing collaboration between a group of alumina producers that aims to understand conditions that can lead to caustic embrittlement and their associated controls. This collaboration includes both funded work at universities and comparison of plant examples of caustic embrittlement, the paper focuses on the latter.