Pitting Corrosion of Stainless Steel 304H in Concentrated MgCl2 Solution and Computer Vision of Pit Morphology

RIP2025-00017: The ambient air used to cool stainless steel (SS) canisters for storing spent nuclear fuel (SNF) contains salt aerosols, which can accumulate on the canister walls. When these salts absorb moisture from the air, they form a corrosive brine, promoting localized corrosion and eventually stress corrosion cracking (SCC). This study investigates the nucleation and growth of pitting corrosion in a concentrated magnesium chloride (MgCl2) brine, mimicking the conditions on the canister surface at a low relative humidity of 40%. Depending on the applied potentials, electrochemical methods led to the rapid formation of distinct crosshatch or granular pit morphologies on SS304H. In the experimental condition, corrosion primarily propagated laterally, likely due to the high salt concentration in the solution. This morphology could influence the transition from pit formation to crack development by concentrating stress around the sharp corrosion features. To identify critical pit morphological features that could lead to SCC, computer vision based machine learning was applied to the 2D scanning electron microscopy images. The results will lay the foundation for the prediction of pit-to-crack transition based on 3D computer vision.