Several Canadian hydropower facilities have been in service for more than 100 years exposing vital equipment to both physical and chemical stressors from the environment. Recent advances in erosion mitigating technologies such as thermal spray coating techniques have been responsible for the extended material performance; however, these advances still have chemical vulnerabilities in the form of corrosion. In order to combat corrosion, it has been proposed to fabricate erosion resistant coatings using a corrosion resistant material such as stainless steel. The spatiotemporal tracking of the corrosion process occurring at the stainless steel’s heterogeneous microstructure was performed through tandem analyses involving electron and electrochemical microscopies. By understanding the relationship between the chemical composition of the microstructure and local reactivity over time, insight on failure mechanisms of such industrially important material can be obtained.