Corrosion and Environmental Degradation

Corrosion is an electrochemical process

Anodic reactions dissolve or oxidise material while cathodic reactions consume electrons. The environment completes the circuit through ionic transport.

Uniform and localised attack

Uniform corrosion is often predictable. Pitting, crevice corrosion, intergranular attack and stress-corrosion cracking are more dangerous because severe local damage can occur with little overall mass loss.

Passivity

Some alloys form thin protective films that dramatically reduce corrosion rate. Passivity depends on chemistry, potential, temperature, chloride level, surface condition and film stability.

Galvanic coupling

Electrically connected dissimilar materials in an electrolyte can accelerate attack on the less noble member. Area ratio matters: a small anode coupled to a large cathode is especially vulnerable.

Takeaway

Material, environment, geometry, stress and electrical contact must be considered as one corrosion system.