Pitting Corrosion
Definition
Localised attack producing narrow, deep craters where the passive film breaks down. Pitting is self-propagating once initiated because the pit interior becomes an acidified, de-aerated micro-cell.
- Appearance
- Narrow, deep localised craters
- Trigger
- Local breakdown of the protective passive film
- Propagation
- Self-sustaining acidified, oxygen-poor pit interior
- Risk
- Can nucleate fatigue cracks or through-wall leaks
Common questions
Why is pitting corrosion considered more dangerous than uniform corrosion for failure analysis?+
Uniform corrosion removes material evenly and is easy to predict and inspect for, while a pit concentrates metal loss in a small area that can perforate a wall or become a stress riser long before overall corrosion levels look severe.
What evidence at a fracture surface points investigators toward pitting as the origin?+
A single deep, narrow cavity at the crack initiation site, often with corrosion products inside it and a fatigue striation pattern radiating outward, distinguishes a pit-initiated failure from one starting at a machining defect or weld flaw.
Related terms
- Corrosion Fatigue
- Fatigue crack initiation and growth accelerated by a corrosive environment. Unlike SCC, it does not require a specific environment-material combination and can...
- Crevice Corrosion
- Corrosion in confined geometry , under gaskets, at lap joints, between fastener and plate , driven by oxygen depletion and acidification inside...
- Galvanic Corrosion
- Electrochemical attack that accelerates the dissolution of the more active (anodic) metal when two dissimilar metals are electrically coupled in an electrolyte.
- Selective-Phase Corrosion
- Attack that preferentially dissolves one phase or element from a multi-phase alloy, leaving the other phase intact but structurally weakened. Dezincification of...
- Stress-Corrosion Cracking (SCC)
- A failure mode combining sustained tensile stress with a specific corrosive environment, producing branching, often intergranular cracks that grow at stress intensities...