Pitting corrosion is a localized form of corrosion that results in small, but deep, holes or pits on a metal surface. Here are the primary causes:
- Chlorides: Presence of chloride ions, commonly found in saltwater and de-icing salts, can break down the passive oxide layer on metals, leading to pitting.
- Metallurgical Factors: Inhomogeneities in the metal, such as inclusions or second-phase particles, can act as initiation sites for pitting.
- Localized Chemical Conditions: Areas with stagnant solutions, crevices, or deposits can create localized environments that promote pitting.
- Temperature: Higher temperatures accelerate the rate of pitting corrosion by increasing the chemical activity and diffusion rates.
- pH Levels: Low pH (acidic conditions) can destabilize the protective oxide layer, making the metal more susceptible to pitting.
Prevention:
- Material Selection: Use corrosion-resistant alloys, such as stainless steel or titanium, especially those with higher molybdenum content.
- Protective Coatings: Apply coatings or surface treatments to protect the metal surface from aggressive environments.
- Environmental Control: Avoid stagnant conditions and ensure proper drainage and cleaning to remove corrosive agents.
- Cathodic Protection: Employ cathodic protection systems to prevent pitting in susceptible environments.
By addressing these causes and implementing preventive strategies, the risk of pitting corrosion can be significantly reduced, ensuring the longevity and reliability of metal components.