Selective leaching — also known as dealloying — is a corrosion process in which one element in an alloy (like zinc in brass or iron in cast iron) is preferentially removed, weakening the metal structure. Effective prevention methods include:
- Alloy Selection: Use dealloying-resistant materials, such as dezincification-resistant brass (DZR) or high-silicon cast iron, especially in plumbing, valves, and pump components.
- Barrier Coatings: Apply protective coatings like thin dense chrome, epoxy, or polymer linings to isolate the alloy from corrosive environments.
- Corrosion Inhibitors: Add chemical inhibitors (e.g., orthophosphates) to water systems to reduce leaching potential.
- Environmental Control: Design systems to avoid stagnant water, acidic pH, or high chloride concentrations — all of which accelerate leaching.
- Cathodic Protection: Use galvanic or impressed current systems to counteract electrochemical reactions that drive selective leaching.
These strategies are especially important in marine systems, potable water lines, fire protection systems, and chemical processing equipment, where long-term material integrity is critical.