Dealloying

One of the most well-known examples of dealloying (or selective leaching) is dezincification of brass. In this process, zinc is selectively removed from brass — an alloy of copper and zinc — when it’s exposed to aggressive environments, especially those containing chlorides or mildly acidic water.

As zinc dissolves out of the alloy, a weakened, porous structure made mostly of copper remains. This deterioration significantly reduces the strength, ductility, and pressure-holding capacity of brass components.

Where it happens: Dezincification frequently affects brass plumbing fittings, valves, and pipes in municipal water systems or industrial cooling circuits — especially when water chemistry isn’t properly controlled.

Selective leaching — often called dealloying — occurs when one element in a metal alloy is preferentially removed by corrosion, leaving behind a weakened structure. Common examples include zinc loss in brass or iron leaching from cast iron. To prevent this, consider the following strategies:

• Choose resistant alloys: Use materials specifically designed to resist dealloying, such as DZR (Dezincification-Resistant) brass or high-silicon cast iron for pumps, valves, and piping.
• Apply barrier coatings: Protective coatings like thin dense chrome, epoxies, or polymer linings prevent corrosive media from reaching the base metal.
• Use corrosion inhibitors: Chemicals like orthophosphates can be added to water systems to help suppress the electrochemical reactions behind selective leaching.
• Control environmental factors: Avoid stagnant flow, maintain neutral pH, and reduce chloride levels in system design and maintenance.
• Implement cathodic protection: Galvanic or impressed current systems can neutralize corrosion-driving voltages across vulnerable surfaces.

These techniques are essential in high-risk settings like potable water infrastructure, marine equipment, fire suppression systems, and chemical processing plants.