Brass is a metal alloy composed primarily of copper and zinc, valued for its strength, workability, and aesthetic appeal. When this material is exposed to water, it is susceptible to a specific type of degradation known as corrosion. Brass does corrode in water, but this process is fundamentally different from the uniform rusting observed in iron or steel. The corrosion in brass is typically a selective, non-uniform attack that compromises the integrity of the material over time.
The Primary Corrosion Mechanism: Dezincification
The main form of corrosion affecting brass in water environments is called dezincification, a process of selective leaching. This mechanism involves the preferential removal of the more reactive zinc component from the copper-zinc alloy. The zinc atoms are dissolved into the water, leaving behind a porous, spongy mass of copper.
Zinc is the less noble metal in the alloy, making it more susceptible to an electrochemical reaction with the surrounding water, which acts as an electrolyte. As the zinc is stripped away, the remaining copper structure is highly porous and lacks the density of the original alloy. This internal structural breakdown severely compromises the integrity of the brass, leading to a loss of mechanical strength and ductility. Materials with zinc content above 15% are particularly susceptible to this process.
Environmental Factors That Accelerate Damage
The rate at which dezincification occurs is heavily influenced by the specific characteristics of the water in contact with the brass. A high concentration of chloride ions, commonly found in treated municipal water supplies, significantly accelerates the leaching of zinc. The presence of these aggressive ions destabilizes the protective oxide layer that naturally forms on the brass surface.
Water with a low pH, meaning it is slightly acidic, also promotes a faster corrosion rate. Elevated water temperatures, particularly in hot water systems, increase the energy of the chemical reactions involved, boosting the rapid dissolution of zinc. High levels of dissolved oxygen in the water further drive the electrochemical reactions required for the selective leaching process.
Furthermore, areas of low flow or stagnant water conditions allow corrosive agents to accumulate and remain in prolonged contact with the brass surface. This localized concentration of aggressive factors intensifies the rate of attack at specific points in a system.
Identifying Signs of Corrosion and Practical Consequences
The most visible sign of dezincification is a distinct color change on the brass surface. The original yellow color of the alloy is replaced by a pink or reddish hue, which is the color of the pure copper left behind after the zinc has been removed. White, chalk-like deposits of zinc oxide may also be present on the external surface of the component.
This internal structural damage has serious practical consequences, particularly in plumbing systems. The weakened, porous copper material can no longer withstand normal operating pressures, often leading to the development of pinhole leaks. In valves and fittings, the loss of material can cause the component to become brittle and fragile.
This structural decay increases the risk of catastrophic failure, such as the sudden bursting of a pipe or the breakdown of a valve mechanism. Furthermore, the porous copper residue and corrosion byproducts can accumulate, leading to blockages and reduced water flow within the system.
Strategies for Mitigation and Prevention
Specialized alloys known as Dezincification Resistant (DZR) brass are engineered to significantly slow down this corrosion process. DZR brass is often identified by markings like “DR” or specific alloy designations such as CW602N.
These resistant alloys are formulated either by limiting the zinc content to below 15% or by adding small amounts of inhibiting elements, such as arsenic, antimony, or phosphorus. These additives stabilize the alloy’s microstructure and suppress the selective leaching of zinc. Utilizing DZR brass is important in hot water distribution systems where the risk of accelerated corrosion is highest.
Water quality management offers another layer of protection, particularly in closed-loop industrial systems. Adjusting the water’s pH to a more neutral or slightly alkaline range can help reduce the corrosion potential. In some situations, the introduction of chemical corrosion inhibitors can form a protective layer on the brass surface.