Galvanic Corrosion Demystified: Dissimilar Metals and System Design

When it comes to cooling water systems in large buildings and campuses, corrosion is more than just an eyesore—it can be a silent destroyer of critical infrastructure. Among the many forms of corrosion, galvanic corrosion stands out for its tendency to develop quickly when certain metals come into direct contact. Facility managers often find themselves facing unexpected leaks, rapid material degradation, and ballooning repair costs if this form of corrosion isn’t understood and properly managed.

Below, we break down how galvanic corrosion works, why it’s so damaging, and what steps you can take to prevent it in your facility.

Understanding the “Battery Effect”

Galvanic corrosion occurs when two dissimilar metals come into contact in the presence of an electrolyte—often, in facility operations, that electrolyte is the water circulating through a cooling tower, chiller, or HVAC loop. When metals such as steel and brass, or steel and copper, are connected, an electrochemical process begins. One metal (the “anode”) starts to corrode, while the other (the “cathode”) is protected. The flow of electrons between the two metals behaves much like a battery circuit. Over time, the anodic metal experiences accelerated decay. The result? Pitting, leaks, and eventual system failures.

Real-World Examples of Premature Failures

A common illustration of galvanic corrosion is found where a steel pipe nipple threads directly into a brass or copper fitting. The steel—being more active on the galvanic series—corrodes quickly, while the brass or copper remains relatively unharmed. In some cases, schedule 40 steel pipe can fail in as few as 6–10 years when paired improperly with a more noble metal and exposed to moderate or high-flow water. Even small components, like galvanized screws threaded into stainless steel, can initiate the corrosion process. This leads to equipment that looks sound on the outside but may be dangerously weakened in hidden areas.

Perhaps the most serious form of galvanic corrosion arises when dissolved copper in the water system plates onto steel surfaces. Even tiny amounts of copper can deposit on steel, effectively transforming it into a cathode. Once that happens, the steel corrodes at an accelerated pace. Because this process is often localized and difficult to spot, the damage can be extensive before anyone notices signs of a problem.

What’s at Stake for Facility Managers

Unchecked galvanic corrosion can lead to expensive, unplanned shutdowns in schools, hospitals, data centers, and other mission-critical environments. Slow leaks can become fast leaks, causing water damage that undermines building structures or disrupts operations. In industrial and laboratory settings, contaminated water from corroded lines can also affect production quality or research integrity. Ultimately, corrosion that goes unnoticed or unmanaged can severely shorten the lifecycle of pipes, valves, and heat exchangers—leading to higher capital and operational expenses.

Design Solutions and Best Practices

Fortunately, there are several strategies to curb galvanic corrosion:

1. Use Dielectric Unions: These fittings prevent direct metal-to-metal contact by incorporating non-conductive materials (e.g., plastic sleeves or washers), thus interrupting the electrical pathway.
2. Select Compatible Alloys: Whenever feasible, choose pipes, valves, and fittings that are close on the galvanic series. Using metals that have minimal potential difference drastically reduces corrosion risk.
3. Sacrificial Anodes: In certain systems, installing a third metal (like zinc or magnesium) diverts corrosive action away from the more important metals. However, sacrificial anodes must be properly sized, monitored, and replaced as needed.
4. Water Chemistry Control: Keeping dissolved copper and other metals in check by managing pH, alkalinity, and inhibitor levels is essential. Corrosion inhibitors, such as azoles for copper alloys, can help reduce plating onto steel components.
5. Regular Inspections and Monitoring: Periodic water testing, ultrasound scanning, or other non-destructive testing methods can reveal early signs of galvanic corrosion, allowing you to take action before failures occur.

Final Thoughts

Galvanic corrosion is a frequent culprit in cooling water systems that rely on multiple metals in their design. By recognizing the “battery effect,” facility managers can make informed decisions about metallurgy, chemical treatments, and maintenance protocols. In the long run, these preventive measures and design considerations can substantially extend equipment life, reduce emergency repairs, and keep your facility running smoothly year-round.