Galvanic Corrosion: Preventing Failures in Closed Loop Systems

In industrial and commercial water systems, especially closed loops, corrosion isn’t just a nuisance – it’s a system-threatening risk. One of the most overlooked but destructive forms of corrosion is galvanic corrosion, a phenomenon that occurs when two dissimilar metals are in electrical contact within the presence of an electrolyte solution. Without careful attention to system design and treatment strategies, galvanic corrosion can quietly compromise metallic structures, degrade performance, and lead to significant corrosion-related failures in piping, pumps, heat exchangers, and fittings.

Understanding what causes galvanic corrosion, how it behaves in closed loop systems, and how to prevent it is essential for engineers, facility managers, and operators looking to minimize lifecycle costs, extend equipment life, and maintain water system integrity.

What Is Galvanic Corrosion?

Galvanic corrosion – also called bimetallic corrosion – is a type of electrochemical corrosion that occurs when two dissimilar metals are in direct contact in the presence of a conductive medium, usually an electrolyte like water. The difference in electrical potential between the two metals sets up a galvanic cell, causing one metal (the anodic metal) to corrode more rapidly while the other (the cathodic metal) is protected.

 

How It Works (Simplified):

1. Two metals – say, copper and carbon steel – are joined in a piping system.
2. Water in the system acts as the electrolyte, facilitating electron flow.
3. The less noble metal (more active on the galvanic series) becomes the anode and begins to corrode.
4. The more noble metal (like copper or stainless steel) becomes the cathode, attracting electrons and remaining protected.

The resulting galvanic corrosion current causes material loss on the anodic surface, leading to accelerated corrosion around joints, fittings, and structural connections – especially where electrical isolation is not properly implemented.

Real-World Examples of Galvanic Corrosion

• Copper pipe connected to galvanized steel: The zinc coating on galvanized steel acts as the anode and undergoes galvanic corrosion, eventually failing near the connection point.
• Stainless steel fasteners on carbon steel supports: The carbon steel corrodes around the joint, while the stainless steel remains largely unaffected.
• Marine environments: Aluminum hulls in contact with steel supports or copper skin face rapid galvanic degradation due to the high conductivity of saltwater.

In all these cases, galvanic coupling between dissimilar metals creates a hidden failure point – often only visible once significant galvanic corrosion has already occurred.

Why Closed Loop Systems Are Especially Vulnerable

While closed loop systems are often seen as lower risk due to their controlled environments and reduced oxygen exposure, they are not immune to galvanic corrosion. In fact, several factors increase risk:

• Initial fill water with high conductivity can create a corrosive electrolyte.
• Systems with dissimilar materials – like copper, stainless steel, and carbon steel – are common.
• Improper or degraded corrosion inhibitors fail to protect vulnerable metals.
• Micro-leaks introduce oxygen, increasing conductivity and corrosion potential.

Because water isn’t regularly flushed, galvanic reactions can persist unnoticed until corrosion rates reach failure thresholds – particularly near welds, valves, and heat exchangers.

How Galvanic Corrosion Happens in Closed Loop Systems

Galvanic corrosion in closed loop systems is often misunderstood or underestimated because the system is sealed and not exposed to large volumes of makeup water. But in reality, several design and maintenance factors make closed loops vulnerable, especially over time.

These systems commonly combine different metals – such as carbon steel, copper, stainless steel, aluminum, or galvanized steel – in piping, fittings, heat exchangers, or structural supports. When these dissimilar metals are connected and immersed in water, they form an electrochemical cell. Water acts as the corrosive electrolyte, and a galvanic current can begin flowing between the metals.

Without the presence of oxygen, the reaction is slower – but it still occurs, especially if the system has high conductivity, is chemically unbalanced, or contains micro-leaks introducing air over time.

Common conditions that accelerate galvanic corrosion in closed loops include:

• Initial system fill with high TDS (total dissolved solids) – Untreated water provides a conductive electrolyte, especially if it includes chloride, sulfate, or dissolved salts.
• Differing anodic index values between materials – For example, copper and carbon steel have enough voltage difference to drive a corrosion cell under certain conditions.
• Improper inhibitor dosage or degradation – When corrosion inhibitors are underfed, depleted, or not formulated to protect multiple metals, galvanic activity accelerates.
• Relative surface area mismatch – A small anodic metal (like a carbon steel fastener) in contact with a large cathodic metal (like stainless steel paneling) corrodes faster due to the surface area effect.

Even small galvanic couplings – such as stainless steel fasteners bolted to carbon steel frames – can lead to crevice corrosion and failure over time if left untreated.

Learn more about preventing corrosion through water treatment.

Examples of Galvanic Pairings in Closed Loops

Understanding which metals are galvanically active against one another is critical to both system design and troubleshooting. Here are a few practical examples of pairings that can lead to accelerated corrosion:

• Copper pipe and galvanized steel – This is a textbook case. The zinc coating on galvanized steel acts as the anodic metal and corrodes first, especially at joints or threaded fittings.
• Aluminum heat exchangers and stainless steel components – In high-conductivity systems, the aluminum exchanger surface becomes vulnerable due to its active position in the galvanic series.
• Carbon steel tees and copper risers – If uninsulated and untreated, this common combo can produce visible signs of corrosion in a matter of months.

In marine-adjacent environments or facilities using salt-based water softeners, conductivity is often higher, which increases galvanic current flow and shortens time to failure.

The Role of Electrolyte Composition

The presence of an electrolyte – meaning a conductive liquid – is essential for a galvanic reaction to occur. In most closed loop systems, the electrolyte is the system water itself, and its corrosiveness depends on:

• pH level – Low pH (acidic water) is highly corrosive to most metals, especially carbon steel and aluminum.
• Dissolved oxygen – Though closed systems are low in oxygen by design, leaks, fresh fill water, or poor deaeration allow O₂ to enter and drive corrosion reactions.
• Chloride and sulfate content – These ions increase conductivity and corrosion potential – especially in systems with galvanized steel, where zinc is especially vulnerable.
• Temperature – Higher operating temps accelerate all forms of corrosion, including galvanic.

Even in low-oxygen environments, electrochemical processes continue at measurable rates, particularly when systems lack electrical isolation or proper chemical treatment.

Material Compatibility and the Galvanic Series

Choosing compatible materials is one of the most effective design-based ways to minimize galvanic corrosion. Engineers often reference the galvanic series, which ranks metals based on their nobility (resistance to corrosion) in seawater or a comparable electrolyte.

When two metals are far apart on the galvanic series and placed in direct contact, the one lower on the list (less noble) becomes the anodic metal and corrodes. Examples:

• Zinc is highly anodic – often used for cathodic protection
• Aluminum and carbon steel are moderately active
• Copper, stainless steel, and nickel alloys are more noble

Systems using metallic coatings or zinc-based corrosion inhibitors rely on this principle to protect structural connections and reduce the risk of accelerated corrosion at contact points.

Factors That Accelerate Galvanic Corrosion

In closed loop systems, galvanic corrosion is rarely caused by a single design flaw. It’s typically the result of multiple compounding factors – including material choices, system chemistry, physical design, and operational conditions. The more of these elements are present in combination, the faster corrosion occurs.

Material Pairings Without Isolation

When two dissimilar metals are connected without proper electrical insulation, galvanic activity becomes inevitable. This is especially problematic when:

• More noble metals like stainless steel or copper are joined to less noble metals such as carbon steel or galvanized steel.
• The surface area ratio is imbalanced – for example, a small anodic metal (carbon steel bolt) on a large cathodic metal (stainless steel plate) corrodes at an accelerated rate.
• The metals are joined using conductive gaskets, fittings, or fasteners that allow current flow through the connection.

Electrical continuity between two metals creates a galvanic circuit, and without electrical isolation, current flows freely and corrosion occurs rapidly at the anodic interface.

Presence of a Corrosive Electrolyte

Even in a closed loop system, the fluid circulating through the system may have qualities that make it highly conductive. Conditions that contribute to a corrosive electrolyte solution include:

• High conductivity from dissolved solids (e.g. chlorides, sulfates, iron ions)
• Low or unstable pH, which promotes general and galvanic corrosion
• Biological activity that releases organic acids and gases, creating micro-pockets of corrosive conditions
• Use of improperly treated makeup water that raises the ionic load of the system

As conductivity increases, so does the galvanic current – which in turn increases the corrosion rate at anodic sites. This is why water chemistry should be tightly controlled and monitored in all closed loop systems.

Microbiological Activity

Microbiologically Influenced Corrosion (MIC) can exacerbate galvanic reactions. Biofilms act as local electrolyte modifiers – they trap oxygen and shift pH in specific areas, creating corrosive micro environments.

When bacteria colonize metallic surfaces, especially around welds or connections, they produce acidic byproducts and elevate localized electrical conductivity. This creates miniaturized corrosion cells that behave similarly to classic galvanic coupling – but are harder to detect and treat.

Left unchecked, this form of crevice corrosion can lead to under-deposit corrosion and pitting, particularly on carbon steel and copper alloys.

Temperature and Pressure Extremes

Heat accelerates every step of the electrochemical reaction involved in galvanic corrosion. This includes:

• Increased mobility of ions in the electrolyte
• Faster degradation of corrosion inhibitors
• Elevated reaction rates between anodic and cathodic surfaces

Closed loop systems used in heating applications, such as hot water loops or steam condensate systems, face higher corrosion risk than chilled water systems – especially if the metallurgy includes aluminum heat exchangers or galvanized piping.

Systems under elevated pressure can also force more dissolved gases (oxygen, CO₂) into solution, increasing both uniform and localized corrosion risks.

Design-Related Triggers

Certain mechanical and design choices increase the chances of galvanic reaction:

• Turbulence at fittings and tees can strip protective films, exposing raw metal
• Dead legs and low-flow zones allow sediment, corrosion products, or biological growth to accumulate
• Mixed-metal assemblies used in heat exchangers or skid systems often combine stainless steel, carbon steel, and copper – a high-risk combination if not protected chemically
• Threaded joints and gaskets often bring dissimilar materials into contact at vulnerable points

Proper design review and standardization of materials during system construction is key to limiting unnecessary galvanic coupling and avoiding the need for future retrofits.

How to Prevent Galvanic Corrosion in Closed Loop Systems

Preventing galvanic corrosion in closed loop systems requires a combined strategy of smart design choices, proper material selection, chemical treatment, and operational discipline. While no system is entirely immune, a well-constructed and well-managed loop can operate for years without measurable degradation.

Use Compatible Materials

The first and most effective step in minimizing galvanic corrosion is choosing compatible metals during system design. The further apart two metals are on the galvanic series, the greater the potential for galvanic activity when they’re connected.

Best practices include:

• Avoiding direct connections between metals with large nobility differences (e.g. zinc and copper, or aluminum and stainless steel)
• Standardizing metallurgy across piping, fittings, and heat exchangers to reduce dissimilar pairings
• Referencing anodic index charts or galvanic series tables when evaluating material combinations for system components

In cases where different metals must be used (e.g. for mechanical or thermal performance), the focus should shift to isolating those materials.

Electrically Isolate Dissimilar Metals

If mixed metals can’t be avoided, they must be electrically insulated to break the circuit that enables galvanic coupling. This is done by:

• Installing non-conductive gaskets, bushings, or dielectric unions between dissimilar metal joints
• Using coatings or sleeves on bolts, fasteners, or pipe connections
• Ensuring that electrical continuity is broken in places where dissimilar metals come into contact in the presence of water

This strategy is especially important in structural connections, such as where stainless steel fasteners meet carbon steel supports, or in heat exchangers that involve copper tubes in steel shells.

Apply Corrosion Inhibitors

A chemical treatment program tailored to the system’s metals is essential. Inhibitors function by forming a protective film over metal surfaces, reducing reactivity and suppressing the electrochemical process.

Key inhibitor types for closed loops:

• Nitrite-based blends – Effective for carbon steel, especially when pH and conductivity are controlled
• Molybdate and silicate inhibitors – Provide multi-metal protection, particularly for systems with copper and stainless steel
• Zinc salts – Used for sacrificial protection in some formulations but must be balanced to avoid precipitation
• Polymer dispersants – Help keep metal ions, debris, and biofilm from depositing and creating crevice corrosion

The most effective programs are multi-functional, combining corrosion inhibition, pH buffering, and microbiological control into one formulation to minimize chemical interactions and simplify dosing.

Maintain Water Chemistry

Chemical inhibitors can only work if the system’s water chemistry is within acceptable operating limits. Routine monitoring is critical to sustaining corrosion protection and identifying shifts before damage occurs.

Parameters to monitor include:

• pH – Target range depends on metals present; most loops aim for 8.0–10.5 for mild steel systems
• Conductivity – Should be low and stable; sudden increases may signal leaks, contamination, or chemical imbalance
• Inhibitor residuals – Must be tested regularly and adjusted based on system volume, losses, and degradation
• Iron, copper, and zinc levels – Rising metal ion concentrations may indicate active corrosion or material loss

Sampling should occur at representative points in the system – including near risers, heat exchangers, and pump discharges – and tracked over time to establish performance trends.

Minimize Oxygen Intrusion

Oxygen is a key contributor to both general and galvanic corrosion. Even in a closed loop, oxygen can enter through:

• System fill water that hasn’t been properly deaerated
• Leaks or loose fittings
• Open expansion tanks or improper venting
• Use of non-barrier tubing or gaskets

Best practices to limit oxygen exposure include:

• Using closed expansion tanks and air separators
• Filling systems with deoxygenated water or using scavengers
• Promptly addressing leaks or pressure losses
• Employing pressure-maintenance systems to prevent oxygen ingress

Avoid Material Traps and Dead Legs

System geometry plays a big role in corrosion risk. Avoiding dead legs, low-flow zones, or mixing tees with poor circulation helps:

• Prevent sediment accumulation and under-deposit corrosion
• Minimize temperature differentials that create condensation or stratification
• Ensure consistent chemical distribution throughout the system

Proper flushing during startup and occasional flow balancing can also prevent localized conditions that drive galvanic reaction.

How R2J Supports Galvanic Corrosion Prevention

Preventing galvanic corrosion in closed loop systems isn’t just about chemistry – it’s about integrating the right design, monitoring, and treatment strategies into one cohesive program. At R2J, we specialize in helping facility operators, engineers, and service contractors build and maintain systems that are reliable, cost-effective, and corrosion-resistant.

System Assessments & Site evaluations

Our Certified Water Technologists perform in-depth system audits, mapping piping and component metallurgy to identify galvanic risk areas like copper-to-steel or aluminum-to-stainless interfaces. They also test for water conductivity, pH, and oxygen levels to detect corrosion potential early

Custom-Tailored Chemical Treatment Programs

We develop and supply closed loop corrosion inhibitor blends that are:

• Multi-metal compatible, protecting carbon steel, copper, aluminum, and stainless steel
• Formulated to support electrical isolation strategies and system design constraints
• Optimized for low conductivity and stable pH environments
• Supported with detailed dosing, testing, and monitoring guidelines

Whether you’re managing a heating loop in a commercial building or a high-efficiency industrial cooling circuit, our products are designed to minimize corrosion reactions and extend system life.

R2J supplies a full line of closed system treatments including multi-metal corrosion inhibitors, scale reducers, and oxygen scavengers tailored to each loop.

Ongoing Monitoring and Technical Support

R2J offers routine testing support, on-site inspections, and remote water quality monitoring to keep your loop chemistry in check. We work with your operations team to:

• Catch early signs of galvanic current activity
• Adjust inhibitor levels and system parameters as conditions change
• Prevent scaling, fouling, and crevice corrosion before they cause downtime

From commissioning to ongoing optimization, we help ensure your loop stays efficient, compliant, and corrosion-free.

Frequently Asked Questions

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Build a More Resilient Closed Loop System with R2J

Galvanic corrosion doesn’t have to be an inevitable part of operating a closed loop system. With the right design, materials, and treatment program, you can minimize risk, reduce long-term maintenance costs, and extend the life of your critical infrastructure.

R2J partners with facilities across industries to deliver practical, evidence-backed water treatment strategies that prevent corrosion from the inside out. If you’re ready to build smarter, more stable closed loop systems, we’re here to help.

Contact us today to learn how R2J can help you prevent galvanic corrosion before it starts.