Avoiding Galvanic Corrosion When Mixing Metals in Fabrication

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Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte such as moisture or condensation, causing the less noble metal to corrode faster. To avoid it, select compatible metal pairs, electrically isolate the joints, control the area ratio, and specify suitable fasteners and finishes.

Understanding the Galvanic Series

Every metal has a position in the galvanic series, which ranks metals by their tendency to corrode when coupled in an electrolyte. Metals far apart in the series create a larger potential difference and a stronger corrosion driving force.

Stainless steel is passive and sits near the noble end, so it usually acts as the cathode. The partner metal, such as carbon steel, aluminum or galvanized surfaces, becomes the anode and is the one that deteriorates. Checking the series before finalizing a design is the simplest first step.

Choosing Compatible Metal Pairs

Where possible, choose metals close together in the galvanic series. Stainless steel grades coupled with other stainless grades present minimal risk, while stainless against aluminum or plain carbon steel needs careful management.

Prefer matching alloy families for structural joints
Avoid direct contact between stainless and aluminum in wet areas
Confirm the grade with the engineer before ordering components

Electrical Isolation Methods

Breaking the electrical path is the most reliable protection. Non-conductive gaskets, sleeves, washers and coatings placed between dissimilar metals stop current from flowing between them.

Nylon or EPDM washers, isolating bushings and tape-based barriers are common choices. Isolation must cover the whole contact surface, because a single bridging fastener or drip of water can reconnect the circuit.

Area Ratio and Design Geometry

The ratio of cathode area to anode area strongly affects corrosion speed. A large stainless component connected to a small carbon steel or aluminum part concentrates the corrosion current on that small area, which can fail quickly.

Where a dissimilar joint is unavoidable, design the more noble, larger part as the less exposed element, or use a larger, more protected anodic section so that any loss is spread out and easier to manage.

Fasteners, Welds and Surface Finishes

Fasteners are a frequent weak point. Use stainless steel bolts, nuts and screws with a compatible grade for stainless assemblies, and avoid zinc-plated or plain carbon fasteners in direct contact with stainless parts.

Finishing also matters. Hot-dip galvanizing and powder coating provide barrier protection, but scratches or damaged coatings expose the base metal. Specify coating thickness and inspect edges, holes and weld zones after finishing.

Environment and Maintenance Considerations

Exposure conditions define how severe galvanic attack will be. Coastal air, condensation, standing water, road salts and industrial pollutants all increase electrolyte activity and accelerate corrosion.

Provide drainage so water does not collect at joints
Clean stainless surfaces periodically to remove deposits
Inspect dissimilar joints during routine maintenance visits

Frequently asked questions

Does stainless steel always cause galvanic corrosion when touching other metals?

Not always. Corrosion depends on the metal pair, the presence of an electrolyte and the area ratio. Dry indoor joints with proper isolation usually show little or no attack.

Can I weld stainless steel directly to carbon steel?

Dissimilar welding is possible with the right filler metal, but the weld joint can still be vulnerable in wet service. Discuss the joint with the engineer to determine whether isolation or mechanical connection is more suitable.

Are plastic washers enough to prevent galvanic corrosion?

They help considerably when they fully separate the metals and are not damaged during installation. Sleeves and sealants are also needed on bolted joints to stop moisture bridging the gap.

Which fasteners should I use with stainless steel assemblies?

Use stainless steel fasteners of a compatible grade. Avoid plain carbon or zinc-plated fasteners in contact with stainless, as they will corrode and can stain or weaken the joint.

Common mistakes to avoid

Using zinc-plated or carbon steel bolts in stainless assemblies and leaving bare metal edges exposed after cutting or drilling are the most common errors. Both create an easy path for galvanic attack that is often discovered only after damage appears.

Our recommendation

Specify the material pairing, isolation method and fastener grade on the drawing before production, and request a finishing check on all cut edges and holes. Designing out dissimilar contact is always more reliable than relying on coatings alone.

Summary

Galvanic corrosion is manageable through compatible material selection, electrical isolation, sensible area ratios and correct fasteners and finishes. Planning these details early avoids costly repairs later.

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