Understanding the Nuts and Bolts of Galvanic (or Bimetallic/Dissimilar Metal) Corrosion | Knowledge & Awareness is Key!

First, we need to better understand why galvanic corrosion exists.?

Galvanic corrosion occurs when two uniquely different metals are physically in contact with each other and immersed in a common electrolyte (e.g.,?water/moisture) or when the same metal is exposed to an electrolyte with different concentrations. In a galvanic (or bimetallic) couple, the more active metal (the anode) corrodes at an accelerated rate, and the more noble metal?(the cathode) corrodes at a slower rate.

Galvanic corrosion frequently afflicts structures?such as commercial roofing, infrastructure elements, and facades. It is very common in the restoration of existing structural steel and concrete reinforcement.

In the presence of moisture or grime, metals with varying electrochemical potentials encounter each other, setting off electrochemical reactions that lead?to the deterioration of one or both metals. You are quite literally creating a battery with the movement of electrons. That’s when corrosion begins!

Key Metal Combinations

(See Dissimilar Metals Chart below.)

The combination of dissimilar metals will either accelerate the corrosion process or do nothing…but it’s important to understand which combinations of metals will work against you.

1. Aluminum and Cast Iron?| NO REACTION
2. Copper and Steel?| CORROSIVE ACTION!
3. Stainless Steel and Aluminum?| BORDERLINE / NO REACTION
4. Nickle Copper and Steel | CORROSIVE ACTION!

Identifying Galvanic Corrosion

Galvanic corrosion often manifests as chalky mineral deposits, sometimes tinged with a rusty-orange hue (ferrous corrosion). These clusters usually accumulate in concealed areas of a building, such as behind panel systems or under parapet caps. This corrosion may remain undetected until it causes interior water leaks or fosters mold growth, underscoring the importance of proactive assistance and scheduled condition and maintenance.?Identify dissimilar metals quickly and make corrections before things get really bad!

Expert Insights

Robert Caputo , an authority in galvanic corrosion, underscores the significance of routine inspections to detect and address galvanic corrosion before it escalates into severe structural issues. Rob advocates partnering with seasoned specialty contractors for annual roof, garage,?and facade inspections, facilitating early detection and mitigation of corrosion-related concerns.

ALWAYS LOOK! BE PROACTIVE, NOT REACTIVE!

Prevention and Mitigation

• The separation of dissimilar metals should be your first line of defense when possible.

? Between bolts, fasteners, and materials in general.

? Spacer materials like rubber, plastic, nylon, or neoprene can be interposed between metals to provide electrical insulation and minimize corrosion risk.

• Coating materials (i.e. – bituminous coatings, zinc-rich primers, epoxies, etc.) ?

? Zinc-rich primers are sacrificial coatings and slow the process down.

• The inclusion of zinc anodes within concrete repairs as sacrificial anodes to help take the brunt of corrosion instead of the structural steel or reinforcement.
• Elimination of the electrolyte (i.e. – water or salty water) that will close the circuit required to induce corrosion.

? Waterproofing systems are a great way to remove the intrusion of water.

• Induced current systems are also an option to help slow or halt the corrosion process down.

Stainless fasteners offer another effective strategy for avoiding galvanic corrosion, providing a compatible alternative to traditional metal fastenings.

Conclusion

Galvanic corrosion poses a substantial threat to the structural integrity of buildings; being aware of this during and after construction is key to avoiding future issues. Making proactive maintenance and preventive measures imperative is always prudent for any property manager and/or owner. By comprehending the causes and manifestations of galvanic corrosion and adopting appropriate mitigation strategies, property owners and managers can safeguard their investments and ensure the longevity of their buildings.

For more information on galvanic corrosion and proactive maintenance solutions, contact your nearest Western Specialty Contractors branch.?We are here to help guide you and be your partner!

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