What matters most
Galvanic corrosion requires an electrical connection, a shared electrolyte, and a difference in corrosion potential under the actual exposure. A series helps indicate relative tendency in a specified environment, but electrolyte chemistry, passivity, area ratio, coatings, geometry, and polarization determine whether the couple becomes consequential.
Key takeaways
- Use a galvanic series developed for the relevant environment; a seawater ranking is not automatically a soil or potable-water ranking.
- Potential difference indicates driving tendency, not a stand-alone metal-loss rate.
- A small anodic area connected to a large cathodic area can concentrate attack.
- Stainless alloys and other passive materials can change behavior when passivity breaks down.
First confirm that a galvanic cell can exist
Dissimilar conductive materials must be electrically connected and share an ion-conducting electrolyte path. If either connection is absent, the same galvanic couple does not operate. Real systems may gain an unintended connection through bonding, reinforcing steel, grounding, supports, conductive fluids, or another remote path.
The evaluation should trace the complete circuit rather than focus only on metals touching at the leak location.
Use a series for the correct environment
A galvanic series ranks corrosion potentials measured in a particular electrolyte and condition. Soil, seawater, potable water, wastewater, condensate, concrete pore solution, and industrial fluids do not create identical rankings or kinetics.
Alloy composition, temperature, oxygen, flow, deposits, and surface condition also matter. A chart should state the environment and should be used as screening context, not as a universal compatibility certificate.
Do not confuse potential difference with corrosion rate
Greater potential separation can indicate a stronger galvanic driving tendency, but actual current and metal loss depend on polarization, electrolyte resistance, geometry, surface films, reaction kinetics, and time. Potential alone cannot produce a project-specific rate.
Field damage patterns, electrical continuity, exposure measurements, and material identification are needed before attributing a failure to galvanic action.
Evaluate cathode-to-anode area ratio
A small exposed anodic component coupled to a large cathodic surface may carry concentrated current density and deteriorate rapidly. The reverse area relationship can be less severe even when the same two metals are present.
Coatings change effective areas. If a nominally anodic member is coated but has a small defect while a large cathode remains exposed, attack can concentrate at the defect. Geometry and coating condition belong in every meaningful compatibility evaluation.
Account for passivity, crevices, and coatings
Stainless steel, aluminum, and other alloys can rely on passive films. Chlorides, crevices, low oxygen, temperature, deposits, and local chemistry can destabilize passivity and shift behavior. The alloy name alone does not establish its in-service electrochemical state.
Coating both members, coating only one member, isolating the connection, or changing drainage can produce different outcomes. Any control recommendation must reflect the actual assembly and governing design requirements.
Turn the chart into an engineering evaluation
Identify exact materials and grades, exposed areas, surface condition, coatings, joints, bonds, isolation, electrolyte, temperature, flow, geometry, and operating conditions. Map the damage relative to transitions and test continuity rather than assuming it.
Calicore provides galvanic evaluations and failure investigations. It can recommend further isolation, monitoring, material review, or specialist involvement, but does not provide cathodic-protection system design.
This article is general educational information, not a project-specific engineering conclusion. Site conditions, service environment, material, geometry, governing documents, and available evidence must be evaluated for the actual project. Calicore Engineering does not currently provide cathodic protection system design.
Frequently asked
Questions about this topic
Are stainless steel and carbon steel always incompatible?+
No. The outcome depends on environment, passivity, exposed area, electrical connection, coatings, geometry, and the consequence of localized attack.
Can a red-and-green compatibility chart determine service life?+
No. It may screen combinations, but service life requires project-specific material, exposure, geometry, protection, and time-based evidence.
Do two different metals cause galvanic corrosion if they do not touch?+
They can still be electrically connected through a remote conductive path. Both an electrical connection and a shared electrolyte path must be evaluated.
Primary references and further reading
- AMPP — What Is Corrosion?
- Caltrans — Corrosion Guidelines Public guidance discussing galvanic and infrastructure corrosion concepts.