Galvanic Compatibility: Cast Iron + Stainless Steel
High Risk — 0.35V Anodic Index Difference
Cast Iron will corrode preferentially in this pairing.
Compatibility Assessment
The 0.35V difference puts this in the high-risk category. Stainless steel components on cast iron housings or pipes will accelerate corrosion of the cast iron.
| Property | Cast Iron | Stainless Steel |
|---|---|---|
| Anodic Index | 0.85V | 0.5V |
| Galvanic Role | Anode (corrodes) | Cathode (protected) |
| Voltage Difference | 0.35V — High Risk | |
Compatibility by Environment
The acceptable voltage difference depends on the operating environment:
- Harsh (outdoor/marine): ❌ Not recommended (>0.15V)
- Normal (indoor/uncontrolled): ⚠️ Use caution (>0.25V)
- Controlled (HVAC): ✅ Compatible (≤0.50V)
Thresholds per MIL-STD-889 guidelines. Harsh = saltwater, industrial, outdoor. Normal = warehouse, uncontrolled indoor. Controlled = temperature/humidity regulated.
How Galvanic Corrosion Works
When two dissimilar metals are in electrical contact and exposed to an electrolyte (water, especially saltwater), an electrochemical cell forms:
- The more anodic (active) metal — Cast Iron in this case — loses electrons and corrodes.
- The more cathodic (noble) metal — Stainless Steel — is protected and may even corrode less than it would alone.
- The corrosion rate increases with the voltage difference between the metals and the amount of moisture present.
The area ratio also matters critically: a small piece of anodic metal in contact with a large cathodic surface will corrode much faster than the reverse. For example, cast iron rivets in a stainless steel sheet will fail quickly, while stainless steel rivets in cast iron are less problematic.
Prevention Strategies
- Insulating gaskets/washers: Place non-conductive material between the metals to break the electrical path.
- Protective coatings: Apply paint, lacquer, or specialized coatings to one or both metals.
- Sacrificial anodes: In critical applications, add a more anodic (active) metal that corrodes preferentially.
- Design for drainage: Ensure water cannot pool at the junction of dissimilar metals.
Related Metal Pairings
- Aluminum + Stainless Steel — High Risk (0.4V)
- Steel + Stainless Steel — High Risk (0.35V)
- Stainless Steel + Copper — Low Risk (0.15V)
- Stainless Steel + Brass — Low Risk (0.1V)
- Stainless Steel + Bronze — Low Risk (0.1V)
- Stainless Steel + Titanium — Low Risk (0.2V)
Check any metal combination
Use our Interactive Galvanic Compatibility Checker to test any two metals for galvanic corrosion risk — including anodic index, environment ratings, and prevention recommendations.
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