Galvanic Corrosion Risk Calculator
Screen galvanic corrosion risk between two dissimilar metals in contact, from potential difference and area ratio.
🔗 What is the Galvanic Corrosion Risk Calculator?
This galvanic corrosion risk calculator screens how likely two dissimilar metals in contact are to suffer accelerated corrosion when joined in a shared electrolyte, such as seawater, rain, or soil moisture. It looks up each metal's approximate position on the galvanic series, computes the potential difference between them, and combines that with the ratio of exposed cathode area to anode area to produce a simplified risk score.
This kind of screening is routine in marine hardware design, plumbing and piping systems mixing copper and steel, aircraft fastener selection, and outdoor structural connections where stainless steel, aluminum, and steel often meet. A designer bolting an aluminum bracket to a stainless steel frame, for example, needs to know upfront whether that pairing is a serious corrosion risk or a manageable one.
A common misconception is that potential difference alone determines corrosion severity. In reality, the area ratio between the two metals matters just as much: a large cathode paired with a tiny anode concentrates the same total galvanic current onto a small area, dramatically raising local current density and corrosion rate at the anode, even for a modest potential difference.
This calculator is useful for mechanical and marine engineers, materials selection teams, and students who need a fast first-pass galvanic risk screen without pulling out a full galvanic series reference table by hand.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Aluminum bracket bolted to passive stainless steel
Example 2 - Small copper fitting on a larger mild steel pipe
Example 3 - Passive stainless steel against titanium
❓ Frequently Asked Questions
🔗 Related Calculators
What causes galvanic corrosion?
Galvanic corrosion happens when two dissimilar metals with different electrode potentials are in electrical contact within a shared electrolyte. The less noble (more active) metal becomes the anode and corrodes faster than it would alone, while the more noble metal is cathodically protected.
What is the galvanic series?
The galvanic series ranks metals and alloys by their measured corrosion potential in a specific electrolyte, most commonly seawater. Metals higher (more negative/active) on the list corrode preferentially when coupled to metals lower (more positive/noble) on the list.
Why does the area ratio matter in galvanic corrosion?
The total galvanic current flowing between the two metals is roughly fixed by the circuit, but that current concentrates onto whichever electrode has the smaller area. A large cathode and small anode means high current density, and therefore much faster corrosion, at the anode.
Which metal corrodes in a galvanic couple?
The less noble metal, the one with the more negative potential on the galvanic series, becomes the anode and corrodes. The more noble metal becomes the cathode and is protected, corroding slower than it would on its own.
How can I prevent galvanic corrosion between two metals?
Choose metals close together on the galvanic series, electrically insulate the joint with a non-conductive gasket or coating, avoid a small-anode/large-cathode area ratio, or apply a sacrificial anode of an even more active metal to protect both.
Is stainless steel always safe to pair with other metals?
No. Stainless steel behaves very differently depending on whether its passive oxide film is intact. Passive stainless steel is quite noble and can accelerate corrosion of a less noble metal it is paired with, especially if the stainless area is large relative to the other metal.
What does a high risk score mean in this calculator?
A high score combines a large potential difference with an unfavorable (large cathode, small anode) area ratio. It flags pairings that are likely to cause fast, concentrated corrosion at the anode and should be avoided or isolated in design.
Does galvanic corrosion happen in dry air?
No, galvanic corrosion requires a continuous electrolyte path (moisture, humidity, seawater, soil) connecting both metals. Two dissimilar metals bolted together in a genuinely dry indoor environment will not experience meaningful galvanic corrosion.
What is a sacrificial anode?
A sacrificial anode is a deliberately chosen active metal, commonly zinc, magnesium, or aluminum, electrically connected to a structure to make itself the anode in the galvanic couple. It corrodes away over time so the protected structure does not.
Why is aluminum often a concern when paired with stainless steel or copper?
Aluminum sits well toward the active end of the galvanic series, while stainless steel (passive) and copper sit much closer to the noble end. The resulting large potential difference, especially with a small aluminum fastener against a large stainless or copper part, is a classic severe-risk pairing.