Galvanic Series & Dissimilar Metal Corrosion Calculator

The fundamental driving force for galvanic corrosion is the difference in electrochemical potential between the two metals when measured in the same environment. This is the Open Circuit Potential (OCP) difference, or Electromotive Force (EMF).

Here, $E_{cathode}$ and $E_{anode}$ are the standard potentials (in Volts) of the noble and active metals from the galvanic series. A positive EMF indicates a spontaneous reaction where the anode will corrode.

The actual galvanic current density ($i_{galv}$), which determines the corrosion rate of the anode, is calculated using a simplified circuit model. The EMF drives current through the total resistance, which is the sum of the anode's polarization resistance ($R_p$) and the solution resistance ($R_{sol}$).

Variables:
- $i_{galv}$: Galvanic current density at the anode surface (A/cm²).
- $R_p$: Anode Polarization Resistance (Ω·cm²). It represents how easily the anode surface undergoes the corrosion reaction.
- $R_{sol}$: Solution Resistance, approximated as $ \frac{1}{\kappa \cdot A_a} $ where $\kappa$ is conductivity.
- $A_a$: Anode Area (cm²). This is crucial because the total current is distributed over this area to get the density.

Marine & Offshore Structures: Bolts and fasteners made of stainless steel (cathode) connecting aluminum hull plates (anode) will cause rapid pitting of the aluminum in seawater. This simulator helps select compatible metals or specify protective coatings and sacrificial anodes.

Automotive Engineering: Dissimilar metal joints are everywhere, like aluminum body panels attached to steel frames. Engineers use tools like this for first-pass screening to predict corrosion risk in environments with road salt, guiding decisions on insulation, sealants, and material choice.

Aerospace Design: Aircraft use advanced alloys like titanium and carbon-fiber composites (cathodic) alongside aluminum alloys. Predicting galvanic current density is critical for the longevity of joints and fasteners, especially in humid or coastal operational environments.

CAE Integration in Electronics: In microelectronics, tiny solder joints (anode) connect to gold-plated contacts (cathode). Moisture can create a galvanic cell. The calculated current density from this model can be used as a boundary condition in Finite Element Method (FEM) software like COMSOL's Corrosion Module to visualize current distribution and identify hot spots for failure.

There are a few key points you should be aware of when starting to use this tool. First, "the galvanic series can change depending on the environment." This tool's reference is "seawater." However, in environments like fresh water, soil, or specific chemical solutions within a plant, the order of metals can reverse. Stainless steel is typically noble, but it can become active in oxygen-depleted environments. So, always verify the application environment.

Next, understand that "the risk level is not absolute." Even if the tool outputs "Danger," the actual corrosion rate can vary greatly with environmental conductivity and temperature. For instance, in dry air where little current flows, a large potential difference often isn't a problem. Conversely, a "Caution" level pairing can cause severe damage in a short time if constantly exposed to saltwater. Please use the output strictly as a relative guideline.

Finally, consider "whether you are only looking at the initial state." As corrosion progresses, surfaces can become covered with oxide films or corrosion products can build up, increasing resistance. This can sometimes reduce the current (passivation). On the other hand, if the anode area continuously decreases, "self-eating" can occur, where the current density increases and accelerates corrosion. The tool's calculation is for the "initial, momentary" state. To consider changes over time, more advanced analysis incorporating polarization curve data is necessary.