Metal Pair Settings
10
7.0
50 Ω
5 kg
Results
—
EMF (V)
—
Corrosion Current (mA)
—
Corrosion Rate (mm/yr)
—
Anode Life (yr)
Calculate galvanic corrosion current between dissimilar metal pairs and visualize the Pourbaix E-pH diagram. Estimate sacrificial anode life for cathodic protection design.
The driving force for galvanic corrosion is the difference in electrochemical potential between the two metals. The net current is limited by the polarization of the electrodes and the resistance of the electrolyte path.
$$I_{corr}= \frac{E_{cathode}- E_{anode}}{R_{sol}+ R_{pol}}$$Where:
$I_{corr}$ = Galvanic corrosion current (A)
$E_{cathode}, E_{anode}$ = Electrode potentials of the metals (V), which depend on material and pH.
$R_{sol}$ = Solution Resistance (Ω) - you control this in the simulator.
$R_{pol}$ = Combined polarization resistance of the electrodes.
The lifetime of a sacrificial anode is determined by its mass, the corrosion current, and its electrochemical capacity (how much charge it can provide per unit mass as it dissolves).
$$t_{life}= \frac{m \cdot C \cdot u}{I_{corr}}$$Where:
$t_{life}$ = Anode service life (years)
$m$ = Anode Mass (kg) - a direct input in the tool.
$C$ = Theoretical electrochemical capacity (A·h/kg)
$u$ = Utilization factor (typically ~0.85)
$I_{corr}$ = Corrosion current from the first equation.
Ship Hull & Offshore Structure Protection: Large blocks of zinc or aluminum alloys are welded to the steel hull below the waterline. These anodes corrode preferentially, preventing the expensive steel structure from rusting. The simulator helps engineers determine the number and mass of anodes needed for a vessel's expected dockyard period.
Underground Pipelines & Storage Tanks: Buried steel pipelines are protected by connecting them to magnesium anode bags placed in the surrounding soil. The area ratio (pipe surface vs. anode surface) and soil resistivity (simulated by Solution Resistance) are critical design parameters calculated with tools like this.
Automotive & Aerospace Components: Dissimilar metal joints are common, like aluminum body panels with steel fasteners. Engineers use this principle to select compatible materials or design insulating gaskets to prevent unintended galvanic cells from forming due to road spray or humidity.
Water Heaters & Domestic Plumbing: Many water heaters have a replaceable "sacrificial rod" made of magnesium or aluminum suspended in the tank. It corrodes instead of the steel tank lining, dramatically extending the appliance's life. The life estimate function directly models this maintenance schedule.
When you start using this type of calculation tool, there are a few common pitfalls. The first is assuming that a larger potential difference always means more severe corrosion. While the driving force does increase, the actual corrosion current is heavily influenced by the circuit's total resistance $R_{total}$. For example, connecting iron and copper in pure water (high resistance) results in much slower corrosion compared to seawater (low resistance). If you adjust the "solution resistance" parameter in the tool, you should see the current value drop significantly.
The second point is not accounting for the material's "surface condition". The Pourbaix diagrams and equilibrium potentials in this tool assume clean, bare metal surfaces. In reality, surfaces may have oxide films (passive films) or peeling paint. For instance, aluminum is often protected by a passive film, so its actual corrosion rate is usually slower than the theoretical value. Conversely, if that film is locally damaged, corrosion can progress rapidly in that spot (pitting corrosion), so caution is needed.
The third point is the practical sense of area ratio. You can easily set something like "A_cathode / A_anode = 100" in the tool, which in the field corresponds to scenarios like "a single small stainless steel bolt fastening a large carbon steel plate." The calculation will show a sharp increase in the corrosion rate of the anode (the bolt). In design, the golden rule is to "keep the cathode area small and the anode area large." When dissimilar metal contact is necessary, remember that the basic approach is to electrically isolate them using insulating washers or coatings.
These corrosion and protection calculations are actually connected at the root to various other fields. Battery engineering is a prime example. Galvanic corrosion is essentially an unintentionally formed "short-circuited battery." Conversely, in developing lithium-ion batteries or fuel cells, calculating the electromotive force and current from electrode material combinations and controlling interfacial reactions are based on the very same fundamental theory this tool uses.
Another field is Electrochemical Machining (ECM). While corrosion is the "unwanted dissolution of material," there is a technology that actively utilizes this principle to machine hard metals into complex shapes. The principle of dissolving the anode (the workpiece) is the same; the advanced aspect lies in the precise control of the tool (cathode) shape and electrolyte resistance.
Finally, it's deeply related to Materials Surface Engineering. For corrosion protection, plating (e.g., galvanizing) and anodizing (like anodized aluminum) are widely used. These are technologies that intentionally increase the resistance $R_{total}$ by forming a protective surface layer or alter the material's own potential. If you're considering "galvanized steel sheet" in the tool, try thinking of the parameters while visualizing the two-layer structure: the anode is the zinc coating and the cathode is the underlying steel sheet. This will deepen your understanding.
As a next step, I recommend learning about "polarization diagrams". This tool's calculation uses a simplified model based on the equilibrium potential difference, but the actual corrosion rate is determined by how easily the anode dissolves (anode polarization) and how readily reduction reactions (e.g., oxygen reduction) occur at the cathode (cathode polarization). Understanding the "Tafel extrapolation method", which determines the corrosion current from the intersection of polarization curves, will enable you to make more realistic assessments.
Mathematically, Faraday's law appearing here can be viewed as a simple form of a one-dimensional advection-diffusion equation. If you want to track corrosion progression more rigorously over time and space (in the depth direction), there is the world of corrosion simulation using the Finite Element Method (FEM). This is a fairly advanced CAE domain that couples and solves for changes in electric field distribution accompanying changes in the corroded area's shape.
For a practical next topic, try tackling "localized corrosion". This tool calculates based on the premise of "general corrosion," where the entire surface dissolves uniformly. However, the problems encountered in the field are often corrosion types that concentrate "locally," such as pitting, crevice corrosion, and stress corrosion cracking. Since these occur due to combinations of material, environment, and stress, a good next learning goal would be to research their mechanisms and prevention methods (e.g., selecting molybdenum-containing stainless steels).