Galvanic Corrosion and Area Ratio
Computes galvanic current and anode penetration for two dissimilar metals, then reverses the area ratio.
Example
You enter
- More active metal's potential (V) -0.61
- More noble metal's potential (V) -0.36
- Cathodic current density (mA/sq ft) 5
- Cathode area (sq in) 1000
- Anode area (sq in) 1
- Anode consumption (lb per A-yr) 20.1
- Anode density (lb/cu ft) 490
You get
- Driving voltage 0.25
- Galvanic current 34.72 mA, set by what the cathode supports
- Anode current density a per ft² 5
- Attack on the anode, as given 2.461 in/yr at 5.00 A/sq ft
- With the areas reversed 0.00246 mils/yr -- immeasurably small
- Attack ratio 1000000
Checked against published worked examples from: King Fahd University of Petroleum and Minerals.
Details, formula, and sources
ScopeA steel fastener in a copper plate corrodes 2.5 in a year; the reverse is immeasurable -- a million times less. A small cathode is safe, a small anode is not.
Formula or tablegalvanic current = cathodic current density x cathode area; anode current density = that current / anode area; penetration = anode density x electrochemical equivalent / metal density.
Source and editionPotentials measured in the actual service electrolyte; published galvanic series and the materials engineer govern.
Free accessPublic electrochemistry; galvanic series are widely published.
What governsEstimate. AHJ and licensed professional govern.
API field namesanode_potential_v, cathode_potential_v, cathodic_current_density_ma_per_sqft, cathode_area_sqin, anode_area_sqin, electrochemical_equivalent_lb_per_a_yr, anode_density_pcf, driving_voltage_v, galvanic_current_ma, anode_current_density_a_per_sqft, penetration_in_per_year, reversed_penetration_mils_per_year, attack_ratio
- Cathodic limit current is set by what the cathode supportsspec-v1770 method
- Electrolyte potentials are specific to the service electrolyte and temperaturefield measurement