Corrosion & Cathodic Protection

Corrosion Rate (Faraday)

CR = 3.27×10⁻³·i_corr·EW/ρ (mm/yr), i_corr in µA/cm².

i_corr (µA/cm²)

Equiv. weight EW (g)

Density ρ (g/cm³)

Anode current density ∝ A_cathode/A_anode. Small anode = danger.

Cathode area (cm²)

Anode area (cm²)

Galvanic current density on cathode (µA/cm²)

I = i_protect·area; sacrificial-anode life from capacity.

Structure area (m²)

Protect current (mA/m²)

Anode mass (kg)

Capacity (A·h/kg)

Utilization

life = (current − minimum) / corrosion rate.

Current wall (mm)

Min allowable (mm)

Rate (mm/yr)

Formula reference

Faraday rate: CR(mm/yr)=3.27×10⁻³·i_corr·EW/ρ and CR(mpy)=0.129·i_corr·EW/ρ, i_corr in µA/cm². EW = atomic weight / electrons transferred.

Galvanic: anode current density i_anode=(A_cathode/A_anode)·i_galv; the cathode-to-anode area ratio multiplies attack at the anode.

Cathodic protection: required current I=i_protect·area; anode charge Q=mass·capacity·utilization; life =Q/I.

Remaining life: =(t_current−t_min)/CR.