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#070 Electrolytic Corrosion Protect Measures - 3

Category : Corrosion - Corrosion Protection
February18, 2011

(3) Anodic Corrosion protection

This is a method of corrosion protection by passivation of metals using anode polarization. It was initially adopted for stainless steels which require relatively small electrical potential for passivating and maintaining the passivated states. Thereafter, it was used for Ti and Ni, then for steels today.

When applying the anodic corrosion protect methods, following three points would be the issues

(1) Required Max. Electrical Curren

If the peak currents required to passivate active state metals are large, high capacity power supplies would initially be needed, and this would be uneconomical. However, small currents would be enough to slowly passivate as opposed to the large currents needed for rapid passivation.

(2) Passivation Electrical Potential Ranges

If the metal's passivation potential range is narrow, the anodic corrosion protect method would be difficult to apply since the metal may be re-activated or excessively passivated. The range is considered to be at least 50mV.

(3) Passivated State Maintenance Current

Certain current values are needed to maintain the metals in passivated states. Required maintenance current value increases with temperature increase as well as corrosiveness of the environments.

[Table 1] Passivation Maintenance Current Value
Metal TypesCurrent Density(mA/m2
18-8 Stainless Steel
25Cr-20Ni Stainless Steel
18-8 Stainless Steel w/Mo
13Cr Stainless Steel
25Cr Stainless Steel
HASTELLOY B (64Ni-28Mo-5Fe)
Carpenter20 (20Cr-29Ni-2.5Mo-3.5Cu)
Mild Steel150