Friday, December 4, 2009

How Do We Know When We Have Enough Cathodic Protection?
























We know whether or not we have enough current by measuring the potential of the steel against a standard reference electrode, usually silver silver/chloride (Ag/AgCl sw.), but sometimes zinc (sw.).


Current flow onto any metal shifts its normal potential in the negative direction. History has shown that if steel receives enough current to shift the potential to (-) 0.800 V vs. silver / silver chloride (Ag / AgCl), the corrosion is essentially stopped.

Due to the nature of the films which form, the minimum (-0.800 V) potential is rarely the optimum potential, and designers try to achieve a potential between (-) 0.950 V and (-) 1.000 V vs. Ag/AgCl sw.

Figure 3: Protected vs Unprotected structures as verified by cathodic protection potential

by: Richard Baxter, Jim Britton
Source: http://www.cathodicprotection101.com/

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