Cathodic potential, disadvantage steel

The high consumption rates, as well as low-driving voltage, are the primary disadvantages of the galvanic anode method of cathodic protection. The open circuit potential between steel and magnesium is on the order of 1 V, while zinc and aluminum are somewhat less. Thus, with this method, it is imperative that a low-resistance circuit be established by installation of many anodes in a low-resistance medium. The anodes installed should also be sized in accordance with their respective consumption rates to provide the necessary design life. 

An important aspect of cathodic protection is the means to monitor the effectiveness and the criteria for protection. Criteria recommended by NACE (RP0169-96) for the CP of steel and cast iron piping are given in Table 4 [24]. Although several criteria are described for CP of steel structures, the most commonly used criterion is that the steel structure to be protected should be maintained at a potential more negative than —0.85 V versus Cu/CuSOr reference electrode. The primary disadvantages of this criterion are no connection of the potential of the steel to the corrosion rate, and a large difference in protective... 

Some disadvantages still exist During operation, anode and cathode side are forced to pass crucial electrochemical potentials leading to corrosion for most stainless steels. 

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