Laboratory Corrosion Investigation of Some CP Criteria

Criteria for effective cathodic protection (CP) of steel structures presently in use are extremely important. Three primary criteria for CP of underground steel are listed in Section 6 of NACE Standard RP-01-69. An additional criterion, the E-log I curve is found in the original version of this Standard.

In this paper an assessment of the Tafel (E-log I curve) CP criterion is made based on the cathodic polarization curve of steel in simulated soil environment. The results are compared with the two most frequently used and accepted CP criteria, 100 mV polarization shift and -850 mV (CSE) with respect to the immediately adjacent soil. Metallic coupons have also been installed to corroborate the obtained results.

Although the applicability of E-log I criterion has been subject to considerable discussion it could be an interesting alternative for those underground structures where conventional means of assessment are difficult.