PRCI PR-75-9310


Chemical and Electrochemical Conditions on Steel at Disbonded CoatingsPerdomo, J. J.; Payer, J.H.Pipeline Research Council International / 10-Jun-1995 / 204 pages

Case Western Reserve University
The objective of this research was to study the effects of cathodic protection at coating holidays and associated areas of disbondment through simultaneous determination of the electro-chemical reactions and chemical changes taking place in the environment adjacent to the steel substrate. Primary parameters of interest were applied potential, solution conductivity, pH oxygen in solution. The experimental plan was comprised of six interrelated studies involving both laboratory simulations and modeling. It was found that an effective CP system provides sufficient current flow at the exposed steel surface to modify the ground water in the immediate environment by lowering soluble oxygen levels and increasing its alkalinity. Further, corrosion protection is achieved in the shielded areas under the disbonded coating where current flow is minimal, through this chemical modification of the aqueous environment, and it is not necessary that current flow into all of the disbonded region. Three conditions of import to pipeline corrosion protection were also simulated in this investigation. Chemical environment and electric potential distribution within disbond regions were measured for the affects of interruption and reapplication of current; the occurrence of wet/dry cycles at the holiday and the presence of prior corrosion products.

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