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Galvanic corrosion of several alloys has been examined before in simple acids or salt solutions, and good predictive capability has been achieved using numerical solution of appropriate Tafel equations. In this paper, more complex solutions, containing an acid and an oxidizing agent, are examined. Galvanic current measurements and gravimetric (weight-loss) corrosion measurements indicated that galvanic current measurement is not always a reliable method to determine the difference in corrosion rate of an alloy between the coupled and uncoupled conditions. Sometimes an alloy showing a cathodic current showed an increase in corrosion rate while another alloy showing an anodic current showed a decrease in corrosion rate. Graphical superposition of polarization curves in the oxidizing solutions did result in correct prediction of galvanic potential and current in most cases. However, in order to predict the change in corrosion rate of an alloy on coupling to another, polarization curves of the coupled alloys in both the oxidizing solution and the solution without the oxidizing agent have to be superimposed.
galvanic corrosion, oxidizing solutions, acids, zero resistance ammeter, nickel-base alloys, duplex stainless steels, titanium, graphite, austenitic stainless steels, corrosion potential, polarization, current, coupling, active-passive regions
Engineer, Haynes International, Inc., Kokomo, IN
Research associate, Conoco Inc., Ponca City, OK