Vehicle heat exchangers are exposed to a number of aqueous environments ranging from inhibited coolants to seawater. Frequently, the design of the heat exchanger results in a galvanic couple between copper and a stainless steel. This couple can either prevent or promote pitting and crevice corrosion of the stainless steel member. This paper demonstrates the use of electrochemical corrosion measurement techniques to predict this behavior. Stainless steels which have acceptable, marginal and unacceptable resistance to localized corrosion when coupled to copper in aggressive environments are described.
Potentiodynamic polarization curves for a variety of stainless steels were measured in artificial seawater to determine their pitting and critical protection potentials. Mixed potential measurements for these alloys galvanically coupled to copper were then made to predict the localized corrosion behavior of the stainless steel. The analysis of localized corrosion behavior based on potential measurements was augmented by measurements of zero resistance ammeter currents. Mass change data and visual observations were used to confirm the results of the electrochemical measurements. The effect of temperature on localized corrosion of the stainless steels coupled to copper was also investigated.
Heat exchangers can be designed with copper clad steel or stainless steel as a self brazing material. The techniques described in this paper can be used to determine the corrosion resistance of these materials in heat exchanger environments where there is little service experience.