TP24-06 Positive Impact Elevated Temperatures on Yellow Metal Passivation in Recirculating Cooling Systems

In typical aqueous conditions, if temperature increases, metallurgical corrosion rates and other reactions increase concomitantly. As a rule of thumb, it is often said that corrosion rates double for every ten degrees (Celsius) that the temperature increases. This general rule applies to metals in aqueous environments without the presence of corrosion inhibitors. Also, the water is often of low hardness where salt saturation is below the threshold for deposition. Industrial recirculating water systems tend to circumvent that rule since they are often operating in supersaturated conditions and in the presence of corrosion inhibitors for iron and copper metallurgies. Coupon bypass racks are often used as a proxy for corrosion monitoring, but those almost always operate at significantly lower temperatures than the heat exchangers. There have been reports from the field that yellow metal coupons in bypass racks exhibited significantly higher corrosion rates when compared to retractable coupons taken on the same systems immediately downstream of the heat exchanger, at the warmest temperatures. This paper will explore the positive impacts of increasing temperature on passivating copper metallurgies under industrial recirculating conditions and aim to provide an explanation by examining the surface chemistry at various temperatures.