A Contribution on the Acidified Copper Sulfate Test for Intergranular Corrosion of Austenitic Stainless Steels

Abstract

It has been widely known in the acidified copper sulfate test (Strauss' test) for intergranular corrosion of stainless steels that the boiling time required for inspecting the characteristics can be remarkably reduced by the presence of metallic copper. For the purpose of clarifying the role of copper, the change of potentials of Pt, Cu and stainless steels was followed in the Strauss' solution of containing various amounts of copper. The effect of the following factors on the equilibrium potential (Pt-potential) was also examined in order to obtain the knowledge of actual testing conditions. (a) The amount of copper chips. (b) The ratio of the surface area of specimen to the volume of solution. (c) Contact between the specimen and copper chips. (d) Contamination of the solution due to the corrosion products.
It was found that the presence of copper accelerate the establishment of equilibrium condition among Cu, Cu⁺ and Cu⁺⁺, and that the mixedd potential of stainless steel specimen shifts quickly to the potential region of producing the intergranular attack in accordance with the production of Cu. The mixed potential of the specimen is always found to be slightly more active (within few mV) than the equilibrium potential of Cu⁺/Cu⁺⁺ system. From these results it was ascertained that the copper-added test would correspond to a certain kind of corrosion test under controlledpotential.