Effect of electrode potential and material grade on the behavior of stress corrosion cracking of pure copper in synthetic seawater containing sulfide

In general, copper is thermodynamically stable under anaerobic condition, so that corrosion due to water reduction hardly propagate on copper. However, in the presence of sulfide, copper loses its thermodynamical stability and corrodes as copper sulfide, and is susceptible to stress corrosion cracking (SCC) depending on environmental condition. In this study, slow strain rate tests (SSRT) were performed in synthetic sea water containing sodium sulfide and the effect of electrode potential and the difference of material grade were examined. The results were summarized as follows; 1) The SCC susceptibilities tend to be lowered with increasing the electrode potentials up to +300mV above corrosion potential in nitrogen atmosphere. However, it was indicated that the SCC susceptibility at nobler potential far over +300mV above corrosion potential were raised again. 2) In comparison of oxygen free copper and phosphorous deoxidized copper, the former tended to be allowed to crack initiation more readily, but the mechanical properties such as tensile strength and elongation were almost equal in both materials. 3) In order to apply the SSRT with buffer material, a test column attached to a specimen was developed. As the result of SSRT of phosphorous deoxidized copper using the column, no SCC was observed in 0.001M-Na2S at -420mV vs SCE, which is the corrosion potential in buffer material under anaerobic condition (nitrogen atmosphere). (author)