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

Taniguchi, Naoki ; Kawasaki, Manabu; Naito, Morimasa 

In general, copper is thermodynamically stable under anaerobic condition, so that corrosion due to water reduction can not occurr 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 at the electrode potentials of +100 mV and +300 mV above Ecorr (corrosion potential in anaerobic condition) were lower than that at a level of Ecorr. In case of Ecorr +700 mV, the SCC susceptibilities became larger than those in Ecorr +100 mV and Ecorr +300 mV. (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 0.001 M - NaS at -420 mV vs SCE, which is the rest potential under anaerobic condition (nitrogen atmosphere) in buffer material.