Slow strain rate tests (SSRT) were carried out in synthetic sea water on three kinds of high tensile strength steels (HT60, HT80 and SNCM439) being used for offshore structures. In this study, their mechanical properties were measured and the specimen surface and fractured surface were examined after the tests. Also the parameters characterizing the test results were examined.
Among various parameters, the reduction in area (RA) and the true fracture stress (σf) were found to vary clearly depending upon the aggresiveness of testing environment and the kind of steels. They were lower in sea water at the cathodic protection potential (-0.80V vs. Ag/AgCl) than in sea water without it (Ecorr), and the trend was more remarkable for HT80 and SNCM439 steels which had higher tensile strength than HT60 steel. Another parameter, the maximum crack length, Δa, obtained from the quasi-cleavage fracture surface, showed the same clear difference depending upon testing environment and the kind of steels. The maximum crack length, Δa, of SNCM439 steel was 500μm at the cathodic protection potential (-0.80V vs. Ag/AgCl) in sea water.
It can be concluded that the maximum crack length, Δa, is related to the susceptibility of stress corrosion cracking and is a good parameter for SCC evaluation by means of SSRT.
