Stress Corrosion Cracking of Carbon Steel and Low Alloy Steel in High Temperature Water

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Abstract
The SSRT method, electrochemically controlled SSRT method and measurement of anodic polarization curve are conducted in high temperature water for a carbon steel (STS 42) and a low alloy steel (SFVV 2) to study the environmental effects on SCC (disolved oxygen, temperature and potential). The following results are obtained. (1) The carbon steel and the low alloy steel show SCC susceptibility in oxygenated high temperature pure water, while they do not show the SCC susceptibility in deaerated pure water. (2) The low alloy steel is more susceptible to SCC than the carbon steel. (3) SCC occurs only in the high temperature water (over 200°C). (4) From the results of electrochemically controlled SSRT method in 0.1M Na2SO4 solution at 250°C, SCC occurs only in the potential region of higher than -400mV (vs SHE). (5) The anodic ploarization curves of the carbon steel in the Na2SO4 solution indicate that the steel passivates at 250°C but does not passivate at 150°C. The passivation is divided into two regions at 250°C, that is, the first passivation below -400mV and the second passivation above -400mV (vs. SHE). Judging from the Potential -pH diagram of Fe-H2O, the second passivation is attributed to the formation of Fe2O3.

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