Effects of reduced sulfur on the corrosion behavior of Alloy 600 in high-temperature water

The effects of reduced sulfur on the corrosion behavior of Alloy 600 MA were investigated in deaerated 0.01 M of sodium sulfate (Na2SO4), sodium tetrathionate (Na2S4O6), and sodium thiosulfate (Na2S2O3) solutions using potentiodynamic polarization and stress corrosion cracking (SCC) tests at 300 °C and 340 °C. The polarization curves of Alloy 600 MA showed a stable passivity in the Na2SO4 solution; however, the solutions of Na2S4O6 and Na2S2O3 showed accelerated anodic dissolution. The SCC susceptibility of Alloy 600 MA increased in the following order: in the Na2S2O3, Na2SO4, and Na2S4O6 solutions. Results of deposits and spectra taken from an energy dispersive X-ray system confirmed the existence of reduced sulfur.