Effect of Corrosion Inhibition on the Stress Corrosion Cracking of UNS S31603 Austenitic Stainless Steel

Brine recirculation pumps are essential components used for circulation of brine in multi-stage flashing chambers desalination plants. Failure of these pumps would result in shutdown of the desalination plants. The rotating parts of these pumps (shaft and impeller) are usually made out of stainless steels or Duplex stainless steels. The pressure parts (casings) are usually made out of Ni-resist ductile irons (NDI). In recent years there have been a number of cases in which NDI casing materials failed by stress corrosion cracking (SCC) especially in the Arabian Gulf region. This makes re-evaluation and further studies on the performance of these materials of paramount importance due to process-related economic and reliability considerations. As possible substitutes to NDI casing materials, the authors of this research have recently published material demonstrating the superiority of the SCC resistance of the super DSS, UNS S32750, over the ASS, UNS S31603, in hot brine environment. Economically, the idea of using chemical corrosion inhibitors to enhance the SCC resistance of the ASS, UNS S31603, is appealing, non famous and worth looking at. In this work the effect of corrosion inhibition on the corrosion resistance and SCC of the ASS, UNS S31603, in hot brine environment, is investigated. Brine water was injected with typical treat rate of 350 ppm of passivating type commercially available Molybdate corrosion inhibitor. Theoretically the corrosion inhibitor was proposed to improve the corrosion resistance of ASS, UNS S31603, in brine solution. Electrochemical polarization measurements and SCC tests were used to evaluate the performance of the metal under inhibited and uninhibited environments. Results have shown that treating the brine with this particular type of inhibitor under this particular treat rate and test conditions increased the pitting tendency of the ASS, UNS S31603. Results from both SCC tests and electrochemical measurements are in agreement and both role out the possibility of enhancing corrosion resistance and SCC of ASS UNS S31603 using Molybdate inhibitor.