Repassivation of high alloy stainless steels in chlorinated sea water

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Repassivation of high alloy stainless steels in chlorinated sea water

Francis, R. / Irwin, J.B. / Byrne, G.

Tests were carried out to investigate the ability of Zeron 100 super duplex (UNS S32760) and 6Mo superaustenitic (UNS S31254) stainless steels to repassivate during short temperature upsets in sea water cooling systems (70 deg C). Zeron 100 has about a 50 % chance of suffering crevice corrosion during short term (about 24 h) temperature upsets at 70 deg C in chlorinated sea water. On specimens of Zeron 100 which do initiate crevice corrosion, repassivation will occur within a few hours when the temperature is restored to normal (30-40 deg C), under the present test conditions. The superior resistance of Zeron 100 to short process upsets when compared with other super duplex and superaustenitic alloys is believed to be due to the alloy's superior resistance to hydrochloric acid. It has been found that 6Mo austenitic stainless steel is very susceptible to crevice corrosion under temperature upset conditions and repassivation on reduction of the temperature is difficult. Service experience supports the laboratory results, verifying the high resistance of Zeron 100 to crevice corrosion in chlorinated sea water at elevated temperature, and the lack of resistance of 6Mo austenitic alloys.