EVALUATION OF CREVICE CORROSION RESISTANCE OF DUPLEX AND SUPER DUPLEX STAINLESS STEELS FOR SEAWATER PUMPS

摘要

The crevice corrosion resistance of duplex and super duplex stainless steels used for seawater pumps was evaluated by comparing the results of immersion tests conducted using actual seawater in the Middle East (Arabian Gulf and Red Sea) and Tokyo Bay with the electrochemical behavior of the stainless steels in artificial seawater, concentrated artificial seawater, and acidic condensed chloride ion solution. The crevice corrosion occurrence rates (C. C. O. R.) in actual seawater decreased as the pitting resistance equivalent (PRE) of the materials became higher, the C. C. O. R.s varied depending on the manufacturing methods of the materials (rolled or cast). The pitting potential in artificial seawater correlated with the C. C. O. R.s in the Middle Eastern seas regardless of the manufacturing methods. Further, the potentiostatic polarization behavior in the artificial seawater and the concentrated artificial seawater with their water temperatures controlled ranging from 20 to 40 °C suggested the possibility that the high C. C. O. R.s observed in the Middle Eastern seas are mainly attributed to the seawater temperature and that the higher corrosion growth rate observed in the Arabian Gulf verses that in the Red Sea is mainly attributed to the salt concentration.