Incubation time for crevice corrosion of stainless steels in environments containing chloride ions such as sea water was evaluated by potentiostatic methods. Current density of specimens with and without crevice were measured at a current - time curve just after polish of the sample's surface. And, dependence of QINCU (amount of dissolved metal ions during estimated incubation time) and tINCU ( estimated incubation time for crevice corrosion) on potential were clarified by the experiments above. The tINCU was decreased with increasing potentials. On the other hand, QINCU was almost independent of potentials. Decrease of tINCU with increasing potentials was due to increase of iINCU with potential. Amount of dissolved metal ions required for occurrence of crevice corrosion and depassivation pH which is fundamental cause for crevice corrosion are found to be almost independent of potential.
Growth rates of crevice corrosion for various stainless steels in sea water environments were evaluated under potentiostatic condition. And perforation time for the stainless steel plate was estimated by time dependence of the maximum crevice corrosion depth. Crevice corrosion resistance of stainless steels deteriorated with increase of chloride ion concentration. Crevice corrosion initiated and grew for all the stainless steels tested in this study in the solutions with more than 100 ppm chloride ion. Dmax, maximum crevice corrosion depth, was approximated as power low function as Dmax=A·tm. Term A, Dmax at 1 hour, was increased with chloride ion concentration. On the other hand, term m showed from 0.3 to 0.5 independent with chloride concentration. It seems that values of m should be explained by dissolved morphology at corrosion crevice and assuming rate determining step for metal dissolution. For example, perforation time of crevice corrosion for the 1 mm thick SUS 304 stainless steel in 19 ppm chloride ion solution at 50ºC was estimated about 4 years, 21 years for SUS316L stainless steel and 66 years for SUS329J4L stainless steel. And perforation times for SUS304 stainless steel were almost same under potentiostatic condition between 300 mV (vs. SSE) and 440 mV (vs. SSE).
The External Pressure Balanced Reference Electrode (EPBRE) system was applied to the electrochemical measurements in high temperature and high pressure aqueous solutions. Irreversible potentials arisen in the EPBRE system, such as liquid junction potential and thermal junction potentials were studied with comparison to the internal reference electrode system in 0.1 M KCl solutions at high temperatures. It was demonstrated that the potential measured by EPBRE system can be converted to the potentials referenced to standard hydrogen electrode potential at high temperature and also at 25ºC. The contribution of liquid junction potential and thermal diffusion potentials to the measured values was also evaluated in the EPBRE system.