抄録
To evaluate corrosion resistence of stainless steels in hot water containing about 25-300ppm Cl- at max. 80°C, anodic polarization measurements and corrosion tests have been carried out on the specimens having various types of crevice. Initiation of crevice corrosion was accelerated by existence of active sites such as oxide films with residue of vaporized tap water on the specimen surface. During corrosion test for max. 27 weeks in 100ppm Cl- aq. solution crevice corrosion took place on some of the specimens having active sites, but the growth could not be observed at any specimens after removing into tap water containing about 25ppm Cl-. On spot welded specimens, only pitting corrosion took place in ultra low carbon ferritic stainless steels, while intergranular corrosion and stress corrosion cracking (SCC) also took place in type 430 and type 304 steels respectively. Based on the change in couple current between crevice-containing and crevice-free specimens, pitting inside the crevice appeared to grow early in the test period and to become inactive thereafter. On the other hand intergranular corrosion and SCC appeared to continue through the test periods. Corrosion tests of stainless steel tubes, which were carried out using circulating water containing max. 300ppm Cl- at 80°C for 47 weeks, showed almost the same results as described above. In type 304 tubes SCC was observed at the crevice parts under silicon rubber tube joints, while only pitting corrosion took place in ferritic stainless steel. It was estimated by analysis of corrosion potential-time curves that the crevice corrosion grew steadily in type 304 steels, but tended to become inactive gradually in ferritic stainless steels.
