オーステナイト系ステンレス鋼の低温外面応力腐食割れと有害イオン種

抄録

Field analyses of insulation in process plants and laboratory simulation tests have been done to clarify the External Stress Corrosion Cracking (ESCC) of austenitic stainless steel equipment and piping. It was shown that the about 70% of the insulation in Japanese process plants are so much contaminated with externally introduced chloride ions and unacceptable level of ASTM specification. These insulations are also contaminated with flouride ions which will be a potential detrimental ion for low temperature ESCC. Laboratory simulation tests on fluoride ions revealed that the heavily sensitized Type 304 stainless steel could easily suffer intergranular SCC even at ambient temperature within extremely short time. Weld gas during wet welding condition, weld scale, a kind of anti-sputter reagent are assumed to be possible fluoride sources. Fluoride SCC is, however, mitigated by the addition of some kinds of inhibitor.