Enhanced Corrosion Fatigue Resistance of AISI304 Bellows Expansion by Modifying the Bellows Shape

摘要

Bellows are widely used as the element of expansion joint in various piping systems. The U-shaped bellows is one of popular expansion joints which have widely been used. Mostly, these bellows are made from austenitic stainless steel such as AISI304. Metastable austenitic stainless steels such as AISI304 transforms to deformation-induced martensite (DIM) if it is plastically deformed, and in the case subjected to the cyclic deformation, its critical plastic strain range is 0.3%. The formation of DIM renders them to lose its corrosion resistance. Particularly, the austenitic stainless steels with DIM tend to lose the resistance to localized corrosion such as pitting corrosion when they are exposed to chloride solutions. In order to avoid the transformation, new μ-shaped bellows are proposed to extend the corrosion fatigue life by modifying the shape to have smaller plastic strain range than the critical value. It was demonstrated that μ-shaped bellows have six times higher fatigue life than conventional U-shaped counterpart. The relations between the formation of cracks and DIM have been focused.