Multiaxial corrosion fatigue in steels for offshore applications

Structures in offshore applications are often subjected to corrosive environment in addition to complex cyclic loads. Such conditions impose additional constraints while designing them. Some industries use coatings to protect them while some prefer electrochemical process like cathodic protection. In this study, a cathodic potential of -950 mV was used to study the multiaxial corrosion fatigue behavior of these steels. In free corrosion, fatigue lives and the endurance limit were suppressed due to corrosion due to the formation of corrosion pits that favor early, multiple crack initiations. The detrimental effect of corrosive environment was not enhanced by equibiaxial tension. The crack growth mechanism was different: transgranular brittle decohesion in uniaxial loading and mostly intergranular in biaxial tension. Cathodic protection enhances the H-induced embrittlement of the grain boundaries.