Pushing the Boundaries of Corrosion Resistant Alloys

Abstract

Materials selection for oil and gas production systems operating in seawater environments is based on two international standards, ISO 21457 and NORSOK M-001, where different alloys are ranked according to their relative localised corrosion resistance based on their content of specific alloying elements, namely Cr, Mo, N, and W. In this regard, the relative localised corrosion resistance of stainless steels is expressed in an empirically derived equation known as the Pitting Resistance Equivalent (PRE). This research aims to define the environmental limits of selected austenitic stainless steels and nickel-based alloy 718 in seawater by quantifying their crevice corrosion resistance across temperature and potential ranges. Induction times for stable crevice corrosion initiation will be measured, and environment-time-dependent material selection maps will be created for seawater service. This approach will guide material selection beyond the limitations of PRE, allowing study of minor Mo content changes on localized corrosion resistance of austenitic stainless steels.