Material Challenge for Carbon Capture and Storage - Crevice Corrosion Susceptibility of Super Austenitic Stainless Steel UNS NO8031 (Alloy 31) and Duplex Stainless Steel S32101 in CO_2 Saturated Saline Brine

摘要

Corrosion resistance of duplex stainless steel UNS S32101 and super austenitic stainless steel UNS NO8031 (alloy 31) was investigated in crevice conditions in a corrosive environment (saline brine, T = 60 °C, CO_2-flow rate 3-5 L/h, normal pressure) using electrochemical and metallographic techniques. Rectangular rubber was used to form a metalon-metal-crevice configuration. Potentiodynamic measurements have been carried out in order to determine critical pitting and repassivation potentials. Potentiostatic measurements at different potentials have been performed and the dependence of pit depth on the potential applied in crevice conditions was investigated. It was shown that the repassivation potential of duplex stainless steel S32101 coincides with its corrosion potential. Strong pitting corrosion occurred after potentiodynamic measurements with pit depths up to 100 μm. Otherwise, stainless steel UNS NO8031 shows about 0.5 V difference between the free corrosion potential and the repassivation potential and did not show any signs of pitting corrosion after polarization measurements. Slight rouging effects have been observed. By potentiostatic measurements on duplex stainless steel S32101 potentials slightly more positive than the corrosion potentials causing strong pitting corrosion, and pit depths up to 650 urn were measured. Super austenitic stainless steel UNS NO8031 did not exhibit any signs of pitting corrosion even by applying potentials much more positive than the corrosion potential.