51313-02427-Crevice Corrosion Susceptibility of UNS NO8031 and Duplex Steel S32101 in CO2 Saturated Saline Brine

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Product Number: 51313-02427-SG

ISBN: 02427 2013 CP

Author: Oleksandra Yevtushenko

Publication Date: 2013

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CCS can be a safe and efficient method for carbon capturing and storing of billions of tons of carbon dioxide underground for thousands of years and therefore has the potential to reduce global CO2 emissions. By injection of CO2 in deep aquifer fluids corrosion effects on pipeline steels can occur due to high salinity of such fluids temperature and construction caused crevices.

Corrosion resistance of duplex steel S32101 and alloy 31 was investigated in crevice conditions in a corrosive environment (saline brine T = 60 °C CO2-flow rate 3 – 5 L/h normal pressure) using electrochemical and metallographic techniques. Because of instability of the natural fluid known as Stuttgart Aquifer fluid (North German Basin) at normal pressure the artificial brine with similar chemical composition and high chloride content (143.3 g/L) was prepared for laboratory investigations. After the saturation with CO2 the pH of the brine was measured to be 5.8 6.0. Rectangular rubber was used to form a metal/non-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 steel S32101 coincides with its corrosion potential. Strong pitting corrosion occurred after potentiodynamic measurements with pit depths up to 100 µm. Otherwise alloy 31 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 steel S32101 potentials slightly more positive than the corrosion potentials causing strong pitting corrosion and pit depths up to 650 µm were measured. Alloy 31 did not present any signs of pitting corrosion even by applying the potentials much more positive than the corrosion potential.

It can be concluded that due to its excellent corrosion resistance alloy 31 can be a promising alternative when putting this material into operation in environments with crevices similar to those investigated in the laboratory.