Determination of the critical pitting temperature of stainless steel using electrochemical testing techniques
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Corrosion resistance alloys (CRAs) used in oil and gas industry may suffer severe localized corrosion such as pitting and crevice corrosion. Critical pitting temperatures (CPT) determined by ASTM G48-03 and ASTM G150-99 standard procedures are suitable for ranking the susceptibility of stainless steel to pitting corrosion but not appropriate for predicting pitting corrosion of stainless steel under production conditions. Some researchers have proposed the use of electrochemical noise (ECN) to estimate values of CPT on stainless steel. However the criteria used to determine these values are not consistent among them. A methodology based on electrochemical testing techniques was implemented to measure the CPT of SS 316L in 1 M, 2M sodium chloride and 6% ferric chloride solutions in a temperature range of 0-80C. Results suggest that the interpretation of electrochemical noise data may result in a false CPT. The use of a combination of electrochemical noise, cyclic potentiodynamic polarization and potentiostatic technique can be used to determine the correct CPT for stable pitting. High temperature tests in autoclaves simulating production conditions in the future are recommended for the verification of this methodology. 2012 by NACE International.
