09424 Crevice Corrosion of Alloy 22 at the Open Circuit Potential in Hot Chloride Solutions

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Product Number: 51300-09424-SG

ISBN: 09424 2009 CP

Author: Martin A. Rodriguez, Raul B. Rebak and Ricardo M. Carranza

Publication Date: 2009

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tudied in short term tests. Mill Annealed (MA) and thermally aged PCA (Prism Crevice Assembly) specimens were used. Thermally aged specimens were obtained by aging at 760 ºC for 10 hours. Precipitation of secondary phases (TCP: Topologically Close Packed phases) at grain boundaries occurred. Electrochemical tests performed included open circuit potential monitoring for up to 48 hours, electrochemical impedance spectroscopy (EIS) and galvanic coupling with an MA Alloy 22 foil. Crevice corrosion propagation started in Alloy 22 after a few hours of immersion in pH 2, NaCl at 90 ºC. Steady state open circuit potential was higher for thermally aged specimens than for MA specimens. Galvanic coupling was performed in order to asses the effect of an increasing cathodic area. Galvanic current and potential were recorded with time. A potential maximum was correlated with a current minimum, indicating the onset of crevice corrosion propagation. Crevice corrosion kinetics was limited by oxygen reduction on passive Alloy 22 surface areas. Crevice corrosion attacked area and propagation potential (ECORR) were set to balance oxygen reduction rate. Oxygen reduction on passive Alloy 22 was inhibited. Low crevice corrosion propagation rates can be expected for crevice corrosion provided that oxygen is the only oxidant and the ratio of creviced area / passive area is large.

Keywords: N06022, chloride, crevice corrosion, thermal aging, galvanic coupling