07577 Long-Term Electrochemical Behavior of Creviced and Non-Creviced Alloy 22 in CaCl2 + Ca(NO3)2 Brines

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Product Number: 51300-07577-SG

ISBN: 07577 2007 CP

Author: Raul B. Rebak, Martin A. Rodriguez, and Marshall L. Stuart

Publication Date: 2007

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This paper discusses the evolution of Ecorr and corrosion rate (CR) of Alloy 22 specimens in 18 m CaCl2 + 9 m Ca(NO3)2 and 18 m CaCl2 + 0.9 m Ca(NO3)2 brines at 155°C. Two types of specimens were used, polished as-welded (ASW) creviced and non-creviced specimens and as-welded plus solution heat-treated (ASW+SHT) creviced specimens. The latter contained the black annealing oxide film on the surface. Results show that, in a few immersion days Ecorr reached a stable value higher than the open circuit potential of a platinum electrode in 18 m CaCl2 + 9 m Ca(NO3)2 for all specimens tested. Specimens tested in this solution did not suffer any type of localized attack. On the other hand, Ecorr showed oscillations of up to 600 mV in 18 m CaCl2 + 0.9 m Ca(NO3)2 during the entire immersion period. These oscillations were due to pitting corrosion development. Crevice corrosion was not observed in any testing case. Corrosion rates for specimens in the latter solution ([NO3 -]/[Cl-] = 0.05) were one order of magnitude higher than for specimens in the second one ([NO3 -]/[Cl-] = 0.5). Nitrate showed to be able to inhibit localized attack even in hot concentrated chloride brines when present in a ratio of [NO3 -]/[Cl-] = 0.5.