10246 Effects of Electropolishing & Thermal Annealing on Corrosion/Release Behavior of Nicrfe Alloy 690

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Product Number: 51300-10246-SG

ISBN: 10246 2010 CP

Author: J. T. Orr, S. E. Ziemniak, B. B. Penney, P. C. Sander and M. E. Hanson

Publication Date: 2010

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Electropolishing surfaces of UNS N06690 reduced the corrosion rate by about 90%, relative to asmachined surfaces, in deaerated, pH-adjusted water at 500°F. Testing was carried out in a Ti autoclave, in an effort to minimize pick-up of ferrous corrosion products from the autoclave. It was demonstrated that base metal was released to solution more rapidly at the beginning of the test, before a stable oxide film was able to passivate the coupon surface. After the film was established, metal release and oxide film growth proceeded more slowly. The film was Cr-rich, and consisted of fine crystals with a diameter of about 20 nm on electropolished surfaces, but consisted of fine and coarse crystals on the asmachined surfaces. Unlike previous corrosion/release tests, the major phase identified in the corrosion film was non-stoichiometric CrOOH rather than spinels of the form AB₂O₄. Minor amounts of spinel were identified, along with Ni metal. Thermal annealing of corrosion coupons also reduced corrosion rates of UNS N06690, but was not as effective as electropolishing.

Keywords: corrosion, UNS N06690, electropolishing, high temperature