The objective of this study was to determine the effect of digester liquor composition on the likelihood of stress corrosion cracking of steel under freely corroding conditions.

Slow strain rate tests of A516gr70 pressure vessel steel in NaOH-Na2S- Na2CO3 solutions at 90 C under controlled potentials showed stress corrosion cracking in a narrow range of potentials centered on -890 mV (SCE) . The free corrosion potential (Ecorr) of this steel was measured for up to 28 days in 25 different solutions containing 20 to 80 g/l NaOH, 10 to 50 g/l Na2S, 3 to 11 g/l Na2S2O3, and 0 to 2 g/l So to establish the effect of solution composition on Ecorr and, thereby, to determine those compositions that may cause cracking. Results showed that Ecorr is either in the active range (< -940 mV SCE) with FeS as the corrosion product, or in the passive range (> -800 mV SCE) with Fe3O4 as the corrosion product. For some compositions, Ecorr stayed in the cracking range for many hours before moving into the active or passive range. A regression equation relating Ecorr to solution composition was derived from the data.

Subject
Sulfur, Digesters, Materials, Composition, Liquor, Potential range, Free corrosion potential, Corrosion cracking, Polarization curves, Steel, Carbon steel, Corrosion potential, Stress corrosion cracking
© 1986 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1986
Association for Materials Protection and Performance (AMPP)
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