The combined effect of water and oxygen on stress corrosion cracking of carbon-manganese steel in liquid and vapourous ammonia has been studied in detail. The highest susceptibility to SCC was found in liquid ammonia with 3-10 ppm oxygen and a water content lower than 100 ppm. SCC can occur in ammonia with an oxygen content down to 0.5 ppm when the water content is very low. A borderline for safe operation is given as function of oxygen and water content.

It has been demonstrated that SCC can occur in a cooled vapour phase when the ammonia is inhibited in the liquid phase by water additions up to 0.27. The SCC susceptibility in the vapour phase is dependent upon liquid phase composition and the degree of cooling.

Stress corrosion cracking has been found in different carbon-manganese steels and a nickel steel tested at -33°C. It is suggested that the fact that no cracking has been experienced in storage tanks operating at -33°C is due to the lack of oxygen in the environment.

Subject
Water, Materials, Intergranular stress corrosion cracking, Composition, Ammonia, Vapors, Liquids, Stress, Mechanical failure, Corrosion inhibitors, Steel, Oxygen, Stress corrosion cracking
© 1987 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).
1987
Association for Materials Protection and Performance (AMPP)
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