Cracking of constructional steels in anhydrous-ammonia service has been known since the 1950's.1)* It was not until 1962, however, that cracking was reproduced in test specimens and identified as stress-corrosion cracking as a result of an extensive investigation by the Research Committee of the Agricultural Ammonia Institute (presently part of the Fertilizer Institute).2) This work also determined that air contamination in ammonia is the necessary ingredient to produce stress corrosion and that water in small amounts inhibits it. In the same work the committee recommended that (1) agricultural ammonia should contain 0.2 percent water as an inhibitor, (2) air contamination should be eliminated from ammonia systems, and (3) tanks over 36 inches (910 mm) in diameter should be fully stress-relieved or fabricated with hot-formed or stress-relieved heads. As a consequence of manufacturers and users following these recommendations, reported occurrences of cracking essentially disappeared in agricultural nurse, applicator, and storage tanks.

Subject
Water, Regulations, Inspection, Ammonia, Stress cracking, Intergranular cracking, Internal inspection, Repair, Steel, Hardness, Quenching and tempering, Heat treatment, Stress corrosion cracking
© 1976 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).
1976
Association for Materials Protection and Performance (AMPP)
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