Stress corrosion cracking (SCC) of copper alloys, particularly brasses, has been a serious industrial problem for many years and the subject of numerous studies. Generally, SCC of brass has been attributed to the presence of ammonia. Copper alloy CDA 220 brass (90 Cu-10 Zn) is considered fairly resistant to NH3 SCC because of its low Zn content. However, recently we have noted intergranular failures of CDA 220 brass rupture discs originating on the atmospheric side. Surface analysis of the failed discs showed the presence of N or S compounds.

A series of SCC tests was conducted with rupture discs to determine the susceptibility of CDA 220 to SCC from N and S compounds. Possible replacement copper alloys and nickel alloys were also tested. The results show that copper alloys CDA 220 and CDA 101 (99.99 Cu) are cracked in nitrite solutions. CDA 220 cracked in ammoniacal CuSO4 (Mattsson's solution), but CDA 101 was resistant. CDA 220 was resistant to aqueous NH3 solutions. Other alloys tested were 90/10 Cu-Ni, beryllium copper, nickel 201 and nickel alloy 600. These alloys were resistant to cracking, except for Ni 201, which failed in acidic sulfide solutions.

Surface analysis showed that NO2− may be reduced to NH3 during cracking. Also, corrodants may be oxidized by air, making interpretation of surface analysis results more difficult. A discussion of the origin or the corrodants and the susceptibility of the potential alloys to SCC in service is given.

Subject
Corrosion failures, Nitrites, Nickel based alloys, Leak detection, Sulfites, Copper alloys, X-ray spectroscopy, Intergranular cracking, Surface analysis, Fluids, Copper nickel alloys, Cracking, 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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