This paper describes a program to develop a monitoring device to detect stress-corrosion cracking conditions in chemical process equipment before damage occurs. This device utilizes a metallic specimen cyclically stressed at slow frequency, while being exposed directly in the chemical stream. The cyclic stressing upsets passive film repair after breakdown and thus accelerates crack growth, similar to that which occurs in slow-strain rate tests. The stress cycle does not, however, lead to fatique failure during reasonable time periods. As cracks propagate into the specimen, they reduce its stiffness, leading to an increase in specimen deflection. The deflection is continuously monitored and the increase serves as the signal of incipient cracking. The device has been evaluated in the laboratory with a variety of alloy-environment combinations, in which it reliably detected cracking conditions in advance of visible cracking on fixed displacement specimens. The system also detected changes in environment from non-cracking to cracking conditions, the situation it is designed to detect in chemical plant service. These developmental experiments are discussed in this report.

Subject
Materials, Crack propagation, Corrosion detection, Stress cracking, Stress, Sodium chloride solution, U bends, Deflection, Equipment, Stainless steel, Brass, Cracking, Stress corrosion cracking
© 1984 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).
1984
Association for Materials Protection and Performance (AMPP)
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