During a 198U turnaround at an ammonia plant, all of the converter exit piping was tested for hydrogen damage using the ultrasonic attenuation method. The results indicated that a 15 foot (4.6 m) length of C-½ Mo piping had significant hydrogen damage. Further examination revealed numerous blisters on the ID of the pipe. A metallurgical examination showed extensive fissuring and decarburization to about 40% of the pipe wall.

A detailed analysis using extraction metallurgy techniques revealed that the carbide structure in the C-½ Mo material was essentially all Fe3C, even though the chemistry of the pipe had 0.58 wt % Mo. Accordingly, the resistance to hydrogen attack of the pipe was similar to carbon steel and probably occurred over the entire 11-year period when it was in service. The attack would have been enhanced somewhat during the last 14-24 months, when the converter exit temperature was increased.

Subject
Materials, Piping, Hydrogen damage, Carbides, Materials performance, Hydrogen attack, Ammonia, Mechanical damage, Steel, Carbon steel, Carbon, Blistering, Hydrogen
© 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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