A section of NPS 36 inch diameter 1-1/4Cr - 1/2Mo inlet piping to a continuously regenerating catalytic reforming reactor split open at the long-seam weld after 100,000 hours service. The results of metallurgical analysis confirmed failure by creep crack growth initiating at the ID, yet accelerated creep tests using the Omega method showed that the failed piping exhibited excellent creep strength and creep ductility in both base and weld metals. In addition, a piping stress analysis demonstrated that the piping design was in compliance with the ASME B31.3 Piping Code (1). Detailed finite element analysis revealed that the failure was promoted by peaking of the long-seam weld which caused highly localized bending stresses that are only partially relaxed after long term high temperature exposure. The peaked geometry satisfies existing fabrication tolerances for commonly used long-seam welded refinery piping including the ASTM A691 specification (2).

Subject
Materials, Piping, Geometry, Inspection, Stress cracking, Thermal stress, Base metals, Stress, Mechanical failure, Weld seams, Creep, Cracking, Weld metal
Keywords:
catalytic reformer, piping, low chrome, 1-1/4Cr - 1/2Mo, creep, long-seam weld, failure, cracking, peaking, high temperature
© 1995 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).
1995
Association for Materials Protection and Performance (AMPP)
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