An investigation was conducted into the fracture of the Serapta pipeline, which occurred at the site of mechanical damage, inflicted when a 2" (51 mm) gas sales line was ploughed-in across the line 12 years prior to failure. Optical microscopy, metallography, micro hardness testing, and scanning electron microscopy (SEM) were applied to the examination of the fracture. It was discovered that the fracture was initiated by a fatigue mechanism, at a sharp furrow in the gouge. Subsequently, corrosion became the dominant mode and stress corrosion cracking (SCC) occurred. When the crack became large enough for propagation, it was rapidly arrested as the pipe steel was above the ductile to brittle transition temperature (DBTT). Ductile rupture was found at the end of the fracture, indicating high energy absorption which explained the rapid termination of the fracture. The root cause of the failure was mechanical damage to the pipeline. All such known damage should be removed from pipelines or at least effectively recoated.

Subject
Pipe surfaces, Piping, Secondary cracks, Pipelines, Crack propagation, Stress cracking, Mechanical failure, Steel, Fatigue, Fracture, Cracks, Stress corrosion cracking, Hydrogen stress cracking
© 1988 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).
1988
Association for Materials Protection and Performance (AMPP)
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