Steel catenary and top tension risers for deepwater oil and gas field developments are subject to corrosive environments on both internal and external surfaces and to fatigue loading. The girth welds control, the fatigue life of such structures. Therefore, there is a need to quantify the fatigue performance of girth welds under the influence of the external seawater, typically with cathodic protection, and the internal environment, which may contain water, CO2, H2S and chloride and bicarbonate ions. The effect of temperature must also be taken into account.

This paper presents a review of published data to illustrate the effects of seawater, sweet (CO2) and sour (H2S) exposure on corrosion fatigue of welds in carbon steels and corrosion resistant alloys (CRAs). In view of the dominance of the fatigue crack propagation process in the fatigue lives of girth welds, particular attention is paid to fatigue crack propagation data. The data indicate the range of predominantly detrimental effects of the various environments on the fatigue performance of welded carbon steel and CRAs and illustrate the effects of weld microstructure. Limitations of existing data are discussed. Challenges remain with respect to design of welded risers against corrosion fatigue and the data required to meet these challenges are discussed.

Subject
Risers, Test methods, Corrosion fatigue, Materials, Corrosion rate, Sour environments, Crack propagation, Corrosion cracking, Stress cracking, Seawater, Steel, Stress corrosion cracking, Hydrogen stress cracking
Keywords:
Corrosion fatigue, fatigue crack propagation, deepwater, risers, welds, seawater, sour service, sweet service
© 2004 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).
2004
Association for Materials Protection and Performance (AMPP)
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