Unbonded flexible pipes are often used as an alternative solution to rigid steel pipes for the offshore oil and gas industry. With increased development of deepwater fields the demand for unbounded flexible pipes has also increased. The flexible pipe cross section is a complex structure which creates unique operating conditions for carbon steel wires used as armouring layers. In the last years an extensive research programme has focused on prediction of the working environment for armouring wires in flexible pipes, as well as corrosion rates and fatigue life encountered in these environments.

This paper presents work on predicting the fluid composition and pH of the annulus environment in unbonded flexible pipes. This includes measuring of fluid permeation in polymers, CO2 and sour corrosion of steel in confined areas and the development of a mathematical model. The predicted annulus environment is used for a fit for purpose qualification of armouring steel wires in sour environments in accordance with NACE MR0175/ISO15156 for both static and dynamic applications.

Subject
Test methods, Corrosion fatigue, Materials, Piping, Corrosion rate, Annulus, Sour environments, Wiring, Permeation, Stress, Polymers, Steel, Sulfide stress cracking
Keywords:
unbonded flexible pipe, annulus environment, permeation model, confined environment, pH model, CO2 corrosion, sour corrosion, sulphide stress cracking, hydrogen induced cracking, corrosion fatigue
© 2006 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).
2006
Association for Materials Protection and Performance (AMPP)
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