A corrosion failure was experienced in the gas compression module of the Gorm C platform in the Danish sector of the North Sea. It was found that the carbon steel discharge pipe from IP compressor A had ruptured causing gas to leak to the module. This paper describes the subsequent investigation into the corrosion mechanism responsible.

The pattern of corrosion seen in the ruptured Gorm C pipe shows clearly that the corrosion is related to the injection of H2S scavenger into the dry gas phase, 5% relative humidity (RH) at 135°C. The corrosion attack is seen as a gradual increase in metal loss from just downstream of the scavenger injection point to the point of rupture immediately after the first bend. The metal loss is seen where a continuous phase of liquid scavenger is expected to be present. Corrosion tests carried out on the commercial scavenger product containing the active component 1,3,5-tri(2-hydroxyethyl)-(2H,4H,6H)- hexahydro-1,3,5-Triazine show clearly that the corrosivity as a function of temperature increases dramatically at a temperature of 80-100°C. This is attributed to a thermal breakdown of the product reverting to the reactants of formaldehyde and monoethanolamine (MEA), and, in turn, in the formation of formic acid, which reacts with MEA to form the salt. This is supported by the finding of ester /carboxylic acid, proportional to the metal loss, in the surface layer of the pipe. Inclusion of CO2 in the corrosion tests results in a further increase in corrosivity, probably due to the absence of a protective iron carbonate layer that would be expected to form on carbon steel in the presence of CO2 at the given test conditions.

Subject
Acids, Salt formation, Piping, Salts, Corrosion rate, Formates, Corrosion testing, Metal loss, Acetates, Formic acid, Deposit corrosion, Linear polarization resistance, Samples
Keywords:
carbon steel, corrosion, H2S scavenger
© 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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