The objective of this paper is to describe a structured process for response to unexpected metal loss in geothermal resource production. Application of the process is illustrated by describing a case history.

The Kawerau geothermal power generating station in New Zealand uses pH modification to mitigate scaling in flashed brine piping and injection wells. After nine months of operation, significant metal loss was observed in various areas of the steel piping and pressure vessels. The metal loss was generally localized and most extreme in areas of high velocity, turbulence, two-phase flow and low pH.

Mitigation of the metal loss included studies of the conditions responsible for the damage, the related process controls, evaluation of alternative alloys, and tests of various methods of optimizing the cost effectiveness of corrosion resistant alloys. In addition, inspection and monitoring methods were reviewed and revised. Ultimately, the evaluation program demonstrated that a combination of formats for using corrosion resistant alloys could be the most cost effective. Those formats included:

  • Stainless steel or NiCrMo weld metal overlays

  • Application of stainless steel plates and platelets welded to steel substrates in corrosion-susceptible areas

  • NiCrMo alloys applied by thermal spraying (high velocity arc spraying)

  • Solid corrosion resistant alloys in selected areas

Subject
Steel surfaces, Materials, Piping, Corrosion resistant alloys, Stainless alloys, Corrosion rate, Metal loss, Material degradation, Fluids, Corrosion resistance, Stainless steel, Weld metal, Stress corrosion cracking
Keywords:
cladding, duplex stainless steel, geothermal, stress corrosion cracking, thermal spray, weld overlay
© 2013 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).
2013
Association for Materials Protection and Performance (AMPP)
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