At the Soultz-sous-Forêts Enhanced Geothermal System (EGS) site, impairment of cast iron and mild steel surfaces was observed on downhole equipment like production pump, production pipes and some parts of the inner casing. The impairment went always along with arsenic enrichment in the related corrosion layer with increasing arsenic concentration close to severe corrosion damages. The related level of enrichment, which could reach several tenth of weight percent, rose the question whether or not arsenic is a trigger or a result of corrosion phenomena at the Soultz-sous-Forêts EGS site.

This question is of importance for the Soultz location and other locations in the Upper Rhine Graben region as cast iron and mild steels are frequently used for downhole equipment like casing, production pipes and in some components of the production pump. An intense re-evaluation of downhole equipment showed that at the Soultz location arsenic is very probably enriched by adsorption on iron oxide surfaces and is therefore a result but not a trigger of electrochemical corrosion. The surface impairment is caused by transformation of the metal surface into iron oxide with high concentrations of adsorbed arsenic and, in some cases, antimony. Severe arsenic and antimony enrichment was found in combination with galvanic corrosion caused by connection of mild steel to ferritic-austenitic stainless steel. In this specific case, the deposition of pure arsenic and antimony cannot be excluded but it is considered to be a result and not the original trigger of the corrosion process.

Subject
Pipe surfaces, Electrochemical corrosion, Materials, Piping, Iron oxide, Antimony, Metal surfaces, Oxide layers, Oxide surfaces, Cast iron, Brines, Carbon steel, Deposit corrosion
Keywords:
EGS, Soultz-sous-Forêts, arsenic accumulation, mild steel, cast iron, LSP failure
© 2016 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).
2016
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.