Supercritical water oxidation (SCWO) is a promising and very effective method for the oxidation of organic wastes. Its high solubility for organic compounds and its special physical properties (i.e. density, viscosity) resulting in a key advantage over standard processes like incineration. Due to the formation of HCl during oxidation of chlorine organics, a severe corrosion attack of most of the materials has been observed. This paper describes the results of investigations of high temperature alloys like alloy No. 214, alloy 602 Ca, g-30 alloy alloy 625 and alloy 686, exposed at 400 bar and 420°C for 24 hours in a CH2Cl2/H2O2 mixture with about 2000 wppm of chloride.

The weight losses of all, samples varied between 3 mg/cm2 for G-30 alloy and about 73 mg/cm2 for alloy 686. The alloy No. 214 showed an increased corrosion for the preoxidized material, whereas the corrosion rate of alloy 602 CA was reduced by a factor of 3 due to the preoxidation at 900°C, prior to SCWO-exposure. The post mortem analysis revealed that alloy 686 has lost most of its nickel down to a depth of about 150 μm. The G-30 alloy showed a good corrosion behavior because of the formation of a protective oxide layer during the exposure. The layer was homogeneous with a thickness of about 12 μm, but a slight nickel leaching was observed, too.

Subject
Materials, Corrosion resistant alloys, Metal surfaces, Reactors, Nickel based alloys, Molybdenum alloys, Oxide layers, Supercritical water oxidation, Weight loss, Nickel, Aluminum alloys, Titanium alloys, Alloys
Keywords:
SCWO, supercritical water, corrosion, oxidation, hydrochloric acid, high temperature, high pressure, nickel base alloys
© 1998 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).
1998
Association for Materials Protection and Performance (AMPP)
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