In coal liquefaction and petroleum refinery reactors, such corrosive environments to include hydrogen sulfide, chlorides, hydrogen, etc. are encountered and the equipment is internally protected by stainless steels against corrosion. It would be useful if construction materials were coated by more corrosion resistant materials than stainless steels, then the predicted corrosion damages such as stress corrosion cracking and sulfidation attack as well as hydrogen attack could be suppressed and would be effective in increasing reliability of reactor vessels and their components. In this study, various kinds of coated materials with Cr-Mo steel substrate were manufactured and tested for their basic properties related to hydrogen permeation and corrosion protection.

Firstly, hydrogen permeation behavior of as-coated materials were measured in pure hydrogen environment to evaluate the effect of coating layer against hydrogen permeation and to clarify its mechanism. Spray coatings had no resistance to hydrogen permeation at all. Metal coatings, which include aluminium hot-dip plating, aluminium diffusion coating and chromium diffusion coating showed positive resistance to hydrogen permeation which seems to result from superficial oxide layer. Ceramic coating such as CVD(Chemical Vapor Deposition) also showed positive resistance to hydrogen permeation though hydrogen seems to permeate through defects in the coated layer to weaken its resistance to some degree.

Secondly, coated materials were presulfided to simulate the surface condition which would be produced in the corrosive environment of coal liquefaction process and then were tested for studying the resistance of the coating layer against hydrogen permeation and for clarifing the mechanism. Plasma spray coatings with Al2O3/50Ni-50Cr layer acquired the resistance to hydrogen permeation in as-sulfided condition. Metal coatings such as aluminium hot-dip plating, aluminium diffusion coating and chromium diffusion coating showed the resistance as sulfided, too. Both materials kept corrosion-resistant againt sulfiding attack. Among those surface modification technologies, plasma thermal spray coatings are considered especially feasible for the refinery reactor applications.

Subject
Materials, Hydrogen permeation, Substrates, Diffusion, Aluminum, Oxide layers, Hydrogen attack, Plasma, Metals, Sulfidation, Metallic coatings, Ceramic coatings, Hydrogen
Keywords:
hydrogen permeation, hydrogen attack, sulfidation attack, surface modification, ceramic layer, coal liquefaction, refinery
© 1993 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).
1993
Association for Materials Protection and Performance (AMPP)
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