The expanded use of electroless nickel coatings in transportation and process industry applications as a corrosion resistant coating and lining has increased the need for more well defined methods of surface preparation and quality control. In contrast to organic coatings no NACE standards have been developed for metallic coatings to insure consistent performance in the field. Existing pretreatment standards and inspection techniques have little or no relevance to metallic coatings such as electroless nickel.

This paper explores present surface preparation methods for carbon steel and high alloy steels for electroless nickel plating. The technical issues involved in proper removal of surface contamination is presented along with a characterization of the influence of these process steps on coating adhesion. To avoid selecting an ideal surface upon which to perform the studies, a used, previously blasted tank car section was used for this investigation.

SEM photomicrographs, EDS analysis, and corrosion test results show that an electroclean - electroactivation cleaning procedure preceeded by a NACE Number 1 white metal blast prior to electroless nickel plating offers an excellent surface treatment combination tested on an old previously used tank car substrate. Several other surface preparation methods were also investigated. Among them, acid (50%, HCl) activation may be a good alternate treatment when electroclean-electroactivation is not practical. In general, however, corrosion tests perform on samples plated with low phosphorus electroless nickel and tested in 73% caustic at 280°F show less than 1.0 μm/y compared to 9.4 μm/y for Alloy 200 even when optimum surface preparation methods were not used.

Further work is required to develop the optimum preplating procedure which will remove embedded blast media and residual corrosion products from the surface, reduce disturbed metal, and produce a completely pore-free coating for critical applications. In particular, corrosion resistance of electroless nickel in acidic environments can, in some cases, present potential accelerated galvanic corrosion of the base metal. As a result, additional characterization of surface preparation methods designed to achieve a holiday free coating will be necessary.

Subject
Acids, Nickel coatings, Coating application, Steel surfaces, Coatings, Plating, Metal surfaces, Corrosion products, Metals, Steel, Electroless nickel, Soil, Cleaning
© 1988 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).
1988
Association for Materials Protection and Performance (AMPP)
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