Corrosion evaluation of sodium molybdate-based products shows that selection of inhibitive blends as chromate replacements needs to be carefully considered. The inhibitor efficiency of some products depends on oxygen concentration and the passivation of aluminum is not always stable in their presence.

Also, radioactivity due to Na24 was found when sodium molybdate-based products were applied in nuclear component cooling water systems (CCW). Therefore, a more radioactivity resistant new molybdate-based product of high purity reagents grade formulation was developed for nuclear application and it was verified to be as effective as chromate for corrosion protection of mild and cast steels, cast iron, and copper alloys in deionized and non-potable waters under turbulent and static conditions. The results from corrosion evaluations in the laboratory and in the field in closed cooling water systems are described in this work.

This new molybdate-based inhibitor design program considerably decreased the plant operation and maintenance costs, compared to previously used less expensive chromate chemical. In addition, there was also an indirect cost savings due to elimination of potential problems with chromate of environmental impact.

Procedure for chromate removal and its conversion to a new molybdate-based blend in nuclear CCW is also presented. Described nonchromate treatment requires relatively simple field monitoring, measure and control.

Subject
Test methods, Water, Materials, Nuclear power, Corrosion rate, Potassium, Copper alloys, Cooling water systems, Sodium, Corrosion inhibitors, Corrosion protection, Cooling water, Corrosion potential
Keywords:
chromate replacement, inhibitor efficiency, molybdate-based blend, component cooling water system, toxicity, reagent
© 1992 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).
1992
Association for Materials Protection and Performance (AMPP)
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