An effective corrosion inhibitor must protect all metallic components in a cooling system, including the zinc coating of a galvanized cooling tower. This is especially important with the current trend toward more alkaline cooling water treatments.1  Higher pH levels combined with newer deposit control agents may minimize corrosion, scaling, and fouling in the coolers but can simultaneously cause premature failure of a cooling tower made of galvanized steel. Too low a pH without proper corrosion inhibition can also pose a problem.

Following a brief review of theory and previous work, this presentation documents a field investigation using corrosion coupons to simulate galvanized towers treated with phosphate/phosphonate-based corrosion inhibitors. From pH 6.5 to 7.9, zinc coupons exhibited powdery deposits of zinc oxide with silica and calcium and ferric oxides as impurities; at pH 8.3, corrosion deposits tested positive for carbonate and resembled the waxy white adherent basic zinc carbonate reported previously.2,3  For the most part, the coupon corrosion rate for zinc in isolation varied from 1 to 20 mpy (25 to 510 um/y) and from 10 to 30 mpy (250 to 760 um/y) when in contact with steel coupons. An installation employing chromate was used as a control.

Subject
Zinc rich coatings, Water, Corrosion rate, Steel coupons, Metal coupons, Galvanized coatings, Acidity, Corrosion products, Steel, Corrosion data, Corrosion coupons, Deposit corrosion, Zinc
Keywords:
Chromate, Cooling, Corrosion, Coupons, Galvanized, Inhibitor, Phosphate, Phosphonate, Molybdate, Water
© 1990 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).
1990
Association for Materials Protection and Performance (AMPP)
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