Mechanism of coating delamination of polyethylene coated pipe has been studied under cathodic protection and natural immersion in hot water, changing pH, disolved oxygen content, and temperature.

On the basis of the results of this invenstigation, good hot water resistant polyethylene coated pipe has been developed by improving chemical treatment and primer for under-coating. The conclusions are as follows

  1. Coating delamination is mainly attributed to hydroxyl ion generated by oxygen reduction reaction.

  2. Oxygen reaches coating-pipe interface through polyethylene layer, water and cations enter from the edge of coating defect.

  3. The rate-determining step is chemical bond rupture process at coating-pipe interface by hydroxyl ion.

  4. Mechanism of coating delamination under cathodic protection should be the same under natural immersion, because of the same activation energy of coating delamination under both conditions.

  5. Hot water resistant polyethylene coated pipe has been developed by improving chromate and epoxy primer pretreatment.

  6. Its coating delamination was smaller than 10mm in length under cathodic protection (-1.5V vs. SCE) in 3% NaCl solution at 80°C for 30days, and does not occur under natural immersion in water at 80°C for 30days.

Subject
Primers, Water, Coatings, Cathodic disbondment, Epoxy coatings, Pretreatment, Steel, Potassium chloride, Oxygen, Coating defects, Polyethylene, Cations, Delamination
© 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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