Standard test methods for evaluating the performance of external pipe coatings have been used for many years. Although there may be variations in the test parameters, the same basic tests have been used. For high temperature service, the effects of the test parameters are generally approximated by increasing the test temperature. What is missing in this testing regimen, is long-term ageing in hot-wet or hot-dry conditions to determine the integrity of the coating system. In this study, high temperature Fusion Bonded Epoxy (FBE) and three-layer polypropylene coatings (3LPP) were evaluated after long immersion times in hot water or dry heat ageing to determine if the coatings will embrittle, crack, or disintegrate with time. Free films of FBE immersed in hot water at various temperatures were also performed to determine percent weight gains over 28 weeks. The performance of high temperature FBE products were compared to standard FBE to determine just how much improvement would be obtained for the high temperature products over the standard FBE. Immersion tests with and without cathodic polarization of the test samples was performed to compare the effects on adhesion, time to blistering and corrosion of the steel substrate.

High temperature FBE did perform better than standard FBE for blistering resistance, moisture permeation and cathodic disbondment resistance. Percent weight gains of free films of FBE immersed in water at 190 - 230°F (88-110°C) were highly variable between samples with weight gains in the range of 4-63%. However, limited comparative data suggest that high weight gains do not appear to affect coating performance. Immersions of FBE exposed to cathodic polarization of –1v SCE were found to have significantly greater resistance to blistering and retention of adhesion strength than nonpolarized samples. Ageing of FBE at 260°F (127°C) had excellent resistance to embrittlement for exposures up to 6 years. Longterm ageing of 3LPP in hot-dry conditions developed cracking in the PP layer. Cracking occurred much less for samples immersed at high temperatures. Disbondment was the primary failure mode in hot immersions.

Subject
Coating performance, Water, Coatings, Weight gain, Fusion bonded epoxy coating, Mechanical failure, Color, Immersion, Cracking, Blistering, Adhesion, Three-layer polypropylene coating, High temperature
Keywords:
Fusion Bond Epoxy, external pipe coatings, three-layer polypropylene pipe coating, high temperature pipe coatings, test methods
© 2006 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).
2006
Association for Materials Protection and Performance (AMPP)
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