The use of HEDP (1-hydroxyethylidene-1,1-diphosphonic acid) in the treatment of industrial boilers to reduce deposition and condition sludge has been studied. Laboratory work has demonstrated that it has threshold inhibition, sequestration, and crystal modification properties; also, previous autoclave experiments at pressures up to 8.4×106 Pa (1200 psig) have proven its stability. This paper explores the stability and efficacy of HEDP in industrial boilers.

Experiments, involving a variety of operating conditions, were conducted using several boilers. Feedwater and continuous blowdown samples were analyzed to determine HEDP stability and hardness transport. Additionally, boiler inspection reports before and after its use were reviewed in an attempt to correlate the condition of drum and tube surfaces with hardness transport.

Results of this study show that: HEDP helps prevent scale deposits, including those containing iron, on boiler surfaces and in many instances removes existing scale deposits; the stability of this phosphonate permits it to perform in boilers; the small quantities of orthophosphate that are formed as a result of some decomposition will not interfere with phosphate or EDTA programs; and dissolved oxygen catalyzes breakdown, therefore it should be fed to completely deaerated feedwater. Finally, transport data may not be an accurate indicator of boiler surface conditions.

Subject
Acids, Stability, Decomposition, Phosphonates, Inspection, Scale deposition, Feedwater, Phosphates, Cycles of concentration, Scale, Boilers, Deposit corrosion, Hardness
© 1983 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).
1983
Association for Materials Protection and Performance (AMPP)
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