Ammonium Chloride (NH4Cl) corrosion is an aggressive form of localized, underdeposit corrosion commonly found in overhead equipment and piping associated with crude and hydroprocessing units. This happens when ammonia and hydrochloric acid in the vapor react to form NH4Cl salt. Being hygroscopic, NH4Cl absorbs moisture leading to severe localized attack. Since this form of corrosion is highly unpredictable; appropriate operational, materials and chemical controls should to be set in place. However, this is not always the case. Additionally, models developed in the lab have not been very successful at predicting corrosion rates in the field. This paper summarizes key case studies where this form of corrosion was observed. Best practices for process control and corrosion mitigation strategies have been recommended based on the learnings from these failures.

Subject
Acids, Salt formation, Corrosion failures, Water, Piping, Modeling, Salts, Tubes, Vapors, Corrosion scales, Crude, Towers, Chlorides
Keywords:
ammonium chloride corrosion, underdeposit corrosion, under-salt attack, neutralizer, salt fouling, NH4Cl corrosion mechanism, ionic equilibria modeling
© 2017 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).
2017
Association for Materials Protection and Performance (AMPP)
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