Currently, evaporator tubes used to concentrate “wet process” phosphoric acid are made from high-chromium stainless steels and high-chromium nickel-iron alloys. While these offer good resistance to this highly contaminated chemical, improved materials are sought by the agrichemical industry, in the hope of extended use of evaporator tubes.

The objectives during the development of this new alloy were enhanced resistance to “wet process” phosphoric acid, high resistance to chloride-induced pitting and crevice attack (since the chloride content of this acid is usually high), and high thermal stability. These were attained with a simple ternary system, essentially Ni-33Cr-8Mo. Due in part to its high thermal stability, no problems were encountered in making production quantities of plates, sheets, bars, wires, welded tubes, and seamless tubes.

In this paper, the experimental findings and the corrosion characteristics of the chosen composition are defined. In particular, its advantages in “wet process” phosphoric acid and its resistance to localized attack in a ferric chloride solution are discussed.

Subject
Acids, New alloys, Materials, Molybdenum, Acid concentration, Nickel based alloys, Molybdenum alloys, Thermal stability, Chromium, Chemical resistance, Pitting, Phosphoric acid, Chloride stress corrosion cracking
Keywords:
Nickel Alloys, Phosphoric Acid, Agrichemical
© 2004 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).
2004
Association for Materials Protection and Performance (AMPP)
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