Sulfuric acid is one of the basic raw materials for the chemical industry. It is used in numerous processes as a reagent, as a catalyst and as a drying agent.

Sulfuric acid is very corrosive. AISI types 304 and 316 stainless steels are used to handle very diluted acid at low temperature. At higher concentrations and temperatures the use of materials like high alloyed stainless steels and nickel based alloys becomes necessary. Alloy 20, alloy 825, alloy 31, alloy 59 and Ni-Mo-alloys are some examples.

The high alloyed austenitic stainless steel alloy 31 (UNS N08031) and the nickel-chromium- molybdenum alloy 59 (UNS N06059) exhibit good corrosion resistance in sulfuric acid as well as good resistance to pitting and crevice corrosion. Therefore, they find extensive application e.g. in flue-gas desulphurization units of coal fire power plants, in the transportation and recycling of waste sulfuric acid as well as in heaters and coolers also for chloride contaminated acid.

This paper compares the corrosion behavior of alloy 31 and alloy 59 in sulfuric acid environments. Corrosion data under different conditions are presented and discussed. The electrochemical behavior of both materials was studied as well. Results of laboratory testing are presented together with examples of applications.

Subject
Acids, Materials, Corrosion resistant alloys, Stainless alloys, Corrosion rate, Sulfuric acid, Nickel based alloys, Molybdenum alloys, Nickel chromium molybdenum alloys, Copper alloys, Corrosion resistance, Alloys, Chlorides
Keywords:
sulfuric acid, alloy 59 (UNS N06059), alloy 31 (UNS N08031), corrosion behavior, isocorrosion diagram
© 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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