Carbon steel is the main construction material in HYDROFLUORIC ACID (HF) alkylation units. Carbon steel has good corrosion resistance to anhydrous HF (AHF) below 160°F (71°C). The corrosion resistance is due to the formation of an inorganic iron fluoride scale on the carbon steel surface that protects the steel from further corrosion. The presence of an adherent and continuous scale is essential in keeping the corrosion rate at a minimum.

Several cases of accelerated and selective corrosion of piping components operating within prescribed process conditions were experienced. The corrosion was mainly a general metal loss.

The corrosion was observed in one piping but not in the adjoining different pieces of pipe or flange. This led to extensive chemical and metallurgical examination of the steel components to determine the cause of this selective, accelerated corrosion. Residual elements were found to have pronounced influence on the corrosion resistance of carbon steel.

This paper outlines the findings of the field samples and supporting laboratory test data.

Subject
Piping, Fluorides, Chromium, Steel coupons, Iron, Flanges, Corrosion scales, Steel, Carbon steel, Corrosion resistance, Copper, Nickel, Elements
Keywords:
Carbon Steel, Alkylation, Anhydrous HF, Iron Fluoride, Residual Elements, Selective Corrosion
© 1993 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).
1993
Association for Materials Protection and Performance (AMPP)
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