A study of the polarization behavior of AISI type 420 stainless steel was conducted in solutions containing differing amounts of HCO3-, H2S, Cl-, and CO2. The study concentrated on determining the influence of these environmental variables on pitting. It was found that the chloride concentration must be greater than a critical value before pitting will occur, and that this value is a function of the amount of the pit-inhibiting anion, HCO3-, present. The critical value is independent of H2S. Beyond the critical value, the pitting potential decreases with increasing chloride. The amount of chloride necessary for pitting to occur at the rest potential was obtained by extraplation of the pitting potential vs. chloride data. Unlike the critical concentration, the amount of chloride necessary to cause pitting at the rest potential was greatly reduced by the presence of H2S.

AISI type 420 stainless steel was sometimes observed to spontaneously polarize hundreds of millivolts more noble than the original open circuit potential.

This behavior can lead to pitting in some environments. Because H2S eliminates the possibility of spontaneous polarization, its presence in small amounts can sometimes be advantageous.

Subject
Pits, Materials, Chloride ion concentration, Passive films, Polarization curves, Electric potential, Pitting, Stainless steel, Polarization, Chlorides, Electrodes, Rest potential, Electrode potential
© 1987 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).
1987
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.