The effects of chloride and phosphoric acid on three different materials (C-276, UNS N08028, and UNS N083671) have been studied by electrochemical tests. The electrochemical tests were performed in deaerated solutions, at two different levels of sodium chloride and phosphoric acid at a fixed temperature of 95°C. Potentiodynamic polarization scans in NaCl solution have been carried out to determine the pitting and the repassivation potentials for N08028 and N08367 and the range of passivity of alloy C-276. These tests help to rank the materials based on resistance to localized corrosion. All the tested alloys show a range of passivity. C-276 showed the best corrosion resistance under all tests conditions. N08367 performed better than N08028. Alloy C-276 has the highest range of passivity followed by N08367 and N08028. Under all test conditions C-276 doesn’t exhibit pitting but shows transpassive dissolution of chromium. In the most aggravated condition alloy C-276 shows passivity range of about 800mV (-100 mV to +700 mV) followed by N08367 of about 300mV. Pitting potential of alloy N08367 is + 300 mV higher than N08028. Passive current density of C-276 is lower than N08028 and N08367 in most of the conditions. Alloy C-276 and N08367 were sensitized and tested accordingly. Sensitization of those alloys affected their behaviour under tested conditions. For both those alloys sensitization decreased the resistance to localized corrosion. Both pitting and repassivation potential was plotted as a function of chloride concentration and pH. The effect of the carbide precipitation and intergranular corrosion are also discussed from the results of electrochemical tests and microstructural examination. C-276 performed better than N08367 and N08028 in both the sensitized and the non-sensitized conditions.

Subject
Pits, Corrosion resistant alloys, Nickel based alloys, Molybdenum alloys, Repassivation potentials, Sodium chloride, Sensitization, Pitting, Phosphoric acid, Corrosion resistance, Localized corrosion, Alloys, Chlorides
Keywords:
Chloride, phosphoric acid, alloy C-276, sensitization, polarization scan, repassivation potential, intergranular attack
© 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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