The effects of chlorinated (1 mg/l) seawater at flow velocities of 0.3 m/s and 2.4 m/s on the freely corroding and galvanic corrosion behavior of three passive film forming alloys (Ti50, Ti6Al-4V and IN625) and two non-passive film formers (CA715 and Monel) were investigated. Results show that the passive film formers exhibit a marked electropositive shift in open circuit potential in chlorinated seawater as compared to natural (non-chlorinated) seawater; while the nonpassive film formers (CA715 and Monel 400) show a slight electronegative shift in open circircuit potential in chlorinated seawater. No corrosion occurred on the passive film forming alloys under any conditions. The non-passive film formers displayed a different behavior. Average uniform corrosion rate for Monel under freely corroding conditions was slightly lower in chlorinated seawater at both test velocities as compared to natural seawater test results; while 70-30 CuNi did not demonstrate any significant differences in average uniform corrosion rate (freely corroding) between natural and chlorinated seawater results. A thin brown adherent film was observed on all surfaces exposed to recirculated and refreshed chlorinated seawater. Energy dispersive x-ray microanalysis (EDXRM) indicates this film contains appreciable levels of manganese.

Galvanic couple tests show that the corrosion rate of the anodic member of the galvanic couples (CA715 and Monel 400 in this investigation) was significantly lower in 1 mg/l chlorinated seawater as compared to results from natural (non-chlorinated) seawater. This was true for both velocities (0.3 m/s and 2.4 m/s) and for different cathode: anode area ratios.

Anodic and cathodic polarization tests were conducted on Ti6Al4V and CA715 in 1 mg/l chlorinated and non-chlorinated ASTM ocean water under quiescent conditions. Results show a decrease in resistance to cathodic polarization of the Ti6Al4V in chlorinated ASTM ocean water. It is postulated that it is this change in cathodic polarization of the passive film forming alloys (Ti and IN625) in chlorinated seawater that is responsible for the reduction in corrosion rate of Monel and 70-30 CuNi when coupled to the more noble passive film formers in chlorinated seawater.

Subject
Water, Materials, Corrosion rate, Circuit potentials, Chlorinated seawater, Chlorination, Passive films, Natural seawater, Seawater, Open circuits, Film formation, Galvanic coupling, Monel alloys
© 1985 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).
1985
Association for Materials Protection and Performance (AMPP)
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