The exploration and exploitation of deep seawater present promising prospects for many industries. Hence, the use of reliable materials resistant to corrosion in deep seawater conditions is required. In natural seawater, many parameters can influence the kinetics of corrosion such as: temperature, oxygen content, biofilm and fouling activity, flow rates and hydrostatic pressure. For passive materials such as Cr Ni Mo stainless steels and nickel-based alloys, the specificity of the above parameters in deep sea environment might have an impact on both initiation and propagation phases of localized corrosion (e.g. pitting and crevice corrosion), and no or limited field data obtained in deep sea can be found in the literature. Currently, there are still many questions on the corrosion behavior of metallic materials in deep seawater since the results obtained in laboratory or from near-surface seawater cannot be extrapolated to deep seawater environments, especially in terms of bacterial activity which can significantly impact the localized corrosion resistance of passive alloys (cf. biofilm-induced ennoblement).

In this study, 13-Cr Ferritic, Austenitic, Lean Duplex, Duplex, Super Duplex, Super Austenitic, Hyper Duplex Stainless Steels and Nickel based alloys were exposed during 11 months at 1020 and 2020 m water depth in the Atlantic Ocean to evaluate their corrosion behavior. Structural carbon steel S355 was also exposed under similar conditions. Polyvinylidene difluoride (PVDF) crevice gaskets according to ISO18070:2015 were used to assess the crevice corrosion at two different gasket pressures, namely 3 and 20 N/mm2. Potential monitoring was performed in-situ (at both 1020 m and 2020 m) in order to characterize the formation of electroactive biofilms at the surface of passive alloys in these environments. At each exposure depth, the environment was characterized using environmental sensors, e.g. temperature, flow velocity, dissolved oxygen, salinity. The obtained results allowed i) ranking the passive material in terms of resistance to pitting and crevice corrosion in deep water at 4°C, ii) comparing biofilm electroactivity and corrosion rates at 1020 and 2020 m depth.

Subject
Water depth, Water, Materials, Stainless alloys, Gaskets, Seawater, Biofilms, Crevices, Crevice corrosion, Deep water, Pitting, Corrosion resistance, Stainless steel
Keywords:
Deepsea corrosion, seawater, biofilm, stainless steels, nickel-based alloys
© 2019 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).
2019
Association for Materials Protection and Performance (AMPP)
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