*Article* **Cathodic Protection of Complex Carbon Steel Structures in Seawater**

**Philippe Refait 1,\*, Anne-Marie Grolleau 2, Marc Jeannin 1 and René Sabot 1**

> 1 LaSIE, UMR 7356 CNRS, La Rochelle Université, 17000 La Rochelle, France

2 CESMAN/CM Naval Group Research, Marine Corrosion & Cathodic Protection Department, 50104 Cherbourg-en-Cotentin, France

**\*** Correspondence: prefait@univ-lr.fr; Tel.: +33-5-46-45-82-27

**Abstract:** Cathodic protection efficiency of complex carbon steel structures in confined seawater environment was studied using a specific experimental device. Schematically, this device consisted of a Plexiglas matrix, crossed by a channel 50 cm long, 5 mm deep, 1.5 to 5 cm wide, which moreover included four bends at 90◦. Seawater flowed continuously inside the channel over 12 steel coupons embedded in the Plexiglas matrix. Cathodic protection was applied at a constant potential of −1060 mV vs. Ag/AgCl-seawater with respect to a reference electrode located outside the channel, at the seawater flow entry. The potential of four selected coupons was monitored over time via a microelectrode set close to each coupon. It varied significantly with the distance separating the coupons from the channel entry. At the end of the 3.5-month experiment, a polarization curve was acquired. The residual corrosion rate under cathodic protection was estimated via the extrapolation of the anodic Tafel line. It varied from <1 μm yr<sup>−</sup><sup>1</sup> to 16 μm yr<sup>−</sup>1, depending on the potential reached by the coupon (between −900 and −1040 mV vs. Ag/AgCl-seawater) at the end of the experiment and on the properties of the calcareous deposit formed on the steel surface.

**Keywords:** seawater; cathodic protection; carbon steel; calcareous deposit; marine renewable energy

#### **Citation:** Refait, P.; Grolleau, A.-M.; Jeannin, M.; Sabot, R. Cathodic Protection of Complex Carbon Steel Structures in Seawater. *Corros. Mater. Degrad.* **2022**, *3*, 439–453. https:// doi.org/10.3390/cmd3030026

Academic Editor: María Criado Sanz

Received: 11 July 2022 Accepted: 9 August 2022 Published: 12 August 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
