PH'D Defense Mme Marie Minola

Abstract : Currently, the optimization of corrosion protection system for offshore structures, with the prediction of their degradation state, are major challenges. These protection systems yield electromagnetic fields leading to the appearance of chat is called an electrical signature of ships. For Navy vessels, this represents a risk of being detected by different types of sensors. Thus it becomes essential to work on the electric discretion of ships. This signature would depend on the physical conditions of the environment, but also on the surface state of the immersed metals: propeller and hull. An assessment of the actual impact of these parameters is important for a realistic prediction of this signature by numerical simulation. CorOns solver has been developed in this context, this solver is based on the method of Boundary Element Method (“BEM”) and its development is at the origin of an inter-laboratory collaboration (DGA, G2Elab and LEPMI). As most of computational tools, experimental results are required especially to fix boundary conditions. This PhD project was carried out to enrich the solver databases and in order to have better understanding of the evolution of the interfaces according to the different corrosion scenarios encountered in real conditions . Electrochemical techniques such as electrochemical impedance spectroscopy and voltammetry were used to meet these expectations, by characterizing the different interfaces present in a ship’s hull: material of propeller and hull. The results obtained confirmed the dependence of the measured current densities and thus indirectly the electrical signature of the ships, with the electrolyte temperature, aeration, and agitation and also with the surface state of the metals. An increase of temperature of 10°C leads to an increase of 20 µA.cm-2 for the unpainted carbon steel. Similarly, a variation of the aeration conditions of the electrolyte increased the corrosion rate of the martensitic steel representing the propeller material under cathodic polarization. In contrary, the aging of interfaces characterized by the formation of calcareous deposit under PCCI, led to a decrease in current densities. These current densities were not affected by switch-off ICCP period, but the calcareous deposit nature changed. Larger-scale tests (1/100th model) gave similar results validating the use of laboratory polarization curves obtained on “laboratory” samples to determine boundary conditions for the computational tool CorOns, for NAB material.

Supervisor : Virginie ROCHE, Jean-Claude LEPRETRE
 

Virginie ROCHE		MAITRE DE CONFERENCE HDR		Grenoble INP		Directeur de thèse
Bernard TRIBOLLET		PROFESSEUR EMERITE		Sorbonne Université		Rapporteur
Philippe REFAIT		PROFESSEUR DES UNIVERSITES		Université de la Rochelle		Rapporteur
Olivier CHADEBEC		DIRECTEUR DE RECHERCHE		CNRS délégation Alpes		Examinateur
Olivier DEVOS		PROFESSEUR DES UNIVERSITES		Université de Bordeaux		Examinateur
Ricardo  NOGUEIRA		PROFESSEUR		Khalifa University		Examinateur
Eric SAINT-AMAN		PROFESSEUR DES UNIVERSITES		Université Grenoble Alpes		Examinateur
Cédric GOEAU		INGENIEUR DOCTEUR		Techniques navales Brest		Examinateur