• Pinaud, O.
• Rouve, L-L.
• Nale, M.
• Roche, Virginie
• Leprêtre, Jc.
• Minola, M.
• Chadebec, Olivier
• Goeau, C.

Abstract

As underwater structure, ships are protected by a suitable cathodic protection system to prevent and reduce significantly the corrosion phenomenon. This protective system, called Impressed Current Cathodic Protection (ICCP), creates an underwater electrical current. Then, this current generates an electromagnetic field also referred as electrical signature that could be detectable by sensors. Therefore, this work refers to the electrochemical characterization of the materials used in the naval framework in addition to a better comprehension of the corrosion phenomenon. The final goal is to predict electrical signatures of ships under different corrosion conditions. These predictions will be done by numerical simulations using the models of material that we work on and the simulation software developed by the G2Elab.In a first time, polarization laws of different materials present on the immersed hull and electrically connected are obtained: the hull material DH36 steel (coated and uncoated), the propeller with different material possibilities (stainless steel 316L, martensitic or Nickel Aluminum bronze alloy) and zinc for sacrificial anodes to complete the cathodic protection system. The first step of this project is to be able to model the metal/electrolyte interface following the environmental conditions: speed, temperature, polarization state, aging coating and galvanic coupling. The second step will be to test theses founded models at bigger scale on a ship model. To achieve these goals, it’s important to understand what happens physically at the interface and to model the different corrosion phenomena which take place at the interface. To model interface experimentally, Electrical Equivalent Circuits are used. These Electrical Equivalent Circuits, commonly called EEC, are obtained by fitting Electrochemical Impedance Spectroscopy measurementsdata. To complete EIS investigations and confirm the different models, potentiodynamic curves and Scanning Electron Microscopy with EDX analyses were also performed.From the first results, Electrical Equivalent Circuits (EEC) of the behavior of metallic interface (hull) are proposed for different polarizations and environmental conditions: anodic, corrosion potential and cathodic (ICCP potential: -0,8 VECS). In complement EEC investigations will be made under temperature variations and dynamic conditions for hull steel samples at its corrosion potential. In future experimentations, the propeller material will be characterized following the same type of parameters variations (temperature, speed, polarization state ...)Painted hull steel samples give equivalent results. Whatever experimental conditions, freshly painted hull steel samples show an almost pure capacitance behavior. To model this behavior a simple Randle circuit, which only take into account the impedance of the paint, is used. In case of uncoated hull steel, EEC are more complex and change following the polarization and experimental conditions. In all cases, a deposit is formed but its nature and protective behavior change with polarization: a formation of calcareous deposit under cathodic polarization and corrosion products deposit under anodic polarization. That requires in consequence to include additional impedances in the EEC modeling: impedance of a deposit or diffusion impedance for example. Temperature variation and dynamic conditions influence the kinetic of the different interfacial phenomena.

Topics

• nickel
• stainless steel
• corrosion
• scanning electron microscopy
• simulation
• aluminium
• zinc
• electrochemical-induced impedance spectroscopy
• aging
• Energy-dispersive X-ray spectroscopy
• interfacial
• aging
• aluminum bronze