For Modeling Electrochemical Corrosion Processes and Cathodic Protection Design
Electrochemical Corrosion is Everywhere
Corrosion costs the world upwards of $1 trillion each year. Most corrosion occurs due to electrochemical reaction processes taking place underwater and in wet or humid environments. The Corrosion Module allows engineers and scientists to investigate these processes, gain an understanding of the extent to which corrosion could occur over the lifetime of a structure, and implement preventative measures to inhibit electrochemical corrosion, in order to protect their structures. The module can be used to simulate corrosion at the microscale in order to investigate the fundamental mechanisms, and at larger scales to determine how to protect massive or long-ranging structures from corroding.
Understanding Corrosion is Key
The Corrosion Module includes features, interfaces, and example models that enable a straightforward approach to the simulation of all electrochemical corrosion processes, such as galvanic, pitting, and crevice corrosion. Transport in corrosive and corroded material is accounted for through the dynamic modeling of changes in the corroding surface and the electrolyte in contact with such surface. The Corrosion Module includes standard interfaces for modeling the corrosion potential and current distributions of corrosion processes where the electrochemical reaction kinetics can be described by the Tafel, Butler-Volmer, or other user-defined equations. The electrochemical reactions are fully resolved together with electric potentials in electrolytes and metal structures, homogeneous chemical reactions, and phenomena unique to corrosion processes such as the change of the shape of a metal surface due to corrosion.
- Concentrations of corrosion species along the length of a crevice
- Electrolyte potential on the hull of a ship during ICCP
- Iron concentration and contours of the electrolyte potential in the tertiary current distribution study of the galvanic corrosion of a galvanized nail.
Optimizing Corrosion Protection Systems
The Corrosion Module also allows you to design effective corrosion protection systems. This includes the simulation of Impressed Cathodic Current Protection (ICCP), sacrificial anodes, and anodic protection, where anodic current is impressed on corroding material to enforce passivation.
By using the Corrosion Module to investigate the specific protection mechanisms at the microscale, you can extract parameters that may be used to simulate larger structure, for example hydroxide film growth on protected structures. You can import CAD files containing your designs in COMSOL Multiphysics, and then set up the description of the protection process. Upon identifying regions in your structure that are susceptible to accelerated corrosion, you can specify the placement of sacrificial anodes, and where cathodic or anodic protection currents should be impressed.
Another application of the module is to estimate the effect of stray currents on the corrosion of buried structures or structures under water. You can then also use the module to optimize the positioning of protective electrodes to avoid this corrosion mechanism. When correctly designed, these electrodes mediate the uptake of stray currents without corroding the structure placed close to a stray current source, e.g. a railroad.
Modeling the Extended Effects of Electrochemical Corrosion
The impact corrosion can have on a structure over time can be downright catastrophic. As corrosion removes material from a structure, it may compromise its structural integrity.
In some cases, you may want to do a structural analysis in combination with corrosion analysis to see which parts of the structure are subjected to high stresses and strains. Corrosion in these parts may be devastating, so you want to make sure that these parts are protected. To understand the corrosion effects and to optimize your corrosion protection design, you can combine the Corrosion Module with the Structural Mechanics Module. This is thanks to the extensive power of COMSOL Multiphysics, which allows you to directly couple models built in one module with any other module.
In other cases, turbulent and multiphase flow may need to be combined with transport of chemical species. You can then use the CFD Module in combination with the mass transport interfaces in the Corrosion Module to obtain accurate mass transport descriptions.
Submarines: Corrosion Protection or Enemy Detection?
David Schaefer University of Duisburg-Essen, Duisburg, Germany Germany's Technical Center for Ships and Naval Weapons, Bundeswehr, Germany
Submarines create underwater electric potential (UEP) signatures when using corrosion protection systems. These signatures are detectable by enemy vessels, an undesirable effect of the corrosion protection. Germany’s Technical Center for Ships and Naval Weapons (WTD 71) has worked with the Laboratory for General and Theoretical Electrical ...
Cyclic Voltammetry at an Electrode
Cyclic voltammetry is a common analytical electrochemical technique, where the potential at a working electrode is swept over a range and back again while the current is recorded. The current-voltage waveform, referred to as a voltammogram, provides information about the reactivity and mass transport properties of an electrolyte. For large ...
Electrochemical Impedance Spectroscopy
Electrochemical impedance spectroscopy (EIS) is a common technique in which a small oscillating perturbation in cell potential is applied to an electrochemical system so as to interrogate the kinetic and transport properties. The Electroanalysis interface is used with a frequency domain study to simulate EIS for a range of electrode reaction ...
Ship Hull Corrosion Mitigation
Impressed current cathodic protection is a commonly employed strategy to mitigate the ship hull corrosion where an external current is applied to the hull surface, polarizing it to a lower potential. In this model, the effect of propeller coating on the current demand is demonstrated.
Oil Platform Corrosion Protection Using Sacrificial Anodes
Steel structures immersed in seawater can be protected from corrosion through cathodic protection. This protection can be achieved by an impressed external current or by using sacrificial anodes. The use of sacrificial anodes is often preferred due to its simplicity. This example models the primary current distribution of a corrosion protection ...
This tutorial example serves as an introduction to the Corrosion Module and models the metal oxidation and oxygen reduction current densities on the surface of a galvanized nail, surrounded by a piece of wet wood, which acts as electrolyte. The protecting zinc layer on the nail is not fully covering, so that at the tip of the nail the underlaying ...
Crevice Corrosion with Electrode Deformation
This model exemplifies the basic principles of crevice corrosion and how a time-dependent study can be used to simulate the electrode deformation. The model is in 2D and the polarization data for the corrosion reaction is taken from a paper by Absulsalam and others. The model and the results are similar to a 1D model by Brackman and others. ...
Cathodic Protection of Steel in Concrete
This example models cathodic protection of a steel reinforcing bar in concrete. Three different electrochemical reactions are considered on the steel surface. Charge and oxygen transport are modeled in the concrete domain, where the electrolyte conductivity and oxygen diffusivity depend on the moisture content. The impact of different ...
This model simulates atmospheric galvanic corrosion of an aluminum alloy in contact with steel. The electrolyte film thickness depends on the relative humidity of the surrounding air and the salt load density of NaCl crystals on the metal surface. Empirical expressions for the oxygen diffusivity and solubility are also included in the model in ...
Model of a Diffuse Double Layer
In the diffuse double layer and within the first few nanometers of an electrode surface, the assumption of electroneutrality is not valid due to charge separation. Typically, the diffuse double layer may be of interest when modeling very thin layers of electrolyte including those in electrochemical capacitors and microelectrodes. This example ...