Corrosion

You can use the Electrodynamic Potential model in Simcenter STAR-CCM+ to help you to understand and predict the effect of corrosion.

For metal structures that are prone to corrosion, the challenge is to maximize the design life of the structure by preventing corrosion. The ability to understand and predict corrosion behavior using Simcenter STAR-CCM+ lets you compare corrosion prevention methods and select the optimal solution for each specific scenario—even with complex geometries.

One way to prevent corrosion is using cathodic protection. The concept of cathodic protection is straightforward. However, finding the optimal level of protection is a more complex consideration. Insufficient cathodic protection results in corrosion. Over-protection can result in negative effects such as hydrogen embrittlement, which weakens high-strength steels and increases the likelihood of the structure fracturing.

Using Simcenter STAR-CCM+, you can optimize the location and size of the sacrificial anodes that prevent corrosion. This process makes sure that the level of cathodic protection that a structure receives is most effective in prolonging the life of the structure. Simulating the cathodic protection of a structure is also cost effective as it prevents wasting expensive anodes unnecessarily.

You can use corrosion modeling in Simcenter STAR-CCM+ for modeling cathodic protection on:

ship hulls
oil rigs and gas pipes
bridges
reinforced concrete
underground structures

To model corrosion, follow the procedure that is set out in Modeling Electrochemical Surface Reactions.

What Is Corrosion?

Corrosion is an electrochemical process which occurs naturally when metals react to form compounds that are more stable than their pure elemental form. During corrosion, a number of electrochemical surface reactions occur at the interface between the metal and the electrolyte. See Electrochemical Surface Reactions.

Metal atoms lose electrons and become ions which are soluble in the electrolyte. When metals lose electrons, the reaction is known as oxidation—an example of an anodic reaction. The following reaction shows the oxidation of iron:

$F e$ $F e^{2 +} + 2 e^{-}$

The electrolyte accepts electrons from the metal and forms ions. When substances accept electrons, the reaction is known as reduction—an example of a cathodic reaction. The following reaction shows the reduction of water:

$2 H_{2} O + 2 e^{-}$ $H_{2} + 2 O H^{-}$

The ions that are produced during corrosion form compounds that are, in most instances, soluble in the electrolyte. The corrosion rate depends on the potential drop at the interface between the metal and the electrolyte. Overall, corrosion causes metals to break down and so weaken metal structures and reduce their lifespan.

In the diagram below, iron, $F e$ , is corroding in the presence of water, $H_{2} O$ , and oxygen, $O_{2}$ , and losing electrons, $e^{-}$ , to form iron ions, $F e^{2 +}$ . The water and oxygen accept electrons from the iron to form hydroxide ions, $O H^{-}$ :

One method of preventing corrosion is by cathodic protection.

What is Cathodic Protection?

Cathodic protection is a process that is used to prevent a metal from corroding by creating an electrochemical cell in which the protected metal forms the cathode.

There are several ways to create an electrochemical cell for the purpose of cathodic protection, including:

Actively imposing a direct electrical current on the metal from a power supply
Using galvanic anodes

Using Galvanic Anodes

When galvanic anodes are used for cathodic protection, metal anodes are attached to the metal structure that requires protection. The anodes are made of a metal with an equilibrium potential that is greater than that of the metal structure. Since the anodes are less noble than the metal, the electrolyte potential is greater near the anodes than near the metal structure. This potential difference results in ion current flow from the anodes to the metal structure. Ions and electrons are produced at the anode, the ions travel through the electrolyte, and electrons travel through the metal circuit. Ions and electrons then recombine at the cathode. The potential drop through the metal circuit is usually much smaller than the potential drop through the electrolyte, since the metal has a much higher conductivity.

The current flow that is supplied to the metal structure prevents the metal structure from undergoing oxidation.

To model cathodic protection, follow the procedure that is set out in Modeling Electrochemical Surface Reactions.