Cathodic Protection

Cathodic protection is used to control the corrosion of a metal surface by creating a current flow from the cathodic protection system to the structure. There are two basic methods; Galvanic and Impressed Current. In a galvanic cathodic protection system, the anodes connected to the structure requiring protection have a natural potential that is more negative than the structure’s. When the anodes are connected, a current flows from the anode (which is at a more negative potential) to the structure (which is at a less negative potential) in a DC circuit. OPERA has been used extensively to analyse this type of behaviour, primarily in the marine marketplace for corrosion protection of ships and boats.

Applications:

  • Ship hulls
  • Pipelines
  • Steel in concrete
  • Heat Exchangers
  • Marine piles and walls

For a typical marine galvanic CP analysis, Opera requires a model of the exterior surface of the vessel including
– Impressed current anodes
– Sacrificial anodes
– Painted and unprotected areas

The volume of sea and sea-bed surrounding vessel meshed with finite elements and material conductivity is specified.

Current density in sea for +500 A impressed current

Current density in sea for +500 A impressed current

Opera’s results post-processing allows for the interrogation of many useful results, including:
– Potential distribution on vessel, showing the effectiveness of CP system.
– Electric field distribution anywhere in modelled volume of sea and sea-bed
– Current density distribution anywhere in modelled volume of sea and sea-bed
– Resultant magnetic field from currents flowing in sea and sea-bed

FAQ

Is it possible to perform Cathodic Protection calculations using Finite Element Analysis such as Opera?

You can use Opera’s static solver to perform current flow calculations, which are suitable for cathodic protection (CP) modelling on ships / submarines. CP systems inject current into the conducting sea-water / sea-bed (which do need to be included in the model in this case) to modify the electrochemical potential distribution that occurs because the ship is made from different metals and
causes corrosion. The modified potential distribution then prevents (or at least reduces) corrosion.

Is it possible to analyse Ferromagnetic & Eddy Current Signatures in a Marine Environment using Opera? How will the modelling of the surrounding sea-water be taken into account?

With regard to ferromagnetic and eddy current signatures from ships and submarines, you need the static and dynamic electromagnetic modules of Opera-3d (with Modeller / Post) to do these calculations. A high frequency solver is not needed - in these type of calculations, the sea-water does not have any effect and can be treated as free-space. In defence applications, the signatures have to be minimized without reducing the effectiveness of any cathodic protection system. Opera’s static solver can help in this by modelling the ship and CP system to determine if (a) the CP system is effective (from the potential solution) and (b) the signatures are sufficiently low.