Dutch research institute Deltares has developed a new tool to model water replenishment and the chemical reactions of internal Impressed Current Cathodic Protection (ICCP) systems.
In recent years, there has been an increased awareness of the risk of corrosion inside monopiles, Deltares said. This awareness is mainly stimulated by inspections and decommissioning of existing foundations, where more corrosion than expected was observed.
This has led to the installation of internal corrosion protection systems. A commonly used corrosion protection system, both internally and externally, is an ICCP system.
On the anode side of the ICCP system, H^+ is released, which lowers the pH level of the fluid and may result in local acidification. If the internal water becomes too acid, this may damage internal cables or other fittings.
To prevent stagnant water, and hence acidification of the fluid, the monopile foundation is fitted with replenishment holes. The rate at which the water is exchanged depends on the open area and the location of the replenishment holes, as well as, the external flow conditions such as waves and tidal flows. The pH level inside the pile is governed by the rate at which water is replenished in combination with the chemical reactions on the anode and cathode of the corrosion protection system.
The new tool couples a hydrodynamic flow model to a water quality model DELWAQ. With this new tool, Deltares is said to be able to determine wave action and pressures inside the monopile, the effect of marine growth, flow velocities through replenishment holes and pH levels of the fluid in the monopile for representative met-ocean conditions.
This information can be used to advise on the positioning and the size and location of water and air replenishment, the research institute said.