The Problem of Corrosion Scale in Ballast Tanks

In the marine industry, the buildup of heavy layers of corrosion scale in steel ballast tanks can be a major problem for ship operators. Ballast tanks are required to be in sound condition, and deterioration of ballast tank walls may make a vessel un-seaworthy.

Corrosion scale needs to be removed from tank walls to allow for proper inspection of the structural steel and allow coating to prevent future corrosion. The three conventional methods of removing tank scale are time consuming and costly:

• Shot-blasting
• Hydro-blasting
• Manual removal

The GalvoClean™ Solution

Now there is a better solution. The GalvoClean method is an electrolytic process proven to reduce the man-hours and costs in removing scale by at least thirty percent (30%) compared to conventional methods. The scale-to-steel interface is subjected to a chemical reaction which causes the release of hydrogen, thereby releasing the scale from the steel substrate.

What the GalvoClean treatment achieves:

• Clean Steel. The steel structure remains unaffected by the process.
• Removal of Poor Coatings. Disbonded coatings are removed during the process, while bonded coatings are not disturbed.

Major Benefits of the GalvoClean™ System

• No chemicals used.
• No coating damage where the coating soundly adheres to steel.
• No corrosion of exposed steel during the process. The magnesium used actually protects the steel.
• Release of hydrogen only affects areas which need de-scaling.
• Installation and dismantling procedures are very rapid. No time consuming welding required.
• Electrical measuring equipment monitors the progress of de-scaling and allows recording.
• New coatings can be applied immediately following procedure.

The GalvoClean™ Process

The GalvoClean system utilizes high potential magnesium ribbon and specially designed connection clamps. The magnesium ribbon is connected inside the ballast tank so that all surfaces to be cleaned are in direct “sight” of the ribbon, as the process works within a “line of sight” principle. This can be compared to installing an ordinary lighting system, where the requirement is to achieve no shadows.

After installation of the ribbon is complete, the tank is filled with clean, low resistivity seawater. The system is left to work for approximately seven to ten days, while being monitored electrically. Once the cleaning is complete, the tank is drained of all water, so that the scale and GalvoClean remnants can be removed from the tank.

After draining, the tank is hydro-blasted using equipment capable of providing pressures between 300 and 500 bar (4,000 and 7,000 psi). This will remove any loose scale from horizontal surfaces as well as any salt deposits, which have built up during the process. No disc sanding is required.

Once the loose scale has been removed from the tank and the area has completely dried, the steel can be recoated with no further treatment. In addition, cathodic protection anodes should be installed to supplement the coating system to prevent further scale and corrosion.