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
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.
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.
The Problem of Corrosion
Scale in Ballast Tanks
