The Thames barrier was erected in 1989 to provide flood control to the upper reaches of the Thames River including the heavily populated areas of London. The gates could be raised from the riverbed into a vertical defense position in the event high surge tides threatened the London metropolitan area.
In October of 1997 a sand dredger, the Sand Kite, wrecked into one of the main gates of the Thames barrier. The ship was damaged and dumped its load of sand and aggregate, then sank onto the gate where it sat for several days atop its load. This caused paint failure and premature corrosion on the flat face of the gate. The failure of this gate could have had potentially disastrous effects on London, with flooding damage estimated at UK$21 Billion and extensive loss of life.
The UK’s Environment Agency had several requirements for the any repairs that were undertaken on the damaged gate. The barrier gate could not be taken out of service and had to be able to be closed at any time with a 1-hour notice to the cleaning contractor. In addition, there could be no environmental pollution or potential release into the environment during the surface preparation procedures. The twice-daily 21-foot tides and heavily traveled river created logistics problems for any repair to the gates. Because of these constraints any surface preparation that required stationary staging was rejected.
The remotely controlled, vacuum attached JetTractm system provided by UHP Projects, Inc. was used to clean and prepare the surface of the gate for recoating. This system uses Ultra High Pressure (40,000 PSI) waterjets to strip the coatings from the surface. A patented seal allows the remote JetTractm crawler to attach itself to the gate using vacuum supplied by a remote vacuum skid. The paint and water is completely contained in a vacuum shroud and removed down a hose to a vacuum system located on a barge. The JetTractm crawler is remotely controlled and can move in any direction in both the horizontal and vertical positions as well as overhead.