Emergency Underwater Repair Pack Wessex System 110 Typical examples of repairs that can be achieved with this pack
During site trials a UW43HV repair system was evaluated with leaks simulated to represent typical situations found on surface ships.
One typical repair situation involved a mild steel plate with a split about 50mm long, fitted to a water pressure tank and subject to a pressure of 130 kPa (20 psi). A pad of open-celled foam 250mm x 160mm x 25mm was impregnated with resin mix and backed with a 250mm x 160mm piece of mild steel plate. This combination was placed, foam down, over the split and compressed to approximately 3mm by means of a wooden strong back and G cramps at either end. The leak was stopped on application of the pressure. After curing, the strong back was removed and the water pressure was increased to 206 kPa (30 psi) when the plate bowed, but the repair showed no sign of leakage. (See Illustration No.1)
A second example was provided by a 50mm internal diameter mild steel pipe welded to mild steel flanges with a 1mm hole drilled through the weld between flange and pipe. The condition of the steel was slightly corroded and wet. The pipe was water-filled before the repair was attempted. A foam pad 75mm x 25mm x 25mm was impregnated with resin mix and compressed over the leak by means of a G cramp and crudely shaped mild steel tool. A water pressure of 275 kPa (40 psi) was applied immediately after completing the repair and this was increased to 550 kPa (80 psi) four hours later when slight weeping was noticed. This pressure was maintained over the weekend after which it was increased to 4.14 MPa (600 psi) with no sign of leakage. (See Illustration No. 2)
Illustration No. 1
Illustration No. 2
Repairs can be effectively carried out underwater when the hull of a vessel is damaged below the water line. If the damage is slight, i.e. where the integrity of GRP structure is not threatened in terms of mechanical strength, but with glass fibre exposed, there is the possibility of water ingress into the laminate, the UW43HV can be trowelled onto the damaged zone and faired to shape. If it is possible, the diver will prepare the surface of the damaged area as directed. The resin and hardener components are then mixed on board the ship and taken below in a closed container to the repair zone. The diver applies the UW43HV epoxy to the damaged hull with the large broad bladed spatula, firmly pressing the epoxy onto the GRP substrate. This action is necessary to 'squeeze out' the water between the structure and the first application of resin. With the initial application of resin in position it is possible to build up the epoxy thickness required, fairing to the contour of the structure as the material is applied. This type of application will prevent water penetration between the glass fibre and resin.
If the underwater damage is severe and there is a gouge, say 12mm to 25mm thick, or a split in the hull allowing an ingress of water, thoroughly impregnate a section of the polyurethane foam with the UW43HV epoxy mix. As already detailed, this is achieved by laying the pre-cut foam pad onto the polyethylene sheet provided and working the resin into the foam with the broad knife supplied.
The impregnated material is then wrapped in the polyethylene sheet for the diver to take down to the damaged zone. He will push the resin/foam pad into the gouge or split with the broad knife, forcing the material into the deepest sections of the damaged area. This operation will have an immediate self-sealing effect and the hydrostatic pressure will not only hold the impregnated foam in place, it will also compress the repair material in the gouge or split thereby restricting the flow of resin from the foam. The UW43HV will cure in the cellular structure of the foam and bond itself to the GRP laminate thus effecting a temporary repair to the damaged hull.
Emergency repairs to leaking pipes, tanks and joints may be made using the UW43HV in conjunction with an open cell soft polyurethane foam carrier supplied in this pack. The adhesive should be mixed in the normal way and then worked thoroughly into a pre-cut foam pad of the appropriate size and shape. This is achieved by laying the pre-cut foam pad onto the polyethylene sheet provided and pushing or working the mixed epoxy UW43HV into the foam with the broad knife supplied. The adhesive must also be worked into the damaged substrate.
The impregnated pad is then pressed strongly against the leak and held in place under pressure with a shaped metal backing plate for example, throughout the cure period or until a sufficiently high joint strength has been developed. In certain circumstances, a hot air blower may be used to accelerate this curing process and an adequate joint strength may be developed within an hour. In any event, if the repair is to be successful, the leak will be stopped immediately upon application of the resin-soaked foam, in which case there will be no objection to leaving the clamping device in position for as long as necessary.
Wessex Barrier Cream should be rubbed into the hands and the protective gloves should be worn when the adhesive is being used. Accidental skin contamination should be removed using the resin removing cream supplied with this pack.