A rugged elastomer technology developed by Pronal that made the deep sea flotation tanks used to raise wreckage from the ocean liner, Titanic, is employed in Australia to protect workers on the huge Tugun desalination plant on the Gold Coast.
The GCD Alliance tunneling crew has deployed the custom-fabricated Pronal seals, 60m under water to maximise safety for workers in sub-sea tunnels connected to intake and discharge risers that ultimately feed the plant processing up to 125ML a day of potable water.
The 1900mm outside diameter by 520mm wide inflatable seals are wrapped around the nose of RPC Technologies’ glass reinforced plastic (GRP) plugs located near the base of the risers to provide optimum levels of safety for construction workers in tunnels 30m below the seabed and extending more than 2km from the ocean floor risers to shore.
The custom fabricated Pronal seals, distributed in Australia by Air Springs Supply, are a part of a family of offshore exploration, construction and energy and resources development technology made to the same exacting standards as the elastomer bags used to pluck Titanic artifacts from the Atlantic ocean floor 4000m down.
According to RPC Technologies, once the GRP Alliance plug is in position at the correct depth in the riser, the seal is inflated to enable dewatering of the flooded riser, which safely allows breakthrough into the tunnels. The inflated seal remains in place around the plug for the duration of the construction phase, to provide the safety required by the GCD Alliance constructing the tunnel systems, comprising Gold Coast Water, John Holland, Veolia Water Australia, Sinclair Knight Merz and Cardno.
The project required that the risers can be safely sealed to allow the tunnels to be dewatered. While the risers are entirely empty of water during tunnel construction, they also needed to be initially filled with water to overcome the effects of buoyancy while they are grouted in place in the drilled excavations. Therefore, RPC Technologies had to develop a way of dewatering after installation before providing ongoing protection.
Dewatering of the risers on the ocean floor was accomplished by flooding them with compressed air to force water out through an exit tube at the top dome enclosure of the riser, after which air pressure in the riser was restored to equilibrium with the tunnels to which it would be connected. Then the seals were inflated around the plug at 2000kPa to provide permanent sealing and protection, so work could proceed in the tunnels in a safe environment.
RPC Technologies’ glass reinforced plastic (GRP) liners and plugs, were constructed to stringent standards of a material that exceeds the requirements of a 100-year design life. It needed to be light enough to be installed in one piece, required little or no maintenance, be relatively inexpensive, available in a short time frame and have enough structural capacity to overcome all construction and operating loads imposed on it. It also needed to have hydraulic characteristics and provide the protection and performance required below the ocean floor to shield tunnel workers from the 60m head of water that lay above them.
The top dome enclosure on the risers would be sufficient protection against flooding without the GRP plug and seals. However, if the dome is damaged in some way, workers could be at risk because of the sudden ingress of water. To prevent this, the GRP plug was purpose-designed constructed, then fitted with the Pronal seal.
The clearance between the plug and the inner wall of the riser was maintained at a maximum of 15mm. If a situation arose where the dome was damaged and the hydraulic seal failed, the nominated clearance would slow down the flow of water to a rate where it would take 24 hours to fill the connecting tunnel, providing adequate time for workers to evacuate. Air Springs Supply observe that the combination of RPC Technologies’ plug design and the precision fabricated seals provide a double level of safety.
According to Air Springs Supply, the seals are custom manufactured and tested to more than 6000kPa to provide safety for applications such as this. The seals are similar to Pronal products used offshore in demanding situations in much deeper waters than this application, for example, Pronal’s complete Packer-Can system is used for the installation of oil rig platform legs.
These seals and systems are suitable for expanding ranges of offshore and underwater construction, engineering, energy development and maintenance tasks. Pronal design and manufacture standard and custom-engineered flexible structures aimed at ensuring safety and floatability. These structures are used to lift and position underwater loads and also to assist divers to move equipment on the seabed.
The high performance Pronal seals match the rugged, lightweight and cost-effective fibre composite plug used in the Tugun desalination project. The RPC Technologies’ plug is a part of a range of RPC Technologies fibre composite products, which include small to large bore piping, tanks, mine ventilation ducting, odour containment systems, specialty process vessels and ventilation and exhaust stacks.
Following are the Pronal products included in the Tugun desalination project:
- Underwater parachutes and lifting units
- Deep sea flotation tanks
- Recovery and decommissioning equipment
- Jacket equipment system including complete “Packer-Can” system for installation of platform legs
- Buoyancy bags and cushions
- Pipe stoppers and plugs
- Hyperbaric welding habitats
- Doors and sleeves
- Clamping systems pipeline intervention systems
- Oil booms
- Flexible tanks
- Push-pull stoppers
- Shock cells
- Barge bumpers
- Rub strips
- Pipe pullers
- Oil membranes
- Flex connectors
For special applications, specific systems are designed and modified by Pronal to deal with situations subject to particular constraints.