IHC Hydrohammer, based in Kinderdijk, The Netherlands, has developed the Pyrodriver tool to push an anchor or a pile into the seabed. By burning a rocket propellant in a combustion chamber, a large force is created acting upward on a reaction mass, in return producing an equal and opposite force acting downward on the follower and the plate anchor.
Maximum internal pressures can be 600-900 bar. The fuel is in different combustion chambers on the device and can be fired individually from the surface vessel. IHC fitted the power pack to the piledriver, so there is no need for a large diameter umbilical or hoses from the surface. Sufficient chambers are present to drive one pile or anchor to the specified penetration depth.
Energy transfer time from the tool to the pile is very long compared to the normally used impact hammers, the company says. Where impact hammers transfer the energy within 5-7 ms, the PyroDriver can do the same in 150-400 ms. Only limited shots are required to drive the anchor or pile.
Water is the main component of the reaction mass. Scale model tests in France and full-scale tests in Canada have proven the method of using water as a reaction mass. During an onshore test in Canada IHC drove 42-in. piles in firm clays. An ROV controls the system. Before the tool is lowered, the company sets the electronic module for control of the ignition system to "short circuit" for all the primers and starts data acquisition. The ROV already has communication lines to the surface vessel and also has some spare optical lines that can be used for communication with the tool. The ROV docks to the tool at the seabed.
Kuito trials
In July 2003, the prototype of the PyroDriver had its first deployment, installing SBM's Velpa (vertically loaded plate anchor) in an offshore test campaign of the company's new anchor system. SBM undertook a large R&D program to develop the Velpa plate anchor as an alternative for the large suction installed piles suitable for permanent taut mooring systems in the very soft clays that are common off West Africa. Extensive laboratory, centrifuge, and onshore tests were first performed with the Velpa system.
Three full-scale Velpas (4, 8, and 12 sq m) were fabricated and successfully tested offshore West Africa at the Kuito field in the South Atlantic Ocean (near mainland Angola) in about 450 m water depth. The purpose of the test was three-fold:
- Testing the pull-out and holding capacity of the new plate anchors
- Testing operational capabilities of the prototype
- Proving offshore handling and seabed stability of the Velpa/ Pyrodriver concept.
The three Velpas were driven to anchor depth at about 15 m below mudline using the prototype. The Velpas were first deployed with a follower and self-penetrated prior to being driven to target depth. When the tool and follower were retrieved, the Velpas were rotated to accommodate the required taut mooring system configuration. The anchor size and depth were limited, so the Normand Progress, which has a bollard-pull capacity of 300 tons, could perform a pull-out test. Each anchor was rotated and pulled.
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Future plans
Every shot with the device gives information about the soil penetrated. The displacement of the pile or plate anchor and the applied load are measured. From this, the resistance to driving and the static soil resistance can be calculated. Penetrations of 1.2 m per shot have been measured.
Currently, a new PyroDriver is being developed for the full-scale Velpa. The new tool will be optimized for penetration of the plate anchor with a minimum of shots in water depths to 3,000 m. The device is an efficient tool to install anchors and piles in ultra-deepwater. Standard IHC Hydrohammers are capable of installing anchor points to a water depth of 1,000 m. In water depths below 1,500 m, however, the winch with the hydraulic hoses – or alternatively with an electric umbilical when a high voltage underwater power pack is used to drive the hydraulic hammer – becomes large and heavy. In these situations, IHC Hydrohammer says, the PyroDriver with its compact power pack on the hammer could prove to be an attractive solution with in principle no water depth restrictions.
For information, contact Samy Alhayari at SBM in Monaco or Rob van Foeken at IHC Hydrohammer in Kinderdijk for the PyroDriver.
