Eager.one was consulted by Van Oord Offshore Wind for a new type of Anode Cage Installation Aid. Van Oord contracted Eager.one, based upon Eager.one’s previous experience supplying tools for installing Anode Cages over monopiles of offshore windfarm foundations.
Previous supplied tools were based on installing Anode Cages by means of a jack-up vessel. And most of these Anode Cages were designed for installation by means of a spreader. However, the request of Van Oord was different. The Anode Cage will be installed from a floating vessel (Van Oord Svanen) and tolerances are marginal.
The challenge presented to the Eager.one team was to design an installation aid that can install the Anode Cage over the monopile, while preventing collision between the Anode Cage and the monopile. This will be done by means of a service crane with limited capacity, from a floating vessel.
Weight restrictions, precise handling and monitoring were the main operational challenges, starting with how to position the Anode Cage (AC) over the monopile (MP).
Installing the AC directly over the MP is not possible due to the motions of the vessel and marginal tolerances. Therefore the ACIA, with the AC connected to it, will first be lifted onto the MP.
Once positioned according to the required heading, the three synchronized winches will lower the AC over the ACIA towards the MP flange; see diagrams at the right. By means of eye-to-eye slings the AC is connected to a lowering ring. This is an aluminium circular truss frame that will guide the ACs towards the installation position.
Spring-loaded wheels are connected to the lowering ring. These wheels follow the ACIA structure down to the MP and make sure that the AC will stay exactly centered and will not collide with the MP.
The hydraulics and electrical and instrumentation fitted onto the lowering ring are powered via the umbilical winch fitted onto the ACIA.
The design of the ACIA had weight restrictions and therefore lightweight materials such as aluminum were used.
The AC will be lowered to the installation position. This will be monitored by means of cameras, supported by lighting for visual confirmation of the AC position. In addition, the exact position can be determined by a pay-out measuring system in the winches.
As soon as the AC has reached the installation position, the pin-pushers will release the eye-to-eye sling on one side. In case the sling is stuck the secondary pin-pushers can release the other side of the sling as a mitigation. Once installed, the aluminium ring will be lifted back to the ACIA base, that is still positioned on top of the MP. After completion the ACIA will be lifted to the barge for a following AC installation.
The Factory Acceptance Test has been successfully completed in the second week of January. The ACIA will now be prepared for transport to the onshore harbour for commissioning and training of the Van Oord operational crew.
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The Anode Cage Installation Aid, also called the ACIA, is specifically designed to install an Anode Cage over a monopile, while preventing collision between the Anode Cage and the monopile. This will be done by means of a service crane with limited capacity, from a floating vessel.
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