Acergy is close to completing the building and installation of a new J-Lay tower with enhanced capabilities for its offshore construction ship Acergy Polaris.
The completed J-Lay tower, which has been designed and built by Huisman-Itrec in the Netherlands, will be transported to Port Gentil in Gabon where it will be integrated with the vessel. This will be the final stage in its enhancement, which in addition to the new J-Lay tower has involved a significant amount of upgrade work on the ship, including hull reinforcement and other preparatory work. The ship will be ready to lay the flowlines at the Greater Plutonio field for BP later on this year.
Aerial view of the completed J-lay equipment.
TheAcergy Polaris is a very versatile offshore construction ship which has been a critical component in all of the major projects such as Girassol and Erha that Acergy has been responsible for over the years in the deepwater regions of West Africa. The ship, which is 137 m long and 39 m wide with full dynamic positioning, is currently equipped with a 1,500-metric ton crane and an existing J-Lay tower.
As part of the enhancement work, the existing J-Lay tower will be removed and prepared for transportation to the Far East where it will be installed on theSapura 3000, a new pipelay ship currently being built by Sapura-Acergy to operate specifically in the growing Asia-Pacific region.
The new J-lay tower viewed from the quay side.
The new J-Lay tower, which is 80 m high, has a static capacity of 750 metric tons, giving it the capability to install most of the required deepwater flowlines down to a depth of 3,000 m. The system can deal with pipe which has a diameter ranging from 4 to 24-in., with the possibility to pass special items up to 78-in.-diameter through the system.
The tower will be supplied with double joints made onshore, which are fitted with a collar at one end, then stored on the deck of the vessel. A double joint is transported horizontally from the deck of the ship to the tower entry level with a pipe elevator system, where it is loaded into the erector arm which upends the pipe and passes it over to the tower handling system. The pipe is then lowered down and aligned with the pipeline end held in the support bushing at the first work station.
Here the pipe is welded and possibly inspected before the load is transferred to the travelling table at the top of the tower and the completed pipe string is lowered down to the bushing. At the second work station, which is below the welding station, the field joint coating is applied and if required the weld can be inspected.
One of the key features of both of the Acergy J-Lay towers is their ability to gimbal and take up the most appropriate position for the prevailing weather conditions. The original J-Lay tower can be orientated and held in a fixed position through a system of jacks.
The new J-Lay tower has a completely different gimballing system based on a type of cardan spider arrangement. This allows the tower to be positioned quickly and held at a maximum tilt angle of 15° with an azimuth range of 180°. As a result of the design of the system, the new tower also has the capability of active gimballing to cancel out the ship motions. This can be most beneficial as it can enhance the fatigue life of the laid product as well reducing maximum bending. The tower support structure can also be tilted inboard by up to 43o, bringing the tower’s center of gravity back inside the ship for international transit.
One of the most important aspects of any pipelay system is the ability to handle large mid-line and end termination structures efficiently. This was considered from day one by the Acergy project team, with the new tower being capable of dealing with large pipeline structure with the pipe catenary held by the tower at all time. It is not necessary to hold the catenary on the crane as is mandatory with other pipelay systems.
The abandonment and recovery (A&R) system which forms part of the new J-Lay tower is initially fitted with 3,200 m of 109 mm steel wire with a capacity of 350 metric tons. This can be replaced with a 154-mm steel wire when it is necessary to employ the tower’s full capacity of 750 metric tons.
In addition to the A&R functions required for pipelay activities, the A&R system has been designed as a deepwater deployment system capable of installing subsea templates, suction anchors, and other types of subsea hardware.
Ian Frazer, Acergy
