In June 2011 DLT were awarded the contract by Swiber Offshore Construction Services to design and supply two synchronized hydraulic jacking systems for use in the float over installation of the 13,400 tonne process platform (AP) and the 8,000 tonne living quarter platform (AQ) for ONGC's B193 oil/gas process complex in the Arabian Sea, located 75 km offshore from Mumbai in a water depth of 70m. Both systems were delivered to the customer in early 2012 and were used onshore for weighing of the topsides in October 2012 and for offshore installation in December 2012.
The float over jacking system was designed by DLT for maximum safety, flexibility for future use, and for economic transport between sites in standard shipping containers. Each of the two systems is made up of identical 1250 tonne 3m stroke hydraulic rams powered by four outlet electrically powered variable flow hydraulic power packs which were sized for a full load lifting speed of up to 70 mm/minute and a fast full load lowering speed of up to 1000 mm/minute for final load transfer to the jacket and separation of the barge. Central monitoring and control is provided by our DL-P40 CANbus heavy lifting computer control system, which is sufficiently accurate to be used for weighing the top sides prior to load out.
On the AP there were 16 No 1250 tonne 3m stroke rams arranged into four pool groups of four rams each, as shown below. On the AQ there were 12 No 1250 te 3m stroke rams arranged in four pool groups of three rams each. The rams were specially designed to work with up to 8% side load at full extension. As all the rams and power packs are identical they can be used in any configuration for future operations where it may be necessary to have greater lifting capacity and more than four support points. The main consideration in the design of the system was the safety and security of the float over wet mating operations, which was achieved by including a high level of redundancy. The system was designed to be able to complete the topside installation in the event that any one ram in each support group completely fails, any one power pack completely fails or even if the central computer control system completely fails. In each of these cases there are back up systems in place to take over and complete the operation with the minimum of delay.
Both topsides were installed in December 2012.