On Nov. 16, Jiangnan Shipbuilding, a subsidiary of China Shipbuilding Group, welcomed its annual finale – the successful launch of a 40,000 cubic meter medium-sized liquefied petroleum gas (MGC) vessel on its No. 0 platform. This vessel is the first cooperation between Jiangnan Shipbuilding and Japan’s KUMIAI and the first MGC vessel built by Jiangnan Shipbuilding, achieving a breakthrough of “zero” in this vessel type in China.
The vessel is 180 meters in length and 30 meters in width, and is classed by American Bureau of Shipping (ABS).
The ship’s cargo hold is equipped with three independent fully-cooled A-type liquid tanks with a total capacity of 40,000 cubic meters, which can carry not only liquefied petroleum gas (LPG) but also petrochemical products such as ammonia and vinyl chloride monomer (VCM).
The vessel’s liquid tank is built with low-temperature carbon manganese steel to meet the material requirements for liquid ammonia loading; the bow line adopts Jiangnan Shipbuilding’s independently developed and optimized micro-spherical bulb bow and sets energy-saving rudder ball to make the speed and fuel consumption indicators reach the international leading level; the engine room is arranged with dual-fuel main engine and shaft generator to meet the latest emission and environmental protection requirements and EEDI-3 low-carbon requirements; the main deck is arranged with two 500 The main deck is equipped with 2 deck tanks of 500 cubic meters to meet the owner’s requirements for gas supply system and cargo exchange, which greatly improves the market competitiveness of this type of vessel.
This vessel is the first time that an A-type tank LPG vessel is built on a slipway and launched with a floating tank. The project team encountered considerable difficulties in order to effectively reduce the deformation of the vessel and ensure the safety of the launch.
Firstly, the main scale of the ship is too wide, and the outer side is easy to produce downward deformation; secondly, unlike the bottom saddles of C-type liquid tank which are distributed in a track type and only need to be fixed in the middle, the bottom saddles of A-type liquid tank are evenly distributed in the bottom plane of the ship, and the saddles on both sides away from the middle of the bottom are not supported by the launching trolley, so the deformation is not controllable; thirdly, the ship has a special structural form, and the longitudinal strong frame and the position of the launching trolley cannot be aligned; fourthly, the liquid tank of the ship is the first time to be built and launched with a floating tank. Fourthly, the liquid tank of the LPG ship is connected with the main hull by vertical support and fixed by epoxy casting, if the deformation of the connection is too large, it may lead to epoxy cracking.
In order to reduce the deformation of the hull during the launching process, to ensure the safety of the launch, Jiangnan Research Institute based on the former ship launching experience, the use of finite element modeling, the calculation of extreme conditions, complete the structural safety review, proposed the use of the launch trolley and module trolley joint shift program.
“Because the ship’s bottom is wider and the launching trolley track is fixed, the supportable range is narrow, and it is not enough to rely on the support of the launching trolley alone. In order to make the bottom of the ship more evenly stressed and reduce the deformation of the hull on both sides, the help of extra support is also needed, so the scheme of linkage of module trolley and launching trolley is created.” Gu Minghui, the ship’s chief builder, introduced. This is also the first time Jiangnan Shipbuilding has adopted this scheme for launching.
During the construction process, the construction team always insisted on the “three zeroes” concept of clearing structure, clearing opinions and clearing change orders, implementing difficult points and breaking them one by one, so that the structural completion of the ship was extremely high and laid a solid foundation for the subsequent mooring test.
During the period, considering the lifting capacity of the gantry crane on the platform, the two largest deck ring sections needed to be lifted by floating crane. Production and operation department, Jiangnan Research Institute, piggybacking department, precision management department, dockyard department and other departments to consult planning, decided to the full width of the deck two ring sections to form a giant general group piggybacking, so that it can be done once lifting, compared to separate lifting save three days cycle, thus improving the utilization rate of the platform site. The early general grouping of the full-width decks, on the other hand, front-loaded open fire operations such as welding, reducing the workload of sub-shield operations for full-width embarkation and reducing operational risks.
Precise planning and adequate production preparation shortened the construction to delivery painting cycle significantly: 60A full-width deck was delivered in 7 days and 60E full-width deck was delivered in 10 days, which was 5 days shorter than the conventional cycle and laid a solid foundation for the completion of the whole ship.