Solve the problem of laying large-diameter thin-walled pipes in shallow water.
The laying of submarine pipelines has a long history in the world. Since the first submarine pipeline was laid in the Gulf of Mexico in the United States in 1954 by Brow Root Marine Engineering, the world has successfully laid submarine pipelines of various types and diameters in offshore waters. With the increase of water depth in the sea area, the pipe laying technology has also been greatly developed. So far, the main laying methods include water surface drag and drop method, underwater drag and drop method, bottom drag method, bottom bottom drag method, pipe laying method and J-type pipe laying method in deep water area. The pipe depth is more than 610m, and the pipe laying equipment has been developed from the traditional box pipelaying vessel to the boat pipelaying vessel, the semi-submersible pipelaying vessel and the dynamic positioning pipelaying vessel.
The laying of submarine pipelines in China started late. In 1973, China first landed a submarine oil pipeline in the vicinity of Huangdao, Shandong Province. In 1985, Bohai Petroleum Offshore Engineering Co., Ltd. successfully paved 1.6km (drilling platform) by using the surface drag method in the buried North Oilfield. Submarine oil pipeline. With the deepening of the opening up of China's offshore oil industry and the advancement of offshore pipelaying technology and equipment, the submarine pipelines that have been laid and laid in China's seas are close to 2000km. 1 Conventional pipelaying vessels laying submarine pipelines There are many methods for laying submarine pipelines. Some methods are suitable for installing small diameter pipes, while others are suitable for deep water pipe laying operations. The use of pipelaying vessels to lay submarine pipelines is one of the most common pipe laying methods. The main advantages of laying submarine pipelines by pipelaying vessels are high operating efficiency, good pipe deformation and strength control, deep working waters, and the ability to abandon pipes and shelter from wind.
Submarine pipeline design is usually carried out in accordance with internationally accepted specifications. The main factors to be considered are pipeline routing, seabed conditions, pipeline design life, operational data, pipeline size, environmental data, piping material properties and anti-corrosion coatings. Submarine pipeline design mainly includes pipeline size and wall thickness design, process flow analysis, pipeline stability calculation, expansion displacement design, laying stress calculation, abandonment and recovery calculation, riser design, pipeline free span analysis and pipeline anti-corrosion design.
According to statistics, the submarine pipelines laid by conventional pipe laying methods in China's offshore areas account for more than 97% of the total number of pipelaying pipes. The pipelaying methods of each pipelaying ship are essentially the same. At present, the domestic sea pipe laying operation process is: 1) the cargo barge supplies the pipe to the pipe pipe barge, the deck crane hoist the pipe to the pipe rack on the pipe pipe bar, and 2) when the pipe is laid, the crane will pipe Transfer from the storage rack to an automatic feeding frame, and then to the collimating station, where the welding and weld nondestructive inspection are carried out; 3) After the pipe joint is welded, the joint is coated with an anti-corrosive coating; 4) Carrying the pipe-laying The escrow on the pipe-laying vessel supports the pipe and forms the S-shaped () pipe during the pipe-laying operation, while the tensioner rotating along the production line generates a rear drag force to control the curvature of the pipe when it falls to the seabed. . The stinger and the tensioner have a considerable influence on the working ability of the pipe-laying vessel. If the tension is not enough, or the bracket is not long enough, the overhanging section of the pipe will be lengthened, that is, the stress of the pipe will increase, causing the pipe to break (the pipe Buckling and wrinkling occur).
2 Background of the problem of shallow-water large-diameter thin-walled pipe laying The problem of shallow-water large-diameter thin-walled pipe laying is based on the actual needs of the freshwater pipeline laying project. The special characteristics of shallow-water large-diameter thin-walled pipelines are as follows: 1) The pipeline is a large-diameter thin-walled steel pipe with an inner diameter of 1 000 mm, a wall thickness of only 14, and a ratio of diameter to wall thickness greater than 70; 2) the construction environment is in shallow sea The sea conditions are complex, and the conventional pipelaying method will encounter a series of problems, such as the unloading form of the pipe in the vertical plane, the internal stress during laying, and how the pipelaying ship itself completes the abandonment operation before the wind shelter and After the tube picking operation, etc.
The basic principle of using conventional pipelaying vessels for shallow-water large-diameter thin-walled pipelines is: 1) controlling the water level in the laying steel pipe, relying on buoyancy to maintain the normal curve shape of the pipe in the vertical plane; 2) relying on the lateral traction ship's pulling rope To overcome the lateral force of the lateral flow to the lowering pipe; 3) when the pipelaying vessel moves forward, the towing vessel does not move forward.
3 New laying method 3.1 Schematic diagram and principle of the new laying operation method To solve the problems existing in the laying of large-diameter thin-walled pipes by conventional pipe-laying vessels, it is proposed to adopt a novel laying construction device ().
1 pipe-laying ship 2 - inclined rail 3 - pipe-laying ship fixed bracket 4-M steel pipe 5 - lifting bracket 6 - bracket ship 7 - connecting steel pipe end and traction car steel cable 8 - traction car 9 A tight pipe with steel cable. 10 - Tensioning Pipe Winch 11 - A view of the connecting cable laying device between the pipe laying vessel and the carrier vessel. As shown, 1 and 6 are the pipelaying vessel and the carrier vessel, respectively. The two sides of the bracket ship and the pipe-laying ship are connected by two steel cables. The main equipment on the pipelaying vessel is inclined rails, fixed brackets, traction trolleys and winches for tensioning pipelines. The fixing bracket is fixed at the tail of the pipelaying vessel, and the steel pipe supporting the laying forms an S shape. The inclined rails are arranged on the center line of the pipelaying vessel, and the inclination angle is designed according to the design needs. There is a traction trolley on the inclined rail, and the traction trolley is connected with the steel pipe and the winch by a steel cable to generate the tension required when laying the pipe. There are 8 positioning steel cables on the pipelaying ship, in addition to two steel cables for the forward traction pipe laying.
The bracket boat is positioned by four positioning cables. The main equipment on the bracket is two lifting brackets. Adjusting the lifting bracket up and down and the angle of rotation can improve the stress during pipe laying. The lifting bracket can be used for abandoning and picking up the pipe.
The basic principles of the new pipe laying operation method: 1) relying on the traction trolley, steel cable and winch system to provide the pipe tensioning force, relying on the system to cooperate with the lifting bracket on the carrier ship to carry out the pipe picking and abandoning pipe operations; 2) relying on the lifting bracket on the bracket to adjust the shape of the pipeline to adapt to different water depth operations; 3) relying on the lifting bracket to transmit the lateral flow force received by the pipeline to the hull; 4) when the pipe laying vessel moves forward, The carrier boat moves forward together.
3.2 Advantages of the new laying method and the device The two lifting brackets on the carrier ship are used to control the pipeline and transfer the gravity of the pipeline to the hull. This is unlike the conventional pipelaying ship which has a long section of the pipe in a suspended state, so that the stress of the pipe Increase.
When the pipeline is subjected to the flow force, a part of the flow force is transmitted to the carrier by the lifting bracket, and the hull is automatically tilted by an angle under the action of the heeling moment, and the generated recovery torque is balanced with the heeling moment generated by the flow force. And conventional pipelaying vessels do not have this feature.
During normal pipe laying operations, the deformation of the pipe is controlled by adjusting the distance between the carrier ship and the pipelaying vessel and the lifting bracket. Tests have shown that the bracketing effect of the bracket ship is obvious, and the stress of the curved section of the pipe can be reduced.
When the pipe is abandoned, the lifting brackets (both front and rear ends of the bracket ship) coordinate with the traction trolley and the winch, and the pipe can be slowly placed on the seabed.
When picking up the pipe, first align the lifting bracket with the submarine pipeline and raise it to a suitable height, and at the same time determine the working position of the pipelaying vessel, then lift the pipe to lift the pipe, and then drag the pipe onto the pipe laying vessel.
As shown, due to the cooperation of the carrier boat, there is no need for a large tension during the pipe laying operation, and the tension generated by the winch can meet the requirements of use, unlike the tension of a conventional pipelaying vessel that requires a large tension. Device.
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