With the gradual depletion of land energy, sea energy development has become a key area, so the importance of the construction of submarine pipeline is increasingly prominent. Since the 20th century, the United States in the 1950s, the first submarine pipeline in Mexico since the laying of the first submarine pipeline laying the depth of the world’s largest submarine pipeline 3052m, and China there is no deep-sea pipeline with the production of pipe precedent.
China has more than 3 million km2 of marine land area, and actively develop and use marine oil and gas resources, is part of the national energy strategy. In recent years, with the domestic offshore oil and gas exploration equipment and technology capacity enhancement, as well as large domestic steel pipe and pipe plant pipe linepipe production equipment and development capabilities continue to improve, submarine pipeline construction has made great progress .
South China Sea Liwan submarine pipeline project is China’s first deep-sea gas project. Deep-water section of the pipeline will be laid in the 1500 meters deep sea, steel pipe to withstand the external pressure of 15MPa, the internal pressure of 29.4MPa, but also to withstand wind, waves, water, ice and seismic environmental load caused by pipeline translation and vibration, Therefore, the requirements of steel pipe with the ability to resist large deformation, requiring high strength steel pipe, wall thickness, diameter, with a large aspect ratio and excellent fracture toughness.
- To ensure that the steel has excellent fracture toughness. Because the pipeline in the deep sea service, in the event of fracture, will be a major disaster. In order to make steel pipe has excellent fracture toughness, must meet the CTOD, DWTT and CVN and other performance indicators, so the raw material composition of the alloy composition demanding, high purity steel, while the steel residual elements As, Sb , Sn, Bi, Pb and B have strict requirements, raw materials, control and smelting difficult.
- Thickness specifications, low-temperature fracture toughness difficult to achieve technical requirements. DWTT performance requirements of steel at the test temperature of -10 ℃, the average percentage of the shear area of 85%, for the steel plate is required to test temperature -20 ℃, the percentage of the shear area to achieve this requirement, which for thick steel plate It is difficult to achieve, because the compression ratio is small, difficult to control the central segregation, and the other is the thickness of the various parts of the grain size uneven.
- The yield strength fluctuation range of steel pipe is narrow, and the horizontal and vertical are the same requirements, in the steel pipe production control difficult.
- Steel pipe diameter to diameter ratio, forming difficulties, deformation strengthening, pipe performance before and after the difference is also large.
1500 meters deep pipeline with a large number of smooth production and successful use, creating a straight seam submerged arc welded pipe for the first of its kind in the deep sea, which is to enter the deep sea mileage card, with great economic and social benefits.