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No matter what kind of scheme is adopted for offshore oil and gas fields, it is necessary to transport oil and gas from the inside of the formation to the platform, FPSO, or onshore terminal. Laying submarine pipelines is the most direct and effective transportation method. Submarine oil and gas pipelines are the "lifeline" of offshore oil and gas production systems. The longest submarine pipeline in the world is the Langled pipeline from Norway to the United Kingdom, with a total length of 1,200 kilometers. It was put into operation in 2007. The world record for the depth of the sea where the pipeline is located is 2775 meters, which was created by the "Solitaire" pipelaying vessel. At present, the submarine oil and gas pipelines laid in China exceed 6,000 kilometers. The longest submarine pipeline is the Yacheng 13-1 gas field, and the gas pipeline is 778 kilometers long.
What does a subsea oil and gas pipeline look like?
Submarine pipes are pipes that are laid on the sea floor and continuously transport oil, gas, and water. For example: Offshore oil and gas facilities are all valuable "points". Only by connecting "points" through "lines" such as oil and gas pipelines can a complete system be formed and the overall value of the production system be brought into play. Submarine pipelines mainly include flat pipes, expansion elbows, and risers. Submarine flat pipes are laid on the sea floor and are the main force for submarine oil and gas transportation. Expansion bends are used to connect flat subsea pipes to risers. Affected by the temperature difference of seawater, the steel pipe has the phenomenon of thermal expansion and contraction, and the expansion bend can compensate for the change in the length of the sea pipe. The riser is a vertical pipeline on the sea floor, connecting the flat sea tube to the offshore production facilities. Deep water risers usually stand in the water in a free state, such as top pre-tensioned risers (TTR), steel catenary risers (SCR), flexible risers, tower risers, and so on. In addition, a crossover pipe is also necessary, which connects the tree and the production manifold. According to the different output (oil, gas, water) and output of the oil field, select the corresponding pipe diameter and structure of the subsea pipe. Theoretically, the larger the output, the thicker the pipe diameter.
In order to prevent the hydrates formed by deep water, low temperature and high pressure from blocking sea pipelines, thermal insulation pipelines are needed; while offshore heavy oil needs to be transported after the platform is heated, it is necessary to use hot oil transportation technology and thermal insulation pipeline structure. Electric heat tracing subsea pipe adds "warm baby" to the subsea pipe. In order to increase the stability of the pipeline, concrete counterweight sea pipes emerged at the historic moment.
The different materials of the submarine pipe determine the production cost, anti-erosion ability, gravity requirements and performance during welding. At present, carbon steel API 5L X56 and above are generally used.