Offshore, polar, and deepwater oil and gas fields face harsh service conditions such as wave, current, and seawater corrosion, which require higher quality requirements than onshore pipelines, and subsea oil and gas pipelines typically have service periods of more than 20 years, requiring the use of high-performance pipeline steel. DNV-OS-F101 Seabed Pipeline Specification has strict requirements on the transverse strength, longitudinal strength, low-temperature dynamic tear resistance, weldability, strain resistance and acid medium corrosion resistance of submarine pipeline steel.
The longest offshore pipeline in the world is the Langeled natural gas pipeline, which was laid between Norway and Causation from 2004 to 2007, with a length of 1173km and the deepest point is 2775m.here are offshore pipeline engineering in recent years:
Projects | Laying depth,m | Steel grades | O.D,mm | W.T，mm |
Mexico Gulf ITP pipeline | 2412 | 610 | 24.1-34.3 | |
Mediterranean Medgaz pipeline | 2160 | 610 | / | |
Lehthys gas field pipeline | 2160 | X65 | 1067 | 29.6-40.1 |
The North Sea Langard pipeline | 1000 | X70 | 1016 | 34 |
On May 23, 2020, the sea pipeline of the Lingshui 17-2 project, China's first deepwater gas field, was successfully laid at 1,532 meters, breaking China's new record for sea pipeline laying and the first operation at 1,500 meters of "ultra-deepwater". The project used more than 10,000 tons of undersea steel pipeline from Henggang, Hunan province. The simulation experiments of the external pressure of these deep-sea pipelines show that the steel tube can withstand 35Mpa and can be used for external pressure above 35m water depth.
projects | Steel grades | Specifications | Pipe consumption,t | Laying depth，m |
CNOOC Chunxiao Gas Field | X60 | 711*15.9 | 68645 | 90-110 |
CNOOC Ledong Gas Field | X65 | 610*(13.6-18.7) | 27000 | 93.5 |
Liwan pipeline in, South China Sea | X65 X70 | 762*20.2/758.8*23.6/765.2*31.8 | 96000 | 10-190 |
559*28 | 44000 | 1380-1480 |
The deepwater steel pipeline is characterized by large wall thickness relative to outer diameter ratio, high dimensional precision, etc. This is because the submarine pipeline has been in service in the marine environment of low temperature, high pressure and strong corrosion for a long time. It not only bears a load of internal and external pressure, axial force and bending moment but also bears the dynamic load of alternating external pressure, wave and current. The strength, wall thickness, and dimension roundness of steel pipe are particularly important to prevent pipeline damage. Meanwhile, with the continuous increase of pipeline laying depth and conveying pressure, high steel grade, large pipe diameter, and large wall thickness are the development trend for the offshore pipeline.