API 5L line pipe for oil and gas line pipe

Gas pipelines can be divided into three types: gas gathering pipelines, gas pipelines, and gas distribution pipelines according to their uses.

①Gas gathering pipeline: the pipeline from the wellhead of the gas field through the gathering station to the gas treatment plant or the starting gas compressor station, which is mainly used to collect untreated natural gas extracted from the stratum. Due to the high pressure of the gas well, the pressure of the gas gathering pipeline is generally above 100 kgf/cm2, and the pipe diameter is 50 to 150 mm.

②Gas pipelines: pipelines from gas processing plants or starting gas compressor stations of gas sources to gas distribution centers, large users or gas storages in major cities, as well as pipelines that communicate with each other between gas sources. After processing, the pipeline is in line with pipeline transportation. Quality standard natural gas (see pipeline gas transmission technology) is the main part of the entire gas transmission system. The diameter of the gas pipeline is larger than that of the gas gathering pipeline and the gas distribution pipeline. The largest gas pipeline has a diameter of 1420 mm. The natural gas is transported under pressure from the starting point compressor station and the compressor stations along the line. The gas transmission pressure is 70-80 kgf/cm2, and the total length of the pipeline can reach thousands of kilometers.

③Gas distribution pipeline: the pipeline from the urban pressure regulating and metering station to the user branch line has low pressure, multiple branches, dense pipe network, and small pipe diameter. In addition to the large number of steel pipes, low-pressure gas distribution pipes can also be made of plastic pipes or other materials. .

X-60 low-alloy steel (strength limit of 42 kgf/cm2) is widely used for pipes, and higher-strength materials such as X-65 and X-70 have begun to be used. In order to reduce the frictional resistance in the pipeline, new steel pipes over 426 mm have generally been coated with internal coatings.

Gases of different physical properties are transported sequentially in the same pipeline, and gaseous and liquid natural gas pipeline transport tests at -70°C and 77 kgf/cm2 high pressure. The natural gas pipeline transportation system consists of two parts: pipeline gas transmission station and line system. The line system includes pipelines, valve rooms along the route, crossing buildings (see pipeline crossing project and pipeline crossing project), cathodic protection station (see pipeline anticorrosion), pipeline communication system, dispatching and automatic monitoring system (see pipeline monitoring), etc.

Steel pipe is the main material of pipeline. Natural gas transmission steel pipe is a special metallurgical product formed by deep processing of plate (belt). Due to differences in process technology, the organization of pipeline steel has certain differences in pipeline steel produced by various manufacturers. With the continuous development of pipeline steel research, Canada and other countries have laid test sections of X100 and X120 pipeline steel. In the Jining tie-line pipeline project in China, X80-grade pipeline steel was used for the 7.71km test section for the first time. The 4,843km-long West-East Gas Pipeline of the second-line trunk line uses X80 steel grade pipe steel with a diameter of 1219mm, which increases the gas transmission pressure to 12Mpa. Generally speaking, X80 steel is a dual-phase structure of ferrite and bainite, X100 pipe steel is a bainite structure, and X120 pipe steel is ultra-low carbon bainite and martensite.

For natural gas pipelines, strength, toughness and weldability are the three most basic quality control indicators [6].