Urban gas pipelines include main gas pipelines, distribution pipelines, user introduction pipes and indoor gas pipelines, each of which has different uses. According to the different gas transmission pressure, it can be divided into low pressure (not higher than 0.01MPa), medium pressure (0.01~0.4MPa), secondary high pressure (0.4~1.6MPa) and high pressure (1.6~4.0MPa). Generally speaking, the higher the pipeline pressure, the greater the possibility of pipeline leakage, and the higher the quality requirements of the pipeline; but the use of higher pressure pipelines can reduce the initial investment of the entire pipeline network. Pipes with different uses, different pressures and different diameters must have different materials and different processes.
In the urban gas pipeline network, steel pipes are generally used for high-pressure, sub-high-pressure pipelines and gas main pipes, but there are also problems in the selection of steel pipe types. In recent years, the straight seam welded steel pipe has gradually replaced the spiral pipe in the pipeline with higher pressure. At present, the price of high-frequency electric resistance welded steel pipe (ERW) is lower than that of spiral pipe (SSAW), and its quality reliability is higher than that of spiral pipe. It has a good cost performance and is more and more widely used. There is a way to take the pipe outer diameter ￠≤406mm using straight seam resistance welded ERW steel pipe, ￠>406mm using straight seam double-sided submerged arc welded steel pipe (UOE forming process).
In terms of medium and low pressure pipelines, PE pipes have the advantages of good flexibility, corrosion resistance, and smooth inner wall of pipes, etc., making PE80 material PE pipes become the main pipes for small diameter medium and low pressure gas pipeline networks. In foreign countries, high-density PE100 material PE pipe has become the first choice for buried medium and low pressure gas pipeline pipes due to its incomparable advantages in price and maintenance cost. However, when the pipe diameter is larger and larger than the economic limit diameter of the PE pipe, the steel pipe should be selected. For example, medium-pressure pipes above DN200 are mainly made of straight seam electric resistance welded ERW steel pipes.
In the city, the population is accumulated, the vehicles are concentrated, the construction area is numerous, the underground facilities are complex, and the gas pipeline is located in a special environment, so higher requirements are put forward for the selection of the pipeline. Straight seam steel pipes should be selected in key areas to reduce the length of the pipe welding seam, improve the quality of the welding seam, and reduce the possibility of accidents. In addition, when determining the steel grade of the pipeline, it should be reduced by one level on the basis of the steel grade selected according to the economic ratio to increase the wall thickness of the pipeline and improve the linear stiffness of the pipeline.
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