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Types and Characteristics of Outdoor Gas Pipelines

Posted: 03/23/2021 17:34:56 Hits: 10

There are three kinds of pipes that can be used for conveying gas: ductile iron pipes, welded steel pipes and PE pipes.

Ductile iron pipes
A ductile iron pipe refers to a pipe that is made from molten iron with the size 18 or above by adding a nodulizer, and then it passes through a centrifuge with high speed.

In gas engineering, it is suitable for gas pipelines with design pressure of medium pressure A and below. Centrifugal ductile iron pipes have the advantages of low damage rates, reliable operation, convenient construction, quick maintenance and good corrosion resistance performance. The rock shield pipe is a newly developed series. It is suitable for trenchless construction because of its good hardness. Therefore, it is widely used in the construction of pipelines that cross roads, rivers and buildings. The ZINALIUM series of pipelines are also a series of pipelines for areas with severe soil corrosion. The principle is to uniformly cover the surface of the pipeline with special zinc-aluminum alloy through an external spraying process. After a protective film is formed, the corrosion resistance of the pipeline can be increased several times. Therefore, the ZINALIUM pipe can be widely used in areas with strong soil corrosion.

In the comparative study of applications of ductile iron pipes and PE pipes, relevant scholars have also come to some conclusions. Centrifugal ductile iron pipes are harder than PE pipes, but the cost difference between the two is not much different. At the same time, the anti-corrosion performance of centrifugal ductile iron pipes is better than that of steel pipes.

Welded steel pipes
The steel coil is used as the raw material, which is formed by the extrusion process at regular temperature, and it is welded on both sides by automatic submerged arc welding of the welding process. The steel coil that is welded is called a welded pipe. According to the production process, a welded pipe is generally divided into straight seam welded steel pipes and spiral seam welded steel pipes. Straight seam welded pipes have relatively simple processes and their production costs are low, so the production efficiency is high and its market develops rapidly. In the manufacturing process of spiral welded pipes, not only can welded steel pipes with large diameters be made of narrower metal materials, but also welded steel pipes with different diameters can be made of metal materials with the same width. Although spiral welded steel pipes generally have higher strength than straight seam welded steel pipes, their production efficiency is low due to the large amount of welding in the production process. Compared with straight seam welded steel pipes with the same length, the welding length is increased about 30% to 100%. Therefore, in actual production, the welded pipe with a smaller diameter has straight seams, while that with a big diameter has spiral seams. In gas engineering, Q235B materials are generally used to make welded steel pipes.

Seamless steel pipes
Different from the production form of welded steel pipes, seamless steel pipes are steel pipes made of a single piece of metal without seams on its surface. Therefore, they are superior to welded steel pipes based on pressure resistance, and their costs are also higher than those of welded steel pipes. There are two production processes for seamless steel pipes: hot rolling and cold drawing. The hot rolling process is generally suitable for pipes with large diameters or thick thickness, while the cold drawing process is suitable for pipes with small diameters or relatively low strength and smooth external and internal surfaces. The seamless steel pipe commonly used in gas engineering is generally made from 20 steel or Q345D.

PE pipes
Internationally, polyethylene pipe materials from PE32 to PE100 are divided into five grades. In terms of raw materials, the materials of gas pipes in China are mainly PE80 and PE100. SDR11 and SDR17.6 are commonly used according to wall thickness of pipes. Compared with metal pipes, PE pipes have the advantages of a long service life, good corrosion resistance, good flexibility, simple and convenient construction. However, their mechanical strength is low, and their hardness is not as good as that of metal pipes. When PE pipes are impacted by hard objects, it is easy to cause perforation. Their oxidation resistance is also poor, so they are suitable for being used underground. Sunlight should be avoided during storage and transportation. PE pipes don't have electrical conductivity, there are certain technical requirements for the detection and positioning of the pipeline's position.

Figure 2-3 Polyethylene PE pipes for gas

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