The biggest difference between straight seam high frequency resistance welded pipe (ERW) and seamless steel pipe is that ERW has welds, which is also the key to the quality of ERW steel pipes. Modern ERW steel pipe production technology and equipment, due to years of unremitting efforts internationally, especially in the United States, make the seamlessness of ERW steel pipe a relatively satisfactory solution. Some people divide the seamlessness of ERW steel pipes into geometric seamlessness and physical seamlessness.

Geometric seamless is to remove the internal and external burrs of the ERW steel pipe. Due to the continuous improvement and perfection of the internal deburring system structure and tools, the deburring of large and medium-diameter steel pipes has been better treated. Internal burrs can be controlled within -0.2mm~+0.5mm. Physical seamlessness refers to the difference between the internal metallographic structure of the weld and the base metal, which leads to a decrease in the mechanical properties of the weld area, and measures need to be taken to make it uniform. The high-frequency welding thermal processing of ERW steel pipe forms a temperature distribution gradient near the edge of the tube blank, forming characteristic areas such as melting zone, semi-melting zone, superheated structure, normalizing zone, incomplete normalizing zone, and fire. Area. Among them, because the welding temperature of the superheated zone is above 100, the austenite grains grow up sharply, and a hard and brittle coarse crystal phase will be formed under cooling conditions. In addition, the existence of temperature gradients can cause welding stress. In this way, the mechanical properties of the weld size are lower than that of the mother village.

Physical seamlessization is through the local conventional heat treatment process of the weld, that is, the intermediate frequency induction heating device is used to heat the weld area to AC3 (927°C), and then the air cooling process with a length of 60m is performed at a speed of 20m/min, and water cooling can be used if necessary. The method is adopted to achieve the purpose of eliminating stress, softening and refining the structure, and improving the comprehensive mechanical properties of the welding heat-affected zone. So far, the world's advanced explosive remnants of war units have generally adopted this method to deal with welds, and achieved good results. The high-quality ERW steel pipe not only cannot distinguish the welds, but also the weld coefficient reaches 1, which realizes the matching of the weld area with the base metal.

At the same time, ERW steel pipe has the advantage of using hot rolled coil as raw material, and the uniform wall thickness can be controlled at about plus or minus 0.2mm. Both ends of the steel pipe conform to the American API standard or GB/T9711.1 standard. Goods and other advantages. In recent years, various natural gas pipeline network projects and gas companies have widely adopted ERW steel pipes as the main pipe materials for urban pipeline networks.

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