Electric Resistance Welded Pipe For Urban Underground Pipeline Laying

"ERW steel pipe" is a straight seam electric resistance welded pipe. English Electric Resistance Welding, abbreviated as ERW, is used to transport vapor and liquid objects such as oil and natural gas, and can meet various requirements of high and low pressure. At present, it plays an important role in the world of transportation pipes.

1. The welded pipe is made of steel plate welded by high-frequency electric resistance welded pipe (ERW welded pipe), straight seam electric welded pipe (LSAW steel pipe), spiral welded pipe(SSAW steel pipe) . In electrical engineering, it is indicated by "SC". It can be used as a water gas pipe or a threading pipe, which is relatively thick.
2. the line pipe is also the wire tube, relatively thin, with the "T", can only be used for threading.
3. The ERW tube is a “high-frequency resistance welded steel pipe”. It is different from the ordinary welded pipe welding process. The weld is made of the base material of the steel strip body, and the mechanical strength is better than that of the general welded pipe.

ERW stands for resistance welding, which has the characteristics of high production efficiency, low cost, material saving, and easy automation. Therefore, it is widely used in aviation and aerospace, energy, electronics, automotive, light industry and other industrial sectors are one of the important welding processes.

The biggest difference between ERW steel pipe and seamless steel pipe is that ERW has a welded seam, which is the key to the quality of ERW steel pipe. Modern ERW steel pipe production process and design preparation, due to the international efforts, especially the United States and other years of unremitting efforts, the seamlessization of ERW steel pipe has been relatively satisfactory. Some people have divided the seamlessness of ERW steel pipes into geometric seamless and physical seamless.

Geometric seamlessness is to remove the internal and external burrs of the ERW steel pipe. Due to the continuous improvement and improvement of the structure and cutter of the inner burr removal system, the removal of the inner burr of the large and medium diameter steel pipe has been well treated. The inner burr can be controlled at about -0.2mm to about 0.5mm.

Physical seamlessness means that there is a difference between the metallographic structure inside the weld and the base metal, which leads to a decrease in the mechanical properties of the weld zone, and measures need to be taken to make it uniform and uniform.

The high-frequency welding heat process of the ERW steel pipe causes a temperature distribution gradient near the edge of the tube blank, and forms a melting zone, a semi-melting zone, an overheated structure, a normalized zone, an incomplete normalized zone, and a tempered zone. In the superheated zone structure, the austenite grains grow sharply due to the welding temperature above 1000 °C, and a hard and brittle coarse crystal phase is formed under cooling conditions, and the existence of a temperature gradient causes welding stress. In this way, a weld bead is formed.

Where the regional mechanical properties are lower than that of the parent metal, the physical seamlessness is to heat the weld zone to AC3 (927 °C) by means of a local conventional heat treatment process of the weld, and then to a length of 60 m and a speed of 20 m/min. The air cooling process is re-cooled when needed. The use of this method achieves the purpose of eliminating stress, softening and refining the structure, and improving the comprehensive mechanical properties of the
heat affected zone of the weld. So far, the world's advanced ERW units have generally adopted this method to treat the welds, and have achieved good results. The high-quality ERW steel pipe can not only identify the weld seam, but also achieve a weld seam coefficient of 1, which achieves the matching of the weld zone structure with the base metal.

ERW steel pipe has the advantages of using the hot-rolled coil as raw material, and the wall thickness can be controlled to ±0.2mm. The two ends of the steel pipe are according to the American API standard or GB/T9711.1 standard, and the advantages of trimming, beveling and length are fixed. In recent years, various natural gas pipeline network engineering and gas companies have widely adopted ERW steel pipes as the main steel pipes of urban pipe networks.

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