ERW steel pipe is abbreviated as ERW for straight seam electric resistance welded pipe. It is used to transport oil, natural gas and other vapor-liquid objects. It can meet various requirements of high and low pressure. At present, it occupies a pivotal position in the field of transportation pipes in the world.
The biggest difference between ERW steel pipes and seamless steel pipes is that ERW has welds, which is also the key to the quality of ERW steel pipes. The seamlessness of ERW steel pipe is mainly through the expansion and reduction process. The expansion and reduction process is a continuous rolling process of the hollow base metal without mandrel. This is not a fake product that deceives consumers, but a steel pipe produced according to the needs of the equipment,The seamlessness of ERW steel pipe is between pure seamless and welded pipe, the quality is better than that of welded pipe, and the cost is lower than pure seamless, it is an ideal substitute product.
Some people divide the seamlessness of ERW steel pipes into geometric seamlessness and physical seamlessness.
1. Geometric seamlessness is to remove the internal and external burrs of ERW steel pipes. Due to the continuous improvement and perfection of the structure and tool of the internal burr removal system, the removal of internal burrs in large and medium diameter steel pipes has been well handled. The internal burr can be controlled at about -0.2mm~O.5mm.
2. Physical seamlessness means that there is a difference between the metallographic structure inside the weld and the base metal, which leads to the decline of the mechanical properties of the weld area, and measures need to be taken to make it uniform and consistent. The high-frequency welding thermal process of ERW steel pipe causes a temperature distribution gradient near the edge of the tube blank, and forms characteristic regions such as melting zone, semi-melting zone, overheated structure, normalizing zone, incomplete normalizing zone, and tempering zone. Among them, because the welding temperature is above 1000 °C, the austenite grains grow rapidly in the superheated zone, and a hard and brittle coarse-grained phase will be formed under cooling conditions. In addition, the existence of temperature gradient will generate welding stress. In this way, a situation in which the mechanical properties of the weld zone are lower than that of the base metal is formed.Physical seamlessness is to heat the weld area to AC3 (927°C) through the local conventional heat treatment process of the weld, that is, to use an intermediate frequency induction heating device to heat the weld area to AC3 (927°C), and then perform an air-cooling process with a length of 60m and a speed of 20m/min, and water-cooling when necessary.
The use of this method achieves 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 ERW units have generally adopted this method to process welds, and have achieved good results. The high-quality ERW steel pipe not only cannot distinguish the weld, but also the weld coefficient reaches 1, which realizes the matching of the structure of the weld area and the base metal.
ERW steel pipe has the advantages of using hot-rolled coil as raw material, the uniform wall thickness can be controlled at about ±0.2mm, the two ends of the steel pipe are in accordance with the American APl standard, the end is trimmed and beveled, and the length of delivery is fixed. In recent years, various natural gas pipeline projects and gas companies have widely adopted ERW steel pipes as the main steel pipes for urban pipeline networks.
How to tell
1. The seamlessness of ERW steel pipe is basically fixed length, and it is generally 6 meters, 9 meters or 12 meters. Indeterminate length of seamless steel pipe in the same city
2. The cross section of the pipe head
3. Pickling
The biggest difference between ERW steel pipes and seamless steel pipes is that ERW has welds, which is also the key to the quality of ERW steel pipes. The seamlessness of ERW steel pipe is mainly through the expansion and reduction process. The expansion and reduction process is a continuous rolling process of the hollow base metal without mandrel. This is not a fake product that deceives consumers, but a steel pipe produced according to the needs of the equipment,The seamlessness of ERW steel pipe is between pure seamless and welded pipe, the quality is better than that of welded pipe, and the cost is lower than pure seamless, it is an ideal substitute product.
Some people divide the seamlessness of ERW steel pipes into geometric seamlessness and physical seamlessness.
1. Geometric seamlessness is to remove the internal and external burrs of ERW steel pipes. Due to the continuous improvement and perfection of the structure and tool of the internal burr removal system, the removal of internal burrs in large and medium diameter steel pipes has been well handled. The internal burr can be controlled at about -0.2mm~O.5mm.
2. Physical seamlessness means that there is a difference between the metallographic structure inside the weld and the base metal, which leads to the decline of the mechanical properties of the weld area, and measures need to be taken to make it uniform and consistent. The high-frequency welding thermal process of ERW steel pipe causes a temperature distribution gradient near the edge of the tube blank, and forms characteristic regions such as melting zone, semi-melting zone, overheated structure, normalizing zone, incomplete normalizing zone, and tempering zone. Among them, because the welding temperature is above 1000 °C, the austenite grains grow rapidly in the superheated zone, and a hard and brittle coarse-grained phase will be formed under cooling conditions. In addition, the existence of temperature gradient will generate welding stress. In this way, a situation in which the mechanical properties of the weld zone are lower than that of the base metal is formed.Physical seamlessness is to heat the weld area to AC3 (927°C) through the local conventional heat treatment process of the weld, that is, to use an intermediate frequency induction heating device to heat the weld area to AC3 (927°C), and then perform an air-cooling process with a length of 60m and a speed of 20m/min, and water-cooling when necessary.
The use of this method achieves 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 ERW units have generally adopted this method to process welds, and have achieved good results. The high-quality ERW steel pipe not only cannot distinguish the weld, but also the weld coefficient reaches 1, which realizes the matching of the structure of the weld area and the base metal.
ERW steel pipe has the advantages of using hot-rolled coil as raw material, the uniform wall thickness can be controlled at about ±0.2mm, the two ends of the steel pipe are in accordance with the American APl standard, the end is trimmed and beveled, and the length of delivery is fixed. In recent years, various natural gas pipeline projects and gas companies have widely adopted ERW steel pipes as the main steel pipes for urban pipeline networks.
How to tell
1. The seamlessness of ERW steel pipe is basically fixed length, and it is generally 6 meters, 9 meters or 12 meters. Indeterminate length of seamless steel pipe in the same city
2. The cross section of the pipe head
3. Pickling
