“ERW steel pipe” is a straight seam resistance welded pipe, ERW means electric resistance welding, electric resistance welding has the characteristics of high production efficiency, low cost, material saving, and easy automation, so it is widely used in aviation, aerospace, energy, electronics, automotive and other light industrial sectors, is one of the important welding processes. ERW steel pipes mainly 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, they occupy a pivotal position in the field of transportation pipes in the world.
Classification of welded pipe
- Welded pipes are round pipes welded from steel plates, which are divided into high-frequency resistance welded pipes (ERW welded pipes), straight seam arc welded pipes (LSAW), and spiral welded pipes. “SC” is used in electrical engineering area to indicate that it can be used as a water gas pipe or a threaded pipe, which is relatively thick.
- Threading tube is actually a wire guiding tube, it is relatively thin. It is indicated by “T” and can only be used as a wire guiding tube.
- The ERW pipe is a “high-frequency resistance welded steel pipe”, which is different from the ordinary welding process of welding pipe . The welding seam is made by melting the base metal of the steel plate body, and the mechanical strength is better than that of the ordinary welded pipe.
The difference between ERW steel pipe and seamless steel pipe
The biggest difference between ERW steel pipe and seamless steel pipe is that ERW has a welding seam, which is also the key to the quality of ERW steel pipe. Due to years of unremitting efforts in the world, especially the United States, have made the seamless ERW steel pipe has been relatively satisfactory with modern ERW steel pipe production technology and equipment.
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 of the structure and cutting tool of the internal burr removal system, the internal burr removal of large and medium diameter ERW steel pipes has been better treated. The internal burr can be controlled from -0.2mm to 0.5mm.
Physical seamless means that there is a difference between the metallographic structure inside the weld and the base metal, which causes the mechanical properties of the weld area to decrease. 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, and forms characteristic regions such as melting zone, semi-melting zone, overheating zone, normalizing zone, incomplete normalizing zone, and tempering zone. The microstructure in the superheated zone is austenite grains that grow sharply due to the welding temperature above 1000 ° C. Under cooling conditions, hard and brittle coarse grain phases will be formed. In addition, the existence of temperature gradients will generate welding stress. In this way, a situation where the mechanical properties of the weld area are lower than the base material is formed. The physical seamlessness is to heat the weld area to AC3 (927 ° C) by using an intermediate frequency induction heating device through a conventional heat treatment process of the weld seam, and then perform 60m Air cooling process with length and speed of 20m / min, water cooling 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 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.
High-quality ERW steel pipes not only cannot identify the weld seam, but also have a weld coefficient upto 1, which achieves a match between the structure of the weld zone and the base metal.
ERW steel pipe adopt hot-rolled coil as the raw material, and the wall thickness can be controlled within ± 0.2mm uniformly. The two ends of the steel pipe are in accordance with the American APl standard or GB / T9711.1 standard. In recent years, various natural gas pipeline network projects and gas companies have widely adopted ERW steel pipes as the main steel pipes of urban pipeline networks.
No matter what specifications and usages of ERW steel pipe or seamless steel pipe, IMRI Steel can meet your needs. If you have any customization or purchasing requirements, please don’t hesitate to contact us!