The biggest difference between ERW tube
and seamless steel pipe
lies in the fact that ERW has a welded seam, which is the key to the quality of ERW steel pipe. Modern ERW pipe production technology and equipment, due to the international, especially the United States and other unremitting efforts for many years, making ERW seamless steel pipe has been a relatively satisfactory solution. Some people divide ERW pipes into seamless and physically seamless ones. Geometrical smoothing removes the inner and outer burrs of the ERW tube. Due to the continuous improvement and improvement of the structure and tool of the internal burr removal system, the removal of burrs in large and medium sized steel tubes has been better handled. Internal burrs can be controlled around -0.2mm to O.5mm. Physical seamlessness means that there is a difference between the metallographic structure inside the weld seam and the base metal and the mechanical properties of the weld zone are degraded, and measures must be taken to make it uniform and uniform. The high-frequency welding thermal process of ERW steel pipe causes a gradient of temperature distribution near the edge of the tube blank, and forms a melting zone, a semi-melt zone, a superheated zone, a normal zone, an incompletely normal zone, and a tempered zone. In the overheat zone, due to the welding temperature above 1000°C, the austenite grain grows sharply and forms a hard and brittle coarse grain phase under cooling conditions. In addition, the existence of a temperature gradient will generate welding stress. In this way, the mechanical properties of the weld zone are lower than that of the parent material. Physical seamlessness is through the local conventional heat treatment process of the weld seam. The intermediate zone heating device is used to heat the weld zone to AC3 (927°C) and then to 60m. The air-cooling process with a length and speed of 20m/min is re-cooled when needed. The use of this method achieves the goal of eliminating stress, softening and refining the structure, and improving the overall mechanical properties of the weld heat affected zone. So far, the world's advanced ERW units have generally adopted this method to treat welds and have achieved good results. High-quality ERW steel tubes not only fail to interpret welds, but also have a weld coefficient of 1 that enables the weld area to match the parent metal.
ERW steel pipe is made of hot-rolled steel plate as raw material, its wall thickness can be controlled uniformly at ±0.2mm, and the two ends of steel pipe are according to American APl standard or GB/T9711.1 standard, repaired end beveling, fixed length delivery, etc. advantage. In recent years, various natural gas pipeline network projects and gas companies have widely adopted ERW steel pipe
s as the main steel pipes of urban pipe networks.