The inner burr can be controlled in the range of -0.2mm to O.5mm. Physical seamless steel pipe refers to the difference between the metallographic structure and the base metal in the weld, which results in the decrease of mechanical properties in the weld area. Measures should be taken to make it uniform and uniform. The thermal process of high frequency welding of ERW pipe results in the gradient of temperature distribution near the edge of billet, and forms the characteristic areas of melting zone, semi-melting zone, superheated structure, normalizing zone, incomplete normalizing zone and tempering zone.
The austenite grains grow sharply in the superheated zone because of the welding temperature above 1000 C. Hard and brittle coarse grains will be formed under cooling conditions. In addition, the existence of temperature gradient will produce welding stress. In this way, the mechanical properties of the weld zone are lower than that of the base metal. Physical seamless means that the weld zone is heated to AC3 (927 C) by means of the conventional heat treatment process of the weld zone, then air-cooled at a speed of 20 m/min and 60 m in length, and then water-cooled when needed. This method can eliminate stress, soften and refine the structure, and improve the comprehensive mechanical properties of welding heat affected zone. So far, this method has been widely used in advanced ERW units in the world to treat welds, and good results have been achieved. High quality ERW pipe not only can not identify the weld, but also the weld coefficient reaches, which realizes the matching of the weld zone structure with the base metal.