Difference Between High Frequency Straight Seam Welded Pipe and Seamless Steel Tube

Electric Resistance Welding (ERW) and seamless steel pipe is the biggest difference lies in the ERW has a weld, which is the key to the quality of ERW steel pipe. Modern ERW steel pipe production process and equipment, as the international community, especially the United States and other years of unremitting efforts, making the ERW seamless steel pipe has been a more satisfactory solution.

It was the ERW seamless steel pipe is divided into geometric seamless and physical seamless. Geometric seamless ERW steel pipe is to remove the internal and external glitches. Due to the structure and tool of the inner burr removal system, the burr removal of large and medium-sized steel pipes has been well handled. The burr can be controlled in -0.2mm ~ +0.5 mm or so. Physical seamless means that there is a difference between the microstructure of the weld metal and the base metal, which leads to the decrease of the mechanical properties of the weld area, and needs to take measures to make it uniform and uniform.

The high-frequency welding heat process of ERW steel tube caused the temperature gradient in the vicinity of the edge of the tube, and formed characteristic regions such as melting zone, semi-melting zone, superheating structure, normalizing zone, incomplete normalizing zone and tempering zone. In the superheat zone, the austenite grain grows abruptly under the condition that the welding temperature is above 1000 , and the hard and brittle coarse crystal phase is formed under the cooling condition. Besides, the existence of the temperature gradient will produce welding stress.

In this way, the formation of the mechanical properties of the weld zone lower than the base metal case, the physical seamless through the local conventional weld heat treatment process is the use of medium frequency induction heating device will weld area heated to AC3 (927 ), and then 60m Length, speed 20m / min in the air-cooled process, if necessary, then water cooling. The use of this method to eliminate stress, soften and refine the organization, improve the comprehensive heat-affected zone mechanical properties of the purpose. At present, the world's most advanced ERW unit has been widely used this method to deal with the weld, has achieved good results. High-quality ERW steel pipe not only can not argue out the weld, and weld coefficient of 1, to achieve the weld area of the organization and the base material match.