Some people coming into contact with steel tube for the first time don’t know the difference between seamless pipe and ERW steel pipe. Actually, the biggest difference between ERW steel pipe and seamless pipe is there is a welding seam on ERW steel pipe, this is also the key to the quality of ERW steel pipe. Modern production process and equipment of ERW steel pipe, in the international community, due to years of unremitting efforts by many countries, especially the United States, making the ERW steel pipe seamless has been more satisfied with the solution.
ERW steel pipe seamless was divided into geometric seamless and physical seamless by some people:
About geometric seamless, its definition is removing the burr of ERW steel pipe on the inside and outside. As the continuous improvement of the structure of the inner burr removal system and cutting tool, the clearance of the burrs in the large and medium diameter pipes has been well handled. Burr can be controlled in the -0.2mm ~ O.5mm or so.
Physical seamless means that the difference between the metallographic structure inside the weld and the base metal results in a decrease in the mechanical properties of the weld area. It is necessary to take measures to make it uniform and consistent. The high-frequency welding process of ERW steel pipe, resulted in the temperature distribution gradient near the edge of the tube, and formed melting zone, semi-melting zone, superheated organization, normalized area, incomplete normalized area, tempered area and other characteristic areas. Due to the welding temperature in the superheated organization is above 1000 ℃, the austenite grain grows rapidly, the hard and brittle coarse crystalline phase is formed under cooling conditions. In addition, the existence of temperature gradient will produce welding stress. In this way, the situation that the weld area of mechanical properties is lower than the base metal situation will be formed. Physical seamless is the local conventional heat treatment process of weld (that is using medium frequency induction heating device to heat weld region to AC3 (927 ℃)), and then proceed the 60m length, the speed of 20m / min air cooling process.If it is necessary, the water cooling will be carried. The use of this method has achieved the purpose of eliminating stress, softening and refining the structure, and improving the comprehensive mechanical properties of the heat affected zone. So far, this method has been widely used by the world’s most advanced ERW unit to deal with the weld, and that has achieved good results. The high-quality ERW steel pipe not only can not discern the weld, and the weld coefficient can reach to 1, achieves the weld area organization and base metal match.
Due to use hot-rolled coil as raw material, the wall thickness can be controlled evenly in the ± 0.2mm or so, and the two ends of the steel pipe according to the United States APl or GB / T9711.1 standard, ERW steel pipe has obvious advantages, such as repairing end groove, the specified length of delivery, etc. In recent years, the natural gas pipeline network engineering and gas companies have widely used ERW steel pipe as the main pipe network pipe.