What is electric resistance welded tube?

ERW is a general term for electric resistance welded tubes, and ERW is the first letter of the corresponding English word. Electric resistance welded steel pipes are divided into AC welded steel pipes and DC welded steel pipes. AC welding is divided into low frequency welding, intermediate frequency welding, super intermediate frequency welding and high frequency welding according to the frequency. High-frequency welding is mainly used for the production of thin-walled steel pipes or ordinary wall-thick steel pipes, and high-frequency welding is divided into contact welding and induction welding. DC welding is generally used for small diameter steel pipes. Therefore, in general, the high-frequency welded pipe is included in the ERW welded pipe, which is a kind of ERW welded pipe produced by the high-frequency welding process. ERW longitudinal welded pipe is a steel pipe with advanced product performance, leading quality and relatively economical in the field of oil and gas storage and transportation.

The concept of electric resistance welded steel pipe

1. Welded pipes are round pipes welded by steel plates, which are divided into high-frequency electric resistance welded pipes (ERW pipes), straight seam arc welded pipes (LSAW), and spiral welded pipes.
In electrical engineering, "SC" is used to indicate that it can be used as a water gas pipe or a threading pipe, and it is relatively thick.
2. The line pipe is also the wire pipe, which is relatively thin and is represented by "T", and it can only be used as a threading pipe. 3. ERW pipe is a "high-frequency resistance welded steel pipe". It is different from the welding process of ordinary welded pipes. The weld seam is formed by melting the base material of the steel strip body, and its mechanical strength is better than that of ordinary welded pipes.
ERW means resistance welding. Resistance welding has the characteristics of high production efficiency, low cost, material saving, and easy automation. Therefore, it is widely used in various industrial sectors such as aviation, aerospace, energy, electronics, automobiles, and light industry. It is one of the important welding processes. one.

ERW straight seam welded pipes are generally used as wire casings in the power industry. Performance characteristics: 100% ultrasonic testing of the base metal ensures the internal quality of the pipe body; there is no uncoiling-disc shearing process, and the base metal is pressed , less scratches; the finished pipe after stress relief basically has no residual stress; the weld seam is short, and the probability of defects is small; wet sour natural gas can be transported conditionally; after diameter expansion, the geometric dimension accuracy of the steel pipe is high; welding After the forming is completed, it is carried out along a straight line in a horizontal position. Therefore, the control of staggered sides, slits, and pipe diameter circumference is better, and the welding quality is excellent.

According to GB/T3092 "Welded Steel Pipes for Low-Pressure Fluid Transmission", the nominal diameter of the welded pipe is 6~150mm, the nominal wall thickness is 2.0~6.0mm, and the length of the welded pipe is usually 4~10 meters. The length of the ruler leaves the factory. The surface quality of the steel pipe should be smooth, and defects such as folding, cracks, delamination, and lap welding are not allowed. The surface of the steel pipe is allowed to have minor defects such as scratches, scratches, weld misalignment, burns and scars that do not exceed the negative deviation of the wall thickness. The thickening of the wall thickness and the presence of inner seam weld bars are allowed at the weld.

ERW vs seamless pipe

The biggest difference between ERW steel pipe and seamless steel pipe is that ERW has a weld seam, which is also the key to the quality of ERW steel pipe. Modern ERW steel pipe production technology and equipment, due to the unremitting efforts of the world, especially the United States, have made the seamlessness of ERW steel pipes a relatively satisfactory solution. Some people divide the seamlessness of ERW steel pipes into geometric seamlessness and physical seamlessness. Geometric seamlessness is to remove the internal and external burrs of ERW steel pipes.

Due to the continuous improvement and improvement of the structure of the internal burr removal system and the cutting tools, the removal of the internal burrs of large and medium-diameter steel pipes has been better handled. The internal burr can be controlled at about -0.2mm ~ O.5mm. Physical seamlessness means that there is a difference between the metallographic structure inside the weld and the base metal, which leads to a decrease in the mechanical properties of the weld area, and measures need to be taken to make it uniform and consistent. The high-frequency welding heat process of ERW steel pipe causes the temperature distribution gradient near the edge of the tube blank, and forms characteristic areas such as melting zone, semi-melting zone, overheated structure, normalizing zone, incomplete normalizing zone, and tempering zone. Among them, due to the welding temperature above 1000°C in the superheated zone, the austenite grains grow rapidly, and a hard and brittle coarse-grained phase will be formed under cooling conditions. In addition, the existence of temperature gradients will generate welding stress.

In this way, the mechanical properties of the weld area are lower than those of the base metal. The physical seamlessness is to heat the weld area to AC3 (927°C) with a medium-frequency induction heating device through the local conventional heat treatment process of the weld, and then carry out 60m Air cooling process with length and speed at 20m/min, and water cooling when necessary. 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, advanced ERW units in the world have generally used this method to process welds, and good results have been obtained. The high-quality ERW steel pipe is not only unable to distinguish the weld seam, but also has a weld seam coefficient of 1, which realizes the matching of the weld seam area structure and the base material.