What Is ERW Pipe?

The term "ERW pipe" refers to straight seam electric resistance welded pipe, also known as English Electric Resistance Welding or ERW. ERW pipe is used to transport oil, natural gas, and other vapor-liquid objects and can withstand a range of high and low-pressure requirements. It is a key component of the global transportation pipe market.

1. The welded pipe is a round pipe that is joined together by steel plates. It can be spiral welded, straight seam arc welded, or high-frequency resistance welded. In electrical engineering, the designation "SC" denotes that a pipe is relatively thick and can be used as a threading pipe or a water gas pipe.

2. The line pipe, denoted by the letter "T," is a wire pipe that is relatively thin and is only intended for use in threading pipes.

3. "High-frequency resistance welded steel pipe" (ERW pipe) is a welding technique distinct from that used to create regular welded pipe. The base metal of the steel strip body is melted during the welding process, resulting in a seam with greater mechanical strength than regular welded pipes. Resistance welding is known as ERW. Resistance welding has the advantages of high automation, low cost, material savings, and high production efficiency. As a result, it is frequently used in a variety of industrial sectors, including the light industry, aviation, aerospace, energy, and electronics. It is a crucial aspect of the welding process. 

The welded seam on ERW pipe, which is also the secret to their superior quality, is the main distinction between them and seamless steel pipes. Some people distinguish between geometric seamlessness and physical seamlessness when describing the seamlessness of ERW pipe. For ERW pipe, geometric seamless is used to remove both internal and external burrs. Internal burr removal in large and medium-diameter steel pipes has been successfully managed thanks to ongoing refinement and perfection of the system's structure and tool. At -0.2mm to O.5mm, the internal burr can be controlled. Physical seamlessness denotes a difference in the metallographic structure of the base metal and the weld, which impairs the mechanical properties of the weld area and necessitates taking steps to make the weld area uniform and consistent. The melting zone, semi-melting zone, overheated structure, normalizing zone, incomplete normalizing zone, and tempering zone are all typical regions created by the high-frequency welding thermal process of ERW pipe near the edge of the tube blank. Among them, the austenite grains grow quickly in the superheated zone due to the welding temperature being above 1000 °C, and under cooling conditions, a hard and brittle coarse-grained phase will form. Additionally, the presence of a temperature gradient will cause stress during welding. In this way, the weld area's mechanical properties are inferior to those of the base metal. The weld area is heated to AC3 (927°C) through the local conventional heat treatment process of the weld, that is, using an intermediate frequency induction heating device, and then for 60m. This produces a physically seamless weld. A 20 m/min air cooling process is used when necessary, along with water cooling. The purpose of using this technique is to eliminate stress, soften and refine the structure, and enhance all mechanical aspects of the welding heat-affected zone. The majority of the advanced ERW pipe units in the world have so far used this technique to process welds, and they have seen positive results. The high-quality ERW pipe not only makes it impossible to tell where the weld is, but it also achieves a weld coefficient of 1, realizing structural alignment between the base metal and the weld area.

The advantages of ERW pipe include the use of hot-rolled coil as the raw material, control of the uniform wall thickness at about 0.2mm, compliance with American APl or GB/T9711.1 standards at both ends, trimming and beveling of the ends, fixed delivery length, etc. In recent years, ERW pipe has become the predominant steel pipe for urban pipeline networks thanks to numerous natural gas pipeline projects and gas companies.