ERW pipe, shorted for electronic resistance welded pipe, is manufactured by cold forming the steel coil into a round cylindrical pipe. Current passes between the two edges of the steel to heat the steel to a point at which the edges are able to connect together to form a bond using the actual welding process. ERW is normally used to transport liquid, such as petrol and gas, playing a significant role in the world line pipe transporting area.
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Seamless steel pipe, or SMLS, refers to a hollow steel pipe having no seam around. Due to its unique feature of strength and anti-bending, seamless pipe is widely used in construction, oil refining and chemical industries.
According to the definition of ERW pipes and seamless pipes above, it’s obvious that there are some differences between them.
Tube billet, a key raw material in manufacturing process, is a solid round bar of steel used to produce many pipe products. Compared with seamless pipes, the chemical structure of the tube billet of ERW pipe has more advantages. The processing method such as desulfurization, dephosphorization and degassing makes the purity of ERW pipe billet much higher. The adding-in of specific chemical elements improves the toughness and the strength of the tube billet.
Besides, the ERW pipe tube billet is made of hot-rolled steel strip with cold rolling process while the seamless pipe tube billet is produced in hot rolling condition. The situation where seamless pipe tube billet is produced has some negative effects on the grain size, thus resulting in a less satisfying performance.
Seamless pipe is formed when steel in the billet is heated and then either pushed or pulled over a mandrel with a piercing point located in the center of the billet. This produces a hollow tube or “shell”. The tube is then further processed until it becomes the desired size and wall thickness. The whole manufacturing process doesn’t involve any welding part, so there is no welding line in seamless pipes. ERW pipe is cold formed a strip steel into a round pipe section, the edges of which are heated by high frequency welder. Then the welding is inspected electronically and cooled down by air and water.
The biggest visible difference between ERW pipes and seamless pipes in structure is that ERW pipe has a welding seam which is produced by the welding process while seamless pipe doesn’t. The less recognizable the welding line is, the better ERW pipe will be. Nowadays, with the advancement of the technology, two ways are coming into use to eliminate the welding line, the geometric seamless and physical seamless. Geometric seamlessly is to remove the burr inside and outside of the ERW pipes. Physical seamlessly refers to the difference between the microstructure and the parent metal on the inside of welding line resulted in decrease of the welding area and mechanical properties.
In contrast to the ERW pipes, seamless pipes, without the seam or the welding line, is able to maintain a uniform shape and great strength under high pressure, temperature or heavy loads.
Seamless pipe owns three unique advantages, namely high pressure endurance, great strength and uniformity of structure.
Seamless pipe is most favored by its high pressure endurance. Normally, the weakest part of pipes is the welding line, but seamless pipe doesn’t have a seam, so the entire circumference of the pipe can evenly withstand high pressure. Besides, owing to the lack of the welding line, seamless pipe is able to support its own weight as well the heavy loaded weight, and maintain its original structure. There advantages bring seamless pipe a number of commercial applications, not only in oil field, but also in ship building, offshore rigs, pressure vessel and so on.
As for ERW pipe, one of the biggest benefits is that only the tube billet ends are heated during the manufacturing process, therefore the rest of the whole ERW pipe remains clean and only the welding part needs to be cleaned. This reduces the post-welding cleaning work, largely increasing the working efficiency and saving cost. Besides, owing to the almost clean and smooth surface, ERW pipes are easy to be applies with coating method.
Generally speaking, though having much difference in making process and structure, ERW pipes and seamless pipes in Anson Company are both widely applied in oil and gas transporting field. Both pipes complied with API specification are acceptable for most applications. To fully enjoy the benefits of the two pipes, customers shall choose the more suitable pipe based on their own actual needs.
