Introduction And Difference Between Seamless and Welded Pipes
Seamless Steel Pipe is made from a solid round steel ‘billet’ which is heated and pushed or pulled over a form until the steel is shaped into a hollow tube. Seamless pipes are manufactured in a variety of size and schedule. However, there is a restriction on the manufacturing of large diameter pipe. Seamless pipes are widely used in the manufacturing of pipe fittings such as bends, elbows, and tees. 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. The seamless steel pipe will ideally be a solid metal tube with each end connected to another tube without having any welding joint. These pipes have threads either at one end or at both ends and can be threaded to the end of another hollow tube or pipe. 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. Due to its unique feature of strength and anti-bending, seamless pipe is widely used in number of commercial applications, not only in oil field, but also in ship building, offshore rigs, pressure vessel, construction, chemical industries and so on.
To manufacture Welded/ERW (electronic resistance welded pipe) Steel Pipes, HR Coils are required. Welded Pipe is manufactured by cold forming the steel coil into a round cylindrical pipe. To manufacture welded pipe, first plate or coil is rolled in the circular section with the help of plate bending machine or by a roller in the case of continues process. Once the circular section is rolled from the plate, the pipe can be welded with or without filler material. Welded pipe can be manufactured in large size without any upper restriction. Welded pipe with filler material can be used in the manufacturing of long radius bends and elbow. Welded pipes are cheaper with compared to the seamless pipe and also weak due to the weld. ERW is normally used to transport liquid, such as petrol and gas, playing a significant role in the world line pipe transporting area. 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. Welded steel pipe, such as water pipes, generally through the flat plate by welding after bending up, you can find a seam in the above; is generally thicker in diameter spiral weld. In performance, especially on the bearing capacity has greatly improved as compared with ordinary steel, it is often used for high voltage devices. Such as hydraulic equipment, piping connections.
- Length: A Seamless steel pipe is relatively short in length, whereas welded tubes can be manufactured in long continuous lengths.
- Corrosion: A Seamless steel pipe generally doesn’t show any sign of corrosion until and unless it is subjected to a highly corrosive environment, whereas the weld area in the welded tube is much more prone to corrosion attacks. A welded area is considered to be in homogeneous, thus it exhibits a different malleability and less corrosion resistance as well as greater dimensional variation. A Seamless steel pipe eliminates any such issues and thus offers high corrosion resistance.
- Cost and prices: Usually the seamless steel pipe cost is higher than welded steel pipes, because the raw material, manufacturing equipment and processes. But sometimes by the market pressure, welded pipe is more expensive, so if you met this situation, don’t hesitate to purchase the seamless steel pipe for the same dimensions.
- Appearance difference: Seamless steel pipe uses steel billet as raw material. The outer surface defects of billet cannot be eliminated by hot rolling process, it is only polished after the product finished. In the process of wall reduction, the defect can only get partially eliminated.
Welded steel pipe made by hot rolled coil as raw material, the surface quality of coil is just the pipe’s surface quality, and easy to control.The surface of hot rolled coil have high quality.
So Welded steel pipe surface quality is much better than seamless steel pipe.
- Molding Process: Seamless steel pipe and welded pipe are mainly different molding process. Seamless steel pipe can be formed one time in the rolling process. Welded steel pipe is manufacturing with steel strip or steel plate, through bending and different welding processes.
- Performance and Usage: Seamless steel pipe has better pressure capacity, strength is higher than ERW welded steel pipe. So it is widely applied in high pressure equipment, and thermal, boiler industries.
Generally the welding seam of the welded steel pipe is the weak point, the quality affect overall performance.
In general, welded steel pipes can withhold 20% less working pressure than seamless ones. This reliability is the prime factor why people go for seamless steel pipe. As a matter of fact, all the industrial pipelines are done with seamless pipes only because the pipes undergo extreme thermal, chemical and mechanical workloads. Welded pipes are more preferred in aerospace, automobile and electronics industries where the budget is comparatively low, and so is the work pressure put on the pipes.
- Welding performance: Average Welded Pipe and seamless steel pipe the chemical composition has a certain difference. The production of seamless steel component is only astm the basic requirements.
- Wall thickness and diameter: Small thin-walled pipe preferably by welding production. Large thick-walled pipe is best made with the seamless method.
- The welded steel pipe weld area is its weak link, weld quality is also affecting the overall performance of the main factors. The presence of any seam on a welded pipe acts as a weak point, however if the tube is seamless, it tends to be solid and overcome various industrial forces and pressures while in operation.
How to Identify Seamless or ERW Stainless Steel pipes?
To identify that a pipe supplied is seamless or ERW, Simply read the stencil on the side of the pipe
If it is ASTM A53, Type S means seamless.
Type F is furnace but welded,
Type E is Electrical resist welded.
That’s how. It is the easiest way to identify whether pipe is seamless or ERW.
In short, Seamless is marketed on an outdated myth that it does not have flaws but that welded has an inherent flaw throughout the length of each tube, as stated above. Intuitively this concept is easily accepted by purchasers and designers with limited experience with the various products. Each product form and manufacturing method has its own inherent problems and potential defects.