Seamless Steel Pipe VS Welded Steel Pipe
As an important part of steel products, steel pipes are divided into two types: welded steel pipes and seamless steel tubes due to their different manufacturing processes and the shape of the pipes used.
Seamless steel pipes are rarely used in the construction department, and most of them are steel pipes welded with steel plates, referred to as welded pipes. Scaffolding steel pipe is a straight welded pipe.
The blanks used for welded steel pipes are steel plates or strip steels, which are divided into furnace welded pipes, electric welding (resistance welded) pipes and automatic arc welded pipes due to different welding processes. Due to the different welding forms, it is divided into straight welded pipe and spiral welded pipe.
A steel pipe made of a single piece of metal and having no seams on its surface is called a seamless steel pipe. Due to different manufacturing processes, it is divided into two types: hot-rolled (extrusion) seamless steel pipe and cold drawn (rolled) seamless steel pipe.
Hot rolling (extrusion seamless steel pipe): round tube billet → heating → perforation → three-roll cross-rolling, continuous rolling or extrusion → pipe removal → sizing (or reducing diameter) → cooling → blank pipe → straightening → water pressure Test (or flaw detection) → mark → warehousing.
Cold drawn (rolled) seamless steel pipe: round tube billet → heating → perforation → head → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → blank pipe → heat treatment → straightening → Hydraulic test (inspection) → mark → storage.
- Comparison of wall thickness tolerance between welded pipe and seamless steel pipe: stainless steel seamless pipe can achieve small diameter and large wall thickness and large diameter and large wall thickness, but it is generally limited by length; but the wall thickness of stainless steel welded pipe can be made thinner, can achieve large diameter and small wall thickness and small diameter The small wall thickness, in theory, how long the stainless steel coil is, how long the welded pipe can be. In other words, the thicker the more suitable the use of seamless tubes, the thinner the more suitable the use of welded pipes. The average wall thickness and concentricity of the pipe are better than stainless steel seamless pipes in this respect. Because the thickness tolerance of the cold rolled sheet is relatively average, the deformation during the forming process is average. The seamless tube rolling process is affected by factors such as equipment accuracy, and has the problem of uneven thickness and concentricity, but the roundness is better than that of the welded pipe. Welded pipe: hot-rolled coil is used as raw material, the thickness limit of modern hot-joining can be controlled within 0.05mm, and the seamless steel pipe is produced by round steel perforation, the wall thickness deviation is large, and the subsequent hot rolling can partially eliminate the wall thickness. Inhomogeneity, but the most advanced unit can only be controlled within ±5~10%t, corresponding to a steel pipe with a thickness of 8.94mm. Seamless steel pipe: The limit of wall thickness control accuracy is 0.9mm.
- Welded pipe and seamless steel pipe comparison outer diameter tolerance: steel pipe, adopting cold-bending forming, the sizing is completed by 0.6% reduction, and the process temperature is basically constant at room temperature, so the outer diameter control is accurate and the fluctuation range is small, which is beneficial to prevent black leather buckle. Seamless steel pipe: It adopts hot-rolling forming process, and its sizing is completed at 8000C. The raw material composition, cooling conditions and cooling state of the steel pipe have a great influence on the outer diameter, so the outer diameter control is difficult to be accurate and fluctuates. The range is large.
- Comparative tensile test of welded pipe and seamless steel pipe: the tensile performance indexes of seamless steel tubes and welded pipes are in line with API standards, but the strength of seamless steel tubes is generally at the upper limit, and the plasticity is at the lower limit. In comparison, the strength index of welded pipes is in an optimal state, and the plasticity index is higher than the standard 33.3%. For the raw material of welded pipe, the performance of hot rolled coil is guaranteed by means of microalloying smelting, refining outside the furnace and controlled cooling and rolling. The seamless steel pipe mainly relies on the means of increasing the carbon content, and it is difficult to ensure the reasonable matching of strength and plasticity. .
- Welded pipe and seamless steel pipe comparison ovality: welded pipe: Cold-formed, so the outer diameter control is accurate and the fluctuation range is small. Seamless steel pipe: The hot rolling forming process, the raw material composition of the steel pipe, the cooling condition and the cooling state of the roll have a great influence on the outer diameter, so the outer diameter control is difficult to be accurate and the fluctuation range is large.
- Welded pipe and seamless steel pipe hardness: the raw material of the welded pipe, the hot-rolled coil, has extremely high precision in controlled rolling and cold rolling, which ensures uniform performance of each part of the coil.
- Welded pipe and seamless steel pipe comparison grain: the raw material of the welded pipe – hot-rolled coil is made of wide and thick continuous casting billet, with thick fine-grained surface solidified layer, no columnar crystal region and shrinkage and looseness, small composition deviation and dense structure; in the subsequent rolling process The application of controlled cold rolling technology further ensures the grain size of raw materials.
- Welded pipe and seamless steel pipe are more resistant to crushing test: the welded pipe is characterized by its raw materials and pipe making process. Its wall thickness uniformity and ellipticity are far superior to seamless steel tubes, which is the main reason for the anti-crushing performance higher than seamless steel tubes.
- Comparative test of welded pipe and seamless steel pipe: since the impact toughness of the welded base metal is several times that of the seamless steel pipe, the impact toughness at the weld is the key to the welded pipe. By controlling the impurity content of the raw material, the height and direction of the longitudinal burr, the shape of the formed edge, the welding angle, the welding speed, and the heating The process parameters such as power and frequency, welding extrusion amount, intermediate frequency decoupling temperature and depth, and air cooling section length ensure that the impact energy of the weld is more than 60% of the base metal. If further optimization, the weld impact energy can be close to the base metal. Thereby achieving seamless performance.
- Comparative blasting test of welded pipe and seamless steel pipe: the performance of the blasting test of the welded pipe is much higher than the standard requirement, mainly due to the uniformity of the wall thickness of the welded pipe and the uniform outer diameter.
- Straightness of welded pipe and seamless steel pipe: the welded pipe is cold-worked and has straightening in the state of reducing the diameter, plus an infinite multiple, so the straightness is good; the seamless steel pipe is formed in a plastic state, plus a single ruler (continuous rolling is 3~) 4 times ruler) Tube end straightness is relatively difficult to control.
- Comparative appearance of welded pipe and seamless steel pipe: the main difference between seamless steel tubes and seamed steel tubes is that seamless steel tubes have no welds. The outer surface defects of the blank used in the seamless steel pipe cannot be eliminated by the hot rolling process, and the defects can only be polished after the finished product is finished; for the spiral track left after the piercing, only part of the elimination can be obtained in the process of reducing the wall. The welded pipe adopts hot rolled coil as the raw material. The surface quality of the coiled sheet is the surface quality of the welded pipe, and the surface quality of the hot rolled coil is easy to control and the quality is high, so the surface quality of the welded pipe is much better than that of the seamless steel pipe. The surface of the welded pipe has: straight seam or spiral seam. The seamless steel pipe has better pressure bearing capacity and better sealing performance than the seamed steel pipe, and is suitable for occasions with harsh working conditions.
- Comparative performance of welded pipe and seamless steel pipe: the averageness, appearance quality, tube expansion performance, bending and pier head performance of stainless steel welded pipes are better. Because the performance of the cold-rolled sheet is better than that of the pipe, and the welded pipe is generally solid solution on-line, the heat treatment is relatively average, and the performance is more stable. Stainless steel seamless tubes are sampled at different locations on the same tube and performance will vary. Generally, the precision of the welded pipe is higher, the wall thickness is more uniform, and the brightness of the inside and outside of the stainless steel pipe member is high (the surface brightness of the steel pipe determined by the surface grade of the steel plate), and the steel can be freely fixed. Therefore, it exhibits its economy and aesthetics in the use of high precision, medium and low pressure fluids. The accuracy of the seamless steel pipe is low, the wall thickness is uneven, the brightness inside and outside the pipe is low, the length of the fixed length is high, and the pitting and black spots on the inner and outer surfaces are not easily removed.
- The price of welded pipe and seamless steel pipe: the price of welded pipes is cheaper than seamless steel pipes.
- Welded pipe and seamless steel pipe have comparative pressure capacity: under the same specifications, the stainless steel seamless steel pipe has a slightly higher pressure bearing capacity than the welded pipe. However, since the stainless steel welded pipe is formed by rolling a stainless steel plate, the processing is relatively simple, and the delivery time is shorter. The stainless steel seamless pipe should be from the beginning of the round steel, after the perforation, after many times of cold drawing and cold rolling processing, and then through solution annealing and pickling to produce the finished product, the production cycle is longer.
Source: China Welded Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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