Questions regarding welded pipes and seamless pipes

The forming processes for welded pipes and seamless pipes are different; the most obvious difference is that welded pipes have seams, while seamless pipes do not have any welds. For this reason, their mechanical properties also differ. The former is only applicable to low pressures and ordinary medium fluids ； The latter is mostly used for fluids under high pressure and temperature that are of great importance.

Can it be the same when welded together and when shaped together? Of course they’re different; seamless steel pipes are definitely superior to Dai Feng steel pipes

The maximum outer diameter of seamless pipes is 426; those with a diameter larger than 426 need to be rolled, while those with a diameter smaller than 426 are selected according to standards.

Welded pipes (seamed steel pipes) can be rolled manually and are used in low-pressure environments, whereas seamless pipes require production by specialized manufacturers and are used in higher-pressure environments.

Everyone is being too general; you can refer to the “Practical Hardware Handbook”

The main difference lies in the manufacturing process: welded pipes are primarily formed by welding, such as spiral welded pipes and straight-seam welded pipes, while seamless pipes are made through cold drawing or hot rolling.

This is an outdated concept; nowadays, many long-distance pipelines use welded pipes of the X70 and X80 grades, which can withstand pressures of up to 10 MPa. They feature high strength and thin wall thicknesses, which helps to significantly reduce construction costs. A typical example is the West-East Gas Pipeline II, where many of the pipelines have a diameter of over 1 meter.

The mechanical properties of the weld zone, heat-affected zone, and base metal in welded pipes vary, whereas the mechanical properties of seamless steel pipes are relatively uniform. The 8th floor mentioned that welded pipes are used for the West-to-East Gas Pipeline project. I think it’s not so much that the mechanical properties of welded pipes are better than those of seamless pipes, but rather that the manufacturing cost of large-diameter seamless pipes with a diameter of over 1 meter is high; when the mechanical properties meet the required standards, using welded pipes is a more cost-effective option. Of course, with technological advancements, the performance of welded pipes and seamless pipes is definitely becoming increasingly similar. This post was last edited by foxbat on 2009-4-28 09:52]

Different welding processes require different operating conditions.

Seamless pipes have an attractive appearance, and their mechanical properties are better than those of welded pipes. The welded pipes we use here are mostly in the form of coiled steel, which is then welded; stress relief treatment is required after welding. From this perspective, seamless pipes aren’t either easily usable; sometimes they don’t have the dimensions we need, so there’s no other choice but to weld them in this way

Welded steel pipes: The raw materials used for welded steel pipes are steel plates or strips. Depending on the welding process, they are classified into furnace-welded pipes, electric welding (resistance welding) pipes, and automatic arc welding pipes. Depending on the welding method, it is divided into straight-seam welded pipes and spiral welded pipes. Based on their end shape, they are further divided into round welded pipes and shaped welded pipes (square, flat, etc.). Welded pipes are classified into the following types depending on their material and application: GB/T3091-1993 (Galvanized welded steel pipes for low-pressure fluid transport). Primarily used for transporting fluids at relatively low pressures such as water, gas, air, oil, and heating water or steam, as well as for other applications. Its representative material is Q235A grade steel. 　　GB/T3092-1993 (Galvanized welded steel pipes for low-pressure fluid transport). Primarily used for transporting fluids at relatively low pressures such as water, gas, air, oil, and heating water or steam, as well as for other applications. Its representative material is Q235A grade steel. GB/T14291-1992 (Welded steel pipes for conveying fluids in mining applications). Primarily used as straight-seam welded steel pipes for mine air compression, drainage, and gas drainage. The representative materials are Q235A and grade B steel. GB/T14980-1994 (Large-diameter electric welded steel pipes for low-pressure fluid transport). It is mainly used for transporting low-pressure fluids such as water, sewage, gas, air, and heating steam, as well as for other purposes. Its representative material is Q235A grade steel. 　　GB/T12770-1991 (Welded stainless steel pipes for mechanical structures). It is mainly used in machinery, automobiles, bicycles, furniture, hotel and restaurant decoration, as well as other mechanical components and structural parts. The representative materials include 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc. 　　GB/T12771-1991 (Welded stainless steel pipes for fluid transport). It is mainly used for transporting low-pressure corrosive media. The representative materials include 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, etc. 　　(2) Seamless steel pipes: Depending on their manufacturing processes, they are further divided into hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes. Cold-drawn (rolled) tubes are further divided into round tubes and shaped tubes. 　　a. Process flow overview 　　Hot rolling (extrusion of seamless steel pipes): Round tube billet → Heating → Piercing → Three-roller skew rolling, continuous rolling or extrusion → Tube removal → Dimensioning (or reduction in diameter) → Cooling → Billet tube → Straightening → Hydrostatic testing (or flaw detection) → Marking → Storage. 　　Cold-drawn (rolled) seamless steel tubes: round tube billet → heating → piercing → end forming → annealing → acid washing → oiling (copper plating) → multiple passes of cold drawing (cold rolling) → tube blank → heat treatment → straightening → hydrostatic testing (flaw detection) → marking → storage. 　　b. Seamless steel pipes are classified into the following types depending on their uses: GB/T8162-1999 (seamless steel pipes for structural use). It is mainly used in general structures and mechanical structures. Its representative materials (grade numbers): carbon steel 20, 45 steel ； Alloy steels such as Q345, 20Cr, 40Cr, 20CrMo, 30-35CrMo, 42CrMo, etc. 　　GB/T8163-1999 (Seamless steel tubes for transporting fluids). It is mainly used for fluid transport pipelines in engineering and large-scale equipment. The representative materials (grade numbers) are 20, Q345, etc. 　　GB3087-1999 (Seamless steel tubes for low and medium pressure boilers). Primarily used for pipes that transport low and medium pressure fluids in industrial and domestic boilers. The representative materials are steel grades 10 and 20. 　　GB5310-1995 (Seamless steel tubes for high-pressure boilers). It is mainly used for high-temperature and high-pressure fluid transfer manifolds and pipelines in power plant and nuclear power plant boilers. Representative materials include 20G, 12Cr1MoVG, 15CrMoG, etc. 　　GB5312-1999 (Seamless steel tubes for ships – carbon steel and carbon-manganese steel). Primarily used for pressure-resistant pipes of grades I and II in ship boilers and superheaters, etc. The representative materials include steel grades such as 360, 410, and 460. 　　GB1479-2000 (Seamless steel pipes for high-pressure fertilizer equipment). It is mainly used for pipelines that transport high-temperature and high-pressure fluids in fertilizer production equipment. The representative materials include 20, 16Mn, 12CrMo, 12Cr2Mo, etc. 　　GB9948-1988 (Seamless steel pipes for petroleum cracking). It is mainly used in boilers, heat exchangers, and fluid transport pipelines in oil refineries. The representative materials include 20, 12CrMo, 1Cr5Mo, 1Cr19Ni11Nb, etc. 　　GB18248-2000 (Seamless steel tubes for gas cylinders). It is mainly used for manufacturing various gas and hydraulic cylinders. The representative materials include 37Mn, 34Mn2V, 35CrMo, etc. 　　GB/T17396-1998 (Hot-rolled seamless steel tubes for hydraulic struts). It is mainly used to manufacture hydraulic supports and cylinders for coal mines, as well as other hydraulic cylinders and columns. The representative materials include 20, 45, 27SiMn, etc. 　　GB3093-1986 (High-pressure seamless steel tubes for diesel engines). Mainly used for high-pressure fuel pipes in diesel engine injection systems. Its steel pipes are generally cold-drawn pipes, with 20A being the representative material. 　　GB/T3639-1983 (Precision seamless steel tubes drawn or rolled cold). Steel pipes primarily used in mechanical structures and carbon compression equipment, requiring high dimensional accuracy and good surface finish. Its representative materials include 20, 45 steel, etc. 　　GB/T3094-1986 (Cold-drawn seamless steel tubes – Special-shaped steel tubes). It is mainly used to manufacture various structural components and parts, with materials consisting of high-quality carbon structural steel and low-alloy structural steel. 　　GB/T8713-1988 (Precision inner-diameter seamless steel tubes for hydraulic and pneumatic cylinders). Primarily used to manufacture cold-drawn or cold-rolled seamless steel tubes with precise inner diameter dimensions for hydraulic and pneumatic cylinder barrels. The representative materials include 20, 45 steel, etc. 　　GB13296-1991 (Seamless stainless steel tubes for boilers and heat exchangers). It is mainly used in boilers, superheaters, heat exchangers, condensers, catalytic tubes, etc. in chemical enterprises. High-temperature, high-pressure, and corrosion-resistant steel pipes are used. The representative materials include 0Cr18Ni9, 1Cr18Ni9Ti, 0Cr18Ni12Mo2Ti, etc. 　　GB/T14975-1994 (Seamless stainless steel tubes for structural use). Steel pipes that are resistant to atmospheric and acid corrosion and possess a certain degree of strength, primarily used in general structures (such as hotel and restaurant decorations) as well as in the mechanical systems of chemical industry facilities. The representative materials include 0-3Cr13, 0Cr18Ni9, 1Cr18Ni9Ti, 0Cr18Ni12Mo2Ti, etc. 　　GB/T14976-1994 (Stainless steel seamless pipes for fluid transport). Mainly used for pipelines transporting corrosive media. The representative materials include 0Cr13, 0Cr18Ni9, 1Cr18Ni9Ti, 0Cr17Ni12Mo2, 0Cr18Ni12Mo2Ti, etc. 　　YB/T5035-1993 (Seamless steel tubes for automobile half-shaft sleeves). Mainly used for producing hot-rolled seamless steel tubes made of high-quality carbon structural steel and alloy structural steel, which are employed in manufacturing automobile half-shaft sleeves and axle housings for drive axles. The representative materials include 45, 45Mn2, 40Cr, 20CrNi3A, etc. 　　API SPEC5CT-1999 (Specification for Casing and Tubing) is a standard developed and published by the American Petroleum Institute (abbreviated as “API”) and is used worldwide. Among them: Casing: Tubes that extend from the ground surface into the well, serving as a lining for the well walls; these tubes are connected to each other using couplings. The main material grades include J55, N80, P110, etc., as well as steel grades resistant to hydrogen sulfide corrosion such as C90 and T95. Its lower steel grades (J55, N80) can be used for welded steel pipes. Oil pipe: A pipe that is inserted into the casing from the surface of the ground all the way to the oil layer, with the pipes being connected to each other either through couplings or in an integral manner. Its function is then for the pump to transport the oil from the reservoir to the surface through the oil pipes. The main materials are steel grades such as J55, N80, P110, as well as C90 and T95, which are resistant to hydrogen sulfide corrosion. Its lower steel grades (J55, N80) can be used for welded steel pipes. 　　API SPEC 5L-2000 (Pipeline Steel Specification) was developed and published by the American Petroleum Institute, and is widely used around the world. 　　Piping: It is used to transport oil, gas, or water that emerges from the ground through pipelines to petroleum and natural gas processing facilities. Piping pipes come in two types: seamless and welded pipes. Their ends can be flat, threaded, or socketed; the methods of connection include end welding, flange connection, and socket fitting. The main materials for this pipe are steel grades such as B, X42, X56, X65, and X70.

Seamless steel pipes are formed in one step during rolling. Welded steel pipes are formed by rolling followed by welding, and there are generally spiral welding and straight welding. Seamless pipes offer better performance, though they are also more expensive

Welded pipes (seamed steel pipes) can be rolled manually and are used in low-pressure environments, while seamless pipes require production by specialized manufacturers and are used in higher-pressure environments. Please indicate the source as Haichuan Chemical Industry Forum when reproducing this content: http://bbs.hcbbs.com/. The address of this post is: http://bbs.hcbbs.com/viewthread.php?tid=453238

In the early years, due to issues with manufacturing processes and technology, the use of welded pipes was limited. Nowadays, for large-diameter pipes, except for a very small number of forged pipes used in ultra-high pressure applications, welded pipes are generally what are used. Welded pipes can also be used in high-pressure and high-temperature conditions, although the welding process requires higher standards and more stringent inspection. The composite pipes we use even specify that they are manufactured by rolling and welding explosive composite sheets

The wall thickness of the welded pipe is relatively uniform and its appearance is good, but it has low pressure resistance and poor high-temperature tolerance； Seamless pipes are formed through cold drawing, cold rolling, or hot rolling; they possess strong compressive strength and a higher temperature resistance compared to welded pipes.