What are the production processes of welded pipe?

What are the production processes of welded pipe?

Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or strip after curling and welding. Generally, the length is 6 meters. The production process of welded steel pipe is simple, the production efficiency is high, the varieties and specifications are more, the equipment investment is less, but the general strength is lower than seamless steel pipe.

The development of steel pipe production technology began with the rise of bicycle manufacturing industry. The development of oil in the early 19th century, the manufacture of ships, boilers and airplanes during the two world wars, the manufacture of thermal power boilers after the Second World War, the development of chemical industry and the drilling, production and transportation of oil and natural gas all strongly promoted the development of steel pipe industry in variety, output and quality. Generally, according to the production method, the steel pipe is divided into seamless steel pipe and welded steel pipe. This time, we mainly introduce the welded steel pipe.
Welded steel pipe is a kind of seamless steel pipe. Its production is the process of bending the pipe blank (steel plate and steel strip) into the required cross-section shape and size pipe by various forming methods, and then welding the weld with different welding methods to get the steel pipe. Compared with seamless steel pipe, welded pipe has the characteristics of high product precision, especially wall thickness precision, simple main equipment, small occupation, continuous operation in production, flexible production and wide product range of the unit.

Welded pipe can be divided into SSAW (spiral submerged arc welding), LSAW (longitudinally submerged submerged arc welding) and ERW (electric resistance welding).

Production technology of spiral steel pipe

  • (1) raw materials are steel coil, welding wire and flux. Before putting in, strict physical and chemical inspection should be passed.
  • (2) single wire or double wire submerged arc welding is selected for the butt joint of the strip steel head and tail, and active submerged arc welding is selected after the steel pipe is rolled.
  • (3) before being formed, the surface of the strip shall be cleaned, transported and bent by flattening, trimming and planing.
  • (4) select the pressure of electric contact pressure gauge to control and transport the oil cylinder on both sides of the machine to ensure the smooth transportation of the steel strip.
  • (5) use external control or internal control roll forming.
  • (6) choose the welding gap control equipment to ensure that the welding gap is satisfied with the welding requirements, and the pipe diameter, edge offset and welding gap are strictly controlled.
  • (7) both inner welding and outer welding select American Lincoln welding machine for single wire or double wire submerged arc welding, and then obtain stable welding quality.
  • (8) welded welds are checked by online ultrasonic active injury meter to ensure the non-destructive testing coverage of spiral welds. If there is a defect, take the initiative to alarm and spray symbols, the production workers can adjust the process parameters at any time to eliminate the defects in time.
  • (9) the steel pipe is cut into a single root by using an air plasma cutting machine.
  • (10) after cutting into a single steel pipe, each batch of steel pipes should be subjected to severe first inspection guidelines to check the mechanical properties, chemical composition and fusion conditions of welds, the surface quality of steel pipes, as well as the non-destructive testing to ensure that the production process is qualified, can be formally put into production.
  • (11) for the parts with connected acoustic flaw detection symbols on the weld, the manual ultrasonic wave and X-ray reexamination shall be carried out. If there is a defect, the non-destructive examination shall be carried out again after the repair until it is admitted that the defect has been eliminated.
  • (12) the spot pipes of the butt weld of the steel strip and the T-joint intersecting with the spiral Weld are all checked by X-ray TV or film.
  • (13) each steel pipe shall pass hydrostatic pressure test, and the pressure shall be radial seal. The test pressure and timing are strictly controlled by the steel pipe water pressure microcomputer testing equipment. Active printing record of test parameters.
  • (14) mechanical processing of pipe end makes the straightness of end surface, groove angle and obtuse edge accurately controlled.

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Production technology of LSAW pipe

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The (LSAW) of straight seam embedded arc welded pipe generally takes steel plate as raw material, and through different forming processes, adopts double-sided submerged arc welding and post-welding expanding to form welded pipe. The welding technology of submerged arc welding straight seam steel pipe is submerged arc welding technology, which adopts filled welding and particle protective agent submerged arc welding, and its diameter can reach 1500mm.
Submerged arc welding straight seam steel pipe is divided into UO(UO E), RB(RBE), JCO(JCOE) and other types according to its different forming methods. The steel plate is first pressed into U-shape in the molding die, then pressed into O-shape, and then submerged arc welding is carried out inside and outside. After welding, it is usually expanded at the end or in the full length range. It is called UO E welded pipe, the one without expanding is called UO welded pipe. Roll Bending of the steel plate, then submerged arc welding inside and outside. After welding, the expansion is RBE welded pipe or RB welded pipe without expansion. Form the steel plate in the order of type J to type C to type O. After welding, use J C OE welded pipe with expanding diameter or J C O welded pipe without expanding diameter.

Forming process of UOE LSAW pipe:

The three main forming processes of UOE LSAW pipe forming process include: steel plate pre bending, u forming and O forming. Each process uses a special forming press to complete three processes of steel plate edge pre bending, U-forming and O-forming in turn to deform the steel plate into a circular pipe. As shown in the figure:

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Forming process of JCOE LSAW pipe:

Forming: after several times of step stamping on JC0 forming machine, the first half of the steel plate is pressed into “J”, then the other half of the steel plate is pressed into “J” to form “C”, finally the “0” shape pipe blank is formed by pressing from the middle. 

JCOE manufacturing technology is a kind of welded pipe forming technology developed in the 1990s. The main forming process of this technology is to mill (or plane) the edge of the steel plate first, then pre bend the longitudinal edge, and then form it in the order of J-type → C-type → O-type. The basic principle of each stamping step is three-point bending.
Due to the multi pass progressive pressing, the following problems must be solved: how to determine the die shape, upper die stroke and lower die spacing, and how many passes are needed to ensure the most appropriate bending radius and the best open rough pipe blank. These problems are related to the steel plate material, the specific mechanical properties of different steel plate manufacturers, and the steel pipe specifications (diameter and wall thickness), so they are very complicated. It mainly depends on the “trial and error method”, that is, whenever a new specification or new steel grade is replaced, a certain number of small samples are taken for pressure test to find out the appropriate stamping amount. Trial and error method is more reliable, but the efficiency is relatively low. Because there are many process parameters, it is very troublesome to only pass the trial and error method. In order to obtain a set of mature technology, it even needs several months of trial and error process. And in the process of trial and error, the fixed shape and spacing of the lower die are often used, and only the stroke of the punch is explored, so the result may not be optimal, and the ability of the unit is not brought into full play. Therefore, it is very necessary to systematically study the influencing factors of its forming, establish a certain theory or even formula, and formulate the forming process with trial and error experience, so as to reduce the cost and time of trial production and improve the production efficiency.

Comparison of JCO and UO molding methods:

JCO forming is progressive pressure forming, which changes the forming process from two steps of UO forming to multi steps. In the forming process, the deformation of steel plate is uniform, the residual stress is small, and the surface is not scratched. The processed steel pipe has greater flexibility in the size range of diameter and wall thickness. It can produce large quantities of products and small quantities of products. It can produce large diameter high strength thick wall steel pipe and small diameter thick wall steel pipe. It has incomparable advantages in the production of high grade thick wall steel pipe, especially in the production of medium and small diameter thick wall steel pipe. It can meet more requirements of users in steel pipe specifications. The investment is small, but the production efficiency is low. Generally, the annual output is 100000 ~ 250000 tons.
Uo molding, using u and O twice pressure molding, is characterized by large capacity and high output. Generally, the annual output can reach 300000 ~ 1 million tons, which is suitable for single specification mass production. The investment is huge, which is hard for developing countries to bear.

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Production process of straight seam high frequency welded pipe

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Straight seam high frequency welded pipe (ERW) is made of hot rolled coil which is formed by forming machine. The skin effect and proximity effect of high frequency current are used to heat and melt the edge of pipe blank, and pressure welding is carried out under the action of extrusion roll to realize production.

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Standard of welded pipe

Common materials of welded pipe are: Q235A, Q235C, Q235B, 16Mn, 20Mn, Q345, L245, L290, X42, X46, X60, X80, 0Cr13, 1Cr17, 00cr19ni11, 1Cr18Ni9, 0cr18ni11nb, etc.
Steel plate or strip is used for welding steel pipe, which can be divided into furnace welded pipe, electric welding (resistance welding) pipe and automatic arc welded pipe due to different welding process. Because of the different welding forms, it can be divided into straight welded pipe and spiral welded pipe. Because of its end shape, it can be divided into round welded pipe and special-shaped (square, flat, etc.) welded pipe. Welded pipe can be divided into the following categories due to its different materials and uses:

  • GB / t3091-2008 (welded steel pipe for low pressure fluid transmission): it is mainly used for conveying water, gas, air, oil, heating hot water or steam and other general low pressure fluid and other purposes. Its representative material is Q235A steel.
  • GB / t14291-2006 (welded steel pipe for mine fluid transportation): it is mainly used for straight seam welded steel pipe for mine air pressure, drainage and shaft gas drainage. Its representative material is Q235A and B grade steel.
  • GB / t12770-2002 (stainless steel welded steel pipe for mechanical structure): mainly used for machinery, automobile, bicycle, furniture, hotel and restaurant decoration and other mechanical parts and structural parts. Its representative materials are 0Cr13, 1Cr17, 00cr19ni11, 1Cr18Ni9, 0cr18ni11nb, etc.
  • GB / t12771-1991 (stainless steel welded pipe for fluid transportation): mainly used for conveying low pressure corrosive medium. The representative materials are 0Cr13, 0Cr19Ni9, 00cr19ni11, 00Cr17, 0cr18ni11nb, 0017cr17ni14mo2, etc.
  • In addition, stainless steel pipes for decoration (GB / T 18705-2002), stainless steel pipes for building decoration (JG / T 3030-1995), and welded steel pipes for heat exchanger (yb4103-2000).

Classification of welded pipe

Classify by use

It is also divided into general welded pipe, galvanized welded pipe, blown oxygen welded pipe, wire casing, metric welded pipe, roller pipe, deep well pump pipe, automobile pipe, transformer pipe, electric welding thin-walled pipe, electric welding shaped pipe, bracket pipe and spiral welded pipe.

  • General welded pipe: General welded pipe is used to transport low pressure fluid. Made of Q195A, Q215A, 235a steel. It can also be made of other soft steel that is easy to weld. Water pressure, bending, flattening and other experiments on steel pipes have to be carried out. There are certain requirements for surface quality. Usually the delivery length is 4-10m, and it is often required to deliver goods according to the fixed scale (or multiple scale). The specification of welded pipe is expressed with nominal caliber (millimeters or inches). The nominal caliber is different from the actual one. Welded pipe has two types of ordinary steel pipe and thick steel pipe according to the regulation wall thickness, steel pipes are divided into two types, with and without threads, according to the form of pipe ends.
  • Galvanized steel pipe: in order to improve the corrosion resistance of steel pipes, ordinary steel pipes (black pipes) are galvanized. Galvanized steel pipe is divided into two kinds: Hot galvanizing and galvanized, hot galvanizing and galvanized layer thickness, low cost of galvanized.
  • Oxygen blowing welded pipe: it is used as steel oxygen blowing pipe for steelmaking. Generally, small diameter welded steel pipes are used. Made with 08, 10, 15, 20 or Q195-Q235 steel strips. In order to prevent corrosion, some are aluminized.
  • Wire casing: It is also ordinary carbon steel welded steel pipe, which is used in concrete and various structure power distribution projects, with the common nominal diameter ranging from 13-76mm. The wire casing wall is thin, mostly used after coating or galvanized, and cold bending test is required.
  • Metric welded pipe: its specification is used as the form of seamless pipe, and it should use the welded steel pipe with the outer diameter * mm wall thickness, and ordinary carbon steel, high quality carbon steel or ordinary low alloy steel’s tropical and cold belt welding, or it can be made after tropical welding and cooling. Metric welded pipes can be divided into ordinary energy and thin-walled and ordinary structural parts, such as transmission shaft, or conveying fluid. Thin-walled pipes are used to produce furniture and lamps. The strength and bending test of steel pipes must be guaranteed.
  • Idler Tube: used for electric welding steel pipe with roller of belt conveyor, generally made of Q215, everywhere a, B steel and 20 steel, with diameter of 63.5-219.0mm. For the bending degree of the pipe, the end face should be perpendicular to the center line, and the ovality has certain requirements, and the water pressure and flattening test are generally carried out.
  • Transformer Tube: used to manufacture vent pipes of Transformers and Other Heat Exchangers, made of ordinary carbon steel, with flattening, flaring, bending and hydraulic pressure tests required. Steel pipes are delivered with a fixed scale or times the scale, which has certain requirements for the bending degree of steel pipes.
  • Irregular Tube: square pipe, rectangular pipe, hat pipe, steel pipe for doors and windows made of ordinary carbon structural steel and 16Mn steel band are mainly used as agricultural machinery components, steel windows and doors.
  • Welding thin wall Tube: mainly used to make furniture, toys, lamps, etc. In recent years, thin-walled pipes made of stainless steel belt have been widely used, such as high-grade furniture, decoration, fence, etc.
  • Spiral welded pipe: roll low carbon structural steel or low alloy structural steel belt into pipe blank according to a certain spiral angle (called forming angle), and then weld the pipe seam to make it, it can produce large diameter steel pipes with narrower steel strips. Screw welded pipe is mainly used for oil and natural gas transportation pipelines, and its specifications are indicated by outer diameter * wall thickness. For spiral welded pipes with single-sided welding and double-sided welding, the welded pipes should ensure that the hydraulic pressure test and the tensile strength and cold bending performance of the welded joints should comply with the regulations.

Classified by production method

(1) According to the process — arc welded pipe, resistance welded pipe (high frequency, low frequency), gas welded pipe, furnace welded pipe.
(2) divide according to weld seam — straight seam welded pipe, spiral welded pipe.

Classified by section shape

(1) steel pipes with simple fracture — round steel pipes, square steel pipes, oval-circular steel pipes, triangular steel pipes, hexagonal steel pipes, diamond steel pipes, octagonal steel pipes, semi-circular steel pipes, and others.
(2) the steel pipe with complex cross section-hexagon steel pipe, five-petal plum blossom steel pipe, double convex steel pipe, double concave steel pipe, melon seed steel pipe, conical steel pipe, corrugated steel pipe, watchcase steel pipe and others.

Sort by wall thickness

Thin-walled steel pipe and thick-walled steel pipe.
Classified by end shape
It is divided into round welded pipe and special-shaped (square, flat, etc.) welded pipe.

Classification supplement

  • 1. Ordinary carbon steel wire casing (GB/T3640-88) is a steel pipe used to protect wires in electrical installation projects such as industrial and civil buildings and installation of machinery and equipment.
  • 2. Straight seam electric welding steel pipe (YB242-63) is a steel pipe with longitudinal parallel Weld and steel pipe. It is usually divided into metric welding steel pipe, electric welding thin wall pipe, transformer cooling oil pipe, etc.
  • 3. Pressure fluid transportation with spiral seam submerged arc welding steel pipe (SY5036-83) is a hot-rolled steel strip coil as a pipe blank, often thermal spiral forming, double-sided submerged arc welding, used for pressure fluid transportation of spiral seam steel pipe. The steel pipe has strong pressure-bearing ability and good welding performance. After various strict scientific inspection and testing, it is safe and reliable to use. The diameter of steel pipe is large, the transportation efficiency is high, and the investment in laying pipelines can be saved. Pipelines mainly used for transporting oil and natural gas.
  • 4. The high-frequency welding steel pipe (SY5038-83) with spiral seam used for conveying pressure fluid is made of hot-rolled steel strip, which is often made of warm spiral forming and welded by high-frequency lap welding method, spiral seam high frequency welding steel pipe used for pressure-bearing fluid transportation. The steel pipe has strong pressure-bearing ability and good plasticity, which is convenient for welding and processing forming. After various strict and scientific inspection and testing, it is safe and reliable to use, large diameter of steel pipe and high transportation efficiency, it can also save investment in laying pipelines. It is mainly used for laying pipelines for transferring oil, natural gas, etc.
  • 5. Spiral slit submerged arc welding steel pipe (SY/T5037-2000), which is generally used for conveying low pressure fluid, is made of hot-rolled steel strip coil as the pipe blank, which is often made by temperature spiral forming and double-sided automatic submerged arc welding or single-sided welding, submerged arc welding steel pipes for transportation of general low-pressure fluids such as gas, air and steam.
  • 6. General low-voltage fluid conveying spiral seam high-frequency welding steel pipe (SY5039-83) is made of hot-rolled steel strip coil as pipe blank, often warm spiral forming, high frequency lap welding is used to weld the high frequency welding steel pipe with spiral seam used for the transportation of general low pressure fluid.
  • 7. Pile Spiral welding seam steel pipe (SY5040-83) is made of hot rolled steel strip coil as pipe blank, often hot spiral forming, double-sided submerged arc welding or high frequency welding, used for civil engineering building structure, wharf, bridge and other basic piles.

Source:  China Welded Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.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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