Welded Steel Pipe

A: Welded pipe starts out as a long, coiled ribbon of steel called a skelp. The skelp is cut to the desired length, resulting in a flat rectangular sheet. The width of that sheet’s shorter ends will become the pipe’s outside circumference, a value that can be used to calculate its eventual outside diameter.
The rectangular sheets are fed through a rolling machine that curls the longer sides up toward one another, forming a cylinder. In the ERW process, high-frequency electrical current is passed between the edges, causing them to melt and fuse together.
An advantage of ERW pipe is that no fusion metals are used and the weld seam cannot be seen or felt. That’s opposed to double submerged arc welding (DSAW), which leaves behind an obvious weld bead that must then be eliminated depending on the application.
Welded pipe manufacturing techniques have improved over the years. Perhaps the most important advancement has been the switch to high-frequency electric currents for welding. Prior to the 1970s, low-frequency current was used. Weld seams produced from low-frequency ERW were more prone to corrosion and seam failure.
Most welded pipe types require heat treatment after manufacture.

A: First check the raw materials such as steel, and enter the construction site only after the inspection meets the standards.
Check whether the welding materials are qualified and stored in accordance with the regulations. Pay attention to see if there is rust on the surface of the welding material. If the steel pipe has been rusted or mildewed, it will not work.
The cleaning of the welding area should be managed well, and the welding area should be kept clean and dust-free, and there should be no water, oil, rust and other dirt, and external defects of the weld should be prevented.
Select the welding method, try to test the welding first, and then apply the welding principle. In order to avoid welding quality accidents caused by wrong use of welding wire.
Look at the groove size before pre-welding. Pay attention to check whether the gap, blunt edge, etc. meet the process requirements.
Welders should clean the slag first when repairing the welding work to see if the joints are treated. There should be no oil, rust and other dirt on the groove.

A: Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or steel strip after being crimped and welded. Welded steel pipes have simple production process, high production efficiency, many varieties and specifications, and less equipment investment, but the general strength is lower than that of seamless steel pipes. Since the 1930s, with the rapid development of continuous rolling production of high-quality strip steel and the advancement of welding and inspection technology, the quality of welds has been continuously improved, the varieties and specifications of welded steel pipes have been increasing, and more and more fields have replaced non-ferrous steel. Seam steel pipe. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the form of the weld.

A: High frequency resistance welding:
Utilizing the skin effect of high-frequency current and the proximity effect, the edge of the steel billet strip is rapidly heated to the molten state. The molten metal is then squeezed and pressed by the squeezing roller to achieve welding.
Submerged arc welding:
The welding method involves the coverage of flux. The weld metal pool solidifies into a weld under the protection of the flux coating, with the flux melt layer cooling to form a slag shell over the outer surface of the weld.
Tungsten inert gas welding (TIG):
Tungsten inert gas shielded welding utilizes pure tungsten or activated tungsten (such as thorium tungsten, cerium tungsten, etc.) as the electrode. This method involves using tungsten arc welding electrodes generated between the hot-melt parent metal and filler wire under inert gas protection.
Melting inert gas welding (GMAW):
The process involves the use of welding wire as electrodes for inert gas welding.
CO2 gas shielded welding:
CO2 gas shielded welding uses a protective gas with a purity greater than 99.8% CO2 for arc welding.
Mixed gas welding:
This method involves using two or more gases, in a certain proportion, as a protective gas for gas shielded welding. In TIG welding, argon is commonly utilized as the shielding gas.
Pulse TIG:
Pulse TIG involves maintaining the main arc of the ionization channel using base current and periodically introducing a pulse of high peak current of the same polarity to melt the molten metal and control the transition of argon arc welding.
Plasma arc welding:
Through the restraining action of the water-cooling nozzle on the arc, a plasma arc with higher energy density is used for welding.
Hot brazing:
In this welding process, a metal material with a lower melting point than the base metal is used as a brazing filler metal. The weldment and brazing filler metal are heated to a temperature higher than the melting point of the filler metal and lower than that of the base metal. This allows for wetting of the base metal with the brazing filler metal, gap filling, and mutual diffusion with the parent material, resulting in the brazing connection method. The induction brazing commonly utilizes a composite brazing method.

A: Straight seam welded steel pipe (LSAW/ERW)
Straight seam welded steel pipe is a steel pipe made by butting the edges of steel plates or coils and then welding them along a straight line. This kind of steel pipe has good strength and low production cost, but its strength is slightly lower than that of spiral welded steel pipes of the same specification.
Spiral welded pipe (SSAW)
Spiral welded pipe is a steel pipe formed by rolling strip steel into a cylinder and welding it in a spiral direction. This kind of steel pipe has higher strength, but the production cost is slightly higher.

A: Different In Nature
a. Seamless steel pipe: a steel pipe made of a single piece of metal with no seams on the surface.
b. Welded steel pipes: steel strips or steel plates that are bent and deformed into round or square shapes and then welded into steel pipes with seams on the surface.
The Characteristics Are Different
a. Seamless steel pipe: the maximum diameter is 650mm, and the minimum diameter is 0.3mm. According to different uses, there are thick-walled pipes and thin-walled pipes.
b. Welded steel pipes: T-welded steel pipes have strong corrosion resistance in acidic environments when they contain Ni. In environments containing sulfuric acid or hydrochloric acid, the higher the Ni content in the T-welded steel pipes, the stronger the corrosion resistance. Under normal circumstances, only adding Cr to the T-welded steel pipe can prevent corrosion.
The Role Is Different
a. Seamless steel pipes: seamless steel pipes are mainly used as petroleum geological drilling pipes, cracking pipes for petrochemicals, boiler pipes, bearing pipes, and high-precision structural steel pipes for automobiles, tractors, and aviation.
b. Welded steel pipes: electric welded steel pipes are used in oil drilling and machinery manufacturing, etc.; furnace welded pipes can be used as water gas pipes, and large-diameter longitudinally welded pipes are used for high-pressure oil and gas transportation; spiral welded pipes are used for oil and gas transportation, pipe piles, bridge piers, etc.

A: According to different welding methods, it can be divided into arc welded pipe, high frequency or low-frequency resistance welded pipe, gas welded pipe, furnace welded pipe, Bondi pipe, etc.
Electric welded steel pipe: used in oil drilling and machinery manufacturing.
Furnace welded pipes: can be used as water gas pipes, etc., large-diameter longitudinally welded pipes are used for high-pressure oil and gas transportation, etc.; spiral welded pipes are used for oil and gas transportation, pipe piles, bridge piers, etc.
According to the weld shape, it can be divided into straight seam welded pipe and spiral welded pipe.
Longitudinal welded pipe: The production process is simple, the production efficiency is high, the cost is low, and the development is fast.
Spiral welded pipe: The strength is generally higher than that of straight seam welded pipes. A narrower blank can be used to produce welded pipes with larger pipe diameters, and a billet with the same width can also be used to produce welded pipes with different pipe diameters. But compared with the straight seam pipe of the same length, the weld length is increased by 30-100%, and the production speed is lower. Therefore, most of the smaller diameter welded pipes adopt straight seam welding, and the large diameter welded pipes mostly adopt spiral welding.
According to the purpose, it is divided into general welded pipe, galvanized welded pipe, oxygen-blowing welded pipe, wire casing, metric welded pipe, roller pipe, deep well pump pipe, automobile pipe, transformer pipe, electric welded thin-walled pipe, electric welded special-shaped pipe, and spiral welded pipe.
According to the shape of the end, it is divided into round welded pipe and special-shaped (square, flat, etc.) welded pipe.
Other Categories
GB/T3091-1993 (Galvanized welded steel pipe for low-pressure fluid transportation). Mainly used to transport water, gas, air, oil, heating hot water or steam, and other generally lower pressure fluids and other purposes. Its representative material is Q235A grade steel.
GB/T3092-1993 (Galvanized welded steel pipe for low-pressure fluid transportation). Mainly used for conveying water, gas, air, oil, heating hot water or steam, and other generally lower pressure fluids and other purposes. Its representative material is Q235A grade steel.
GB/T14291-1992 (Welded steel pipe for mining fluid transportation). Mainly used for straight seam welded steel pipes for mine pressure, drainage, and shaft gas discharge. Its representative material is Q235A, Grade B steel. GB/T14980-1994 (Large diameter electric welded steel pipe for low-pressure fluid transportation). It is mainly used to transport low-pressure fluids such as water, sewage, gas, air, heating steam, and other purposes. Its representative material is Q235A grade steel.
GB/T12770-1991 (stainless steel welded steel pipe for mechanical structure). Mainly used in machinery, automobiles, bicycles, 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 steel pipe for fluid transportation). Mainly used to transport low-pressure corrosive media. Representative materials are 0Cr13, 0Cr19Ni9, 00Cr19Ni11, 00Cr17, 0Cr18Ni11Nb, 0017Cr17Ni14Mo2, etc.

A: SAW steel pipe (Submerged Arc Welding Steel Pipe), it can be classified into longitudinal submerged arc welding steel pipe (LSAW steel pipe) and spiral submerged arc welding steel pipe (SSAW steel pipe). SAW is a manufacturing process using submerged arc welding of steel,this process produces high current density, which prevents the flux layer from losing heat quickly and concentrates in the welding region. Commonly used standard is API 5L.
Submerged arc weld of high quality, high production efficiency, arc and smoke a few characteristics of submerged arc welded pipe is widely used in pressure vessels,pipe manufacturing, beams, low pressure fluid, steel works.
LSAW steel pipe (Longitudinal submerged arc welded steel pipe)
Longitudinal submerged arc steel pipe is a steel pipe with a weld seam parallel to the longitudinal direction of the steel pipe. It is made of hot-rolled or cold-rolled steel plates or steel strips that are curled and welded. The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is rapid. Straight seam steel pipes are widely used in water supply projects, petrochemical industry, chemical industry, electric power industry, agricultural irrigation, and urban construction.
SSAW steel pipe (Spiral welded steel pipe)
Spiral welded steel pipe is made of strip steel coils as raw materials, rolled into tube blanks at a certain spiral angle, and then welded together. It can use narrow strip steel to produce large diameters. steel pipe. Spiral steel pipes are mainly used in drainage and water supply projects, fluid liquid, and solid transportation pipelines. It is widely used in urban construction and municipal engineering.
The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. Welded pipes with larger diameters can be produced from narrower billets, and welded pipes with different diameters can also be produced from billets of the same width. However, compared with straight seam pipes of the same length, the weld length is increased by 30~100%, and the production speed is lower.

A: Welded pipe, also known as welded steel pipe, is basically made of steel plates or steel strips that are curled and welded. The production process of welded steel pipes is simple, the production efficiency is high, there are many varieties and specifications, and less equipment, but its general strength is lower than that of seamless steel pipes. Since the 1930s, with the rapid development of high-quality strip rolling production and the advancement of welding inspection technology, the quality of welds has continued to improve, the varieties and specifications of welded steel pipes have increased, and seamless steel pipes have been used in more and more fields. replaced. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the weld form.
Single radius forming method of welded steel pipe
There are three single-radius roll forming methods: circumferential bending forming method, edge bending forming method and center bending forming method. The single-radius forming method is that the pass shape consists of a single radius. The horizontal rollers and vertical rollers of the forming machine are alternately arranged. The strip passes between the horizontal rollers and the vertical rollers, and the flat plate is gradually bent into a round tube.
Welded steel pipe circumferential bending forming method
The strip is bent and deformed simultaneously in the entire width direction, and the bending radius of each frame gradually decreases; the bending forming method starts from the edge of the strip, with the bending radius unchanged, gradually increasing the deformation angle, and reducing the width of the middle part of the strip until the strip is The steel becomes rounded and closed; the center bending forming method starts from the center of the strip and gradually expands to the edges on both sides with a constant bending radius until it becomes round and closed.
Welded steel pipe double radius forming method (comprehensive bending forming method)
Combined deformation uses more than two basic deformation methods, but the edge forming method + circumferential forming method is widely used. The forming method of comprehensive deformation of the edge and circumference of the tube blank uses the hole radius of the extrusion roller or the radius of the finished tube as the edge bending radius to bend the edge of the steel strip to a certain deformation angle, which remains basically unchanged in each subsequent forming stage. , and the bending forming in the middle part of the steel strip is distributed according to the circumferential bending forming method. The forming process of this method is stable, the deformation is uniform, the relative elongation of the edge is small, and the forming quality is good.
Application scope of welded steel pipe:
Welded steel pipe products are widely used in boilers, automobiles, ships and buildings, light structural door and window steel and furniture, various agricultural machinery, scaffolding, wire pipes, high-rise shelves, containers, etc. All can meet customer requirements, and special welded pipes can be processed according to customer requirements.

A: When the factories manufacture welded steel pipe, the strip is fed into the welded pipe unit, rolled by the multi-way roll, the strip is gradually rolled up to form the circular tube with the opening gap, the pressing amount of the pressing roller is adjusted so that the gap of the weld is controlled at 1 ~ And make the ends of the weld flush. If the gap is too large, resulting in reduced proximity effect, insufficient eddy current heat, weld intergranular junction failure caused by non-fusion or cracking. If the gap is too small is caused by the adjacent effect increases, welding heat is too large, resulting in weld burns; or weld seam formed a deep pit after squeezing and rolling, which affects the surface quality of the weld.
1.The control of welding temperature
The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the correlation formula, the high-frequency eddy current heat is mainly affected by the current frequency, the eddy current thermal power is proportional to the square of the current excitation frequency, and the excitation frequency is excited by the excitation voltage, Current and capacitance, inductance effects.
The excitation frequency formula is:
F = 1 / [2π (CL) 1/2]
Where the f-excitation frequency (Hz); the capacitance (F) in the C-excitation circuit, the capacitance = the charge / voltage; the inductance, inductance = magnetic flux / current in the L-excitation circuit
In the above equation, the excitation frequency is inversely proportional to the capacitance in the excitation circuit, the square root of the inductance, or is proportional to the square root of the voltage and current. As long as the capacitance, inductance or voltage in the loop is changed, the current can change the magnitude of the excitation frequency Control the purpose of welding temperature. For low carbon steel, welding temperature control at 1250 ~ 1460 ℃, to meet the wall thickness of 3 ~ 5mm penetration requirements. In addition, the welding temperature can also be achieved by adjusting the welding speed.
When the input heat is insufficient, the edge of the heated weld does not reach the welding temperature, the metal structure remains solid, forming unmelted or not penetrated; when the input heat is insufficient, the edge of the heated weld exceeds the welding temperature, Burn or drop, so that the weld to form a melting hole.
2.The control of extrusion pressure
After the two edges of the tube are heated to the welding temperature, the common metal grains penetrate and crystallize under the extrusion of the squeeze roll to form a firm weld. If the extrusion pressure is too small, the number of common crystals is small, the weld metal strength decreases, the force will produce cracking; if the extrusion force is too large, will make the molten state of the metal is squeezed out of the weld, The weld strength, and will produce a lot of internal and external burrs, and even lead to welding joints and other defects.
3.The control of high-frequency induction coil position
The high frequency induction loop should be as close as possible to the squeeze roller position. If the induction circle is far away from the squeeze roller, the effective heating time is longer, the heat affected zone is wider, the weld strength decreases; on the contrary, the edge of the weld is insufficiently heated, and the molding is bad after extrusion.
4. The control of resistance
The resistance is a or a group of pipe dedicated magnetic bar, the cross-sectional area of the resistor should not be less than 70% of the cross-sectional area of the pipe diameter, the role is to make the induction coil, pipe edge and the edge of the magnet to form an electromagnetic induction Loop, resulting in proximity effects, eddy current heat concentrated in the vicinity of the edge of the pipe weld, so that the edge of the tube heated to the welding temperature. The resistor is dragged in a tube with a wire and its center position should be relatively fixed at the center of the squeeze roller. When the boot, due to the rapid movement of the tube, the resistance of the inner wall of the tube by the friction and wear and tear, need to be replaced frequently.
5.Clear the scar
The weld by welding and extrusion will produce scar, need to clear. The cleaning method is to fix the tool in the rack, the rapid movement of the welding pipe, scraping scrap scar. The burrs inside the pipe are generally not cleared.

A: Good value for money: through the above introduction, the hardness and strength of welded pipe should be no doubt. Welded pipe relative to seamless pipe, in the same environment, welded pipe can be made lighter and thinner, can save a lot of cost, in large-scale especially transportation projects, is a very good choice.
Customizable: the length of welded pipe can be customized according to the specific project, and welded pipe can be linked in different ways – spiral, welded, flange, etc., with strong flexibility.
Adaptability: no matter oil, gas, crude oil, etc., welded pipe can be used to transport, and the production speed of welded pipe is relatively fast, for urgent projects, welded pipe is a good choice.