What Is A LSAW Steel Pipe?

What is a LSAW steel pipe?
(Longitudinally Submerged Arc Welding steel pipe) LSAW steel pipe in leaflets plate as raw material, the steel plate in the mold or molding machine pressure (volume) into using double-sided submerged arc welding and flaring from production. A wide range of the finished product specifications, weld toughness, ductility, uniformity and dense, with a large diameter, wall thickness, high pressure resistance, low-temperature corrosion resistance, etc.. Required steel pipe in the construction of high-strength, high toughness, high-quality long-distance oil and gas pipelines, mostly large diameter thick wall LSAW.

Longitudinally welded steel pipes are used in onshore and offshore oil and gas pipelines requiring critical service, high performance and tight tolerances. LSAW pipes are also used in conveyance of flammable & nonflammable liquids, and as structural members in construction projects.

lsaw pipes banner - What Is A LSAW Steel Pipe?

LSAW pipe (longitudinal Submerged Arc Welding Pipe)  is fromed by JCOE with one straight welded seam, the outer diameters usually from 323mm to 1420mm. When the outer diameter is 914.4mm above, it’s allowed two straight welded seams. LSAW pipe is used to convey low pressure liquid meida or high pressure petroleum or natural gas, and can be also used widely in structural supports or foundation. The advantage for LSAW type is they could produce more thick wall thickness of pipes, maximum to 120mm. 
Outer Diameter: 219mm-1820mm
Wall Thickness: 5.0mm-50mm
Length: 6mtr-18mtr
End:square ends (straight cut, saw cut, and torch cut). or beveled for welding, beveled,
Surface: Lightly oiled, Hot dip galvanized, Electro galvanized, Black, Bare, Varnish coating/Anti rust oil, Protective Coatings
Packing:Plastic plugs in both ends, Hexagonal bundles of max. 2,000kg with several steel strips, Two tags on each bundle, Wrapped in waterproof paper, PVC sleeve, and sackcloth with several steel strips, Plastic caps.
Test:Chemical Component Analysis, Mechanical Properties (Ultimate tensile strength, Yield
strength, Elongation), Technical Properties (Flattening Test, Bending Test, Blow Test, Impact Test), Exterior Size Inspection, Hydrostatic Test, X-ray Test.

What Are the JCOE LSAW Steel Pipe Forming Processes?

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JCOE lsaw steel pipe manufacturing process is a new type of welded steel pipe forming technology that was developed in the 1990s. The main forming process of this technology is to mill the edge (or planing edge) of the steel plate before the steel plate width direction. Pre-bending, and then step-by-step molding in the order of J letter type → C letter type → O letter type, and multiple times of pressure stamping in the forming process, the three-point bending mold is used as the basic principle. Since the raw material steel plate of lsaw steel pipe is formed by multiple progressive die pressing, it is necessary to solve the following basic problems: 
1. How to determine the shape of the die, the stroke of the upper die and the spacing of the lower die 
2. How many punches are required to ensure the most suitable punching Bending radii and optimal open O-tube. These problems are different from the steel plate material, the specific mechanical properties of the steel plate production plant, and the steel pipe type (diameter and wall thickness). Whenever the production changes the new specifications or the new steel plate material, a certain number of samples are tested and the appropriate production and processing data are explored. The trial and error method is more reliable because the trial and error method is based on the scientific data of imported JCOE molding equipment from Germany. Due to the large number of JCOE process parameters of lsaw steel pipe, not only the production process data is determined by trial and error, but also a few months of debugging process in order to obtain a mature process.
Production Method of Large Diameter LSAW Steel Pipe
One. Production process introduction of large diameter lsaw steel pipe
Rolling machine→Uncoiler→Unwinder→Retripper leveling machine→Vertical roll centering→Shear butt welding→Strip position control (double-head vertical roller)→Disc shearing→Strip position control (Double-head vertical roller )→ Edge Milling Machine (Fine Milling X Groove)→ Double End Roller→ Strip Surface Cleaning of Strips→ Double End Roller→ Conveyer→ Strip Feeding and Strip Position Control→ Molding Machine→ Inner Welding→ Outside Welding → steel pipe righting device → plasma cutting → straight seam steel pipe outlet
Two. Production process details of large diameter lsaw steel pipe
1. Work before forming
Raw materials are steel coils, welding wire, and flux. Have to go through rigorous physical and chemical tests before investing. The butt joints of the steel strips are welded with monofilament or double wire submerged arc welding. After the steel tube is rolled, automatic submerged arc welding is used for welding.
2. Molding process
The electric contact pressure gauge is used to control the pressure of the compression cylinders on both sides of the conveyor to ensure the smooth delivery of the strip. The main machine is positioned at the center. Therefore, the adjustment of the vertical roller (especially before and after the head) should be checked frequently to ensure the strict delivery edge of the strip. Run on the route specified by the process and pass the designed meshing point. External control or internal control roll forming is used to check whether the perimeter, ellipticity, straightness, etc. of the steel pipe comply with the standard requirements. If it does not meet the requirements, it will continue to be adjusted until it meets the requirements.
3. Welding process
The weld gap control device is used to ensure that the weld gap satisfies the welding requirements. The pipe diameter, the amount of misalignment, and the weld gap are all strictly controlled. The quality of the forming seam should be observed continuously, and it should be found that the misaligned edges, open seams, etc. Fine-tune the angle of the rear axle in time to ensure the quality of the forming; when the situation is abnormal, check whether the working width of the strip, the pre-bending condition of the edge, the position of the delivery line, the angle of the small roller, etc. have changed, and take corrective measures in time. Hebei’s straight seam steel pipe manufacturers currently use the United States Lincoln welding machine for single wire or double wire submerged arc welding in order to obtain stable welding quality. Straight seam steel pipe manufacturers shall continuously observe the quality of the forming joints, and shall promptly fine-tune the rear axle angle to ensure the molding quality in the case of misaligned edges, open seams, etc.; if the conditions are abnormal, check the working width, edge pre-bending condition, and delivery of the steel strip. Whether there is any change in the line position, the small roller angle, etc., and take corrective measures in time.
4. Detection
The welded welds were all inspected on-line by an automatic ultrasonic flaw detector to ensure 100% non-destructive inspection coverage of the spiral weld. If there are defects, they will be automatically alarmed and painted. The production workers will adjust the process parameters at any time to eliminate defects in time. When the nominal diameter D ≥ 426mm, the internal defects of the steel pipe should be cleaned and repaired inside; when D ≤ 426mm, the internal defects can be removed from the outside to perform the external welding. After repair welding, the weld must be ground and the remaining wall thickness after grinding should be within the specified wall thickness tolerance. Before repairing the welded steel pipe into the next process, it is necessary to carefully inspect whether there is any missing or missed defect on the steel pipe and correct it before proceeding to the next process. The butt-welded joints of the steel butt-welded joints and the spiral welds were all examined by X-ray television or film. Each pipe was hydrostatically tested and the pressure was radial sealed. The test pressure and time are strictly controlled by the steel pipe hydraulic pressure testing device. Test parameters are automatically printed and recorded.
5. Packaging out of the library
Pipe end machining, so that the end face perpendicularity, groove angle and blunt edge are accurately controlled. An air plasma cutter cuts the steel tube into individual pieces. After the blade is blunt or damaged, the new blade should be replaced immediately. The new blade must be sharpened with a stone before use, and it must not be ground with a grinder. After the blade is broken, it can be used after applying grinding stone again after grinding with a grinder.
Pressure Pipeline of LSAW Steel Pipe
1. Definition of lsaw steel pipe pressure pipeline
LSAW steel pipe pressure piping should include all straight seam steel pipe pipes that use pressure to deliver gas or liquid. From the point of view of safety production, it is the name of the straight seam steel pipe pressure vessel. Therefore, it is not a pressure pipe in a simple sense. The possibility of accidents and the hazard of the accident define the scope of the straight seam steel pipe pressure pipe. The pressure line uses a certain pressure, a tubular device for conveying gas or liquid, a liquid medium having a temperature higher than or equal to the standard boiling point, and a pipe having a nominal diameter of more than 25 mm. Straight seam steel pipe pressure equipment, in addition to its own blasting, will also cause explosions and fires due to leakage of the medium.
2. Application of lsaw steel pipe pressure pipeline
LSAW steel pipe pressure piping is an important part of the production process, mainly using a certain pressure, as well as the role of distributing, metering, controlling and cutting the flow medium.
Transportation is one of the five major transportation industries along with railway, highway, water and shipping. Straight seam steel pipe pressure pipes are widely used in chemical, petroleum, electric power, metallurgy, city gas and heating systems, high temperature, corrosive, toxic and radioactive media, and the quantity and quality of straight seam steel pipe applications are important. status.
3, Composition of lsaw steel pipe pressure pipeline
The pipeline consists of straight seam steel pipe, pipe support and so on. Used to transport, distribute, control or stop fluid flow.
The pipe system is referred to as the pipe system and is a plurality of pipes divided according to fluid design conditions. Pipe components and straight seam steel pipes are called pressure pipe components. They are flanges, gaskets, tight parts, valves and special parts for pipes that are connected or assembled into pipes.
Process Characteristics of LSAW Welding
LSAW welding of laser welding machine is an automatic welding equipment that automatically completes the straight weld seam of the welding workpiece through automation and mechanization. Straight seam welder is also called straight seam automatic welder, and longitudinal seam automatic welder is a kind of automatic welder. It can replace large amounts of manpower, greatly increase production efficiency and welding quality, reduce labor costs, and improve the welding workers’ working environment. Such as large-scale transformer shell corner seam welding, large barrel straight seam welding, solar water heater barrel straight seam welding, production line belt straight seam welding, H-beam welding, etc., are a large number of straight seam welding machine. Features of lsaw welding of laser welding machine:
1, Power
The average laser power is 300W, and the maximum power at work can reach about 400W, which is higher than that of other companies. When the laser welding machine is used for a long time, the power will decrease. But our equipment power can reach 400W, even if the power is attenuated after long-term use, it can still reach 300W. Virtually extended the use of equipment, but also for the company to save maintenance costs.
2, Electro-optical conversion efficiency is higher
Electro-optical conversion efficiency is high and the output laser power will be greater. Such as: 12KW power supply, the conversion rate is about 2% -3%, the output power is 300W. Our laser welding machine, because of its high electro-optical conversion efficiency, can reach 400W after years of testing.
3, Strong stability
The use of special-grade rod crystals in crystal matching has a better consistency of performance, a uniform light separation effect, a uniform light distribution, and a high conversion efficiency.
Straight seam welding machine equipment can be widely used in solar water heaters, aviation, aerospace vehicles, stainless steel barrel, thin-walled pressure vessels, auto parts, household appliances, medical machinery, building decoration, food machinery and other manufacturing industries need all the straight seam welding occasion. This equipment is used for automatic welding production of flat and tubular workpieces with flat butt-welding filler metal seams. The bookplates have I-groove butt joints and single-sided welding (can be double-sided). The welding distortion is small, the weld bead is neat and beautiful.
Ovality and Bending of LSAW Steel Pipe
In the cross-section of the lsaw steel pipe, there is a phenomenon that the outer diameter is not equal, that is, there is a maximum outer diameter and a minimum outer diameter which are not necessarily mutually perpendicular, and the difference between the maximum outer diameter and the minimum outer diameter is ellipticity (or not Roundness). In order to control the ellipticity, some lsaw steel pipe standards specify the allowable index of ellipticity, which is generally specified as not to exceed 80% of the outer diameter tolerance (executed after consultation by the supply and demand sides).
LSAW steel pipe is curved in the length direction, and its curve degree is called curvature. The bending degree specified in the standard is generally divided into the following two types: Partial bending: Using a one-meter-long straight ruler at the maximum bending of the steel pipe, measure the chord height (mm), which is the value of the local bending degree. Its unit is Mm/m indicates the method is 2.5mm/m. This method also applies to tube end curvature. Full-length total bending: Using a string, pull from both ends of the tube, measure the maximum chord height (mm) at the bend of the steel tube, and convert it into the length (in meters) as the percentage of the length of the tube.
Quality Inspection Method of LSAW Steel Pipe
The quality inspection method of lsaw steel pipe is as follows:
1, Judging from the surface, that is, in appearance inspection. The appearance inspection of welded joints is a simple and widely used inspection method. It is an important part of the inspection of finished products. It mainly finds the defects on the weld surface and the deviation in dimensions. It is usually visually inspected and tested with tools such as standard templates, gauges, and magnifiers. If the weld surface defects, there may be defects inside the weld.
2. Physical method inspection: The physical inspection method is a method that uses some physical phenomena to measure or test. Inspection of defects in materials or workpieces is generally performed by means of non-destructive testing. Non-destructive testing includes ultrasonic testing, ray testing, penetrant testing, and magnetic testing.
3, The strength of the pressure vessel inspection: pressure vessel, in addition to the sealing test, but also for strength testing. There are two kinds of pressure test and pressure test. They all test the tightness of welds in vessels and pipes that work under pressure. The air pressure test is more sensitive and quicker than the water pressure test. At the same time, the product after the test does not need to be drained. This is especially true for products that are difficult to drain. Be applicable. However, the test is more dangerous than the hydrostatic test. When carrying out tests, corresponding safety measures must be observed to prevent accidents during the test.
4. Test for compactness: For welding vessels that store liquids or gases, the non-dense weld defects, such as penetrating cracks, pores, slag inclusions, incomplete penetration, and loose structures, can be detected by the compactness test. Denseness test methods include: kerosene test, water load test, water test, etc.
5, Hydrostatic test each pipe should be done hydrostatic pressure test without leakage phenomenon, the test pressure to calculate the test pressure P = 2ST/D type S to hydrostatic pressure test stress Mpa, the test stress of the hydrostatic test corresponding the steel strip standard specifies 60% of the minimum yield (Q235 is 235Mpa). Regulatory time: D <508 test pressure retention time of not less than 5 seconds; D ≥ 508 test pressure to maintain time of not less than 10 seconds 4 Non-destructive testing Pipe repair welding, strip-to-head welding and circumferential joints should be X-ray or ultrasonic inspection. Spiral welds for the transport of flammable ordinary fluids shall be subjected to 100% SX-ray or ultrasonic inspection. Spiral welds used for steel, such as water, sewage, air, and heating steam, shall be subjected to X-ray or Ultrasonic inspection spot checks (20%).
Ultrasonic Testing of Transverse Cracks in Welds of LSAW Steel Pipe
Transverse crack in the weld of thick-walled lsaw steel pipe
D36, D36-Z35 and S355 structural steel plates with thickness of 20~50mm are used respectively to produce marine experience exchanges through the JCOE forming method. The lsaw steel pipe of the 54.HAN GUAN welded pipe platform are 508~1372mm in diameter. The weld seam adopts X-shaped groove, the inner weld is three-wire submerged arc welding, and the outer welding is multi-layer multi-channel three-wire submerged arc welding. Ultrasonic testing of the weld was carried out after 24h or 48h of welding. Lateral scanning revealed that there were forest-like echoes in the middle of the weld wall thickness. Further testing found that sometimes the entire weld was intermittently with similar signals, and the depth was in the weld. centre position. In order to find out the nature of the defect, X-ray filming was performed on some of the places where the reflected signal was the highest, and no defects were found. Magnetic particle inspection was performed again after carbon arc gouging, and it was confirmed that the defect was a transverse crack.
Ultrasonic testing method for transverse crack defects in welds
The transverse crack is more harmful, and the ultrasonic detection is more difficult than other defects. This is mainly because the ultrasonic detection is difficult to distinguish the nature of the defect. In order to improve the detection rate of transverse cracks and accurately determine the transverse cracks, combined with the standard regulations of AWS D1.1/D1.1M and API RP 2X, the scanning methods of ultrasonic waves for transverse cracks are summarized. Practice has proved that these methods are effective for detecting and judging transverse cracks in thick-walled welds.
Ultrasonic discrimination of transverse crack
When using the above “parallel scan with high weld seam” method to detect the transverse defects of the weld, if a reflection signal is found, the weld height of the weld can be smoothed, and the defect plane, depth position, and further Defect height, defect reflection characteristics, defect orientation, defect waveform, dynamic waveform, echo envelope and other parameters, combined with groove form, material properties, welding process and welding method, etc. The actual nature of the decision is made and the location of the defect is determined. Then use the gouging to grind the anatomy and then verify the magnetic particle test. During the detection process, the steps for discriminating transverse cracks are as follows:
(1) Firstly, in the lateral scanning sensitivity (this time is 6-12 dB higher than the longitudinal scanning sensitivity), the probe is placed on the weld directly for parallel scanning;
(2) After the horizontal defects are found, select the echo position with higher amplitude from 1 to 2, and analyze the weld height after the weld is leveled. The reflection amplitude is lower than 20% of the DAC display, in principle, it is not fixed;
(3) Using a surround scan to determine whether the defect is a point defect, and if it is a point defect, it is not further characterized;
(4) Observe the static waveform and the dynamic waveform, and analyze the amplitude variation of the defect signal to determine whether it is a transverse crack. There are four basic ways of moving the probe, namely, left and right movement, back and forth movement, fixed point rotation and surround motion. The corresponding dynamic waveform also has four forms, as shown in Figure 5. Or the gouging is repaired to the depth of the defect and verified by magnetic particle inspection as a transverse crack. When the number of defects is small, the repair process can be directly performed without verification.
Transverse crack treatment
Once the defect is determined to be a transverse crack, a repair process must be performed. The transverse crack should be determined by the depth and width of the gouging and grinding before rework. To ensure complete rework, the depth determined by the ultrasonic inspection should be increased by a few millimeters. In addition, after the gouging and grinding, the magnetic powder inspection must be carried out before the repair welding repair. It should be noted that the sidewall groove is also in the detection range to ensure that the defects are completely removed, and then welded by the repair welding personnel, otherwise it is difficult to ensure the crack. Complete eradication. Low-hydrogen welding wire (strip) should be used for rework. It must be preheated before rework. After gouging, clean and repair the carbon deposit to expose the metallic luster. After rework, take necessary slow-cooling protection measures, such as welding with asbestos after welding. Slowly sew. In addition, for the re-repair inspection of transverse cracks, it must be strictly checked at 24h or 48h after welding.
Non-destructive Testing of LSAW Steel Pipe
1. Basic requirements for the appearance of lsaw welds
Before the non-destructive testing of lsaw steel pipes, the inspection of the weld appearance shall meet the requirements. The general requirements for the appearance of lsaw welds and the surface quality of welded joints are as follows: the appearance of the weld should be well formed, and the width should be 2 mm per side over the edge of the groove. The height of the fillet of the fillet weld shall comply with the design regulations and the shape shall be smooth transition. The surface of the welded joint should be:
(1) Cracks, unfused, pores, slag inclusions, and splashes are not allowed.
(2) Pipes, stainless steels and alloy steel pipe weld surfaces with a design temperature lower than -29 degrees shall not have undercuts. Other material pipe weld seam undercut depth should be greater than 0.5mm, continuous undercut length should be no more than 100mm, and the total length of the undercut on both sides of the weld is not more than 10% of the total length of the weld.
(3) The surface of the weld shall not be lower than the surface of the pipe. The weld bead height is not more than 3mm (the maximum width of the welded joint group to the rear bevel).
(4) The wrong side of the welded joint shall not exceed 10% of the wall thickness and shall not exceed 2 mm.
2. Surface nondestructive testing
The principle of non-destructive testing method for the surface of lsaw steel pipe: magnetic powder testing should be used for ferromagnetic material steel pipe; penetration testing should be used for non-ferromagnetic material steel pipe. For welded joints with a tendency to delay cracking, the surface non-destructive inspection shall be carried out after the welding has been cooled for a certain period of time; for welded joints with a tendency to reheat cracking, the surface non-destructive inspection shall be carried out once after welding and after heat treatment. The application of surface non-destructive testing is carried out according to the standard requirements. The detection objects and applications are generally as follows:
(1) Quality inspection of the outer surface of the pipe material.
(2) Detection of surface defects of important butt welds.
(3) Inspection of surface defects of important fillet welds.
(4) Surface defect detection of welded joints of important socket welding and jumper tee branch pipes.
(5) Surface defect detection after pipe bending.
(6) The material is quenched and the groove is detected by the welded joint.
(7) Detection of non-austenitic stainless steel pipe bevels whose design temperature is lower than or equal to minus 29 degrees Celsius.
(8) Double-sided weldment stipulates the inspection of the roots after the roots are cleaned
(9) When the welding fixture on the alloy pipe having the hardening tendency is cut by the oxyacetylene flame, the defect of the grinding portion is detected.
3. Radiation detection and ultrasonic testing

The main objects of radiation detection and ultrasonic testing are the butt joints of straight seam steel pipes and the butt joints of butt welded pipe fittings. Non-destructive testing methods are selected according to the design documents. For the detection of welded joints of titanium, aluminum and aluminum alloys, copper and copper alloys, nickel and nickel alloys, the radiation detection method should be used. For welds with a tendency to delay cracking, the ray inspection and ultrasonic testing shall be performed after the welding has cooled for a certain period of time. When the main pipe in the casing has a girth weld, the weld shall be operated with 100% ray inspection, and the concealed operation may be carried out after the test pressure is passed. The welded joints on the pipeline covered by the reinforcing ring or the support pad shall be 100% ray-tested and shall be covered after passing the test. For welds specified for intermediate inspection of welding, non-destructive testing shall be carried out after visual inspection. Radiographic and ultrasonic testing shall be carried out after non-destructive testing of the surface.

The welded 

joints that have been inspected shall continue to be welded after passing the assessment.
Flaw Detection Tests of LSAW Steel Pipe
LSAW steel pipes have several flaw detection tests. LSAW steel pipes are now used more and more widely. According to different projects, the standards for using steel pipes are also different. Generally speaking, steel structures, piling, sewage discharge pipes, etc. There is no requirement for flaw detection of steel pipes, no need for flaw detection, and the projects used for flaw detection are: natural gas pipelines, oil pipelines, fire pipelines, etc. These projects have extremely strict requirements for flaw detection, and some strength flaw detection standards are related to The safety of the project is even related to the safety of people’s lives.
There are two types of flaw detection that are most widely used. One is ultrasonic flaw detection. This type of flaw detection is to use ultrasonic energy to penetrate into the depth of the metal material and to reflect at the edge of the interface when one section enters another section. A method of part defect, when the ultrasonic beam passes from the probe to the inside of the metal from the surface of the part, the reflected wave occurs when the defect and the bottom surface of the part are encountered, and the pulse waveform is formed on the screen of the detecting instrument, which is based on the pulse waveform. To determine the location of the defect and the size of the defect, cracks, inclusions, stomata, blisters, etc… When a defect is detected, there will be a professional technical manual for repair, and the repair is completed. After the inspection is qualified, the pipeline can be ensured to be leak-proof during the use of the project, and the pipeline is guaranteed.
The other type is X-ray flaw detection, which is also widely used. X-ray is a method of detecting internal defects of a weld by using a certain kind of radiation. X-rays can penetrate the metal material to different degrees, and cause photosensitivity to the photo film. Using this property to detect welds, because the weld defects have different absorption abilities, the intensity of the rays falling on the film is different, and the sensitivity of the film is different, so that the shape of the defects can be accurately and reliably detected. , location and size.
The welding used for lsaw steel pipes is now submerged arc welding. The steel pipes welded by this welding method usually have no welding defects. The difference between ultrasonic and X-ray lies in those, X-ray inspection, low sensitivity, inconvenient, slow detection speed, high cost of radiographic film, difficulty in finding small cracks and unfusion, etc. Ultrasonic detection has large thickness and high sensitivity. Convenient, fast, low cost, harmless to the human body. This is the difference between the two.
Fracture of LSAW Steel Pipe in Production
Fracture of lsaw steel pipe, mechanical properties of hydraulic (pneumatic) parts used in design, brittle fracture is also related to the use temperature of the component.
It has been found through research that when the temperature is lower than a certain temperature value, it is found that the data will be transformed into a brittle state, and the impact absorption work is obviously reduced. This phenomenon is called cold brittleness, and low stress brittle fracture occurs in high-strength metal materials. In the process, the data organization is far from uniform and isotropic, there will be cracks, and there will be defects such as inclusions and pores. These defects can be regarded as microcracks in the material. Therefore, the design should also select the data with the appropriate cold-brittle transition temperature according to the working temperature of the component.
In general, it is assumed that the data is uniform and continuous isotropic. According to this method, the design is considered safe and sometimes accidental breakage occurs. Due to defects such as cracks in the hot-rolled billet or high-precision cold-drawn tubes being formed into cylinders, the seamless steel tubes are cold-drawn. There is almost no plastic deformation occurring during the fracture during use, and it is generally brittle fracture.
Brittle fracture is caused by various reasons. For example, when there are precipitates on the grain boundary, whether the strength is stronger or weaker than the strength of the matrix, the crack is caused; the segregation of inclusions on the grain boundary is also the cause of the fracture; Even under the action of an alternating load far below the yield limit, fatigue fracture can occur.
Cold Expansion of LSAW Steel Pipe
The role of cold expansion of lsaw steel pipe:
(1) Improve the geometrical dimensional accuracy of the pipe body and pipe end of the lsaw steel pipe, so that the diameter and roundness of the pipe body and the pipe end and the diameter difference between the two ends of the steel pipe meet the standard requirements, which is convenient for on-site welding construction.
(2) Reducing the uneven deformation of the forming and welding process of lsaw steel pipe, reducing the residual stress of the pipe body caused by molding and welding, improving the distribution and improving the overall mechanical properties of the steel pipe.
(3) Conduct a comprehensive and effective inspection of the overall performance of the steel pipe.
(4) The cold expansion diameter also has the effect of improving the straightness of lsaw steel pipe, especially the straightening effect on the smaller diameter straight seam submerged arc welded pipe.
After the cold expansion of the lsaw steel pipe, the diameter of the pipe body and the pipe end will increase by about one percent. The diameter, the roundness and the diameter difference between the two ends of the steel pipe are greatly improved, and the straightness of the steel pipe is also greatly improved. The length is reduced by about 0.5%, and the wall thickness is reduced by about 0.8%. In the development of the lsaw steel pipe process, these changes should be fully considered to determine the width, length and thickness of the pipe sheet and the outer diameter of the steel pipe before the diameter expansion, so as to avoid the geometrical dimension of the steel pipe after the expansion is not up to the final requirements. 
Application and Introduction of LSAW Steel Pipe in The Automotive Field
The main types of lsaw steel pipes for automobiles include automobile automobile silencer pipes, transmission shaft pipes, thrust pipes, condenser pipes, exhaust pipes, steering shaft pipes, and shock absorber oil storage pipes. 
The lsaw steel valve plate is composed of a vertical plate, a backing plate and a large round steel plate. The valve plate of this structure, the pad battle station board can be indirectly cut, and the small square steel plate requires the craftsperson to first calculate the blanking size, and then press the required shape to make the shaped tire, and the tire will be used. The small square steel plate is repressed and formed. The middle part of the valve plate is curved, and the edge is not a flat surface. Then it is necessary to make a tire for each specification valve, otherwise it is impossible to press out the required shape. The connecting butterfly valve butterfly valve has the advantages of old volume, heavy weight, flexible measures, convenient assembly and disassembly.
The lsaw steel pipe connecting rod butterfly valve is mainly composed of a driving device, a valve plate, a valve body, a main shaft, a rod solution and the like. The opening and closing of the valve does not depend on the drive assembly to drive the spindle to move the linkage mechanism, thereby completing the opening and closing of the valve plate. Regardless of the time the valve is closing and not closed, the valve plate and its interlocking components are always in the non-media pack. When the valve is closed, the valve plate is subjected to all the pressure of the medium, which causes the static member to deform. When the valve is closed, the valve plate is washed by the medium and the vibration of the valve plate itself caused by the fixing of the medium.
How to Solve the Rust Phenomenon of Double-sided Submerged Arc Welded Pipe
After the double-sided submerged arc welded pipe(dsaw pipe) is rusted, the surface of the steel is mainly polished by using a wire brush or the like, and the cleaning and preheating of the spiral pipe can remove the loose or raised scale, rust, welding slag and the like. The descaling of manual tools can reach Sa2 level, and the rust removal of power tools can reach Sa3 level. If the surface of the lsaw steel pipe is attached with strong iron oxide scale, the rust removal effect of the tool is not ideal, and the anchor depth required for anti-corrosion construction cannot be achieved.
On the basis of the traditional application, a new application has been added, which makes the use of the lsaw steel pipe more abundant, and at the same time reduces the use cost of the lsaw steel pipe. The radio frequency sensor provides 200 volts, 50 amps of smooth flow through the lsaw steel tube, and the experimental sample is heated by induction. The lsaw tube itself does not get hot, but the experimental sample will have a significant fever. When the heating temperature exceeds the arc melting machine, the radio frequency sensor will provide more control, allowing the scientist to adjust the specific composition ratio of the alloy. LSAW steel pipe has strong pressure bearing capacity and good plasticity, which is convenient for welding and processing. Generally, double-sided submerged arc welded pipe (SY5037-83) for low-pressure fluid transportation is made of water by double-sided automatic submerged arc welding or single-sided welding. Gas, air and steam.
Repair of S355 LSAW Steel Pipe Transverse Crack
In recent years, with the development of the national economy, thick-walled LSAW steel pipe have been increasingly used in offshore platforms, high-temperature and high-pressure vessels, and wind power pipe piles. The production of such steel pipes generally uses D36 steel, S355 steel and structural steel plates with Z-direction properties. The thickness of the plates is large, the carbon content is high, and the carbon equivalent is high. The weldability is poor, and the hardenability tends to be large. The welding performance of the joints is reduced, and cold cracks are easily generated, especially the transverse cracks are more likely to appear. After the occurrence of welding cracks, in addition to the necessary control measures, it is also necessary to pay attention to the timely repair of the workpiece. Taking S355 steel as an example to illustrate the repair measures after the occurrence of transverse cracks in welding. specifically is:
1, Confirming the defect
A 100% UT inspection was performed on all welds and the location, length, depth and direction of the cracks were marked. If the entire weld has defects, it is recommended to shave the entire weld back to submerged arc welding. Local arc welding is recommended for local rework.
2, Preheating before planing
The preheating temperature is 110-170°C, and the preheating temperature detection position is not less than 150mm on both sides of the weld, and the heating range is within 500mm from the periphery of the defect.
3, Gouging
The gouging range is that the two sides of the crack defect are outward and the good weld is not less than 50mm. The outward gouging is carried out at the ends of the gouging. The transition plane and the vertical line are at least greater than 45°. Gouging carbon rod angle should be below 60 °, especially in the cracks to be reached, the angle is as small as possible.
4, Polishing
Polished to no black skin, the surface after grinding should be a smooth transition, there should be no sharp pits.
5, PT
Permeate testing (PT) after cooling to the appropriate temperature.
6, Polished
According to the PT test result, it is polished and polished until there is no red line.
7, MT
After grinding, magnetic particle testing (MT) is performed to confirm that there is no residual crack, otherwise it should be continued until MT detects no crack.
8, Preheating before welding
The recommended preheating temperature is 110-170°C. The preheating temperature detection position is not less than 150mm on both sides of the weld and the heating range is within 500mm from the weld.
9, Welding
According to the repair welding instructions, the width of the weld bead should not exceed 15mm, and the road can be divided. Arc welding or automatic submerged arc welding can be used.
10, After welding insulation, slow cooling
11, Post-weld heat treatment
Post-weld heat treatment is mainly diffusive hydrogen, reducing post-weld residual stress, for the rigidity of the weldment has a special “hydrogen treatment”, “relief heat treatment.” The recommended heat treatment system is: After the welding is completed, the ceramic electric blanket is used to heat it to 200° C., and the heat is turned off after being kept warm for 2 hours.
12, Post-weld testing
48 hours after the completion of welding, the NDT test was performed as required to confirm the return of the pass.
Difference of Bearing Capacity of Several LSAW Steel Pipe
The bearing capacity of a lsaw steel pipe is related to two points. One point is the mechanical properties of the steel, which is related to the commonly stated yield point, tensile strength, elongation and impact toughness. The other point is related to the geometrical characteristics of the section. Generally, a circular straight welded pipe has the strongest resistance to local buckling, and thus it is the best member to withstand radial internal pressure and radial external pressure.
Under the same steel number, equal area and the same supporting conditions, the rectangular slanted steel pipe has strong eccentric compression bearing capacity, and the circular and square steel tubes have the strongest compressive bearing capacity, but the square and rectangular lsaw steel pipes are subject to the ability of the nip to resist local buckling is not as good as that of a circular steel tube. Compared with the lsaw steel pipe, the seamless steel pipe has a complicated production process, high quality and high price, and is less used in engineering, and the latter is applied more.
At present, the lsaw steel pipe made of steel can combine the advantages of the two, so that the straight seam steel pipe can be laterally compressed, and the compressive strength can be doubled, and at the same time, due to the existence of straight seam steel pipe The rigidity of the steel pipe is improved, and the two work together, thereby greatly improving the bearing capacity.
Source: China LSAW Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.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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