Pipe welding procedure
Under the welded steel pipe from the top of the arc, from top to bottom all-position welding technique, the method of welding speed, weld appearance, good welding quality, you can save welding materials, reduce labor intensity, which is a common SMAW can not be compared and now more widely used in large-caliber long-distance pipeline welding in all position of power in the construction of low-welded large diameter thin-walled tube has some promotional value.
Under the welding usually select the appropriate welding current, electrode angle and welding speed, straight through drag down or suppress arcing swing slightly to finish welding. Ordinary electrode prone drip drip molten iron and slag under question, and the use of the pipeline dedicated to welding electrodes, welding specifications strictly enforced, you can solve these problems. Cellulose type electrode welding slag less, arc force, stiffness enough to prevent the molten slag and drip down and penetrating arc large, especially for thick-walled containers and welded steel pipe hit the bottom, you can eliminating the root shovel operation, thereby improving work efficiency, improve working conditions, but because of its high hydrogen content of the weld, so for domestic high-pressure pipe welding current commonly used cellulose electrode backing plus low hydrogen electrodes and filler cap surface welding.
The right set of tubes and tack welding is on ensuring the quality of the welding, the back of a good weld is an important factor. Tack welding seam is part of a formal, not only requires forming side welding, but also to ensure the welding quality. Tack welding length 20mm, a thickness of about 3mm, gentle slopes on both sides of the weld should be ground into shape, in order to facilitate joint.
Next to the welding electrode is very important to use the correct angle. Backing weld, filling and capping rod angle is basically the same, but the arc length and transport of a different form. Next to the weld, the weld is controlled by the length and width of the main forms of transportation of the arc, arc and arc close attention to the wrong location should open.
Under the welding usually select the appropriate welding current, electrode angle and welding speed, straight through to suppress arcing swing slightly drag down or to complete the welding. Under ordinary electrode prone drip drip molten iron and slag problems, while the use of dedicated pipeline under the welding electrode.
(1) SMAW. Since the flexibility of manual welding and soldering equipment demanding other reasons, for outdoor pipeline welding, SMAW workload still 40% to 50%.
(2) Cellulose To the welding process. Cellulose next to the welding process is widely used at home and abroad as a welding process, including steel is used in all of the following X70 large diameter thin-walled pipe welding. Welding speed, root welding performance, weld radiographic inspection pass rate, excellent economy.
(3) To set a low hydrogen type electrode welding. The process of cellulose downward welding process compared to slower root welding, mainly for the extreme weather conditions, transport sour gas and high sulfur oil medium, for low temperature toughness demanding welding pipe or thick-walled tube .
(4) To set a cellulose electrode backing weld, CO2 gas shielded welding filler surface. Since CO2 welding with high productivity, low cost, in recent years has been the promotion and application, but the oil and gas pipeline welding, to achieve all-position welding, must be in a smaller current range, with a short transitional forms completed, and short-circuit transition mode for backing weld prone to defects such as lack of penetration. Therefore, the use of cellulose electrode backing to achieve set a single-sided welding, forming the back, and then use high efficiency CO2 gas shielded welding filler surface.
(5) Self-shielded flux cored wire semiautomatic welding. Self-shielded flux cored wire for semi-automatic welding special occasion outdoors on a windy, it does not use CO2, the gas produced by the cored protection, wind resistance, and can be used for high deposition rate of the pipeline all-position welding.
(6) High CO2 gas shielded welding semi-automatic or fully automatic welding. At present, foreign have produced a pair of welding current and voltage waveforms timely control or power control on the output characteristics of high-performance power, Lincoln’s STT Surface Tension Transfer Welding Waveform Control Technology belongs to the category. Welding equipment based on improved performance, making the semi-automatic and fully automatic pipeline welding CO2 gas can be properly achieved, which greatly improve the welding efficiency and welding quality.
Welding method of low carbon steel at a low temperature
Under the harsh winter conditions of low-carbon steel welding, due to the cooling speed of welded joint fastly make the crack tends to increase, especially in the first weld Heavy structures susceptible to cracking, for which the process must take the following measures:
- preheat, welding process strictly maintain interpass temperature should not fall below the preheating temperature.
- the use of ultra low hydrogen or hydrogen welding materials.
- to increase the welding current when the tack welding, the welding speed slows down, due to increase tack-welded bead cross-sectional area and length, preheated if necessary.
- the whole should be a continuous weld seam finish, avoid interruptions.
- arc groove on the surface of the base material should not be beyond the need to fill the crater when extinction.
- not possible under low temperature conditions, bending, straightening and assembly weldments.
ERW steel pipe welding process
ERW steel pipes in industrial production and civilian sectors have a wide range of applications, for water, oil, gas and other fluid transported using the pipeline has a convenient, fast and low cost several advantages, especially in long-distance transport process, which can show it advantages in the long course of the inner wall of the pipe is formed on the deposition or dirt.
If the pipeline will form scale or private dirt, will form the inner wall of the pipeline grease or wax accumulated in the industrial gas pipeline will also form coke coke and other dirt. The dirt deposited in the pipeline fluid greatly increases the resistance during transport not only the transmission efficiency and the power consumption required for transporting fluids also increased significantly. Dirt will cause corrosion on the pipe material and cause serious damage to pipe rupture, transmission fluid leakage losses, and even cause shutdown. Pipeline corrosion is often caused by contaminated pipeline transportation Economically, the main safety significant harm. With the increase in pipe and pressure pipe increased age increased, run run, drip, scaling, corrosion, plugging and explosion emerging pipeline not only will these failures appear normal production and life will be adversely affected to people’s lives and property caused irreparable damage, so the need for regular cleaning of the pipeline. Clean pipes according to the specific circumstances of different scaling using a variety of methods, such as using acid, alkali or surfactant aqueous solution of chemicals closed loop pipeline cleaning, you can also use ultrasound, water jet, or other physical means to dirt peeled and removed from the wall but lighter in the early stages of pipe scale adoption Erw pipe welding process may be a simple, low cost but good effect method. Erw pipe welding process in the industry, also known as Erw pipe welding process.
Pigging is a special polyurethane material shaped like a bullet of materials, shrink resistance, high strength. Erw pipe welding process technology to remove pipe scale, sediment or foreign body for the purpose of a technology. Its working principle is put into Pig launchers after launching the forward direction of the media in Pig pressure difference, the formation of forward thrust, the Pig advancing along the pipeline, during operation, Pig slightly deformed. Pig itself or its attachments in the customs fouling constantly in contact with the wall, squeezing against fouling, scrapers, erosion, vibration broken, remove the pipe structure, sediment and foreign matter. At the same time, the medium in the tube wall through said cooking Pig gap formed annulus is formed when the high speed jet, its role in the front region is formed like a vacuum, is conducive to the operation of Pig, and the scraped The impact of fouling slag, stirred and timely discharge tube, effectively prevents dirt accumulation of residue in the tube to avoid the clogging phenomenon.
Pigging is characterized because it is composed of polyurethane foam with good flexibility so that, in the conduit line of the elbow, tee fittings and small pipe section can be bent easily through and has good wear resistance, it is possible to walk long distances in the pipeline. In cleaning up to several kilometers and the shape of complex mechanical cleaning pipes or jet cleaning has difficulty using Erw steel pipe welding process can often better to complete cleaning tasks.
Seamless welding process
Seamless welding technology in the welding mold showed excellent performance and improved a considerable part accuracy, finish and appearance, to shorten the manufacturing cycle of the mold.
Overcoming the mold aesthetic shortcomings that has welding and affect the joints.
With the growing global market demand for high-quality parts, people are increasingly turning to the seamless welding technology can improve the accuracy of parts. Seamless welding technology can not only help eliminate mold weld, but also to improve the accuracy of parts, finish and appearance of considerable.at the same time, the seamless welding technology implement efficient control and shorten the processing cycle of the mold in the injection molding process. Because of the technology products with excellent surface finish, so there is no need to adopt the second sputtering and annealing, to avoid dimensional changes caused by the secondary contraction.
In the mold production process, the cooling lines arranged in the vicinity of the mold surface, the surface finish of the product is always less uniform. The new process, the flow of the mold core and cavity cooling lines near the resin injection region can make the quality of products to get a better guarantee.
The new seamless welding techniques used in modern machine tools and some new technology. In accordance with the process requirements of the new technology, processing similar to the mesh of the mold core and cavity, the fourth axis milling machine in order to avoid its movement and the second fixture, which can improve the tolerance of dimensional accuracy.
The board of fins and the water chamber cooling lines to be more widely applied to further improve product quality and seamless weld finish.
Pipeline weld inspection process
Before pressure pipeline do the nondestructive testing, visual inspection of weld inspection ruler should meet the requirements.
General requirements for pressure pipe weld appearance and surface quality of welded joints are as follows:
welding should look good shape, width of each side edge bevel overshadowed 2mm appropriate. Fillet weld leg length should meet the design requirements, the level of regulation of small form factor should be smooth transition.
Welded joint surface does not allow cracks, lack of fusion, porosity, slag, spatter exist.
Pipeline design temperature is below -29 degrees, fan ruler of hardened stainless steel and alloy steel pipes tend to be larger weld surface, without undercut. Pipe weld undercut other materials should be greater than the depth of 0.5mm, continuous undercut length should not exceed 100mm, and both sides of the weld undercut grow at 10 percent of the total weld length. Weld surface not less than the pipe surface. Weld reinforcement, And no more than 3mm, (to a maximum width of weld joints on the groove). Welded joints wrong side wall thickness should not exceed 10% and not more than 2mm.
On the surface of nondestructive testing
Surface pressure pipeline NDT method selection principle: magnetic iron pipe should be used in magnetic particle testing; non-ferromagnetic steel should be used in penetration testing. There is a tendency to delayed cracking of welded joints, the surface should be non-destructive testing of cooling after welding certain time; reheat cracking tendency of welded joints, the surface should be in non-destructive testing and post-weld heat treatment once each.
Ray inspection and ultrasonic testing
Ray inspection and ultrasonic testing is the main target of the butt joint pressure pipe and pipe fittings for butt joints. NDT methods chosen by the design documents. Titanium, aluminum and aluminum alloy, copper and copper alloys, welded joints to detect nickel and nickel alloys, and should be used in radiation detection methods. There is a tendency to delay weld cracks, its ray inspection and ultrasonic testing should be at a certain time of cooling after welding.
When the head of a folder inside the casing has a girth weld, the weld should be operating 100% ray detection, covert operations can be carried out after passing through the pressure test. Reinforcement rings or bearing plate is covered with welded joints shall be 100% of the pipe-ray inspection, after passing then covered.
Examination of the provisions of the middle seam welding, non-destructive testing should be carried out after passing visual inspection, radiography and ultrasonic testing should be performed after the surf
Source: China Welded Steel Pipe Manufacturer – Yaang pipe fitting 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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