Spiral seam welded pipe hydrostatic burst test

Spiral seam welded pipe hydrostatic burst test is a destructive test, tube sheet through the entire plate surface ultrasonic flaw inspection, pipe weld inspection by X-ray inspection, hydrostatic testing, ultrasonic flaw detection, thickness and tensile performance test after passing to qualified steel pipe as a burst test. For critical oil and gas pipelines with spiral seam welded pipe, in the technical standard book require manufacturers to do hydrostatic pipe burst test, and provide a burst test report.

Blasting field locations should be selected in the absence of personnel and motor vehicles have passed a safe place; when set in the underground or semi-underground, blasting tests when they set up warning signs to prevent persons and motor vehicles. The device consists of blasting proving ground burst test units, feed pump, high-pressure injection pump, electric control box, computer control systems, pressure sensors, temperature sensors and other components. 4m from the bursting pipe installed at both ends of electronic cameras, surveillance blast scene, you can see through the monitor screen blasting process.

By burst test, to verify product performance and process reasonable. Burst pressure and other relevant data for the design of units and users to provide reference; pipe manufacturers through experimental analysis to find areas of improvement to help improve product quality. Spiral seam welded pipe burst test device. Spiral seam welded pipe manufacturers should have burst Proving Ground, generally divided into temporary and permanent blasting blasting Proving Ground Proving Ground.

Spiral pipe stress analysis

Spiral Pipe Pipeline of the force is a very complicated situation. Spiral Pipe has affected transmission medium pressure, temperature effects were shed hoop stress generated axial stress; tube bearing capacity of the soil outside the pipe caused by different points along the length of the side asked the uniform settlement for bending sheet cows force; buried by soil pressure pipe above below the top soil by heavy, pipe weight, medium weight reaction force generated by such. Moreover, changes in the soil (plus landslide) external mechanical impact force, but also the pipe is compromised.

Spiral steel pipe inner force is clear. Calculation is simple. Spiral steel pipe outside force is not clear (large random factors), stress analysis is also more complicated. In recent years, although the next few pipeline workers in this area have been studied and published many articles, but still difficult as the design basis. The current practice is to pipe the force generated by the media for the design basis, and left a large degree of safety backup.

In the safety in addition to considering the tube on the force generated by external causes, we should also consider the spiral steel pipe (including material and weld) that may arise outside the specified defects in the construction and handling, transportation, F Q, etc. Yim Sang to sodium pipe may damage (scratches, indenting, etc.). Degree of safety is based on the long-term practical experience to determine, issued by the former Ministry of Petroleum Industry Pipeline design standards, due to internal pressure generated hoop stress control in the range of 0.72 yield limit due to the hoop stress and thermal stress generated when composed of axial stress over the yield limit stress control in 0.9 range.

Security too large will result in an increase in capital base construction, low waste Road safety will spiral pipe accident increases. It should be noted that the incident is not caused due to the internal medium, or when the hoop stress occurs in overstressing old (because both have very low limit range), mostly due to an external force and the spiral steel pipe itself and the construction the deficiencies.

Spiral pipe advantages

Because spiral steel pipe heat transfer coefficient, compact, easy to clean, stain resistance, etc, in the boiler, quench boiler, a variety of petrochemical equipment in the heat exchanger, the heat exchanger has a very wide range of applications. Spiral steel pipe is the low carbon steel or low alloy carbon steel strip at a certain angle of spiral rolled into tube. Representing the ground with spiral seam welded together and then the tube is made, it can use a narrow strip production of large diameter steel pipe.

Spiral steel pipe is mainly used for oil and gas pipelines, outer wall with its specifications expressed. Spiral steel pipe with single-sided and double-sided welding welding, pipe should ensure that hydrostatic test, weld tensile strength and cold performance to meet the requirements. The ground heat combined with the construction of pile foundation has become the application of ground source heat pump technology, a new hot spot. In the current domestic and international small pile pipe applications, the main extension of the drill pipe and piling pipe U-shaped or W-shaped cloth tube technology. However, the use of U-and W-shaped piles buried piping configuration has less heat transfer area, easy to set gas pipe at the top of the pipe blockage shortcomings. The spiral has a higher heat transfer coefficient than the straight tube, can be arranged in the same space, a larger heat transfer area, more security features.

Therefore, we propose a pile spiral buried ground source heat pump system. Spiral in the production and the frequent use of some quality problems occur, in some aspects of normal use, the need for identification of the quality spiral, according to a certain performance test methods and, in actual use can have a significant role, then how to identify counterfeit spiral approach: appearance often pitted surface phenomenon. Generally the whole amount would be better proportionality, mainly taking into account the cumulative error and probability theory this problem. As shoddy coil manufacturers to pursue profits, rolling groove rolling most often exceeded. Surface is easy to produce scarring. The spiral steel quality uniform composition. The tonnage of high cold shear, cut head face smooth and neat, but shoddy material because material is poor, there are often cut off the meat head end of the phenomenon, that is uneven, and no metallic luster.

Spiral pipe decarbonization technology

Spiral steel pipe is low carbon steel or low alloy steel strip at a certain angle helix (called molding angle) rolled into a tube, then welded together to form the tube, it can be used a narrow strip production of large diameter pipe. Spiral is mainly used for oil and gas pipeline, outer wall with its specifications expressed. Spiral single-sided and double-sided welding welding, pipe should ensure that hydrostatic test, weld tensile strength and cold performance to meet the requirements.

The service life of spiral steel pipe and spiral steel surface decarburization is a definite link, if the surface decarburization, the spiral strength and wear resistance will be reduced, directly affect the spiral of life. If the decarburization of a spiral is not clean, then spiral hardness and wear resistance of the surface layer will be a corresponding decrease and the quenching process, because of changes in the volume of the outer surface caused by the workpiece the formation of cracks.

Solving the main problem of surface decarburization is to carry out the heat treatment step, since decarburization and oxidation spiral are performed simultaneously, so the heat treatment process, the spiral should try to prevent contact with the air, this can improve the decarburization phenomenon. The medium resulting spiral surface decarburization is mainly oxygen, water vapor and carbon dioxide an oxidizing gas, when these gases and heated contact spiral, spiral may cause oxidation and decarburization, therefore, controlling the furnace carbon dioxide and carbon monoxide ratio is very important. In fact, the spiral forging furnace, a protective nitrogen gas added is very effective, nitrogen can dissipate some of the oxidizing gas, reducing spiral decarburization.

Mild steel pipe online normalization cooling control

Mild steel pipe cooling from the austenite state heat treatment process is a key step, because ultimately depends on the performance of steel cooling transformation of austenite after the organization, so in what way to get what tissue cooling is essential. Workpiece cooling rate usually based on objective, necessary and possible to determine, on-line normalization of the cooling pipe is mainly used for air-cooled and air-cooled cooling way. Online normalization cooling control has two aspects, one is the middle of a small cooling bed, two is subtracted sizing or large cooling bed sheets, these two aspects of the cooling performance of the final product has a direct impact.

When the end of rolling mill, due to the large amount of rolling deformation and recrystallization rolling in, which makes the waste pipe after rolling fine grains can be obtained, if the time taken to rapid cooling measures to capillary rapidly cooled to less rI pill, you can prevent the austenite grain, fine grain size to maintain state for the creation of conditions for normalizing. For medium shortage tube wall thickness is rapid cooling after rolling is more important, the general cooling rate is often used to improve the air (mist cooling can also be considered).

Online normalization pipe cooling bed in the middle of the completion of certain small cooling after entering the reheating furnace heating continued. One thing to note, that we must control the waste pipe into the blast furnace temperature to avoid the phase transition is not yet complete in the previous furnace, or likely to cause the phenomenon of mixed crystals. After sizing or large cooling bed sheets after reduction obtained after cooling the final tissue, which is to get the final properties. Therefore, the large cooling bed gasification process cooling is online often a key step. Cooling temperature and the cooling rate is directly related to the final selection of the performance condition. It should be noted that, in the final cooling process cooling methods must be carefully chosen, if cooled properly, it may cause bends or pipe with a big difference on the performance of such phenomena.

Use of spiral pipe in pipeline

Industrial development of the second pipe climax will surely come. Spiral steel pipe will be put into research, enhance pipeline capacity. In fact, spiral steel pipeline transportation has many advantages, insufficient transmission capacity is poor response. For just freezing point, high waxy crude oil, higher than the designed capacity, subject to existing pipeline capacity and pressure pumping capacity constraints; below the designed capacity, thermal conditions will be subject to the constraints of the existing pipeline. With the development of society, now with the offshore oil and gas field development, subsea pipeline has also been rapid development, which of course the pipeline steel are rising ever higher. Spiral pipe diameter, high strength, and practical features make it a first choice for many long pipeline pipeline. To overcome this fixed point, only with DRA and depressant.

How to avoid pipeline ruptures have a method, the base metal and weld flattening test, guided bend test, ground test, Charpy impact test and many toughness inspection targets. This is because the long-distance pipeline hundreds of kilometers long and some even more than a thousand kilometers long welds, weld too much, plus the construction and damage caused during transport and so on, so that the probability increases between buildings. Not only for the gas pipeline has a higher toughness requirements, oil pipeline in recent years also made a high impact toughness requirements. With the improvement of spiral steel strength grade and diameter increases, the impact toughness of the material because people understand the importance, in many parts of the world have occurred fragility and fracture toughness of pipeline accidents. Pipe toughness of steel pipe has actually become an important indicator. Spiral steel pipe and ductile crack extension instability instability expansion. For long-distance pipeline, it should completely avoid the crack is very difficult, in fact, at home and abroad are difficult to fully achieve.

Anti-corrosion steel areas for improvement analysis

Anti-corrosion steel in various industries gradually also widely used, the overall analysis, anti-corrosion steel main thing used in petroleum and chemical gas, heat, and sewage treatment, water, bridges, steel piling and marine water pipeline project and other fields. Now that the anti-corrosion steel pipe factory corrosion performance gradually strengthening, anti-corrosion steel not only good corrosion resistance, and thermal insulation function is relatively good, heat loss is only for the traditional pipe off 25%, long run can save a lot of power, significantly reduce power costs, anti-corrosion steel pipe still has relatively strong waterproof and resistant to corrosion, does not require the laying of pipe trench, you can directly buried underground or underwater, construction Introduction agile, total cost is also low.

Currently it has a relatively low temperature premise with excellent resistance to corrosion and impact resistance, which can be directly buried underground permafrost, the use of life expectancy reached between 30-50 million, the exact device and application can make the pipe network maintenance costs reduced, another advantage is that you can set the alarm system, active monitoring of pipeline leakage problems, the precise fault status indication and active alarms. However, the current anti-corrosion steel pipe factory is faced with antiseptic coating performance issues, like the layout of various processes, equipment selection, surface quality, heating, coating temperature, cooling, transmission accuracy, poor control will lead paint layer adhesion force is small, too thin, cracking or bubbles and other defects, strict implementation of norms and scientific method of operation of the control deficiencies, ensure anti-corrosion steel yield is also very important, so these problems are corrosion steel Plant should be noted and solution, the overall analysis, anti-corrosion steel pipe in the future development still has much room for growth.

Application of thin-walled seamless mild steel pipe

Seamless safe, reliable, environmental health, affordable, thin wall seamless mild steel pipe and new, reliable, simple and convenient method of connecting successfully developed, it has more advantages other pipe irreplaceable, engineering will become increasingly multi-use will become increasingly popular, a good prospect.

As China's reform and opening up policy, the rapid growth of the national economy gain, urban housing, public buildings and the construction of a large number of tourist facilities, hot water supply and domestic water supply put forward new demands. Especially water quality problems, there is growing emphasis on the requirements are also rising. Galvanized steel pipe because of this common and easy to corrosion, under the influence of relevant national policies, will gradually withdraw from the stage of history, plastic pipe, composite pipe and copper pipe system has become a common pipe. But in many cases, the stainless steel pipe more advantages, especially wall thickness of only 0.6 ~ 1.2mm thin-walled stainless steel tube in high quality drinking water systems, hot water systems and to safety, health priority water supply system, with safe, reliable, environmental health, affordable and so on. Domestic and international engineering has been proven to be the best overall performance of water supply systems, new, energy-saving and environmental protection is one of the pipes, but also a very competitive water pipe, is bound to improve water quality, improve people's living standards play no comparable role.

Elimination of cold drawn seamless steel pipe breakage

Foreign precision cold drawn seamless steel pipe is generally added to the metal alloy material way to improve the performance of the cold drawn seamless steel tubes, are required to stress annealing, to eliminate the residual stress material, to improve the organization of materials, improve the plasticity of the material, thus preventing seamless fracture failure occurs purposes.

At present, cold drawn seamless steel tubes are made of ordinary 45 # or 20 # steel 27SiMn steel, cold drawn deformed through the metal strength; however, it is at the expense of metal ductility, toughness for the price. Precision cold drawn seamless steel is its high dimensional accuracy and high strength properties and based on the market, it must ensure that the amount of deformation in a certain range, in order to maximize the performance of materials, to reduce the material adversely affected.

Cold drawn seamless steel pipe deformation is too small to reach the surface finish and dimensional accuracy requirements, but also unable to reach members of the strength index; deformation is too large, seamless plasticity, toughness decreases too much, but the grain is pulled excessively elongate, forming a fibrous tissue, a significant anisotropy metals. Cold drawn seamless steel tube in the axial direction, parallel to the elongate direction of the grain, the intensity increased; cold drawn seamless radially perpendicular to the elongated direction of the grain, but lower strength, and maximum stress of the hydraulic cylinder is present in the radial direction of seamless, so much distortion on the performance of fully drawn tubes unfavorable. For steel and fibrous tissue appears dislocations, vacancies and other crystal defects are generally taken annealing or normalizing heat treatment methods to eliminate them. The purpose is to refine the grain annealing to remove tissue defects, reduce hardness, improved ductility, but also facilitate cold. Annealing equipment of seamless mild steel pipe is indispensable, therefore, to develop an appropriate annealing process is to ensure that cold drawn seamless organization qualified defective product is not a necessary condition for a fracture. If the manufacturers in order to unilaterally reduce production costs, reduce the annealing process is bound to adversely affect the quality of products.

High-frequency welding of straight seam welded steel pipe

High-frequency welding is based on the principle of electromagnetic induction and the exchange of electric charge in a conductor skin effect, eddy current heating effect and proximity effect, so that the weld edges of the steel locally heated to a molten state, the roller of the extrusion, the crystals butt welds achieved indirectly together, so as to achieve the purpose of the welding seam high frequency induction welding is a welding (or pressure contact welding), it does not need weld filler, no welding spatter, weld heat affected zone narrow, beautiful welding molding, welding good mechanical properties etc., so in the production of steel has been widely applied.

Is the use of high-frequency welding pipe alternating the skin effect and proximity effect, steel (steel) by roll forming, the formation of a circular cross-section tube disconnected, near the induction coil inside the tube near the center of rotation of a or a group of impedance device (magnet), the impedance tube opening is formed with an electromagnetic induction loops in the skin effect and proximity effect under the action of the opening edge of the tube produces a powerful and concentrated thermal effects, the weld edge rapidly heated to the desired temperature by the pressure roller welding extrusion, the molten metal to achieve indirect co-crystal after cooling to form a strong butt weld.

The cause of the seamless steel tube high brittleness breakage

High brittleness seamless steel pipe production process because there is no annealing, annealing is refine the organization, eliminate stress, reduce the hardness or eliminate dendritic segregation heated to high temperatures for the purpose of maintaining a certain time, and then slowly cooled to room temperature.

Annealing is divided into two categories: first, annealing is not dependent lattice structure changes only can be achieved by the thermal motion of atoms annealing purposes, including non-ferrous metal alloy ingot homogenization, annealing steel castings, annealing of malleable cast iron, steel and non-ferrous metal plastic processing after recrystallization annealing and stress relief annealing and removing excess material dissolved hydrogen dehydrogenation annealing. The second category is based on solid phase transformation annealing annealing, including steel products, and a handful of non-ferrous metal products used in fully annealed, incomplete annealing, isothermal annealing, annealing of the ball and so on. This type of annealing process is accompanied by changes in the lattice structure, as re-crystallization occurs, as it is known as recrystallization, established on the basis of such a change is called annealing recrystallization annealing. That second annealing.

Seamless steel pipe production process produces severe dendritic segregation and internal stress, in order to eliminate such defects for homogenization, also known as annealing. Because this process consumes energy costs of working hours, so only apply complex shape or composition of complex large and extra large pieces. Cold rolled steel, cold-drawn steel wire and steel strip and cold-pressed steel products, because work hardening, so that material can not continue processing, subject to recrystallization annealing to eliminate work hardening. Important parts of steel commonly used low-temperature annealing to eliminate internal stress or dehydrogenation.

Submerged arc welding principles of spiral welded pipe

Submerged arc welding steel pipes, wires and steel poles are connected to the power supply, the welding power supply can be AC ​​can also be DC, province DC, the pipe connected to the power supply negative wire connected to the positive power supply wire through the tip charged by the wire feeder to - set the pace toward the workpiece conveyor, arcing between the wire and the workpiece burning. Stability of the arc is burning out the wire feed speed and wire melting rate to decide, when the speed is consistent arc to stabilize combustion. Control wire feed speed, and so often give uniform arc voltage Tuen give 2 ways, and with the welding power characteristic curve and the outer arc static characteristic curve related. Because the tube is welded with a welding current density (welding current A / wire cut solid plot mm ') is large, generally more than 50 A / mm' characteristics, so the use of arc welding to maintain isokinetic give stable combustion is possible, external power supply characteristic curve can be steep drop or constant current characteristic curves can be obtained outside the arc stable combustion.

Submerged arc welding pipe welding, flux wire inside the front into the welding area, and always covered with a welding arc weld zone * cooled and cooled crust mutual shrink factor because do not ask, crusts will automatically fall off, the excess flux party talks were automatically separated and recovered. Spiral submerged arc welded pipe welding, the wire down the conveyor, steel mechanical movement, it is also known as automatic submerged arc welding. The award is the wire drive system and flux welding on mobile devices, known as semi-automatic submerged arc welding.

Application of Double-sided submerged arc spiral pipe

Submerged arc welding was invented in 1940, a new welding method, and in front of it the same place manual welding or the use of slag to protect it, but this is not a slag electrode coating, is designed smelting flux out. The flux system consists of a funnel filled with flux through a pipeline to be welded to the front. The second difference is not used electrode using wire, because the wire can be continuously sent; electrode, we gotta burn a welding electrode head gave a throw, and the operation was stopped, and then for electrode welding. After wire changed, with the delivery device and the wire coil wire, the wire is continuously sent, this welding process is continuous feeding of the wire and the solder to melt under the coverage of the particulate ignition of the arc, the welding wire, base material and flux melting and evaporation constitute part of a cavity, the cavity inside the arc is stable combustion, so call it submerged arc welding. Arc is buried inside the cavity.

In this way, the first advantage is fully automated; second advantage, it is carried out under submerged arc welding, the heat exchange and so it is relatively strong protection performance, higher quality weld out; third advantage as submerged arc welding arc welding flux buried underneath, so it can use a large current, welding efficiency is relatively high, the recent progress of our country's natural gas pipeline project, the pipeline is a high-strength steel, this pipeline prefabricated factory inside the first paragraph, and then get on the site, in the field welding, this pipeline in the factory production process is the use of submerged arc welding, submerged arc welding has become now, there are double wire submerged arc welding, there are multi-wire submerged arc welding, to further improve efficiency.

Non-destructive testing in the role of spiral welded pipe production

Nondestructive testing technology, also known as non-destructive testing techniques. It is the use of certain physical properties of the substance or group defective structure bound to the differential changes in physical phenomenon, without damage, the detected object does not damage the performance and shape of the premise, by measuring these changes understanding and evaluation of plant material to be detected, the nature of products and equipment components, status, quality, or internal structure of a particular detection technique.

In a small spiral steel pipe production process, the role of non-destructive testing are two points; First, raw materials, semi-finished products, rife provides continuous, real-time process quality control, especially spiral pipe welding quality control and production process quality (such as heat treatment, expansion diameter, flat head and hydrostatic test or defects caused by the expansion of the original defect), timely detection of primitive and production processes of various defects and this appears to be controlled to prevent does not meet the quality requirements of raw materials / semi-finished products into the next process ; Second, Liu pipe small defects accurate qualitative and quantitative and positioning, thus providing guidance disposed of; three are based on the acceptance of non-standard vague to the production of spiral welded pipe for quality grading, to meet different customer needs. Yuan right detection technology allows us the safest and most economical way to health and the use of wide spiral welded pipe products.

In the field of nondestructive testing technology has been able to force the effective application of non-destructive testing "France has reached many dozens in the spiral welded pipe manufacturing field, the most common non-destructive methods for the detection of food: ray inspection (only T), ultrasonic testing (uT ), penetrant testing (FP), eddy current testing, magnetic particle testing (MT), etc. This is also the first developed Chia conventional detection methods.

The application of thick-walled steel pipe in the pipe welding process

Welded joints groove forms commonly used in the construction pipeline welding groove type for the API standard 30 ° V-groove, suitable for manual welding. But for the thick-walled steel pipe, this type of groove weld joint type filler metal volume, high labor intensity, and not suitable for automatic soldering, welding, usually semi-automatic welding with 23 ° V-groove, with a narrow gap welding composite groove patterns. Welding energy needs into account to determine the composition of the base metal, weld material type, for drug skin (cored flux) metallurgical reactions and the effect of shielding gas protection, preheat condition, interpass temperature control of the tube specifications , the wire (strip) in diameter, the heat affected zone embrittlement and softening tendencies, the desired microstructure and mechanical properties, as well as welding position, welding passes, each weld thickness, weld and form of such a transition droplet factor. Preheating and interpass temperature by slowing the purpose of preheating the base material and reducing the stress state of the cooling rate of the weld root to prevent cold cracking roots. Construction of the pipeline welding preheat temperature range should be considered the strength of the base material, organizational performance variation, diameter and wall thickness, and the amount of hydrogen welding materials and other factors.

For multilayer welding thick-walled steel pipe, but also consider the weld interpass temperature control to control the cooling rate near the weld zone. Interpass temperature and preheat temperature generally similar. Avoid overheating the seam zone near the premise that higher layer temperature prevents multi-layer welding cold cracks. Heat treatment after welding and heat treatment pipeline construction is generally not performed after the heat treatment after welding and heat treatment. But for construction in the alpine region, when the preheat and interpass temperature control is difficult to play a greater role, it is necessary to take some of welded joints and heat treatment after hot measures to ensure that the organization and performance of welded joints. In pipe welding construction process should take into account the high strength, thick-walled steel pipe is exposed to the impact of external stress. Taking into account the ambient temperature, humidity and wind speed on the environmental impact of different welding methods, to take the necessary measures to ensure the welding quality.

Corrosion resistance of stainless steel

All metals and reaction of oxygen in the atmosphere, the surface oxide film. Unfortunately, in the iron oxide formed on carbon steel proceed oxidation, corrosion continues to expand, forming holes. You can use paint or oxidation-resistant metal (eg, zinc, nickel and chromium) plating to ensure the steel surface, but, as people know, this protection is only a film. If the protective layer is damaged, the following steel began to rust.

Corrosion resistance of stainless steel depends on chromium, but because chromium is an integral part of the steel, so protection methods vary. The addition amount of chromium 10.5%, the atmospheric corrosion resistance of steel significantly increased, higher chromium content, while still being improved corrosion resistance, but not obvious. The reason is of steel with a chromium alloying treatment, the change in the type of surface oxide became similar to pure chromium metal oxide formed on the surface. This tight adhesion of chromium-rich oxide protective surface to prevent further oxidation. This thin oxide layer, through which you can see the surface of the natural luster of steel, the stainless steel has a unique surface. Moreover, if the surface is damaged, the exposed steel surface and atmospheric reactions will self repair, re-formation of this kind of "passive film" and continue to play a protective role. Therefore, all of the stainless steel have a common characteristic, that chromium content of 10.5% or more. And building construction applications usually only about six kinds of steel. They contain 17 to 22% chromium, preferably of steel also contains nickel. Add molybdenum can be further improved atmospheric corrosion resistance, especially resistance to chloride-containing atmospheric corrosion.

The main production methods of large diameter welded pipe

Used to transport large diameter pipes, manufactured using various welding methods, such as using electric arc welding under flux layer, the contact resistance welding, flash welding and other welding and high frequency currents. Press the seam can be divided into straight seam welded and spiral welded two ways, straight seam welding production process is composed of the following main steps: forming tube within the model to make double-sided welding, welding steel pipe imposed on small expanding.

The method currently used is the most complete with a huge three-step molding production press with die no longitudinal joints 12 meters long pipe, and the shape and size are very accurate. The gas pipeline is the most common method used solvent layer under the double seam welding speeds of up to 140 ^ -150 m / hour. Soldering should be repaired weld, then cut the head and pipe sizing. The modern sizing method is applied to the inner pipe hydraulic diameter to the expansion diameter of 1.5-2.5% pots, fixed length to diameter, on the other hand to improve the yield limit of about 20%.

Nickel is an excellent corrosion-resistant materials, is an important alloying element in steel. Nickel is the formation of austenite in the steel elements, but to obtain pure carbon-nickel austenitic steels, nickel volume to reach 24%; whereas only 27% of nickel when the steel corrosion in certain media Corrosion can significantly changed. So Nickel alone can not constitute a stainless steel. However, both nickel and chromium present in the stainless steel, the nickel-containing stainless steel, but has many valuable properties. Based on the above case shows, nickel as an alloying element in stainless steel effect, is that it enables high-chromium steel tissue changes, so that the corrosion resistance of stainless steel and obtain certain improved process performance.

Manufacturing of mild steel pipe

Mild steel pipe is made of steel ingot made ​​of perforated or solid tube capillary, and then by hot-rolled, cold-rolled or cold-call is made. Mild steel pipe in China's steel industry has an important position.

The raw material is carbon steel pipe round tube, tube embryos to go through a cutting machine cutting the growth of about one meter of the billet, and by conveyor belt to the furnace heating. Heating the billet is fed into the furnace, the temperature is about 1200 degrees Celsius. Fuel is hydrogen or acetylene. Furnace temperature control is the key issue. Circle tube came out through the pressure punching machine wear air. Generally more common punch is tapered roller punching machine, punching machine such high production efficiency, product quality, perforated expanding volume, you can wear a variety of steels. After perforation, round tube has been three roll rolling, rolling or extrusion. Squeeze off the tube after sizing. Sizing mill rotating at high speed through a cone drill holes into the billet to form pipe. Pipe diameter from the sizing mill to determine the length of the drill diameter. The pipe sizing after entering the cooling tower through water cooling pipe after cooling, will be straightening. Steel belt sent by straightening the metal detection machine (or water pressure test) for internal testing. If the pipe internal cracks, bubbles and other problems will be detected. Steel quality even after rigorous hand-selected. Steel quality, the use of spray paint number, size, production batch number. Hanging by a crane into the warehouse.

Features and Applications of mild steel pipe

A four-layer structure of the mild steel pipe, the inner layer is extruded thermoplastic tube, the liquid in the transmission from the seal; intermediate layers lining the carbon-filled polyethylene tube, which is resistant to long-term ability of UV radiation , and to exclude external static. The outermost layer is the thickness of the extruded outer shield to protect the pipe from external influences bottom. Flexible pipe for standard pressure ratings to ANSI classification.

Canada a long 2km, 6in diameter of the pipe, was shut down due to corrosion problems. The pipeline's route to go through 5 to 6 zone landowners apply for the construction of a new pipeline particularly difficult, therefore, decided to repair the pipeline. Wellstream adoption repair method is a mild steel pipe to the old, so you can not re-apply for the purchase of new pipe, which saves costs and reduces damage to the environment. The repair pipeline transporting liquid carbon dioxide is used to inject the wellhead to increase oil production. Wellhead in place leading to a 90 ° bend with two and a highway through the office. Pipe penetration to elapse before the pigging operation, removal of obstacles such work.

Terminal fitting is designed to be able to maintain structural integrity to meet, to ensure the inner and outer extruded layer of the sealing requirements, and to ensure the tension and pressure load transfer to the tube structure. Terminal parts of the sample after blasting and axial tensile test.

Definition of seamless steel tube

Seamless hollow sections, a large number of channels for transporting fluids, such as the transportation of oil, natural gas, coal gas, water and some solid materials, pipes and so on. Steel pipe and solid steel bar, etc. compared to the same torsional strength in bending, lighter,which is an economic cross-section steel, widely used in the manufacture of structural parts and mechanical parts, such as drill pipe, automotive drive shafts, bicycle Rack and construction using steel scaffolding steel pipe manufacturing annular parts, can improve material utilization, simplify the manufacturing process, saving material and machining time, such as bearing rings, jack sets, has been widely used to make steel. Steel or a variety of conventional weapons indispensable material, barrel, barrel, etc. to make steel. By cross-sectional shape of the pipe can be divided into tube and shaped tubes. Since the perimeter of equal conditions, the maximum area of ​​a circle with a circular tube can carry more fluid. In addition, the circular cross section to withstand internal or external radial pressure, the force is uniform, so the vast majority of the pipe is pipe.

However, the tube also has some limitations, such as by plane bending conditions, the tube is not as good as square, rectangular tube bending strength, some of the farm skeleton, steel and wood furniture to common square, rectangular tube. According to different uses should also have other cross-sectional shapes of the shaped pipe.

Shoddy methods of identification
1. Shoddy seamless easily scratched because of shoddy seamless equipment is very easy to produce burrs, scratches steel surface. Deep scratches reduce the strength of steel.
2. Seamless shoddy no metallic luster, pale red color of iron or the like.
3. Shoddy seamless thin and low transverse ribs, a phenomenon often sufficient dissatisfaction, because the manufacturers to achieve large negative tolerance, finished the first few channels reduction is too large, iron-type small, hole filling dissatisfaction.
4. Shoddy seamless oval in cross section, because the manufacturers in order to save material and finished before the two rollers amount of reduction is too large, the strength of this seamless greatly decreased, and does not comply with seamless Dimensions standards.
5. Quality seamless uniform composition, high tonnage cold shear, cut head face smooth and neat, and seamless as shoddy material is poor, there are often cut off the meat head end of the phenomenon, that is uneven, and no metallic luster . And because less shoddy product manufacturers cutting head, head and tail will be a big ears.
6. Inferior seamless steel tube material containing impurities, the density of steel is small, and the size tolerance serious, so there is no case of a vernier caliper can check it for weighing. Generally the whole amount would be better proportionality, mainly taking into account the cumulative error and probability theory this problem.

Affecting large diameter seamless uniform quenching factor

There are currently seamless quench tank water quenching processes and external water quenching tank.

Tank water quenching the easiest way is to dip quenching; but easy to make steel upper and lower parts of the cooling rate is inconsistent, pipe bending. The application of external water quenching trough the more successful is the "while rotating the pipe for steel pipe inner surface axial water, water quenching the outer surface layer flow," the water quenching heat treatment process. Comparison dip quenching, quenching to add the axial injection dip, spray plus axially outer laminar jet injection and to add the axial injection cooling methods such as cooling capacity of the outer tube and the inner surface of the laminar jet cooling capacity axial injection process strong quenching efficiency. If accompanied by pipe rotation system that allows uniform cooling pipe in the circumferential direction and cooling minimal deformation. Steel inner and outer surface cooling in the form of different, often cause uneven cooling pipe, resulting in deformation. Produced within the axial injection direction along the length of pipe uneven cooling water through the partial adjustment layers to make up the amount given. Large diameter seamless mild steel pipe quenching, the factors that most influence the pipe diameter, pipe rotation speed and water wetting angle on steel radial cooling uniformity.

Manual welding thick-walled steel pipe

Welding method of thick-walled steel pipe is the most commonly used manual welding, manual welding: manual welding is a very common, easy to use welding methods arc length is adjusted by human hands, it depends on the gap between the electrodes and the workpiece the size of the same time, when the carrier as the arc when welding the weld filler material also.

This welding thick-walled steel pipe method is very simple and can be used to weld almost all materials for outdoor use, it has good adaptability, even in the underwater use have no problem. Most welders can TIG welding electrode welding , the arc length determined by the human hand: when you change the gap electrode and the workpiece, you have to change the length of the arc, in most cases, welding using direct current, the arc electrode both as carrier and also as filler weld material from the alloy or non-alloy electrode metal core wire and the electrode coating composition of this layer of coating to protect the weld from air violations, while stabilizing the arc it also caused the formation of slag layer to protect the weld it shape. welding bars to titanium type electrode, but also seal in nature, depending on the coating thickness and composition. titanium rod easy to weld, weld flat appearance. Additionally, welding slag is easy to remove if the rod storage for a long time, must be re-baked roast because moisture from the air will quickly accumulate in the electrode, so says manual welding thick steel is the most commonly used method.

Physical phenomena of submerged arc welding

Currently, spiral steel pipe is widely used double-sided submerged arc spiral pipe welding technology, the following of what the submerged arc welding process and the characteristics of the formation.

SAW principle:
Submerged arc welding is the use of thermal energy for electric arc welding, and manual arc welding is different: submerged arc welding wire is exposed, the above does not paint, submerged arc flux is pre indeed be welded at the shop, submerged arc welding wire into the flux, the arc is burning under the flux.

SAW formation process:
Wire and the workpiece, press the start button is pressed after the power of the moment the wire and the workpiece, wire Withdrawing arc ignition, welding carriage to move forward, the conveying wire under continuous to maintain the arc burning under the flux layer, the bottom of the arc the formation of the weld pool. Around the arc, flux melted to form a cavity. The voids and pool continues to advance, and the rear metal solidification bath to form a continuous weld. Since this process is carried out under the flux, so we can not see with the naked eye. By means of X-ray photography can be seen.

As the spiral pipe welding using submerged arc welding technology, in addition to such high production efficiency; production auxiliary less time, saving time for welding; welding conditions clean and no spatter, saving clean-up time; weld quality is high. But also for the delivery of spiral welded pipe plant provides the necessary conditions for making large spiral pipe production time is guaranteed, so is still widely used with.

LSAW steel pipe weld transverse cracks cause analysis

LSAW pipe welding when the first pre-welded, then welded inside, and finally outside welding. For different diameters, different wall thickness welded steel pipe welding comparing the situation found: thin-walled pipe welding, the weld was bright red back white; thick-walled pipe welding, the weld back red dark red; intermediate wall pipe welding, the weld on the back red light in between. This phenomenon indicates that different thickness of steel pipe welding seam on the back there is a large temperature difference, this difference will cause stress in the longitudinal direction of the pipe wall thickness distribution are different.

Factors affecting the size of the tensile stress is mainly welding seam weld both sides of the maximum temperature and cooling rate. Since the front of the weld puddle temperature is much higher than the melting point, the temperature of the opposite weld metal is far below the melting point of the front of the cooling heat weld way to pass through the heat conduction to the reverse side, so that the cooling rate of the weld opposite lower the front of the weld cooling rate. When the temperature of the weld opposite high, close to both sides simultaneously stretching the resulting longitudinal tensile stress is small; when the welding temperature is lower sides, close to the elastic deformation in the opposite state to free expansion, the resulting longitudinal tensile stress is also small; when the temperature in the middle of the weld zone opposite, the resulting longitudinal tensile stress is large, it is easier to produce a range of transverse cracks.

Pipe welding stress distribution with different plate welding, pipe, straight seam welded pipe due to be bound by the resulting longitudinal tensile stress than the big flat welding. When the weld is cooled, without considering the ambient temperature in the case, the weld seam is greater than the cooling rate of the front opposite the cooling speed when the weld is cooled to generate compressed reverse plastic deformation temperature range, the opposite will shrinkage bending deformation of the front seam and the front generate additional longitudinal tensile stress, if the temperature of the weld is still in front of the solid - liquid between the brittle temperature range, the tensile stress in the dual role of the weld may have transverse cracks, and due to bending deformation of the weld surface closer to the larger tensile stress, which is the lateral surface or cracks in the weld seam to strengthen the main reason.

High-frequency steel pipe welding seam impact toughness

How to improve the high frequency weld toughness steel tube technology is a major problem. In mass production practice based on analysis of the impact of ERW steel pipes Eimpact toughness of a variety of factors. That in order to further improve the impact toughness of the weld, to meet long pipeline steel pipe for high toughness proposed training requirements, the need to start from the quality control of raw materials, steel coils, combined with manufacturing processes, enhance forming, welding and post weld heat treatment line for quality control .

Frequency tube welding process is the use of high-frequency current generated by the skin should principle the back edge of the hot-rolled coil was heated to a molten state, and then by mechanical extrusion welding. Through the process of its production of steel pipe weld fusion center will be a white line, fusion line both sides of the heat affected zone will produce from the central to the direction of extension and external surfaces of the metal flow lines.

As is the use of high frequency welding tube material as the base material, so the performance of the weld and base metal significant performance relationship. In ordinary materials, weld and base metal ductile-brittle transition temperature curve. In general the material, the base metal and weld Charpy impact test values ​​of absorbed energy difference is small. In contrast, in high toughness materials, there are large differences in impact toughness was significantly inferior to the base material, but significantly better than ordinary materials welds. From this high impact toughness weld center tube generally lower than the impact toughness of the base metal, even with the ductile material, although the toughness of the weld is improved, but not completely improved impact toughness of weld center.

Ultrasonic flaw detection technology for qualitative evaluation method

Currently the most widely used is the A-scan display type ultrasonic pulse reflection detector. After a long practice of ultrasonic testing, ultrasonic testing of many of its large number of personnel contact materials, products and manufacturing processes have a full understanding and verified through a lot of anatomical analysis, has accumulated rich experience in the detection through A-scan display type ultrasonic pulse echo flaw detector, according to the defect appears on the oscilloscope screen echo waveform shape, such as a video display or radio show, from the wave velocity, echo echo the forefront of the trailing edge of a steep decline in the extent and speed (down slope) , wave shape as well as echo Zhankuan flaw echo when moving the probe changes (amplitude, position, quantity, shape, dynamic envelope, etc.), but also the end of wave based on the observed multiple times, the end of wave height losses , defects are detected according to the location member, the distribution, the equivalent defect size (the reflectance of), extended, combined with the specific product, material characteristics and manufacturing processes make comprehensive judgment, evaluation of the type and nature of the defect . And sometimes also by changing the frequency of the ultrasonic pulse transmitted to change the beam diameter of the (take the focus of the probe or a different diameter, etc.) to observe the variation of defect echo, thereby identifying the material of the reflection metallurgical defects or organization.

In this regard there are a lot of lessons learned and information reports, for example, determine the white point of steel forgings, inclusions, residual shrinkage, coarse-grained, center porosity, box-shaped segregation and porosity in the weld, slag, incomplete penetration, lack of fusion, cracks and so on. Must be noted that this judgment ultrasonic testing method relies heavily on the experience, skill level and on specific products, materials and manufacturing processes to fully understand its limitations is great, difficult to promote a common evaluation method. Further, as the flaw echo A-scan display defect information displayed is extremely limited, mainly shows the volatility of size, position and shape of the echo envelope and the phase response of the ultrasonic defect, spectral and other important information will not be displayed , but the latter two with the nature and type of defect has a close relationship, which is currently the majority of ultrasonic testing personnel committed to research to explore the issue.

ERW straight welded pipe weld shape

High-frequency welding pipe ERW process is the use of high frequency current generated by the skin effect of the principle of the edge of the hot rolled coil is heated to a molten state, and then by mechanical extrusion welding. Indeed through this process to produce welded steel pipe weld fusion center will have a white line on both sides of the fusion line will produce heat affected zone extending from the middle to the surface of the metal flow lines. During the welding process, the metal tube experienced a cold, hot, then cold thermal cycling process, therefore, the physical and chemical properties of the base material, grain size, non-metallic inclusions, forming and welding conditions and heat treatment process, and this will the weld toughness properties, especially impact punch. In the pipe production process, the impact toughness by selecting coil to ensure the performance of welded steel base metal, combined with adjustment of the welding process to ensure the best possible control and reduce defects, guarantees a high performance of the weld.

Welding quality of weld seam by the appearance of the weld morphology, surface conditions and the mechanical properties of the weld testing and metallographic analysis to judge. In the production process, the curved shape and the surface condition of the seam welding process can be adjusted to provide a reference. Mechanical properties testing generally in accordance with the standard requirements or customer specific requirements. Appearing in a variety of pipe production quality defects are caused by many factors, but mainly due to the weld quality problems inside and outside edge of the plate and extrusion temperature and the heating temperature does not match the result. Board outside edge temperature can not exceed the range of inconsistency, otherwise it will have serious quality problems. One of the more typical problem is the two extremes burnt and cold welding. Burnt is to ensure that all of the inner and outer "penetration", resulting in high temperature side of the "burnt." When removing burrs, the oxides can be found and impurities remain in the right side, the naked eye can see the formation of cracks or holes are not welded. By flattening slightly lighter degree can check out. Or to limit the scope of the outside temperature exceeds a certain cause other side appeared cold welding. When the temperature is not completely outside the above range, the quality of the welding must be checked to determine. Heating of the slab edge is consistent by observing the inner and outer weld burrs or protrusions are the same size can be. Generally indicates the outer edge of the outer coarse protrusions on the inside edge of the heating intensity, whereas the inner edge of the high temperature. Between a heating temperature of the pressing amount is appropriate bonding surface will ultimately affect the strength of the weld and weld appearance. Typically the welding process, the following occurs: When asked appearance quality, often appear soldering temperature is too low; when stressed weld strength, it usually occurs soldering temperature is too high; Or proper welding temperature, extrusion volume control improper. Typically, the amount of compression can have a proper range, when the squeeze is large, due to lower heating temperature; when pressing volume is small, appropriately increasing the heating temperature, which ensures that the weld strength and weld shape to achieve better combined effect.

Application of the welded steel pipe

Since the invention of welded steel pipes, more widely, welded steel pipes is included: double submerged arc welded pipe, high frequency steel pipe, spiral steel pipe, they each have their own characteristics in different areas to play a different role. Longitudinal Submerged arc welding is the use of such molding process JCOE or UOE steel plate having an opening into a tube then submerged arc welding, reliable product quality, can be used for oil and natural gas transmission, structural engineering. HF strip steel is molded into a tube having an opening, and then high-frequency welding, production weld I SAW pipe is much better than the higher, the product used for low-pressure fluid transfer and architectural decoration columns, etc.. Spiral steel pipe is the use of steel production, and its main feature is available with a specification of the strip can produce various caliber products, spiral weld quality lower than the submerged arc welded pipe, used for low-pressure fluid, decorative columns, etc..

In recent years as technology continues to evolve welded steel pipe production technology continues to improve, the quality is improving, such as seamless steel pipe out, it will get welded steel hot-rolled products, as compared with steel pipe prices high, so that in many fields instead of welded steel seamless application.

How to distinguish stretch reducing pipe and straight seam welded pipe

Weld quality directly determines the quality of the pipe, that is to say, it is welded and seamless biggest difference lies. Longitudinal high-frequency welding or submerged arc welding, the carbon can not be eliminated straight sets crevices, welds, and the mother just converge together, and no one fully integrated, stand the test of time and pressure. Tension Reducing heat welded steel pipe in the pipe even after high temperature of about 800 degrees after heating, the overall annealing, after this series of processes, the weld performance close to the parent organization, well done seamlessly from seam to transition.

Different process also caused the differences in product quality, tension reducing steel pipe in steel pipe also conducted a straight seam welded pipe after welding are not do process: online clearing outside burr. The presence of burrs impact tube fluid - flow, burrs blocking the normal flow of fluid, to produce swirl. According to principles of fluid mechanics, the weld must increase local compression, discontinuity of the pipe safety factor is also greatly reduced, reducing the tension in the steel production process fully considered the risks that exist glitch for burr removal, making it uniform thickness, no difference in appearance with the seamless tube. So from this point of view, hot stretch reducing pipe joints from having also completed a seamless transition, of course, not limited to the difference between the above two points, but illustrates the Longitudinal and stretch reducing pipe also there are significant differences. Longitudinal latter carried out on the basis of clear internal and external burrs online, the overall heating type variable and a series of new processing technology, so that it has been a qualitative leap in the field of the widespread use of high-pressure, Longitudinal generally used in low voltage environment for water gas transmission or steel.

The advantages of new seamless welding technology

Seamless welding technology demonstrated exceptional performance in welding the welding mold, increase part accuracy, finish and appearance of observability and shorten the mold manufacturing cycle. Overcomes the welding process in the mold seam affect aesthetic shortcomings.

Seamless welding technology, not only can help eliminate mold seam, but also a corresponding increase part accuracy, finish and appearance of observability. Meanwhile, seamless welding technology in injection molding efficient control of the implementation of the process, shortening the processing cycle of the mold. Since the process of production of products with excellent surface finish, it is not necessary with the second deposition and annealing, thus avoiding the second contraction due to changes caused by the size.

In the past, the production process of the mold, cooling lines arranged in the vicinity of the mold surface, the surface finish of the product is not always uniform. In some relatively new process, through the mold core and cavity cooling water pipeline around the area set up in the resin injection, can get a better product quality assurance.

The new seamless welding technology uses a modern machine tools and some new technology. In accordance with the technical requirements of new technologies, processing similar to the mesh mold core and cavity, in order to prevent its movement and the second clamping, using the fourth axis milling machine, this can increase the tolerance of dimensional accuracy. Plate fin and the water chamber cooling lines have also been more widely used, and further improve product quality and seamless welded finish.

High-frequency welded pipe welding speed

Typical frequency welded pipe flow: uncoiling - strip leveler - head and tail cut - strip butt - Looper material storage - Forming - Welding - clear the glitch - Sizing - testing - fly cut - initial inspection - Tube Straightening - pipe processing - hydrostatic testing - flaw detection - printing and coating - finished. Welding speed of the welding process of the main parameters, which the heating system, the welding speed and the deformation speed of each crystal.

In the high-frequency welded pipe, the weld quality welding speed with the acceleration of progress. This is because the heating time can be shortened to narrow the width of the heating zone edge, reducing the time of forming a metal oxide, if the welding speed is reduced, not only the heating zone widened, and the width of the melting zone with the heat input and change, the formation of within the burr bigger. In low-speed welding, heat input less difficult to weld, do not meet the specified value prone to defects.

Double-sided spiral submerged arc spiral pipe welding technology

Using double-sided spiral submerged arc spiral pipe welding technology, the narrowband (board) volume continuous welded steel pipe. In our natural gas and other long-distance gas pipeline project has been widely used, is our long-distance gas pipeline project using the main tube.

Spiral steel pipes are widely used in natural gas, petroleum, chemical, electric power, heat, water, steam heating, hydropower penstock, power, water and other long-distance pipelines and piling, dredging, bridges, steel and other engineering fields.

Spiral Pipe thermal fatigue stability generally refers to work in hot and cold alternating cracks under the action of the ability to resist. Of cold, heat generated by alternating said thermal fatigue crack crack. In the mold die casting, forging die thermal fatigue scrapped mainly due to poor stability are prone to thermal fatigue cracking. For the mold steel, its stability is mainly determined by the thermal fatigue toughness and strength. Therefore, stability, good thermal fatigue mold steel must have good toughness and high strength (wet strength) a good fit.

Spiral steel pipe surface by high velocity impact and turbulence of the fluid-like, and to abrasion and corrosion damage, known corrosion and wear. Impact corrosion is the main form of wear and corrosion resistance. Spiral steel pipe under the impact of high-speed fluid, the protective film damage, break at the bare metal accelerate corrosion. If the fluid contains solid particles, spiral steel pipe corrosion and wear is even more serious. Its exterior features are: localized grooves, corrugated, round and valleys shaped, usually show directionality. Exposed to the movement of fluid in equipment such as: pipes, tees, valves, blowers, centrifuges, impellers, heat exchangers, exhaust duct, etc. can have an impact corrosion. Soft metals such as copper and lead more serious.

Spiral pipe uses and knowledge

Spiral steel pipe is the industrial, construction and other industries widely used kind of steel. It is a strip coil as raw material, often warm extrusion molding, with automatic double-sided submerged arc welding process wire spiral welded steel pipe. Mainly used in water engineering, petrochemical industry, chemical industry, power industry, agricultural irrigation, urban construction. Spiral steel pipe for the transport of liquids: water supply and drainage. For gas transportation: gas, steam, liquefied petroleum gas. For structural purposes: as piling pipe for bridges; docks, roads, buildings and other structures tube. Spiral Pipe Plant it in the transportation of gas, transportation has played a significant role.

Spiral steel pipe pressure transmission fluid with spiral submerged arc welded pipe is mainly used to transport oil, natural gas pipelines; pressure transmission fluid with frequency spiral welded steel pipes, lap welding method with high frequency welding, pressure fluid transport frequency spiral welded steel pipe. Strong pressure steel, plastic, and easy welding and machining molding; generally low pressure liquid delivery spiral submerged arc welded pipe, using double-sided automatic submerged arc welding or welding into the legal system for water, gas, air and steam low pressure liquid delivery SAW pipe.

Spiral Pipe Plant Longitudinal generally higher than its strength, can narrow the billet production of large diameter pipe, you can also use the same width of the billet production of different pipe diameters. But with the same length of straight pipe joints than weld length of 30 to 100%, and lower production rate. Therefore, the smaller diameter pipe is mostly a straight seam welded, large diameter spiral welded pipe is mostly used.

Spiral welded pipe anti-corrosion technology

Since the quality of the individual spiral steel pipe is relatively large, it must be stacked in the outdoors, but this will be difficult to avoid the sun and rain, so the rusty spiral welded pipe has been plagued by storage time and conditions.

The main use of tools such as a wire brush to polish the surface of the steel, spiral welded pipe cleaning and preheating can remove loose or warped oxide, rust, welding slag. Hand tools rust can reach Sa2 grade power tools rust Sa3 level can be achieved, if the steel surface firmly attached to the iron skin, the effect is not ideal tools rust, anti-corrosion construction required to reach the depth of anchor pattern.

Acid by solvent, emulsion cleaning fluid pressure welded steel pipe surfaces to achieve the removal of oil, grease, dust, lubricants and similar organic matter, but it can not remove the steel surface rust, oxide, flux, etc., Therefore, in the production of corrosion only as an adjunct. Generally use two methods to do chemical and electrolytic pickling treatment, pipeline corrosion using only chemical pickling can descaling, rust, old paint, sometimes used as a sand blasting after reprocessing. Although chemical cleaning can achieve a certain surface cleanliness and roughness, but the anchor pattern shallow, and easy on the environment caused by pollution stacking spiral welded pipe. Rational use of means to clean up the rusty pipe fittings for a long time when the guarantee services in the production and create more production efficiency.

How to avoid large diameter spiral pipe corrosion

All metals and reaction of oxygen in the atmosphere, the surface oxide film. Unfortunately, in the iron oxide formed on carbon steel proceed oxidation, corrosion continues to expand, forming holes. You can use paint or oxidation-resistant metal (eg, zinc, nickel and chromium) plating to ensure the steel surface, but, as people know, this protection is only a film. If the protective layer is damaged, the following steel began to rust.

Large diameter spiral steel pipe corrosion resistance depends on corrosion, coal tar epoxy anticorrosive is one of the components, so the protection methods vary. Strengthen the anti-corrosion paint material reaches level, large diameter spiral pipe atmospheric corrosion resistance can significantly increase, but higher strength corrosion, although still improve corrosion resistance, but not obvious. The reason is used for large diameter spiral steel pipe anti-corrosion processing of the processing, the change in the type of surface oxide became similar to the large diameter spiral pipe is formed on the surface of the metal oxide. This tight adhesion of large diameter spiral pipe oxide protective surface to prevent further oxidation. This oxide layer is very thin, it can be seen through the large diameter spiral steel pipe surface natural luster, making large-diameter spiral pipe has a unique surface. Moreover, if the surface is damaged, the exposed surface of large diameter spiral pipe and atmospheric reaction to self-repair, re-formation of this oxide "passive film" and continue to play a protective role. Therefore, all of the large diameter spiral pipe elements have a common characteristic, corrosion prevention of corrosion is the best way.

Straight seam welded steel pipe standard treatment

Straight seam steel pipe weld heat treatment is a new skill to eliminate residual stress. The data preheated before welding to the heat treatment temperature after the welding process and welding pieces of the heating was continued to adhere to this temperature, after completion of welding heat applied to its cotton insulation slow cooling. This approach could usefully down welding residual stress, progressive metal's resistance to stress corrosion.

Useful heat treatment after welding the welding residual stress decrease, and the heat treatment temperature is higher, the better the effect of residual stress relief. Large diameter steel pipe weld heat treatment can also be useful for the progress of large-diameter pipe resistance to stress corrosion ability, after the heat treatment temperature is higher, resistance to stress corrosion can progress more obvious. Dispersion of metal carbide coating the workpiece is placed special skill medium, dispersed appearance of acting on the workpiece to form a layer of several tens of microns microns metal carbide layer. Large diameter steel pipe anti-corrosion of buried pipes and tubes inside out corrosion, are made of galvanized wire hanging, spraying compressive strength of not less than 30 N/mm2 cement mortar fabric.

Because the internal weld destructive testing of the pipeline project in the water supply pipe attributed to large, especially the thickness t = 30 mm steel tube is utilized as a pipe bridge, we must accept the internal water pressure, but also bear the weight of steel pipes and water bodies constituted moment, so the welding quality requirements are particularly high. About the pipe bridge of t = 30 mm thick with a large-diameter steel pipe, the longitudinal seam and girth welds were attributed to a class, the demand for 100% of the X-ray film viewing and 100% of the ultrasonic flaw view; while the thickness t = 24 mm buried steel pipe, welded longitudinal seam attributed to a class for 20% of the X-ray film viewing and 50% of the ultrasonic flaw viewing.

Temperature control of high-frequency straight seam welded steel pipe

Straight seam welded steel pipe temperature is mainly affected by the impact of high-frequency eddy current heating power, according to the formula, high-frequency eddy current heating power by the frequency of the secondary effects of eddy current heating power with frequency proportional to the square encouraged; while encouraging current frequency but also by encouraging voltage, current and capacitance, inductance. Straight pipe joints and encouragement to encourage frequency circuit of the capacitance and inductance is proportional to the square root, perhaps with the voltage and current proportional to the square, just change the circuit capacitance, inductance, or voltage and current to change the size to encourage frequency, so as to achieve control of welding temperature. About low carbon steel, welding temperature control in 1250 ~ 1460 ℃, can reach 3 ~ 5mm wall thickness penetration requirements. In addition, the soldering temperature welding speed can also be done through conditioning.

High-frequency welding straight seam welded steel pipe will strip into the unit, the multi-channel roll rolling, strip and gradually rolled to form a gap ashamed round tube, adjust the amount of reduction squeeze rollers, so that the weld gap lies in the 1 ~ 3mm, make weld ends flush. Straight seam steel pipe should be as close to the high-frequency induction loop squeeze roller position. If the induction coil is farther away from the squeeze rollers, ineffective heating time is longer, wider heat-affected zone, weld strength landing; Conversely, lack of weld edge heating, extrusion molding bad.

Sided submerged arc welding straight seam steel pipe technology advantages

Double submerged arc welded (LSAW-Longitudinal Submerged Arc Welded) was invented in 1940, a new welding method, it and the front of the manual welding the same place or the use of slag to protect it, but this is not a slag electrode coating . Straight seam double submerged arc welding and manual welding the same place or the use of slag to protect it, but this is not a slag electrode coating, which is designed out of the melting flux. The flux system consists of a funnel filled with flux through a pipeline to be welded to the front. The second difference is not used electrode using wire, because the wire can be continuously sent; electrode, we gotta burn a welding electrode head gave a throw, and the operation was stopped, and then for electrode welding.

In this way, the first advantage is fully automated; second advantage, it is carried out under submerged arc welding, the heat exchange and so it is relatively strong protection performance, higher quality weld out; third advantage as submerged arc welding arc welding flux buried underneath, so it can use a large current, welding efficiency is relatively high, the recent progress of our country's natural gas pipeline project. After wire changed, with the delivery device and the wire coil wire, the wire is continuously sent, this welding process is continuous feeding of the wire and the solder to melt under the coverage of the particulate ignition of the arc, the welding wire, base material and flux melting and evaporation constitute part of a cavity, the cavity inside the arc is stable combustion, so call it submerged arc welding. Arc is buried inside the cavity. Pipe is a high-strength steel, this pipe prefabricated in the factory inside the first paragraph, and then get on the site, in the field welding, this pipeline in the factory production process is the use of submerged arc welding, submerged arc now has become, a double wire submerged arc welding, as well as multi-wire submerged arc welding, to further improve efficiency.