LSAW steel pipe heat treatment online and off-line

LSAW steel pipe online heat treatment:
After the steel pipe welding, using two groups or more intermediate ring induction heating equipment to the whole pipe heating, which in a short period of time to often required temperature 900 ~ 920 ℃, and heat preservation time, air cooling below 400 ℃ after normal cooling, make whole tube organizations to improve.

LSAW steel pipe offline often in the furnace heat treatment:
Straight seam steel pipe overall heat treatment device have chamber furnace and roller hearth furnace, using nitrogen or hydrogen nitrogen mixture gas as protective atmosphere, to achieve no oxidation or light condition. As a result of the chamber furnace production efficiency is low, now often use roller hearth heat treatment furnace in succession.Whole heat treatment features are: in the process, the wall inside there is no difference in temperature, won't produce residual stress, heating and holding time can be adjusted, to adapt to the complex heat treatment specification, also can use the computer for automatic control, but the roller-hearth furnace equipment complex, high cost of operation.

According to the production process, straight seam steel pipe can be divided into high frequency straight seam steel pipe and submerged arc welding straight seam steel pipe.Submerged arc welding and straight seam steel pipe according to the different forming methods is divided into UOE, RBE, JCOE steel pipes, etc.Which according to the purpose is different, and different production working procedure, after. (can be roughly divided into the scaffold tube, fluid pipe, wire casing, stent tube, guardrail tube etc) under the wing of bohai xiang straight seam steel pipe manufacturer to introduce one of the most common high frequency straight seam submerged arc weld steel pipe and straight seam steel pipe forming process and production process:
1. The plate used in the manufacture of large diameter submerged-arc welding straight seam steel pipe, steel plate into the production line after the first full plate ultrasonic inspection;

2. The edge milling: through the two edges of the steel plate edge milling machine double-sided milling, make it meet the requirements of plate, plate edge parallelism and groove shape;

3. The bending edge: the use of bending machine for plate bending, make the edge of curvature;

4. Molding: on the JCO forming machine bending of the plate after half after many step punching, pressure into a "J" shape, and the other half of the steel plate bending, same pressure into a "C" shape, eventually forming the opening "O" shape
5. Early welding: the forming of straight seam welded steel pipe joint with gas protection welding and continuous welding (MAG);

6. The welding: the columns more wire submerged arc welding wire (up to 4) in the straight seam welded steel pipe inside;

7. The welding: adopting many wire submerged arc welding of columns in the side of straight seam submerged arc welding steel pipe welding;

8. Ultrasonic inspection Ⅰ: inside and outside of straight seam welded steel pipe weld and weld on both sides of the base of 100% of the check;

9. X-ray Ⅰ: 100% of inside and outside weld X-ray industrial TV inspection, using image processing system to ensure the sensitivity of detection;
10. Hole enlargement of submerged arc welding and straight seam steel pipe length hole diameter in order to improve the size precision of steel tube, and improve the distribution of stress in steel tube;

11. Hydraulic pressure test: steel pipe after hydrostatic testing machine for hole enlargement by root inspection to ensure the test pressure of steel tube meet the standard requirements, the machine has the function of automatic recording and storing;

12. Chamfering: after the inspection of steel pipe to pipe processing, meet the requirements of tube end groove size;

13. The ultrasonic inspection Ⅱ: root by ultrasonic inspection to check again after the straight seam welded steel pipe in the hole diameter, water pressure may produce defects;

14. X-ray Ⅱ: for hole enlargement and after water pressure test of tube X-ray industrial TV inspection and pipe weld shooting;

15. The pipe magnetic powder inspection: check on this to find out the pipe defect;

16. Corrosion protection and coating: qualified steel pipe according to user requirements for corrosion protection and coating.

The requirement of the production line of galvanized steel pipe

Galvanized steel pipe to the requirement of the production line has a special, especially in the production environment, a good environment can help us better production, improve production efficiency and production quality, especially the galvanized steel pipe product of this need a stable environment.

Firstly, it shouled ensure the production line for process, equipment, heating, ventilation, drainage and other aspects of meticulous work, all work must be around the center of the quality of the galvanized steel pipe, as long as the quality assurance of galvanized steel pipe is good, all other factors we can all achieve.

Galvanization steel tube is very wide USES, especially in some natural gas pipeline, heating and so on need high strength and quality of pipeline industry, galvanized steel pipe has more obvious advantages than other steel pipe.Galvanized steel pipe used as water heating, generate a lot of rust scale, after a few years tube flow including not only pollute the sanitary ware, and mixed with smooth wall not breed bacteria, heavy metal corrosion caused by the water content is too high, cause serious damage to human body health.In order to make the galvanized steel pipe has a bright appearance and good corrosion resistance, in addition to the hot galvanizing technology on, also can use electric galvanizing technology.

Problems of steel pipe concrete structure

With excellent seismic performance is an important feature CFT for reasonable and safe to promote this type of structure in the earthquake zone, must be studied in depth the dynamic performance. However, recently studied abroad basically only ten experimental study on the dynamic performance of concrete pipe, still does not provide design formulas for calculation of the theoretical and specifications used; while relatively little research on steel concrete creep and fatigue properties, mainly in Experimental study mainly due to lack of reasonable design training methods, to a certain extent, restricted the steel concrete in high-rise buildings and railway bridges and other projects.

As a new steel concrete structure, China has not yet formulated the relevant steel and concrete structural fire design side provisions, so restrict the application of such structures. The structure has been built on, whether it is outsourced to concrete or coated with fire-resistant coating to ensure the safety and structural fire protection requirements are biased ten conservative and wasteful, the lack of scientific and unity. Therefore, on the basis of theoretical research and engineering practice, should be worked out for our country's steel concrete structure fire code as soon as possible.

N-point steel beams of concrete structures has been a focus of engineering applications and research. Although the design rules and many researchers recently made a number of nodes in the form, but it should be incorporated into the design rules as soon as possible, to provide a foundation for the promotion and application of steel pipe concrete structure. In addition, the dynamic performance of the node structure set up training as a key, relatively few studies of construction difficulties static properties.

Since most ordinary steel concrete structure is characterized by high Bian to a few anti-bearing capacity and good ductility, toughness, and can only be used as a pillar, not used as flexural members, it is of limited use. From the research literature at home and abroad to see prestressed steel concrete composite spatial structure and the advantages of prestressed concrete steel combination of technology, generally used only as a building pillars and arches of the bridge, not applied to the space frame or net title medium-sized racks space structure or member. If its in-depth study to ascertain the force deformation characteristics and failure mechanism of prestressed concrete steel structure, the establishment of computing theory and design methods, you can expand the applications of this new type of composite structure.

Spiral pipe welding technology

Because spiral pipe is with weld, so as to withstand the pressure of the liquid will be distributed on each side of the tube to enhance the strength of the tube. While generally large pipe if rolled steel plate welded directly straight, need a larger plate, greatly increasing the difficulty of making, it will use a large diameter spiral pipe spiral steel pipe (double-sided spiral submerged arc welded pipe) is a strip coil for raw materials, often warm extrusion molding, automatic double-sided submerged arc welding process wire spiral welded pipe joints. Another one is welded steel pipe, steel roll after it is welded to the vertical seam welds. Spiral welded pipe is welded steel spiral roll, seam spiral shape.
 
Welded steel pipe refers to a steel strip or plate bending round, square, etc. and then welded into the shape of the joint surface of the pipe. Welded steel pipe used is steel or steel billets. Since the 1930s, with the development of high-quality steel rolling production as well as the rapid development of welding and inspection technology, and constantly improve the quality of welds, welding steel pipe increasing varieties and specifications, and in more and more areas instead of non- pipe joints. Seamless steel pipe welded steel pipe is lower than cost, high production efficiency. Seamless steel pipe points, pipe. Points straight seam steel pipe, spiral steel pipe. Longitudinal points ERW (high frequency resistance welding), LSAW (LSAW). Spiral submerged arc welding process is (referred SSAW) and the difference is LSAW weld form, the difference is the difference with the ERW welding process, submerged arc welding (SAW) is to add media (wire, flux), ERW not needs, ERW is melted by frequency heating. Pipe according to production methods can be divided into two categories: seamless and welded steel pipe. Seamless steel pipe according to production methods can be divided into: hot-rolled seamless pipe, cold drawn tubes, precision steel tubes, thermal expansion, cold spinning tube and squeeze tubes. Seamless steel pipe with high-quality carbon steel or alloy steel, hot-rolled, cold-rolled (pull) of the points. Longitudinal production process is simple, high efficiency, low cost, rapid development. Spiral Welded Longitudinal generally higher than high, can narrow the billet production of large diameter pipe, you can also use the same width of the billet production of different pipe diameters. However, compared with the same length of straight pipe seam weld length of 30 to 100%, and lower production rate. Therefore, most of the smaller diameter pipe straight seam welded, large diameter spiral welded pipe for the most.
 
Currently spiral steel pipe products has a new product plastic composite pipe for hot-dip galvanized steel substrate, the powder coating technology in molten inner wall (wall when needed also) made of plastic coating steel pipe excellent performance. Compared with galvanized pipe, with anti-corrosion, no rust, no fouling, smooth smooth, clean, non-toxic, long life and other advantages. It is more than three times the life test, plastic composite pipe is galvanized pipe. Compared with the plastic pipe, with high mechanical strength, pressure, heat resistance and good.

The difference between the spiral welded and straight seam welding

Welded pipe is a gas pipeline in the common pipe, diameter greater than 426mm (or 508mm) of the pipe is generally known as large-diameter pipe, welded pipe in accordance with the way, can be divided into two kinds of spiral welded pipe and ERW.

Spiral welded pipe is carbon steel or low carbon alloy steel strip at a certain helix angle (also known as molding angle) rolled into a tube, and the tube seam welded steel, it can be used a narrower the production of large diameter steel pipe. Mainly spiral submerged arc welded spiral pipes (SSAW), widely used in the construction of various gas pipeline, with a diameter * thickness specifications indicated. There are one-sided spiral pipe welding and double-sided welding, pipe should ensure that hydrostatic test, weld tensile strength and performance of cold-formed to meet the requirements.

Longitudinal is hot rolled coil after molding machine, so that the coil is deformed into a sleek cylindrical, using high-frequency current skin effect and proximity effect or solder layer under the burning arc welding, so that the tube Edge heating and melting, and to a certain compressive force under the action of the fusion, the final cooling of the molding. Which use high-frequency current to melt the edge of the tube is called high-frequency welded pipe (ERW), using arc melting is called LSAW pipe (LSAW).

Longitudinal main raw material is low carbon steel hot rolled coil, hot-rolled, in petroleum, metallurgy, construction, mining, port, machinery and other industries widely used in oil and natural gas, low water gas transportation, mining fluid transport, belt conveyor roller, automotive transmission and so on.

Square tube welding deformation mode

In the welding deformation theory, we can know, the large size of the weld has led to the greater distortion, welding the same size, welding heat input is greater, will lead to large deformation, large long seam welding, welding deformation will be smaller, the weld asymmetry or asymmetrical arrangement of welding, weld deviation will cause more serious to severe deformation.

Welding specifications through process test and process analysis in determining square tube and rectangular tube butt weld double carbon dioxide gas shielded arc welding is a welding current of the first layer 200-250A, arc voltage of the second layer is 24-26V, its process requirements is the first layer of the weld must be able to ensure good welding, to form, welding current, arc voltage, wire feed speed and welding speed needs to be adjusted more equipment.

Welding sequence to reduce distortion rectangle, welding sequence should be in accordance with the following principles: start with the middle to both sides of the symmetrical hierarchical segmentation welding, it is a good diffusion and release stress, avoiding stress in welding production complex, through the swing welding, soldering at the beginning of the formation of plastic deformation of the narrow region only once, and because of the continuous weaving welding heat input so that the heating area is too large, the compression caused by the large plastic deformation, so large deformation of welding contraction, when welding STAGED because each section is very small, the heat is also very small, each layer is divided into several sections, so each jump welding welding, basically in the cold temperature field reconstruction, each in a narrow corresponding to
the plastic deformation of the longitudinal weld layered linear shrinkage is small, rather than by oscillating continuous-time filling the welding deformation.

ERW pipe flattening cracking analysis

ERW pipe flattening test weld cracking is mostly due to micro-cracks, brittle phase inclusions, coarse grains, caused by the band structure. Rational design of chemical composition, reducing inclusions in steel and ribbon organization, forming, welding and heat treatment process parameters were optimized control, can effectively reduce the weld cracking index inclusions and improve high-frequency ERW pipe weld cracking performance anti-crush. Ferrite / pearlite banded structure is hot-rolled steel in common a phenomenon banded structure has a great influence on the performance of steel, will decrease the ductility and toughness.

Low magnification analysis does not appear in the weld fracture. The microstructure can be judged by the organization does not have near the fracture due to welding temperature changes, which can determine the cause of the pipe welding process is not squashed fracture. Mechanical properties and the results of the analysis show that the spectral composition of the high-strength steel; plasticity respect, 31.25% of the coils of plastic does not meet the standards, 62.5% of the coils of plastic slightly larger than the standard one percentage point or exactly equal to the standard value , only 6.25% of the coil is greater than 30% of the plastic. Overall, high strength steel to, and low plasticity. According to the inclusion of ratings and scanning electron microscopy analysis can be seen, a lot of steel inclusions, and the level of more than 3.0. Serious is the reason for the non-metallic inclusions in a significant cracking. By microstructure analysis and scanning electron microscope analysis shows that strip banded serious, the highest level reached B4.0 level. Produce these banded structure, there are two reasons, one is not properly controlled during hot rolling process resulting in serious banded, the other is the inclusion became banded nucleation mother. On the microstructure, the hot rolling process control process is aggravated by improper banded structure of the main reasons, so the focus is how to eliminate banded controlled rolling process. From the above analysis shows, quantity and high levels of non-metallic inclusions (sulfides) and severe plastic strip banded structure is leading to the main reason for the low and cracking. So steelmaking process should reduce the content of non-metallic inclusions, especially sulfide. Hot rolling finishing temperature should be adjusted to reduce the banded structure.

Submerged arc welding pipe welding squeezing roller adjustment

In the production of high-frequency welded, the shaped state of the seam directly affect the quality of the welded tube, wherein the parallelism of the abutting surfaces of the welded joint is particularly important. The seam welding in the steel process, the main reduction by adjusting the squeezing rollers and the roller gap between the rollers to ensure that the degree of the parallel on two of the commissure. Welding the welding characteristics of the squeeze roll grooved extrusion pressing on the frame between the radii of the grooved rollers squeeze rolls other than about 10% larger, and therefore, the squeezing rollers and the roller surface of the outer pipe of circular cross section over creating a gap, the gap known as the "heel gap." In the actual molding, the pipe can not be perfectly circular cross-section. Under normal circumstances, due to the deformation of the strip edges is not sufficient, Peach section was easy, if not adjusted butt weld surface is not parallel to form a butt, seriously affecting the quality of the weld. If the upper squeeze roller and the other using the same pass squeeze roller radius reduction amount when the adjustment by the squeeze roller removes the V-shaped commissures, on the outer surface of the roller pressing the roller against the surface of the pipe will strongly on the tube surfaces likely to cause injuries, and the formation of a more serious V-shaped seam.

Pipe wall thickness, the higher the strength of the material, V-shaped when welding is not easy to eliminate the commissure. If the roller surface on the outside of the roll has caused a significant but still can not achieve an indentation shaped commissure I described adjustment has reached the limit, proceed to the next on the pressure roller will not only cause serious indentation, but also a more severe V-shaped butt seam. The ideal value of the roll gap with the tube wall thickness and strength of the various and different. For example, when the thin wall thickness generally requires the the roll gap is set smaller in order to increase the stability of welding. As the wall thickness is thick, even if the appropriate expansion of the roll gap, it will not affect the stability of welding. Therefore, when the thick-walled high-strength steel or molded in order to obtain greater "gap followed by" on the expansion of the roll gap and the practice, as long as it does not affect the stability of the expansion of a suitable welding.

In the high-frequency modulation type and welding pipe, through the contact surface and the heating mode and butt seam state relations analysis, using the adjustment of welding squeeze rollers roll gap and reduction methods, accurate and timely manner to ensure the steel plate welding edge welded to achieve a good state. When the I-shape commissure when instructions at this time in a substantially parallel state of the abutment surfaces during welding, does not require adjustment of the extrusion pressure roller; commissures when V-shaped abutment surfaces instructions at this time in the welding process, the lower portion of the first contact surface, can increase the amount of reduction rollers squeeze rolls to achieve an I-shaped state; when the inverted V-shaped commissures, the abutting surfaces described case the welding process, the upper surface of the first contact, by reducing squeeze roll reduction amount reaches the I-shaped state.

Straight seam welded pipe flaw detection methods and technical requirements

Magnetic flux leakage testing of high sensitivity, can well distinguish the pipe outer wall defects, but a long tube, large wall thickness of the pipe after degaussing magnetic flux leakage inspection to be done to deal with; eddy current flaw detection speed, but by the skin effect, the difficult to find defects in the depths of the workpiece; ultrasonic flaw penetrating ability, defect positioning accuracy, low cost, high speed, but testing operations to be coupled, the coupling in the northern winter environment welded easy to freeze, causing inconvenience to the inspection work . In the manufacture and use of welded pipe, the non-destructive testing is performed to ensure the weld quality is particularly important. Pipe commonly used non-destructive testing methods are: for more than 5 mm from the pipe surface offline whole tube of magnetic flux leakage testing, eddy current and ultrasonic testing; verify more than 5 mm from the surface of the pipe welding quality online magnetic flux leakage inspection and eddy current inspection; applicable in thick-walled pipe weld the whole tube offline ultrasonic flaw detection; verification thick-walled pipe welding quality ultrasonic flaw detection.

Refers to the magnetic flux leakage inspection of ferromagnetic material is magnetized, the surface and near-surface defects in material surface leakage magnetic field, discovered by detecting leakage field NDT techniques defects. Magnetic flux leakage inspection of the surface state of the pipe does not ask, detected a greater depth, are widely used in pipe detection abroad, especially oil with domestic pipe detection has also been widely used. When the magnetization is low, the leakage magnetic field is small, and increases slowly; When the magnetic flux density reaches about 80% of the saturation value, the peak of the defect with the increase of the leakage magnetic field the magnetization increases rapidly, but when a ferromagnetic material into the the magnetic saturation magnetization increases outside little influence on the magnetic field strength of the defect. Therefore, the magnetic circuit should be developed so that the material being tested as nearly saturation magnetization state. A huge influence on the direction of the leakage defects in the magnetic detection accuracy when the defect perpendicular to the main plane of the magnetization direction of the magnetic field, generated by the leakage magnetic field is the strongest. The same weakness leakage magnetic field maximum surface of the duct, and with increasing burial depth gradually decreases when the burial depth is sufficiently large, the leakage magnetic field will tend to zero. Defect size is also a great influence on the leakage magnetic field, the same width and the depth when the defect is not the same, with the increase of the leakage magnetic field to increase the depth of the defect in a certain range of the approximate linear relationship between the two.

For pipe weld often produce "inner burr adsorption", eddy current testing equipment often erroneously reported as defects. Frequently appeared in eddy current testing process glitch due to electromagnetic forces adsorbed on the seam, leaving the eddy current magnetic field exposure steel automatic degaussing device, there is no magnetic attraction after the glitch automatically fall, and then manually re-defect detection and no awkward questions displayed. Due to the skin effect, as the distance between the detection coil and the pipe is subject, the detection sensitivity is gradually reduced, so that, for the same size of the defect, as reflected in the pipe wall will be smaller than the amplitude of a signal tube wall defects on. Pipe full pipe eddy current testing equipment capacity in the probe and the inner surface of the outer surface of the pipe defects regard is determined by many factors, but the most important thing is dependent on the wall thickness of the pipe was seized and eddy current excitation frequency and magnetic saturation intensity ; the same time, the choice of instrumental parameters should consider the impact of the physical parameters of the subject to be welded conductivity and magnetic permeability, etc. of the eddy-current flaw detection precision.

Double-sided submerged arc automatic welding machine

Straight seam steel pipe double-sided submerged arc automatic welding machine can be divided into internal welding and outside welding of straight seam welded steel pipe

Straight seam steel pipe outside sided submerged arc welding machine, straight seam in the steel industry as "outside welding" outside, the so-called straight seam welded steel pipe refers to closely co-ordinated pre-process after welding, can be understood as follows: When the straight stitch After the pre-weld pipe from the welding process welding procedure is to be outside rather than inside the welding. The reason is: Whether straight seam welded steel pipe outside, or from physical deformation by heat pipe inside straight seam welded steel pipe will shadow, if the first outer seam welded straight seam steel pipe, the data can be the greatest degree of reduced physical deformation of straight pipe joints size. Straight pipe joints due to project needs, require a higher quality of welds, weld start working outside, you can ensure the greatest degree of straight seam welded steel pipe weld penetration resistance, straight seam steel pipe welds beautifully, and straight seam straightness of the linear weld pipe.

Straight seam steel-sided submerged arc welding inside, straight seam in the steel industry as "the weld." Straight seam steel tube welder, Lincoln uses the same equipment imported from Germany, and flux. Straight seam welded steel pipe is straight seam steel pipe welds in priority. The reason: it is not only difficult to weld, the weld requires the highest level of straight seam steel pipe weld inspection on this within the solder can be seen. Straight seam steel pipe welder at work within the current large degree of penetration depth, and less prone to the human eye. Seasoned team leader within the welder can be adjusted from a straight seam steel pipe weld television industry track, as well as outside the hot spot welds when welding from within, in order to make adjustments based on the size of the hot spot welding speeds. Steel-sided submerged arc welding using German into Lincoln automatic welding machine, straight seam welded steel pipe automatic welding flux using straight seam steel pipes imported from Germany, supporting internal and external welding flux, straight seam steel pipe welding equipment before working inside and outside of welding flux through the filter, the filter is too large particles, because when submerged arc flux, exceeding the size of the solder particles will affect straight seam steel pipe welds uniform cooling time, if not straight seam steel pipe welds standard time temperature range, the standard rate of cooling, are may affect the level of straight seam steel pipe welds NDT.

The importance of seamless tube end defect detection after welding

Seamless steel ingot made of perforated or solid through the capillary tube, and then by hot-rolled, cold-rolled or cold call is made. Seamless steel hollow section with a lot of fluids used for pipeline transportation, such as the transportation of oil, natural gas, gas, water and some solid materials, pipes and the like. Compared to other steel and solid steel bar, the same torsional strength in bending, lighter, 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

In addition, with seamless 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 manufacture steel. Steel or a variety of conventional weapons indispensable material, barrel, barrel, etc. to make steel. Steel shapes in different cross-sectional area can be divided into tube and shaped tubes. Since in circumference equal conditions, the largest area of ​​a circle with a circular tube can carry more fluid. Magnetic particle testing or penetrant testing of seamless steel tubes can be effectively found surface cracks, folding, heavy leather surface defects, hairline, pinholes. For ferromagnetic materials, magnetic particle testing method should be given priority, because of its high detection sensitivity; For non-ferromagnetic material, such as stainless steel seamless pipe, then using penetration testing method.

When both ends of the cut is less reserve margin, due to structural reasons, the detection device may not be effective at both ends of the detection head, and the tip is the most likely site of the presence of cracks or other defects. If the end of the cracks tend to have potential, weld heat affected during installation is also possible to make a potential crack. Therefore, it should be noted that after the detection of certain seamless steel butt area, to detect defects in the expansion pipe ends.

Oil casing and practical performance tests

Tubing and casing used in the oil and gas wells rely threaded steel pipe connected to the hundreds column, in the underground to the combined effects of various forces and subject to corrosive media, poor conditions of service as long as there is a steel pipe is a fault, it abandoned wells could cause huge economic losses. Therefore, the quality of oil casing pipe and threaded means quality, especially threaded quality is critical, requires inspection by the root, foolproof. Quality oil casing, in addition to the chemical composition, microstructure, mechanical properties, geometric dimensions and appearance quality assurance needs, the practical performance of the oil casing is of great importance. Because it is a concentrated expression of the above-mentioned quality of content, users are most worried about is performance factors, as well as oil and gas wells string design essential parameters and basis. With the development of oil and gas drilling industry, deep and ultra-deep growing number of bottom hole pressure and temperature rising, the coexistence of various corrosive media, making the oil casing of service environment is deteriorating. User according to API 5CT and oil, gas drilling actual needs, and constantly on the functional performance test oil casing made more and more urgent requirements.

Thousands of meters deep oil and gas wells in the drilling for oil, gas, oil must be hundreds of root screwed into the casing string to thousands of meters under the oil, gas wells. Oil casing in oil and gas wells to be affected by the combined effects of different variable load, different temperatures and corrosive media. The service is very complex conditions, bad. Correctness of the oil casing pipe and threaded connection string quality and is very critical, they are not only directly affect the sealing performance of the threaded connection string, but also directly affect the strength of the connection string in the thread and the oil, gas use lifetime. Is cementing casing pipe, one-time use. After cementing a permanent place on the ground is not made out. It points catheter surface casing, casing and production casing. The forces which are summarized as follows:

By axial tension caused by the weight of the role of the column itself, its size with the string tension diameter, wall thickness, and the total length of the size of the change. It can make a connection string in the thread slipping, can also make a column in the tube to take off. At the same time will reduce casing collapse resistance, especially in concentrated or ultra-deep well on the small size of the casing greater impact. To withstand the well bore instability in the underground rock formations such as easy to collapse, creeping rock salt formation and expansion, as well as water and mud endures pressure. Especially to withstand rock or rock crawling body to move a huge squeeze pressure. This external pressure can lead to casing collapse, especially caused by oil casing fall. Casing to resist the internal pressure inside the pipe mud, water, oil or gas column. Especially in the well or well kick off. The inner casing pressure is even greater, often burst failure occurs at this time. However, under the pressure of the inner casing, tubing string threaded connection strength will be raised.

Galvanized seamless tube process

Zinc is soluble in acid, can also be dissolved in alkali, so called amphoteric metals. Zinc hardly changed in the dry air. In humid air, the zinc surface will generate basic zinc carbonate film. Containing sulfur dioxide, hydrogen sulfide and marine atmosphere, zinc corrosion resistance is poor, especially in the hot and humid atmosphere containing organic acid, the zinc coating can easily be corroded. On steel substrate, the zinc coating are anodic coating, it is mainly used to prevent corrosion of iron and steel, the merits of its relationship with the protective properties of the coating thickness is very big. After passivation of zinc coating, dyeing or coating protective agent, can significantly improve its protective and decorative. In recent years, with the development of galvanizing process, using high-performance zinc brightener, galvanized from mere protection purposes ingress protection - decorative applications.

Zinc coating process:
1, dehydroepiandrosterone
2, passivation
3, coloring

Galvanized seamless tube process include: original board ready → plated hot dip after treatment → finished product inspection before plating process. Accordance with the customary pre-plating treatment is often based on different methods of the hot dip galvanizing process is divided into the line and the line outside the annealing annealing two categories.

Outside the line annealing: Before hot-rolled or cold-rolled steel sheet is hot-dip galvanizing operations into the line, the first pumping hearth or hood-type annealing furnace annealing furnace recrystallization annealing, so that the line does not exist galvanized the annealing process. Before the hot-dip galvanized steel must maintain a presence of dirt, oxide and other active surface clean pure iron. This method is for the method of pickling annealed to remove surface scale, and then coated with a layer protected by a zinc chloride or zinc chloride, and a mixed solvent consisting of the composition, thereby preventing re-oxidation of the steel sheet .

In-line annealing: is provided directly by the cold-or hot-rolled coil plant as raw hot galvanized plate, protecting the gas line in the hot dip galvanizing operations recrystallization annealing.

Seamless casing pipe process

Seamless casing pipe process: physical and chemical test tube into the factory cut length → pickling → Check → heating → grinding → pickling → Check perforation cleanup → annealing → phosphide saponification → drawing → straightening → NDT Automation Painted → bundling package → storage.

Ingredients request
Because of the non-metallic inclusions OCTG, gas content and other requirements more stringent, while the chemical composition requirements, the lower S, P content requirements; thus requiring the original wood materials into the furnace and pouring system dry, clean, good baked into the furnace steel material requirements including S, low P content. According to the above requirements, develop ingredients structure: 45% ~ 60% iron + iron, 40% to 55% of high quality scrap (low phosphorus), slag (lime) 150 kg / furnace.

EAF process control
Electric control is the focus of the pre-oxidation do to P operations. Made good foaming slag, oxidation endpoint carbon> 0.10%, carried out during the pre-deoxy-manganese alloy steel used in the steel-third of the time to add a little stream with steel Al blocks. Should use low-phosphorus alloys, manganese alloys alloying operations.

Refining Process Control
Because electric furnace process control better, refining furnace slag in place good fluidity, deep-deoxy change slag refining process faster, adjusted by the content of the slag condition, slag basicity average of 3.5, Σ (FeO) ≤0.5%, white residue retention time in 30 min or more, deoxy-sufficient, smelting ideal composition control. Contents of the other residual elements Zn, Pb, Sb, Cu, As, Sn, Bi, etc. are ≤0.006%. LF out of the top steel feeding Ca-Si-wire operation, carried out after VD vacuum treatment of steel, the vacuum (<67 Pa) hold time> 15 min, piercing. After the soft argon no less than 10 min, further removal of the steel gas inclusions.

Casting Process Control
Casting process using full protection, low superheat pouring tundish high level and the constant pull speed operation, reduced inclusions in steel content. Tundish superheat were controlled within 25 ℃, the casting speed steady at 0.65m / min; using high quality powder and mold electromagnetic stirring technology, help to improve the physical quality of the slab to prevent all kinds of surface defects and low magnification produce. If the casting machine two cold water properly controlled, can cause thermal stress in the uneven distribution of high-temperature range, or straightening temperature is brittle temperature range, leaving the slab surface cracks. casing pipe brittle temperature range appear in the third 750 ~ 920 ℃. For this purpose two weak cold cold adopted to ensure the straightening temperature> 920 ℃, to prevent stress cracks.

Rolling process control
To make the performance of hot-rolled steel tube wells meet API specifications of steel, hot-rolled steel tube must be prepared tissue. Therefore, the provisions of the slab is heated evenly, open rolling temperature control in 1150 ~ 1220 ℃, rolling rhythm control is good, the finish rolling temperature at 920 ~ 950 ℃.

The difference between cold-rolled steel and hot rolled steel

The cold mechanical properties of hot rolled steel sheet is less than the cold rolled, but also inferior forging, but has good toughness and ductility cold-rolled steel sheet due to a certain degree of hardening, low toughness, but can achieve a better yield than prone to accidents and other parts for cold-formed spring, and because the yield point closer to the tensile strength, of course, there is no danger of predictability in the load exceeds the allowable load.

The difference between cold-rolled steel and hot rolled steel
1) cold plate surface without the use of cold rolling and processing scale, good quality. Hot plate with hot ligation work surface oxide, thickness have under poor.
2) hot-rolled sheet toughness and surface roughness of the poor, lower prices, and cold rolled sheet stretching, good toughness, but more expensive.
3) rolled into cold-rolled and hot-rolled, in order to distinguish between the recrystallization temperature point.
4) cold-rolled: generally used for the production of cold-rolled strip, its high rolling speed, hot: hot forging temperature and the temperature of similar
5) Do not plated hot rolling plate surface into a dark brown, not plated cold rolled plate surface is the gray. Plating can be distinguished from the smoothness of the surface smoothness of cold rolled plate is higher than the hot rolling plate.

Steel pipe hardness knowledge

The hardness of the material to resist a hard object represents pressed into the surface of its capabilities. It is one of the important performance indicators of metallic materials. The higher general hardness, wear resistance, the better. Common indicators hardness Brinell hardness, Rockwell hardness and Vickers hardness.

1. Brinell hardness (HB)
To a certain load (usually 3000kg) to a certain size (diameter typically 10mm) hardened steel ball pressed into the surface of the material, for a period of time to go after load, the ratio of the area of the load and its indentation, that is Brinell hardness value (HB), units of kgf / mm2 (N / mm2).

2. Rockwell hardness (HR)
When HB> 450 or the sample is too small, can not be used Brinell hardness test and switched to a Rockwell hardness measurement. It is the apex angle of 120 ° with a cone or a diamond 1.59,3.18mm diameter steel ball pressed into a load at a certain surface of the material, determined by the depth of the indentation in the material hardness. Depending on the hardness of the test material, three different sub-scale is expressed: HRA: 60kg load and the use of the diamond is pressed into the filter cone hardness obtained high hardness material (such as cemented carbide, etc.) is used. HRB: is the use of 100kg load and 1.58mm diameter hardened steel ball, hardness obtained for the lower hardness of the material (e.g. anneal steel, cast iron, etc.). HRC: is the use of a diamond cone and a 150kg load hardness obtained is pressed into the high hardness material (such as hardened steel, etc.) is used.

3. Vickers hardness (HV) with 120kg load, and an apex angle of less than 136 ° square cone diamond is pressed into the material is pressed into the surface of the material divided by the surface area of ??the indentation load value with the pits, i.e. Vickers hardness HV value (kgf / mm2).

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Perforation of square tube

Square tube commonly used in various building structures and engineering structures such as beams, bridges, transmission towers, material handling equipment, ships, industrial furnace, reaction tower, container frame and warehouse shelves and other construction steel - square tube in the construction industry plays a very important role, the majority of builders and building materials has always been a topic of concern. Many of square tube defects resulting in perforation, so the tube power transfer process is the production of a key square tube procedure.

Many of square tube defects resulting in perforation, so the tube power transfer process is the production of a key square tube procedure. Perforation main difficulty lies in the low alloy high perforation performance, when necessary in order to ensure the quality of the deformation parameters of rational choice perforation. Small amount of compression will cause perforation process is unstable, so the critical amount of compression former child should head the amount of compression is generally set at about seven percent, otherwise it will not bite, even before moving to increase or card. Increasing the amount of compression of the front of the plug will form the inside of the bore and Chen Sheng defects. So if you want to overcome the problem, then the tube also centering, centering empty and depth to compare based on other steels.

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Steel tube temperature control

Straight seam welded steel pipe secondary effects of high frequency eddy current temperature by thermal power, according to the formula, the impact of high-frequency eddy current frequency by secondary thermal power, thermal power and eddy current is proportional to the square of the frequency of encouragement; and encourage current frequency but also by encourage the voltage, current and capacitance, inductance. Frequency straight seam steel encouragement and encouragement circuit capacitance, inductance is proportional to the square root, perhaps with the square root of the voltage, current, just change the circuit capacitance, inductance, or voltage, current, frequency can be altered to encourage the size, in order to reach control means soldering temperatures. On low-carbon steel, welding temperature control in 1250 ~ 1460 ℃, can be satisfied with the tube wall thickness 3 ~ 5mm penetration request. In addition, the soldering temperature welding speed can also be achieved through conditioning. Straight pipe joints should be fixed as close to the high-frequency induction loop squeeze roll position. If the squeeze roll farther away from the induction coil, ineffective heating work longer, wider heat-affected zone, weld strength landing; conversely, lack of weld edge heating, extrusion molding after bad. High-frequency straight seam steel pipe welded pipe unit into the strip, the multi-channel roll rolling, and gradually rolled strip steel, round tube there is ashamed constitute gap adjustment reduction squeeze rollers, so that the weld gap rests in the 1 ~ 3mm, and weld the ends flush.