Search Results

Characteristics of seamless steel pipe products: 1, chemical analysis: the chemical composition of the chemical analysis, chemical composition in line with the standard requirements. 2. Air pressure. The pressure test of pressure seamless steel pipe by the pressure test, in the specified pressure value does not keep not less than 5 seconds, not leak, conventional supply water pressure test for 2.45MPa. pressure test for P=0.5MPAa. 3, corrosion test: the industrial corrosion resistant seamless steel pipe is in accordance with the standard or the two sides of the agreement of the corrosion method of seamless steel pipe corrosion resistance test, no intergranular corrosion tendency. 4, process performance test: flattening test. Tensile test. Impact test. Flaring test. Hardness test. Metallographic test. Bending test. Nondestructive testing (including eddy current flaw. X-ray and ultrasonic inspection). 5, the implementation of standards: China: GB/T14975-2002.GB/T14976-2002.GB13296-91.GB9948-88.GB5310-95.GB2270-80 United States: A213/A213-99a.ASTN312/A312M-00b.ASTM A269-00.ASTMA511-96. ASTM Japan: JIS3463.JIS3446.JIS3448.JIS3459 Germany: characteristics of DIN2462 seamless steel pipe products.

Most metals and alloys at high temperatures can not react with nitrogen at high temperatures, but atomic nitrogen can react with many steel. And penetrate into steel to form a brittle nitride surface layer. Iron, aluminum, titanium, chromium and other alloying elements may be involved in these reactions. The main source of atomic nitrogen is the decomposition of ammonia. Ammonia converter, ammonia plant production heater and in 371 degrees ~593 DEG C, the nitriding furnace of operation under a high pressure ~10.5Kg/mm2 are ammonia decomposition. In the atmosphere, appearance of chromium carbide in low chromium steels. It may subject to corrosion of nitrogen atoms and chromium nitride, and the release of carbon and hydrogen methane generation, as mentioned above, this may generate white and crack, or one of them. But the chromium content of more than 12%, the carbide of these steels is more stable than chromium nitride, so the reaction in front will not appear, so the stainless steel tube is now used in the high temperature environment of hot ammonia. Hydrogen corrosion may occur in ammonia synthesis, hydrogen desulfurization and hydrogenation reaction and petroleum refining unit. Carbon steel is not suitable for high pressure hydrogen device with 232 degree centigrade. Hydrogen diffusion into the steel, and the grain boundary or zone of pearlite and cementite reaction and produce methane, methane (gas) would not spread to outside the steel and gather together, white and crack or one of them in the metal. To prevent the generation of methane, cementite must be replaced by stable carbide and steel must be added to the chromium, vanadium, titanium or drill. Data indicate that increasing chromium content allows higher operating temperature and hydrogen partial pressure of formation of chromium carbide in the steel, and it meets the hydrogen is stable. Under harsh operating conditions (temperature above 593 DEG C) and chromium content greater than 12% chromium steel and austenitic stainless steel pipe in the known all application are resistant to stress corrosion. The state of the stainless steel tube in ammonia is determined by the temperature, pressure, gas concentration and the content of chromium and nickel. The experimental results show that the corrosion rate of ferrite or martensite stainless steel tube is higher than that of austenitic stainless steel, and the corrosion resistance of the latter is better. Corrosion rate increases with increasing content. Austenitic stainless steel tube in high temperature halogen vapor, corrosion is very serious, the corrosion of fluorine than chlorine. For high R Ni-C stainless steel pipe, the upper limit of the temperature in the dry gas, the fluorine is 249, and the chlorine is 316.

Austenitic stainless steel with solid solution treatment to soften the generally stainless steel pipe is heated to 950 to 1150 DEG C, heat preservation period of time, so as to fully uniformly dissolved in austenite and rapid quenching cooling water, carbon and other alloy elements to less precipitation, pure austenite carbides and various alloying elements, called solid solution treatment. The effect of solution treatment was 3. The stainless steel pipe with uniform microstructure and composition, the raw material is particularly important, because segments of hot-rolled wire rod rolling temperature and cooling rate, resulting in inconsistent organizational structure. Atomic activity is increased under high temperature, dissolve sigma phase, chemical composition tends to be uniform, fast cooling after won a homogeneous single-phase organization. The elimination of work hardening, in order to continue cold processing. Through solid solution treatment, skew lattice restoration, elongated and broken grains recrystallize, eliminate stress, steel pipe tensile strength decreased, the elongation at break increased. The corrosion resistance of stainless steel in the natural recovery. Due to the cold processing of carbide precipitation, crystal lattice defects, so that the corrosion resistance of stainless steel. Recovery of corrosion resistance of steel pipe after solid solution treatment to the best state. For stainless steel pipes, the 3 elements of solid solution treatment are temperature, holding time and cooling rate. The solid solution temperature is mainly determined by the chemical composition. Generally speaking, the types of alloying elements, the content of high grade, solid solution temperature should be increased accordingly. In particular, manganese, molybdenum, nickel, silicon content of high steel, only to increase the solid solution temperature, so that it fully dissolved in order to achieve the softening effect. But stabilized steel, such as 1Cr18Ni9Ti, the solid solution temperature is high, the carbide of the stable chemical elements fully dissolved in the austenite, in the subsequent cooling will be in the form of Cr23C6 in the grain boundary precipitation, resulting in intergranular corrosion. In order to make the stable element of carbide (TiC and NbC) does not decompose, does not dissolve, generally uses the lower solid solution temperature.

First, the magnetic test is the most simple method to distinguish between annealed austenitic stainless steel and ferritic stainless steel pipe. Non magnetic steel is austenitic stainless steel, but the high pressure after cold working with mild magnetic; and pure chromium steels and low alloy steels is strong magnetic steel. Two. One of the remarkable characteristics of the stainless steel pipes is that the corrosion resistance of concentrated nitric acid and dilute nitric acid is inherent. This property makes it easy to distinguish from most other metals or alloys. However, the high carbon type 420 and 440 steel in the nitric acid point test is slightly affected by corrosion, non-ferrous metals encountered when concentrated nitric acid will be corroded. And dilute nitric acid has strong corrosive to carbon steel. Third, sulfuric acid copper sulfate test copper test is fast to distinguish between ordinary carbon steel and all kinds of stainless steel pipe is the most simple method. The concentration of copper sulfate solution was 5~10%. Before the test, the test area should be thoroughly cleaned of oil or various impurities, and polishing cloth polishing a small region, then dropping to clean up after the regional drop note copper sulfate solution. Ordinary carbon steel or iron within a few seconds it will form a layer on the surface of copper, and the surface of the stainless steel does not produce copper precipitation or copper color. Four, sulfuric acid test sulfuric acid immersion stainless steel pipes test can be 302 and 316 and 317 and 304 to distinguish. The cutting edge of the sample should be finely ground, then the volume concentration of 20~30%, temperature of 60~66 c c c (1.42) in the proportion of clean and passivation for half an hour. The volume concentration of sulfuric acid test solution was 10%, heated to 71 degrees when.302 and 304 stainless steel immersed in the hot solution, rapid corrosion and a large number of bubbles, sample within a few minutes of black; and 316 and 317 steel specimens is not subject to corrosion or reaction is very slow (bubble) sample in 10 to 15 minutes do not change color. It can make the test more accurate if the test specimen with known composition is used to make an approximate comparison.

Stainless steel elbow classification: according to the angle, there are 45 degree stainless steel elbow and 90 degree stainless steel elbow, 180 degree stainless steel elbow three most commonly used, in addition, according to the needs of the project also includes 60 degree stainless steel elbow and other non normal angle bend. Stainless steel elbow material: cast iron, stainless steel, alloy steel, cast iron and carbon steel can be calcined. The connection between the pipe and the pipe is: direct welding (the most common way) flange connection, threaded connection with socket connection, etc.. According to the production process can be pided into: stainless steel welding elbow, stainless steel stamping elbow, stainless steel casting elbow, etc.. Pipe fitting used in the installation of a pipe, for the connection of the pipe bend. Purpose: connect two nominal diameter of the same or different pipe, so that the pipeline for a certain angle turn. 1 material is pided into: carbon steel, cast steel, alloy steel, stainless steel, copper, aluminum alloy, etc.. (but the wooden factory is pure forging) 2 pision of the production method can be pided into: pushing, pressing, forging, casting, etc.. (now it’s usually pure). 3 makes the standard can be pided into: GB, standard, water, electricity, American Standard German standard, Japanese standard etc.. 4 according to its radius of curvature to pide: can be pided into long radius stainless steel elbow and short radius stainless steel elbow. Long radius stainless steel elbow refers to its radius of curvature is equal to 1.5 times the diameter of the tube, that is, R=1.5D. Short radius stainless steel elbow means that the radius of curvature is equal to the outer diameter of the pipe, that is, R=1.0D. (D is the diameter of the stainless steel elbow, R is the radius of curvature). 5 if according to the pressure level, about 17 kinds, and American Standard pipe is the same: sch5s, sch10s, sch10, sch20, sch30, sch40s, STD, sch40, sch60, sch80s, XS; sch80, SCH100, sch120, sch140, sch160, XXS. The most commonly used is two kinds of STD and XS. Technical requirements: 1 because most of fittings for welding, in order to improve the welding quality, end vehicles into the groove, leave a certain angle, with boundary, this requirement is quite strict, edge thick, at an angle of number and range of deviation is provided. The surface quality and mechanical properties are basically the same as that of the tube. In order to convenient welding, steel pipe and the connecting pipe are the same. 2 The pipe fitting should be through the surface treatment, the inner and outer surface of the oxide scale through shot blasting, and then coated with anticorrosive paint. This is for export needs, in addition, in the country is to facilitate the transport to prevent rust oxidation, to do this work. 3 is the packaging requirements for small pipes, such as export, you need to do wooden box, about 1 cubic meter, this provision in the case the number of stainless steel elbows about not more than a ton, the standard allows the suit, large sets of small, but the total weight usually do not more than 1 ton. For large y to a single package, like 24 “must be a single package. The other is labeled packaging, labeling is to indicate size, number, batch number, manufacturer trademark etc.

304 stainless steel is a kind of universal, it widely used for requirements of making good comprehensive properties, resistance to corrosion and formability of equipment and parts. 301 stainless steel in the deformation, showing a clear working hardening phenomenon, is used to require a variety of high strength occasions. 302 stainless steel, in essence, is a variant of the 304 stainless steel with a higher carbon content, which can be obtained by cold rolling. 302B is a kind of stainless steel with high silicon content. It has high temperature oxidation resistance. 303 and 303 se is respectively containing sulfur and selenium free cutting stainless steel, used mainly for easy cutting and table and high degree. 303 stainless steel is also used for making machine parts of hot upsetting, because under this kind of condition, the stainless steel has good hot workability. 304L is a variant of the 304 stainless steel tube with a low carbon content, which is used for welding. The lower carbon content makes the carbide precipitates in the heat affected zone near the weld to the least, and the carbide precipitates may lead to intergranular corrosion in some environments. 304N is a nitrogen containing stainless steel, nitrogen is added to improve the strength of steel. 305 and 384 stainless steel containing high nickel, the low rate of hardening of the processing, suitable for various occasions of high requirements for cold forming. 308 stainless steel for the production of electrode. 309, 314, 310 and 330 stainless steel nickel, chromium content is relatively high, in order to improve the steel at high temperature oxidation resistance and creep strength. While 30S5 and 310S are 309 and 310 stainless steel variants, the difference is that the carbon content is low, in order to make the weld near the carbide reduced to the least. 330 stainless steel has a particularly high anti carburizing capacity and thermal shock resistance. 316 and 317 type stainless steel containing aluminum, and therefore in the marine and chemical industry in the environment of the point of corrosion resistance of the earth is better than 304 stainless steel. Among them, type 316 stainless steel by variants including low carbon stainless steel 316L, nitrogen containing high strength stainless steel 316N and high sulfur free cutting stainless steel 316F. 321, 347 and 348, respectively, with titanium, niobium and tantalum, niobium stabilized stainless steel, suitable for the use of welding components at high temperature. 348 is a kind of stainless steel, which is suitable for nuclear power industry, and has a certain limit to the volume of tantalum and diamond.

One: chemical and petrochemical processing industry in this area involves a wide range, the conditions of complex, perse media, but also the use of duplex stainless steel earlier and more areas. At present 20 million, large and multiple sets of 10 million tons below in small methanol synthesis reaction is the catalyst pipes are using duplex stainless steel, large and medium-sized device adopts 2205 pipe, using imported pipe is more, small device the domestic 18-5Mo steel pipe. Using the domestic similar DP3 steel 00C25Ni7Mo3WCuN duplex stainless steel do seawater cooler pipe of ethylene plant in Sinopec Shanghai Petrochemical Company catalyst regeneration cooler, water inlet temperature of 40t has been used intermittently for 15 years, the effect is very good. Pulverized coal gasification plant of Henan coal chemical plant the number of cooler are imported 2205 steel pipe manufacturing. In the next 5 years, China petrochemical industry rapid development, construction, the proposed large-scale petrochemical project popularity nationwide, according to the current understanding of the construction and planning of the construction project, and 2005 the petrochemical industries of stainless steel pipe annual demand of about 1.6 million T with the improvement of domestic stainless steel product quality and special grades of product development, application in the future 5 years in China petrochemical industry of stainless steel will continue to increase. 2: duplex stainless steel pipe for petroleum and natural gas industries this is one of the main areas of the abroad application of duplex stainless steel, the laying of oil and gas transportation pipeline has been 1000km domestic only oilfield of the South China Sea and the use of a small amount, all of the imported. In addition, the west east gas transmission project in the west of the Tarim basin gas pipeline to consider the use of duplex stainless steel pipe, the domestic production and production conditions. Oil refining industry is the earliest use made of duplex stainless steel department, Nanjing, Zhenhai, Tianjin, Jinan and other refining and chemical company are more concentrated in often the top lining of vacuum distillation tower (or composite panel) tower components, air cooler and water coolers and other, the longest has been used for 20 years. The production of small size duplex stainless steel seamless pipe, the domestic has been relatively mature, the current urgent need to solve the larger size of seamless pipe and welded pipe production, production processes to be developed. In addition, how to double the price of stainless steel products down, but also a matter of domestic development of duplex stainless steel. Although expand production, production of marketable products is very important, can not be ignored to make use of the new technology and new process, using molybdenum oxide as a substitute of metal molybdenum, nickel oxide instead of metal nickel, reduce smelting costs, promote the use of duplex stainless steel casting technology, to increase the rate of finished products. Three: duplex stainless steel pipe in chemical fertilizer industry application of chemical fertilizer industry by domestic 0Cr25Ni6Mo3CuN aging strengthening duplex stainless steel, using the wear and corrosion resistance, for urea plant process pipelines of various specifications of the high pressure stop valve etc., the effect is good. Currently used in urea production of CO2 stripping process and ammonia stripping is the high alloy austenitic stainless steel, and titanium, China has begun to in large scale urea plant of ammonium carbamate pump with high chromium centrifugal duplex stainless steel to replace the urea grade 316L stainless steel. Since the 1980s, the engineering company to develop the aces urea process gas stripper, ammonium carbamate condenser and high pressure decomposition tower and three sets of high voltage equipment are used DP-12 containing trace of tungsten and copper 25Cr-7Ni-3Mo-N steel) and R-500Cr25Ni6.5Mo1.5N duplex stainless steel. The former is used to manufacture gas provided, condensing pipe, pipe decomposition and pipeline transportation,, the latter used for high voltage equipment shell. 2005 the petrochemical industries of stainless steel pipe the annual demand of about 7800t is expected in 2010 will increase to 9600t stainless steel the national code of some 10 years without amendment and revision of national standard must consider the duplex stainless steel nano scale and the revised. Abroad for the total yield 80%2205 grades specially formulated products factory inspection of user acceptance specification, also should consider the introduction and absorption, emptiness of the existing test methods and standards to promote duplex stainless steel production and order. In addition, vigorously develop the duplex stainless steel industrial and commercial potential market (such as the construction industry – structure, bridge, concrete with steel, such as manufacturing industry containers, tanks, chemical transport ship, speedboat, tanker; and if the household facilities – high level water tank, an electric water heater, live real water auto pipe) and developed, probation, promotion developed abroad and suitable for national conditions of our country (lack of nickel and chromium) some new varieties (such as low nickel saving diduplex stainless steel) believe that the promotion of duplex stainless steel has a very broad application prospects.

Compression spring constitutive relationship, bolt pretension and flange contact with consideration of the nonlinearity of the gasket. From the results of finite element calculation from both inside and outside edge of the flange axial displacement difference (i.e. relative deflection) is then pided by the inner and outer flange diameter difference. Will take over the combined flange, gasket, bolt as a system of pre tightening, operating, 3-D nonlinear finite element simulation design and hydrostatic test condition and to the integrity and tightness was evaluated. The conclusion is drawn as follows: 1 the selection of bolt preload is very important. One of the feasible methods is to select the proper preload by the Water formula and the finite element calculation and its strength and seal, and the 2 combined flange stress has similar distribution rule under different working conditions. Stress along the circumference of the flange to cyclical changes, the maximum stress discontinuities on the structure of the two flange connection, the flange stress strength evaluation; 3 due to the deflection of the flange bolts happen to combined tension and bending deformation. At the same time, there axial tensile stress and bending stress, and bending force can not be ignored; the gasket stress along the circumferential direction with only minor fluctuations, along the width from the inside to the outside gradually increases, this is due to the flange of the stiffness is much larger than that of the gasket, and the occurrence of deflection caused by flange 4 larger diameter, angle is large, and angle with pressure increase and change. The greater the flange angle, the more uneven distribution of the gasket stress along the width of the gasket, resulting in the narrow width of the effective seal, and even the outer side of the gasket. Therefore, the assessment of flange sealing need to be investigated from two aspects of the gasket stress and flange angle. Flange sealing rely solely on the analysis is not enough, still need to test, test leak rate is within the allowable range; 5 phosgene absorption tower combined flange at low temperature work has not yet been considered in cold shrinkage, temperature and low temperature performance data, wait for the following research. The flange gasket under three working conditions of operation, design and hydrostatic test rap values and 2.52.75 4.125MPa according to the calculation and DN200 flange gasket under various conditions of minimum pressure stress the absolute value for the minimum pressure of 20.5MPaDN600 flange gasket stress absolute value respectively when fumed over pumping values, respectively. According to this criterion, indicating that the combination flange can meet the general requirements of the seal. Flange angle deflection due to the three coordination deformation by 2010 ASME VIII a stiffness refers to the number and limited angular rotation of flange bending of bending deformation occurs in the bolt assembly load, internal pressure (operation) and a gasket counter force under the action of the flange body, a gasket non-uniform compression and bolts. For integral flange and angle limit of not more than 0.3 on flange rotation limit, the appearance is on the body of the flange bending stiffness is proposed, but the fundamental purpose is to guarantee the close of the flange; because of the greater the corner flange, gasket along the width of the pressure should stress distribution is not uniform, and even lead to the outboard gasket stress and crushing, the effective sealing width, increase the leakage rate. Therefore, the flange seal must be guaranteed from two aspects of the limitation of the gasket stress and the flange angle. Table 23 lists the corner of the combined flange under different conditions.

Tee pipe fittings of material selection Using hot drawing skill produces in the process of tee, the original data of metallographic arrangement, impact strength, patience and weldability of parameters will be the base attack a repeat of the heat change. Selected for this demand information is not as long as excellent high temperature plasticity, easy to deformation processing; Together on the premise of meet the weldability, it is necessary to have good hardenability, to ensure that the tee after proper heat treatment, can make its connected with the main pipe with fundamental equal strong patience and excellent weldability, this is the basic demand for hot drawing tee selection. Excellent weldability, suitable hardenability, high temperature plastic, after hot working with high strong patience is the basic principle of hot drawing tee data selection, reasonable disposal of the several aspects of necessary. 1. The large-diameter molding and high temperature plasticity Tee pipe fittings production process essence is the high temperature hot working again for data process, data in high temperature conditions should have excellent plasticity, easy to deformation processing; Its formability, besides is conditioned by the mold material of high temperature plastic deformation of tee pipe fittings processing has a great influence, it was to hot tee deformation processing temperature pull the skills of the root, also avoid tee pipe fittings in the process of forming crack controlled according to the shortcomings. Data of high temperature plastic stand or fall reflects this kind of material at high temperature of plastic bump, shorten the section of steel rate one temperature curve is an important physical parameter of paint materials high temperature delay plastic. Containing niobium (Nb) steel in the austenite of low temperature zone and high temperature low temperature zone + ferrite austenite have plastic drop in appearance, the former with niobium compound in austenite in low temperature zone along the austenite grain boundary to separate, the latter with the high low temperature zone + ferrite austenite occur along austenite grain boundary proeutectoid ferrite. 2. Hardenability and low carbon content Tee from both at home and abroad indicate that natural gas transport pipeline with WPHY70 produce high strength, large diameter tee skill is not very sophisticated, thus complete the X60 tee pipe fittings to WPHY70 tee pipe fittings production skills to break has important practical significance. The strength of the hot drawing tee is done through quenching + back to fiery disposition skills, both the original data after quenching cooling quenching arrangement, the amount of satisfied by fiery disposition, tee intensity reached WPHY70 grade of steel demand. The higher the data hardenability and the higher the strength after quenching, improve the hardenability, it needs to add endowment guess C, Mn, Cr, Ni, Mo, Nb, V and affect the hardenability of alloying elements. But, although the increase of the content of alloy elements, improve the hardenability, but together can make the data of carbon equivalent, weldable function. Therefore, hardenability, appropriate low carbon equivalent is the first question of WPHY70 tee selection. Under the condition of the goods, to satisfied outdoor harsh welding skill requirements, line pipe carbon equivalent control in C.. 0.40 or less, fittings, commodities carbon equivalent control in G. Below 0.44 or less. Far low carbon equivalent of parent metal contained in C, Mn, Cr, Ni, Mo, Nb, V, etc on the hardenability dedication larger alloy element content is very low, small data hardenability coefficient, obviously, in this case, the weak hardenability steel just relying on the progress hardenability high strength is relatively difficult to ensure that the tee. Metallographic arrangement is the main factor resolution steel mechanics performance, metallographic arrange varieties and amount of different, led to the difference between its mechanical performance. Weak hardenability steel can use quenching after many subtle quenching intensity of arrangement for progress. Change of quenching medium, add phase change super-cooling degree, in order to obtain more martensite and bainite is arranged, and then advances the 3-way intensity. Domestic tee pipe fittings of traditional material thinking is based on the bag yesterday of energy such as electricity, chemical industry pipeline and equipped with the special needs of the warp and woof of above, mostly in alloy steel, heat-resistant steel, high manganese steel and general carbon steel is given priority to, such as power plant main steam control path using tee pipe fitting material for 12 crlnovp22 heat-resisting steel, general pipe tee pipe material selection for the 20, 209, Q345 steel, corrosive environment with 306 l, etc. The connotation of the traditional material tensile strength, bending strength, patience and other mechanical performance index and weldability and oil and gas pipeline with control steel has bigger distance, three general steel 20, 209, general pipeline Q345 steel not only data such as strong patience is low, its weldability cannot compared with pipeline steel with high strength control, pressure vessel with 14 15 mnmonbg mnmovg, steel, strength can be satisfied with the demand, but a 30. C charpy impact patience can not meet the demand planning parameters. Line with control steel although have high strength, high tolerance and good weldability strengths, but because of its low alloy content, low hardenability and defects, is not suitable for directly chosen for hot drawing tee pipe fittings production data, tee pipe fittings used in domestic natural gas pipeline data needs to be studied. To sum up, think about C, Mn, Nb, V and alloy element content on the strength of X70 grade three special plate strong patience and weldability, the effect of Nb, V, Mo alloy element content on the influence of carbon equivalent and ambitions hardenability, and the content of micro alloying elements on the influence of molding temperature, choose low carbon alloy steel composition planning road, give full play to the Nb, V and intense form carbide elements separated reinforcement and hallooing grain growth effect, study American standard MSS SP75-1998 rules WPHY series of pipe steel, put forward the “west-east gas pipeline project of X70 tee pipe fittings for steel order skill conditions”.

The corrosion resistance of the steel elbow pipe fittings depends on the alloy elements contained in the steel. Chromium is thesteel elbow pipe fittings was the basic elements of corrosion resistance, when the Cr content in steel reached 1.2%, chromium and the corrosive medium in the role of oxygen, on the surface of steel formed a layer of very thin oxide film (self passivation film), can prevent the steel matrix further erosion. Steel elbow pipe fittings will not produce corrosion, pitting, corrosion or wear. Stainless steel is still one of the highest strength materials used in building materials. Because the stainless steel has good corrosion resistance, so it can make structural components to maintain the integrity of the project design. Chromium stainless steel stamping elbow is set high mechanical strength and extensibility in a body, easy manufacturing and processing of parts, accounting personnel to meet the architects and structural design. In addition to chromium, the commonly used alloy elements are nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., in order to meet the requirements of various uses for stainless steel stamping elbow organization and function. Hemming and sealing bottom of fitting, increase pipe end strength to the outside of the tube or inside hemming or pipe end sealed tube; change the cross-section of the pipe fittings, according to the requirements, circular section variable is square, oval, polygon, etc.; with flange and circular edge of the pipe, the former refers to at the end of the pipe to the medial or lateral convex, while the latter refers to in the side of the circumference of the pipe to form a bulge or groove of pipe. The technical requirements of these kinds of pipe fittings are to be carried out under certain technical requirements, and need reasonable processing methods, and reasonable production and processing of the methods and processes.

Y type tee needed feeding strain method, forming manipulation of the most difficult because wall thin, its primary forming difficulty lies in along the axial feeding, under the effect of axial force, if the lack of internal pressure head instability wrinkling is easy to attack, especially the y-shaped tee as fill material than the big, unilateral mending shoes than T tee tube internal high pressure forming, so the wrinkling control more difficult. Progressive forming inner pressure, however, branch item of easy cracking attacks caused excessive thinning, and, if the internal pressure booster has shaken or it is no good opportunity, again after corrugate pipe will attack craze, namely two shortcomings exist together, as shown in figure 3 b. This article through the manipulation of the inductive skills measures such as loading path, and to prevent wrinkling and cracking defects, the end of the ultra-thin y-shaped tee forming. For aerospace tee pipe fittings need all the thin-walled aluminum alloy, choose 5 kneading a03 aluminum alloy pipe, the internal high pressure forming aluminum alloy tee for discussion. Its head diameter D – 40 t, branch pipe axis and head Angle, branch pipe diameter D = 36 t. Its diameter-thick ratio reaches 40, director of wrinkling and branch pipe, high pressure forming crack is still need some processing of key problem. In the 1960 s of hydraulic bulge forming tee skills, forming pressure is less than 30 mpa, forming precision; In the 1990 s, because of the ultrahigh pressure and computer manipulation skills break, the rapid development of internal high pressure forming ability, for the thin-walled tube all the multipass fine supply for more than a new skill path through seminars and use first touch the T tube high pressure forming t-pipe, Y type tee and cross cross pipe, etc., meantime y-shaped tee because of the asymmetry, forming the most difficult. T type tee in thin-walled tube high pressure forming, the German experts put forward T tee tube high pressure forming mould clamping force, axial feed force, backstepping punch, plastic pressure formula for technology parameters, such as budget, axial instability criterion was deduced. Experts in the United States, when the pressure is not high, friction is satisfied with the coulomb’s law; In contact pressure near the pipe metal at the stress of the event, need to introduce the pure shear stress model, gives the branch pipe pushing force calculation formula of the punch, a beneficial effect to prevent the top of the branch pipe cracking. Japanese expert seminar elongation, hardening exponent and the filling rate of the data on the effects of aluminum alloy T tee branch pipe height. Primary discussion of the wall thickness is larger domestic experts T hydraulic extrusion forming t-pipe, choose low pressure, three-way pipe diameter and thickness ratio (hereinafter referred to as diameter-thick ratio) is less than 3518 ~ 1 ¨, less, high pressure forming aspects for discussion. American experts on the internal high pressure forming technology parameters of Y type tees budget to choose stainless steel tube billet diameter thick than 34, developed the branch Angle for 600 Y type tee. Shanghai jiaotong university, this paper introduces a y-shaped tee hydraulic extrusion mold equipment, can make the biggest diameter tee thickness ratio. The article first introduces Harbin industrial university in Y type tee tube high pressure forming over the years has made some research achievements, especially in diameter-thick ratio of 183 stainless steel Y type tee and diameter of 40 ratio of thick aluminum alloy y-shaped three-way tube internal high pressure forming research results. Pressure forming, because branch and director of the Angle, the branch of obtuse Angle side and acute side, information activity, difficult for shoes also is different. To grasp the tee both sides decided to fill capacity is remind mending shoes in Y type tee forming, the influence of the obtuse Angle to fill recycle ratio and acute side filling capacity is define as the loading ratio, the stainless steel thin wall tee practice feeding ratio 5.0. Because of lower aluminium alloy material plastic, after adding preform has the tee pipe fittings of internal high pressure forming process, the preform and the end tee pipe fittings as shown in figure 4. Branch pipe maximum height of 0.71 D. The obtuse Angle side filling capacity is a practice of 1.22 D, and acute side filling rate of only 0.06 D, the loading ratio has reached 20, can all the loading along the obtuse Angle lateral side. Because with thin wall and aluminum alloy pipe and steel mould friction coefficient between data to a district activity comparison difficult, in the process of axial feeding easy corrugate faults, as shown in figure 5 a. Together, because of the aluminum alloy material hardening exponent only 0.23, far below the stainless steel material, the forming process is used for the top branch crack faults, usually along with the wrinkling and cracking, and this shortcoming is similar to that of a thin-walled stainless steel tee forming, as shown in figure 5 b. As long as after forming difficulty preform differentiation, and reasonable control loading paths, the ability to prevent faults, shape and dimension satisfied with the requirements of the parts. For all components in aerospace lightweight piping system to supply a new path. Internal high pressure forming has a forcing all the forming characteristics of single section components, can use hollow pipe material to make all the variable cross-section components, so in aviation, aerospace and car parts to improve the internal flow field, such as cutting seam, progressive components reliability, progressive fatigue strength, etc.

Inspection personnel to implement incoming inspection before should be understanding pipe fittings manufacturing process, clear the weak link in the pipe. The scientific inspection technology and advanced inspection methods, determine the reasonable proportion of sampling and testing focus, effectively play the role of quality control and check. Elbow Elbow for changing the direction of the pipe fittings, seamless elbow and welded elbow, the seamless elbow mostly adopt hot pushingpipe method manufacturing is straight pipe set on the mandrel, mandrel head for bending of the core head (or horn shaped core head), ox horn core head by induction heating, the external forces are applied at the other end of the pipe section, in the induction heating and under the action of external force, straight pipe push made certain curvature radius of elbow. Mainly to the welded elbow plate is pressed into a certain shape and then welded. Can also be used to push and seamless steel pipe. According to the manufacturing process of the seamless elbow, the outer side of the elbow is in tension stress state, and the wall thickness is easy to be thinned, the inner side is in the stress state, and the wall thickness is easy to be thickened or folded. For weld elbow, the weld seam is a complex part of stress distribution, which is easy to produce crack and weld defects.