Elbows in the pipeline system, the elbow is to change the direction of the pipe fittings. According to the angle, there are 45 ° and 90 ° 180 ° three most commonly used, in addition to engineering needs also include 60 ° and other abnormal angle elbow. Elbow materials are cast iron, stainless steel, alloy steel, malleable iron, carbon steel, non-ferrous metals and plastics. The ways to connect with the pipe are: direct welding (the most common way) flange connection, hot melt connection, electric fusion connection, thread connection and socket connection. According to the production process can be divided into: welding elbow, stamping elbow, pushing elbow, casting elbow, welding elbow and so on. Other Names: 90 degree bend, right angle bend, love and bend, etc.
Plumbing installation commonly used in a connection with the pipe for the connection of the bend, used to change the direction of the pipeline. Other names: 90 ° elbow, right angle bend, love bend, stamping elbow, pressing elbow, mechanism elbow, welding elbow, etc.
Use: Connect two pipes with the same or different nominal diameter, make the pipe turn 90 °, 45 °, 180 ° and various degrees. Bending radius is less than or equal to 1.5 times the diameter of the elbow, more than 1.5 times of the diameter belongs to the elbow.
Pipe installation commonly used in a connection with the pipe, connecting two nominal diameter of the same or different pipe, so that the pipeline to do a certain angle turn, nominal pressure of 1-1.6 Mpa.
Material partition
Carbon Steel: ASTM / ASME A234 WPB, WPC
Alloy: ASTM/ASME A234 WP 1-WP 12-WP 11-WP 22-WP 5-WP 91-WP911、15Mo3 15CrMoV、 35CrMoV
Stainless steel: ASTM/ASME A403 WP 304-304L-304H-304LN-304N ASTM/ASME A403 WP 316-316L-316H-316LN-316N-316Ti ASTM/ASME A403 WP 321-321H ASTM/ASME A403 WP 347-347H
Cryogenic steel: ASTM/ASME A402 WPL3-WPL 6
Nenggang: ASTM/ASME A860 WPHY 42-46-52-60-65-70
Cast steel, alloy steel, stainless steel, copper, aluminum alloy, plastic, argon Ge Li, PVC, PPR, RFPP (reinforced polypropylene) and so on.
It can be divided into pushing, pressing, forging, casting and so on.
Manufacturing standards can be divided into national standard, electric standard, ship standard, chemical standard, water standard, American standard, german standard, japanese standard, russian standard, etc.
According to its radius of curvature: can be divided into long radius elbow and short radius elbow. Long radius elbow refers to the outer diameter of the pipe whose radius of curvature is equal to 1.5 times, that is, R = 1.5D; A short radius elbow means that its radius of curvature is equal to the outside diameter of the tube, i.e. R = 1.0D. (D is the diameter of the elbow and R is the radius of curvature).
According to the pressure level: about seventeen kinds, and the United States is the same standard pipe, There are: Sch 5s, Sch 10s, Sch 10, Ch 20, Sh 30, Sp 40, STD, Sw 40, Ss 60, S 80, XS; Sch80、SCH100、Sch120、Sch140、Sch160、XXS; The most commonly used are STD and XS.
According to different shapes can be divided into: groove elbow, card sleeve elbow, double elbow, flange elbow, diameter elbow, stay seat elbow, internal and external teeth elbow, stamping elbow, push elbow, socket elbow, welding elbow, wire elbow and so on.
Process flow:
Seamless elbow:
An elbow is a pipe fitting used at the turn of a pipe. In the pipeline system used in all pipe fittings, the largest proportion, about 80%. Usually, the elbow of different material or wall thickness choose different forming process. Manufacturers commonly used seamless elbow forming process has hot push, stamping, extrusion and so on.
Hot push forming:
The forming process of hot push elbow is a process of using special elbow push machine, mandrel and heating device to make the blank on the die move forward under the push of push machine. The deformation characteristics of the hot push elbow are that the diameter of the tube blank is determined according to the law of the volume unchanged before and after the plastic deformation of the metallic material. The diameter of the tube billet is smaller than that of the elbow, and the deformation process of the blank is controlled by the mandrel, so that the compressed metal in the inner arc can flow and compensate to the other parts which are thinned due to expanding, so as to obtain the elbow with uniform wall thickness. The forming process of the hot push elbow has beautiful appearance, uniform wall thickness and continuous operation. It is suitable for mass production, so it becomes the main forming method of carbon steel and alloy steel elbow, and is also used in the forming of stainless steel elbow with some specifications. The heating methods of forming process include medium frequency or high frequency induction heating (heating ring can be multi-circle or single-circle), flame heating and reverberatory furnace heating, which heating method depends on the forming product requirements and energy conditions.

Stamping forming elbow is the first forming process used in the mass production of seamless elbow. It has been replaced by hot push or other forming process in the production of commonly used elbow. But in some specifications of the elbow due to production quantity is small, wall thickness is too thick or too thin.
The product is still in use when there are special requirements. The pipe blank equal to the outside diameter of the elbow is used for forming the elbow, which is directly pressed by the press in the die. Before stamping, the tube blank is placed on the lower die, the inner core and the end die are loaded into the tube, the upper die moves downward to press, and the elbow is formed by the constraint of the outer die and the support of the inner die. Compared with the hot pushing process, the appearance quality of stamping forming is not as good as the former. When forming, the outer arc of the stamping elbow is in the stretched state, and there is no excess metal in other parts to compensate, so the wall thickness of the outside arc is reduced by about 10%. However, due to the characteristics of single piece production and low cost, stamping elbow technology is mostly used for small batch, thick wall elbow manufacturing. Stamping elbow points cold stamping and hot stamping two, usually according to material properties and equipment capacity to choose cold stamping or hot stamping. The forming process of cold extrusion elbow is to use a special elbow forming machine, The tube blank is put into the outer mold, and after the upper and lower mold is combined, under the push of the push rod, the tube billet moves along the gap reserved between the inner mold and the outer model to complete the forming process. The elbow made by the inner and outer die cold extrusion technology has beautiful appearance, uniform wall thickness and small size deviation, so the stainless steel elbow, especially the thin-walled stainless steel elbows, is made by this technology. The precision of inner and outer mold used in this process is high. The wall thickness deviation of the tube is also more stringent requirements.
Medium plate welding:
Press the middle plate to make half of the elbow section and weld the two sections together. This process is generally used for more than DN700 elbow.
Other forming methods:
In addition to the above three common forming processes, the forming process of seamless elbow also uses the tube billet extruded into the outer mold, and then through the pipe billet inner ball shaping. However, this process is relatively complex, difficult to operate, and the forming quality is not as good as the aforementioned process, so it is rarely used.
Scope of Use
Because the elbow has good comprehensive performance, it is widely used in chemical industry, construction, water supply, drainage, petroleum, light and heavy industry, refrigeration, sanitation, plumbing, fire, electric power, aerospace, shipbuilding and other basic engineering.
Technical requirements
Required to control the radius of curvature. For example, if the radius length is 1.5D, the radius of curvature must be within the required tolerance. Since most of these pipes are used for welding, in order to improve the welding quality, The end of the car into a groove, leaving a certain angle, with a certain edge, this requirement is also more stringent, the thickness of the edge, the angle of how much and the range of deviation have provisions, the geometric size of the pipe than a lot of items. Elbow surface quality and mechanical properties and pipe is basically the same. For ease of welding, the steel material of the pipe to be connected is the same.
Key points of production
Stainless steel elbow:
1, the electrode should be kept dry, titanium calcium type should be dried at 150 °C for 1 hour, Low hydrogen type should be dried at 200-250 °C for 1 hour (can not be repeated drying, otherwise the coating is easy to crack and peel), to prevent the electrode coating stick oil and other dirt, so as not to cause the increase of carbon content in the weld and affect the quality of the weldment. During welding of elbow, carbide precipitates by repeated heating, which reduces corrosion resistance and mechanical properties. After welding hardening, easy to crack. If the same type of electrode welding, must be more than 300 °C preheating and welding 700 °C after slow cooling treatment. If the weldment can not be heat treated after welding, chrome nickel stainless steel electrode should be used.
2, in order to improve the corrosion resistance and weldability of stainless steel elbow and appropriately increase the amount of stability elements Ti, Nb, Mo, etc., Better weldability, using the same type of chrome stainless steel electrode, should be more than 200 °C preheating and welding 800 °C tempering treatment. If the weldment can not be heat treated, chrome nickel stainless steel electrode should be used.
3, stainless steel elbow has certain corrosion resistance (oxidizing acid, organic acid, cavitation), heat resistance and wear resistance. Usually used in power plants, chemicals, petroleum and other equipment materials. Stainless steel elbow weldability is poor, should pay attention to the welding process, heat treatment conditions and selection of suitable electrode.

Development prospect
China is already the world’s largest producer and consumer of building materials. The main building materials products such as cement, flat glass, building and sanitary ceramics, stone and wall materials have ranked first in the world for many years. At the same time, the quality of building materials continues to improve, energy and raw material consumption decreased year by year, a variety of new building materials continue to emerge, building materials products continue to upgrade. Cangzhou pipeline equipment manufacturing base is strong. The existing production enterprises more than 3200, including large-scale (sales income of more than 5 million yuan) 222 enterprises, employing 124,000 people. The main products are a variety of special steel, stainless steel, carbon steel and other seamless steel pipe, low and high pressure boiler tubes, oil drilling pipe and other steel pipe; Various head, flange, size head, tee and other elbow pipe fittings; All kinds of stainless steel flange, forging flange; All kinds of pipe rack, meter, oil blowout preventer and other pipe fittings; All kinds of polyethylene pipes, polypropylene pipes and other plastic pipes, a total of 16 categories, more than 370 varieties, 3500 kinds of specifications. The main manufacturing processes are hot-rolled straight seam welding, spiral double-sided submerged arc welding, forge, forging, medium frequency push, cold forming, hot extrusion, etc., the maximum processing diameter of the pipeline is 2020mm. Products are widely used in municipal, petrochemical, West-to-East gas transmission, shipbuilding and nuclear power and other engineering fields, the annual design processing capacity of 25 million tons. In 2010, enterprises above designated size achieved industrial added value of 13 billion yuan, an increase of 31.7% year on year, accounting for 16.1% of the total value-added of enterprises above specified size. The pipeline equipment manufacturing industry in Cangzhou is striding forward to the goal of “three highs” (on the scale, on the level and on the equipment) and “three heights” (high-end, high voltage and high added value), and urged the capacity of pipeline equipment manufacture to reach 30 million tons. Cangzhou will become a well-known “pipeline equipment manufacturing and R & D base” and “pipeline and equipment capital.” “Eleventh Five-Year Plan” infrastructure investment has been chess to the plate, highway, railway and other infrastructure construction investment explosion growth and ordinary civil construction investment steady growth, so that the construction industry is in the boom upward stage. At the same time, under the background of building an energy saving society and strengthening the independent innovation ability of the country, energy saving and technology innovation will be the hot spot of the industry. Plastic pipe fittings and pipes set off a pipe fitting boom again.