Research and development of X80 steel induction heating pipe bend used in China Russia east line – 45 ℃ low temperature environment oil and gas pipeline project

About China–Russia East-Route Natural Gas Pipeline:

The China–Russia East-Route Natural Gas Pipeline was officially put into operation on December 2, 2019. The Pipeline includes the section Russia, often referred to as Power of Siberia gas pipeline, the cross-border section and the section in China. The gas is mainly supplied from the Kovyktinskoye Gas field in Irkutsk Oblast and the Chayandinskoye Gas field in Sakha Republic (Yakutia) in East Siberia, Russia.

The Chinese section of China–Russia East-Route Natural Gas Pipeline with the largest diameter and the highest pressure currently in the country, starts from Heihe city, Heilongjiang Province in the north winding all its way to Shanghai municipality in the south. As planned, it will be constructed and put into operation in three subsections. The north subsection (Heihe City – Changling County) was put into operation this time, and the middle subsection (Changling County – Yongqing County) and the south subsection (Yongqing County – Shanghai City) are scheduled to be launched in 2020 and 2023 respectively.

In May 2014, Gazprom and CNPC signed the Sales and Purchase Agreement for gas to be supplied via the China-Russia East-Route Natural Gas Pipeline. According to the contract, Russia will export gas to China for 30 years via the route since it’s put into operation, and the volume will gradually increase to 38 bcm per annum.

38 bcm	30 years
Design capacity: 38 bcm per annum	Contract period: 30 years

The China–Russia East-Route Natural Gas Pipeline is a landmark project of China-Russia energy cooperation and a paradigm of deep convergence of both countries’ interests and win-win cooperation. The operation of the pipeline will further optimize China’s regional gas consumption structure and enable a multisource supply of gas, which is of great significance for China to ensure gas supply in winter and win the Blue Sky Protection Campaign. The construction and operation of the pipeline have also driven the development of infrastructure and supporting industries, created job opportunities, and promoted the economic growth in places along the route.

162 million tons	1.82 million tons
CO2 emissions can be cut by 162 million tons	SO2 emissions can be cut by 1.82 million tons

China’s long-distance oil and gas pipeline runs from west to East, through high altitude and extremely low temperature areas. For a long time, due to the limitations of high-strength LSAW welding joints and high-strength induction heating pipe bend hot bending technology, only welded pipe products with service temperature of no less than – 20 ℃ can be produced. For pipe bends working at – 30 ℃ or worse, in order to prevent the occurrence of low temperature brittle fracture, only heat tracing and insulation measures can be taken for exposed pipe bends [1-7]. According to the feedback from the operation of many long-distance pipelines, such as the second west to east gas transmission line, the heat tracing and insulation measures can solve the problem of low temperature brittle fracture of exposed pipe bends to a certain extent, but it will lead to open circuit and temperature loss due to the aging of the heat tracing wire. At the same time, the insulation material covering the heat tracing wire will degrade the insulation performance due to the continuous high temperature, which will lead to the electric burning loss of the pipe wall between the pipe wall and the heat tracing wire. In addition, it was found that the local corrosion of the pipe body was caused by the natural water absorption of the insulation material near the interface of the pipe wall covering the insulation layer. According to the current needs of low-temperature station pipe for long-distance pipeline in China, TMCP controlled rolling material with similar composition to steel pipe for long-distance pipeline engineering construction is selected in this study, and the trial production and development of new product of X80 steel grade induction heating pipe bend suitable for – 45 ℃ are carried out, in order to provide technical support and material support for the construction of national major pipeline engineering.

Test materials and methods

Test material

The c-mn-mo type X80 pipeline steel produced by TMCP control rolling technology belongs to acicular ferrite + granular bainite steel, which gives full play to the four strengthening mechanisms of metal materials. This kind of material not only has high strength and toughness, but also has good weldability due to its w (c) < 0.1%. It has become one of the first choice materials for large diameter and high pressure gas pipeline [8-10]. However, after the second hot processing, its rolling control effect will be greatly lost [11-12]. Therefore, in this study, in combination with the characteristics of induction heating pipe bend and the requirements of low temperature toughness technology of – 45 ℃ X80 steel grade induction heating pipe bend, Mo, V and other strong carbide forming elements are added, and in order to obtain excellent low temperature toughness and high strength matching, Ni element is added to make X80 steel plate with two specific components. Φ 1219mm × 22.0mm (No. 1 × 3) and Φ 1422mm × 33.8mm (No. 2 × 3) X80 steel grade LSAW pipes with two specific components are used as the main pipe of induction heating pipe bend. See Table 1 for chemical composition and table 2 for mechanical properties.

Table.1 Main chemical composition of pipe bend main

Table.2 Mechanical properties of pipe bend main

Test method

The production mode of induction heating pipe bend can be divided into integral heating and local heating [13-14]. In the former process, both the straight pipe section and the bending section materials need to be heated to AC3 + (50-100) ℃, so that the materials can be plastic formed in austenite state; in the latter process, the straight pipe section does not need to be heated to maintain the rolling state of the original steel plate. For X70 and X80 high-strength induction heating pipe bends, the final products are usually delivered in tempered state considering the factors of strength and toughness matching and residual stress control. Based on this, the research is carried out in the following two aspects: ① cut six 400 mm long short sections of vertical pipe body on the bending section of Φ 1219 mm × 22.0 mm multi wire LSAW induction heating pipe bend of X80 steel grade, and heat the five short sections in the box furnace to 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃ respectively, and then air cool them for 60 minutes, then conduct the heat treatment of back fire; ② Φ 1422 of X80 steel grade The vertical pipe body on the induction heating pipe bend main pipe of mm × 33.8 mm multi-channel single wire LSAW intercepts two sections of about 1000 mm long short section axially, heats one short section in the box furnace to 960 ℃, keeps the temperature for 50 min, cools it in 6% NaCl solution, then heats the other one with it in the box furnace to 550 ℃, keeps the temperature for 60 min, and air cools it, and carries out the heat treatment of back fire.

Test results and analysis of mechanical properties

The influence of tempering temperature on the impact toughness of the welded joint of the as rolled pipe bend main

On the original main pipe of Φ 1219mm × 22.0mm and Φ 1422mm × 33.8mm induction heating pipe bend of X80 steel grade and the short joints of the main pipe after different heat treatment, the center line of the sample is the center line of the wall thickness of the welded joint of the pipe body, and the Charpy V-notch impact test sample of 10 mm × 10 mm × 55 mm is taken. In accordance with ASTM a370-2009, a series of impact tests were carried out on zbc2752-b Charpy pendulum tester at – 20 ~ – 60 ℃.
Figure 1 shows the change curve of Charpy impact energy with tempering temperature of Φ 1219mm × 22.0mm pipe bend main welded joint of X80 steel grade. It can be seen from Figure 1 that under the same test temperature, after quenching, the sample is tempered at 450 ℃, 500 ℃, 550 ℃, 600 ℃ and 650 ℃, the Charpy impact energy in the center of the weld is significantly lower than that in the original joint, and the value of Charpy impact energy decrease is greater with the increase of tempering temperature. This is related to the coalescence of fine acicular ferrite lath in the pre austenite grain in the weld structure after reheating, and the broadening of ferrite lath, resulting in the coarsening of effective ferrite grain in the weld. Through careful analysis of the data, it is found that although the toughness of the weld decreases after quenching and tempering, the minimum Charpy impact energy measured at the temperature of no higher than 550 ℃ is greater than 100 except that the Charpy impact energy measured at – 50 ℃ is 97 J J. Compared with the current oil and gas transmission pipeline engineering, there is still a large margin in the technical specifications for the brittleness cracking resistance of X80 steel grade high-strength induction heating pipe bend welding joint. Therefore, after induction heating and proper tempering heat treatment, the welded joint of X80 steel grade Φ 1219mm × 22.0mm steel pipe with multi wire single pass welding process still has enough anti brittle cracking ability.

Fig.1 Change curve of Charpy impact energy with tempering temperature of Φ 1219 mm × 22.0 mm pipe bend main welded joint of X80 steel grade

Figure 2 shows the change curve of Charpy impact energy of welded joint of X80 steel grade Φ 1422 mm × 33.8 mm pipe bend main with test temperature. It can be seen from Figure 2 that the low-temperature Charpy impact toughness of the weld center is the highest under the as welded condition, followed by the quenching + tempering condition, and the Charpy impact energy under the direct tempering condition is the worst. The single wire multi pass welding method [15-18] is adopted for the welded joint of thick wall pipe bend main pipe in the welding stage. The metallographic structure of the weld is greatly improved compared with the multi wire single pass welding, and the change characteristics of the microstructure and properties after the secondary heating are basically the same as that of the Φ 1219mm × 22.0mm main pipe of Grade X80 steel. -Under the condition of 45 ℃, the Charpy impact energy of the weld decreased sharply after direct tempering, while the Charpy impact energy of the weld in the state of quenching + tempering heat treatment decreased, but the overall Charpy impact energy was not less than 100 J, which is also the reason why the overall heating mode is usually used instead of the local heating mode in the heat bending process of X80 steel grade induction heating pipe bend.

Fig.2 Charpy impact energy curve of welded joint of X80 steel grade Φ 1422 mm × 33.8 mm pipe bend main with test temperature

The influence of tempering temperature on the strength and toughness of as rolled pipe bend main

Fig. 3 shows the change curve of mechanical properties of X80 steel grade Φ 1219mm × 22.0mm pipe bend main with tempering temperature after quenching at 980 ℃ and tempering at 550 ℃, 600 ℃, 650 ℃ and 700 ℃. It can be seen from Figure 3 that the Charpy impact energy of the base metal at the series test temperature fluctuates to a certain extent. When the tempering temperature is 650 ℃, the Charpy impact energy of the sample is the largest, but the Charpy impact toughness deteriorates sharply after tempering at 700 ℃. After tempering at 550 ℃, 600 ℃ and 650 ℃, the yield strength and tensile strength of the base metal are higher than those of the original base metal. After tempering at 700 ℃, the tensile strength of the welded joint and the base metal has no obvious change, and the yield strength drops sharply, which is related to the recrystallization of some structures when the heating temperature is higher than 700 ℃. Therefore, after quenching at 980 ℃ and tempering at 550 ℃, the base metal and welded joint have good hot working properties.

Fig.3 Change curve of mechanical properties of pipe bend main with tempering temperature at 980 ℃

Hot bending of pipe bend and evaluation of its physical and chemical properties

Heating of main pipe

The overall heating method is selected, and the Φ 1422 mm × 33.8 mm straight seam submerged arc induction heating pipe bend main of X80 steel grade is respectively welded by single wire multi pass welding and multi wire single pass welding (No. is 3 × 10 and 4 × 10 respectively), and one pipe bend with an angle of 15 ° is respectively simmered according to the heating temperature of 940-1020 ℃, propulsion speed of 10-30 mm / min, cooling water pressure of 0.15-2.5 MPa. In a 14 m × 6 m box type gas furnace, the induction heating pipe bend was heated to 550 ℃ for 70 min, and then the heat treatment was carried out.

Tensile test of pipe bend

The transverse tensile specimens were cut from the outer arc side pipe body and weld of the straight pipe section, the inner arc side of the bending section pipe body, the neutral area, the outer arc side pipe body and weld after heat treatment. The specification of the specimens was 12.7 mm from the internal diameter of the gauge distance, and the circular rod tensile specimens with a diameter of 10 mm were taken along the longitudinal direction at the left and right bending transitions of the pipe bend. On the sht4106 tensile testing machine, the tensile test is carried out according to ASTM A370 standard, and the test results are shown in Table 3. It can be seen from table 3 that the tensile properties of induction heating pipe bends meet the design requirements.

Table.3 Tensile test results of induction heating pipe bend

Impact test

The Charpy V-notch impact specimens of 10 mm × 10 mm × 55 mm were taken from the pipe bend with the center of the wall thickness of the pipe bend and the depth of 7 mm from the upper and lower surfaces of the welded joint as the sample center. On the zbc2752-b Charpy pendulum test machine, a series of impact tests were carried out under the conditions of 0 ℃, – 10 ℃, – 20 ℃, – 30 ℃, – 45 ℃ and – 60 ℃ according to ASTM a370-2009. The curve of Charpy impact toughness of each part of the pipe body with temperature change is shown in Figure 4. It can be seen from Fig. 4 (a) and Fig. 4 (b) that the Charpy impact absorption energy value of 3 × 4 × pipe bend base metal and weld of 1 / 2 wall thickness sample can meet the specification requirements under the test condition of – 45 ℃. It is found from Fig. 4 (c) that the Charpy impact absorption energy of the upper and lower surface layers of the 4 × pipe bend weld is abnormally low, and its value does not conform to the distribution rule of the toughness of the thick wall material after tempering heat treatment.

Hardness test

At the pipe bend pipe body and weld joint, the hardness samples of the cross section are taken in the vertical pipe body axial direction. Using hsv-30 Vickers hardness tester, according to the requirements of ASTM A370 standard, select 3 points 1.5mm away from the inner and outer surfaces and at the center of wall thickness, respectively, and conduct 10 kg load Vickers hardness test. The results show that the hardness of the base metal of the two pipe bends is in the range of 208-246hv10, among which the hardness of the welds of the three pipe bends is 183-227hv10, and the hardness of the welds of the four pipe bends is 207-273hv10. The hardness test results meet the requirements of the engineering design (≤ 285hv10).

Fig.4 Curve of impact toughness with temperature at different parts of pipe bend

Metallographic analysis

Take metallographic samples from the inner and outer arc of pipe bend section, and observe its structure under mef4m metallographic microscope, as shown in Figure 5. The microstructure of the tube is polygonal ferrite + granular bainite + a small amount of pearlite. Figure 5 (a) shows the structure of the base metal of the 3-pipe bend, and the grain size evaluation result is about Grade 11. Although the weld structures of 3 × 3 and 4 × 4 × 3 are acicular ferrite + polygonal ferrite + granular bainite, the former still inherits the advantages of fine structure in the original single wire multi pass weld. After the hot bending of the pipe bend, the upper, lower surface and center structures show signs of growth, but not obvious coarsening. The structure of the 1 / 2 wall thickness of the weld in the bending section of 3 × 3 pipe bend is shown in Fig. 5 (b). 4. As the heat input of pipe bend welding is higher than that of single wire multi pass welding, the microstructure of as welded joint is smaller than that of single wire multi pass welding, and the microstructure of different wall thickness is different. In the pipe bend forming stage, due to the skin effect of induction heating, the heating temperature of the weld near the outer layer is higher than that of the weld center. On the one hand, a large number of fine acicular ferrite in the original as cast condition near the surface weld tends to merge, which makes the effective grain coarsening of ferrite. At the same time, after hot bending, due to the existence of weld segregation during cooling, the surface layer is rapidly cooled from austenitizing temperature, and part of the structure is transformed into a certain amount of coarse granular bainite (see Fig. 5 (c)). Due to the lower heating temperature of the weld at 1 / 2 of the wall thickness compared with the outer layer, the effective grain will grow due to the combination of some acicular ferrite, but under the specific process control conditions, it does not significantly coarsen, basically inherits the characteristics of fine acicular ferrite in the original weld, while the microstructure of the weld near the surface layer is significantly coarsened (see Figure 5 (d)). The microstructure of the material determines its mechanical properties. The fine acicular ferrite has good impact toughness, while the coarse bainite has low toughness. Under the specific process conditions of induction heating, the defects of single pass welding seam with large thick wall and multi wire are further enlarged, and the relative center of the surface layer of the weld will obviously deteriorate and become brittle after the second heat treatment.

Fig.5 Metallographic structure of induction heating pipe bend

Result analysis

Induction heating can give full play to the advantages of fast heating speed, high efficiency and easy control of bending angle. However, for high-strength induction heating pipe bends used for oil and gas transportation, the weld joint of the main pipe has poor thermal stability due to its typical acicular ferrite structure. Once the heating temperature is higher than the temperature of the phase change point, the weld joint will be due to the combination of acicular ferrite Moreover, the toughness of the effective grains is deteriorated rapidly due to coarsening. Under the condition that the wall thickness is not very large, special technological means shall be adopted to limit the heating temperature of the weld on the bending heating belt of the main pipe to not higher than the critical coarsening temperature of the acicular ferrite, which can not only ensure the forming of the pipe on the heating belt of the main pipe under the normal heating temperature, but also enable the weld structure of the pipe bend to basically inherit the characteristics of the original fine acicular ferrite structure, So that the base metal and the weld of the pipe bend can obtain the comprehensive mechanical properties with good strength and toughness matching. According to practical experience, the above process measures are close to 30% for wall thickness Mm pipe bend is not suitable, which is mainly related to the following factors: on the one hand, the normal hot bending forming of pipe bend is the most ideal under the austenitizing temperature state of materials, and under this condition, the original fine acicular ferrite lath in the weld inevitably has the trend of merging and growing up, and the weld itself has the trend of heating embrittlement; on the other hand, reducing the heating temperature can provide The range of the effective process parameter adjustment window of induction heating pipe bending control will be narrowed, which will lead to the overload of the pushing power demand of the pipe bender and the out of control of the forming quality of the pipe bending section. Based on the above analysis, it is a good idea to improve the main pipe welding method and choose the single wire multi pass welding method to obtain the fine weld structure, that is to say, to obtain the finer and more uniform structure in the as welded state by improving the welding method.
According to the full wall thickness of 3 ා and 4 ා welds and the metallographic structure of Charpy impact specimen, the microstructure of multi wire welding line is larger than that of single wire multi pass welding due to its larger energy, and there are a large number of coarse granular bainite structures in the metallographic structure near the inner surface of the welds in different parts of 4 specimens. Due to the poor crack initiation and propagation resistance of this structure, the weld has a smaller impact load It is possible to crack and expand and fracture. 4. The microstructure of the near surface layer and the weld center of the external welding of the sample are similar. Although they are acicular ferrite + granular bainite, the heating temperature of the weld near the surface layer is higher than that of the weld center due to the skin effect of induction heating. The original very small acicular ferrite in the as cast condition tends to merge after heating, which makes the effective grain coarsening and the toughness decreasing, but it is located in the wall thickness of 1 /Because of the fine acicular ferrite structure in the original weld, the two welds have good impact toughness, and the test results can still meet the standard requirements.

Conclusion

• (1) The joint structure of X80 welded pipe has the characteristics of secondary heating and embrittlement. For thick wall induction heating pipe bend, single wire multi pass welding can effectively inhibit the secondary heating of welded joint, which makes the acicular ferrite strip in the weld joint merge and coarsen. Considering the toughness requirements of straight pipe and bending section of pipe bend, X80 steel grade induction heating pipe bend can only be produced by integral hot bending.
• (2) After quenching and tempering heat treatment, the tensile strength of the main pipe of X80 steel grade Φ 1422 mm × 33.8 mm single wire multi pass induction heating pipe bend can meet the strength requirements of X80 steel grade induction heating pipe bend, and the Charpy impact toughness under – 45 ℃ low temperature can meet the design requirements of China Russia east pipeline project.

Difference Between A Pipe Elbow And A Pipe Bend

What is a pipe bend?

A pipe bend is the generic term for what is called in piping as an “offset” – a change in direction of the piping. A bend is usually meant to mean nothing more than that there is a “bend” – a change in direction of the piping (usually for some specific reason) – but it lacks specific, engineering definition as to direction and degree. Bends are usually custom-made (using a bending machine) on site and suited for a specific need.

Pipe bends typically have a minimum bending radius of 1.5 times pipe radius (R). If this bending radius is less than 1.5R, it is called Elbow. Reference to any international / industry standard need to be traced. 1.5, 3 and 4.5 R are the most common bending radii in industry.

A pipe bend typically flows smoother since there are not irregular surfaces on the inside of the pipe, nor does the fluid have to change direction abruptly.

The most basic difference of them is the elbow relatively short than bend, R = 1D to 2 D is elbow More than 2D is bend. In the production process, cold bends can use Bending Machine to bend by ready-made straight bend. One-time completed also don’t need second corrosion. But elbow need manufacturers make to order, to do anti-corrosion, order cycle is long. Elbow price is higher than bend. But cost performance is much higher than bend. It is well-known that bend do not have anticorrosive processing is easy damaged, but the price is cheap so are  used very much in some demand which not very high engineering.

In the west-east gas transmission of course, cold bends cost is low. elbow need manufacturers make to order, needs corrosion, order cycle is long,but cold bends can use ready-made straight bend by Bending Machine to bend. One-time completed also don’t need second corrosion. The cold bend construction technology need follow oil standard .west-east gas transmission have the enterprise standard,but we can use either elbow nor bend in open area.  Sunny Steel Enterprise warn broad customers betweenness elbow and bend performance price is differ ,please carefully choose after consider it.

The pipe bends should be as per the standard of  ANSI/ASME B16.49 which did not specific the bending radius and angle , the regular pipe bend radius are 2.5D, 3D ,5D ,7D or 8D , but it can be any other bending radius according to the design need, and bending angle can be in any degree, 5 ,10 ,15, 90 degree or any other. People said “All bends are elbows but all elbows are not bend”, it is not true . Actually “All elbows are pipe bends but not all bends are elbows”  is more reasonable.

Industrial Processes 
Bending, squeezing, pressing, forging, machining and more
Industries Served
Our pipe elbows are widely used in many industries, such as power generation, petroleum, natural gas, chemicals, shipbuilding, heating, papermaking, metallurgy and so on.

The production process of stainless steel pipe bend

According to the different manufacturing methods, the stainless steel pipe bend can be divided into three types, namely, the bending pipe, the punching pipe and the welded pipe. Which can be divided into two types of bending bending and bending. When the stainless steel tube for bending the pipe along the longitudinal direction under pressure, leading to pipe wall thickness of the pipe is shortened, the lateral pipe subjected to tensile, elongation, wall thinning and tube; center without force, deformation will not occur. The cross section of stainless steel tube is changed from round to oval. Bend in the production of the need to pay attention to, when the piping system, when the bending radius design does not require the minimum bending radius of the bend to meet certain standards.

Cold bending of stainless steel pipe bend. Bending pipe in the heating process, the heating process should be slow and uniform, so as to ensure the thermal conductivity of the pipe, we should pay attention to avoid overheating and carburizing.

Bending technology is widely used in the field of boilers and pressure vessels. In many industries, such as aerospace, shipbuilding and other industries, the quality of the pipe bend has a direct impact on the structural rationality, safety and reliability of the product. Therefore, bending the quality of the pipe is the most critical, and grasp the technical conditions of the pipe is the most important. In the cold bending of the pipe bend, the need to choose a reasonable mandrel formation and master the correct method of use.

Because the inner side of the bending tube in bending when wrinkling, core tube is when they bend the tube relative bending radius is small, in order to obtain high quality pipe fittings, pipe is in the bending process, in which are inserted into a suitable mandrel, thereby avoiding method of flattening and wrinkling phenomenon stainless steel pipe bending appears when arc. Because the tube has a certain elasticity, so when bending force is removed, a rebound angle of pipe bend. In the bending angle, should consider increasing the angle.

How to Calculate a Pipe Bend?

Whether you are bending pipe for running electrical conduit or a metal project, calculating the bend for the start and end point can be an important factor. While there are different types of pipe benders on the market, they all share a common identification for the operation. Identified on all pipe benders is the size of pipe the unit will bend along with a number called the “take up.” The take up measurement is used for adding or deducting an allowance in the overall length of the bend. By following a basic process, you can calculate pipe bends regardless of the type of bender or the diameter of pipe.

Instructions

1. Identify the take up measurement that is located on the pipe-bending shoe itself. This is the addition or deduction of measurement to the length of pipe from the front mark on the bending shoe. Also be aware that there is a second centre-of-bend mark located approximately in the centre of the bending shoe. Also located along the running length of the shoe are angle markings with lines. These numbers and lines correspond to actual angles that can be bent into the pipe by aligning the pipe with the angled line marked on the outside of the shoe.

2. Bend a 90-degree angle on a ½-diameter pipe with a ½-inch bender. The process will remain the same for different sized pipes and benders, but only the take up measurement will be different. Identified on the shoe for the ½-inch pipe may be the wording “stub take up 5 inches from arrow or line.” The 5 inches is the amount you will deduct from the overall length of the 90-degree bend measurement.

3. Use the measuring tape and pencil and place a mark at 12 inches from the end of the pipe. This will be the distance from the bend to the end of the pipe. By using the deduction measurement on the shoe, measure back 5 inches from the 12-inch mark and make a solid pencil line.

4. Lay the pipe on a level surface and insert the pipe into the bender. The solid pencil mark should be placed 5 inches back from the 12-inch mark and should be aligned with the front mark or arrow on the bending shoe. Pull back on the handle in a smooth motion until the pipe sits at a 90-degree position to the level surface. Place the small level against the upright portion of the pipe and check for level. This will give you a perfect 90-degree bend. Check the height of the overall bend by placing the end of the tape measure on the level base and measure the end of the pipe. It should read 12 inches exactly.

5. Practice with other angled bends by using the deduction measurement and the centre of the bend mark on the shoe. All pipe benders may have their own quirks and slight measurement adjustments that will have to be done. The actual end result also depends on how well and secure you hold the pipe in the bender, prior to the first bend you place on the pipe.

What is a pipe elbow?

A pipe elbow, on the other hand, is a specific, standard, engineered bend pre-fabricated as a spool piece and designed to either be screwed, flanged, or welded to the piping it is associated with. An elbow can be 45o or 90o. There can also be custom-designed elbows, although most are catagorized as either “short radius” or long radius”.

A pipe bend can be an elbow; an elbow does not mean a bend. If you use the term elbow, it should also carry the qualifiers of type (45 or 90o) and radius (short or long) – besides the nominal size.

 The ends may be machined for butt welding (SW) or socketed welding(SW) etc.

Most pipe elbows are available in short radius or long radius variants. When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow.

Elbows are categorized based on various design features as below:

• Long Radius (LR) Elbow is also called LR elbow – means the radius is 1.5 times the pipe diameter
  • L/R 45°Elbow: Long radius 45 degree elbow changes the direction by 45 degrees.
  • L/R 90°Elbow: Long radius 90 degree elbow changes the direction by 90 degrees.
  • L/R 180°Elbow: Long Radius 180 degree return bend allows complete reversal of flow.
• Short Radius (SR) Elbow is also called SR elbow, – means the radius is 1.0 times the pipe diameter
• Short radiu 45°Elbow: Short radius 45° elbow changes the direction by 45 degrees.
• Short radius 90°Elbow: Short Radius 90° elbow is same as LR90 except for the measurement between end of elbow to center line is 1 x NPS.
• Short radius 180° Elbow: Short Radius 180° return bend allows complete reversal of flow

Processing:

The physical difference between Long Radius and Short Radius Elbows is graphically illustrated in the attached Workbook that I have put together for this thread.

The following is the criteria I use when deciding which to use:

Long Radius Elbows are used when:

there is a need to keep the frictional fluid pressure loss down to a minimum;
there is ample space and volume to allow for a wider turn and generate less pressure drop;
the fluid being transported is abrasive or has solids in it.

Short Radius Elbows are used when:

there is a need to reduce the cost of elbows;
there is a scarcity of space and volume to allow a Long Radius type.

SIZE RANGE:

• Seamless elbow: 1/2″-24″ DN15-DN600
• Welding elbow: 6″-72″ DN150-DN1800
• Wall thickness: Sch5-Sch160 XXS

MATERIALS

• Carbon steel: ASTM/ASME A234 WPB-WPC
• Alloy steel: –WP 22-WP 5-WP 91-WP 911
  • ASTM A335 P22
  • ASME SA335 P91 elbow
  • ASTM A234 WP 11
• Low temperature steel: ASTM/ASME A402 WPL 3-WPL 6
• High performance steel: ASTM/ASME A860 WPHY 42-46-52-60-65-70
• 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

What is a 45 Degree Elbow?

45 Degree Elbow is also known as “45 bends or 45 ells”. The 45° pipe elbow is used to connect tubes at a 45° pipe angle. As the name suggests, this is a pipe fitting device which is bent in such a way to produce 45° change in the direction of flow of the fluid/gas in the pipe.

Like a 90° elbow, the 45 Degree Elbow also attaches readily to pipes of various materials like plastic, copper, cast iron, steel, lead, rubber etc. They are typically made as LR (Long Radius) elbows. These types of elbows are available in various sizes (in mm or inches). They are available with different male to female BSP thread connections. Providing a wide choice of colors, these 45 Degree Elbows can be manufactured to meet different specifications, in terms of size and diameter.

What is a 90 Degree Elbow?

A 90 degree elbow is also called a “90 bend” or “90 ell”. It is a fitting which is bent in such a way to produce 90 degree change in the direction of flow in the pipe. It used to change the direction in piping and is also sometimes called a “quarter bend”. A 90 degree elbow attaches readily to plastic, copper, cast iron, steel and lead. It can also attach to rubber with stainless steel clamps. It is available in many materials like silicone, rubber compounds, galvanized steel, etc. The main application of an elbow (90 degree) is to connect hoses to valves, water pressure pumps, and deck drains. These elbows can be made from tough nylon material or NPT thread.

BUTT WELD PIPE FITTING BEVEL

• All welded pipe fittings have bevelled end to allow for ease of welding.
• This bevel allows for full penetration weld in most cases.
• There are two types of bevels;
  Plain Bevel and Compound Bevel: according to the bevel of welding pipe fittings construction .
• ASME B16.28, Buttwelding Short Radius Elbows and Returns

Industrial Processes: Bending, squeezing, pressing, forging, machining and more ANSI/ASME B16.25, Buttwelding Ends 
ANSI/ASME B16.25 Standard covers the preparation of butt welding ends of piping components to be joined into a piping system by welding.

APPLICATION OF PIPE ELBOWS:

Petroleum, chemical, power, gas, metallurgy, shipbuilding, construction, etc.

How to calculate a 90 degree elbow center and 45 degree elbow center?

If your elbow is a short radius it is 1 times your nominal pipe diameter. If it is a long radius it is 1 1/2 times your nominal pipe diameter.show me the exact pattern of long radius.

• (90/2tan*Dia*1.5*25.4)
• (45/2tan*Dia*1.5*25.4)
• u will obtain Ur answer in (mm)
• For 90 degree elbow (Dia*38.1) this formula used for only 90 degree elbow.
• For 45 degree elbow (45/2of tan*Dia*1.5*25.4) this answer obtained in (mm).

Difference between a pipe elbow and a pipe bend is as follows:

1. Pipe Bend is a generic term for any offset or change of direction in the piping. It is a vague term that also includes elbows.
2. An elbow is an engineering term and they are classified as 90 deg or 45 deg, short or long radius.
3. Pipe elbows have industrial standards and have limitations to size, bend radius and angle. The angles are usually 45 deg or 90 degrees. All others offsets are classified as pipe bends.
4. Bends are generally made or fabricated as per the need of the piping; however elbows are pre fabricated and standard, and are available off the shelf.
5. Bends are never sharp corners but elbows are. Pipe bending techniques have constraint as to how much material thinning can be allowed to safely contain the pressure of the fluid to be contained.  As elbows are pre fabricated, cast or butt welded, they can be sharp like right angles and return elbows which are 180 degrees.
6. Elbow is a standard fitting but bends are custom fabricated.
7. In bends as the pipe is bent and there is no welding involved, there is less pipe friction and flow is smoother. In elbows, the welding can create some friction.
8. All elbows are bends but all bends are not elbows.
9. Bend has a larger radius then elbows.
10. Generally the most basic difference is the radius of curvature. Elbows generally have radius of curvature between one to twice the diameter of the pipe.  Bends have a radius of curvature more than twice the diameter.

Source: China Stainless Steel pipe bend Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]

Please notice that you might be interested in the other technical articles we’ve published:

• How to get high quality pipe bend
• Difference Between A pipe bend And A pipe bend
• How to Calculate a pipe bend
• How to get high quality pipe bend
• Stainless steel pipe bend
• The production process of stainless steel pipe bend
• Experimental Study on Local Erosion of 304 Stainless Steel pipe bends with Gas Carrying Sand

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