In a piping system, an pipe elbow is a pipe fitting that changes the direction of the pipe. According to the angle, there are three most commonly used 45° and 90°180°, and other abnormal angle elbows such as 60° are also included according to engineering needs. Elbows are made of cast iron, stainless steel, alloy steel, malleable iron, carbon steel, non-ferrous metals and plastics. The way to connect to the pipe is: direct welding (the most common way) flange connection, hot melt connection, fused connection, threaded connection and socket connection. According to the production process, it can be divided into: welding elbow, punching elbow, push elbow, casting elbow, butt weld elbow.

## What is a long radius elbow?

The center line of one end to the opposite face. This is known as the “center to face” distance and is equivalent to the radius through which the elbow is bent.
The center to face distance for a “long” radius elbow, the LR radius elbows have a center to end distance that is 1.5 times the NPS in inches (R = 1.5D), if it is more than 1.5 times, it is a bend. D is the diameter of the elbow. Long radii are commonly used. Generally, the default is also a long radius. Where the pressure is high or the flow rate is high, a long radius is used. If the resistance of the solid conveying pipe is strict, a larger radius elbow is used.

## What is a short radius elbow?

Short radius elbow’s radius is equal to the NPS in inches (R = 1.0D). Short radii are generally used in low pressure fluids or where the elbows are limited during installation. Long-radius elbows are preferred if there are no conditions or are not specified in the contract.

for example, we will find the center to face distance of NPS 2 elbows (the A distance on the image)

• 90°-LR : = 1½ x 2(NPS) x 25.4 A=76.2 mm
• 180°-LR : = 2 times the 90° LR elbow A=152.4 mm
• 90°-SR : = 2(NPS) x 25.4 A=50.8 mm
• 180°-SR : = 2 times the 90° SR elbow A=101.6 mm

The center to face distance for a “long” radius elbow, abbreviated LR always is “1½ x Nominal Pipe Size (NPS) (1½D)”, while the center to face distance for a “short” radius elbow, abbreviated SR even is to nominal pipe size.

## Types of elbows Types of long radius (LR) elbows

• 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 elbow changes the direction by 180 degrees.

## Types of short radius (SR) elbows

• S/R 45°Elbow – Short radius 45° elbow changes the direction by 45 degrees.
• S/R 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.
• S/R 180°Elbow- Short Radius 180° return bend allows complete reversal of flow.

## ASME B16.9 Butt weld 45/90 degree Long Radius Elbow Dimensions

 NPS O.D. D 90 degrees Long Radius Center-to-End A 45 degrees Long Radius Center-to-End B 90 degrees 3D Center-to-End A 45 degrees 3D Center-to-End B 1/2 21.3 38 16 – – 3/4 26.7 38 19 57 24 1 33.4 38 22 76 31 1¼ 42.2 48 25 95 39 1½ 48.3 57 29 114 47 2 60.3 76 35 152 63 2½ 73 95 44 190 79 3 88.9 114 51 229 95 3½ 101.6 133 57 267 111 4 114.3 152 64 305 127 5 141.3 190 79 381 157 6 168.3 229 95 457 189 8 219.1 305 127 610 252 10 273 381 159 762 316 12 323.8 457 190 914 378 14 355.6 533 222 1067 441 16 406.4 610 254 1219 505 18 457 686 286 1372 568 20 508 762 318 1524 632 22 559 838 343 1676 694 24 610 914 381 1829 757 26 660 991 406 1981 821 28 711 1067 438 2134 883 30 762 1143 470 2286 964 32 813 1219 502 2438 1010 34 864 1295 533 2591 1073 36 914 1372 565 2743 1135 38 965 1448 600 2896 1200 40 1016 1524 632 3048 1264 42 1067 1600 660 3200 1326 44 1118 1676 695 3353 1389 46 1168 1753 727 3505 1453 48 1219 1829 759 3658 1516

## ASME B16.9 45°/90° Long Radius Elbow Dimensional Tolerance

 DIMENSIONAL TOLERANCES – ELBOWS For all fittings Elbows 90/45 deg 180° Returns Nominal Pipe Size (NPS) Outside Ø  at Bevel Inside Ø  at End Wall Thickness  t / t1 Center to End Dim. A-B-C-M Center to Center Dim. O Back to Face Dim. K Align- ment of Ends U 1/2 a 2 1/2 1 0,8 Not 2 7 7 1 3 a 3 1/2 1 1,6 less 2 7 7 1 4 +2 -1 1,6 than 2 7 7 1 5 a 6 +3 -1 1,6 87,50% 2 7 7 1 8 2 1,6 of nominal 2 7 7 1 10 +4 -3 3,2 tickness 2 7 7 2 12 a 18 +4 -3 3,2 3 10 7 2 20 a 24 +6 -5 4,8 3 10 7 2 26 a 30 +7 -5 4,8 3 ….. ….. ….. 32 a 48 +7 -5 4,8 5 ….. ….. …..

## ASME B16.9 Butt weld 180 degree Long Radius Elbow Dimensions

 NPS O.D. D 180° Long Radius Center to Center O Back to Face K 1/2 21.3 76 48 3/4 26.7 76 51 1 33.4 76 56 1¼ 42.2 95 70 1½ 48.3 114 83 2 60.3 152 106 2½ 73 190 132 3 88.9 229 159 3½ 101.6 267 184 4 114.3 305 210 5 141.3 381 262 6 168.3 457 313 8 219.1 610 414 10 273 762 518 12 323.8 914 619 14 355.6 1067 711 16 406.4 1219 813 18 457 1372 914 20 508 1524 1016 22 559 1676 1118 24 610 1829 1219

## ASME B16.9 180° Long Radius Elbow Dimensional Tolerance

 For all fittings 180° Returns Nominal Pipe Size (NPS) Outside Ø  at Bevel Inside Ø at End Wall Thickness  t / t1 Center to Center Dim. O Back to Face Dim. K Align- ment of Ends U 1/2 a 2 1/2 1 0,8 Not 7 7 1 3 a 3 1/2 1 1,6 less 7 7 1 4 +2 -1 1,6 than 7 7 1 5 a 6 +3 -1 1,6 87,50% 7 7 1 8 2 1,6 of nominal 7 7 1 10 +4 -3 3,2 thickness 7 7 2 12 a 18 +4 -3 3,2 10 7 2 20 a 24 +6 -5 4,8 10 7 2 26 a 30 +7 -5 4,8 ….. ….. ….. 32 a 48 +7 -5 4,8 ….. ….. …..

## ASME B16.9 Butt weld 45 degree Short Radius Elbow Dimensions

 Nom. Pipe Size Pipe Sched. or No. Center- to-end Dimen. Outside Dia. Inside Dia. Wall Thick. Approx. Weight (lb.) F OD ID T STANDARD WEIGHT 1/2 40 5/8 0.840 0.622 0.109 0.1 3/4 40 7/16 1.050 0.824 0.113 0.1 1 40 7/8 1.315 1.049 0.133 0.2 1 1/4 40 1 1.660 1.380 0.140 0.4 1 1/2 40 1 1/8 1.900 1.610 0.145 0.5 2 40 1 3/8 2.375 2.067 0.154 0.9 2 1/2 40 1 3/4 2.875 2.469 0.203 1.5 3 40 2 3.500 3.068 0.216 2.5 3 1/2 40 2 1/4 4.000 3.548 0.226 3.5 4 40 2 1/2 4.500 4.026 0.237 4.8 5 40 3 1/8 5.563 5.047 0.258 7.8 6 40 3 3/4 6.625 6.065 0.280 12 8 40 5 8.625 7.981 0.322 23 10 40 6 1/4 10.750 10.020 0.365 42 12 – 7 1/2 12.750 12.000 0.375 61 14 30 8 3/4 14.000 13.250 0.375 79 16 30 10 16.000 15.250 0.375 103 18 – 11 1/4 18.000 17.250 0.375 132 20 20 12 1/2 20.000 19.250 0.375 160 22 20 13 1/2 22.000 21.250 0.375 195 24 20 15 24.000 23.250 0.375 238 EXTRA STRONG Nom. Pipe Size Pipe Sched. or No. Center- to-end Dimen. Outside Dia. Inside Dia. Wall Thick. Approx. Weight (lb.) F OD ID T 1/2 80 5/8 0.840 0.546 0.147 0.2 3/4 80 7/16 1.050 0.742 0.154 0.3 1 80 7/8 1.315 0.957 0.179 0.4 1 1/4 80 1 1.660 1.278 0.191 0.5 1 1/2 80 1 1/8 1.900 1.500 0.200 0.6 2 80 1 3/8 2.375 1.939 0.218 1.1 2 1/2 80 1 3/4 2.875 2.323 0.276 2.1 3 80 2 3.500 2.900 0.300 3.5 3 1/2 80 2 1/4 4.000 3.364 0.318 4.8 4 80 2 1/2 4.500 3.826 0.337 6.5 5 80 3 1/8 5.563 4.813 0.375 11 6 80 3 3/4 6.625 5.761 0.432 18 8 80 5 8.625 7.625 0.500 35 10 60 6 1/4 10.750 9.750 0.500 56 12 – 7 1/2 12.750 11.750 0.500 80 14 – 8 3/4 14.000 13.000 0.500 100 16 40 10 16.000 15.000 0.500 131 18 – 11 1/4 18.000 17.000 0.500 172 20 30 12 1/2 20.000 19.000 0.500 210 22 30 13 1/2 22.000 21.000 0.500 259 24 – 15 24.000 23.000 0.500 302

## Ansi 16.9 tolerances – 45 Degree short radius elbow

 DIMENSIONAL TOLERANCES – ELBOWS For all fittings Elbows 90/45 deg 180° Returns Nominal Pipe Size (NPS) Outside Ø  at Bevel Inside Ø  at End Wall Thickness  t / t1 Center to End Dim. A-B-C-M Center to Center Dim. O Back to Face Dim. K Align- ment of Ends U 1/2 a 2 1/2 1 0,8 Not 2 7 7 1 3 a 3 1/2 1 1,6 less 2 7 7 1 4 +2 -1 1,6 than 2 7 7 1 5 a 6 +3 -1 1,6 87,50% 2 7 7 1 8 2 1,6 of nominal 2 7 7 1 10 +4 -3 3,2 tickness 2 7 7 2 12 a 18 +4 -3 3,2 3 10 7 2 20 a 24 +6 -5 4,8 3 10 7 2 26 a 30 +7 -5 4,8 3 ….. ….. ….. 32 a 48 +7 -5 4,8 5 ….. ….. …..

## ASME B16.9 90 degree Short Radius Elbow Dimensional

 NPS O.D. D Center-to-End A 1 33.4 25 1¼ 42.2 32 1½ 48.3 38 2 60.3 51 2½ 73 64 3 88.9 76 3½ 101.6 89 4 114.3 102 5 141.3 127 6 168.3 152 8 219.1 203 10 273 254 12 323.8 305 14 355.6 356 16 406.4 406 18 457 457 20 508 508 22 559 559 24 610 610

## ASME B16.9 90°Short Radius Elbow Dimensional Tolerance

 Nominal Pipe Size 1/2 to 2½ 3 to 3½ 4 5 to 8 10 to 18 20 to 24 26 to 30 32 to 48 Outside Diameter at Bevel (D) + 1.6 – 0.8 1.6 1.6 + 2.4 – 1.6 + 4 – 3.2 + 6.4 – 4.8 + 6.4 – 4.8 + 6.4 – 4.8 Inside Diameter at End 0.8 1.6 1.6 1.6 3.2 4.8 + 6.4 – 4.8 + 6.4 – 4.8 Center-to-End (A) 2 2 2 2 2 2 3 5 Wall Thickness (t) Not less than 87.5% of Nominal Wall Thickness

## ASME B16.9 Butt weld 180 degree Short radius Elbow Dimensions

 NPS O.D.D 180° Short radius 180° Short Radius Center toCenterO Back toFaceK Center toCenterO Back toFaceK 1/2 21.3 76 48 – – 3/4 26.7 76 51 – – 1 33.4 76 56 51 41 1¼ 42.2 95 70 64 52 1½ 48.3 114 83 76 62 2 60.3 152 106 102 81 2½ 73 190 132 127 100 3 88.9 229 159 152 121 3½ 101.6 267 184 178 140 4 114.3 305 210 203 159 5 141.3 381 262 254 197 6 168.3 457 313 305 237 8 219.1 610 414 406 313 10 273 762 518 508 391 12 323.8 914 619 610 467 14 355.6 1067 711 711 533 16 406.4 1219 813 813 610 18 457 1372 914 914 686 20 508 1524 1016 1016 762 22 559 1676 1118 1118 838 24 610 1829 1219 1219 914

## ASME B16.9 180° Short Radius Elbow Dimensional Tolerance

 For all fittings 180° Returns Nominal Pipe Size (NPS) Outside Ø at Bevel Inside Øat End Wall Thickness t / t1 Center to Center Dim.O Back to Face Dim.K Align- ment of EndsU 1/2 a 2 1/2 1 0,8 Not 7 7 1 3 a 3 1/2 1 1,6 less 7 7 1 4 +2 -1 1,6 than 7 7 1 5 a 6 +3 -1 1,6 87,50% 7 7 1 8 2 1,6 of nominal 7 7 1 10 +4 -3 3,2 thickness 7 7 2 12 a 18 +4 -3 3,2 10 7 2 20 a 24 +6 -5 4,8 10 7 2 26 a 30 +7 -5 4,8 ….. ….. ….. 32 a 48 +7 -5 4,8 ….. ….. …..

## What is the difference between a long radius elbow and a short radius elbow?

For example:
ASME B16.9

• Short Radius Elbow = 1 x NPS
• Long Radius Elbow = 1.5 x NPS

Lets take an 18″-SCH XH seamless long radius elbow, Material: SA-234-WP11 a Design Temperature of 400°F, ASME Section VIII, Division I (Table IID) has an allowable stress of 16800 psi.
Using a B16.9 long radius elbow the allowable stress would be 16800psi. we recall there was a reduction in the allowable stress of (A) * 16800. What I am looking for is what the value of (A) is and the referenced code/paragraph.

1. There are two types of pipes in the process installation, namely the outer diameter and the nominal size of the pipe. D, DN, refers to the nominal size of the pipe. It does not represent the inner diameter of the pipe or the outer diameter of the pipe. It is a nominal size designed and used. The elbow is the elbow, and the manufacturing method is divided into the push elbow, the extrusion elbow and the welded miter elbow. The structure length is 1.0D, 1.5D, 2.0D. At present, there are two kinds of norms implemented in this area in China: metric and imperial. For example: 1.5D steel seamless elbow, DN100 outer diameter ¢108 and ¢114.3, actual structural length L152, DN200 outer diameter ¢219 and ¢216.3, actual structural length L302. In use, long radius elbow (R = 15DN): in general, should be preferred; short radius elbow (R = 1.0DN): mostly used in applications where size is limited. Its high working pressure should not exceed 0.8 times of the long radius elbow of the same specification.
2. Elbow (R = nDN): used to ease the scouring and kinetic energy of the media at the corner, available to R = 3DN, 6DN, 10DN, 20DN.
3. According to different manufacturing methods, it is divided into push elbow, extrusion elbow and welded miter elbow.
4. Pushing elbows and extrusion elbows: Commonly used for welding mitered elbows on medium and small-sized pipes with strict media conditions: It is often used on large-sized pipes with moderate media conditions, and the bending radius is not less than 1.5 times the nominal diameter. When the miter angle of the miter elbow is greater than 450, it should not be used on highly toxic, flammable medium pipes, or on pipes subjected to mechanical vibration, pressure pulsation and alternating load due to temperature changes.

## LR or SR elbow to use?

1. The short radius elbow is used in tight areas, while the long radius is used under normal working conditions.
2. The long radius elbow is better than short radius elbow when it is scoured and worn.
3. The position of the two elbows should be determined according to the practical conditions, because the positions are necessary.

## How to purchase elbows?

1. Detecting the back arc of the elbow: Seamless elbow detection of the thickness of the back arc is an important task. Many large pipe elbow manufacturers or strict engineering inspection of the back arc is a must. It is related to the safety and stability of the pipeline operation.
2. Everyone knows that both the pipeline and the seamless elbow are under pressure, that is, the pressure is very large when running. Under normal circumstances, the safety factor of the thickness of the seamless elbow designed and installed is about six times. For example, the 219*8 seamless elbow, the pipeline medium is ordinary water, the temperature is usually not higher than one hundred degrees Celsius, and the pressure required to blast such a seamless elbow is about 300 kg, that is, The pressure inside the pipeline needs to reach PN30, and the seamless elbow will be blasted, and the operating pressure of this elbow is probably about it. It is estimated that the maximum will not exceed PN6.4, which is generally around PN4.0, of course. With the corrosion of the pipeline, the seamless elbow will also be corroded to varying degrees. In order to ensure its safe operation, the necessity of overhaul is great.
3. The current process of making seamless elbows will lead to the phenomenon of back arc thinning. Under normal circumstances, the wall thickness of the mouth will be about two millimeters thinner than the back arc. The common thickness and pressure will not be thin even if the back arc is thinned. There are too many safety hazards, because the elbow has not been replaced until the elbow has a dangerous accident. But as a rigorous project, what is not the same, and the medium inside the pipeline is also responsible, not just water. There may be oil or other impurities, the temperature is high and the pressure is high, and the thickness of the back arc as the weak place determines the life of the seamless elbow. Therefore, the importance of detecting the back arc is naturally great. With a thickness gauge, read the thickness of a point at the elbow directly.
4. Detect the inner and outer diameters of the elbow: For example, the outer diameter dimension D of the elbow is detected: the data of the upper limit and the lower limit are referenced, and the actually measured outer diameter of the product is qualified between the upper and lower limits, and the unqualified product is outside the upper or lower limit range.
Chart detection range: 90° elbow 1.5D outer diameter dimension D, height is H and outer arc size W

5. Detect the wall thickness of the elbow: use the thickness gauge to directly read the thickness of the thinnest part of the elbow.
6. Detect the center height of the elbow: first measure the length of the outer circle of the elbow. Using this length value /1.57, the value obtained by subtracting half of the diameter of the elbow is the center height of the elbow.
7. Detecting the weight of the elbow: The elbow is made of steel pipe. We only know the weight of the elbow when the elbow is cut, and the size of the elbow and the back arc of the elbow. The dimensions are basically the same. Let’s calculate the length of the back arc of the elbow: the diameter of the elbow is D, the radius of curvature is 1.5D, and the length of the back arc of the elbow is (1.5+0.5)*D*2*3.14/4 Simplification we can get, 1.5 times elbow back arc length L = D * 3.14. This is only an estimate. The value of the Chinese standard is slightly smaller than this value. After the length of the back arc is L, the weight of the steel pipe is calculated by the calculation formula of the steel pipe: (Da)*a*0.02466*L/1000, ( a is the wall thickness of the elbow), the unit of this weight is KG, so we can get the weight of the carbon steel elbow. If it is a stainless steel elbow, just replace 0.02466 with 0.02491. The calculated theoretical weight is then compared to the actual weight.
8. Radiographic inspection of elbows: Radiographic inspection detects volumetric defects of elbows, such as pores, slag inclusions, shrinkage cavities, and looseness.

Through a series of tests, you will be able to purchase good quality elbows.

Source: China Steel Elbows Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.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.)

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

References:

• www.yaang.com

## How to calculate long radius elbow Center?

Formula for calculating center to end distance of such elbows is as follows:
Elbow length in mm = Tan(Elbow Angle/2) X Elbow Radius in mm
For 90° Long Radius elbows, center to end dimension given in dimension tables of ASME B16.9 is same as radius of elbow. This is because Tan(90/2) i.e. Tan 45 is 1.
Normally custom elbow angles from 45 degree to 90 are cut from 90 degree standard elbow. But for custom elbow angles smaller than 45 degree, elbow is normally cut from existing standard 45 degree elbow. Center to end dimension given in dimension tables for 45 degree elbow must be divided by Tan(22.5) to get elbow radius for standard 45 degree elbow. Then we can use above formula to get elbow angle for custom degrees.

The elbow radius mean curvature radius. If the radius is the same as pipe diameter, it called short radius elbow, also called SR elbow, normally for low pressure and low speed pipelines.
If the radius is larger than pipe diameter, R ≥ 1.5 Diameter, then we call it a long radius elbow (LR Elbow), applied for high pressure and high flow rate pipelines.

## What is Long radius 90 degree elbow?

90 degree LR elbow are installed between different lengths pipe or tubing. It helps to change direction at 90 degree, and is commonly used to connect hoses to pumps, deck drains and valve.

## What is Short radius 90 degree elbow?

90 degree SR elbow is the same as the pipe elbow mentioned above, but the diameter is shorter. Therefore, this kind of steel elbow is often used when space is not enough.

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