Long Radius Elbow VS Short Radius Elbow

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.

Elbows are available in two radius types, Short radius elbow (1D) and Long radius elbow (1.5D).

What is a long radius elbow What is a short radius elbow
Types of elbows Long Radius Elbow vs Short Radius Elbow
LR or SR elbow to use How to purchase elbows

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.

bw elbows1 1 - Long Radius Elbow VS Short Radius Elbow

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

Long radius elbows Long Radius (LR) Elbows – 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 elbow changes the direction by 180 degrees.

Dimensions of 45 degree LR elbow  Dimensions of 90 degree LR elbow  Dimensions of 180 degree LR elbow

Types of short radius (SR) elbows

Short radius elbows Short Radius (SR) Elbows – radius is 1.0 times the pipe diameter

  • 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.

Dimensions of 45 degree SR elbow  Dimensions of 90 degree SR elbow  Dimensions of 180 degree SR elbow

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

45 deg long redius dimen - Long Radius Elbow VS Short Radius Elbow90 deg long redius dimen - Long Radius Elbow VS Short Radius Elbow

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

42.2

48

25

95

39

48.3

57

29

114

47

2

60.3

76

35

152

63

73

95

44

190

79

3

88.9

114

51

229

95

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

180 deg long redius dimen - Long Radius Elbow VS Short Radius Elbow

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
42.2 95 70
48.3 114 83
2 60.3 152 106
73 190 132
3 88.9 229 159
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

45 deg short redius dimen - Long Radius Elbow VS Short Radius Elbow

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

90 deg short redius dimen - Long Radius Elbow VS Short Radius Elbow

NPS O.D.
D
Center-to-End
A
1 33.4 25
42.2 32
48.3 38
2 60.3 51
73 64
3 88.9 76
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

180 deg short redius dimen - Long Radius Elbow VS Short Radius Elbow

NPS O.D.
D
180° Short radius 180° Short Radius
Center to
Center
O
Back to
Face
K
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 51 41
42.2 95 70 64 52
48.3 114 83 76 62
2 60.3 152 106 102 81
73 190 132 127 100
3 88.9 229 159 152 121
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 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 ….. ….. …..

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

The elbow is divided into its radius of curvature and can be divided into a long radius elbow and a short radius elbow. The long radius elbow refers to the outer diameter of the tube 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 outer diameter of the tube, ie R = D. Where D is the diameter of the elbow and R is the radius of curvature. Normal use of the length of the radius Sometimes to reduce the loss of resistance or elbow wear, the elbow with a larger bending radius will be used (in fact, it is not called elbow); when there is a limit on the installation position, a short radius elbow will be used.

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
     20180124161507 65188 - Long Radius Elbow VS Short Radius Elbow
  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.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

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

References:

  • www.yaang.com

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