Long Radius vs Short Radius Elbow
1.5D against 1.0D: how much length the tighter elbow saves, and how much pressure drop and erosion it costs you to save it.
- Long radius
- Centreline radius = 1.5 × NPS
- Short radius
- Centreline radius = 1.0 × NPS
- Average length saved
- 4.57 in
- Pressure drop
- Short radius roughly double
Short answer. A long radius elbow turns through a centreline radius of 1.5 times the nominal size; a short radius elbow uses 1.0 times. Long radius is the default everywhere — lower pressure drop, less erosion, and easier to inspect. Short radius exists for one reason: it fits where a long radius will not. Use it only where space genuinely forces it.
Two radii, one standard
ASME B16.9 sets the long radius elbow centre-to-end at A = 1.5 × NPS and the short radius elbow at A = 1.0 × NPS. Both dimensions depend on NPS alone — they do not change with wall thickness or schedule, so one table covers every schedule in that size.
Across the 19 sizes tabulated for both, the short radius elbow saves an average of 4.57 in per fitting. On a compact skid or inside a vessel skirt that can be the difference between a layout that fits and one that does not.
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| NPS | Long radius centre-to-end | Short radius centre-to-end | Length saved | SR / LR ratio |
|---|---|---|---|---|
| NPS 1 | 1.5038.10 mm | 1.0025.40 mm | +0.50 in | 0.67 |
| NPS 1 1/4 | 1.8847.75 mm | 1.2531.75 mm | +0.63 in | 0.66 |
| NPS 1 1/2 | 2.2557.15 mm | 1.5038.10 mm | +0.75 in | 0.67 |
| NPS 2 | 3.0076.20 mm | 2.0050.80 mm | +1.00 in | 0.67 |
| NPS 2 1/2 | 3.7595.25 mm | 2.5063.50 mm | +1.25 in | 0.67 |
| NPS 3 | 4.50114.30 mm | 3.0076.20 mm | +1.50 in | 0.67 |
| NPS 3 1/2 | 5.25133.35 mm | 3.5088.90 mm | +1.75 in | 0.67 |
| NPS 4 | 6.00152.40 mm | 4.00101.60 mm | +2.00 in | 0.67 |
| NPS 5 | 7.50190.50 mm | 5.00127.00 mm | +2.50 in | 0.67 |
| NPS 6 | 9.00228.60 mm | 6.00152.40 mm | +3.00 in | 0.67 |
| NPS 8 | 12.00304.80 mm | 8.00203.20 mm | +4.00 in | 0.67 |
| NPS 10 | 15.00381.00 mm | 10.00254.00 mm | +5.00 in | 0.67 |
| NPS 12 | 18.00457.20 mm | 12.00304.80 mm | +6.00 in | 0.67 |
| NPS 14 | 21.00533.40 mm | 14.00355.60 mm | +7.00 in | 0.67 |
| NPS 16 | 24.00609.60 mm | 16.00406.40 mm | +8.00 in | 0.67 |
| NPS 18 | 27.00685.80 mm | 18.00457.20 mm | +9.00 in | 0.67 |
| NPS 20 | 30.00762.00 mm | 20.00508.00 mm | +10.00 in | 0.67 |
| NPS 22 | 33.00838.20 mm | 22.00558.80 mm | +11.00 in | 0.67 |
| NPS 24 | 36.00914.40 mm | 24.00609.60 mm | +12.00 in | 0.67 |
Dimensions are a function of NPS only and apply to every schedule in that size.
What the tighter turn costs
Pressure drop through a short radius elbow is roughly twice that of a long radius elbow — commonly quoted as an equivalent length of about 30 pipe diameters against 16 for the long radius, though the exact figures depend on the correlation used. On a system with many elbows that adds up to real pump head.
The tighter turn also concentrates erosion. In slurry, catalyst, flashing and any particle-laden service, the outer heel of a short radius elbow wears through markedly faster. Erosive services normally specify long radius as a minimum and often go to 3D or 5D bends instead.
Long radius (1.5D)
- The default — assume it unless something forces otherwise
- About half the pressure drop of a short radius elbow
- Better erosion and wear behaviour
- Easier to pig, inspect and radiograph
- Needs more space, which is its only real drawback
Short radius (1.0D)
- Fits where a long radius elbow will not
- Useful on compact skids, in vessel internals and headers
- Roughly double the pressure drop
- Higher erosion at the heel; poor in slurry service
- Cannot be pigged in most systems
Dimensions: 90° long radius elbow · 90° short radius elbow · 90° vs 45° · all B16.9 fittings.
Common questions
What is the difference between LR and SR elbows?
The centreline radius. A long radius elbow uses 1.5 times the nominal pipe size; a short radius elbow uses 1.0 times. The short radius elbow is more compact and has roughly twice the pressure drop.
When should a short radius elbow be used?
Only when space forces it. Most piping specifications require long radius as standard and treat short radius as an exception needing justification.
Do LR and SR elbows have the same pressure rating?
Yes. B16.9 fittings are rated by their matching pipe wall, so an elbow in a given schedule and material carries the same rating regardless of radius.
Are elbow dimensions affected by schedule?
No. ASME B16.9 centre-to-end dimensions depend only on NPS. The schedule sets the wall thickness and the weld end preparation, not the length.