Long radius (LR) and short radius (SR) describe the centerline bend radius of butt weld elbows. The choice affects pressure drop, erosion, space and cost – here is the complete comparison.
The Difference
A long radius elbow has a centerline radius of 1.5 x NPS – a 6″ LR elbow bends with a 9″ radius. A short radius elbow bends at 1.0 x NPS – half the footprint. Both are made per ASME B16.9 in 45°, 90° and 180° versions; SR exists only for 90° and 180° (45° is LR only).
Comparison Table
| Factor | Long Radius (LR) | Short Radius (SR) |
|---|---|---|
| Bend radius | 1.5 x NPS | 1.0 x NPS |
| Pressure drop | Lower (gentler turn) | ~1.5x higher loss |
| Erosion | Lower wall wear | Faster wear on abrasive media |
| Space needed | More | 25% less per turn |
| Typical use | Process lines, pump discharge, slurries | Skids, marine, tight retrofits |
| Cost | Standard | Similar or slightly higher |
Selection Rules
Default to LR for process piping – lower pressure drop, less erosion on abrasive or high-velocity media, and lower stress at the welds. Choose SR where the layout physically cannot fit LR: inside equipment skids, between closely spaced walls, marine engine rooms, and compact retrofits. Some older plants are built entirely in SR; replacement fittings must match. Note that pump suctions generally avoid SR elbows entirely – the abrupt turn disturbs flow into the impeller.
FAQs
Can I replace an SR elbow with LR? Only if the pipe legs can absorb the extra length – LR is 0.5 x NPS longer per fitting. Check clearances and re-cut the spools.
Do LR and SR cost the same? Similar – SR sometimes slightly more due to lower production volume. Choose by engineering need, not price. See our 90° elbow page for ordering.
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