ASME B16.28

Covers — short radius elbows and returns:

• Sizes from NPS 1/2 to NPS 24.
• 90° Short Radius (SR) elbows.
• 180° Short Radius (SR) returns.
• Wall thickness matching the connecting pipe schedule (like B16.9).

Does NOT cover (exclusions) — the following are governed elsewhere:

• 45° elbows (SR is not standardized for 45°).
• Long radius (LR) elbows, tees, reducers, and standard fittings → ASME B16.9.

The defining and singular characteristic of B16.28 fittings is their tight bend radius:

• Radius Length — The center-to-face dimension of a Short Radius (SR) elbow is exactly 1 times the Nominal Pipe Size (1D). For example, an NPS 10 SR elbow has a 10-inch radius.
• Comparison to LR — A standard B16.9 Long Radius (LR) elbow has a radius of 1.5 times the NPS (1.5D). An NPS 10 LR elbow has a 15-inch radius. This means an SR elbow saves 5 inches of space in each direction.

Short radius elbows are considered an exception in piping design rather than the rule. They are primarily utilized in extremely tight skid-mounted equipment packages, submarine and ship engine rooms, and dense heating coils where a standard 1.5D elbow simply will not fit physically.

However, this space savings comes at a massive hydraulic and mechanical cost. Because of the abrupt change in flow direction, SR elbows induce significantly higher pressure drop, extreme turbulence, and rapid erosion rates inside the pipe compared to standard LR elbows. They also have a higher Stress Intensification Factor (SIF) in piping flexibility analysis, making them more prone to fatigue failure.