What Is an Elbolet? Elbow Outlet Fitting
An elbolet is a forged branch connection fitting designed to create an outlet directly from a pipe elbow. The contoured base matches the curved outer surface (extrados) of a 90-degree long-radius elbow, and the branch end provides a butt weld connection for the branch pipe. Elbolets are manufactured per MSS SP-97 and solve the problem of creating branch connections on elbows without cutting into straight pipe sections.
| Property | Detail |
|---|---|
| Standard | MSS SP-97 |
| Installation location | Extrados of 90° LR elbows |
| Branch angle | 90° to elbow surface (radial) |
| Branch end | Butt weld bevel (per ASME B16.25) |
| Elbow end | Contoured to match elbow OD curvature |
| Size range | Elbow: NPS 4 to NPS 36; Branch: NPS 1/2 to NPS 12 |
| Materials | ASTM A105 (CS), A182 F304/F316/F11/F22 (alloy/SS), A350 LF2 |
| Reinforcement | Integral |
When to Use an Elbolet
Elbolets address a specific piping layout problem: the need for a branch connection at an elbow location. This situation arises when:
- Space constraints prevent adding a tee before or after the elbow
- Instrument taps must be located at the elbow to measure pressure or temperature at the bend
- Drain connections are needed at the low point of an elbow (though typically on the intrados for drains)
- Vent connections are required at the high point of an elbow
| Branch/Elbow Ratio | Recommended Fitting |
|---|---|
| < 0.5 | Elbolet (standard) |
| 0.5 to 1.0 | Fabricated tee-elbow combination |
| Any (small bore) | Sockolet or threadolet on elbow |
Elbolet vs Cutting Into Straight Pipe
The alternative to an elbolet is rearranging the piping: insert a tee in the straight run before or after the elbow, and route the branch pipe accordingly. This approach is preferred when possible because:
| Factor | Elbolet on Elbow | Tee in Straight Run |
|---|---|---|
| Stress analysis | Complex (curved geometry) | Standard (well-documented SIFs) |
| Fabrication | Requires precise fit to curved surface | Standard tee welding |
| NDE | More difficult (curved weld) | Standard procedures |
| Availability | Less common than weldolets | Standard tees readily available |
| Cost | Higher (specialty fitting) | Lower |
However, when the piping layout genuinely requires a branch at the elbow location, the elbolet provides a code-compliant, integrally reinforced solution.
Installation Notes
Elbolets are installed at the 45-degree position on the elbow arc (the midpoint of the 90-degree turn). The contoured base must match the specific elbow radius, so the elbow schedule and radius (LR or SR) must be specified when ordering the elbolet.
The hole in the elbow is cut perpendicular to the elbow surface at the installation point. The elbolet is welded with a full-penetration groove weld. Inspection typically involves ultrasonic or radiographic testing.
Elbolet Variants
Like other o-let fittings, the elbolet family includes variants based on the branch end connection:
| Variant | Branch End | Application |
|---|---|---|
| Elbolet (BW) | Butt weld | Standard branch piping |
| Sockolet on elbow | Socket weld | Small-bore branches (NPS 2 and below) |
| Threadolet on elbow | Threaded NPT | Instrument connections, vent/drain taps |
For dimensional charts of all branch outlet fittings, see weldolet/elbolet/sockolet sizes.
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