What Is a Butt Weld Fitting?
A butt weld (BW) fitting is a pipe component joined to the pipeline by a full-penetration circumferential butt weld. This connection method produces a continuous, leak-free joint with strength equal to the pipe itself. BW fittings are the standard choice for process piping above NPS 2 in oil and gas, petrochemical, and power plants.
| Property | Detail |
|---|---|
| Standard | ASME B16.9 (factory-made wrought BW fittings) |
| Size range | NPS 1/2 to NPS 48 (seamless up to ~NPS 24) |
| Types | Elbows, tees, reducers, caps, stub ends |
| End preparation | Beveled ends (37.5° bevel per ASME B16.25) |
| Wall thickness | Matches pipe schedule (SCH 5S to SCH XXS) |
| Materials | ASTM A234 (CS), A403 (SS), A815 (duplex), B366 (nickel) |
| Connection | Full-penetration butt weld |
Main Types
Butt weld fittings serve four basic functions in a piping system:
- Elbows change flow direction. Available in 45°, 90°, and 180° (return bend) configurations. Long radius (center-to-end = 1.5 x nominal diameter) is standard; short radius (1D) is used where space is limited.
- Tees create branch connections. Equal tees maintain the same bore throughout; reducing tees step down the branch size.
- Reducers change pipe diameter. Concentric reducers keep the centerline, while eccentric reducers offset it (used at pump suctions to avoid vapor pockets).
- Caps seal pipe ends. A butt weld cap provides a permanent, pressure-rated closure.
Stub ends are also classified as BW fittings. They pair with lap joint flanges to allow bolt-hole alignment without rotating the pipe.
Sizing and Dimensions
All dimensions follow ASME B16.9. Key parameters include center-to-end distance (for elbows and tees), end-to-end length (for reducers and caps), and outside diameter at the bevel end, which must match the connecting pipe OD per ASME B36.10/B36.19.
For example, a 6” SCH 40 long-radius 90° elbow has a center-to-end distance of 228.6 mm (9 inches) and an OD of 168.3 mm.
Materials
BW fitting materials must match the pipe grade. Carbon steel fittings in ASTM A234 WPB match ASTM A106 Gr. B pipe. Stainless steel fittings in ASTM A403 WP316L match A312 TP316L pipe. Mismatching grades introduces galvanic corrosion risk and code non-compliance.
BW Fittings vs Forged Fittings
For pipe sizes NPS 2 and below, socket weld and threaded forged fittings per ASME B16.11 are standard. Above NPS 2, butt weld fittings dominate because the full-penetration weld provides superior fatigue resistance and allows 100% radiographic examination.
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