Dimensional standard
ASME B16.9
Factory-Made Wrought Buttwelding Fittings
ASME B16.9 covers dimensions, tolerances and marking for factory-made wrought buttwelding fittings such as elbows, tees, reducers, caps and stub ends.
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What it covers
- Buttweld elbows (45°, 90°, 180°) in long and short radius.
- Equal and reducing tees, concentric and eccentric reducers.
- Caps, lap joint stub ends and returns.
- Sizes are matched to pipe outside diameters and wall thickness schedules.
Practical notes
Points to specify
- Fitting wall thickness is normally specified by pipe schedule (for example SCH 40, SCH 80, SCH 160 or XXS).
- Centre-to-end and centre-to-centre dimensions are standardised so fittings interchange between makers.
- Weld end preparation for buttweld fittings follows ASME B16.25.
Common questions about ASME B16.9
- What is the difference between long radius and short radius elbows?
- A long radius elbow has a centreline radius of 1.5 times the nominal pipe size; a short radius elbow uses 1.0 times the nominal size, which suits tighter layouts but creates higher pressure drop.
- How is buttweld fitting thickness specified?
- By matching the schedule or wall thickness of the connecting pipe, so the bore and weld ends align.
More references
General guidance only. Work from the current published edition of the standard and your project specification; sizes, grades, classes and documentation are confirmed per enquiry.