PVF Reference Library · Technical Reference

Butt-Weld Fittings

Butt-weld fittings are elbows, tees, reducers and caps with beveled ends that are welded straight to the pipe. This sheet covers the common shapes, the material specs for carbon and stainless steel, and what must match the pipe.

Ref PV-0017ASME B16.9ASTM A234ASTM A403

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Butt-weld (BW) fittings are made to the dimensions in ASME B16.9 (and MSS SP-43 for light-wall stainless). The ends are beveled to be welded to pipe of the same size and wall. Carbon steel fittings are usually ASTM A234 grade WPB. Stainless fittings are ASTM A403 grades such as WP304L and WP316L. Weld end bevels follow ASME B16.25. Butt-weld systems are used for process, steam, oil and gas and other high-pressure or high-temperature lines where threaded or socket-weld joints are not wanted.

How to identify

Read the stencil or stamp on the fitting: maker, material spec and grade (such as WPB or WP316L), size, schedule or wall, and a heat number for traceability. Long-radius elbows are longer and more gradual than short-radius elbows of the same size. See the fitting and flange marking chart.

Common butt-weld fittings

Fitting	Use	Note
90° long-radius elbow	Standard direction change	Center-to-end is 1.5 x NPS for NPS 3/4 and up
90° short-radius elbow	Tight space	Center-to-end is 1.0 x NPS; higher pressure drop
45° elbow	Gentle turn	Long radius
Straight tee	Equal branch
Reducing tee	Smaller branch	Ordered as run x branch
Concentric reducer	Size change on centerline	Vertical lines, pump discharge
Eccentric reducer	Size change with one flat side	Pump suction (flat side up), drainage (flat side down)
Cap	Close a line
Stub end	Used with lap joint flange	See flange types

Key points

Wall thickness (schedule) of the fitting must match the pipe. Mismatched walls need a taper transition.
Material must suit the pipe and service. WPB fittings with A106 or A53 carbon pipe; WP304L or WP316L with matching stainless pipe.
Weld procedures and welder qualifications follow the governing code (such as ASME B31.1 or B31.3).
Pressure ratings for fittings follow the matching pipe under B16.9 rules. Use the piping code for design.
Keep heat numbers and material test reports when traceability is required.

Common mistakes

Using a Schedule 40 fitting on Schedule 80 pipe.
Mixing carbon and stainless fittings without a qualified dissimilar-metal procedure.
Installing an eccentric reducer with the flat side the wrong way at a pump suction.
Grinding the bevel off to fit and changing the weld prep.

Governing standards: ASME B16.9 (factory-made wrought butt-welding fittings); ASME B16.25 (butt-welding ends); ASTM A234 (carbon and alloy steel fittings); ASTM A403 (stainless steel fittings).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

More in Technical Reference

← All PVF sheets