Types of pipe fittings and their uses
Fittings change the direction, size or branching of a pipeline. They come in two families: buttweld fittings (ASME B16.9) for most process piping, and forged socket weld and threaded fittings (ASME B16.11) for small bore.
Elbows
Change direction by 90°, 45° or 180°. Long-radius (LR) elbows have a centreline radius of 1.5 × NPS and are the default; short-radius (SR) elbows (1.0 × NPS) save space at the cost of higher pressure drop. See B16.9 dimensions.
Tees and crosses
Equal tees have the same size on all three ends; reducing tees have a smaller branch. Crosses add a fourth outlet but are rare in process plants because of stress concentration.
Reducers
Concentric reducers keep the centreline, typical in vertical lines. Eccentric reducers keep one side flat — flat-on-top at pump suctions to avoid trapping vapour, flat-on-bottom in pipe racks to keep a constant bottom of pipe.
Caps and stub ends
Caps close a pipe end permanently by welding. Stub ends are short pipe pieces with a lap that work with a lap joint flange — see types of flanges.
Buttweld vs forged fittings
Buttweld fittings match the pipe wall schedule and are welded end to end, giving a smooth bore and full strength. Forged fittings to B16.11 are rated by class — 2000, 3000 and 6000 for threaded; 3000, 6000 and 9000 for socket weld — and are mostly used at NPS 2 and below.
Frequently asked questions
What is the difference between LR and SR elbows?
A long-radius elbow has a centreline radius of 1.5 × the nominal size; a short-radius elbow has 1.0 ×. SR is more compact but causes more pressure drop.
Where should an eccentric reducer be used?
At pump suctions (flat side up, to avoid vapour pockets) and in pipe racks where the bottom of the pipe must stay level.
Which standard covers socket weld fittings?
ASME B16.11, in pressure classes 3000, 6000 and 9000.
Last updated 2026-11-02