Reducers to ASME B16.9: dimensions and drawing

Dimension table ASME B16.9 – reducers

Reducer (concentric and eccentric)

from stock · to order · available on request – what is available how fast, we clarify on request.

Dimensions: as the market supplies them – from manufacturers’ and suppliers’ documentation and from our own product data, checked against ASME B16.9. Tolerances: limit deviations from manufacturers’ and suppliers’ documentation. The dimensions are the same for every schedule – the wall at the welding end is the pipe wall.

The table shows the market dimensions. What we carry from stock or to order is marked – the other sizes we procure on request.

Limit deviations

For the fitting types in the tables above, by size range. The wall may be 12.5 % below the nominal wall at any point, with no upper limit.

This information does not replace purchasing the standard. The limit deviations are given in full in ASME B16.9-2024, section 11 – the minimum wall thickness at the welding end in section 11.1. Available from: ASME (asme.org).

How to measure

• Outside diameter D: measure at the bevel, twice at right angles – the body of a formed fitting may be thicker and is not the reference
• Wall T: the fitting is ordered by schedule, the wall at the bevel equals the pipe wall – measure with an ultrasonic gauge or at the cut face, 87.5 % minimum applies
• Centre-to-end A (90° elbow): lay the elbow on a plate, measure from the bevel face to the intersection of the two leg axes – for a long radius elbow this equals 1.5 × NPS in inches, so a 4 in LR elbow measures 6 in (152 mm)
• Centre-to-end B (45° elbow): not half of A – B = A × tan 22.5°, the tables round it (4 in LR: 2.50 in / 64 mm)
• 180° return: O is centre-to-centre of the two legs (3 × NPS for LR), K is back-to-face – the installed length – check the alignment of the two ends against a straightedge (U)
• Tee: C from the run axis to the run bevel, M from the run axis to the outlet bevel – on reducing tees M is shorter than C, the run length C does not change with the outlet size
• Reducer H: end to end along the axis – the same for concentric and eccentric – on the eccentric reducer measure along the flat generatrix
• Cap E: from the bevel face to the crown – heavy-wall caps (Sch 160, XXS) are longer (E1), the only B16.9 dimension that changes with the wall
• Stub end: F overall length, G lap diameter (fits the bore of the lap joint flange, B16.5 type LJ), R fillet radius – check G and R together with the flange of the same class

Welding ends to ASME B16.25

How the ends of pipes and fittings are prepared for butt welding – unless the order says otherwise:

• wall thickness below x (x = 0.19 in / 4.8 mm for carbon and ferritic alloy steel, 0.12 in / 3 mm for austenitic steel): ends cut square or slightly chamfered, at the manufacturer’s option – no bevel
• wall thickness x to 0.88 in (22 mm) inclusive: plain bevel 37.5° ± 2.5°, root face 0.06 in ± 0.03 in (1.6 mm ± 0.8 mm)
• wall thickness over 0.88 in (22 mm): compound bevel – 37.5° ± 2.5° from the root face up to 0.75 in (19 mm), then 10° ± 2.5° to the outside, root face 0.06 in ± 0.03 in (1.6 mm ± 0.8 mm)
• transition contours from the bevel into the body of the fitting follow ASME B16.9 (maximum envelope) – the catalogue refers to the standard
• minimum wall thickness at the end 87.5 % of nominal (pipe rule) – inside diameter and nominal wall at the ends are specified by the purchaser
• the same bevel geometry applies to pipe (B36.10M ends), fittings (B16.9) and welding neck flanges (B16.5 hub end) – B16.25 is the common end-preparation standard

How to read the table

H is the end-to-end length over both welding ends – the same for concentric and eccentric reducers of a size pair. The eccentric reducer keeps one generatrix straight; order it with the position of the flat side (top or bottom). The size names the large end first, then the small end: 8 × 6.

The wall thickness per schedule is given for steel pipe to ASME B36.10M, all shapes on the ASME B16.9 overview, the standard profile under ASME B16.9.