Pipe Reducer (ASME B16.9)
Buttweld concentric and eccentric reducers to ASME B16.9. NPS ½"–48", all schedules. Available in carbon steel, stainless, alloy, and duplex grades.
Specifications
| Parameter | Concentric | Eccentric |
|---|---|---|
| Standard | ASME B16.9 | |
| Axis alignment | Co-axial (both ends centered) | Offset (one flat side) |
| Size range | NPS ½" × ¼" to 48" × 40" (large end × small end) | |
| Wall thickness | Controlled by larger end schedule per ASME B36.10M | |
| End preparation | Beveled per ASME B16.25 | |
| Typical use | Vertical runs, symmetric flow change | Pump suction, horizontal rack alignment |
Materials
Carbon Steel
A234 WPB, WPC — standard service
Stainless Steel
A403 WP304/L, WP316/L — corrosion resistant
Alloy Steel
A234 WP11, WP22, WP91 — elevated temperature
Duplex / Super Duplex
F51, F53 — offshore and chemical plant
Applications
- →Pump suction reducers (eccentric, flat side up) to prevent air entrainment
- →Pipe rack transitions where bottom-of-pipe elevation must remain constant (eccentric)
- →Vertical header to branch run-down transitions (concentric)
- →Compressor suction and discharge transitions in oil & gas facilities
Calculate Reducer Weight
Select large end NPS, small end NPS, type (concentric/eccentric), schedule, and material.
FAQ
What is the difference between a concentric and eccentric reducer?
A concentric reducer has both ends centered on the same axis — the transition is symmetrical. An eccentric reducer has one flat side, so the centerlines of the two ends are offset. Eccentric reducers are used in horizontal pump suction lines to avoid air pockets (flat side up) and in pipe racks to maintain a common bottom-of-pipe elevation.
How is the reducer end-to-end length determined?
ASME B16.9 specifies the end-to-end length of reducers based on the larger end NPS and the ratio of the smaller-to-larger end. This 'H' dimension is tabulated in the standard and is used as the basis for weight and geometry calculations.
Can a reducer be used in both flow directions?
Yes — a reducer can be installed with flow from large-to-small (convergent, standard practice) or small-to-large (divergent, used in expansion sections). Weight and dimensions are identical regardless of flow direction. Note that a concentric reducer and eccentric reducer of the same end sizes have different weights due to geometry.