Reducer — ASME B16.9
Reducer — a fitting that joins two pipes of different sizes. Concentric reducers keep the centreline in line and suit vertical lines. Eccentric reducers keep one side flat — flat on top at pump suctions to avoid air pockets, flat on the bottom in pipe racks.
- ASME B16.9
- 22 grades
- EN 10204 3.1 / 3.2
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is a reducer?
A reducer is a fitting that joins two pipes of different sizes. Concentric reducers keep the centreline in line and suit vertical lines. Eccentric reducers keep one side flat — flat on top at pump suctions to avoid air pockets, flat on the bottom in pipe racks.
Standards for reducers
Reducer: What to Know Before Ordering
- Concentric and eccentric
- Flat-top on pump suction
- Seamless or welded
Reducer Materials & Grades
| Grade | Material standard | Best for |
|---|---|---|
| Inconel 825 reducer | ASTM B366 WPNICMC | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 904L reducer | ASTM A403 WP904L | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| SS 304 reducer | ASTM A403 WP304 | General corrosion resistance, food, water and architectural work |
| SS 304L reducer | ASTM A403 WP304L | Welded tanks, piping and vessels in general corrosive service |
| SS 310 / 310S reducer | ASTM A403 WP310S | Furnaces, burners and heat treatment at high temperature |
| SS 316 / 316L reducer | ASTM A403 WP316L | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 321 reducer | ASTM A403 WP321 | High-temperature service between 425 and 815 °C |
| SS 347 reducer | ASTM A403 WP347 | Welded high-temperature piping in refineries and power plants |
| Duplex 2205 reducer | ASTM A815 WPS31803 / WPS32205 | Strength with chloride resistance at a stainless-steel budget |
| Super Duplex 2507 reducer | ASTM A815 WPS32750 | Seawater and high-chloride service where strength also matters |
| Inconel 600 reducer | ASTM B366 WPNCI | High-temperature oxidation, caustic and nuclear service |
| Inconel 625 reducer | ASTM B366 WPNCMC | Seawater, high strength and high temperature in one alloy |
| Inconel 718 reducer | a specification not yet established | Very high strength at temperatures up to about 650 °C |
| Incoloy 800 / 800H / 800HT reducer | ASTM B366 WPNIC | Furnaces, petrochemical heaters and high-temperature piping |
| Hastelloy C276 reducer | ASTM B366 WPHC276 | The most aggressive mixed acids, wet chlorine and hypochlorite |
| Hastelloy C22 reducer | ASTM B366 WPHC22 | Mixed oxidising and reducing acids, and weld overlays |
| Monel 400 reducer | ASTM B366 WPNC | Seawater, hydrofluoric acid and marine service |
| Super Duplex S32760 reducer | ASTM A815 WPS32760 | Seawater firewater, injection and offshore piping |
| ASTM A106 Gr B reducer | ASTM A234 WPB | High-temperature process and steam piping in refineries and power plants |
| ASTM A333 Gr 6 reducer | ASTM A420 WPL6 | Cold-climate and refrigerated piping down to −45 °C |
| ASTM A335 P11 reducer | ASTM A234 WP11 | Steam and hot-oil piping up to about 550 °C |
| ASTM A335 P22 reducer | ASTM A234 WP22 | High-pressure steam and hydrogen service up to about 580 °C |
Other pipe fittings
Reducer dimensions — ASME B16.9
Values in mm, the same for every material; the wall thickness matches the pipe schedule.
| NPS | OD | Reducer length H |
|---|---|---|
| ½" | 21.3 | — |
| ¾" | 26.7 | 38 |
| 1" | 33.4 | 51 |
| 1½" | 48.3 | 64 |
| 2" | 60.3 | 76 |
| 3" | 88.9 | 89 |
| 4" | 114.3 | 102 |
| 6" | 168.3 | 140 |
| 8" | 219.1 | 152 |
| 10" | 273.1 | 178 |
| 12" | 323.9 | 203 |
| 16" | 406.4 | 356 |
| 20" | 508.0 | 508 |
| 24" | 610.0 | 508 |
Full chart: ASME B16.9 fitting dimensions.
Reducer — questions buyers ask
What is a reducer?
A reducer is a fitting that joins two pipes of different sizes. Concentric reducers keep the centreline in line and suit vertical lines. Eccentric reducers keep one side flat — flat on top at pump suctions to avoid air pockets, flat on the bottom in pipe racks.
Why use an eccentric reducer at a pump suction?
Installed flat side up, it prevents air pockets that can cause cavitation.
Which grades are reducers available in?
Inconel 825, SS 904L, SS 304, SS 304L, SS 310 / 310S, SS 316 / 316L, SS 321, SS 347, Duplex 2205, Super Duplex 2507, Inconel 600, Inconel 625, Inconel 718, Incoloy 800 / 800H / 800HT, Hastelloy C276, Hastelloy C22, Monel 400, Super Duplex S32760, ASTM A106 Gr B, ASTM A333 Gr 6, ASTM A335 P11, ASTM A335 P22.
Which standard covers reducer dimensions?
ASME B16.9 · MSS SP-43. The material standard depends on the grade.
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026