What Is an ASME B16.5 Threaded Flange?
A threaded (screwed) flange has a tapped bore with a taper pipe thread (NPT) that screws onto the pipe — no welding is required. Covered by ASME B16.5, it is used where hot work or welding is restricted, for small lines, air and water service, and for joints that must be disassembled often. Threads conform to ASME B1.20.1.
Size & Pressure Class Range
- Sizes: NPS 1/2 through NPS 24 (Classes 150–1500); NPS 1/2 through NPS 12 (Class 2500), per ASME B16.5-2025 scope
- Thread: taper pipe thread per ASME B1.20.1 (NPT)
- Connection: screwed onto threaded pipe; no fillet or butt weld
Pressure-Temperature Ratings (Group 1.1 Carbon Steel, at 38°C)
| Class | 150 | 300 | 400 | 600 | 900 | 1500 | 2500 |
|---|---|---|---|---|---|---|---|
| Rating, bar | 19.6 | 51.0 | 68.0 | 102.0 | 153.1 | 255.1 | 425.1 |
Materials & Temperature Limits
| Material | Grade | Temperature Range |
|---|---|---|
| ASTM A105 | Carbon steel forging | -29°C to 425°C |
| ASTM A182 | F304 / F304L / F316 / F316L | Up to 538°C |
| ASTM A350 | LF2 | -46°C to 425°C (low-temperature service) |
Dimensions
Threaded flange dimensions — outside diameter O, minimum thickness tf, hub diameter X, hub length Y, minimum thread length T and counterbore Q — are listed per class in the dimensional tables of ASME B16.5-2025: Table 8 (Class 150), Table 11 (Class 300), Table 14 (Class 400), Table 16 (Class 600), Table 18 (Class 900), Table 20 (Class 1500) and Table 22 (Class 2500), SI units. Thread concentricity and alignment tolerances are specified in ASME B16.5 para. 6.9.
Related Standards
- ASME B16.5 — Pipe Flanges Overview (NPS 1/2–24)
- ASME B16.5 Socket Weld Flanges
- ASME B16.5 Weld Neck Flanges
- ASME B16.11 — Threaded & Socket-Welding Fittings
- Our Flange Range
- ASTM A105 Carbon Steel Forgings
- ASTM A182 F304 Stainless Steel
FAQ
What thread standard do ASME B16.5 threaded flanges use?
A taper pipe thread conforming to ASME B1.20.1 (NPT), per ASME B16.5 para. 6.9.1. The thread is concentric with the flange axis.
When should I specify a threaded flange?
Where welding is prohibited (hot-work permits, explosive areas), for small air/water lines, or for joints that need frequent disassembly. For critical high-pressure service, socket weld or weld neck is preferred.
What sizes are available?
NPS 1/2 through NPS 24 in Classes 150–1500, and NPS 1/2 through NPS 12 in Class 2500, per the ASME B16.5-2025 scope.
Can threaded flanges seal on their own?
The threaded joint is sealed with thread compound or PTFE tape; the flange face still uses a gasket between the two mating flanges, exactly like any other B16.5 flange.
Do you supply threaded flanges in stainless steel?
Yes — A182 F304/F304L/F316/F316L threaded flanges, plus A105 carbon steel and A350 LF2 low-temperature steel, tapped to NPT and gauged per ASME B16.5.