Alloy Steel Flanges
Flanges join pipes, valves, pumps and equipment with a bolted, gasketed joint that can be taken apart. Dimensions and pressure-temperature ratings follow ASME B16.5 (NPS ½"–24") and B16.47 Series A/B (NPS 26"–60"), in classes 150 to 2500.
Choose a grade below for specifications, composition, sizes and weight charts.
Alloy Steel flanges by grade
| Grade | Specification | Key characteristic | Typical use |
|---|---|---|---|
| P1 Flanges | ASTM A182 F1 | About 0.5% molybdenum | Moderate-temperature steam piping |
| P5 Flanges | ASTM A182 F5 | 4–6% chromium for sulphidation resistance | Refinery heater tubes |
| P9 Flanges | ASTM A182 F9 | 8–10% Cr, 1% Mo | Fired heater and furnace tubes |
| P11 Flanges | ASTM A182 F11 | 1–1.5% Cr, 0.44–0.65% Mo | Boiler headers, tubes and steam piping |
| P22 Flanges | ASTM A182 F22 | 1.9–2.6% Cr, 0.87–1.13% Mo | Main steam and hot-reheat piping |
| P91 Flanges | ASTM A182 F91 | Creep-strength-enhanced ferritic (CSEF) steel | Main steam and hot-reheat piping |
How alloy steel flanges are made, sized and tested
How it's madeFlanges are forged from billets (or cut from plate for some blind and plate flanges), heat treated to the material specification, and machined: bore, face, raised face or ring groove, bolt holes and hub bevel.
- Size range
- NPS ½" – 24" (B16.5), 26" – 60" (B16.47 Series A/B); Class 150, 300, 600, 900, 1500, 2500; EN 1092-1 PN 6 – PN 100 on request
- Finish
- Raised face (RF), flat face (FF) or ring-type joint (RTJ); serrated spiral or concentric face finish (typically 3.2 – 6.3 µm Ra)
- Ends
- Weld-neck bevel matched to pipe schedule; socket bore; threaded
Testing & documents
- Chemical and mechanical tests of the forging
- Dimensional inspection to ASME B16.5 / B16.47
- Hardness, impact and IGC tests as specified
- Ultrasonic testing of forgings on request
- EN 10204 3.1 certificate; 3.2 with third-party inspection
Frequently asked questions
What does flange class 150 or 300 mean?
It's the pressure-temperature rating class under ASME B16.5. The allowable working pressure depends on the material group and temperature, not simply "150 psi".
RF or RTJ?
Raised-face flanges with spiral-wound or sheet gaskets are standard. Ring-type joint (RTJ) flanges with metal ring gaskets are used for high pressure and temperature.
Which alloy steel grades are available as flanges?
P1, P5, P9, P11, P22, P91.
Which specifications cover alloy steel flanges?
ASTM A182, depending on grade.
Need alloy steel flanges?
Send grade, size, quantity and destination.