Flange & Forging Materials — Carbon, Stainless and Alloy Steel
The material decides how a flange behaves in service far more than the flange type does. Temperature, chloride level, sour service and cost all narrow the choice before the standard and class are selected.
We machine and forge carbon, stainless, duplex and alloy grades, and supply material certificates to EN 10204 3.1 with every shipment. The comparison below is a starting point — send the service conditions and we will confirm a grade.
Carbon Steel
A105, A105N, A350 LF2, A694 F52/F60, Q235B
Oil, gas, water and steam service; lowest cost
Stainless Steel
304/304L, 316/316L, 321, 347, 2205, 2507, 904L
Chemical, food, marine and chloride-bearing service
Alloy Steel
F5, F9, F11, F22, F91, 4140, 4340
High-temperature refinery and power piping
Material comparison
| Material | Corrosion resistance | Service temperature | Strength | Relative cost | Typical service |
|---|---|---|---|---|---|
| Carbon (A105) | Low | −29 to 425 °C | Medium | Lowest | General piping, steam, water |
| Low-temp (A350 LF2) | Low | −46 to 345 °C | Medium | Low | Cold service, LNG, refrigeration |
| Stainless 304/316L | High | −196 to 400 °C | Medium | Medium | Chemicals, food, marine atmosphere |
| Duplex 2205 | Very high (chlorides) | −50 to 300 °C | High | High | Offshore, desalination, sour service |
| Alloy F11/F22 | Medium | up to 590 °C | High (hot) | High | Refinery, high-pressure steam |
| Alloy F91 | Medium | up to 625 °C | Very high (hot) | Highest | Advanced steam, main steam lines |
For low-temperature impact testing, sour service (NACE MR0175) or elevated-temperature creep data, send the design conditions — those cases need grade-specific verification, not a table. Send the data sheet and we will confirm the grade and the applicable pressure rating in writing.
Certificates and verification
Material certificates to EN 10204 3.1 report the actual chemical composition and mechanical results for the heat, and the heat number is stamped on the part so the certificate can be matched to the component. For stainless and alloy grades, PMI is performed before shipment to confirm the grade and detect mixed material. Where the project requires independent endorsement, 3.2 certification with third-party witnessing is available at the quotation stage. Certificates are issued for the exact heat supplied — not a generic sample from stock.
Temperature is usually the first filter
Below −29 °C, standard carbon steel loses toughness and an impact-tested grade such as A350 LF2 is required. Between ambient and about 425 °C, A105 covers most duties. Above that, creep becomes the design case and chromium-molybdenum grades — F11, F22, F91 — take over. Stainless grades sit outside this ladder: they are chosen for corrosion, and their useful temperature range is set by sensitisation or sigma-phase formation.
Material group changes the rating
ASME B16.5 assigns each material to a group, and the allowable pressure for a given class comes from that group's stress table. A Class 300 flange in carbon steel and a Class 300 flange in 316L share the same dimensions but not necessarily the same allowable pressure at temperature. That is why the material belongs on the purchase order even when the class is unchanged.
Corrosion and sour service
Chlorides decide between 304 and 316, and between 316 and duplex. Sour service (H₂S) adds a hardness limit and a material qualification under NACE MR0175 / ISO 15156 — a standard A105 flange may not comply even though the pressure rating is adequate. For these cases the material, heat treatment and hardness all have to be specified together.
What to send with the inquiry
- Fluid, design temperature and design pressure
- Standard, size and class or PN rating
- Quantity per size and destination port
- Certificate level and any NDT or third-party requirement