1.25Cr-0.5Mo | DIN 1.7335 / 13CrMo4-5 | ASME SA182 | 485 MPa UTS | Service to 593°C | Hydrogen Service (API 941) | Class 150–2500
ASTM A182 F11 alloy steel flanges — 1.25Cr-0.5Mo, ASME SA182
F11 weld neck raised face (WNRF) flanges — high-temperature service to 593°C
ASTM A182 F11 (ASME SA182 F11) is a 1.25% chromium – 0.5% molybdenum (1.25Cr-0.5Mo) low-alloy steel forging specification covering flanges, fittings, and valve bodies for high-temperature piping service. Governed by ASTM A182 — the primary standard for alloy and stainless steel forgings used in elevated-temperature piping — the F11 grade delivers superior creep resistance, better high-temperature strength retention, and improved resistance to high-temperature hydrogen attack compared to plain carbon steel grades such as ASTM A105.
The chromium addition (1.0–1.5%) provides oxidation resistance and solid-solution strengthening at elevated temperatures. The molybdenum addition (0.44–0.65%) is the key element for creep resistance — it retards grain boundary sliding under sustained high-temperature load, allowing F11 flanges to maintain significantly higher allowable pressures above 427°C than A105. ASTM A182 F11 is supplied in three heat treatment conditions: Class 1 (annealed), Class 2 (normalised and tempered — the most widely specified condition for flanges), and Class 3 (quenched and tempered for maximum strength). Tesco Steel & Engineering manufactures F11 flanges in all types — WNRF, SORF, BLRF, SWRF, LJTF, THRF — from NPS ½ to 60, Class 150 to 2500, per ASME B16.5 and B16.47.
Critical PWHT Requirement: Post-Weld Heat Treatment (PWHT) at 675–760°C is mandatory for all pressure-containing welds on F11 flanges per ASME B31.3 Table 331.1.1 — regardless of wall thickness. Failure to PWHT creates a hard, brittle martensitic HAZ prone to hydrogen cracking and stress corrosion cracking in service.
The Cr-Mo alloy steel family provides a step-change in high-temperature performance over carbon steel. Select based on design temperature, H₂ partial pressure, and creep requirement:
| Element | F11 Limit (%) | Role in the Alloy |
|---|---|---|
| Carbon (C) | 0.05 – 0.15 | Controlled at low levels to maintain toughness and weldability; higher C raises strength but degrades weld quality |
| Manganese (Mn) | 0.30 – 0.60 | Mild solid solution strengthener; deoxidiser; controlled to limit hardenability |
| Silicon (Si) | 0.50 – 1.00 | Deoxidiser; provides minor oxidation resistance; F11 has higher Si than F22 — a key compositional difference |
| Phosphorus (P) | ≤ 0.025 | Strictly limited to prevent temper embrittlement (TE) — a critical failure mode in Cr-Mo steels during PWHT and service |
| Sulphur (S) | ≤ 0.025 | Controlled to improve toughness and prevent hot cracking during welding |
| Chromium (Cr) | 1.00 – 1.50 | Primary element for oxidation resistance and corrosion resistance at elevated temperature; contributes to hardenability |
| Molybdenum (Mo) | 0.44 – 0.65 | Key element for creep resistance — stabilises carbides and retards dislocation movement and grain boundary sliding at temperatures above 400°C; provides high-temperature strength retention |
| Property | F11 Class 1 (Annealed) |
F11 Class 2 (N & T — Standard) |
F11 Class 3 (Q & T) |
F22 Class 3 (Q & T) |
A105 (Carbon Steel) |
|---|---|---|---|---|---|
| UTS (MPa min) | 415 | 485 | 515 | 585 | 485 |
| Yield Strength (MPa min) | 205 | 275 | 310 | 380 | 250 |
| Elongation (% min) | 20 | 20 | 20 | 20 | 22 |
| Reduction of Area (% min) | 30 | 30 | 30 | 30 | 30 |
| Hardness (HBW max) | 163 | 197 | 241 | 241 | 187 |
| ASME B16.5 Group | 3.1 | 3.1 | 3.1 | 4 | 1.1 |
| Max Service Temp (°C) | 593 | 593 | 593 | 649 | 538 |
| Mandatory PWHT? | Yes | Yes | Yes | Yes | No (t < 19mm) |
| Min Preheat (°C) | 150 | 150 | 150 | 175 | 93 (t > 25mm) |
| Density (g/cm³) | 7.85 | 7.85 | 7.85 | ||
* F11 Class 2 (normalised & tempered) is the standard supply condition for flanges. Specify Class 2 unless Class 1 or Class 3 is explicitly required by your piping specification.
The key reason to specify F11 over A105 is the pressure-temperature rating at elevated temperatures. ASME B16.5 Group 3.1 (F11) gives significantly higher allowable pressures above 400°C than Group 1.1 (A105):
| Temperature (°C) | A105 Class 150 (bar) Group 1.1 |
F11 Class 150 (bar) Group 3.1 |
F11 Advantage | F11 Class 300 (bar) | F11 Class 600 (bar) |
|---|---|---|---|---|---|
| −29 to 38 | 19.6 | 20.0 | +2% | 51.1 | 102.1 |
| 100 | 17.7 | 20.0 | +13% | 51.1 | 102.1 |
| 200 | 13.8 | 19.7 | +43% | 51.1 | 102.1 |
| 300 | 12.1 | 18.1 | +50% | 47.0 | 93.9 |
| 400 | 9.3 | 16.7 | +80% | 43.4 | 86.8 |
| 450 | 7.5 | 16.0 | +113% | 41.4 | 82.7 |
| 500 | 5.7 | 14.7 | +158% | 38.2 | 76.4 |
| 538 | 4.3 | 13.4 | +212% | 34.8 | 69.6 |
| 593 | N/A | 8.5 | A105 not rated | 22.1 | 44.2 |
* Approximate values per ASME B16.5-2017 Tables 2-1.1 and 2-3.1. At 538°C, F11 Class 150 delivers over 3× the allowable pressure of A105 — making A182 F11 the correct material above 427°C for any sustained-pressure application.
| Type | Abbreviation | Application for High-Temperature F11 Service |
|---|---|---|
| Weld Neck Raised Face | WNRF | The preferred type for all high-temperature and high-pressure F11 service. Butt-welded tapered hub distributes bending stress uniformly — mandatory for Class 900+ and for cyclic thermal service such as steam turbine flanges and boiler header nozzles. |
| Slip-On Raised Face | SORF | Used in moderate-pressure F11 service (Class 150–600) where thermal cycling is limited. Less material than WNRF; however the double fillet weld creates a stress raiser — avoid in severe cyclic temperature service. |
| Blind Raised Face | BLRF | Solid disc to close steam nozzles, high-temperature reactor branch connections, and pressure test isolation points. Must be designed for the full differential pressure at maximum operating temperature. |
| Socket Weld Raised Face | SWRF | Small-bore (NPS ½–2) Class 3000/6000 instrument and utility connections in high-temperature service. The crevice between pipe and socket can trap condensate — may be avoided in steam services with crevice corrosion risk. |
| Threaded / Screwed Raised Face | THRF | Used where welding is not feasible. Not recommended for high-temperature cyclic service due to thread loosening from differential thermal expansion. Suitable for instrument connections and drain/vent points. |
| Ring Type Joint | RTJ | Machined groove for metallic ring gasket. Mandatory for high-pressure Class 900, 1500, 2500 F11 flanges in steam systems, catalytic reformers, and high-temperature reactor nozzles where spiral-wound gaskets are inadequate. |
| Long Weld Neck | LWN | Extended neck acts as both flange and nozzle neck — used on pressure vessel nozzles, boiler drum connections, and heat exchanger channel-head nozzles where a welded neck extension is required. |
| Standard / System | Designation |
|---|---|
| ASTM / ASME (Flanges) | A182 Grade F11 Class 2 / ASME SA182 F11 Cl.2 |
| UNS Number | K11572 (F11 Class 2) |
| DIN Material Number | 1.7335 |
| DIN / EN Steel Grade | 13CrMo4-5 |
| EN Standard (Forgings) | EN 10222-2 Grade 13CrMo4-5 |
| BS Standard | BS 1503 Grade 620 / BS 3604 CrMo15 |
| JIS Standard | JIS G3203 SFCM590B |
| IS Standard | IS 2002 Grade 3 |
| ASME B16.5 Material Group | Group 3.1 (1.25Cr-0.5Mo steels) |
| Filler Metal (GTAW / GMAW) | ER80S-B2 (AWS A5.28) |
| Electrode (SMAW) | E8018-B2 (AWS A5.5) — low-hydrogen |
| Related Pipe Standard | ASTM A335 Grade P11 (seamless pipe) |
| Related Fitting Standard | ASTM A234 Grade WP11 (butt-weld fittings) |
| Higher-Alloy Upgrade | ASTM A182 F22 (2.25Cr-1Mo) / F91 (9Cr-1Mo-V) |
| Standard Supply Parameters | |
|---|---|
| Size Range | NPS ½" to 60" (DN 15 to DN 1500) |
| Pressure Classes (ASME B16.5) | Class 150, 300, 600, 900, 1500, 2500 |
| Pressure Classes (ASME B16.47) | Class 75, 150, 300, 400, 600, 900 (Series A & B) |
| Bore Schedule | STD, XS, XXS, Schedule 10, 20, 40, 80, 120, 160 |
| PN Rating | PN 6, 10, 16, 25, 40, 64, 100, 160, 250, 320, 400 |
| Heat Treatment (Standard) | F11 Class 2 — Normalised and Tempered (N&T) |
| Face Types | RF (Raised Face), FF (Flat Face), RTJ (Ring Type Joint), MF (Male/Female), TG (Tongue & Groove) |
| Face Finish | 125–250 μin Ra AARH (serrated), 63–125 μin (smooth), RTJ groove per ASME B16.20 |
| Material Standard | ASTM A182 / ASME SA182 Grade F11 Class 2 |
| Dimensional Standards | ASME B16.5, ASME B16.47, MSS SP-44, API 6A |
ASME B16.5 Class 150 Raised Face — Representative Dimensions (A182 F11 WNRF)
| NPS | OD (mm) | Bolt Circle (mm) | No. of Bolts | Bolt Size | RF Dia. (mm) | Flange Thickness (mm) |
|---|---|---|---|---|---|---|
| ½" | 89 | 60 | 4 | M12 | 35 | 9.6 |
| 1" | 108 | 79 | 4 | M16 | 51 | 11.2 |
| 1½" | 127 | 98 | 4 | M16 | 73 | 12.7 |
| 2" | 152 | 121 | 4 | M16 | 92 | 14.2 |
| 3" | 190 | 152 | 4 | M20 | 127 | 15.9 |
| 4" | 229 | 190 | 8 | M20 | 157 | 17.5 |
| 6" | 279 | 241 | 8 | M24 | 216 | 20.6 |
| 8" | 343 | 298 | 8 | M24 | 270 | 22.4 |
| 10" | 406 | 362 | 12 | M27 | 324 | 23.9 |
| 12" | 483 | 432 | 12 | M27 | 381 | 25.4 |
| 16" | 597 | 540 | 16 | M30 | 489 | 28.6 |
| 20" | 698 | 635 | 20 | M30 | 597 | 31.8 |
| 24" | 813 | 749 | 20 | M30 | 711 | 34.9 |
* Dimensions per ASME B16.5-2017. Dimensions for Class 300–2500 and ASME B16.47 (NPS 26–60) available on request — contact us for certified drawings.
| Parameter | Requirement for ASTM A182 F11 |
|---|---|
| Filler — GTAW (TIG) | ER80S-B2 (AWS A5.28) — 1.25Cr-0.5Mo matching composition filler wire |
| Electrode — SMAW (Stick) | E8018-B2 (AWS A5.5) — low-hydrogen, 1.25Cr-0.5Mo electrode; bake per AWS before use |
| Wire — FCAW | E81T1-B2 (AWS A5.29) — Cr-Mo flux-cored wire, if FCAW process is qualified by the WPS |
| Preheat Temperature | Minimum 150°C (302°F) for all thicknesses — do not weld cold; preheat uniformly over at least 75 mm each side of the joint |
| Interpass Temperature | Maximum 300°C — excessive interpass temperature causes grain growth and degrades toughness in the HAZ |
| PWHT Temperature | 675–760°C (1250–1400°F) — mandatory for all pressure-containing welds per ASME B31.3 Table 331.1.1 |
| PWHT Hold Time | Minimum 1 hour per 25 mm of weld thickness (minimum 1 hour total). Controlled heating rate ≤ 220°C/h and cooling rate ≤ 280°C/h above 425°C |
| Why PWHT is Critical for F11 | Without PWHT, the HAZ contains hard martensite (>300 HBW) that is susceptible to hydrogen-induced cracking, stress corrosion cracking, and brittle fracture. PWHT tempers the martensite, reduces residual stress, and restores toughness |
| Temper Embrittlement Risk | F11 Cr-Mo steels are susceptible to temper embrittlement (TE) if slowly cooled through 375–575°C in service. Control P + Sn + Sb + As content (J-factor and X-factor) for critical applications; rapid cool after PWHT is beneficial |
| Dissimilar Metal Joints | F11-to-carbon steel (A105): use E8018-B2 or ER80S-B2 filler, apply F11 PWHT requirements (675–760°C). F11-to-stainless: use Inconel 82/182 buttering per applicable WPS |
Power Generation — Steam Systems
Superheater outlet headers, main steam line flanges, reheater connections, turbine steam chest nozzles, and feed water heater flanges in coal, gas, and nuclear power plants operating between 427°C and 593°C.
Petroleum Refinery — Hydrotreating Units
Reactor inlet/outlet flanges, high-temperature heat exchanger nozzles, and reactor effluent air cooler (REAC) inlet flanges in hydrotreaters where hydrogen partial pressure and temperature fall within the F11 Nelson curve safe zone per API 941.
Catalytic Reformers
Platformer and reformer heater inlet/outlet flanges, inter-heater connecting piping flanges, and hydrogen recycle compressor discharge flanges operating at 480–540°C in low-pressure hydrogen environments.
Petrochemical & Chemical Plants
Ethylene cracker transfer line flanges, steam reformer outlet manifold connections, methanol and ammonia synthesis loop high-temperature flanges, and catalytic dehydrogenation unit connections.
Boiler & Pressure Vessel Nozzles
Steam drum nozzles, boiler feed water heater shell nozzles, and waste heat recovery unit (WHRU) flanges in industrial and utility boilers rated above 427°C where A105 carbon steel cannot meet the required allowable pressure.
Oil & Gas — High-Temperature Processing
Amine regenerator reboiler flanges, crude vacuum column feed flanges, and coker unit fractionator bottoms flanges operating at temperatures that exceed the practical range of carbon steel.
Nuclear Power — Secondary Loop
Secondary loop steam generator outlet flanges and main feedwater line connections in some pressurised water reactor (PWR) designs, where creep resistance and high-temperature strength are required.
District Heating & CHP Systems
High-temperature district heating network flanges, combined heat and power (CHP) steam distribution headers, and industrial waste heat recovery piping flanges operating continuously above 427°C.
| Category | Standard | Scope |
|---|---|---|
| Material (Flanges & Forgings) | ASTM A182 / ASME SA182 | Alloy and SS pipe flanges, fittings, and valves — F11 chemistry, mechanical properties, and heat treatment |
| Related Pipe | ASTM A335 Grade P11 / ASME SA335 | Seamless ferritic alloy steel pipe, 1.25Cr-0.5Mo, for high-temperature service |
| Related Fittings | ASTM A234 Grade WP11 / ASME SA234 | Wrought carbon and alloy steel butt-welding fittings for moderate and high temperature service |
| Flange Dimensions | ASME B16.5 | Flanges NPS ½–24, Class 150–2500, RF/FF/RTJ |
| Large Flanges | ASME B16.47 Series A & B | Flanges NPS 26–60 |
| Pipeline Flanges | MSS SP-44 | Steel pipeline flanges — large diameter |
| Quality / MTC | EN 10204 Type 3.1 | Material test certificates with chemistry, mechanical properties, and heat treatment records |
| NDE — MT | ASTM E709 | Magnetic particle examination of alloy steel forgings |
| NDE — UT | ASTM A388 / ASME SA388 | Ultrasonic examination of heavy forgings |
| PWHT / Welding | ASME B31.3 Table 331.1.1 | Mandatory PWHT requirements for P4 (Cr-Mo) materials including F11 |
| H₂ Service | API 941 (Nelson Curves) | Steels for hydrogen service — safe operating envelope for 1.25Cr-0.5Mo vs other Cr-Mo grades |
| Welding Filler | AWS A5.28 / A5.5 | ER80S-B2 (GTAW) and E8018-B2 (SMAW) filler specifications |
| European Standard | EN 10222-2 / EN 1759-1 | 13CrMo4-5 steel forgings / European pipe flanges |
| JIS Standard | JIS B2220 / JIS G3203 | Japanese pipe flanges and Cr-Mo alloy steel forgings |
A182 F11 Weld Neck Flanges (WNRF)
A182 F11 Slip-On Flanges (SORF)
A182 F11 Blind Flanges (BLRF)
Tesco Steel & Engineering manufactures the complete range of ASTM A182 F11 / ASME SA182 F11 Class 2 alloy steel flanges: Weld Neck (WNRF / WNFF / WNRTJ), Slip-On (SORF / SOFF), Blind (BLRF / BLFF / BLRTJ), Socket Weld (SWRF), Threaded / Screwed (THRF), Lap Joint (LJTF), Long Weld Neck (LWN), Spectacle Blind, Orifice Flanges and custom vessel nozzle flanges. All F11 forgings are supplied with normalised & tempered heat treatment records and EN 10204 3.1 MTC as standard. PWHT documentation and weld maps available for turnkey project supply.
For pricing, lead times, and stock availability contact us via Inquiry Form or our technical sales team. Third-party inspection by SGS, Bureau Veritas, TÜV, or Lloyd's accepted. Export documentation (MTCs, Packing Lists, COO, NABL-accredited test reports) available for all international orders.
ASTM A182 F11 (ASME SA182 F11) is a 1.25% Cr – 0.5% Mo low-alloy steel forging specification for high-temperature piping flanges, fittings, and valve bodies. The chromium provides oxidation resistance; the molybdenum provides creep resistance above 400°C. Class 2 (normalised and tempered) is the standard supply condition: min UTS 485 MPa, min YS 275 MPa, max hardness 197 HBW.
ASTM A182 F11 flanges are rated for service up to 593°C (1100°F) per ASME B16.5 Group 3.1. At 538°C, Class 150 F11 is rated 13.4 bar — over 3× higher than A105 carbon steel (4.3 bar) at the same temperature. F11 retains this advantage because the Cr-Mo addition resists creep deformation that causes A105 to weaken rapidly above 427°C.
F11 contains 1.25%Cr-0.5%Mo; F22 contains 2.25%Cr-1%Mo. F22 has higher creep strength (UTS ≥ 585 MPa vs 485 MPa), a higher maximum temperature (649°C vs 593°C), and a higher Nelson curve threshold for hydrogen attack. F11 is the economy choice for 427–593°C; F22 is required for hydrocracker service, temperatures above 593°C, or where F11's Nelson curve limit is exceeded.
Per ASTM A182, F11 contains: C 0.05–0.15%; Mn 0.30–0.60%; Si 0.50–1.00%; P ≤ 0.025%; S ≤ 0.025%; Cr 1.00–1.50%; Mo 0.44–0.65%. The high silicon content (0.50–1.00%) distinguishes F11 from F22 (Si ≤ 0.50%). The tight phosphorus limit (≤ 0.025%) is critical to avoid temper embrittlement in service.
F11 Class 2 (normalised and tempered): min UTS 485 MPa (70 ksi), min yield strength 275 MPa (40 ksi), min elongation 20%, min reduction of area 30%, max hardness 197 HBW. F11 Class 3 (quenched and tempered): min UTS 515 MPa (75 ksi), min YS 310 MPa (45 ksi).
ER80S-B2 (AWS A5.28) for GTAW and E8018-B2 (AWS A5.5) for SMAW — both are 1.25Cr-0.5Mo matching filler metals. Minimum preheat 150°C required. Mandatory PWHT at 675–760°C for all pressure-containing welds per ASME B31.3 Table 331.1.1.
Yes. Per API 941 Nelson curves, F11 (1.25Cr-0.5Mo) can be used in hydrogen service up to approximately 320°C at high H₂ partial pressure, compared to ~220°C for carbon steel. For more demanding H₂ conditions (higher temperature or pressure), upgrade to F22 (2.25Cr-1Mo) or F91 (9Cr-1Mo-V).
F11 Class 2 is in ASME B16.5 Material Group 3.1 (1.25Cr-0.5Mo). Class 150 Group 3.1 at 538°C is rated 13.4 bar, versus 4.3 bar for Group 1.1 (A105) — a 3× pressure advantage at the same temperature and class.
The DIN / EN equivalent is 1.7335 / 13CrMo4-5, covered by EN 10222-2 (forgings) and EN 10028-2 (flat products). The British equivalent is BS 1503 Grade 620 / BS 3604 CrMo15. The JIS equivalent is JIS G3203 SFCM590B.
Yes — PWHT is mandatory for ALL pressure-containing welds on F11 regardless of wall thickness, per ASME B31.3 Table 331.1.1 (P-Number 4 material). Required range: 675–760°C (1250–1400°F), held for minimum 1 hour per 25 mm thickness. Failure to PWHT leaves the HAZ in a hard, brittle martensitic condition susceptible to hydrogen cracking and service cracking.
| Grade | A182 F11 Class 2 |
| UNS | K11572 |
| DIN | 1.7335 / 13CrMo4-5 |
| ASTM | A182 / ASME SA182 |
| Condition | Normalised & Tempered |
| Alloy | 1.25Cr – 0.5Mo |
| Cr | 1.00 – 1.50% |
| Mo | 0.44 – 0.65% |
| C | 0.05 – 0.15% |
| Si | 0.50 – 1.00% |
| UTS (min) | 485 MPa (70 ksi) |
| YS (min) | 275 MPa (40 ksi) |
| Elongation | ≥ 20% |
| Hardness (max) | 197 HBW |
| Density | 7.85 g/cm³ |
| Max Temp | 593°C (1100°F) |
| B16.5 Group | Group 3.1 |
| Filler (GTAW) | ER80S-B2 |
| Electrode (SMAW) | E8018-B2 |
| Preheat (min) | 150°C |
| PWHT | 675–760°C (Mandatory) |
| H₂ Service | API 941 — to ~320°C |
| Sizes | ½" – 60" NB |
| Classes | 150# – 2500# |