Steel A369 FP91
ASTM A369 FP91
A369 FP91 is a 9Cr-1Mo-V modified (P91-type) creep-strength-enhanced ferritic steel supplied as forged and bored pipe, matching A335 P91 and X10CrMoVNb9-1 / 1.4903 (10Cr9Mo1VNb).
Reference datasheet — A369 FP91 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the N+T condition
A369 FP91 tempers and conditions
A369 FP91 is supplied in 5 conditions, soft to hard. N+T is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
~730–760 °C soften anneal (machining stock only) | Interim condition for forgings/fittings that will be re-normalized and tempered after machining; not code-acceptable for service. | 400 | 570 | 28 | 10 HRC | 3 % IACS |
N+T | Pick when hardness must sit at the low end (≤200 HB) for heavy machining or cold bending, accepting slightly lower room-temperature strength. | 450 | 615 | 26 | 190 HB | — |
N+TDefault Normalized and tempered | The only condition in which FP91 pipe is supplied and code-qualified for creep service; fully tempered martensite. | 500 | 660 | 23 | 18 HRC | — |
As-forged / as-bored, prior to final heat treatment | Mill intermediate form of the forged-and-bored pipe; properties are non-uniform and it must receive the full N+T cycle. | 550 | 800 | 16 | 25 HRC | 2.7 % IACS |
Normalized | Intermediate state after normalizing before tempering — hard, brittle and never shipped for service; must be tempered. | 900 | 1,250 | 10 | 43 HRC | — |
What is A369 FP91?
A369 FP91 is a 9Cr-1Mo-V modified (P91-type) creep-strength-enhanced ferritic steel supplied as forged and bored pipe, matching A335 P91 and X10CrMoVNb9-1 / 1.4903 (10Cr9Mo1VNb). It is specified for ultra-high-temperature steam service to 600 °C, offering 500 MPa yield, 660 MPa tensile and 23 % elongation at about 210 HB (18 HRC) in the N+T condition. Welding is procedure-critical (weldability 40/100) with mandatory preheat and 750–770 °C PWHT, and 9 % Cr is not stainless — corrosion resistance rates 30/100, so coatings or insulation are required. P92 is the next step up in creep strength. A369 FP91 has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,450°C (2,642 °F). A369 FP91 has a yield strength of 500 MPa (72.5 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 63% of steel grades. Elongation at break is 23% and the elastic modulus is 218 GPa (31.6 Msi).
What is A369 FP91 used for?
- Main steam piping for ultra-supercritical units
- Hot reheat piping
- Boiler outlet headers
- Superheater and reheater headers
- Forged pipe fittings and elbows
- HRSG high-temperature pipework
- Valve and pump bodies for high-temperature steam
Advantages
- High service temperature — 600°C (1,112 °F), better than 98% of steel grades
- Good corrosion resistance — 30/100, better than 95% of steel grades
Limitations
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
- Poor heat conductor — 26 W/m·K (15 BTU/hr·ft·°F), worse than 87% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
A369 FP91 properties
Typical room-temperature values for A369 FP91-N+T; bars are the position among steel grades.
Physical3
A369 FP91 has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,450°C (2,642 °F).
Mechanical16
A369 FP91 has a yield strength of 500 MPa (72.5 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 63% of steel grades. Elongation at break is 23% and the elastic modulus is 218 GPa (31.6 Msi).
Thermal6
A369 FP91 is rated for continuous service to 600°C (1,112 °F). It conducts heat at 26 W/m·K (15 BTU/hr·ft·°F), worse than 87% of steel grades. Thermal expansion is 10.8 µm/m·K (6 µin/in·°F).
Electrical3
A369 FP91 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (30/100), better than 95% of steel grades.
Sustainability4
Producing a kilogram of A369 FP91 takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 25%.
Manufacturability8
A369 FP91's machinability is fair (45/100, worse than 65% of steel grades); weldability fair (40/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. A369 FP91 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A369 FP91
Is A369 FP91 easy to machine?
Machines like a 200–250 HB tempered alloy steel: rigid setups, carbide inserts, moderate speed and generous feed; expect ~45 % of AISI 1212 tool life and avoid work-hardening dwell.
Can A369 FP91 be welded?
GTAW root + SMAW/FCAW fill with matching 9Cr-1Mo-V consumables, 200–250 °C preheat, interpass ≤300 °C, cool to ~100 °C to transform, then PWHT 750–770 °C — Ni+Mn in the weld metal must be limited to keep Ac1 high.
Can A369 FP91 be formed, bent or molded?
Hot bend/form at 900–1050 °C followed by a full re-normalize and temper; cold bending is limited and any cold work above ~5 % strain calls for re-heat-treatment.
A369 FP91 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | 0.08 – 0.12 | 0.1 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.02 | 0.01 |
| S | ≤ 0.01 | 0 |
| Si | 0.2 – 0.5 | 0.35 |
| Cr | 8 – 9.5 | 8.75 |
| Mo | 0.85 – 1.05 | 0.95 |
| V | 0.18 – 0.25 | 0.21 |
| Nbcolumbium | 0.06 – 0.1 | 0.08 |
| N | 0.03 – 0.07 | 0.05 |
| Ni | ≤ 0.4 | 0.2 |
| Almax, total | ≤ 0.02 | 0.01 |
| Ti | ≤ 0.01 | 0.01 |
| Zr | ≤ 0.01 | 0.01 |
| Fe | balance |
What surface finishes work on A369 FP91?
Not stainless — protect with high-temperature aluminium/silicone paint, phosphating or aluminising for storage and outdoor runs; shot-blast before coating and never leave chloride-bearing residues on the surface.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel A369 FP91 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- A335 P91
- Similar grades
- X10CrMoVNb9-11.490310Cr9Mo1VNb
How much does A369 FP91 cost?
A369 FP91 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
A369 FP91 — frequently asked
What is A369 FP91 used for?
A369 FP91 is typically used for main steam piping for ultra-supercritical units, hot reheat piping, boiler outlet headers, superheater and reheater headers, forged pipe fittings and elbows and HRSG high-temperature pipework. In short: 600 °C steam-line standard; creep-strength-enhanced ferritic grade; strict PWHT requirements.
What is the yield strength of A369 FP91?
A369 FP91 has a typical yield strength of 500 MPa (72.5 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 63% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A369 FP91 easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machines like a 200–250 HB tempered alloy steel: rigid setups, carbide inserts, moderate speed and generous feed; expect ~45 % of AISI 1212 tool life and avoid work-hardening dwell.
Can A369 FP91 be welded?
With care — weldability is rated fair (40/100). GTAW root + SMAW/FCAW fill with matching 9Cr-1Mo-V consumables, 200–250 °C preheat, interpass ≤300 °C, cool to ~100 °C to transform, then PWHT 750–770 °C — Ni+Mn in the weld metal must be limited to keep Ac1 high.
What surface finishes work on A369 FP91?
Not stainless — protect with high-temperature aluminium/silicone paint, phosphating or aluminising for storage and outdoor runs; shot-blast before coating and never leave chloride-bearing residues on the surface.
Can A369 FP91 be formed, bent or molded?
Hot bend/form at 900–1050 °C followed by a full re-normalize and temper; cold bending is limited and any cold work above ~5 % strain calls for re-heat-treatment.
What is the maximum service temperature of A369 FP91?
A369 FP91 is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A369 FP91 N+T and A369 FP91-N?
N+T is the default condition — the only condition in which FP91 pipe is supplied and code-qualified for creep service; fully tempered martensite. N: intermediate state after normalizing before tempering — hard, brittle and never shipped for service; must be tempered. Yield strength is 500 MPa in N+T versus 900 MPa in N.
How much does A369 FP91 cost?
A369 FP91 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM A369/A369M — Carbon and Ferritic Alloy Steel Forged and Bored Pipe for High-Temperature Service — ASTM International (2018)
- ASTM A335/A335M — Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service (Grade P91) — ASTM International (2022)
- EN 10216-2 — Seamless steel tubes for pressure purposes, X10CrMoVNb9-1 (1.4903) — CEN (2020)
- ASME BPVC Section II Part D — Allowable stresses and physical properties, SA-335 P91 — ASME (2023)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Grade 91 seamless pipe technical data — Vallourec / Tenaris (2021)
- GB 5310 — (10Cr9Mo1VNb) — SAC (2017)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.