Steel A369 FP21-ANN (Annealed)
Heat-treated state
ASTM A369 FP21
Softest condition — pick when maximum machinability, bending or lowest residual stress is needed.
Values for the ANN condition
Other A369 FP21 tempers and conditions
A369 FP21 is listed in 3 conditions; see the grade overview at A369 FP21.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNThis page Annealed | Softest condition — pick when maximum machinability, bending or lowest residual stress is needed. | 260 | 480 | 32 | 150 HB | — |
N+TDefault Normalized and tempered | Standard supply condition for FP21 pressure piping: best combination of creep strength, toughness and machinability. | 330 | 530 | 27 | 175 HB | — |
Quenched and tempered | Occasional heavy-wall / high-strength option where a bainitic structure and higher yield are specified by the purchaser. | 450 | 620 | 22 | 19 HRC | — |
What is A369 FP21-ANN?
A369 FP21-ANN is A369 FP21 heat treated to ANN — softest condition — pick when maximum machinability, bending or lowest residual stress is needed. A369 FP21-ANN has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 92% of steel grades. Elongation at break is 32% and the elastic modulus is 207 GPa (30 Msi). A369 FP21-ANN has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,450°C (2,642 °F). N+T is the default condition FabDigit quotes; ANN is available on request or by drawing note.
Advantages
- High service temperature — 595°C (1,103 °F), better than 97% of steel grades
- Ductile — tolerates forming and impact — 32%, better than 95% of steel grades
- Tough — resists crack growth — 140 MPa·√m (127.4 ksi·√in), better than 94% of steel grades
- Easy to machine — 62/100, better than 89% of steel grades
Limitations
- Low strength — 260 MPa (37.7 ksi), worse than 92% of steel grades
A369 FP21-ANN properties
Typical room-temperature values for A369 FP21-ANN; 12 are specific to this condition. Other listed values are A369 FP21 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A369 FP21-ANN has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,450°C (2,642 °F).
Mechanical16
A369 FP21-ANN has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 92% of steel grades. Elongation at break is 32% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
A369 FP21-ANN is rated for continuous service to 595°C (1,103 °F). It conducts heat at 37 W/m·K (21.4 BTU/hr·ft·°F), worse than 71% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
A369 FP21-ANN conducts electricity at 7.5 % IACS, worse than 67% of steel grades.
Chemical & Environmental2
Corrosion resistance is poor (20/100), better than 87% of steel grades.
Sustainability4
Producing a kilogram of A369 FP21-ANN takes about 32 MJ of energy and emits 2.4 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 25%.
Manufacturability7
A369 FP21-ANN's machinability is good (62/100, better than 89% of steel grades); weldability good (55/100); formability good (55/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A369 FP21-ANN
Is A369 FP21 easy to machine?
Machines like a medium-carbon low-alloy steel at ~55 % of AISI 1212; use rigid setups, carbide inserts at moderate speed and generous coolant, and finish-bore after final heat treatment to hold ID tolerance.
Can A369 FP21 be welded?
Weld with matching 3Cr-1Mo (E9015-B3 / ER90S-B3 type) consumables, 200–300 °C preheat/interpass, low hydrogen practice, and 700–760 °C PWHT to avoid HAZ hardening and hydrogen cracking.
Can A369 FP21 be formed, bent or molded?
Hot form/bend at 950–1050 °C followed by re-normalizing and tempering; cold bending is limited by high yield-to-tensile ratio and springback.
What surface finishes work on A369 FP21?
No anodizing; protect with high-temperature aluminium/silicone paint, aluminizing or thermal-spray coatings, and shot blast or pickle mill scale before painting.
A369 FP21 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 | 0.05 – 0.15 | 0.1 |
| Mn | 0.3 – 0.6 | 0.45 |
| Si | ≤ 0.5 | 0.3 |
| P | ≤ 0.03 | 0.01 |
| S | ≤ 0.03 | 0.01 |
| Cr | 2.65 – 3.35 | 3 |
| Mo | 0.8 – 1.06 | 0.95 |
| Fe | balance | — |
A369 FP21-ANN — frequently asked
What is A369 FP21-ANN used for?
A369 FP21-ANN is typically used for high-temperature steam headers, refinery process piping, hot reheat piping, forged header and nozzle fittings, hydrogen-service process lines and fired heater outlet piping. In short: 3Cr-1Mo high-pressure pipe; rated to 595 °C; stronger than FP22.
What is the yield strength of A369 FP21-ANN?
A369 FP21-ANN has a typical yield strength of 260 MPa (37.7 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 92% of steel grades. Strength varies by condition: see the 3 listed tempers.
Is A369 FP21-ANN easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Machines like a medium-carbon low-alloy steel at ~55 % of AISI 1212; use rigid setups, carbide inserts at moderate speed and generous coolant, and finish-bore after final heat treatment to hold ID tolerance.
Can A369 FP21-ANN be welded?
Yes — weldability is rated good (55/100). Weld with matching 3Cr-1Mo (E9015-B3 / ER90S-B3 type) consumables, 200–300 °C preheat/interpass, low hydrogen practice, and 700–760 °C PWHT to avoid HAZ hardening and hydrogen cracking.
What surface finishes work on A369 FP21-ANN?
No anodizing; protect with high-temperature aluminium/silicone paint, aluminizing or thermal-spray coatings, and shot blast or pickle mill scale before painting.
Can A369 FP21-ANN be formed, bent or molded?
Hot form/bend at 950–1050 °C followed by re-normalizing and tempering; cold bending is limited by high yield-to-tensile ratio and springback.
What is the maximum service temperature of A369 FP21-ANN?
A369 FP21-ANN is rated for continuous use to about 595°C (1,103 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A369 FP21 N+T and A369 FP21-ANN?
N+T is the default condition — standard supply condition for FP21 pressure piping: best combination of creep strength, toughness and machinability. ANN: softest condition — pick when maximum machinability, bending or lowest residual stress is needed. Yield strength is 330 MPa in N+T versus 260 MPa in ANN.
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 P21) — ASTM International (2023)
- ASME BPVC Section II Part D — Properties (Metric) — ASME (2023)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 6 — Welding, Brazing, and Soldering (Cr-Mo steels) — ASM International (1993)
- API RP 941 — Steels for Hydrogen Service at Elevated Temperatures — API (2016)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.