Tubewell Steel & Engg. Co. is a leading manufacturer and stockist specializing in Alloy Steel Pipes, Tubes, Fittings and Flanges for critical industrial applications.
9Cr-1Mo-V-Nb creep strength enhanced ferritic (CSEF) seamless pipes for supercritical main steam, hot reheat and HRSG piping.
Tubewell Steel & Engg. Co. manufactures and stocks ASTM A335 P91 pipes – a modified 9Cr-1Mo steel micro-alloyed with vanadium, niobium and nitrogen. Normalized and tempered to a tempered-martensite structure, P91 delivers roughly double the creep strength of P22, enabling thinner, lighter steam lines in supercritical and combined-cycle power plants.
The benchmark creep strength enhanced ferritic steel for modern power plants
ASTM A335 P91 is a seamless 9Cr-1Mo-V-Nb alloy steel pipe belonging to the family of creep strength enhanced ferritic (CSEF) steels. Controlled additions of vanadium (0.18–0.25%), niobium (0.06–0.10%) and nitrogen (0.030–0.070%) form fine, stable MX carbonitride precipitates that pin dislocations and preserve strength during long-term exposure at 565–650°C. The result is a minimum tensile strength of 585 MPa and creep-rupture properties far above P22, combined with the oxidation resistance of 9% chromium and a low thermal expansion coefficient that reduces thermal fatigue.
The properties of P91 depend entirely on correct heat treatment. Our pipes are normalized at 1040–1080°C and tempered at 730–800°C, then verified for hardness within the 190–250 HBW band required by ASTM A335. Both Type 1 and the tighter-chemistry Type 2 are available. Every length is supplied with full heat traceability, 100% PMI, EN 10204 3.1 / 3.2 certificates, IBR Form III-A on request and optional third-party inspection by BV, TÜV, SGS, Lloyd's or EIL.
Standard supply range for ASTM A335 P91 pipes
| Parameter | Details |
|---|---|
| Standard | ASTM A335, ASME SA335 |
| Grade | P91 Type 1 / Type 2 (UNS K91560) |
| Type | Seamless – Hot Finished / Cold Drawn |
| Size (NB) | 1/2" NB to 24" NB |
| Outer Diameter | 21.3 mm to 610 mm |
| Wall Thickness | SCH 40, STD, 60, 80, XS, 100, 120, 140, 160, XXS and heavy-wall MWT |
| Length | Single Random, Double Random, Cut Length (up to 12 m) |
| Ends | Plain End, Bevelled End (ASME B16.25) |
| Heat Treatment | Normalized 1040–1080°C (1900–1975°F) + Tempered 730–800°C (1350–1470°F) |
| Hardness | 190 – 250 HBW (196 – 265 HV) |
| ASME P-Number | P-No. 15E, Group 1 |
| Dimension Standard | ASME B36.10M |
| Testing | Hydrostatic, Ultrasonic, Eddy Current, Flattening, Hardness, Micro-structure, PMI |
| Certificates | EN 10204 3.1 / 3.2, IBR Form III-A, TPI Reports |
International equivalents of A335 P91
| Standard | ASTM | UNS | EN | DIN / W.Nr. | JIS | BS |
|---|---|---|---|---|---|---|
| P91 | A335 P91 | K91560 | X10CrMoVNb9-1 | 1.4903 | STPA 28 | 3604 HFS 91 |
Weight %, as per ASTM A335 (Ti ≤ 0.01, Zr ≤ 0.01)
| Grade | C | Mn | P | S | Si | Cr | Mo | V | Nb | N | Ni | Al |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P91 Type 1 | 0.08 – 0.12 | 0.30 – 0.60 | 0.020 max | 0.010 max | 0.20 – 0.50 | 8.00 – 9.50 | 0.85 – 1.05 | 0.18 – 0.25 | 0.06 – 0.10 | 0.030 – 0.070 | 0.40 max | 0.02 max |
| P91 Type 2 | 0.08 – 0.12 | 0.30 – 0.50 | 0.020 max | 0.005 max | 0.20 – 0.40 | 8.00 – 9.50 | 0.85 – 1.05 | 0.18 – 0.25 | 0.06 – 0.10 | 0.035 – 0.070 | 0.20 max | 0.020 max |
Type 2 additionally restricts residual elements (e.g. Cu, Sn, As, Sb, B) and requires an N/Al ratio of 4.0 min.
Minimum values at room temperature, normalized & tempered condition
| Grade | Tensile Strength | Yield Strength (0.2%) | Elongation (Long.) | Elongation (Trans.) | Hardness |
|---|---|---|---|---|---|
| A335 P91 | 585 MPa (85 ksi) min | 415 MPa (60 ksi) min | 20% min | 13% min | 190 – 250 HBW |
Typical values (for reference)
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.77 g/cm³ | 0.281 lb/in³ |
| Melting Range | 1420 – 1500 °C | 2590 – 2730 °F |
| Modulus of Elasticity | 218 GPa | 31.6 × 10³ ksi |
| Thermal Conductivity (100°C) | 27 W/m·K | 15.6 BTU/h·ft·°F |
| Mean Thermal Expansion (20–300°C) | 11.2 µm/m·°C | 6.2 µin/in·°F |
| Specific Heat | 0.45 J/g·°C | 0.11 BTU/lb·°F |
| Max. Service Temperature | ≈ 650 °C | ≈ 1200 °F |
As per ASME B36.10M – heavy-wall schedules, wall thickness (mm) / weight (kg/m)
| NPS | OD (mm) | SCH 80 WT | SCH 80 Wt | SCH 160 WT | SCH 160 Wt | XXS WT | XXS Wt |
|---|---|---|---|---|---|---|---|
| 1/2" | 21.3 | 3.73 | 1.62 | 4.78 | 1.95 | 7.47 | 2.55 |
| 3/4" | 26.7 | 3.91 | 2.20 | 5.56 | 2.90 | 7.82 | 3.64 |
| 1" | 33.4 | 4.55 | 3.24 | 6.35 | 4.24 | 9.09 | 5.45 |
| 1 1/4" | 42.2 | 4.85 | 4.47 | 6.35 | 5.61 | 9.70 | 7.77 |
| 1 1/2" | 48.3 | 5.08 | 5.41 | 7.14 | 7.25 | 10.15 | 9.56 |
| 2" | 60.3 | 5.54 | 7.48 | 8.74 | 11.11 | 11.07 | 13.44 |
| 2 1/2" | 73.0 | 7.01 | 11.41 | 9.53 | 14.92 | 14.02 | 20.39 |
| 3" | 88.9 | 7.62 | 15.27 | 11.13 | 21.35 | 15.24 | 27.68 |
| 4" | 114.3 | 8.56 | 22.32 | 13.49 | 33.54 | 17.12 | 41.03 |
| 6" | 168.3 | 10.97 | 42.56 | 18.26 | 67.56 | 21.95 | 79.22 |
| 8" | 219.1 | 12.70 | 64.64 | 23.01 | 111.27 | 22.23 | 107.92 |
| 10" | 273.1 | 15.09 | 95.98 | 28.58 | 172.33 | 25.40 | 155.15 |
| 12" | 323.9 | 17.48 | 132.05 | 33.32 | 238.76 | 25.40 | 186.97 |
WT = Wall Thickness in mm, Wt = Weight in kg/m. Values are nominal; actual weights may vary within ASTM tolerances. Sizes 14" – 24" and minimum-wall (MWT) pipes supplied on request.
Where ASTM A335 P91 pipes are used
Main steam and hot reheat piping at high pressure and temperature.
High-pressure superheater headers and HRSG interconnecting piping.
Thick-walled superheater and reheater outlet headers.
Hydrocracker and high-temperature hydrogen service piping.
Steam generator and high-energy piping systems.
Reformer and cracker lines requiring high creep strength.
Quality you can verify on every heat
Large inventory for fast dispatch
MTC EN 10204 3.1 / 3.2
Positive material identification
Pan-India & export shipping
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