ASTM A335 Grade P9 and P91 are part of the ASTM A335 specification, which covers seamless ferritic alloy-steel pipe intended for high-temperature service. These materials are primarily used in power plants, refineries, petrochemical plants, and boiler systems, where resistance to high pressure and high temperature is critical.Grade P9 is an alloy steel containing chromium (8-10%) and molybdenum (0.90-1.10%), which gives it excellent resistance to oxidation, corrosion, and creep at elevated temperatures. It offers good weldability and is commonly used in superheater tubes, reheater tubes, and steam piping. The mechanical properties of P9 include a minimum tensile strength of 415 MPa and a minimum yield strength of 205 MPa.
| NPS | OD (in) | SCH 40 (Std) | SCH 80 (XS) | SCH 160 | SCH XXS |
|---|---|---|---|---|---|
| 1/2" | 0.84 | 0.109 | 0.147 | 0.187 | 0.294 |
| 3/4" | 1.05 | 0.113 | 0.154 | 0.218 | 0.308 |
| 1" | 1.315 | 0.133 | 0.179 | 0.250 | 0.358 |
| 1 1/2" | 1.9 | 0.145 | 0.2 | 0.281 | 0.4 |
| 2" | 2.375 | 0.154 | 0.218 | 0.343 | 0.436 |
| 3" | 3.5 | 0.216 | 0.3 | 0.437 | 0.6 |
| 4" | 4.5 | 0.237 | 0.337 | 0.531 | 0.674 |
| 6" | 6.625 | 0.28 | 0.432 | 0.718 | 0.864 |
| 8" | 8.625 | 0.322 | 0.5 | 0.906 | 1.0 |
| 10" | 10.75 | 0.365 | 0.593 | 1.125 | — |
| 12" | 12.75 | 0.375 | 0.687 | 1.312 | — |
| 14" | 14.0 | 0.375 | 0.75 | 1.437 | — |
| 16" | 16.0 | 0.375 | 0.843 | 1.593 | — |
| 18" | 18.0 | 0.375 | 0.937 | 1.781 | — |
| 20" | 20.0 | 0.375 | 1.031 | 1.968 | — |
| 24" | 24.0 | 0.375 | 1.218 | 2.343 | — |
| ASTM Spec | Material Grade | Type | Key Alloying Elements | Application |
|---|---|---|---|---|
| A106 | Gr. A, B, C | Carbon Steel, Seamless | Carbon, Manganese | High-temp service (boilers, pipelines) |
| A53 | Gr. A, B | Carbon Steel, Seamless/Welded | Carbon, Manganese | Water, gas, steam, air lines |
| A333 | Gr. 1 – Gr. 9 | Low Temp Carbon Steel | Nickel (in some grades) | Cryogenic & low-temp service |
| A335 | P1, P5, P9, P11, P22, P91 | Alloy Steel, Seamless | Chromium, Molybdenum, Vanadium | High-temp, high-pressure (power plants) |
| A312 | TP304, TP316, etc. | Stainless Steel | Chromium, Nickel, Molybdenum | Corrosive environments (chemical plants) |
| A519 | 1020, 4130, etc. | Carbon/Alloy Mech. Tubing | Varies | Mechanical and structural use |
| A179 | — | Carbon Steel (Seamless Tubes) | Carbon, Manganese | Heat exchangers, condensers |
| A192 | — | Carbon Steel (Boiler Tubes) | Carbon, Manganese | High-pressure boiler tubes |
| A210 | Gr. A1, C | Carbon Steel (Boiler Tubes) | Carbon, Manganese | Boiler and superheater tubes |
| A213 | T2, T5, T11, T22, T91 | Alloy Steel (Boiler Tubes) | Chromium, Molybdenum | Heat exchangers, superheaters |
| API 5L | Gr. B, X42–X80 | Carbon Steel, Seamless/Welded | Carbon, Manganese | Pipeline transport (oil, gas, water) |
| NPS (in) | OD (mm) | SCH 40 (WT mm) | SCH 80 (WT mm) |
|---|---|---|---|
| 1/2" | 21.34 | 2.77 | 3.73 |
| 3/4" | 26.67 | 2.87 | 3.91 |
| 1" | 33.40 | 3.38 | 4.55 |
| 1 1/4" | 42.16 | 3.56 | 4.85 |
| 1 1/2" | 48.26 | 3.68 | 5.08 |
| 2" | 60.33 | 3.91 | 5.54 |
| 2 1/2" | 73.03 | 5.16 | 7.01 |
| 3" | 88.90 | 5.49 | 7.62 |
| 4" | 114.30 | 6.02 | 8.56 |
| 5" | 141.30 | 6.55 | 9.53 |
| 6" | 168.28 | 7.11 | 10.97 |
| 8" | 219.08 | 8.18 | 12.70 |
| 10" | 273.05 | 9.27 | 15.09 |
| 12" | 323.85 | 9.53 | 17.48 |
| 14" | 355.60 | 9.53 | 11.13 |
| 16" | 406.40 | 9.53 | 12.70 |
| 18" | 457.20 | 9.53 | 14.27 |
| 20" | 508.00 | 9.53 | 15.09 |
| 24" | 609.60 | 9.53 | 17.48 |
| Element | P9 (% by weight) | P91 (% by weight) |
|---|---|---|
| Carbon (C) | 0.15 – 0.25 | 0.08 – 0.12 |
| Manganese (Mn) | 0.30 – 0.60 | 0.30 – 0.60 |
| Phosphorus (P) | ≤ 0.025 | ≤ 0.020 |
| Sulfur (S) | ≤ 0.025 | ≤ 0.010 |
| Silicon (Si) | 0.25 – 1.00 | 0.20 – 0.50 |
| Chromium (Cr) | 8.00 – 10.00 | 8.00 – 9.50 |
| Molybdenum (Mo) | 0.90 – 1.10 | 0.85 – 1.05 |
| Nickel (Ni) | — | ≤ 0.40 |
| Vanadium (V) | — | 0.18 – 0.25 |
| Niobium (Nb) (Columbium) | — | 0.06 – 0.10 |
| Nitrogen (N) | — | 0.03 – 0.07 |
| Aluminum (Al) | — | ≤ 0.04 |
