ASME SA213 — T11 / T22 Alloy Boiler & Superheater Tubes
Seamless ferritic and austenitic alloy-steel tubes for boilers, superheaters, and heat exchangers. Chrome-moly grades for high-temperature creep resistance.
ASME SA213 (ASTM A213) is the authoritative specification for seamless ferritic and austenitic alloy-steel boiler, superheater, and heat exchanger tubes. Unlike the carbon steel SA106, SA213 covers chrome-moly and stainless grades designed for high-temperature creep resistance. The most commonly specified grades in Indian power plants are T11 (1.25% chromium, 0.5% molybdenum) and T22 (2.25% chromium, 1% molybdenum), which offer superior oxidation resistance and creep strength compared to carbon steel. These tubes operate continuously at temperatures from 450°C up to 600°C in superheater and reheater sections. SA213 tubes are seamless only — the alloy chemistry and elevated temperature requirements preclude welded construction for these critical applications. All SA213 tubes require heat treatment after forming: ferritic grades are normalized and tempered, while austenitic stainless grades require solution annealing.
T11 vs T22 — selecting the right chrome-moly grade
T11 (UNS K11597) contains 1.0–1.5% chromium and 0.44–0.65% molybdenum. It is the entry-level alloy grade, offering good creep resistance up to approximately 550°C. T11 is widely used in the primary superheater sections of subcritical boilers where metal temperatures stay below the grade's threshold.
T22 (UNS K21590) increases chromium to 1.90–2.60% and molybdenum to 0.87–1.13%, providing higher creep strength and oxidation resistance. T22 is specified for final superheater and reheater sections operating between 550°C and 600°C. The higher alloy content also improves resistance to hydrogen attack in refinery hydrogen reformer service.
For metal temperatures exceeding 600°C, engineers typically specify T91/P91 (9% Cr-1% Mo-V-Nb) or austenitic stainless grades like TP304H or TP347H. The cost differential between T11 and T22 is modest — always specify the grade that provides adequate margin above your design metal temperature.
Chemical composition (as per SA213)
- T11: Carbon 0.05–0.15%, Mn 0.30–0.60%, Si 0.50–1.00%, Cr 1.00–1.50%, Mo 0.44–0.65%
- T22: Carbon 0.05–0.15%, Mn 0.30–0.60%, Si 0.50–0.30% max, Cr 1.90–2.60%, Mo 0.87–1.13%
- T5: Carbon 0.15% max, Cr 4.00–6.00%, Mo 0.45–0.65% — higher chrome for refinery service
- T9: Carbon 0.15% max, Cr 8.00–10.00%, Mo 0.90–1.10% — precursor chemistry to T91/P91
- TP304H: Carbon 0.04–0.10%, Cr 18.00–20.00%, Ni 8.00–11.00% — austenitic for highest temperatures
Mechanical properties (as per SA213)
- T11: Yield strength 205 MPa min, Tensile 415 MPa min, Elongation 30% min
- T22: Yield strength 205 MPa min, Tensile 415 MPa min, Elongation 30% min
- T5: Yield strength 205 MPa min, Tensile 415 MPa min, Elongation 30% min
- T9: Yield strength 205 MPa min, Tensile 585 MPa min, Elongation 30% min
- TP304H: Yield strength 205 MPa min, Tensile 515 MPa min, Elongation 35% min
- Hardness: Ferritic grades max 170–220 HB; austenitic grades max 192 HB
Heat treatment requirements
Ferritic alloy grades (T11, T22, T5, T9) must be normalized at 900–930°C and tempered at 650–730°C to develop the required ferrite-bainite microstructure. The heat treatment is mandatory — as-formed tubes cannot meet the mechanical property requirements.
Austenitic grades (TP304H, TP316H, TP347H) require solution annealing at 1040–1100°C followed by rapid cooling to retain the austenitic structure and prevent carbide precipitation.
The heat treatment cycle is certified on the Material Test Certificate (MTC) 3.1 or 3.2. IBR Form III-C documentation references SA213 directly for boiler superheater applications.
| Grade | Cr % | Mo % | Max temp | Typical application |
|---|---|---|---|---|
| T11 | 1.25% | 0.50% | ~550°C | Primary superheater, economizer |
| T22 | 2.25% | 1.00% | ~600°C | Final superheater, reheater |
| T91/P91 | 9.00% | 1.00% | ~650°C | Ultra-supercritical boilers |
| TP304H | 18% | — | ~700°C | High-temp superheaters |
| Size range | 1/8" (3.2 mm) to 5" (127 mm) OD |
|---|---|
| Wall thickness | 0.5 mm minimum; Schedule 40 through XXS |
| Standard | ASME SA213 / ASTM A213 |
| Grades | T11, T22, T5, T9, T91, TP304H, TP316H, TP347H |
| Process | Seamless cold-drawn or hot-finished |
| Heat treatment | Normalized + tempered (ferritic); Solution annealed (austenitic) |
| Length | SRL 4–7 m, DRL 7–14 m; cut-to-length available |
| End finish | Plain end (PE), beveled (BW) for welding |
| Surface | Pickled, annealed, or polished (austenitic grades) |
| Documentation | MTC 3.1/3.2 per EN 10204; IBR Form III-C |
- ASME SA213 — Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes — American Society of Mechanical Engineers
- ASTM A213/A213M — Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes — ASTM International
- Indian Boiler Regulations, 1950 — Form III-C — Boiler tube material certification — Central Boilers Board, Government of India
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