Overview
Specifies seamless ferritic (chrome-moly alloy) and austenitic stainless steel tubes for boilers, superheaters, and heat exchangers operating at elevated temperature under pressure. Ferritic grades range from simple 0.5Mo (T1) through 1.25Cr-0.5Mo (T11), 2.25Cr-1Mo (T22), up to the advanced 9Cr-1Mo-V (T91) and 9Cr-0.5Mo-1.8W-V-Nb (T92). Austenitic grades include TP304H, TP316H, TP321H, and TP347H. All tubes are seamless; welded austenitic boiler tube falls under ASTM A249. Dimensional sizing follows OD and wall thickness (not NPS/schedule).
Scope & Applicability
Applies To Industries
Covers — seamless ferritic and austenitic tubes for pressure service in boilers, superheaters, and heat exchangers.
Ferritic (chrome-moly) grades:
| Grade | Composition | Max. Temp. (°C) | Primary Application |
|---|---|---|---|
| T1 | 0.5Mo | ~480 | Early boiler; now rarely specified |
| T11 | 1.25Cr-0.5Mo | ~550 | Waterwall, economiser, low-temperature SH |
| T22 | 2.25Cr-1Mo | ~580 | Superheater, reheater, fired heater, hydrotreater |
| T91 | 9Cr-1Mo-V | ~650 | Advanced superheater/reheater; high-efficiency boilers |
| T92 | 9Cr-0.5Mo-1.8W-V-Nb | ~650 | USC boilers; higher creep strength than T91 |
| T23 | 2.25Cr-0.25Mo-1.6W-V-Nb-B | ~620 | Improved T22 for membrane walls |
Austenitic stainless grades (high-temperature service):
| Grade | Composition | Max. Temp. (°C) | Key Feature |
|---|---|---|---|
| TP304H | 18Cr-8Ni, high C | ~650 | Higher-C for elevated-temperature strength |
| TP316H | 16Cr-12Ni-2.5Mo, high C | ~650 | +Mo for pitting/corrosion resistance |
| TP321H | 18Cr-10Ni-Ti, high C | ~700 | Ti-stabilised; resistant to sensitisation |
| TP347H | 18Cr-10Ni-Nb, high C | ~700 | Nb-stabilised; widely used in USC superheaters |
| TP310S/H | 25Cr-20Ni | ~900+ | High-chromium; oxidation and carburisation resistance |
Does NOT cover (exclusions):
- Welded austenitic boiler tubes → ASTM A249
- General-service / instrument stainless tubing → ASTM A269
- Alloy-steel and stainless pipe (NPS) → ASTM A335 / A312
- Alloy-steel and stainless pipe fittings → ASTM A234 / A403
- Copper heat-exchanger tubes → ASTM B111
- Boiler construction rules → ASME BPVC Section I (uses SA-213 material)
- Pressure vessel construction → ASME BPVC Section VIII (uses SA-213 material)
Boiler and pressure vessel work under ASME Code must cite SA-213, not A213.
Key Requirements
A213 sets minimum requirements for high-temperature pressure tubes:
Chemical Composition (selected key grades)
| Grade | C (%) | Cr (%) | Mo (%) | Other | Key Control |
|---|---|---|---|---|---|
| T11 | ≤0.15 | 1.00–1.50 | 0.44–0.65 | — | Standard N&T |
| T22 | ≤0.15 | 1.90–2.60 | 0.87–1.13 | — | Standard N&T |
| T91 | 0.08–0.12 | 8.00–9.50 | 0.85–1.05 | V, Nb, N, Al, Ni | Tight C; N/Al balance critical |
| TP304H | 0.04–0.10 | 18.0–20.0 | — | 8–11 Ni | High-C for creep strength |
| TP347H | 0.04–0.10 | 17.0–19.0 | — | Nb 8×C–1.0 | Nb-stabilised, grain size control |
T91 chemistry is the most tightly controlled; carbon must be 0.08–0.12% (not just "≤ 0.15%"). Excess Al inhibits nitrogen strengthening; consult EPRI Grade 91 guidelines for detailed specification.
Mechanical Properties
| Grade | Min. UTS (MPa) | Min. Yield (MPa) | Max. Hardness |
|---|---|---|---|
| T11 | 415 | 205 | 163 HB |
| T22 | 415 | 205 | 163 HB |
| T91 | 585 | 415 | 265 HB |
| TP304H | 515 | 205 | — |
| TP347H | 515 | 205 | — |
Heat Treatment (mandatory, grade-specific)
| Grade Family | Required Treatment | Purpose |
|---|---|---|
| T11, T22 | Normalize + Temper | Develop tempered-bainite for creep strength |
| T91, T92 | Normalize (1040–1080°C) + Temper (730–800°C) | Develop tempered-martensite; hardness verification mandatory |
| Austenitic (TP304H, TP347H) | Solution anneal ≥ 1040°C, rapid cool | Dissolve carbides; maintain corrosion resistance |
Required Tests per Heat/Lot
| Test | Requirement |
|---|---|
| Chemical analysis | Heat and product analysis |
| Tensile test | One per heat per size |
| Hardness (Brinell) | All tubes for T91; all as specified |
| Hydrostatic OR NDE (eddy current / UT) | All tubes |
| Flaring test | One per heat per size (seamless) |
| Grain size (austenitic) | When specified per ASME |
| Visual & dimensional | All tubes |
Technical Details
A213 in Context: The High-Temperature Tube Counterpart
ASTM A213 occupies the same place in the boiler and heat-exchanger world that ASTM A269 occupies in instrument tubing: it is the material specification for seamless pressure tubes. Whereas A269 tubing goes to compression fittings and instrument loops, A213 tubes go into pressure circuits that operate at sustained high temperature — often for 30+ years.
The two major grade families serve different temperature regimes:
Chrome-moly ferritic grades (T11, T22, T91) are the workhorses of fossil-fuel power plants and refinery fired heaters. They offer high strength at elevated temperature through a tempered-martensite or tempered-bainite microstructure developed by controlled heat treatment. T91 (Grade 91) is the most capable ferritic grade and is critical to the economics of ultra-supercritical (USC) power plants, which operate above 600°C steam temperature.
Austenitic stainless H-grades (TP304H, TP347H) provide corrosion resistance at even higher metal temperatures, often used in the final superheater and reheater stages of USC boilers, where metal temperatures can exceed 650°C.
The Grade 91 Challenge
T91/Grade 91 is arguably the most consequential and most often mishandled alloy in power generation:
| Risk Factor | Consequence |
|---|---|
| Carbon below 0.08% | Insufficient hardenability; cannot develop martensite |
| PWHT below 730°C | Hard, untempered HAZ; early creep failure |
| PWHT above Ac₁ (~820°C) | Re-austenises HAZ; no strengthening; softens |
| Hardness > 265 HB | Indicates under-tempered condition |
| Using T9 filler for T91 welds | Incompatible chemistry; different creep rate |
Multiple boiler tube and pipe failures in operating plants worldwide trace directly to one or more of these errors. EPRI publishes detailed Grade 91 welding and inspection guidelines (TR-109191 series) that go beyond ASME Code minimums and should be consulted for all T91 tube installations.
The A213 Grade Family in the Alloy Steel System
A213 tubes do not stand alone — they are part of a consistent alloy steel system:
| Component | Ferritic Grades | Austenitic Grades | Governing Standard |
|---|---|---|---|
| Seamless tube | T11, T22, T91 | TP304H, TP347H | ASTM A213 |
| Welded tube | — | TP304H, TP347H | ASTM A249 |
| Pipe (NPS) | P11, P22, P91 | TP304H, TP347H | ASTM A335 / A312 |
| Fittings | WP11, WP22, WP91 | TP304H, TP347H | ASTM A234 / A403 |
| Forgings | F11, F22, F91 | — | ASTM A182 |
Dimensional Sizing
Like A269, A213 tubing is sized by OD and wall. Typical boiler tube sizes range from ½″ OD (12.7 mm) to 4″ OD (101.6 mm), with walls of 0.065″ (1.65 mm) to 0.500″ (12.7 mm). Heat exchanger tubes commonly use ¾″ or 1″ OD with 16 or 14 BWG walls.
Engineering Notes
Heat treatment records for A213 tubes are engineering evidence — they must be traceable, not assumed.
- Grade 91 (T91) is the highest-risk grade in service — the material requires normalize-at-1040–1080°C followed by temper-at-730–800°C to develop the correct tempered-martensite microstructure. Material tempered below 730°C or above Ac₁ (~820°C) can appear to pass room-temperature mechanical tests yet have severely degraded creep strength. Always verify Brinell hardness: ≤ 265 HB for T91 in the correct condition. Out-of-range hardness is a red flag.
- PWHT requirements for T91 welding are non-negotiable — weld PWHT must be performed at 730–800°C (typically 760°C). Skipping or under-temperature PWHT produces a hard, untempered HAZ that fails under creep before design life. Multiple power plant tube failures worldwide trace to this cause.
- T22 is the refinery workhorse — the 2.25Cr-1Mo grade is the standard for fired heater tubes, hydrogen plant reformer coils, and hydroprocessing service up to ~580°C. It develops creep strength through normalize-and-temper but tolerates slightly more variation than T91.
- Austenitic H-grades are not interchangeable with standard grades — TP304H and TP347H contain higher carbon (0.04–0.10%) than standard TP304/TP347 to maintain elevated-temperature strength. Do not substitute standard austenitic grades in superheater applications specifying H-grades.
- Grain size matters for austenitic grades — ASME BPVC Section I requires minimum grain size ASTM 7 for some austenitic tube grades. Verify MTR records include grain-size certification where specified.
- SA-213 vs. A213 — boiler and pressure vessel construction governed by ASME BPVC uses SA-213 (the ASME version). The chemistry and mechanical requirements are essentially identical, but SA-213 has supplementary requirements and mandatory ASME-qualified certifications. Never substitute A213 for SA-213 in Code-stamped work without Code-authority approval.
- Oxidation and steam-side corrosion — T22 tubes in superheaters develop thick steam-oxidation scale above ~580°C, reducing effective wall. T91 extends the ferritic operating range to ~650°C. Above that, austenitic grades or nickel alloys are required.
Source, Edition & Status
- Publisher
- ASTM International
- Edition Year
- 2022
- Industries
- Power Plant, Petrochemical, Refinery, Chemical Plant
- Last Reviewed
- 2026-07-01
- Last Updated
- 2026-07-01
- Verified By
- Engineering content reviewer
- Content Status
- reviewed
- Official Link
- www.astm.org