Premium SA213 T21 Seamless Alloy Tube for Superheaters, Reheaters, High-Temperature Boilers, Heat Exchangers, and Refinery Service
Womic Steel produces high-quality SA213 T21 Seamless Alloy Steel Tube, manufacturing chromium-molybdenum (3Cr-1Mo) ferritic alloy tubes in accordance with ASTM A213 / ASME SA213 specifications. Our SA213 T21 tubes meet the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, with a minimum tensile strength of 415 MPa and excellent creep resistance at elevated temperatures up to 565°C (1050°F). These seamless alloy tubes are the ideal choice for superheaters, reheaters, high-pressure boilers, heat exchangers, and refinery applications requiring higher creep strength than T22 and better oxidation resistance than T11, without the higher cost and fabrication complexity of 5Cr or 9Cr grades.
Manufacturer: Womic Steel
1. Product Definition and Scope
SA213 T21 (UNS K31545) is a seamless ferritic alloy steel tube specified under ASTM A213 / ASME SA213 for use in boilers, superheaters, heat exchangers, and other high-temperature pressure-containing equipment. The “T21″ designation indicates a nominal composition of 3% chromium and 1% molybdenum. T21 provides enhanced creep-rupture strength over T22 (2.25Cr-1Mo) and improved oxidation resistance, making it a suitable intermediate step between T22 and higher alloy grades for demanding boiler and refinery applications.
Manufacturing Process: T21 tubes are manufactured by the seamless process and are typically supplied in the normalized and tempered condition. The higher chromium (3%) and molybdenum (1%) contents require careful heat treatment to develop the required tempered bainitic or martensitic microstructure.
Grade Designation:
| Designation | Meaning |
| SA213 | ASME specification for seamless ferritic and austenitic alloy-steel tubes for boilers, superheaters, and heat exchangers |
| T21 | Grade designation: 3% Chromium – 1% Molybdenum ferritic alloy |
| UNS K31545 | Unified numbering system designation for T21 |
Equivalent Standards and Grades:
| Standard | Equivalent Grade |
| ASTM A213 / ASME SA213 | T21 |
| ASTM A335 | P21 (pipe form) |
| EN 10216-2 | Not directly, but similar to 10CrMo5-5 |
| JIS G3462 | STBA 26 (similar 5Cr) – not exact. |
Manufacturer: Womic Steel
2. Chemical Composition Requirements
The chemical composition of SA213 T21 is designed to provide higher creep strength and oxidation resistance than T22.
SA213 T21 Chemical Composition (Heat Analysis – Seamless Tube):
| Element | Composition (%) – Minimum | Composition (%) – Maximum |
| Carbon (C) | 0.05 | 0.15 |
| Manganese (Mn) | 0.30 | 0.60 |
| Phosphorus (P) | — | 0.025 |
| Sulfur (S) | — | 0.025 |
| Silicon (Si) | 0.50 | 1.00 |
| Chromium (Cr) | 2.65 | 3.35 |
| Molybdenum (Mo) | 0.80 | 1.06 |
Composition Notes:
| Element | Engineering Note |
| Chromium (2.65-3.35%) | Provides improved oxidation and corrosion resistance over T22 |
| Molybdenum (0.80-1.06%) | Significantly enhances creep strength |
| Silicon (0.50-1.00%) | Improves oxidation resistance |
| Carbon (0.05-0.15%) | Lower than T5 for improved weldability |
T21 offers a creep-rupture strength about 15-20% higher than T22 at 565°C, with similar or slightly better oxidation resistance. It is a logical upgrade when T22 is marginal but T5 is considered overkill or when welding complexity must be minimized.
3. Mechanical Properties
Tensile Requirements (Room Temperature):
| Property | Minimum | Typical | Unit |
| Tensile Strength | 415 MPa (60 ksi) | 480-550 MPa | — |
| Yield Strength (0.2% offset) | 205 MPa (30 ksi) | 280-350 MPa | — |
| Elongation in 2 in. or 50 mm | 30% | 35-40% | — |
Hardness Requirements:
| Property | Maximum |
| Brinell Hardness (HBW) | 163 |
| Rockwell Hardness (HRB) | 85 |
High-Temperature Tensile Properties (Reference Values):
| Temperature (°C) | Tensile Strength (MPa) | Yield Strength (MPa) |
| 20 | 480-550 | 280-350 |
| 400 | 420-480 | 220-280 |
| 500 | 380-450 | 190-250 |
| 565 | 300-380 | 150-210 |
Creep Rupture Strength (Typical Values):
| Temperature (°C) | 100,000 Hour Stress (MPa) |
| 540 | 65-80 |
| 565 | 45-60 |
| 593 | 30-40 |
The creep strength advantage over T22 is most pronounced at higher temperatures, making T21 a suitable material for the hottest sections of subcritical boilers and certain refinery heaters.
4. Heat Treatment Requirements
Heat Treatment Requirements:
| Condition | Process | Temperature Range | Cooling Method |
| Normalized and Tempered | Normalizing + Tempering | 920-980°C + 650-730°C | Air cool + air cool |
| Full Anneal | Austenitize + slow cool | 870-900°C | Furnace cool |
The higher alloy content requires slightly higher normalizing temperature than T22 to ensure full austenitization. Tempering at 650-730°C develops the final mechanical properties.
Manufacturer: Womic Steel provides heat treatment certificates upon request.
5. Dimensional Tolerances
Dimensional tolerances follow ASTM A213 / A1016 as described for other grades:
● Cold drawn OD: ±0.10 mm to ±0.38 mm depending on size.
● Wall thickness: ±10% for cold drawn; sliding scale for hot finished.
● Straightness: 0.2% of length.
● Length: random 5-12 m; specific lengths +50-100 mm / -0.
6. Available Sizes and Specifications
Same size ranges as other SA213 tubes.
Common T21 Tube Sizes (OD x WT in mm):
31.8 x 3.0, 38.1 x 3.5, 44.5 x 4.0, 50.8 x 4.0, 50.8 x 5.0, 60.3 x 5.0, 63.5 x 5.0, 76.2 x 6.0, 88.9 x 6.0, 101.6 x 8.0, 114.3 x 8.0.
Manufacturer: Womic Steel offers T21 tubes to order; inventory on request.
7. Inspection and Testing Requirements
Standard SA213 tests apply.
| Test | Requirement | Frequency |
| Chemical Analysis | Required | Per heat |
| Tensile Test | Required | Per heat |
| Hardness Test | Required | Per heat |
| Flattening Test | Required | Per lot |
| Flaring Test | Required | Per lot |
| Hydrostatic or NDT | 100% | Each tube |
8. Applications
| Industry | Application |
| Power Generation | Superheater and reheater tubes in subcritical and supercritical boilers |
| Combined Cycle HRSGs | High-temperature sections where T22 is insufficient |
| Refining | High-temperature heater tubes, transfer lines, catalytic reformer components |
| Petrochemical | High-temperature heat exchangers, furnace coils |
| Industrial Heating | Radiant tube heaters, convection sections |
T21 is not as common as T11, T22, or T91 but is specified for applications requiring a balance between creep strength, oxidation resistance, and cost.
9. Comparison with T22 and T5
| Grade | Cr (%) | Mo (%) | Creep Strength at 565°C (100kh) | Oxidation Resistance | Weldability |
| T22 | 2.25 | 1.0 | ~35 MPa | Moderate | Good |
| T21 | 3 | 1.0 | ~50 MPa | Good | Good |
| T5 | 5 | 0.5 | ~45 MPa | Better | Fair |
T21 offers improved creep strength over T22 with similar weldability, while T5 provides better corrosion resistance but is harder to weld. The choice depends on the dominant damage mechanism (creep vs. corrosion).
10. Welding Procedure for SA213 T21
T21 has hardenability similar to T22 but requires careful control.
Recommended Welding Processes: GTAW (TIG) for root, SMAW with low-hydrogen electrodes for fill.
Recommended Filler Metals:
| Filler Metal | AWS Classification |
| ER90S-B3 | AWS A5.28 (2.25Cr-1Mo type, commonly used) |
| E9018-B3 | AWS A5.5 |
Critical Requirements:
| Parameter | Requirement |
| Preheating Temperature | 150-200°C (300-400°F) |
| Maximum Interpass Temperature | 300°C (572°F) |
| Post-Weld Heat Treatment (PWHT) | 680-730°C (1250-1350°F) – mandatory |
| PWHT Hold Time | 1 hour per 25mm thickness |
PWHT must be performed to temper the martensitic structure and prevent cracking.
11. Traceability and Marking
Each tube marked with: Manufacturer, ASTM A213/ASME SA213 T21, UNS K31545, size, heat number, length, NDT method.
Marking Example:
| Line | Content |
| Line 1 | Womic Steel ASTM A213/ASME SA213 T21 |
| Line 2 | 50.8mm x 5.0mm x 6.0m |
| Line 3 | Heat No: H12345 / UNS K31545 |
| Line 4 | UT |
12. Quality Documents
● Mill Test Report (EN 10204 Type 3.1) – included
● Heat Treatment Certificate – included
● Hydrostatic/NDT Certificate – included
● Dimensional Inspection Report – included
● Certificate of Origin – included
● Third-Party Inspection – optional
13. Contact Information
Website: www.womicsteel.com
E-mail: sales@womicsteel.com
Tel / WhatsApp / WeChat:
Victor: +86 15575100681
Jack: +86 18390957568
Womic Steel – Your reliable partner for SA213 T21 seamless alloy tubes, stainless steel products, and custom solutions for power generation, refinery, and petrochemical high-temperature applications.
Post time: Oct-15-2026