Austenitic stainless steel boiler tubes are seamless chromium-nickel alloy tubes used in high-temperature boiler heating surfaces, particularly superheaters and reheaters. Representative grades include TP304H, TP321H, TP347H, UNS S30432 and TP310HCbN.
These materials combine elevated-temperature strength with oxidation resistance. Their different compositions, stabilization methods and heat-treatment requirements allow selection for specific steam conditions and boiler designs. The grade must be assessed against the design temperature, pressure, allowable stress and expected service life.
Product Specifications
| Item | Description |
|---|---|
| Product | Seamless austenitic stainless steel boiler tubes |
| Material family | Chromium-nickel austenitic stainless steel |
| Main grades | TP304H, TP321H, TP347H, UNS S30432 and TP310HCbN |
| Product standards | ASTM A213/A213M or ASME SA-213/SA-213M, subject to grade coverage and designation in the specified edition |
| Manufacturing route | Hot-finished or cold-finished seamless tubes |
| Delivery condition | Solution heat-treated according to the selected grade and product standard |
| Dimensions | Outside diameter × wall thickness × length |
| Principal applications | Superheater and reheater tubes |
Size availability and tolerances depend on the grade, manufacturing route and dimensional combination. The purchase specification should identify the wall thickness basis, heat-treatment requirements, surface condition and inspection requirements.
Grades and Material Characteristics
| Grade | Material characteristics |
|---|---|
| TP304H | An 18Cr–8Ni-class steel with a controlled carbon range for elevated-temperature service |
| TP321H | Titanium-stabilized chromium-nickel steel |
| TP347H | Niobium-stabilized chromium-nickel steel |
| UNS S30432 | An 18Cr–9Ni-class steel containing copper, niobium and nitrogen for elevated-temperature strength |
| TP310HCbN | A 25Cr–20Ni-class steel containing niobium and nitrogen |
The H designation identifies specific high-temperature grade requirements. TP304H, TP321H and TP347H should be ordered using their full grade designations rather than assuming a general-purpose or low-carbon stainless steel will meet the same requirements.
S30432 is a distinct material designation. In TP310HCbN, Cb is the historical abbreviation for columbium, now generally called niobium (Nb). Use the designation given in the specified standard edition and inspection documentation.
Chemical Composition
The following table compares selected composition values listed in the Baosteel boiler tube handbook.
| Grade | C, % | Cr, % | Ni, % | Other key alloying elements |
|---|---|---|---|---|
| TP304H | 0.04–0.10 | 18.00–20.00 | 8.00–11.00 | — |
| TP321H | 0.04–0.10 | 17.00–19.00 | 9.00–12.00 | Titanium |
| TP347H | 0.04–0.10 | 17.00–19.00 | 9.00–12.00 | Niobium |
| S30432 | 0.07–0.13 | 17.00–19.00 | 7.50–10.50 | Copper, niobium and nitrogen |
| TP310HCbN | 0.04–0.10 | 24.00–26.00 | 19.00–22.00 | Niobium and nitrogen |
All percentages are by mass. This table presents selected elements only. Complete acceptance requirements, including stabilizing-element limits and residual elements, follow the applicable product standard.
Mechanical Properties
| Grade | Minimum tensile strength, MPa | Minimum yield strength, MPa | Minimum elongation, % |
|---|---|---|---|
| TP304H | 515 | 205 | 35 |
| TP321H | 515 | 205 | 35 |
| TP347H | 515 | 205 | 35 |
| S30432 | 590 | 235 | 35 |
| TP310HCbN | 655 | 295 | 30 |
Data basis for both tables: Baosteel Boiler Tube & Pipe handbook, printed in June 2007. These are historical handbook reference values. Final composition, mechanical properties, specimen conditions, heat treatment and grain-size requirements follow the standard edition and purchase specification stated in the order.
Room-temperature tensile properties do not establish the allowable operating temperature. High-temperature design must consider the applicable allowable stresses, creep performance, oxidation behavior and service conditions.
Material Characteristics
Elevated-Temperature Strength
Controlled carbon and alloying additions contribute to strength at elevated temperatures. Titanium or niobium additions stabilize certain grades, while copper and nitrogen contribute to the alloy design of grades such as S30432.
Long-term performance also depends on heat treatment and microstructure.
Oxidation Resistance
Chromium supports the formation of a protective oxide layer. Higher chromium content can improve oxidation resistance in suitable environments, but grade selection must account for steam-side oxidation and exposure to combustion gases, ash and deposits.
Fabrication Considerations
Austenitic stainless steels generally have greater thermal expansion and lower thermal conductivity than ferritic boiler steels. These differences should be considered when designing bends, supports and joints between different materials.
Welding, forming and any subsequent heat treatment should follow qualified procedures. Consumables and fabrication requirements must suit the selected grade and governing construction code.
Applications
Superheater Tubes
Austenitic stainless steel tubes are used in selected superheater sections where the design requires elevated-temperature strength and oxidation resistance.
Selection depends on tube metal temperature, steam pressure and the external combustion environment.
Reheater Tubes
Reheaters return steam to an elevated temperature between turbine stages. Austenitic grades are used where their properties satisfy the design requirements.
Thermal cycling, oxidation and long-term creep behavior should be considered alongside pressure and temperature.
Inspection and Quality Documentation
Inspection requirements follow the product standard and purchase specification. Depending on the order, they may include:
- Chemical analysis and tensile testing.
- Hardness testing and heat-treatment records.
- Dimensional and surface inspection.
- Flattening, flaring or other specified technological tests.
- Hydrostatic testing and/or specified nondestructive examination.
- Grain-size verification where required for the selected grade.
- Additional material identification or corrosion testing when specified.
Inspection documents should identify the product standard, grade, heat number, dimensions, delivery condition and applicable test results. Traceability should be maintained during cutting and fabrication.
Ordering Information
For a quotation, specify:
- Grade: TP304H, TP321H, TP347H, UNS S30432 or TP310HCbN.
- Standard: the required ASTM or ASME product standard and edition.
- Dimensions: outside diameter, wall thickness and length.
- Wall thickness basis: as required by the selected standard.
- Quantity: number of tubes, total length or weight.
- Delivery condition: required heat treatment and surface condition.
- Application: superheater, reheater or other specified service.
- Inspection: certificate requirements and additional testing.
- Fabrication: drawings and requirements for bending or further processing.
For bent or fabricated tubes, provide drawings showing bend radii, dimensional tolerances and any additional treatment or inspection requirements. Material substitutions require review under the applicable project requirements.