Molybdenum steel boiler tubes are seamless carbon-molybdenum alloy steel tubes used in boiler and heat-transfer equipment. Representative grades include 15MoG, 20MoG and T1, T1a and T1b under ASTM A209/A209M or ASME SA-209/SA-209M.
Molybdenum contributes to elevated-temperature strength and creep resistance. These tubes are selected where the boiler design calls for a carbon-molybdenum steel, with the grade determined by service conditions and the applicable design code.
Product Specifications
| Item | Description |
|---|---|
| Product | Seamless molybdenum steel boiler tubes |
| Material family | Carbon-molybdenum alloy steel |
| Main grades | 15MoG, 20MoG, T1, T1a and T1b |
| Product standards | GB/T 5310; ASTM A209/A209M or ASME SA-209/SA-209M, as applicable |
| Manufacturing route | Hot-finished or cold-finished seamless tubes |
| Dimensions | Outside diameter × wall thickness × length |
| Delivery condition | Heat treatment and surface condition according to the specified standard and order |
Size availability depends on the grade, manufacturing route and dimensional combination. Tolerances and wall thickness requirements should follow the selected product standard rather than a single limit applied to every grade.
Grades and Standards
| Grade | Product standard | Description |
|---|---|---|
| 15MoG | GB/T 5310 | Carbon-molybdenum boiler steel with a lower molybdenum range than 20MoG |
| 20MoG | GB/T 5310 | Carbon-molybdenum boiler steel with a different composition and strength specification |
| T1 | ASTM A209 or ASME SA-209 | Carbon-molybdenum seamless boiler and superheater tube grade |
| T1a | ASTM A209 or ASME SA-209 | A grade with a higher specified carbon range than T1b |
| T1b | ASTM A209 or ASME SA-209 | A grade with a lower carbon limit than T1 and T1a |
Each grade has its own composition, mechanical properties and acceptance requirements. Similar molybdenum contents do not establish equivalence between GB, ASTM and ASME materials.
Chemical Composition
The following values are listed in the Baosteel boiler tube handbook. Its Chinese-grade table references GB 5310-1995, while the T-grade data appear under ASME SA-209M.
| Grade | C, % | Si, % | Mn, % | Mo, % | S, max. % | P, max. % |
|---|---|---|---|---|---|---|
| 15MoG | 0.12–0.20 | 0.17–0.37 | 0.40–0.80 | 0.25–0.35 | 0.020 | 0.025 |
| 20MoG | 0.15–0.25 | 0.17–0.37 | 0.40–0.80 | 0.44–0.65 | 0.020 | 0.025 |
| T1 | 0.10–0.20 | 0.10–0.50 | 0.30–0.80 | 0.44–0.65 | 0.020 | 0.025 |
| T1a | 0.15–0.25 | 0.10–0.50 | 0.30–0.80 | 0.44–0.65 | 0.020 | 0.025 |
| T1b | ≤0.14 | 0.10–0.50 | 0.30–0.80 | 0.44–0.65 | 0.020 | 0.025 |
All percentages are by mass. The table provides a comparison of handbook values; it does not replace the complete chemical requirements of the ordered standard.
Mechanical Properties
| Grade | Tensile strength, MPa | Minimum yield strength, MPa |
|---|---|---|
| 15MoG | 450–600 | 270 |
| 20MoG | ≥415 | 220 |
| T1 | ≥380 | 205 |
| T1a | ≥415 | 220 |
| T1b | ≥365 | 195 |
Data basis for both tables: Baosteel Boiler Tube & Pipe handbook, printed in June 2007. These are historical handbook reference values. Final chemical limits, mechanical properties, heat treatment and test conditions must follow the standard edition and purchase specification stated in the order.
Room-temperature tensile strength alone does not determine high-temperature suitability. Material selection also requires assessment of allowable stress, creep behavior and long-term stability at the design temperature.
Applications
Water Wall Tubes
Selected molybdenum steel grades are used in water wall circuits where the boiler design specifies their elevated-temperature properties. Tube selection depends on pressure, tube metal temperature, circulation conditions and the governing design code.
Superheater Tubes
Carbon-molybdenum steel tubes are used in selected superheater sections to carry steam while exposed to heat from combustion gases. ASTM A209 and ASME SA-209 specifically cover seamless carbon-molybdenum boiler and superheater tubes.
Reheater Tubes
The handbook also identifies reheater applications for the molybdenum steel family. Suitability must be established for the particular grade and service conditions, including thermal cycling and long-term operation.
Manufacturing and Inspection
Seamless tubes are produced by piercing solid billets and subsequent hot working or cold finishing. Final heat treatment should establish the delivery condition required for the selected grade.
Inspection requirements are defined by the product standard and purchase specification. Depending on the order, they may include:
- Chemical analysis and tensile testing.
- Dimensional and surface inspection.
- Flattening, flaring or other specified technological tests.
- Hardness testing where required.
- Hydrostatic testing and/or specified nondestructive examination.
- Additional tests and heat-treatment documentation specified by the project.
Inspection documents should identify the grade, heat number, dimensions, delivery condition and applicable test results. Welding and forming should follow procedures suitable for the material and fabrication code.
Ordering Information
For a quotation, specify:
- Grade: 15MoG, 20MoG, T1, T1a or T1b.
- Standard: the required GB, ASTM or ASME product standard and edition.
- Dimensions: outside diameter, wall thickness and length.
- Wall thickness basis: as permitted by the selected standard.
- Quantity: number of tubes, total length or weight.
- Delivery condition: required heat treatment and surface condition.
- Application: water wall, superheater, reheater or other specified service.
- Inspection: certificate requirements and additional testing.
- Fabrication: drawings and requirements for further processing.
For a proposed material substitution, provide the design conditions and obtain approval under the applicable project requirements.