20G boiler tubes are seamless carbon steel tubes used for boiler pressure parts, particularly water walls and economizers. Specified under GB/T 5310, 20G provides a combination of strength, ductility and fabrication characteristics for applications within the design limits of carbon steel.
Selecting 20G requires consideration of tube metal temperature, operating pressure, wall thickness and the applicable boiler design code. 20G identifies the steel grade, while GB/T 5310 defines the product requirements. The standard edition should be stated in the purchase specification.
Product Specifications
| Item | Description |
|---|---|
| Product | 20G seamless boiler tubes |
| Material | Carbon steel |
| Grade | 20G |
| Product standard | GB/T 5310, edition as specified in the order |
| Manufacturing route | Hot-finished or cold-finished seamless tubes |
| Principal applications | Boiler water walls and economizers |
| Dimensions | Outside diameter × wall thickness × length, as specified |
| Delivery condition | Heat treatment and surface condition according to the applicable standard and order |
Outside diameter and wall thickness must be considered together when specifying a tube. Dimensional tolerances depend on the standard edition, manufacturing route and size. For wall thickness, the order should identify whether the requirement is based on nominal or minimum thickness.
Chemical Composition
The following table gives the 20G composition limits listed in the Baosteel boiler tube handbook.
| Element | Content, mass % |
|---|---|
| Carbon (C) | 0.17–0.24 |
| Silicon (Si) | 0.17–0.37 |
| Manganese (Mn) | 0.35–0.65 |
| Sulfur (S) | ≤0.020 |
| Phosphorus (P) | ≤0.025 |
Carbon contributes to strength, while manganese and silicon support the steel’s strength and steelmaking requirements. Sulfur and phosphorus limits help control impurities.
Full chemical acceptance requirements, including any residual elements, should follow the specified standard edition and purchase specification.
Mechanical Properties
| Property | Handbook reference value |
|---|---|
| Tensile strength | 410–550 MPa |
| Minimum yield strength | 245 MPa |
| Minimum elongation | 24% |
Data basis for both tables: Baosteel Boiler Tube & Pipe handbook, printed in June 2007. Its 20G chemical composition table references GB 5310-1995. These are handbook reference values; final acceptance limits and test conditions follow the standard edition specified in the order.
Room-temperature tensile properties alone do not determine suitability for service. Boiler design also requires assessment of allowable stress at the design temperature and, where relevant, long-term behavior at elevated temperature.
Applications
Water Wall Tubes
20G tubes are used in boiler water walls to carry water or a steam-water mixture and absorb furnace heat. Material selection depends on the design pressure, tube metal temperature and circulation conditions.
Economizer Tubes
Economizers recover heat from flue gas to preheat boiler feedwater. 20G is a material option where the design conditions permit carbon steel. Water chemistry, corrosion and erosion should also be considered when selecting tube dimensions and service allowances.
Internally Rifled Tubes
20G is also listed in the handbook as a material for internally rifled water wall tubes. Internal helical ribs help improve heat transfer by influencing flow inside the tube. Rib geometry, wall thickness and dimensional requirements should be specified on the project drawing.
Manufacturing and Inspection
Seamless tubes are produced from solid billets through piercing and subsequent hot working or cold finishing. Heat treatment establishes the required delivery condition before final inspection.
Inspection requirements should be defined by the applicable standard and purchase specification. Depending on the order, these may include:
- Chemical analysis and tensile testing.
- Outside diameter, wall thickness, length and surface inspection.
- Flattening, flaring or other specified technological tests.
- Hydrostatic testing and/or specified nondestructive examination.
- Impact testing where required, with the test temperature and specimen conditions identified.
The requested inspection certificate should document traceability and the applicable test results. Welding and forming procedures must suit the material and the fabrication code.
Ordering Information
For a quotation, specify:
- Material: 20G.
- Standard: GB/T 5310, including the required edition.
- Dimensions: outside diameter, wall thickness and length.
- Wall thickness basis: nominal or minimum.
- Quantity: total length, number of tubes or weight.
- Delivery condition: required heat treatment and surface condition.
- Inspection: additional tests and certificate requirements.
- Application: water wall, economizer or other specified service.
- Drawings: required for internally rifled or fabricated tubes.
If an ASTM or ASME material is required, specify its product standard and grade separately. Similar applications do not establish automatic equivalence with 20G.