First, the chemical composition of 20G seamless steel tubes:
Carbon: 0.17%-0.24% (variable, increased to 0.17%-0.23%)
Silicon: 0.17%-0.37%
Manganese: 0.35%-0.65%
Phosphorus and Sulfur: ≤0.030% each (some requirements are more stringent, P ≤0.025%, S ≤0.020%)
Chromium, Nickel, and Copper: ≤0.25% each
Molybdenum: ≤0.15% or ≤0.08%
Vanadium: ≤0.08% or ≤0.15%
Total residual elements: ≤0.70%

Second, the mechanical properties of 20G seamless steel pipes:
Tensile strength: 410-550 MPa
Yield strength: ≥245 MPa
Elongation: ≥24% longitudinally, ≥22% transversely
Impact toughness: ≥40J longitudinally, ≥27J transversely
Hardness: ≤197 HB or ≤217 HBW
Low-temperature toughness: Maintains good performance even at low temperatures.

Third, the heat treatment process for 20G seamless steel pipes:
- Normalizing: Temperature range of 880-940°C, used to refine grain size, improve uniformity, and enhance mechanical properties (some sources state that the specific temperature may be adjusted based on production conditions, e.g., normalizing can be substituted for a final rolling temperature ≥900°C).
- Other auxiliary processes:
Tempering: 680-750°C, to eliminate quench brittleness and improve toughness (applicable to other alloy steels).
Quenching and tempering: Tempering may be required for special requirements, such as wall thicknesses ≥40mm.

Fourth, Applications of 20G Seamless Steel Pipe
High-Pressure Boilers: Used in heating surface pipes, economizers, superheaters, and reheaters, withstanding high temperatures and high pressures (≤650°C, ≥9.8 MPa).
Petrochemical Industry: Applications such as reactors, heat exchangers, and pipelines are suitable for corrosive environments.
Nuclear Power and Energy: Applications such as nuclear reactor cooling systems and offshore platform piping require radiation and corrosion resistance.
Machinery and Automotive: Applications such as bearing sleeves and engine exhaust pipes.

Fifth, Common Specifications
Small Diameter: 57×3.5, 76×4, 89×4.5, 108×4.5, or 6″
Medium and Large Diameter: 159×6, 219×6, 273×7 or 8″, 325×8 or 9″, 377×10, and 426×12″
Special Requirements: OD up to 760mm, wall thickness up to 140mm (thermal expansion or cold drawing).

Sixth, Other Features of 20G Seamless Steel Pipe
Surface Quality: The inner and outer walls must be free of defects such as cracks and folds. A slight oxide layer is permitted.
Processability: Deep processing (stamping, bending, etc.) and custom welding are supported.
Corrosion Resistance: Surface treatment (such as plating) enhances corrosion resistance.

Summary: 20G seamless high-pressure boiler steel pipes have become a key material in the industrial sector due to their high strength, resistance to high temperatures and pressures, excellent processability, and wide applicability. Strict control of their chemical composition and heat treatment process ensures stable performance. Common specifications cover a wide range of applications, from general to specialized. Specific model selection should be considered based on actual operating conditions and confirmed with reference to the GB/T5310-2023 standard for technical parameters.