Standard Number: GB/T 3087
Standard Name: Seamless Steel Tubes for Low and Medium Pressure Boilers
Issuing Authority: Issued by the State Administration for Market Regulation and the Standardization Administration of China
Effective Date: The latest version is GB/T 3087-2022, which officially came into effect on November 1, 2022, replacing the previous version GB/T 3087-2008.

II. GB/T 3087-2022 Specifications and Dimensions of Seamless Steel Tubes for Boilers

Outer Diameter (mm)	Wall Thickness (mm)	Length (mm)	Permissible Tolerance	Typical Application
10–22	1.5–3.0	3000–12500	OD ±1.5% (min. ±0.75 mm); WT ±12.5%	Small-diameter tubes (e.g., smoke tubes, small boiler tubes)
25–76	3.0–6.0	4000–12000	OD ±1.0% (min. ±0.50 mm); WT ±10%	Water-wall tubes, boiling water tubes
89–159	4.0–12.0	5000–12000	OD ±0.8%; WT ±8%	Superheater tubes, steam pipelines
168–273	6.0–20.0	6000–12000	OD ±0.6%; WT ±7%	Medium-pressure boiler main steam pipes
325–426	8.0–26.0	6000–12000	OD ±0.5%; WT ±5%	Large boiler headers, economizer tubes

Key Parameter Description

Outer Diameter Range: 10mm~426mm (43 specifications in total), covering all scenarios for low and medium pressure boilers.
Wall Thickness Range: 1.5mm~26mm (29 specifications in total), suitable for different pressure ratings (≤5.9MPa) and temperature conditions (≤450℃).
Length Deviation: Typical length 4000mm~12000mm, allowable deviation for fixed length:
Outer diameter ≤159mm, 0~+15mm;
Outer diameter >159mm, 0~+30mm.
Process Classification:
Hot-rolled tube: Outer diameter ≥32mm, wall thickness 2.5~75mm, suitable for boiler body and mechanical structure;
Cold-rolled tube: Outer diameter can be as small as 5mm, wall thickness ≤0.25mm, higher precision, used for precision components.

III. GB/T 3087-2022 Chemical Composition of Seamless Steel Tubes for Boilers

Grade	Carbon (C) %	Silicon (Si) %	Manganese (Mn) %	Phosphorus (P) %	Sulfur (S) %	Other Element Limits
20 Steel (Grade 20)	0.17–0.24	0.17–0.37	0.35–0.65	≤0.025	≤0.02	Cr ≤0.25%, Ni ≤0.3%, Cu ≤0.2%
20G	≤0.20	≥0.10	0.50–0.90	≤0.035	≤0.035	Strict limits on impurity elements (to reduce hot brittleness / cold brittleness)
20MnG	≤0.20	≥0.10	0.80–1.20	≤0.035	≤0.035	Higher Mn content improves thermal fatigue resistance

IV. GB/T 3087-2022 Mechanical Properties of Seamless Steel Tubes for Boilers

Grade	Tensile Strength (MPa)	Yield Strength (MPa)	Elongation (%)	Impact Absorbed Energy (J/cm²)	High-Temperature Performance (300°C / 450°C)
20 Steel (Grade 20)	410–550	≥245	≥20	≥27 (at 0°C)	≥149 MPa at 300°C; ≥132 MPa at 450°C
20G	≥410	≥245	≥24	≥27 (at 0°C)	Improved high-temperature strength and toughness
20MnG	≥450	≥275	≥22	≥27 (at 0°C)	Manganese enhances thermal fatigue resistance

V. GB/T 3087-2022 Inspection Standard for Seamless Steel Pipes

Inspection Item	Test Method / Standard Requirements	Key Indicators (Example for 20G Steel)
Chemical composition	Direct-reading spectrometer or chemical analysis	C ≤ 0.20%, Mn 0.50–0.90%, Si ≥ 0.10%, P ≤ 0.035%, S ≤ 0.035%
Tensile test	Universal testing machine; measures tensile strength, yield strength, elongation	Tensile strength ≥ 410 MPa; yield strength ≥ 245 MPa; elongation ≥ 24%
Hardness test	Brinell hardness tester (HBW)	Hardness range: 156–217 HBW
Flattening test	Hydraulic press, compressed to 2/3 of the outside diameter; inspect for cracks / delamination	No cracks or delamination
Flaring test	Expand radially by 15%; examine end cracking	No cracking
Cold bending test	Bend diameter = 4D (D = nominal OD), bend 180°	No cracks
Geometrical dimensions	Vernier caliper / micrometer measurement of OD, wall thickness, ovality, straightness	OD tolerance ±10% (for D ≤ 57 mm), wall thickness tolerance ±10%
Surface quality	Visual inspection or magnetic particle testing for defects (cracks, laps, scratches)	Defect depth < 0.05 mm
Nondestructive testing	Eddy current testing (OD ≤ 100 mm) or ultrasonic testing (WT > 5 mm)	No internal porosity, inclusions, or cracks
Hydrostatic test	Hydrostatic pressure test: pressure = 2.5× working pressure (≥15 MPa), holding time ≥10 s	No leakage; no plastic deformation