GB/T 8162: Seamless Steel Tubes for Structural Use — Grades and Properties

Quick Answer

GB/T 8162 (current edition: 2006, with 2012 amendment) is issued by the Standardization Administration of China under SAC/TC183. It governs seamless steel tubes (无缝钢管) used for general structural purposes such as machinery frames, conveyor structures, mine supports, and non-pressure piping. The standard covers hot-rolled (热轧) and cold-drawn (冷拔/冷轧) tubes.

GB/T 8162 is a structural tube standard and explicitly excludes pressure-service applications. For pressure-service seamless tubes in China, the applicable standards are:

• GB/T 8163 — seamless steel tubes for fluid service (pressure piping)
• GB 5310 — seamless steel tubes for boilers and heat exchangers
• GB/T 9948 — seamless steel tubes for petrochemical applications

For rectangular and square structural hollow sections (SHS/RHS), refer to GB/T 6728 (cold-formed) or GB/T 17395 (hot-formed).

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Scope and Applicability

GB/T 8162 applies to circular seamless steel tubes used in:

• Structural frameworks, column bases, and bracing
• Machine components (shafts, cylinders — non-pressure)
• Mine support arches and tunnel lining
• Automotive and agricultural machinery structural members
• General engineering fabrication requiring tubular section

Dimensional range covered:

• Outside diameter (OD): 6–2000 mm (hot-rolled); 6–200 mm (cold-drawn)
• Wall thickness: 0.25–75 mm

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Grade Coverage

GB/T 8162 groups grades into two categories:

Carbon Steel Grades

High-Strength Low-Alloy Grades

Note: The grade designations 10, 20, 35, 45 follow the Chinese steel numbering convention (GB/T 221) where the number represents 100× the mean carbon content (wt%). Grade 20 therefore has approximately 0.20% C (range: 0.17–0.24%).

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Chemical Composition Requirements

Ladle analysis per GB/T 700 and GB/T 1591 procedures. All values wt%.

Carbon Steel Grades (GB/T 8162 Table 1)

HSLA Grades (per GB/T 1591-2008)

Note: Tubes manufactured from Q345 and Q390 are subject to GB/T 1591 chemistry limits in full. For applications requiring the 2018 GB/T 1591 edition (with Q355 redesignation), this should be specifically called out on the purchase order, as GB/T 8162 itself still references the 2008 edition designations.

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Mechanical Properties

Tensile tests per GB/T 228.1 on specimens cut from the tube wall. Properties below are for hot-rolled condition unless noted.

Carbon Steel Grades

For cold-drawn (cold-finished) tubes, mechanical properties are slightly higher due to work-hardening; specific values apply per GB/T 8162 Table 3. Typical cold-drawn Grade 20: ReH ≥ 265 MPa, Rm ≥ 430 MPa, A ≥ 18%.

HSLA Grades — Q345 and Q390

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Dimensional Tolerances

GB/T 8162 specifies two precision classes: normal precision (普通级) and higher precision (较高级). The following are normal precision (most common commercial supply).

Outside Diameter Tolerances (Hot-Rolled)

Wall Thickness Tolerances (Hot-Rolled)

Higher precision class: OD tolerance ±0.75% and wall tolerance ±10%.

Length Tolerances

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Testing and Inspection Requirements

Per GB/T 8162 Clause 9, each lot requires:

1. Chemical analysis — one per heat
2. Tensile test — two specimens per lot from different tubes
3. Flattening test (压扁试验) — for OD ≤ 350 mm; tube flattened until OD/H = 2/3 (carbon grades) or OD/H = 3/4 (HSLA grades); no cracks permitted
4. Hydraulic test — standard: 7 MPa for OD ≤ 50 mm; or eddy current test as alternative
5. Dimensional inspection — OD, wall thickness, length, straightness, mass per unit length

Optional/supplementary tests (if specified on purchase order):

• Impact test (Charpy V-notch): not standard in GB/T 8162 unless invoked; specify temperature and energy
• Ultrasonic examination (超声检验)
• Magnetic particle or liquid penetrant inspection of ends

Lot size: ≤ 50 tonnes of the same grade and nominal dimensions from the same heat.

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Cross-Standard Equivalents

Grade 20 vs. ASTM A106 Grade B: Grade 20 has a similar carbon range (0.17–0.24%) to A106 Gr B (0.30% max), but Grade 20 also specifies a Mn range (0.35–0.65%) and Si range, while A106 Gr B allows higher Mn (max 0.93%). A106 Gr B has a higher minimum tensile strength (415 MPa) than Grade 20 (410 MPa). The two are broadly interchangeable for structural applications, but A106 Gr B is a pressure-service standard while GB/T 8162 Grade 20 is structural only. For pressure service, use GB/T 8163 Grade 20.

Q345 vs. EN S355J2H: S355J2H (EN 10210-1, hot-finished hollow sections) requires Charpy impact at −20 °C (27 J) as standard. GB/T 8162 Q345 does not mandate impact testing unless invoked on the purchase order. If impact-tested tube is required, specify Q345 with Charpy at the appropriate temperature per GB/T 1591 quality grade (C = 0 °C, D = −20 °C, 34 J).

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MTC Verification Checklist

A 质量证明书 for GB/T 8162 structural tube must include:

• Standard number: GB/T 8162 (and edition year — 2006/2012)
• Grade designation (e.g., Grade 20 or Q345)
• Heat number (炉号) and batch/lot number
• Product dimensions: OD × wall thickness × length
• Manufacturing method: hot-rolled (热轧) or cold-drawn (冷拔)
• Ladle chemistry: C, Mn, Si, P, S (for carbon grades); add Nb/V/Ti/CEV for HSLA grades
• Mechanical test results: ReH, Rm, A
• Flattening test result: pass/fail
• Hydraulic test pressure and result (or eddy current certification)
• Dimensional inspection results (OD, wall thickness within tolerance)
• Mill signature, stamp, and quality inspector name
• If impact testing was specified: temperature, individual values, and average

Common MTC issues:

• HSLA tubes supplied with carbon grade MTC (missing CEV, Nb/V/Ti)
• Wall thickness measured values close to −12.5% tolerance limit — check for thin wall
• Flattening test result not reported or incorrectly noted as "hydraulic test passed only"
• Confusion between GB/T 8162 (structural) and GB/T 8163 (fluid service) standard numbers

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Frequently Asked Questions