GB/T 8162-2018 General Seamless Steel Tubes for Structural and Mechanical Purposes

1. Scope  

Applies to general seamless steel tubes for structural and mechanical purposes, not for fluid transport (covered by GB/T 8163 for pressure purposes).

 2. Ordering Information  

Buyers should specify in contracts:  

- Standard number (GB/T 8162-2018)  

- Steel grade (e.g., 20#, 45#, Q345, etc.)  

- Dimensions (outer diameter, wall thickness, length)  

- Special requirements (e.g., heat treatment, testing)  

 3. Main Steel Grades  

Common grades include:  

- Carbon steels: 10#, 20#, 35#, 45#  

- Alloy steels: 16Mn (Q345), 27SiMn, 40Cr, etc.  

 4. Manufacturing Process  

- Hot-rolled or cold-drawn seamless tubes.  

- Heat treatment (annealing, normalizing, or tempering) may be required based on grade.  

 5. Technical Requirements  

- Chemical composition: Must comply with GB/T 699 (carbon steels) or GB/T 3077 (alloy steels).  

- Mechanical properties: Tensile strength, yield strength, elongation per steel grade.  

- Surface quality: Free from cracks, folds, and severe imperfections.  

- Dimensional tolerances: Specified for outer diameter, wall thickness, and length.  

 6. Inspection & Testing  

- Non-destructive testing: Optional unless specified (e.g., ultrasonic or eddy current testing).  

- Mechanical tests: Tensile, hardness, or impact tests as required.  

- Hydrostatic test: Not mandatory unless agreed upon.  

 7. Marking & Packaging  

- Tubes are marked with manufacturer’s name, grade, size, and standard number.  

- Packaging methods (bundling, protection against corrosion) per agreement.  

 Key Differences from Previous Versions  

- GB/T 8162-2018 updated steel grades and tightened tolerances compared to the 2008 edition.  

Main Steel Grades

 1. Carbon Structural Steels (Based on GB/T 699-2015)  

- 10#  

- 20# (Most commonly used)  

- 35#  

- 45# (High-strength applications)  

 2. Alloy Structural Steels (Based on GB/T 3077-2015)  

- Q345 (Equivalent to 16Mn, a low-alloy high-strength steel)  

- 27SiMn (High strength, used in hydraulic supports)  

- 40Cr (Chromium alloy, good hardness and wear resistance)  

- 20Cr  

- 35CrMo (Molybdenum alloy, high-temperature strength)  

- 42CrMo (Higher strength than 35CrMo)  

 3. Other Grades (Less common but included in some applications)  

- 15CrMo (Chromium-molybdenum alloy, heat-resistant)  

- 12CrMoV (For high-temperature service)  

 Key Notes:  

- 20# and Q345 are the most widely used grades for general structural purposes.  

- Higher carbon grades (45#, 40Cr, 42CrMo) are used for high-strength mechanical components.  

- Alloy steels (27SiMn, 35CrMo) are selected for specialized applications requiring toughness or heat resistance.  

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