Summary
JIS G3429 is a Japanese Industrial Standard for High Pressure Gas Cylinder Tubes made of carbon steel. The "STH11" designation specifies the grade of steel, which is a low-carbon manganese steel known for its excellent strength, toughness, and suitability for cold drawing and high-pressure applications.
1. Standard: JIS G3429 - High Pressure Gas Cylinder Tubes
This standard specifies the requirements for seamless steel pipes and tubes intended for the manufacturing of high-pressure gas cylinders. These tubes must withstand high internal pressures and are therefore subject to strict chemical, mechanical, and hydraulic testing requirements.
2. Grade: STH11
"STH" stands for Seamless Tube for High-pressure gas cylinders, and "11" is the grade code.
Key Characteristics of STH11:
Low Carbon Content: Makes the steel highly weldable and formable.
Manganese Addition: Provides solid strength and toughness.
Fine Grain Structure: Ensures good ductility and resistance to impact.
Cold Drawn: The tubes are typically cold-drawn to achieve precise dimensions, a smooth surface finish, and enhanced mechanical properties.
3. Chemical Composition (JIS G3429 Standard Requirements)
The chemical composition (by heat analysis) is a key factor in the performance of STH11.
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.15 - 0.25 |
| Silicon (Si) | 0.15 - 0.35 |
| Manganese (Mn) | 0.90 - 1.40 |
| Phosphorus (P) | ≤ 0.030 |
| Sulfur (S) | ≤ 0.035 |
| Copper (Cu) * | ≤ 0.20 |
Note: Copper is a residual element, and its content is controlled.
4. Mechanical Properties (JIS G3429 Standard Requirements)
The mechanical properties are guaranteed by the manufacturer and are a result of the chemical composition and manufacturing process (especially cold drawing).
| Property | Requirement |
|---|---|
| Tensile Strength (MPa) | ≥ 590 MPa |
| Yield Strength (MPa) | ≥ 400 MPa |
| Elongation (%) | ≥ 25% |
Note: The actual values, especially yield strength, are often significantly higher due to the cold working (drawing) process.
5. Manufacturing Process
The pipes are manufactured as seamless, meaning they are formed from a solid billet of steel without any welded seam. The typical process is:
Hot Piercing: A round billet is heated and pierced to form a hollow shell.
Hot Rolling / Extrusion: The shell is further elongated and shaped.
Cold Drawing (Key Step): The tube is drawn through a die at room temperature. This process:
Achieves precise outer diameter (OD) and wall thickness.
Creates a smooth, high-quality internal and external surface.
Increases tensile and yield strength through work hardening.
6. Common Applications
As the name implies, the primary and most critical application is:
High-Pressure Gas Cylinders:
Industrial gas cylinders (Oxygen, Nitrogen, Argon, Hydrogen, etc.)
Medical gas cylinders
Fire extinguisher shells
SMexico diving tanks
CNG (Compressed Natural Gas) vehicle fuel tanks
7. Equivalent Grades in Other Standards
While no grade is a perfect 1:1 equivalent, STH11 is very similar to the following grades in other international standards:
ISO 9809-1: 30CrMo (This is a very common and direct equivalent used for global gas cylinder manufacturing). Note that 30CrMo contains Chromium and Molybdenum, making it a low-alloy steel, but it serves the same purpose with similar mechanical properties.
DIN / European: 34CrMo4 (Similar to 30CrMo).
ASTM A519: 1026 or 1035 (These are standard carbon steel grades with similar C and Mn content, but they are not specifically certified for gas cylinders).
Important Note: For critical applications like gas cylinders, the specific standard (JIS G3429) and grade (STH11) must be specified and certified. "Equivalents" should only be considered for reference or non-critical applications.
Summary Table
| Feature | Description |
|---|---|
| Standard | JIS G3429 |
| Grade | STH11 |
| Type | Seamless Carbon Steel Pipe |
| Key Use | High-Pressure Gas Cylinders |
| Process | Hot Finished & Cold Drawn |
| Main Characteristics | High Strength, Good Toughness, Excellent for Cold Forming |
| Common Equivalent | ISO 9809-1 30CrMo |
In conclusion, JIS G3429 STH11 represents a high-quality, reliable, and specifically engineered material for the demanding application of containing high-pressure gases. Its properties are carefully balanced to ensure both strength for safety and ductility for manufacturing.
