JIS G3429 STH12 Alloy Seamless Steel Tubes for High Pressure Gas Cylinder

Material

STH12 is a seamless gas-cylinder tube grade under JIS G3429, widely used as the base tube for manufacturing high-pressure steel gas cylinders. It belongs to the C–Mn (manganese steel) family, balancing strength, ductility, and forming performance for cylinder body processing.

Specifications

• Standard: JIS G3429 (Seamless steel tubes for high pressure gas cylinders)

• Tube type: Seamless; hot-finished or cold-finished (marking commonly shown as -S-H / -S-C)

• Typical size range (industry supply):

  • OD: 19.05–114.3 mm

  • WT: 2.0–14 mm

  • Length: up to 16,000 mm

• Typical tolerances (commonly used for cylinder tube supply): OD ±1%, WT +30% (project-specific agreement recommended)

Main Features

• Seamless structure (no weld seam), designed for pressure-bearing cylinder bodies.

• Controlled chemistry suitable for forming, heat treatment planning, and stable performance batch-to-batch.

• Safety-focused inspection basis: hydrostatic testing and/or NDT routes can be specified per order.

Our Advantages

1. “How do you ensure the tube truly meets JIS G3429 chemistry?”
   We control heat chemistry to the JIS G3429 composition window and provide traceable heat/lot identification and inspection documentation aligned with JIS delivery practice.

2. “Can you guarantee pressure integrity (leak-free)?”
   JIS G3429 allows hydrostatic testing; unless a higher pressure is specified by the buyer, the standard uses 5 MPa as the minimum hydrostatic pressure basis and requires no leakage.

3. “Do you support ultrasonic / eddy-current NDT for internal and surface defects?”
   NDT can be specified using ultrasonic or eddy-current routes, and alternative equivalent NDT can be agreed when required by the project or local regulation.

4. “What about surface quality and repair policy?”
   Tubes must have good internal/external surface finish with no harmful defects; surface dressing is permitted within thickness tolerance, while weld repair is not allowed—a key point for cylinder safety.

5. “Will every tube be traceable and properly marked?”
   Marking can include grade, manufacturing method symbol (hot/cold finish), dimensions, and manufacturer ID to support full traceability through cylinder forming and testing.

Chemical Composition 

Unit: wt.% (heat analysis)

Mechanical Properties 

Execution Standards (Common Options by System)

• JIS: JIS G3429 (material tube for cylinders); cylinders referenced by JIS B 8230 / JIS B 8241

• ASTM: ASTM A519 (seamless mechanical tubing, often used for cylinder-related tubing projects); ASTM A372 is also commonly referenced in cylinder supply chains depending on scope and jurisdiction.

• EN / ISO (widely used in Europe & international transport tube systems): EN ISO 11120 / ISO 11120 (refillable seamless steel tubes for compressed gas transport systems); EN 10216 / EN 10297 are often used for pressure-purpose / engineering seamless tubes when specified.

• GOST: GOST 8732-78 (hot-deformed seamless steel pipes) and related seamless pipe standards as specified by project documentation.

• GB: GB/T 18248-2021 (Seamless steel tubes for gas cylinder).

Application Areas

High-pressure gas containment and transport, especially where seamless integrity and traceability are mandatory.

Typical where-used examples:

• Industrial gas cylinders: oxygen, nitrogen, argon, CO₂ shielding gas for welding/cutting.

• Medical cylinders: medical oxygen cylinder bodies and related high-pressure containers.

• Energy & mobility: CNG cylinders / high-pressure storage cylinders (project-specific grade selection required).

• Chemical & specialty gases: high-purity or reactive gases requiring reliable cylinder shells.