JIS G3429 STH11/12 STH21/22 Seamless Steel Tubes for High Pressure Gas Cylinder Applications
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Product Description
JIS G3429 STH11/12 STH21/22 STH31 Seamless Steel Tubes for High Pressure Gas Cylinder
These grades – STH11/12, STH21/22, STH31 – are tube/pipe steel designations used in heat-exchanger and boiler applications, closely mapping to well-known international grades. While exact composition varies by standard and manufacturer, they can be understood through comparison to common reference steels.
STH11 / STH12 – Low-Carbon Boiler/Heat-Exchanger Steels
Equivalent to carbon steel pressure-tube grades such as ASTM A179/A214/A210 low-carbon steels and JIS STB or STB35-type materials.
| Element | Composition Range |
|---|---|
| C | 0.10–0.25 % |
| Si | ≤ 0.35 % |
| Mn | 0.27–0.80 % |
| P | ≤ 0.035 % |
| S | ≤ 0.035 % |
| Cr, Mo, Ni, etc. | Usually not intentionally added (plain carbon steel) |
Designed for:
- Low to moderate temperature service in boilers, condensers, and heat exchangers
- Good formability and weldability due to low carbon content
STH21 / STH22 – Low-Alloy Cr-Mo Steels
Typically chromium-molybdenum pressure-tube steels similar to ASTM A213 T11/T12 and EN 10CrMo5-5, 13CrMo4-5 types.
| Element | Composition Range |
|---|---|
| C | 0.05–0.20 % |
| Si | 0.15–0.50 % |
| Mn | 0.30–0.80 % |
| Cr | About 0.5–1.5 % |
| Mo | About 0.45–0.60 % |
| P | ≤ 0.030–0.035 % |
| S | ≤ 0.030–0.035 % |
Designed for:
- Elevated temperature service (superheaters, reheaters, high-temperature piping)
- Improved creep resistance and oxidation resistance compared with plain carbon steel
STH31 – Higher-Cr-Mo Heat-Resistant Steel
Higher-alloy heat-resistant steel comparable to the 2.25Cr-1Mo class or related heat-resisting tube steels.
| Element | Composition Range |
|---|---|
| C | 0.08–0.20 % |
| Si | 0.15–0.50 % |
| Mn | 0.30–0.80 % |
| Cr | About 1.9–2.6 % |
| Mo | About 0.87–1.1 % |
| P | ≤ 0.030–0.035 % |
| S | ≤ 0.030–0.035 % |
Designed for:
- Higher temperature and pressure applications
- Superheater tubes, boiler tubes in power plants
- Better creep strength and oxidation resistance than STH21/22 group
Important Considerations
Why you should not rely only on generic data:
- Different standards can use similar codes with slightly different limits
- For design, welding procedure qualification, or material selection, you must use official material standards and mill test certificates
How to get the exact composition:
- Identify the governing standard
- Look up that standard or request it from the supplier
- Ask your tube/pipe supplier for the full chemical analysis and mechanical properties
Summary
- STH11/12: Plain carbon boiler/heat-exchanger steels
- STH21/22: Low-alloy Cr-Mo tube steels for higher temperatures
- STH31: Higher-Cr-Mo heat-resistant tube steel for demanding conditions
Important: For any engineering, welding, or safety-critical decisions, always confirm the exact chemistry from the relevant standard or manufacturer's certificate rather than using approximate data alone.
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Company
BEST PIPELINE EQUIPMENT CO.,LTD
Location
China Factory : Suzhou Industrial Park, JiangSu Province,China
Contact Person
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