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Home / Products / Alloy Steel Seamless Pipes / JIS G3429 STH11/12 STH21/22 Seamless Steel Tubes for High Pressure Gas Cylinder Applications
quality JIS G3429 STH11/12 STH21/22 Seamless Steel Tubes for High Pressure Gas Cylinder Applications factory
quality JIS G3429 STH11/12 STH21/22 Seamless Steel Tubes for High Pressure Gas Cylinder Applications factory
quality JIS G3429 STH11/12 STH21/22 Seamless Steel Tubes for High Pressure Gas Cylinder Applications factory

JIS G3429 STH11/12 STH21/22 Seamless Steel Tubes for High Pressure Gas Cylinder Applications

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seamless alloy steel tube

alloy steel seamless tubes

alloy steel pipe
Product Summary
JIS G3429 STH11/12, STH21/22, STH31 seamless steel tubes for high pressure gas cylinders. STH11/12 are low-carbon boiler steels, STH21/22 are Cr-Mo alloys for elevated temperatures, and STH31 offers higher Cr-Mo content for demanding conditions with superior creep strength and oxidation resistance.

Product Details

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JIS G3429 Seamless Steel Tubes

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STH11/12 STH21/22 STH31 Alloy Steel Seamless Pipes

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High Temperature Resistance High Pressure Gas Cylinder Tubes
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
C0.10–0.25 %
Si≤ 0.35 %
Mn0.27–0.80 %
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
C0.05–0.20 %
Si0.15–0.50 %
Mn0.30–0.80 %
CrAbout 0.5–1.5 %
MoAbout 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
C0.08–0.20 %
Si0.15–0.50 %
Mn0.30–0.80 %
CrAbout 1.9–2.6 %
MoAbout 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:
  1. Identify the governing standard
  2. Look up that standard or request it from the supplier
  3. 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.

Mrs. amy

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