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Standard Overview
JIS G3444 STK 400 is a Japanese Industrial Standard (JIS) specification for carbon steel tubes used in mechanical and structural applications. Here is a detailed description of it:
● Standard Number: JIS G3444
Title: Carbon steel tubes for general structural purposes.
● Material Designation: STK 400
STK: Stands for "Structural Tubing, Carbon Steel."
400: Indicates the minimum tensile strength in MPa (Megapascals).
● Specification:
OD: 20MM - 660MM(ERW), 245MM - 1420MM(LSAW)
WT: 1.3MM - 16MM(ERW), 10MM - 50MM(LSAW)
Length: Commonly used 5.8M,6M,12M,or as your requirement.
Surface Treatments: Coating, Hot-dip galvanized, Painting
Application: Civil engineering, Architecture, Steel Towers, Scaffoldings, Struts, Piles for Suppression of Landslide, and other structures.

Chemical Composition (Typical Requirements)
The chemical composition of STK 400 steel tubes generally adheres to the following limits (may vary slightly by manufacturer):
● Carbon (C): Maximum 0.25%
● Silicon (Si): No specific limit
● Manganese (Mn): No specific limit
● Phosphorus (P): Maximum 0.040%
● Sulfur (S): Maximum 0.040%
Note: Exact composition may vary depending on manufacturing processes (e.g., seamless or welded tubes).

Mechanical Properties
Tensile Strength: Minimum 400 N/mm²
Yield Point of Proof Stress: Minimum 235 N/mm²
Elongation: Typically ≥ 20–25% (varies with tube dimensions and Manufacturing method).
Bendability: 90° bend angle with an inside radius of 6D (D is the outside diameter of the tube)
Flattening: Distance between plates (H) is 2/3D
Tensile Strength in Weld Zone: Minimum 400 N/mm²

Manufacturing Methods
Seamless: Marked as "S"
Electric Resistance Butt Welded: Marked as "B"
Automatic Arc Welded: Marked as "A"
Hot Finished: Marked as "H"
Cold Finished: Marked as "C"
As Electric Resistance Welded: Marked as "G"
Surface Finish: Usually plain (black) or galvanized for corrosion resistance (if specified).

Testing And Inspection
Chemical Analysis: To ensure the chemical composition meets the specified limits.
Mechanical Testing: Including tensile tests, flattening tests, and bending tests.
Non-Destructive Testing (NDT): To check for any internal defects.
Surface Inspection: To ensure there are no surface defects.
Dimensional Check: To verify that the dimensions of the pipes meet the required tolerances.

Applications
Structural Purposes: Suitable for general structural applications, civil engineering, construction, steel towers, scaffolding, pillars, piles for landslide suppression, and other structures.
Other Uses: It can also be used in various industries where low-pressure applications are required.

Conclusion
JIS G3444 STK 400 is a versatile carbon steel tube standard offering balanced strength, formability, and weldability for structural uses. Compliance with JIS ensures consistency in quality and performance for industrial applications in Japan and internationally.

JIS G3444 STK400 Carbon Steel Tubes

JIS G3444 STK400 Carbon Steel Tubes Grade: STK400 Standard: JIS G3444 Manufacturing Methods: SMLS, ERW, LSAW... Specification: OD: 20MM - 660MM(ERW), 245MM - 1420MM(LSAW) WT: 1.3MM - 16MM(ERW), 10MM - 50MM(LSAW) Length: Commonly used 5.8M、6M、12M,or as your requirement. Surface Treatments: Powder coating, Hot-dip galvanized, Primer painted Application: Civil engineering, Architecture, Steel Towers, Scaffoldings, Struts, Piles for Suppression of Landslide, and other structures.

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