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JIS G3444: Carbon Steel Tubes For General Structural Purposes
Standard: JIS G3444 - Japanese Industrial Standard specifying requirements for carbon steel tubes primarily intended for general structural applications.

Material: Carbon Steel. These tubes are made primarily from plain carbon steel, with controlled levels of carbon, manganese, phosphorus, and sulfur. Minor alloying elements might be present depending on the specific grade and manufacturer's process, but they are not classified as alloy steels.

Grade Designation (STK XXX): The "STK" prefix indicates "Steel Tube" for structural use ("K" for Kouzou/構造, meaning structure). The number following "STK" represents the minimum specified yield strength (ReH or Rp0.2) in Megapascals (MPa) that the tube must meet.

STK 290: Minimum Yield Strength = 290 MPa
STK 400: Minimum Yield Strength = 400 MPa
STK 490: Minimum Yield Strength = 490 MPa
STK 500: Minimum Yield Strength = 500 MPa
STK 540: Minimum Yield Strength = 540 MPa

The JIS G3444 tubes shall be classified into five grades, and symbols of grade and manufacturing method shall be as given in below.

Symbol of Grade	Symbol of Manufacturing Method
	Tube Manufacturing Method	Finishing Method	Marking
STK 290	Seamless: S Electric resistance welding: E Butt welded: B Automatic arc welded: A	Hot finished: H Cold finished: C As electric resistance welded: G	Hot finished seamless steel tube: -S-H Cold finished seamless steel tube: -S-C As electric resistance welded steel tube: -E-G Hot finished ERW steel tube: -E-H Cold finished ERW steel tube: -E-C Butt welded steel tube: -B Automatic arc welded steel tube: -A
STK 400
STK 490
STK 500
STK 540

1. Dimensions shall be marked by outside diameter and wall thickness.

2. Manufacturer's name or its identifying brand
3. Symbol indicating the type of coating (in the case of using coated steel sheet or coated steel strip).
This abbreviation for this symbol shall be as agreed between the purchaser and the manufacturer.

Chemical Composition
The standard specifies maximum limits for key elements to ensure weldability, formability, and strength. Higher strength grades generally have tighter controls and slightly higher allowable carbon/manganese. Common elements controlled:

Symbol of Grade	C	Si	Mn	P	S
JIS G3444 STK 290	–	–	–	0.050max.	0.050max.
JIS G3444 STK 400	0.25max.	–	–	0.040max.	0.040max.
JIS G3444 STK 490	0.18max.	0.55max.	1.65max.	0.035max.	0.035max.
JIS G3444 STK 500	0.24max.	0.35max.	0.30 to 1.30	0.040max.	0.040max.
JIS G3444 STK 540	0.23max.	0.55max.	1.50max.	0.040max.	0.040max.

Notes:
1. If necessary, other alloy elements than those given in this table may be added.
2. For STK540, the chemical composition of tubes of wall thickness over 12.5 mm may be agreed upon between the purchaser and the manufacturer.

Mechanical Properties
Yield Strength (ReH or Rp0.2): As per the grade number (e.g., ≥ 290 MPa for STK 290).

Tensile Strength (Rm): Minimum tensile strength values are also specified for each grade, generally increasing with the yield strength grade.

Elongation: A minimum percentage elongation after fracture is required to ensure adequate ductility. The required elongation typically decreases as the strength grade increases.

Symbol of Grade	Tensile Strength N/mm2	Yield Point or Proof Stress N/mm2	Weld Tensile N/mm2	Flattening Resistance Strength	Bendability
	Tensile Strength N/mm2	Yield Point or Proof Stress N/mm2	Weld Tensile N/mm2	Distance between Flat Plates (H)	Bending Angle, a)	Inside Radius
	Applicable Outside Diameter
	All Outside Diameters	All Outside Diameters	All Outside Diameters	All Outside Diameters	50 mm or under
JIS G3444 STK 290	290 min.	–	290 min.	2/3D	90°	6D
JIS G3444 STK 400	400 min.	235 min.	400 min.	2/3D	90°	6D
JIS G3444 STK 490	490 min.	315 min.	490 min.	7/8D	90°	6D
JIS G3444 STK 500	500 min.	355 min.	500 min.	7/8D	90°	6D
JIS G3444 STK 540	540 min.	390 min.	540 min.	7/8D	90°	6D

NOTE 1 In this table, D stands for the outside diameter of the tube.
NOTE 2 1 N/mm 2 = 1 MPa
Note a) The bending angle shall be measured from the starting point of the bend.

Common Applications
Structural frameworks in buildings and warehouses.

Trusses and supports in bridges and infrastructure.

Poles (lighting, signage, utility).

Frames and chassis for agricultural machinery, material handling equipment, and general vehicles.

Guard rails, fences, and scaffolding components (where specific standards allow).

General fabrication requiring hollow structural sections (HSS) where high strength or pressure containment is not the primary concern.

Key Characteristics Summary
Standard: JIS G3444 (Japanese Industrial Standard).

Material: Carbon Steel (ERW).

Grades: STK290, STK400, STK490, STK500, STK540 (denoting min. tensile strength in MPa).

Primary Use: General structural applications (non-pressure).

Key Property: Minimum Tensile Strength (as per grade).

Critical Test: Flattening Test (weld integrity & ductility).

Form: Circular Electric-Resistance-Welded (ERW) Tubes.

Condition: Typically As-Welded.

JIS G3444: Carbon Steel Tubes

JIS G3444 indicated welded or consistent carbon steel tubes for general auxiliary purposes, civil designing, engineering, steel towers, frameworks, swaggers, heaps for concealment of avalanche and different structures Grade:STK290,STK400,STK490,STK500,STK540 Outer diameter: 33.4-660mm Wall thickness:2.1-22mm Length:0.8-18m suppliers Method: Hot Rolled. Surface Treatment: Coating, Painting, Galvanized, etc.

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