Quick Answer
Quick Answer
JIS G3444 covers carbon steel circular hollow sections (tubes) for general structural use in four grades — STK290, STK400, STK490, and STK540 — identified by minimum tensile strength in MPa. The standard covers both electric resistance welded (ERW) and seamless tubes, and is the Japanese equivalent of ASTM A500 or EN 10210 for circular structural hollow sections.
JIS G3444 (一般構造用炭素鋼鋼管 — carbon steel tubes for general structural use) specifies the material, dimensional, and testing requirements for circular structural steel tubes used in buildings, bridges, scaffolding, and general fabrication. The standard covers pipe from 21.7 mm OD up to 660.4 mm OD across a range of wall thicknesses. JIS mill certificates for G3444 may be issued in Japanese only or bilingual format — see [/standards/jis-mill-cert-guide] for field-by-field reading guidance.
The "STK" designation comes from Steel Tube (鋼管) for Kōzō (構造 — structure), following the same naming convention as JIS G3101 where the number indicates minimum tensile strength in MPa.
Scope and Applicability
JIS G3444 covers circular steel tubes supplied as:
- ERW (Electric Resistance Welded) tubes — the most common manufacturing method for standard sizes
- Seamless tubes — for thicker wall sections and special orders
- Hot-finished and cold-formed variants
Product applications include:
- Structural columns, handrails, and roof structures
- Sign posts, light poles, and flag poles
- Scaffold tubing and temporary structures
- Mechanical applications not requiring pressure certification
For rectangular and square hollow sections (RHS/SHS), JIS G3466 (角形鋼管) applies. For high-strength structural tubes, JIS G3475 (建築構造用炭素鋼鋼管) specifies the BCR and BCP grades used in building columns.
JIS Grade Designation System
STK grades follow the same G3101 pattern:
- STK = Steel Tube for general structure (一般構造用鋼管)
- Number = minimum tensile strength in MPa
| Grade | Tensile Strength Significance |
|---|---|
| STK290 | 290 MPa minimum tensile |
| STK400 | 400 MPa minimum tensile |
| STK490 | 490 MPa minimum tensile |
| STK540 | 540 MPa minimum tensile |
Grade Coverage
| Grade | Typical Application | Analogous Plate Grade |
|---|---|---|
| STK290 | Light structures, scaffold, agricultural | SS330 equivalent tube |
| STK400 | General structural columns and frames | SS400 equivalent tube |
| STK490 | Medium-strength structural columns | SS490 equivalent tube |
| STK540 | High-strength structural applications | SS540 equivalent tube |
STK400 is the most commonly specified and traded grade, widely used in building construction across Asia.
Chemical Composition Requirements
All values are wt% maximum unless noted. Ladle (heat) analysis.
| Grade | C max | Mn | Si max | P max | S max |
|---|---|---|---|---|---|
| STK290 | 0.25 | — | — | 0.040 | 0.040 |
| STK400 | 0.25 | — | — | 0.040 | 0.040 |
| STK490 | 0.18 | 1.50 max | 0.55 | 0.035 | 0.035 |
| STK540 | 0.25 | 1.50 max | 0.55 | 0.035 | 0.035 |
Notes:
- STK290 and STK400 do not specify Mn or Si limits, similar to the G3101 approach for low-grade general structural steel
- STK490 has a stricter carbon limit (0.18%) reflecting improved weldability requirements
- STK540 allows up to 0.25% C with Mn and Si controlled for consistent strength delivery
Mechanical Properties
STK290
| Wall Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| All | 175 | 290–410 | 30 |
STK400
| Wall Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| ≤ 16 | 245 | 400–510 | 23 |
| > 16 | 215 | 400–510 | 23 |
STK490
| Wall Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| ≤ 16 | 315 | 490–610 | 23 |
| > 16 | 295 | 490–610 | 23 |
STK540
| Wall Thickness (mm) | Yield Strength min (MPa) | Tensile Strength (MPa) | Elongation min % |
|---|---|---|---|
| All | 390 | 540 min | 15 |
Elongation is measured on gauge length proportional to 50 mm for tube specimens; full cross-section or strip specimens per JIS Z 2241.
Impact Test Requirements
JIS G3444 does not require Charpy impact testing for any grade. For structural tube applications requiring guaranteed notch toughness, specify JIS G3475 (building structural tubes, BCR/BCP grades) which includes Charpy requirements.
Dimensional Tolerances for Circular Hollow Sections
JIS G3444 specifies tolerances for the standard circular tube sizes. Key tolerances for ERW tubes:
Outer Diameter Tolerances
| Nominal OD Range (mm) | OD Tolerance |
|---|---|
| ≤ 48.6 | ± 0.5 mm |
| > 48.6, ≤ 114.3 | ± 0.8 mm |
| > 114.3, ≤ 165.2 | ± 1.0 mm |
| > 165.2, ≤ 267.4 | ± 1.2 mm |
| > 267.4, ≤ 660.4 | ± 0.5% of OD |
Wall Thickness Tolerances
| Wall Thickness (mm) | Thickness Tolerance |
|---|---|
| < 4.0 | ± 0.5 mm |
| ≥ 4.0, < 8.0 | ± 12.5% |
| ≥ 8.0 | ± 10.0% |
Length Tolerances
| Nominal Length | Tolerance |
|---|---|
| ≤ 6 m | + 40 mm / −0 mm |
| > 6 m | + 60 mm / −0 mm |
Standard delivery lengths are 3.5 m, 4 m, 5 m, 6 m, and 7 m. Random lengths (mill-run lengths) are also available.
Straightness
Maximum bow: 2 mm per 1 m of length, with total bow not exceeding 0.20% of the total tube length.
JIS Mill Certificate Format
JIS G3444 certificates follow the JIS inspection certificate type framework (3.1A, 3.1B, 3.1C, 3.2) described in [/standards/jis-mill-cert-guide]. A G3444 tube certificate will typically show:
- 規格 (Standard): JIS G3444
- 鋼種 (Steel grade): STK400 (or other)
- 寸法 (Dimensions): Outer diameter × wall thickness × length
- 熱番号 (Heat number)
- 化学成分 (Chemical composition): C, P, S at minimum; Mn and Si for STK490/540
- 機械的性質 (Mechanical properties): YS, UTS, elongation
- 製造方法 (Manufacturing method): ERW (電縫) or seamless (継目無)
Cross-Standard Equivalents
| JIS G3444 | ASTM | EN 10210 (hot-finished) | AS/NZS 1163 | BS EN 10219 (cold-formed) |
|---|---|---|---|---|
| STK290 | A500 Gr.A (approx) | S235H (approx) | C250L0 (approx) | S235H (approx) |
| STK400 | A500 Gr.B (approx) | S275H (approx) | C350L0 (approx) | S275H (approx) |
| STK490 | A500 Gr.C / A572 Gr.50 (approx) | S355H (approx) | C350L0 / C450L0 (approx) | S355H (approx) |
| STK540 | A500 Gr.D (approx) | S420H (approx) | — | S420H (approx) |
All equivalences are approximate. ASTM A500 is cold-formed only; EN 10210 covers hot-finished tubes. Manufacturing method affects mechanical property profiles.
MTC Verification Checklist
When verifying a JIS G3444 mill test certificate:
- Standard confirmed as JIS G3444 (not G3466 for rectangular, or G3475 for building columns)
- Grade (STK400, STK490, etc.) matches purchase order
- Dimensions (OD × wall thickness × length) match order
- Manufacturing method (ERW or seamless) matches specification
- Heat number (熱番号) traceable to physical bundle markings
- C ≤ specified limit for the grade; P and S within limits
- Tensile strength within specified range for grade
- Yield strength meets thickness-appropriate minimum
- Elongation meets minimum
- Certificate type (3.1B, 3.2, etc.) matches contract requirement
- Authorized inspector signature/stamp present
Frequently Asked Questions
What is the difference between JIS G3444 and JIS G3466?
JIS G3444 covers circular hollow sections (round tubes). JIS G3466 covers square and rectangular hollow sections (STKR grades — 角形鋼管). The grade naming is similar: STKR400, STKR490. Both standards use the same strength-based designation system.
Is STK400 the same as ASTM A500 Grade B?
They are approximate equivalents for structural sizing purposes. ASTM A500 Gr.B has a minimum tensile of 400 MPa (58 ksi) and minimum yield of 317 MPa (46 ksi) for round sections — similar to STK400's 400–510 MPa tensile and 245 MPa yield (for t ≤ 16 mm). However, A500 is a cold-formed tube standard while JIS G3444 covers both ERW (which may be either cold-formed or hot-finished) and seamless. Formal compliance with A500 Gr.B requires A500-certified material.
Does JIS G3444 cover rectangular tubes?
No. JIS G3444 covers circular hollow sections only. For square and rectangular hollow sections in Japan, specify JIS G3466 (STKR grades). For building structural columns, JIS G3475 (BCR295, BCR385, etc.) applies.
What does ERW mean on a JIS tube certificate?
ERW stands for Electric Resistance Welded (電縫鋼管 — densetsu kōkan). The tube is formed from strip and the longitudinal seam is welded by resistance heating without filler material. ERW tubes are the standard production method for most structural sizes. Seamless tubes (継目無鋼管 — tsugime nashi kōkan) are available for larger wall thicknesses or when seam-free product is specified.
How do I verify that STK400 tubes meet EN 10210 S355H requirements for a European project?
You cannot use STK400 to satisfy EN 10210 S355H without independent testing or dual certification. S355H requires minimum yield of 355 MPa (thin wall) and minimum tensile of 470 MPa, both higher than STK400 requirements. STK490 is closer to S355H in yield strength, but a formal EN 10210 certificate from a European-certified mill is required for projects invoking EN 10210. Alternatively, some Japanese mills can supply dual-certified material to both JIS G3444 and EN 10210 with appropriate testing and third-party inspection.
Ready to automate your certificate workflow?
Try TestCert free