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STK290
STK400
STK490
STK500
STK540
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
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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
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| STK 400 | |||
| STK 490 | |||
| STK 500 | |||
| STK 540 | |||
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1. Dimensions shall be marked by outside diameter and wall thickness.
2. Manufacturer’s name or its identifying brand3. 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. |
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The tubes must be examined as per the standard, and the heat analysis results must match those in the table below. When the customer requests a product analysis, the tube must be tested as per the standard and the acquired product analysis values must meet the criteria in Table within the tolerances specified in Table of JIS G 0321.
| 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. |
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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. |
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- Tensile Strength and Yield Point or Proof Stress
To ensure the quality of steel tubes, they must be made with high-quality steel sheets or strips. These materials must then be tested to confirm their tensile strength, yield point, and proof stress. The tensile strength in the weld zone is also an important factor, and this must be confirmed as well. However, if the purchaser approves, the test for tensile strength in the weld may be omitted. All of these factors are important in ensuring that steel tubes are of the highest quality and will be able to withstand any stress or weight that is placed upon them.
| Symbol of Grade |
Tensile Strength
N/mm2
|
Yield Point or Proof Stress N/mm2 |
Weld Tensile N/mm2 |
Flattening Resistance Strength | Bendability | |
| 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 |
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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. |
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- Flattening
The flattening test is a method of testing for flaws or cracks in seamless steel tubes, electric resistance welded steel tubes, or butt welded steel tubes. The test involves placing the tube between two plates and applying pressure to the top plate. The distance between the plates is regulated to ensure that the test is accurate. The flattening test is an important part of quality control for steel tubes, and it helps to ensure that the tubes are free from defects.
- Bendability
Tubes that are 50 mm or under in outside diameter can be specified for their bendability instead of their ability to be flattened. Other tubes must be tested for bendability by the standard, and the test piece must be free from flaws or cracks. The acceptable bend angle and an inside radius of bending are specified in the table above. This ensures that the tubes meet the necessary safety standards and can withstand the specified amount of pressure.
- Outside Diameter Tolerance a)
| Classification | Outside Diameter b) |
Tolerances on
Outside Diameter c)
|
Applicable Division |
| Class 1 | Under 50mm | ± 0.5mm |
Applied when there is no specification. Applicable to hot-finished seamless steel tubes. |
| 50mm or Over | ± 1% | ||
| Class 2 | Under 50mm | ± 0.25mm |
Applied when there is a specification. Not applicable to hot-finished seamless steel tubes. |
| 50mm or Over | ± 0.5% | ||
| Notes |
a) For the local parts such as repaired parts if the wall thickness can be confirmed to be within the tolerance in the table below, the outside diameter tolerance of this table need not be applied. |
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b) The method for measuring the outside diameter of tubes exceeding 350mm in outside diameter may be determined by the circumferential length. The mutual conversion of outside diameter D and the circumferential length l shall be by the following formula: D = l / π Where D: outside diameter (mm) l: circumferential length (mm) π：3.1416 |
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c) The tolerances on the outside diameter of ends of electric resistance welded and automatic arc welded steel tubes exceeding 350mm in outside diameter shall be ±0.5%。 |
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- Wall Thickness Tolerance a)
| Classification | For Seamless Steel Tube | For Other than Seamless Steel Tube | Applicable Division | ||
| Wall Thickness | Tolerance of Wall Thickness | Wall Thickness | Tolerance of Wall Thickness | ||
| Class 1 | Under 4mm | +0.6mm, -0.5mm | Under 4mm | +0.6mm, -0.5mm |
Applied when there is no specification.
Applicable to hot-finished seamless steel tubes.
|
| 4mm or Over | +15%, -12.5% | 4mm or Over to and excl. 12mm | +15%, -12.5% | ||
| 12mm or Over | +15%, -1.5mm | ||||
| Class 2 | Under 3mm | ±0.3mm | Under 3mm | ± 0.3mm |
Applied when there is a specification. Not applicable to hot-finished seamless steel tubes. |
| 3mm or Over | ±10% | 3mm or Over to and excl. 12mm | ±10% | ||
| 12mm or Over | +10%，-1.2mm | ||||
| Notes | a) The tolerances on the wall thickness of tubes exceeding 1016.0 mm in outside diameter may be agreed upon between the manufacturer and the purchaser. | ||||
