Grade and Designation
The grade and designation of the tube shall be as given as follows table.
The sub-classification letter symbols A, B, and C, are used to indicate the distinction of manufacturing the tube, cold working process, heat treatment, etc.
| Grade | Designation | |
| Grade 13 | A | STKM 13A |
| B | STKM 13B | |
| C | STKM 13C | |
Method of Manufacture:
The tubes of STKM 13B shall be manufactured by seamless process, electric resistance welding process, or butt-welding process.
STKM 13B tubes shall be manufactured or in cold-finished condition or subjected to appropriate heat treatment.
World standard Comparative with JIS G3445 STKM 13
| NUBER | GRADE | NUBER | GRADE | NUBER | GRADE | NUBER | GRADE | |
| 13 | Grade 13A | STKM 13A | A512 | MT 1025 | 13 | STKM 13A | – | – |
| A513 | MTX 1025 | |||||||
| A519 | MT 1025 | |||||||
| Grade 13B | STKM 13B | – | – | 13 | STKM 13B | 980 | CDS-4 | |
| Grade 13C | STKM 13C | – | – | 13 | STKM 13C | – | – | |
STKM 13(A, B, C) Chemical Composition
| Grade | Designation | Unit % | ||||||
| C | Si | Mn | P | S | Nb or V | |||
| Grade 13 | A | STKM 13A | 0.25 max. | 0.35 max. | 0.30~0.90 | 0.040 max. | 0.040 max. | – |
| B | STKM 13B | |||||||
| C | STKM 13C | |||||||
| Designation | Tensile strength
MPa{ksi} |
Yield point or proof
MPa{ksi} |
Elongation % | Flattening
Strength Distance between flat plates (H) (D is outside dia. of the tube) |
Bending strength | ||||
| No. 4, | No. 4, | Bend angle | Inside radius | ||||||
| No. 11 | No. 5 | (D is outside dia. of the tube) | |||||||
| No. 12 | test pieces Transverse direction | ||||||||
| test pieces Longitudinal direction | |||||||||
| STKM13A | 370{38} min. | 215{22} min. | 30 min. | 25 min. | 2/3 D | 90 | 6 D | ||
| STKM13B | 440{45} min. | 305{31} min. | 20 min. | 15 min. | 3/4 D | 90 | 6 D | ||
| STKM13C | 510{52} min. | 380{39} min. | 15 min. | 10 min. | – | – | – | ||
The STKM 13B tubes shall be practically straight. and the two ends shall be at right angles to the axis of the tube
The STKM 13B tubes shall be free from defects detrimental to practical use.
The surface finish of the STKM 13B tubes, when especially specified, shall be agreed upon by the purchaser and the manufacturer.
| Division | Tolerance on the outside diameter |
| No. 1 | Under 50mm ±0.5mm |
| 50mm or over ±1% | |
| No. 2 | Under 50mm ±0.25mm |
| 50mm or over ±0.5% | |
| No. 3 | Under 25mm ±0.12mm |
| 25mm or over to and excl. 40mm ±0.15mm | |
| 40mm or over to and excl. 50mm ±0.18mm | |
| 50mm or over to and excl. 60mm ±0.20mm | |
| 60mm or over to and excl. 70mm ±0.23mm | |
| 70mm or over to and excl. 80mm ±0.25mm | |
| 80mm or over to and excl. 90mm ±0.30mm | |
| 90mm or over to and excl.100mm ±0.40mm | |
| 100mm or over ±0.50% |
| Division | Tolerances on wall thickness |
| No. 1 | Under 4mm |
| +0.6mm | |
| -0.5mm | |
| 4mm or over | |
| 15% | |
| -12.50% | |
| No. 2 | Under 3mm |
| ±0.3mm | |
| 3mm or over | |
| ±10% |
Standard: JIS G3445
Description Name: STKM 13A steel tubes, STKM 13B steel tubes, STKM 13C steel tubes, JIS G3445 STKM 13B Steel pipes.
Size: 4mm-340mm
W.T.: 1mm-50mm
Shape: Round
Production type: Cold drawn, Cold rolled, Hot rolled, or Electric resistance welding.
Length: Single random length/ Double random length or as customer's actual request max length is 10m
Grade: STKM 13A, STKM 13B, STKM 13C
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