Chemical composition of GB 3087 Grade 20
| Grade | Chemical Composition(%) | |||||||
| C | Si | Mn | P | S | Cr | Cu | Ni | |
| 20 | 0.17～0.23 | 0.17～0.37 | 0.38～0.65 | ≤0.030 | ≤0.030 | 0.3～0.65 | ≤0.25 | ≤0.30 |
Mechanical properties of GB 3087 Grade 20
| Grade | Wall thickness (mm) |
Tensile strength (MPa) |
Yield Strength (MPa) |
Elongation % |
| ≥ | ||||
| 20 | ＜15 | 410～550 | 245 | 20 |
| ≥15 | 225 | |||
Allowable deviation of outer diameter and wall thickness
| Type of steel pipe | Outer diameter(mm) | Tolerance | ||
| ordinary | advanced | |||
| Hot rolled tube | OD | ≤159 | ±10%(min±0.50mm) | ±0.75%(min±0.40mm) |
| ＞159 | ±1.0% | ±0.90% | ||
| WT | ≤20 | ＋15.0%(min＋0.45mm) －12.5% －0.35mm) |
±10%(min±0.30mm) | |
| ＞20 | ±12.5% | ±10% | ||
| OD≥351 | ±15% | |||
| Cold drawn tube | OD | 10～30 | ±0.40mm | ±0.20mm |
| ＞30～50 | ±0.45mm | ±0.25mm | ||
| ＞50 | ±1.0% | ±0.75% | ||
| WT | 1.5～3.0 | +15% -10% |
±10% | |
| ＞3.0 | +12.5% -10% |
±10% | ||
