Steel. 20 St.20 GOST GOST 8731- 74-GOST 8732-78 Seamless Steel Pipe
Steel Material Description
Russian Standard: GOST 8732-78is the Soviet-origin standard for "Hot-worked seamless steel pipes." It specifies the dimensional range, technical requirements, and assortment. The material grade20(or Ст20) refers to a carbon steel with a specific chemical composition and mechanical properties as defined within the GOST system.
Dimensional tolerances for wall thickness can be in the range+12.5% / -15%for certain sizes.
Chinese Standard:Chinese20# steels defined by multiple GB (Guobiao) standards depending on the application. The base standard isGB/T 699(Quality Carbon Structural Steels). For seamless pipes, it is commonly applied underGB/T 8163(for general service fluid delivery) orGB 3087(for low/medium pressure boilers).
While the chemical compositions are very similar and the grades are often considered analogs, there are slight variations in the allowable ranges and residual element limits.
|
Element |
GOST 8732-78 Grade 20 |
Chinese GB/T 699 Grade 20 |
Analysis |
|
Carbon (C) |
0.17-0.24 percent |
0.17-0.23 percent |
Virtually Identical. The ranges overlap completely. |
|
Silicon (Si) |
0.17-0.37 percent |
0.17-0.37 percent |
Identical. |
|
Manganese (Mn) |
0.35-0.65 percent |
0.35-0.65 percent |
Identical. |
|
Sulfur (S) |
≤ 0.040% |
≤ 0.035% |
Key Difference: The Chinese standard has a tighter restriction on Sulfur. Lower sulfur improves steel purity, ductility, and impact toughness. |
|
Phosphorus (P) |
≤ 0.035% |
≤ 0.035% |
Identical. |
|
Chromium (Cr) |
≤ 0.15% (sometimes ≤0.25%) -5 |
≤ 0.25% -4 |
Difference: The GOST standard sometimes has stricter control on residual Cr, though variations exist. |
|
Nickel (Ni) |
≤ 0.30% -5 |
≤ 0.30% -4 |
Identical. |
|
Copper (Cu) |
≤ 0.30% -5 |
≤ 0.25% -3 |
Difference: Chinese standard has slightly stricter control on residual Copper. |
The strength requirements are very close, but the Chinese standards often list slightly higher ductility (elongation) requirements for certain applications.
|
Property |
GOST 8732-78 Grade 20 |
Chinese GB/T 699 Grade 20 |
Analysis |
|
Tensile Strength (σb) |
≥ 410 MPa |
≥ 410 - 540 MPa |
Equivalent. Both meet the minimum of 410 MPa. |
|
Yield Strength (σs) |
≥ 245 MPa |
≥ 245 MPa |
Identical. |
|
Elongation (δ5) |
≥ 21% - 22% |
≥ 24% - 25% |
Difference: Chinese standards (GB/T 699) typically require higher elongation (24-25%) compared to the minimum GOST requirement (approx 21%). This suggests Chinese 20# may have slightly better formability. |
Summary of Key Differences for a Foreign Buyer
|
Feature |
GOST 8732-78 Grade 20 |
Chinese GB/T 699 Grade 20 |
Impact for Buyer |
|
Impurities (S&P) |
Slightly higher allowable S (0.04%) |
Lower S (0.035%) |
Chinese steel is generally "cleaner," offering better welding quality and impact resistance. |
|
Ductility |
Elongation ~21% |
Elongation ≥24% |
Chinese 20# is slightly more ductile and easier to bend/form |
|
Standard Age |
GOST 8732 dates to 1978 (though updated) |
GB standards are updated regularly (e.g., GB/T 8163-2018) |
Chinese standards often align more closely with modern ISO or ASTM requirements for testing. |
|
Application Scope |
General purpose piping, structural |
General purpose + Specific boiler grades (3087) |
If the end use is a boiler/pressure part, you must specify the Chinese equivalent boiler standard (e.g., 20G), not just "20# carbon steel ". |
