The pressure resistance of carbon steel pipes is not a fixed value but is determined by a combination of factors:
1. Material Grade
The material grade is a primary determinant of pressure resistance. Ordinary carbon steel (e.g., Q235) has a tensile strength of about 375-500 MPa, while high-strength carbon steel (e.g., X60) can exceed 517 MPa (per API 5L standard). The higher the material strength, the greater its pressure-bearing capacity.
2. Wall Thickness and Diameter
According to the Barlow formula (P=2St/D, where P is pressure resistance, S is tensile strength, t is wall thickness, and D is outer diameter), under the same material, increasing the wall thickness by 1 mm can improve pressure resistance by about 10-15%. For example, a DN100 SCH40 carbon steel pipe (6mm wall thickness) has a working pressure of about 5.6 MPa, while SCH80 (8mm wall thickness) can reach 7.4 MPa (ASTM A106 data).
3. Manufacturing Process
Seamless pipes (e.g., ASTM A106) generally have higher pressure resistance than welded pipes (e.g., ASTM A53) due to the absence of weld seams, which are potential weak points.
Standard Specifications and Pressure Classifications
Different international standards have clear classifications for the pressure resistance of carbon steel pipes:
ASTM A106 Seamless Pipe: Grade B has a maximum working pressure of 15.8 MPa at room temperature (12mm wall thickness, DN150 condition).
API 5L Line Pipe: X42 grade pipe typically has a design pressure of 10-12 MPa in oil and gas transmission (with a safety factor of 0.72).
Chinese Standard GB/T 8163: 20# carbon steel pipe allows a pressure of 6.4 MPa at 20°C (5mm wall thickness, DN80).
Selection Recommendations for Practical Applications
Safety Factor: Industrial piping typically uses a safety factor of 1.5-4 times the design pressure (higher values for flammable media). For example, steam piping requires additional corrosion allowance per ASME B31.1.
Temperature Correction: At high temperatures (>200°C), the pressure resistance of carbon steel pipes decreases by about 20-30%, and the material's temperature reduction factor must be considered.
Corrosive Environments: If the medium contains H₂S or CO₂, sour-resistant carbon steel (e.g., L245NS) should be used, or the design pressure should be reduced by more than 30%.
