Differences in Material Properties and Mechanical Properties
1. Carbon Steel Valves
- Composition and Strength: Carbon steel contains 0.12%-2.1% carbon, with elements such as manganese and silicon added to enhance performance. Its tensile strength typically ranges from 485-650 MPa (referring to ASTM A216), significantly higher than cast iron's 150-400 MPa (ASTM A48).
- Pressure Resistance: Carbon steel valves can withstand pressure classes 150-2500 (PN16-PN420) and are suitable for high-pressure piping systems, such as those in the petroleum and chemical industries.
- Temperature Adaptability: Operating temperatures range from -29°C to 425°C, maintaining stability even at high temperatures.
2. Cast Iron Valves
- Composition and Brittleness: Cast iron contains 2.1%-4% carbon, is brittle, has poor ductility, and is weak in impact resistance. Gray cast iron (HT200) has a tensile strength of only approximately 200 MPa.
- Pressure Limitation: Pressure ratings are typically Class 125-250 (PN10-PN25), suitable only for low-pressure applications such as water supply and drainage systems.
- Temperature Limitation: The upper limit for long-term use is approximately 120°C; thermal deformation may occur above this temperature.
Application Scenarios and Cost-Effectiveness Comparison
1. Advantages of Carbon Steel Valves
- High-risk environments: Such as refineries and natural gas pipelines, requiring high-pressure and corrosion resistance (can be galvanized or plastic-lined).
- Long-life requirements: Carbon steel has a service life of over 20 years and low maintenance costs.
2. Applications of Cast Iron Valves
- Low-cost projects: Unit prices are approximately one-third of those of carbon steel valves, making them suitable for civil construction projects with limited budgets.
- Low-pressure static systems: Such as fire hoses and irrigation valves, which do not require dynamic loads.
Selection Recommendations and Considerations
1. Preferred Applications for Carbon Steel Valves:
- Operating pressure > 10 MPa or temperature > 150°C
- The medium contains corrosive components (such as acidic fluids).
2. Cast iron is suitable for:
- Water systems operating at normal temperature and pressure, with no frequent on/off operations.
- Low sensitivity to weight (cast iron density is 7.2 g/cm³, carbon steel 7.85 g/cm³).