Carbon Steel Properties
Carbon steel is the most common structural and piping material in industry. Learn its properties, grades, limitations, and where it should and should not be used.
Overview
Carbon steel is an iron-carbon alloy with carbon content up to 2.1%. It is the backbone of industrial piping, structural steel, pressure vessels, and machinery. Its combination of strength, weldability, low cost, and availability makes it the default choice for most non-corrosive applications.
Common grades include ASTM A106 (seamless pipe), A234 (fittings), A105 (flanges), and A36 (structural).
Key Properties
| Property | Value |
|---|---|
| Density | 7850 kg/m³ |
| Tensile strength | 410–550 MPa (A106 Gr B) |
| Yield strength | 240 MPa (A106 Gr B) |
| Melting point | 1420–1540°C |
| Thermal conductivity | 50 W/m·K |
| Coefficient of thermal expansion | 12 × 10⁻⁶ /°C |
| Max service temperature | 425°C (continuous), 540°C (intermittent) |
Advantages
- High strength-to-cost ratio: Stronger than most non-ferrous alternatives at a fraction of the cost.
- Excellent weldability: Can be welded by all common methods (MIG, TIG, stick, submerged arc) with standard procedures.
- Wide availability: Available in every pipe size, schedule, and fitting type worldwide.
- Good machinability: Can be cut, drilled, tapped, and machined with standard tooling.
Limitations
- Corrosion in water and moist environments: Rusts when exposed to moisture and oxygen — requires painting, galvanising, or coatings for outdoor or wet service.
- Not suitable for highly corrosive fluids: Attacked by acids, chlorides, and many chemicals — use stainless steel or non-metallic alternatives.
- Embrittlement at low temperatures: Becomes brittle below -29°C — use low-temperature carbon steel (A333) or austenitic stainless steel for cryogenic service.
- Scale and oxidation above 540°C: Forms oxide scale at high temperatures — use chrome-moly alloy steel for high-temperature service.
Typical Applications
- Steam piping (up to 425°C)
- Water and air piping
- Oil and gas distribution
- Structural steelwork
- Pressure vessels and tanks
- General purpose flanges and fittings
Temperature Limits
| Temperature range | Suitability |
|---|---|
| Below -29°C | Not suitable — use A333 or stainless |
| -29 to 425°C | Suitable (standard grades) |
| 425–540°C | Marginal — consider chrome-moly |
| Above 540°C | Not suitable — oxidation and creep |
Chemical Compatibility
| Chemical | Rating |
|---|---|
| Water (neutral pH) | Fair — corrodes slowly |
| Steam (dry) | Good |
| Demineralised water | Poor — aggressive corrosion |
| Dilute acids | Poor — use stainless or plastic |
| Alkalis (dilute) | Good |
| Chlorides | Poor — pitting and stress corrosion |
| Hydrocarbons | Excellent |
How CHI can help
Ask CHI about carbon steel properties and to determine whether it is suitable for your specific fluid and temperature. The CHI assistant can recommend the right material for your specific application, explain chemical compatibility, and flag when a material is unsuitable for your operating temperature or environment.