API 5CT-2011 K55 Pipeline Steel Coil
API 5CT-2011 K55 Pipeline Steel Coil - Properties, Equivalents & Applications
Complete material data for API 5CT-2011 K55 steel coil: chemical composition, mechanical and physical properties, international equivalents, similar grades and application guide.
Hot rolling, cold forming, welding, normalizing
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API 5CT-2011 K55 Pipeline Steel Coil Introduction
API 5CT K55 is a carbon-manganese steel grade specified for oil country tubular goods (OCTG), primarily used for casing and tubing in the petroleum and natural gas industry. It provides a minimum yield strength of 55 ksi (379 MPa) and excellent weldability, making it suitable for moderate-depth wells. This grade is typically supplied as hot-rolled or normalized coil for manufacturing ERW or spiral welded pipes.
- Yield strength range: 379–552 MPa
- Minimum tensile strength: 655 MPa
- Good formability and weldability
- Cost-effective for standard oilfield applications
API 5CT-2011 K55 Pipeline Steel Coil Chemical Composition
The chemical composition conforms to API 5CT (PSL-1) requirements for K55 grade. Residual elements are controlled to ensure weldability and mechanical properties. Silicon is not specified but typically present in quantities beneficial for deoxidation.
| Element | Content (wt%) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.26 | |
| Manganese (Mn) | ≤ 1.20 | |
| Phosphorus (P) | ≤ 0.030 | |
| Sulfur (S) | ≤ 0.030 | |
| Silicon (Si) | — (not specified) | Typical 0.15–0.35 for deoxidation |
API 5CT-2011 K55 Pipeline Steel Coil Thermal and Electrical Physical Properties
These physical properties are representative for carbon-manganese steel similar to API 5CT K55. Actual values may vary slightly depending on exact composition and processing condition.
| Property | Typical Value | Unit | Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20°C |
| Modulus of elasticity (E) | 200 – 210 | GPa | Room temperature |
| Shear modulus (G) | 80 | GPa | Typical |
| Poisson's ratio (ν) | 0.3 | — | |
| Thermal expansion coefficient (α) | 12.0 × 10⁻⁶ | °C⁻¹ | 20°C to 100°C |
| Thermal conductivity (λ) | 50 | W/(m·K) | At 20°C |
| Specific heat capacity (c) | 480 | J/(kg·K) | |
| Electrical resistivity (ρₑ) | 0.18 | µΩ·m | At 20°C |
API 5CT-2011 K55 Pipeline Steel Coil Mechanical Properties
Mechanical properties are required by API 5CT for K55 grade. The elongation value is the minimum calculated using the API formula (e = 625000·A0.2/U0.9) for an area of 0.2 in²; actual elongation often exceeds 20%. Hardness and impact tests are generally not required for PSL-1 K55 unless specified by the purchaser.
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Yield strength (ReH or Rp0.2) | 379 – 552 | MPa | Room temperature, as per API 5CT |
| Tensile strength (Rm) | ≥ 655 | MPa | Room temperature |
| Elongation (A) | ≥ 15 | % | Gauge length 2 in (50 mm), specimen area 0.2 in²; minimum according to API 5CT formula |
API 5CT-2011 K55 Pipeline Steel Coil Full Equivalent Material Standards and Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| International | ISO 11960:2011 | K55 | Identical to API 5CT K55 |
| China | SY/T 6194 | K55 | Identical to API 5CT K55 |
| United States | API 5CT (2011) | K55 | Original specification |
API 5CT-2011 K55 Pipeline Steel Coil Application Introduction
API 5CT K55 is designed for use as oil country tubular goods. It is widely used in the production of casing and tubing strings that must withstand moderate pressures and loads in oil and gas wells. It can also be employed for some line pipe applications when specified. The good weldability enables efficient manufacturing of ERW and spiral welded pipes.
Product Applications: Oil well casing pipes, Tubing strings, Couplings and pup joints, Spiral welded steel pipes for liquid transportation
Processed into products: Casing joints, Tubing sections, Connector bodies, Pup joints, Cross-over subs
Application industries: Oil and gas exploration and production, Pipeline construction (for certain line pipe applications), Water well casing
API 5CT-2011 K55 Pipeline Steel Coil Similar / Alternative Material Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| API | API 5CT | J55 | Same minimum yield strength but lower tensile strength (≥517 MPa); suitable for less demanding applications |
| API | API 5CT | N80 | Higher strength grade (yield 552–758 MPa, tensile ≥689 MPa); used for deeper wells or higher pressures |
Notes:
API 5CT K55 can be used for both seamless and welded pipes. For sour service (H₂S-containing environments), K55 is generally not recommended unless supplementary tests, hardness controls, or modified heat treatments are applied per NACE MR0175/ISO 15156. Additional requirements such as impact testing (e.g., Charpy V-notch), non-destructive examination, or tightened chemical limits may be imposed when ordering PSL-2 or according to purchaser specifications.
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