1. Difference between API 5CT and API 5L
**API 5CT** specifies requirements for *casing and tubing* used in oil/gas well drilling and production. It covers seamless/welded steel pipes designed for downhole environments (pressure, corrosion).
**API 5L** specifies requirements for *line pipe* used in transporting oil, gas, or water in pipelines. It covers seamless/welded carbon/alloy steel pipes focused on transmission efficiency and safety.
### 2. Difference between API 5L and ASTM A53
**API 5L** is for *pipeline transportation systems*, with stricter requirements for chemical composition, mechanical properties (e.g., Charpy impact testing for PSL 2), and non-destructive testing. Grades range from A25 to X120.
**ASTM A53** is for *general-purpose* (structural, low-pressure fluid) carbon steel pipe. It has simpler requirements (no mandatory impact testing), lower grades (A, B), and allows more manufacturing flexibility. API 5L PSL 1 Grade B is *similar* to A53 Grade B but not identical.
### 3. Specification of API 5L X70
API 5L X70 is a high-strength pipeline steel grade. Key requirements:
- **Minimum Yield Strength:** 485 MPa (70,300 psi) at room temperature.
- **Tensile Strength:** 570–760 MPa (PSL 1) or 570–760 MPa with stricter control (PSL 2).
- **PSL 2 Requirements:** Mandatory Charpy V-notch impact testing, stricter chemical composition (e.g., max carbon equivalent), and additional non-destructive testing (e.g., ultrasonic).
- **Common Applications:** High-pressure transmission pipelines.
### 4. Mechanical Properties of API 5L X80
For PSL 2 (most common in critical applications):
- **Yield Strength:** >= 555 MPa (80,500 psi).
- **Tensile Strength:** 625–825 MPa.
- **Elongation:** Varies by specimen size (e.g., >=18% for standard round bar).
- **Toughness:** Mandatory Charpy impact testing at -20℃ (-4℃F) or lower (minimum absorbed energy specified per wall thickness). Drop-weight tear test (DWTT) often required for fracture control.
### 5. Grades of API 5L Pipe
API 5L includes two categories:
- **Standard Grades:** A25, A, B, X42, X46, X52, X56, X60, X65, X70, X80.
- **Intermediate Grades (less common):** X90, X100, X120.
Grades define minimum yield strength (e.g., X80=80,000 psi yield). Each grade has two Product Specification Levels:
- **PSL 1:** Basic requirements.
- **PSL 2:** Enhanced testing, tighter chemistry, and stricter non-destructive inspection.
