API 5CT L80 - Casing/Tubing for Sour Service
API 5CT L80 is a medium-strength casing and tubing grade specifically designed for sour service (H₂S environments). The "L" historically relates to "Line pipe" and "80" denotes the minimum yield strength of 80,000 psi.
Key Features
| Feature | Description |
|---|---|
| Material | Carbon-Manganese Steel with controlled hardness |
| Primary Use | Sour service wells (H₂S present) |
| Key Property | Sulfide Stress Cracking (SSC) resistance |
| Heat Treatment | Quenched & Tempered (mandatory) |
Mechanical Properties
| Property | Requirement |
|---|---|
| Yield Strength | 552-655 MPa (80-95 ksi) |
| Tensile Strength, min | 655 MPa (95 ksi) |
| Hardness, max | 23 HRC (Rockwell C) – Critical for sour service |
Chemical Requirements (Controlled)
API 5CT specifies maximum limits for certain elements to ensure SSC resistance:
| Element | Maximum (%) |
|---|---|
| Carbon (C) | 0.43 |
| Manganese (Mn) | 1.90 |
| Phosphorus (P) | 0.030 |
| Sulfur (S) | 0.030 |
Why L80 for Sour Service?
Hardness Control: Maximum 23 HRC as per NACE MR0175/ISO 15156 standards.
Quenched & Tempered: Provides uniform microstructure for consistent SSC resistance.
Controlled Chemistry: Limits impurities that worsen cracking susceptibility.
Applications
Production casing/tubing in wells with H₂S.
Intermediate casing in corrosive formations.
A reliable and cost-effective choice for mild to moderately sour environments.
Types of L80
L80-1: Standard Type 1.
L80-9Cr: 9% Chromium alloy for enhanced CO₂ corrosion resistance.
L80-13Cr: 13% Chromium alloy (similar to 420 stainless) for more severe CO₂ corrosion.
Comparison with N80
| Grade | Yield Strength (ksi) | Sour Service? | Key Difference |
|---|---|---|---|
| N80 | 80-110 | NO | Higher strength, no hardness control. |
| L80 | 80-95 | YES | Lower max strength, hardness capped at 23 HRC. |
Simple Rule: For wells with H₂S → Use L80. For wells without H₂S → Use N80 (stronger and cheaper).
Ordering Example
API 5CT L80 Casing, 7" 23#, Range 3, BTC. Hardness ≤ 23 HRC. For sour service.
In summary: API 5CT L80 is the go-to standard grade for sour service applications, offering a proven balance of strength, SSC resistance, and cost. Its mandatory hardness control is the key to its reliability in corrosive wells.
