Although both API 5CT N80 and L80 share the same minimum yield strength of 80,000 psi, they are designed for very different environments. The primary difference is that L80 is a controlled-hardness grade for Sour Service ( H2S ), while N80 is a general-purpose grade for Sweet Service.
N80 and L80 Petroleum Casing Pipe Technical Specifications Comparison Table
| Decision Dimension | Grade N80 (N80-1/N80-Q) | Grade L80 (L80-1) |
| Yield Strength | 80,000 - 110,000 psi | 80,000 - 95,000 psi (Tighter range) |
| Hardness Limit | No requirement | Strictly limited to ≤ 23 HRC |
| Heat Treatment | N80-1: Normalized; N80-Q: Q&T | Mandatory Full-length Q&T |
| Sour Service (SSC) | NONE (Prone to brittle failure) | EXCELLENT (NACE Compliant) |
| API Group | Group 1 or 2 (Depending on type) | Group 2 (Restricted Yield Grade) |
N80 and L80 Seamless Oil Pipe Mechanical Properties Comparison
While their yield strengths are identical, their tensile strengths and hardness requirements differ significantly.
| Property | N80 (N80-1 & N80-Q) | L80 (L80-1) |
| Min. Yield Strength | 80,000 psi (552 MPa) | 80,000 psi (552 MPa) |
| Max. Yield Strength | 110,000 psi (758 MPa) | 95,000 psi (655 MPa) |
| Min. Tensile Strength |
≥ 100,000 psi (689 MPa) |
≥ 95,000 psi (655 MPa) |
| Max. Hardness | No Limit |
≤ 23 HRC (241 HBW) |
N80 and L80 Oilfield Casing Heat Treatment & Manufacturing
The heat treatment process defines the internal grain structure and performance.
N80-1: Typically Normalized. It is the most economical version but lacks the refined structure of Q&T steel.
N80-Q: Quenched & Tempered (Q&T). Stronger and tougher than N80-1, but still lacks the hardness control of L80.
L80: Must be Quenched & Tempered (Q&T). This ensures a uniform, fine-grained tempered martensite structure, which is essential for resisting corrosion.
N80 and L80 OCTG Casing Corrosion Resistance (The Deciding Factor)
N80: Designed for Sweet Service (wells with no or very little H2S ). It is susceptible to rapid brittle failure (SSC) if exposed to high concentrations of Hydrogen Sulfide.
L80: Designed for Sour Service. It is the industry standard for wells containing H2S.
Note: L80 also has a 13Cr version (L80-13Cr) specifically for high CO2 environments, which N80 does not have.
N80 and L80 Deep Well Casing Color Code Identification
Field personnel distinguish these grades by color bands:
N80-1: One Red band.
N80-Q: One Red band + One Green band.
L80-1: One Red band + One Brown band.
N80 and L80 Oil And Gas Casing Pipes Environmental Suitability Table
| Environmental Factor | Choice: N80 | Choice: L80 |
|
H2S (Sour Gas) |
PROHIBITED. High hardness leads to SSC. | PRIMARY CHOICE. Designed for sour service. |
|
CO2 (Sweet Gas) |
Non-corrosive environments only. | L80-13Cr version recommended for CO2. |
| Formation Pressure | High-pressure (High cost-efficiency). | High-pressure (Higher safety margin). |
| Temperature | Ambient / High-temperature. | All temps; toughness superior to N80-1. |
| Well Classification | Standard "Sweet Service". | Critical "Sour Service". |
N80 and L80 Oilfield Casing Pipes Engineering Decision Matrix
| Scenario Description | Recommended Grade | Selection Reasoning |
| Deep Wells (No H2S ) | N80-1 | Lowest cost while ensuring 80 ksi strength. |
| High Pressure (High Toughness) | N80-Q | Quenched & Tempered (Q&T) offers better impact and fatigue resistance than N80-1. |
| Confirmed Sour Well ( H2S ) | L80 | Must control hardness (≤ 23 HRC) to prevent sudden string failure. |
| Offshore / Sensitive Areas | L80 | High workover costs justify the uniform structure and reliability of L80. |
|
CO2 Present (No H2S ) |
L80-13Cr | Both standard N80 and L80 will fail; 13% Chromium stainless is required. |
| Maximum Cost-Efficiency | N80-1 | The most economical choice for the 80 ksi strength level. |
API 5CT OCTG Casing Test and Inspection
API 5CT Oilfield Tubing Factory
FAQ
What is an N80 pipe?
API 5CT N80 is a medium-high strength casing and tubing grade with a minimum yield strength of 80,000 psi, available as N80-1 (Normalized) and N80-Q (Quenched & Tempered). It is a highly cost-effective choice for medium-to-deep wells and high-pressure formations, offering robust collapse resistance at a lower price than L80. However, due to its lack of strict hardness limits, it is designed strictly for Sweet Service (non-H2S environments) and is widely used where both high strength and economy are prioritized.
What is L80 casing?
API 5CT L80 is a restricted-yield, medium-high strength casing grade with a minimum yield strength of 80,000 psi, mandated to be full-length Quenched and Tempered (Q&T). Its defining feature is a strictly controlled maximum hardness of 23 HRC, providing exceptional resistance to Sulfide Stress Cracking (SSC). This makes it the industry standard for Sour Service operations in wells containing Hydrogen Sulfide ( H2S ).
