QUICK DEFINITION: L80 PIPEAPI 5CT Grade L80 Type 1 is a controlled-yield (80,000 psi min), quenched and tempered carbon-manganese steel designed specifically for sour service (H2S) environments where NACE MR0175 compliance is mandatory. Its operational ceiling is strictly defined by a maximum hardness of 23 HRC (API) or 22 HRC (NACE) and a temperature threshold of roughly 150°F (65°C) before significant strength derating occurs.
COMMON FIELD QUESTIONS ABOUT L80 PIPE
Does the API 5CT stamp guarantee NACE MR0175 compliance?
No. API 5CT allows a maximum hardness of 23.0 HRC. NACE MR0175 (Region 3 sour service) requires a maximum of 22.0 HRC. Pipe stamped “API 5CT L80” can legally arrive at 22.8 HRC and be rejected by rig-site inspectors for sour service use.
Can L80 Type 1 handle high CO2 environments?
No. L80 Type 1 is carbon steel, not stainless. In wet environments with CO2 partial pressure > 7 psi (0.05 MPa), it will suffer rapid mesa corrosion (pitting) unless a continuous inhibition batch program is maintained. Use L80-13Cr for CO2 resistance.
Is L80 compatible with N80 couplings?
Strictly No. While they share an 80 ksi yield strength, N80 lacks the hardness controls of L80. Placing a non-NACE N80 coupling on an L80 string in a sour well introduces a catastrophic failure point susceptible to Sulfide Stress Cracking (SSC) within hours of exposure.
The Economic Breaking Point: TCO Analysis
We frequently see procurement teams struggle with the valuation of L80 compared to J55/K55 or proprietary grades. From our operational history, the economic logic for L80 is binary:
The Cost-Effective Zone: L80 is the most economical choice for onshore or shallow offshore wells with any detected H2S (partial pressure > 0.05 psi). The cost premium over J55 (typically 15-20%) is negligible compared to the cost of a single workover caused by SSC failure in lower-grade steels.
The Over-Engineered Risk: Using L80 in strictly “sweet” (0 ppm H2S) low-pressure wells is a waste of CAPEX. N80Q or K55 provides identical tensile utility at a lower price point. Conversely, stretching L80 Type 1 into high-CO2 fields (>3 mol% CO2) to avoid buying 13Cr is a false economy; the inhibitor costs over 5 years will exceed the upfront alloy premium.
Troubleshooting Failure Modes: Hardness vs. Chemistry
The primary failure mechanism for L80 is Sulfide Stress Cracking (SSC), but the root cause is rarely the steel chemistry—it is the heat treatment process. L80 must be Quenched and Tempered (Q&T). We have seen failures where unauthorized “normalized” pipe was passed off as L80. The grain structure was too coarse to arrest crack propagation in H2S environments.
How do we verify L80 integrity on the rack?
Use the Through-Wall Hardness Test. Surface hardness testing (Telebrinell) is often inaccurate due to surface decarburization. We require a laboratory Rockwell C test on a specific coupon (1 per heat) to verify the core hardness does not exceed 22 HRC.
What is the safe operating temperature limit for L80 Type 1?
Standard L80 Type 1 retains full yield strength up to 300°F (149°C). Above 400°F (204°C), yield strength derating factors must be applied, typically reducing effective burst rating by 5-8%.
When L80 pipe Is the Wrong Choice (Negative Constraints)
Despite its versatility, L80 is strictly prohibited in the following scenarios based on our failure analysis data:
pH < 3.5 + H2S: In extremely acidic environments with H2S, L80 Type 1’s passivation layer destabilizes. Even with low hardness, the hydrogen charging rate is too high. You must upgrade to C90 or T95.
High Velocity + CO2: If flow velocity exceeds 15 ft/s (4.5 m/s) in a CO2 environment, L80 Type 1 cannot maintain an inhibitor film. Erosion-corrosion will cut through the pipe wall in months. 13Cr is required.
Oxygenated Fluids: L80 13Cr (a common variant) is disastrously susceptible to pitting if introduced to aerated brines (O2 > 10 ppb). Never use 13Cr for water injection lines unless oxygen is strictly scavenged.
Comparison: L80 vs. Critical Service Grades
Parameter
L80 Type 1
T95 Type 1
C90 Type 1
Yield Strength (psi)
80,000 - 95,000
95,000 - 110,000
90,000 - 105,000
Max Hardness (HRC)
23.0 (API)
25.4 (API)
25.4 (API)
NACE SSC Test
Method A (Optional)
Method A (Mandatory)
Method A (Mandatory)
Price Index
1.0x (Baseline)
2.5x
2.2x
Operational Takeaway: T95 and C90 are not just “stronger L80.” They require significantly stricter manufacturing controls (QC) and mandatory SSC testing. Do not substitute T95 solely for tensile strength without verifying the drilling fluids are compatible with the higher hardness.
What is the maximum H2S partial pressure for L80 Type 1?
Theoretically, NACE MR0175 lists no specific limit for Carbon Steel < 22 HRC. However, in practice, we limit L80 Type 1 to 1.5 psi (0.1 bar) pH2S before mandating SSC testing on the specific heat lot.
Buyer Anxiety FAQ
Will L80 fail in a Sour Gas well?
It will not fail due to H2S cracking if the hardness is confirmed < 22 HRC and the pH is maintained > 3.5. It willfail if you rely solely on the API stamp (allowing 23 HRC) and encounter a region of high stress concentration, such as a dogleg severity > 3°/100ft.
Is L80 compliant with NACE MR0175 by default?
No. This is a critical distinction. “API 5CT L80” is a manufacturing standard. “NACE MR0175” is a performance standard. You must order “API 5CT L80 Type 1 with Supplementary Requirement SR15 (Hardness Testing)” and specify the NACE hardness cap in the PO text.
What is the alternative if L80 tensile strength is too low?
If you need higher tensile strength but must maintain sour service resistance, the direct upgrade path is API 5CT Grade C90 or T95. Do not attempt to use P110 or Q125 in sour environments; they will suffer catastrophic brittle fracture almost instantly upon contact with H2S.
