API 5CT Grade L80 is the industry baseline for controlled-yield OCTG in sour service and mild corrosive environments, yet it remains the most frequently misapplied specification in field operations. Unlike J55 or N80, where failure is usually mechanical (collapse/burst), L80 failures are predominantly environmental: Sulfide Stress Cracking (SSC) in Type 1 and localized pitting or galling in 13Cr. Success requires managing the delta between mill tolerances and downhole realities.
QUICK DEFINITION: L80 PIPEAPI 5CT Grade L80 is a controlled-yield strength (80,000–95,000 psi) steel pipe used primarily in sour service (Type 1) or CO2 environments (13Cr), strictly limited to temperatures below ~350°F (177°C) and hardness levels ≤23 HRC (API) or ≤22 HRC (NACE).
COMMON FIELD QUESTIONS ABOUT L80 PIPE
Can L80 Type 1 pipe withstand high CO2 environments?
No. L80 Type 1 is carbon steel designed for H2S cracking resistance, not weight-loss corrosion. In wet CO2 environments without continuous inhibition, localized corrosion rates can exceed 50 mpy (mm/y), leading to rapid wall loss.
Does the API 5CT stamp guarantee NACE MR0175 compliance?
No. API 5CT permits a maximum hardness of 23.0 HRC. NACE MR0175 (Region 3) limits carbon steel to 22.0 HRC. A pipe stamped "L80" can be 22.8 HRC, legally passing API but failing NACE sour service audits.
What is the absolute H2S limit for L80 13Cr?
1.5 psi (0.1 bar). Standard 13Cr is extremely susceptible to Sulfide Stress Cracking (SSC) if the partial pressure of H2S exceeds 1.5 psi. Above this threshold, you must upgrade to Super 13Cr or Duplex stainless steel.
The Economic Efficiency Frontier: When to Deploy L80
Procurement teams often struggle with the price jump from N80 to L80. The economic logic relies entirely on the Sulfide Stress Cracking (SSC) threshold.
Cost-Effective Zone: L80 Type 1 is the mandatory selection when H2S partial pressure exceeds 0.05 psi (0.003 bar). Below this level, N80Q is sufficient. Using L80 in completely sweet wells is an over-engineered waste of capital (~15-20% premium over N80).
The 13Cr Breakpoint: L80 13Cr becomes economically viable when CO2 partial pressure exceeds 2-3 psi, making batch inhibition of carbon steel logistically impossible or OPEX-prohibitive. However, if water cut is low (<5%) and stable, inhibited carbon steel (L80 Type 1) remains the lower lifecycle cost option.
At what temperature does L80 13Cr become risky?
Above 300°F (149°C), the risk of Chloride Stress Corrosion Cracking (CSCC) in 13Cr increases exponentially, necessitating a move to 22Cr Duplex or Super 13Cr.
The Hardness Trap: API vs. NACE Compliance
The most critical procurement failure regarding L80 Type 1 is the hardness discrepancy. We frequently see pipe rejected at the rig site because the Purchase Order specified "API 5CT L80" but the well plan required "NACE MR0175 Sour Service."
API 5CT technically allows a hardness up to 23 HRC (approx. 241 HBW). However, for Region 3 Sour Service (high H2S), NACE MR0175 mandates a maximum of 22 HRC (237 HBW). Material testing reports (MTRs) from the mill often show heat averages. If the average is 21.5 HRC, statistical variation means individual joints may test at 22.5 HRC, creating a "NACE Fail" condition during spot checks.
What is the minimum yield strength overlap for L80 and N80?
Both grades share a minimum yield of 80,000 psi (551 MPa), meaning their burst and collapse ratings are identical; the difference is purely metallurgical chemistry and heat treatment.
Troubleshooting L80 13Cr Pitting Mechanisms
While L80 13Cr is selected for CO2 resistance, it is famously intolerant of oxygen and stagnant water. A passive chromium oxide film protects the steel, but this film is unstable in the presence of chlorides and oxygen.
Why does 13Cr pit during storage?
If 13Cr pipe is stored in a humid yard with standard mill varnish that has been damaged, moisture traps chlorides against the metal. Without the flow conditions of a producing well to maintain the passive film, rapid pitting occurs. We recommend climate-controlled storage or specialized UV-cured heavy storage compounds for 13Cr inventory held longer than 6 months.
Why does it fail after hydro-testing?
Using raw seawater or untreated brine for hydro-testing 13Cr tubing is a catastrophic error. The dissolved oxygen in the surface water (approx. 8 ppm) combined with chlorides will initiate pitting within 24 hours. If seawater must be used, it must be treated with an oxygen scavenger (to <10 ppb) and a biocide immediately.
When L80 pipe Is the Wrong Choice
Trust is built by knowing when not to sell or use a product. L80 (Type 1 or 13Cr) must be disqualified under these conditions:
pH < 3.5: In extremely acidic environments, L80 Type 1 corrosion rates become unmanageable even with inhibition.
H2S > 1.5 psi (for 13Cr): Standard 13Cr will suffer SSC. Do not attempt to "push" this limit with inhibitors; the cracking mechanism is instantaneous.
Dissolved Oxygen > 10 ppb: Any continuous oxygen ingress (e.g., leaking surface seals, water injection) will destroy L80 13Cr via pitting corrosion.
Comparative Data: L80 vs. Alternatives
Feature
L80 Type 1
L80 13Cr
T95 Type 1
Primary Hazard
H2S (Sour Gas)
CO2 (Sweet Gas)
High Pressure Sour
Yield Strength
80-95 ksi
80-95 ksi
95-110 ksi
Max Hardness
22 HRC (NACE)
23 HRC
25.4 HRC (Special Process)
Cost Index
1.2x
3.5x
2.0x
Operational Takeaway: T95 provides higher collapse resistance for deep wells but requires extremely long lead times for mill qualification. L80 Type 1 is the "off-the-shelf" standard, but stock availability rarely guarantees NACE-compliant hardness without supplementary testing.
Field Forensics FAQ
Will L80 fail if exposed to elemental sulfur?
Yes. Elemental sulfur acts as a catastrophic oxidant. In L80 Type 1, it accelerates sulfide stress cracking; in L80 13Cr, it causes massive localized pitting at temperatures >150°F (65°C), regardless of H2S levels.
Is L80 compatible with standard API Modified thread compound?
Conditional. For L80 Type 1, standard API Modified (containing lead/zinc) is acceptable. For L80 13Cr, "Yellow" API Modified can be used, but many operators prefer metal-free/environmentally friendly dope to avoid bi-metallic corrosion within the thread roots, which can compromise the seal.
What is the alternative if L80 13Cr pitts?
If L80 13Cr fails due to pitting (usually indicating H2S or O2 presence), the immediate upgrade is Super 13Cr (S13Cr-95 or S13Cr-110). Super 13Cr contains Molybdenum (1-2%), which stabilizes the passive film and raises the H2S limit to approx. 4.0 psi.
