API 5CT Grade L80 Type 1 is the foundational metallurgy for onshore sour service completion, yet it remains one of the most misunderstood specifications in the OCTG supply chain. It is not merely a “stronger J55”; it is a controlled-yield, Quenched and Tempered (Q&T) carbon steel strictly engineered to resist Sulfide Stress Cracking (SSC) via hardness control. Engineering teams often default to L80 for any “trace H2S” scenario, but without strict adherence to NACE MR0175/ISO 15156 hardness caps and environmental limits, this pipe can fail catastrophically or bloat completion budgets unnecessarily.
QUICK DEFINITION: L80 PIPE (TYPE 1)API 5CT Grade L80 Type 1 is a Q&T carbon steel OCTG product with a yield strength of 80–95 ksi, designed specifically for sour service (H2S present) environments by limiting maximum hardness to 23 HRC (API) or 22 HRC (NACE), though it offers zero resistance to CO2 weight-loss corrosion without inhibition.
The Economic Breaking Point: L80 Type 1 typically carries a 15–25% price premium over N80Q. The switch to L80 is economically mandatory the moment H2S partial pressure exceeds 0.05 psi (0.003 bar). Below this threshold, N80Q is often acceptable if the pH is buffered. Conversely, L80 becomes an over-engineered budget risk in strictly sweet wells (0 ppm H2S) where N80Q provides identical burst/collapse ratings at a lower cost per foot.
COMMON FIELD QUESTIONS ABOUT L80 PIPE
Can L80 Type 1 be used in high CO2 wells?
No. L80 Type 1 is carbon steel. In wet CO2 environments (>30 psi partial pressure CO2) without aggressive chemical inhibition, it will suffer rapid pitting corrosion. You must upgrade to L80 13Cr or Super 13Cr.
Does an API 5CT stamp guarantee NACE compliance?
No. API 5CT allows hardness up to 23.0 HRC. NACE MR0175 typically requires a maximum of 22.0 HRC for sour regions. Off-the-shelf API pipe may be rejected by rig-site inspectors if it tests at 22.5 HRC.
Can we mix L80 and N80Q in the same string?
Technically Yes, operationally risky. While they share yield strengths (80 ksi) and thread forms, mixing grades creates a crossover risk. If an N80 joint is accidentally run into the sour zone, it will crack. We strictly advise against mixed strings.
The Hardness Trap: 22 HRC vs. 23 HRC
The most frequent failure mode for L80 Type 1 occurs before the pipe is even run: Procurement Specification Mismatch.
API 5CT specifications permit a maximum hardness of 23 HRC (Rockwell C). However, the industry standard for sour service, NACE MR0175 (ISO 15156), mandates a maximum hardness of 22 HRC for carbon steels in Region 3 sour service to ensure immunity to SSC. This 1.0 HRC delta is the difference between a compliant well and a rejected string.
When ordering L80, we strictly require a supplementary requirement (SR 15) or a specific clause limiting hardness to 22 HRC maximum. Relying solely on the standard API spec allows mills to ship pipe with hardness values between 22.1 and 23.0 HRC—perfectly legal per API, but unusable in high-H2S fields.
What is the rejection rate for standard L80 inspected to NACE standards?
Approximately 5-10% of off-the-shelf API L80 joints fail the stricter NACE 22 HRC hardness test during third-party surveillance.
L80 Type 1 vs. N80Q and T95: The Sour Service Decision Matrix
Selecting the correct grade is a balance of tensile requirements, environmental cracking risk, and lead time. Below is the decision matrix our technical team utilizes for onshore intermediate and production strings.
Parameter
N80 (Type Q)
L80 (Type 1)
T95 (Type 1)
Primary Application
Sweet Service / Deep Wells
Sour Service (Standard)
Critical Sour / High Pressure
Min Yield Strength
80,000 psi
80,000 psi
95,000 psi
H2S Tolerance
None / Very Low (<0.05 psi)
High (Unlim. if <22 HRC)
High (Strict QC required)
Max Hardness
No Limit (usually ~24-28 HRC)
23 HRC (API) / 22 HRC (NACE)
25.4 HRC
Cost Baseline
1.0x (Base)
1.25x
2.5x - 3.0x
Operational Takeaway: Never upgrade from L80 to T95 solely for H2S resistance; L80 is actually moreresistant to cracking due to lower yield strength. Only step up to T95 if the burst/collapse pressures at depth require the extra 15,000 psi yield strength to maintain wall thickness geometry.
Does T95 require special handling compared to L80?
Yes. T95 is significantly more notch-sensitive; scratch depths acceptable on L80 (>12.5% wall) can cause catastrophic failure initiation in T95.
When L80 Pipe Is the Wrong Choice
Despite its versatility, L80 Type 1 is strictly prohibited in specific chemical environments. Engineering teams must validate negative constraints before procurement.
1. Low pH / High CO2 Environments
In wells with a partial pressure of CO2 > 30 psi and pH < 4.5, the corrosion rate of L80 Type 1 can exceed 100 mils per year (mpy). In these conditions, general weight-loss corrosion will destroy the string long before SSC becomes a factor. Correct Action: Use 13Cr or Duplex stainless steels.
2. Temperatures Exceeding 1,000°F (Fire Flood)
While rare, thermal recovery projects (fire floods) can exceed the tempering temperature of L80 (approx 1,150°F). Exposure to these temperatures degrades the heat treatment, dropping the yield strength below 80 ksi and invalidating burst ratings. Correct Action: Use non-Q&T grades or specialized high-temp alloys.
3. Acidizing with Uninhibited HCl
L80 Type 1 is highly reactive to Hydrochloric Acid (HCl). Pumping 15% HCl without specific corrosion inhibitors tailored for Q&T carbon steel can result in severe metal loss and hydrogen embrittlement within hours. Correct Action: Verify inhibitor packages for 80-grade steel specifically.
At what pH does L80 Type 1 become unsafe without inhibitors?
Generally, a pH below 4.0 in the presence of chlorides requires continuous chemical inhibition or a metallurgy upgrade.
Frequently Asked Questions (FAQ)
Will L80 pipe fail in sweet gas service?
It can, but not due to cracking. In sweet gas (CO2 only), L80 fails via pitting or “mesa” corrosion. We have seen L80 tubing perforated in less than 24 months in uninhibited sweet gas wells with high water cuts. Do not assume L80 is corrosion-resistant; it is only cracking-resistant.
Is L80 compliant with NACE MR0175 for all temperatures?
Yes, provided the hardness is strictly controlled ≤ 22 HRC. NACE MR0175 / ISO 15156 Table A.2 lists carbon steels as acceptable for any H2S partial pressure and any temperature, assuming the hardness cap is met. However, practical limits on coating/inhibitor effectiveness usually cap usage around 300°F (149°C).
What is the best alternative to L80 if I need higher strength?
If you need higher tensile strength but must maintain sour service resistance, the direct upgrade path is API 5CT Grade C90 or T95. Note that lead times for T95 can be double that of L80 due to the rigorous SSC testing requirements (NACE TM0177 Method A) required at the mill.
