QUICK DEFINITION: L80 PIPEAPI 5CT Grade L80 is a controlled-yield strength (80,000 psi min), quenched and tempered carbon steel pipe designed specifically for sour service (H2S) environments where material hardness must remain below 23 HRC (API) or 22 HRC (NACE) to prevent Sulfide Stress Cracking (SSC).
COMMON FIELD QUESTIONS ABOUT L80 PIPE
Does API 5CT L80 Type 1 automatically meet NACE MR0175?
No. API 5CT allows a maximum hardness of 23.0 HRC. NACE MR0175 (Region 3 sour service) strictly caps hardness at 22.0 HRC. You must specify "NACE Compliant" on the Mill Test Report (MTR) or risk rejecting pipe at the rig site.
Is L80 Type 1 corrosion resistant?
No. L80 Type 1 is cracking resistant in H2S, not weight-loss resistant in CO2. In sweet environments with CO2 partial pressures >7 psi, it requires inhibition or will pit as rapidly as J55 carbon steel.
What is the H2S partial pressure limit for L80 Type 1?
Technically unlimited, provided the hardness is confirmed <22 HRC and the temperature is within standard operating ranges (<175°F for elementary sulfur concerns). It is the standard baseline for high-H2S wells.
The Economic Breaking Point: When to Run L80
We see two primary errors in string design: over-engineering with 13Cr when L80 Type 1 suffices, and under-engineering with N80 in marginal sour wells. L80 becomes the mandatory economic choice the moment H2S partial pressure exceeds 0.05 psi (NACE threshold). Below this, J55 or K55 is sufficient.
However, L80 becomes a liability if vertical depth requires tension loads approaching 80% of pipe body yield. Once you require yield strengths above 80,000 psi in a sour environment, you hit an economic cliff: you must graduate to C90 or T95 grades, which often carry a 35-50% price premium and doubled lead times due to stricter SSC testing requirements.
The Hardness Gap: API vs. Field Reality
The discrepancy between API 5CT and NACE MR0175 is the primary source of rejected OCTG deliveries. API 5CT technically permits L80 to reach 23 HRC. However, in our field operations, any reading above 22.0 HRC is treated as non-compliant for Region 3 Sour Service.
Furthermore, testing methodology matters. Mills typically use Rockwell C (HRC) for speed. Field inspectors often use Equotip or Micro-Vickers. These conversions are not linear.
How do we resolve hardness disputes at the rig?
We specify ASTM E140 conversion tables in the purchase order and designate Laboratory Rockwell C (HRC) as the only binding referee method, rejecting field Equotip readings if they fall within the margin of error (+/- 2 HRC).
Critical Operational Limits
Engineers must distinguish between the mechanical limits of the steel and the chemical limits of the environment.
Parameter
L80 Type 1 (Carbon)
L80 13Cr (Martensitic)
Primary Threat
CO2 Pitting / Weight Loss
Sulfide Stress Cracking (SSC)
Max H2S (Partial Pressure)
Unlimited (if <22 HRC)
1.5 psi (0.10 bar)
Max Temperature
~800°F (Yield degradation starts)
~300°F (SCC risk increases)
pH Sensitivity
Low
High (pH < 3.5 requires upgrade)
Operational Takeaway: Never run standard L80 13Cr if there is a risk of H2S breakthrough >1.5 psi. The material will suffer catastrophic brittle failure. For mixed H2S/CO2 environments, Super 13Cr or Duplex is the minimum viable option.
When L80 Pipe Is the Wrong Choice
Trust is built on negative constraints. We advise strictly against L80 Type 1 in the following scenarios:
High Velocity Wet Gas (>60 ft/s) with CO2: Even with inhibition, the flow velocity will strip the inhibitor film from carbon steel. L80 Type 1 will suffer erosion-corrosion. Upgrade to 13Cr.
Oxygenated Fluids (>10 ppb O2): Do not use L80 13Cr in water injection wells where oxygen scavenging is unreliable. 13Cr is extremely susceptible to pitting in oxygenated chloride environments.
Low pH (< 3.5) Completion Fluids: Acidizing jobs through L80 13Cr tubing without proper inhibitors can destroy the passive chrome oxide layer, leading to rapid mass loss.
Can we acidize through L80 Type 1?
Yes, but corrosion rates accelerate exponentially at temperatures >150°F. We require specific high-temp acid corrosion inhibitors (intensifiers) for any exposure exceeding 4 hours.
Buyer Anxiety FAQ
Will L80 fail in "Sweet" service?
It can. While L80 is designed for sour service, it is still carbon steel. In a sweet well with high water cut and CO2 >30 psi, L80 Type 1 will perforate due to general corrosion unless a continuous inhibitor program is maintained.
Is the pipe compliant if the mill cert says 22.5 HRC?
It is compliant with API 5CT, but it is not compliant with NACE MR0175 for specific sour regions. If your well data indicates Region 3 sour service, you must reject this pipe or perform full-ring SSC testing (NACE TM0177) to prove fitness for service.
What is the alternative if we need higher strength than L80?
If you need 90ksi or 95ksi yield strength in an H2S environment, you cannot simply heat-treat L80 to a higher grade. You must specify API 5CT C90 or T95. These grades involve sophisticated chemistry and quenching processes to maintain SSC resistance at higher yield strengths.
