API 5CT L80 is the foundation sour-service casing grade — the first step up from standard carbon steel grades when a well encounters H2S or demands tighter yield control for collapse performance and connection integrity. What distinguishes L80 from N80 at the same yield level is not strength but control: a mandatory maximum yield of 655 MPa and a hardness ceiling of 23 HRC that make it compatible with NACE MR0175 / ISO 15156 in mild to moderate H2S environments.
ZC Steel Pipe supplies API 5CT L80 casing in all three sub-grades — L80-1, L80-9Cr, and L80-13Cr — to PSL1 and PSL2, with full MTC documentation and third-party inspection available on every order. We supply OCTG to oil and gas operators across Africa, South America and Southeast Asia. This guide covers everything needed to specify L80 correctly for your well environment.
What Is API 5CT L80?
API 5CT L80 is a Group 2 casing and tubing grade governed by API Specification 5CT. The "L" prefix denotes a controlled yield range — distinguishing it from "N" grades which have no yield ceiling. The "80" indicates the minimum yield floor of 80,000 psi.
Three properties define L80 and separate it from uncontrolled grades:
Controlled maximum yield (655 MPa) — prevents the over-hard microstructures that form when yield strength runs high, which is critical for sulphide stress cracking (SSC) resistance in H2S environments.
Mandatory hardness limit (23 HRC) — the NACE MR0175 / ISO 15156 hardness threshold for carbon steel tubulars in sour service. L80-1 is specifically manufactured to comply with this requirement.
Mandatory quench and temper heat treatment — unlike N80 which can be normalised or Q+T, L80 always requires quench and temper to achieve the controlled microstructure. This is not optional and cannot be waived on order.
L80 Sub-Grades — L80-1, L80-9Cr, L80-13Cr
L80 is a family of three metallurgically distinct sub-grades sharing the same yield and hardness requirements but differing fundamentally in alloy content, corrosion resistance, and application envelope.
| Property | L80-1 | L80-9Cr | L80-13Cr |
|---|---|---|---|
| Alloy type | Carbon-manganese steel | 9% chromium alloy | 13% chromium martensitic stainless |
| Cr content | None significant | 8.0–10.0% | 12.0–14.0% |
| H2S sour service | Yes — mild sour (NACE) | Limited — check H2S level | Not suitable above trace H2S |
| CO2 resistance | Limited — requires inhibition | Good | Excellent — passive film |
| Heat treatment | Q+T mandatory | Q+T mandatory | Q+T mandatory |
| Typical use | Sour gas wells, H2S formations | Moderate CO2, steam injection | CO2-rich gas condensate wells |
The most common specification error in L80 procurement: L80-13Cr is frequently misapplied in wells with H2S. Its 13% chromium content provides excellent sweet CO2 corrosion resistance but the martensitic microstructure is susceptible to SSC above very low H2S partial pressures — typically above 0.05 psi / 0.003 MPa. If your well has any meaningful H2S, L80-13Cr requires NACE MR0175 / ISO 15156-3 qualification and standard L80-13Cr will frequently fail. For wells with both significant CO2 and H2S, Super 13Cr or duplex stainless is required.
Mechanical Properties
All three L80 sub-grades share identical mechanical property requirements under API 5CT:
| Property | L80-1 | L80-9Cr | L80-13Cr |
|---|---|---|---|
| Min yield strength | 552 MPa (80,000 psi) | 552 MPa (80,000 psi) | 552 MPa (80,000 psi) |
| Max yield strength | 655 MPa (95,000 psi) | 655 MPa (95,000 psi) | 655 MPa (95,000 psi) |
| Min tensile strength | 655 MPa (95,000 psi) | 655 MPa (95,000 psi) | 655 MPa (95,000 psi) |
| Max hardness | 23 HRC (255 HBW) | 23 HRC (255 HBW) | 23 HRC (255 HBW) |
| Heat treatment | Q+T mandatory | Q+T mandatory | Q+T mandatory |
Chemical Composition
| Element | L80-1 (max %) | L80-9Cr (range %) | L80-13Cr (range %) |
|---|---|---|---|
| Carbon (C) | 0.43 | 0.15 max | 0.22 max |
| Manganese (Mn) | 1.90 max | 0.30–0.60 | 1.00 max |
| Chromium (Cr) | — | 8.00–10.00 | 12.00–14.00 |
| Molybdenum (Mo) | — | 0.90–1.10 | — |
| Silicon (Si) | 0.45 max | 1.00 max | 1.00 max |
| Phosphorus (P) | 0.030 max | 0.020 max | 0.020 max |
| Sulphur (S) | 0.030 max | 0.010 max | 0.010 max |
| Nickel (Ni) | — | — | 0.50 max |
Standard Sizes
| OD (inches) | OD (mm) | Common Weights (lb/ft) | Typical Application |
|---|---|---|---|
| 4½ | 114.3 | 9.50–15.10 | Production tubing, small bore casing |
| 5 | 127.0 | 11.50–18.00 | Production casing |
| 5½ | 139.7 | 14.00–23.00 | Production casing — most common L80 size |
| 7 | 177.8 | 17.00–35.00 | Intermediate and production casing |
| 7⅝ | 193.7 | 24.00–45.30 | Intermediate casing |
| 9⅝ | 244.5 | 32.30–58.40 | Surface and intermediate casing |
| 10¾ | 273.1 | 32.75–65.70 | Surface casing, large bore wells |
| 13⅜ | 339.7 | 48.00–72.00 | Surface casing |
L80 vs N80 — Key Differences
N80 and L80 are the two dominant 80 ksi OCTG grades and the most frequently confused. Substituting one for the other in sour service is a documented engineering failure mode.
| Property | N80-1 | N80Q | L80-1 |
|---|---|---|---|
| Min yield strength | 552 MPa | 552 MPa | 552 MPa |
| Max yield strength | 758 MPa — no ceiling | 758 MPa — no ceiling | 655 MPa — controlled |
| Hardness limit | None | None | 23 HRC mandatory |
| Heat treatment | Normalised or N+T | Q+T | Q+T mandatory |
| Sour service | Not suitable | Not suitable | Yes — mild sour |
| NACE MR0175 | No | No | Yes |
| Relative cost | Lower | Moderate | Higher |
N80Q (quenched and tempered N80) can achieve hardness values well above 23 HRC — particularly in heavy-wall pipe where the Q+T cycle is less uniform. This is exactly the SSC initiation risk that NACE MR0175 is designed to prevent. L80's mandatory hardness cap is a manufacturing quality requirement that forces the mill to control the entire Q+T process. N80Q heat treatment alone does not make it a sour service grade.
PSL-1 vs PSL-2 for L80
| Requirement | L80 PSL-1 | L80 PSL-2 |
|---|---|---|
| NDE of pipe body | Not mandatory | Mandatory — full length UT or EMI |
| NDE of pipe ends | Not mandatory | Mandatory — UT of end areas |
| Dimensional tolerances | Standard | Tighter — OD, wall, straightness |
| Traceability | Heat number | Full heat + pipe number per joint |
| Documentation | Standard MTC | Enhanced — all test results per pipe |
| Typical use | Sweet wells, non-critical | Sour service, HPHT, IOC specifications |
Most major international oil companies — Shell, BP, TotalEnergies, Saudi Aramco — specify PSL-2 as a minimum for all L80 orders regardless of service environment. The cost premium is typically 3–8% and the additional NDE and traceability documentation significantly simplifies third-party audits and regulatory compliance. For any sour service application, specify PSL-2.
Sour Service — L80 and NACE MR0175
L80-1 is the first API 5CT grade specifically designed for H2S-containing environments. Its NACE MR0175 / ISO 15156 compatibility rests on the 23 HRC hardness limit — but the relationship between L80, NACE, and actual sour service qualification is more nuanced than the spec sheet suggests.
The hardness discrepancy: API 5CT specifies L80 maximum hardness as 23 HRC. NACE MR0175 / ISO 15156-2 specifies 22 HRC for carbon steel in sour service. These are not the same number. The resolution is that NACE MR0175 allows individual hardness readings up to 22 HRC, whereas API 5CT's 23 HRC is a production lot maximum. In practice, L80-1 produced to API 5CT will typically measure well below 22 HRC in service — but this must be verified on the MTC, not assumed. Always request full hardness data and verify it against your project NACE compliance requirements before accepting delivery.
Supplementary requirements for sour service L80: For wells where H2S partial pressure exceeds 0.05 psi (0.0003 MPa), L80-1 PSL-2 alone is typically insufficient. Common supplementary requirements for sour service L80 orders:
- SR16 (HIC test) — hydrogen-induced cracking test per NACE TM0284, confirms resistance to internal hydrogen damage in wet H2S
- SR2 (impact testing) — CVN impact test at specified temperature, confirms fracture toughness in low-temperature sour service
- SR13 (hardness survey) — additional hardness testing frequency beyond standard API 5CT requirements
- Company-specific SR — IOCs often add requirements for maximum yield strength, CE limits, or specific NDE coverage
Connection Types for L80
L80 is available with all API 5CT standard connections and premium connections. For sour service strings, connection selection requires additional attention — the connection is often the weakest SSC link in the string.
| Connection | Sour Service Suitability | Notes |
|---|---|---|
| STC | Limited | Not recommended for sour service strings |
| LTC | Moderate | Better than STC; limited in HPHT |
| BTC | Good for most sour applications | Standard for L80 production casing in sour wells |
| Premium | Best — metal-to-metal seal | Required for gas-tight integrity and deep sour wells |
For L80-13Cr in CO2 service, standard API threads can suffer accelerated corrosion at the thread root in high CO2 environments. Premium metal-to-metal seal connections are strongly preferred. ZC Steel Pipe holds independent patents in premium connection designs qualified to API 5C5 CAL IV for all standard L80 sizes.
Application Selection by Well Environment
| Well Environment | Recommended Grade | Key Requirement |
|---|---|---|
| Mild sour gas (H2S below 0.05 psi pp) | L80-1 PSL-2 | 23 HRC max, NACE compliance — verify hardness on MTC |
| Moderate sour (H2S 0.05–1.5 psi pp) | L80-1 PSL-2 + SR16 | HIC test mandatory — consider T95 for deeper wells |
| CO2-rich sweet gas — no H2S | L80-13Cr PSL-1 or PSL-2 | Excellent CO2 resistance — confirm H2S is below threshold |
| CO2 and low H2S (below 0.05 psi pp) | L80-13Cr PSL-2 | Run NACE ISO 15156-3 checklist — consider Super 13Cr |
| Steam injection or geothermal | L80-9Cr | Better high-temperature oxidation resistance than L80-1 |
| Deep sour HPHT | T95 or C110 | L80 may be insufficient for collapse — evaluate T95 or C110 |
L80 covers mild to moderate sour service at normal completion depths. Two scenarios push engineers beyond L80: deep wells where collapse pressure requires higher yield strength than L80's 655 MPa maximum can deliver — where T95 or C110 is evaluated — and severe sour service above 1.5 psi H2S partial pressure where L80-1 SSC resistance is insufficient and Super 13Cr or CRA-lined pipe is required.
How to Specify L80 on a Purchase Order
A complete L80 casing purchase order must include all of the following:
- Standard — API 5CT or ISO 11960
- Grade and sub-grade — L80-1, L80-9Cr, or L80-13Cr (never just "L80")
- OD and nominal weight — e.g. 7 inch × 26.00 lb/ft
- Thread type — STC, LTC, BTC, or premium connection designation
- Range — R1, R2, or R3 (most strings are R3)
- PSL level — PSL-1 or PSL-2 (PSL-2 recommended for all sour service)
- Supplementary requirements — SR16, SR2, SR13 as required by well conditions
- Quantity — in joints or metric tonnes
- Delivery port — for freight planning and lead time
- MTC level — EN 10204 3.1 or 3.2
- Third-party inspection scope — mill visit, witness testing, SGS/BV/TÜV