API 5CT L80 is the foundation sour-service casing grade — the first step up from standard carbon steel grades (N80, K55) when a well encounters H₂S or demands tighter yield control for collapse or connection integrity. Its defining characteristic is not just minimum strength, but a controlled yield band (552–655 MPa) and a mandatory hardness ceiling of 23 HRC — the properties that make it compatible with NACE MR0175 / ISO 15156 in mild H₂S environments and reliably predictable in high-collapse casing string design.
ZC Steel Pipe manufactures and exports API 5CT L80 casing and tubing in all three sub-grades — L80-1, L80-9Cr, and L80-13Cr — to PSL1 and PSL2, with full MTC documentation and third-party inspection. With completed OCTG projects across Africa, the Middle East, and South America, we support engineers from grade selection through to final inspection. This guide covers everything needed to specify L80 correctly.
CONTENTS
What Is API 5CT L80?
L80 Sub-Grades: L80-1, L80-9Cr, L80-13Cr
Chemical & Mechanical Properties
L80 vs N80 — Key Differences
PSL1 vs PSL2 for L80
Sour Service: L80 and NACE MR0175
Connections & Threading
Applications by Well Environment
FAQ
1. What Is API 5CT L80?
API 5CT L80 is a casing and tubing grade defined in API Specification 5CT — the governing standard for oil country tubular goods (OCTG). The "L" prefix denotes a controlled yield range (distinguishing it from the "N" grades which have no yield ceiling), and the "80" indicates the minimum yield strength floor of 80,000 psi.
API 5CT L80 — CORE IDENTITYMinimum yield strength: 552 MPa (80,000 psi) · Maximum yield strength: 655 MPa (95,000 psi) · Minimum tensile strength: 655 MPa (95,000 psi) · Maximum hardness: 23 HRC (255 HBW) · Heat treatment: Quench & temper (mandatory) · Available sub-grades: L80-1, L80-9Cr, L80-13Cr · Standard: API 5CT / ISO 11960
Three properties distinguish L80 from all non-controlled grades and make it the standard choice for corrosive or H₂S-containing wells:
Controlled maximum yield (655 MPa): Prevents the over-hard microstructures that form when yield strength exceeds the NACE threshold — critical for SSC resistance in H₂S environments
Mandatory hardness limit (23 HRC): The NACE MR0175 / ISO 15156-2 hardness ceiling for carbon and low-alloy steel tubulars in sour service — L80-1 is specifically designed to comply
Mandatory Q&T heat treatment: Unlike N80 (which can be normalised or Q&T), L80 requires quench and temper to achieve the controlled microstructure — this is not optional and cannot be waived
See also: What Are the Grades of OCTG Pipe? → | Understanding Steel Grades for Casing and Tubing →
2. L80 Sub-Grades: L80-1, L80-9Cr, L80-13Cr
L80 is not a single material — it is a family of three metallurgically distinct sub-grades that share the same yield and hardness requirements but differ fundamentally in alloy content, corrosion resistance, and application envelope.
L80-1 (Carbon Steel)
Alloy type: Carbon-manganese steel
Cr content: None significant
Sour service: Yes — mild H₂S (NACE)
CO₂ resistance: Limited — requires inhibition
Typical use: Sour gas wells, H₂S-containing formations
L80-9Cr
Alloy type: 9% chromium alloy steel
Cr content: 8.0–10.0%
Sour service: Limited — check H₂S level
CO₂ resistance: Good — better than L80-1
Typical use: Moderate CO₂ environments, steam injection
L80-13Cr
Alloy type: 13% chromium martensitic stainless
Cr content: 12.0–14.0%
Sour service: Sweet to mildly sour only
CO₂ resistance: Excellent — passive film protection
Typical use: CO₂-rich gas condensate wells
Field Note — L80-13Cr Is Not a Sour Service GradeThis is one of the most common specification errors in OCTG procurement. L80-13Cr's 13% chromium content provides excellent resistance to sweet (CO₂-dominated) corrosion, but the martensitic microstructure is susceptible to sulphide stress cracking (SSC) above very low H₂S partial pressures (typically >0.05 psi / 0.003 MPa). If your well has any meaningful H₂S, L80-13Cr requires qualification under NACE MR0175 / ISO 15156-3 — and standard L80-13Cr will frequently fail. For wells with both significant CO₂ and H₂S, Super 13Cr (modified chemistry, lower hardness) or duplex stainless is required. See:
L80-13Cr Metallurgy: Composition, Passivity and the Super Gap →
3. Chemical & Mechanical Properties
3.1 Mechanical Properties (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 |
| Min elongation (2" GL) | ≥ 0.5% per formula | ≥ 0.5% per formula | ≥ 0.5% per formula |
3.2 Chemical Composition (API 5CT)
| 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 |
3.3 Standard Sizes
| OD (inches) | OD (mm) | Common Weight Range (lb/ft) | Typical Application |
| 4½" | 114.3 | 9.50 – 15.10 | Production tubing, small bore casing |
| 5" | 127.0 | 11.50 – 18.00 | Intermediate production casing |
| 5½" | 139.7 | 14.00 – 23.00 | Production casing, most common L80 size |
| 7" | 177.8 | 17.00 – 35.00 | Intermediate casing, 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 |
4. L80 vs N80 — Key Differences
L80 and N80 are the two dominant 80 ksi OCTG grades, and they are frequently confused or incorrectly substituted for each other. Understanding the differences is not academic — it directly determines whether a well completion is safe and compliant in H₂S environments.
| Property | N80 (Type 1 or Q) | L80-1 |
| Min yield strength | 552 MPa (80,000 psi) | 552 MPa (80,000 psi) |
| Max yield strength | No maximum | 655 MPa (95,000 psi) |
| Hardness limit | None specified | 23 HRC max (255 HBW) |
| Heat treatment | N80-1: normalised; N80Q: Q&T | Q&T mandatory |
| Sour service (H₂S) | Not suitable | Suitable (mild sour, NACE MR0175) |
| NACE MR0175 compliant | No | Yes (hardness controlled) |
| Cost vs L80 | Lower — 5–10% cheaper typically | Higher — controlled process premium |
| Interchangeable? | No — not interchangeable in sour service |
Engineering Insight — The Hardness TrapN80Q (quench and tempered N80) can achieve hardness values well above 23 HRC — particularly in the weld zone of ERW pipe or in heavy-wall seamless pipe where the Q&T cycle is less uniform. This is exactly the failure mode that NACE MR0175 is designed to prevent: hard microstructural zones acting as SSC initiation sites in H₂S. L80's mandatory hardness cap is a manufacturing quality requirement, not just a spec number — it requires the mill to control the entire Q&T process to stay within the band. See:
API 5CT vs NACE MR0175: The Hardness Trap Explained → Full comparison: Understanding N80 vs L80 Casing: API 5CT Grade Comparison →
5. PSL1 vs PSL2 for L80
API 5CT defines two Product Specification Levels for L80. The distinction matters most when the pipe is destined for sour service or high-consequence wells.
| Requirement | L80 PSL1 | L80 PSL2 |
| 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 thickness, straightness |
| Traceability | Heat number | Full heat + pipe number traceability |
| Documentation package | Standard MTC | Enhanced — all test results per pipe |
| Typical use | Sweet wells, non-critical completions | Sour service, HPHT, IOC specifications |
Procurement Note — Most IOC Specs Default to PSL2 for All L80Major international oil companies (Shell, BP, Total, Saudi Aramco, ADNOC) typically specify PSL2 as a minimum for all L80 orders regardless of service environment. The cost premium is modest — typically 3–8% — and the additional NDE and traceability documentation significantly simplifies third-party audits, regulatory compliance, and incident investigation. If you are sourcing L80 for an IOC project, assume PSL2 unless the specification explicitly states otherwise. See:
Manufacturing Process of API 5CT PSL1 and PSL2 Casing & Tubing →
6. Sour Service: L80 and NACE MR0175
L80-1 is the first API 5CT grade specifically designed for use in H₂S-containing environments. Its compliance with NACE MR0175 / ISO 15156 is based on the mandatory 23 HRC hardness limit — but the relationship between L80, NACE, and actual well sour service qualification is more nuanced than the spec sheet suggests.
6.1 How NACE MR0175 Applies to L80
NACE MR0175 / ISO 15156-2 defines acceptable materials for equipment in sour service (wet H₂S). For carbon and low-alloy steel tubulars, the primary requirement is a maximum hardness of 22 HRC (250 HV10) in the base metal, welds, and HAZ. API 5CT L80-1's 23 HRC maximum is slightly above this — which creates a compliance question that is often misunderstood.
Critical Engineering Point — L80 Hardness vs NACE MR0175 HardnessAPI 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 measured by a specific test frequency. In practice, L80-1 produced to API 5CT will typically measure well below 22 HRC in service — but this must be verified on the MTR, not assumed. Always request full hardness data on the MTC and verify it against your project's NACE compliance requirements.
6.2 Supplementary Requirements for Sour Service L80
For wells where H₂S partial pressure exceeds 0.05 psi (0.0003 MPa) — the NACE threshold for sour service — L80-1 alone is typically insufficient without supplementary qualification. The most common supplementary requirements specified alongside L80-1 PSL2 for sour service are:
SR16 (HIC test): Hydrogen-induced cracking test per NACE TM0284 — confirms the steel's 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: Many IOCs add their own supplementary requirements for maximum yield strength, CE limits, or specific NDE coverage
Related: L80 Type 1 vs N80Q and T95: The Sour Service Decision Matrix → | 13Cr Compliance: Navigating the API 5CT vs NACE MR0175 Hardness Trap →
7. Connections & Threading
L80 casing is available with all standard API 5CT connection types as well as premium connections. Connection selection for L80 in sour service requires additional consideration — the connection is often the weakest point in an SSC-resistant completion string.
| Connection Type | Sour Service Suitability | Typical L80 Application | Notes |
| Short Thread (STC) | Limited — low tensile efficiency | Surface casing (non-critical) | Not recommended for sour service strings |
| Long Thread (LTC) | Moderate | Intermediate casing | Better seal than STC; still limited in HPHT |
| Buttress Thread (BTC) | Good for most sour applications | Production casing in sour wells | Higher tensile efficiency than STC/LTC; widely used with L80 |
| Premium Connection | Best — metal-to-metal seal | HPHT, deep sour wells, gas-tight requirements | Required for gas-tight integrity; significantly higher cost |
For L80-13Cr in CO₂ service, connection selection is especially critical — standard API threads can suffer accelerated corrosion at the thread root in high-CO₂ environments, and premium metal-to-metal seal connections are strongly preferred.
Related: Understanding Buttress Thread Casing (BTC) → | Connection Types for Casing and Tubing → | Premium Connections vs Standard BTC: When Is the Investment Worth It? →
8. Applications by Well Environment
| Well Environment | Recommended L80 Sub-Grade | Key Requirement | Notes |
| Mild sour gas (H₂S < 0.05 psi pp) | L80-1 PSL2 | 23 HRC max, NACE MR0175 compliance | Standard L80-1; verify hardness on MTR |
| Moderate sour gas (H₂S 0.05–1.5 psi pp) | L80-1 PSL2 + SR16 | HIC test, lower yield band preferred | SR16 HIC test mandatory; consider T95 for deeper wells |
| CO₂-rich sweet gas (no significant H₂S) | L80-13Cr PSL1 or PSL2 | CO₂ partial pressure, temperature | Sweet or very mildly sour only; excellent CO₂ resistance |
| CO₂ + low H₂S (< 0.05 psi pp) | L80-13Cr PSL2 | NACE qualification recommended | Borderline — run NACE ISO 15156-3 checklist; consider Super 13Cr |
| Steam injection / geothermal | L80-9Cr | High temperature oxidation resistance | 9Cr-1Mo provides better high-temp performance than L80-1 |
| Deep sour HPHT | T95 or C110 | Higher collapse, tighter yield control | L80 may be insufficient for collapse — evaluate T95 or C110 |
Engineering Insight — When L80 Is Not EnoughL80 covers mild to moderate sour service at normal completion depths. Two scenarios commonly push engineers beyond L80: (1) deep wells where collapse pressure requires higher yield strength than L80's 655 MPa maximum can deliver — here T95 or P110 with appropriate sour service qualification is evaluated; (2) severe sour service above 1.5 psi H₂S partial pressure where L80-1's SSC resistance is insufficient — here Super 13Cr or CRA-lined pipe is required. See:
P110 vs L80 and T95: Casing Design Yield Traps and Failure Thresholds → For a broader OCTG grade selection framework: How to Choose OCTG Material: A Complete Grade Selection Guide → | Material Selection: 13Cr vs Super 13Cr vs Inhibited Carbon Steel →
9. Frequently Asked Questions
What is API 5CT L80 casing pipe?
API 5CT L80 is a controlled yield-strength casing and tubing grade with a minimum yield of 552 MPa (80,000 psi), a maximum yield of 655 MPa (95,000 psi), and a mandatory hardness limit of 23 HRC. It is produced in three sub-grades — L80-1 (carbon steel), L80-9Cr (9% chromium), and L80-13Cr (13% chromium) — and is the standard choice for sour service wells and CO₂-rich gas condensate wells globally.
What is the difference between L80 and N80?
Both grades share the same 552 MPa minimum yield strength, but L80 has a controlled maximum yield of 655 MPa and a mandatory hardness limit of 23 HRC. N80 has no yield ceiling and no hardness limit. These differences make L80 suitable for mild H₂S service (NACE MR0175) while N80 is restricted to sweet (non-sour) wells only. The two grades are not interchangeable in sour service applications.
Is L80 suitable for sour service?
L80-1 is suitable for mild sour service where H₂S partial pressure is present and NACE MR0175 / ISO 15156 compliance is required. Its 23 HRC hardness limit brings it within the NACE threshold for carbon steel tubulars. For moderate sour service above 0.05 psi H₂S partial pressure, supplementary requirements such as SR16 (HIC testing) should be added to the L80-1 PSL2 specification. L80-13Cr is not a sour service grade and must not be used in wells with significant H₂S.
What is L80-13Cr casing used for?
L80-13Cr (13% chromium martensitic stainless steel) is the standard grade for wells with high CO₂ partial pressure and sweet or very mildly sour conditions. Its passive chromium oxide film provides excellent resistance to sweet (CO₂-driven) corrosion in gas condensate and CO₂-injection wells. It must not be used in wells with H₂S above approximately 0.05 psi partial pressure without specific NACE ISO 15156-3 qualification — standard L80-13Cr will typically fail SSC testing above this threshold.
What are the PSL1 and PSL2 differences for L80?
PSL2 adds mandatory full-length NDE of the pipe body and ends (UT or EMI), tighter dimensional tolerances, and enhanced traceability documentation. PSL1 lacks these mandatory inspection requirements. Most major oil company specifications require PSL2 for all L80 regardless of service classification. For sour service wells, PSL2 is always recommended.
Can L80 and N80 be used interchangeably?
No. They are not interchangeable in sour service wells — substituting N80 for L80 in an H₂S environment removes the hardness control that NACE MR0175 compliance requires. Substituting L80 for N80 in a sweet well is technically permissible but involves unnecessary cost. Always specify the correct grade for the well's service classification and confirm it on the purchase order.
Source API 5CT L80 Casing Pipe from ZC Steel Pipe
ZC Steel Pipe manufactures and exports API 5CT L80 casing and tubing in all three sub-grades — L80-1, L80-9Cr, and L80-13Cr — to PSL1 and PSL2. We supply OCTG projects across Africa, the Middle East, and South America with full MTC documentation, third-party inspection, and technical support on grade and connection selection.
Available with BTC, LTC, STC, and premium connections including ZC-2 gas-tight premium connection. Custom sizes and supplementary requirements (SR16, SR2, SR13) on order-to-make basis.
mandy.w@zcsteelpipe.com
WhatsApp: +86-139-1579-1813
→ Request a Quote
