API 5CT L80 Casing Pipe — Grades, Specifications & Sour Service Guide

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.

A question procurement teams ask us repeatedly is why L80 costs more than N80 when both grades have the same minimum yield. The answer is in the yield ceiling and the hardness test — and the cost of not having them becomes apparent the first time an N80 string is flagged for NACE non-compliance after makeup.

We have seen purchase orders from Middle East operators specifying "L80 sour service" without a sub-grade. Under API 5CT, "L80" without a type designation defaults to L80-1. If the well has significant CO₂ and the engineer expected 13Cr, the order needs to be corrected before production begins — not after the MTC arrives.

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.

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:

For the complete grade ladder with tensile, hardness, and chemistry limits, see the API 5CT specification tables →

To match a grade to your well conditions, use the AI Pipe Grade Selector →

Chemical Composition

L80-1 carbon footnote: Carbon may increase up to 0.50% maximum if oil-quenched or polymer-quenched.

Chemistry interpretation notes:

L80-1 is a broad-tolerance carbon-manganese grade. Its C max of 0.43% is the standard limit; the 0.50% allowance when oil or polymer quenched reflects that faster quench media can achieve the same hardness control with slightly higher carbon. The tighter P and S limits on the chromium grades (0.020% vs 0.030%) reflect their stricter cleanliness requirements for corrosion performance.

L80-13Cr has a defined carbon range of 0.15–0.22% rather than a simple maximum. The 0.15% minimum is meaningful — too little carbon and the martensitic transformation is incomplete, reducing hardness and mechanical performance. The 0.22% upper limit prevents over-hardening. This is a more controlled chemistry than L80-1 and one reason L80-13Cr mills carry a cost premium over L80-1.

L80-9Cr's molybdenum content (0.90–1.10%) contributes significantly to its high-temperature oxidation resistance and creep strength — properties important in steam injection and geothermal environments where L80-1 would be inadequate.

Standard Sizes

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.

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.

Hardness, Yield, and Sour Service — A Worked Example

The relationship between L80's hardness limit and sour service qualification is best understood with a concrete example. Consider a production casing string in a gas well with 0.08 psi H2S partial pressure — above the mild sour threshold but well below severe sour.

Per NACE MR0175 / ISO 15156-2, this environment requires carbon steel tubulars with a maximum hardness of 22 HRC and appropriate SSC qualification.

If the string is L80-1 PSL-2 with SR16 HIC test:

• API 5CT mandates a 23 HRC maximum for the production lot
• Actual individual pipe hardness readings from the MTC should average 18–21 HRC for well-produced L80-1 Q+T
• The NACE 22 HRC limit is met on each joint — verify by requesting individual readings, not just lot average

If the string is N80Q at the same size and weight:

• N80Q has no hardness limit in API 5CT
• Individual N80Q hardness readings in heavy-wall pipe (e.g. 9⅝" 53.5 lb/ft) routinely test 24–28 HRC from the same Q+T process that puts L80-1 at 19 HRC — because N80Q is manufactured without the process controls that enforce the ceiling
• N80Q in this well environment is a NACE MR0175 violation, even though it carries the same minimum yield as L80-1

This example illustrates that the difference between L80 and N80 in sour service is not yield strength — it is the manufacturing quality system that enforces the hardness ceiling. N80Q heat treatment alone does not qualify pipe for sour service.

We use this comparison regularly when procurement teams push back on the L80 cost premium. The premium is not for yield. It is for the process control and documentation that guarantees the hardness ceiling is met on every joint — and for the liability that attaches if it is not.

When Not to Use L80

• H₂S partial pressure above 1.5 psi (0.010 MPa) — L80-1 is designed for mild sour service. Above this threshold, SSC risk exceeds what L80's 23 HRC limit can reliably prevent under all operating conditions, and T95 or C110 should be evaluated.
• Deep wells where collapse requires more than 655 MPa yield — L80's 95 ksi maximum yield is a ceiling, not a target. If your collapse load calculation needs more than 655 MPa, L80 cannot get you there regardless of wall thickness — specify T95 (110 ksi max) or C110 instead.
• L80-13Cr in any well with meaningful H₂S — L80-13Cr's martensitic microstructure is susceptible to SSC above approximately 0.05 psi H₂S partial pressure. This is a very low threshold. If the reservoir has CO₂ and any H₂S, L80-13Cr requires explicit NACE MR0175 / ISO 15156-3 qualification, and Super 13Cr or duplex is usually the safer path.
• High-temperature geothermal above 175°C — L80-1 and L80-13Cr are not suitable for sustained service above this temperature without specific qualification. L80-9Cr has better high-temperature oxidation resistance but also has limits.
• Formations with significant chloride concentration combined with CO₂ and H₂S — at high chloride levels, L80-13Cr loses its passive film protection. The threshold at which 13Cr fails to protect varies with temperature and H₂S — in high-chloride, mixed CO₂/H₂S environments, Super 13Cr or duplex should be evaluated.

PSL-1 vs PSL-2 for L80

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.

From our side, PSL-2 also simplifies the inspection scope we manage at the mill. When traceability runs to the individual joint and all NDE results are logged against a pipe number, discrepancy resolution with third-party inspectors takes hours rather than days. For large-volume orders destined for remote completions in Africa or South America, that documentation discipline is worth more than its cost at delivery.

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

When we quote L80 for sour service projects, we ask for the full corrosive environment data sheet before confirming the supplementary requirement scope. A PO that arrives with "L80-1 PSL-2, sour service" but without H2S and CO2 partial pressures, temperature, and chloride concentration is an incomplete specification. We raise the question before producing because no MTC correction resolves a wrong SR call once the pipe is rolled.

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.

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

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:

1. Standard — API 5CT or ISO 11960
2. Grade and sub-grade — L80-1, L80-9Cr, or L80-13Cr (never just "L80")
3. OD and nominal weight — e.g. 7 inch × 26.00 lb/ft
4. Thread type — STC, LTC, BTC, or premium connection designation
5. Range — R1, R2, or R3 (most strings are R3)
6. PSL level — PSL-1 or PSL-2 (PSL-2 recommended for all sour service)
7. Supplementary requirements — SR16, SR2, SR13 as required by well conditions
8. Quantity — in joints or metric tonnes
9. Delivery port — for freight planning and lead time
10. MTC level — EN 10204 3.1 or 3.2
11. Third-party inspection scope — mill visit, witness testing, SGS/BV/TÜV