API 5CT P110 is the workhorse high-strength casing grade for deep, high-pressure oil and gas wells. At 110,000 psi (758 MPa) minimum yield, it delivers the collapse and burst resistance that shallower grades cannot — making it the standard choice for intermediate and production casing in wells where L80 or T95 fall short on pressure containment. Its defining trade-off is that strength: P110's high yield disqualifies it from sour service under NACE MR0175, which means getting the grade selection right from the outset is critical to well integrity.
ZC Steel Pipe manufactures and exports API 5CT P110 casing and tubing to PSL1 and PSL2, in standard and high-collapse variants, with full MTC documentation and third-party inspection support. This guide covers P110's mechanical and chemical specifications, how it compares to T95 and L80 for grade selection, high-collapse variants, HPHT applications, and what to look for in an MTR.
CONTENTS
What Is API 5CT P110?
Mechanical & Chemical Properties
P110 vs T95 vs L80 — Grade Comparison
P110 and Sour Service
P110 High Collapse (HC) Variants
PSL1 vs PSL2 for P110
HPHT Applications
Connections for P110 Casing
What to Check on a P110 MTR
FAQ
1. What Is API 5CT P110?
API 5CT P110 is a casing and tubing grade defined in API Specification 5CT / ISO 11960. The "P" prefix has no direct metallurgical meaning — it is simply the API designation for this yield tier. The "110" refers to the minimum yield strength floor of 110,000 psi.
API 5CT P110 — CORE IDENTITYMinimum yield strength: 758 MPa (110,000 psi) · Maximum yield strength: 965 MPa (140,000 psi) · Minimum tensile strength: 862 MPa (125,000 psi) · Hardness limit: None specified in API 5CT · Heat treatment: Quench & temper (mandatory) · Sour service: Not suitable under standard NACE MR0175 · Standard: API 5CT / ISO 11960
Three characteristics define P110's position in the OCTG grade ladder:
High minimum yield (758 MPa): Delivers superior collapse resistance and burst capacity for deep, high-pressure wells — the primary reason engineers specify it over L80 or T95
No hardness ceiling: Unlike L80 (23 HRC max) and T95 (25.4 HRC max), P110 has no API-specified hardness limit — which enables the high strength but removes NACE MR0175 compatibility
Mandatory Q&T: Quench and temper heat treatment is required to achieve and control the 758–965 MPa yield band; no alternative heat treatment is permitted
See also: What Are the Grades of OCTG Pipe? → | Understanding Steel Grades for Casing and Tubing →
2. Mechanical & Chemical Properties
2.1 Mechanical Properties (API 5CT)
| Property | Value |
| Minimum yield strength | 758 MPa (110,000 psi) |
| Maximum yield strength | 965 MPa (140,000 psi) |
| Minimum tensile strength | 862 MPa (125,000 psi) |
| Hardness limit | Not specified in API 5CT |
| Heat treatment | Quench & temper (mandatory) |
| Min elongation (2" gauge) | ≥ 0.5% per API 5CT formula |
| Charpy impact (PSL2) | Per API 5CT Table C.36 / SR2 if specified |
2.2 Chemical Composition (API 5CT — typical P110)
| Element | Max % | Notes |
| Carbon (C) | 0.35 | Lower C preferred by some IOC specs for weldability |
| Manganese (Mn) | 1.90 | Higher Mn in some mill chemistries for hardenability |
| Silicon (Si) | 0.45 | Deoxidiser |
| Phosphorus (P) | 0.030 | Tighter limits (0.020) often in company specs |
| Sulphur (S) | 0.030 | Tighter limits (0.010) often in company specs |
| Carbon Equivalent (CE) | Varies by spec | Often ≤ 0.43 in project specifications |
Note: API 5CT does not specify a full chemistry for P110 — only C, Mn, Si, P, and S maximums. Many international project specifications add requirements for Cr, Mo, Ni, V, and CE limits beyond the API minimums.
2.3 Standard Sizes
| OD (inches) | OD (mm) | Common Weight Range (lb/ft) | Typical Application |
| 4½" | 114.3 | 9.50 – 15.10 | Tubing, small production casing |
| 5" | 127.0 | 11.50 – 18.00 | Production casing, deep wells |
| 5½" | 139.7 | 14.00 – 23.00 | Production casing — most common P110 size |
| 7" | 177.8 | 17.00 – 38.00 | Intermediate and production casing |
| 7⅝" | 193.7 | 24.00 – 45.30 | Intermediate casing, deep wells |
| 9⅝" | 244.5 | 32.30 – 58.40 | Intermediate casing |
| 10¾" | 273.1 | 32.75 – 65.70 | Surface and intermediate casing |
| 13⅜" | 339.7 | 48.00 – 72.00 | Surface casing, large bore wells |
3. P110 vs T95 vs L80 — Grade Comparison
The three most commonly compared OCTG grades in the 80–110 ksi range are L80, T95, and P110. The selection between them is driven by two independent variables: required yield strength (determined by collapse/burst loads) and H₂S environment (determined by reservoir chemistry).
| Property | L80-1 | T95 | P110 |
| Min yield strength | 552 MPa (80 ksi) | 655 MPa (95 ksi) | 758 MPa (110 ksi) |
| Max yield strength | 655 MPa (95 ksi) | 758 MPa (110 ksi) | 965 MPa (140 ksi) |
| Max hardness | 23 HRC | 25.4 HRC | Not specified |
| Heat treatment | Q&T mandatory | Q&T mandatory | Q&T mandatory |
| Sour service (H₂S) | Yes — mild sour | Yes — moderate sour | Not suitable |
| NACE MR0175 compliant | Yes | Yes (with qualification) | No |
| Collapse resistance | Baseline | Better than L80 | Best of the three |
| Relative cost | Lowest | Mid | Higher — yield premium |
| Typical well depth | < 3,500 m | 2,500–5,000 m | 3,000 m+ / HPHT |
Choose L80 when…
Well contains: H₂S (sour service)
Depth: Shallow to medium
Collapse load: Within 80 ksi capacity
Priority: NACE compliance + cost
Choose T95 when…
Well contains: Moderate H₂S + higher pressure
Depth: Medium to deep
Collapse load: Exceeds L80 capacity
Priority: Sour service + more strength
Choose P110 when…
Well contains: No significant H₂S (sweet)
Depth: Deep to ultra-deep
Collapse load: Requires 110 ksi capacity
Priority: Maximum strength
Full comparison: P110 vs L80 and T95: Casing Design Yield Traps and Failure Thresholds →
4. P110 and Sour Service
P110 is not permitted in sour service wells under NACE MR0175 / ISO 15156. This is one of the most important grade selection rules in OCTG — and one of the most common sources of well integrity failures when overlooked or worked around.
Critical Engineering Point — P110 Is Prohibited in H₂S ServiceNACE MR0175 / ISO 15156-2 limits carbon and low-alloy steel tubulars in sour service to a maximum hardness of 22 HRC (250 HV10). P110, with its 758 MPa minimum yield and no hardness ceiling, will routinely produce hardness values well above this threshold. High-strength steels above the NACE limits are susceptible to sulphide stress cracking (SSC) — a brittle fracture mechanism that can cause rapid, catastrophic failure in H₂S environments with no ductile warning. Do not substitute P110 for T95 or C110 in sour wells regardless of cost or availability pressures.
The correct grade escalation path for wells with both high pressure and H₂S is:
Mild sour, moderate pressure: L80-1 PSL2 + SR16 (HIC)
Moderate sour, high pressure: T95 PSL2 with NACE qualification
Severe sour, high pressure: C110 or Q125 — both designed specifically for the high-pressure sour service envelope that neither P110 nor T95 can cover
Related: L80 vs N80 vs T95: Which Grade for Sour Service Wells? → | API 5CT vs NACE MR0175: The Hardness Trap Explained →
5. P110 High Collapse (HC) Variants
Standard P110 collapse resistance is calculated using the API 5C3 formula, which assumes worst-case dimensional tolerances for wall thickness and ovality. In practice, a well-made P110 pipe will have actual collapse resistance significantly higher than the API formula predicts — but standard API tolerances prevent engineers from using that extra capacity in their casing design.
P110 High Collapse (P110 HC) addresses this directly: it is produced to tighter dimensional tolerances, particularly wall thickness eccentricity (typically ≤ 10% vs the standard 12.5%) and ovality (typically ≤ 0.5% vs 1.0% for standard pipe). These tighter dims allow the design collapse rating to increase by 15–30% over standard P110 of the same size and weight — without increasing wall thickness or changing grade.
Engineering Insight — When HC Is Worth the PremiumThe P110 HC premium (typically 8–15% over standard P110) pays off quickly in deepwater and HPHT casing design. The alternative — stepping up to a heavier wall standard P110 to hit the same collapse rating — costs more in material weight, increases running loads, and adds wellbore volume that must be cemented. For collapse-critical sections below ~3,000 m TVD, HC grades are often the more economical solution at the system level. See:
P110 HC: Why 0.5% Ovality Controls Matter More Than Yield Strength → Procurement Note — HC Is Not Standardised Across MillsThere is no single API specification for "High Collapse" — each mill and each company spec defines HC tolerances slightly differently. When purchasing P110 HC, always request the mill's specific HC tolerance table, verify it against your casing design software's collapse model, and confirm that the third-party inspector is checking ovality and WT eccentricity to the HC spec, not the standard API tolerance. A P110 HC order received against standard API dimensional tolerances provides no collapse improvement.
6. PSL1 vs PSL2 for P110
| Requirement | P110 PSL1 | P110 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 API | Tighter — OD, WT, straightness |
| Traceability | Heat number | Full heat + pipe number |
| Charpy impact | Not mandatory | Mandatory per Table C.36 |
| Typical use | Moderate depth sweet wells | Deep, HPHT, IOC projects |
For deep and HPHT applications — which represent the majority of P110 usage — PSL2 is the practical minimum. Most IOC project specifications require PSL2 for all P110, and many add supplementary requirements for Charpy testing at low temperature (SR2) and additional hardness surveys.
7. HPHT Applications
High Pressure High Temperature (HPHT) wells — generally defined as wellhead pressure above 690 bar (10,000 psi) and bottomhole temperature above 150°C (302°F) — represent the primary application environment for P110. In these wells, collapse and burst loads can exceed the capacity of all lower-grade OCTG, and P110 is frequently the minimum grade that can achieve the required design safety factors.
Key considerations when specifying P110 for HPHT wells:
Thermal de-rating: P110 yield strength decreases at elevated temperatures — typically 5–8% reduction at 150°C vs ambient. HPHT casing designs must apply a temperature de-rating factor to the nominal yield, which can push the design back toward requiring HC grades or heavier wall
Thermal cycling loads: HPHT wells with large temperature differentials during production vs shut-in generate significant axial thermal loads in the casing string — the connection must be rated for the combined axial, bending, and pressure loads, not just burst and collapse
Cement integrity: High collapse capacity in P110 is only fully realised with competent cement behind the pipe — unsupported P110 in a long cement void can still fail in collapse if the void coincides with the maximum collapse load depth
Related: API 5C5 CAL IV Limitations and Field Failure Modes in HPHT OCTG Connections → | 5 Critical Factors for Specifying Premium Connections and High Collapse Casing →
8. Connections for P110 Casing
| Connection Type | Suitability for P110 | Typical Application | Notes |
| Short Thread (STC) | Not recommended | Not typical for P110 | Tensile efficiency too low for deep P110 strings |
| Long Thread (LTC) | Limited | Surface casing only | Inadequate for HPHT or deep applications |
| Buttress Thread (BTC) | Moderate | Intermediate casing, moderate depth | Acceptable for non-HPHT P110 applications |
| Premium Connection | Required for HPHT | Deep wells, HPHT, gas-tight requirements | Metal-to-metal seal; fully rated to P110 body strength |
For HPHT P110 applications, premium connections are not optional — they are a design requirement. Standard API threads cannot maintain gas-tight integrity under the combined thermal, axial, and pressure cycling loads in deep HPHT completions. ZC Steel Pipe's ZC-2 gas-tight premium connection is rated to full P110 body yield and qualified under API 5C5 CAL III/IV.
Related: Connection Types for Casing and Tubing → | Premium Connections vs Standard BTC: When Is the Investment Worth It? → | Understanding Buttress Thread Casing (BTC) →
9. What to Check on a P110 MTR
The Mill Test Report (MTR) is the primary document for verifying P110 compliance. For a standard P110 PSL2 order, the following should be checked before accepting any consignment:
| MTR Item | What to Verify | Why It Matters |
| Yield strength | 758–965 MPa (110–140 ksi) — both min and max | Over-yield (above 965 MPa) is a non-conformance; pipe is too brittle |
| Tensile strength | ≥ 862 MPa (125 ksi) | Confirms Q&T process produced correct microstructure |
| Hardness (if tested) | Record actual values — no API limit, but note unusually high values | Excessively high hardness (>32 HRC) signals over-quench; brittle risk |
| Heat treatment record | Confirm Q&T — reject normalise or N&T records | P110 requires Q&T; other HT cannot achieve the yield band reliably |
| Chemical composition | C ≤ 0.35%, S ≤ 0.030%, P ≤ 0.030% minimum; check project-specific CE limit | High S and P increase susceptibility to hydrogen damage and brittle fracture |
| NDE records (PSL2) | Full-length UT or EMI body scan + end area UT confirmed | PSL2 NDE is mandatory — absence means the pipe is PSL1 regardless of label |
| Charpy impact (PSL2) | Values, temperature, and specimen size vs your project specification | Confirms toughness at operating temperature — critical for cold environments |
| Dimensional report | OD, WT, straightness per API 5CT; for HC: WT eccentricity and ovality | HC collapse rating is only valid if HC dimensional tolerances were actually met |
Procurement Note — Over-Yield P110 Is a Real ProblemP110's maximum yield of 965 MPa (140 ksi) is a hard limit, not a guideline. Material exceeding 140 ksi yield is technically non-conforming and must be rejected — not because it is "too strong" in a naive sense, but because at those yield levels the steel's fracture toughness and SSC resistance degrade significantly. Over-yield P110 is a documented failure mode in deep-well casing strings, particularly at connection make-up where stress concentrations are highest. Always check the upper yield limit on the MTR, not just the minimum. See:
P110 Compliance: API 5CT Hardness, Heat Treatment and MTR Validation →
10. Frequently Asked Questions
What is API 5CT P110 casing pipe?
API 5CT P110 is a high-strength casing and tubing grade with a minimum yield strength of 758 MPa (110,000 psi) and a maximum yield of 965 MPa (140,000 psi). Produced exclusively by quench and temper heat treatment, it is the standard choice for deep, high-pressure sweet wells where lower grades cannot provide sufficient collapse or burst resistance. P110 has no API-specified hardness limit and is not suitable for H₂S sour service.
Can P110 be used in sour service (H₂S wells)?
No. P110 is not suitable for sour service under NACE MR0175 / ISO 15156. Its high yield strength produces hardness values that exceed the NACE limit for carbon steel tubulars, making it susceptible to sulphide stress cracking (SSC) in H₂S environments. For wells requiring both high pressure resistance and H₂S compatibility, T95 (moderate sour) or C110/Q125 (severe sour, high pressure) should be specified instead.
What is the difference between P110 and T95?
T95 has a lower minimum yield (655 MPa / 95 ksi) with a controlled maximum yield and a mandatory 25.4 HRC hardness limit, making it compatible with NACE MR0175 for moderate sour service. P110 has a higher minimum yield (758 MPa / 110 ksi) with no hardness limit — giving superior collapse and burst performance in deep sweet wells, but disqualifying it from H₂S service. The choice is driven by the presence of H₂S and the required pressure containment.
What is P110 High Collapse (HC) casing?
P110 HC is produced to tighter dimensional tolerances — particularly wall thickness eccentricity (≤ 10%) and pipe ovality (≤ 0.5%) — that allow engineers to use a higher collapse design rating than standard API 5C3 formula permits for the same pipe size and weight. P110 HC is specified for deepwater and HPHT wells where the collapse load governs the casing design. The HC designation is not standardised across mills — always verify the specific tolerances against your casing design model.
What connections are used with P110 casing?
P110 casing is available with BTC, LTC, STC, and premium connections. For HPHT and deep-well applications — the primary use case for P110 — premium metal-to-metal seal connections are required. Standard API threads cannot reliably maintain gas-tight integrity under the combined pressure, axial, and thermal cycling loads in these environments. BTC is acceptable for moderate-depth, non-HPHT P110 applications.
What sizes does P110 casing come in?
P110 casing is available in all standard API 5CT sizes from 4½" (114.3 mm) to 20" (508 mm) OD. The most common sizes for production and intermediate casing strings are 5½", 7", 9⅝", and 13⅜". Wall thickness ranges from approximately 5.21 mm to over 20 mm depending on size and nominal weight per foot.
Source API 5CT P110 Casing Pipe from ZC Steel Pipe
ZC Steel Pipe manufactures and exports API 5CT P110 casing and tubing to PSL1 and PSL2, in standard and high-collapse variants. 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, and premium connections including ZC-2 gas-tight premium connection, rated to full P110 body yield and qualified under API 5C5. Custom wall thicknesses, HC tolerance packages, and supplementary requirements (SR2 Charpy, SR13 hardness survey) available on order-to-make basis.
mandy.w@zcsteelpipe.com
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