API 5CT P110 is the workhorse high-strength casing grade for deep, high-pressure oil and gas wells. At 758 MPa (110,000 psi) minimum yield, it delivers the collapse and burst resistance that L80 and T95 cannot — making it the standard choice for intermediate and production casing in wells where lower grades fall short on pressure containment. Its defining trade-off is the reverse of its strength: P110's high yield disqualifies it from sour service under NACE MR0175, which means getting grade selection right before the purchase order is placed is critical to well integrity.
ZC Steel Pipe supplies API 5CT P110 casing and tubing to PSL-1 and PSL-2, in standard and high-collapse variants, with full MTC documentation and third-party inspection support. We supply OCTG to operators and EPC contractors across Africa, South America and Southeast Asia. In supplying P110 to deep-well projects in West Africa and the Gulf of Guinea, the most common procurement mistake we encounter is a purchase order that specifies P110 without checking whether the formation has H2S — resulting in a non-conforming string that must be replaced before completion. This guide covers everything needed to specify P110 correctly.
What Is API 5CT P110?
API 5CT P110 is a casing and tubing grade defined in API Specification 5CT / ISO 11960. The "110" refers to the minimum yield strength floor of 110,000 psi. Three characteristics define its position in the OCTG grade ladder:
High minimum yield (758 MPa) — delivers superior collapse resistance and burst capacity for deep, high-pressure wells. This is the primary reason engineers specify P110 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. This enables the high strength but removes NACE MR0175 compatibility for sour service.
Mandatory quench and temper — Q+T heat treatment is required to achieve and control the 758–965 MPa yield band. No alternative heat treatment is permitted under API 5CT.
Mechanical Properties
| 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 and temper — mandatory |
| Min elongation | Per API 5CT formula (gauge length dependent) |
| Charpy impact (PSL-2) | Per API 5CT Table C.36 or SR2 if specified |
The maximum yield limit matters as much as the minimum. P110's 965 MPa (140 ksi) upper limit is a hard boundary, not a guideline. Material exceeding 140 ksi yield is non-conforming and must be rejected — at those yield levels fracture toughness degrades significantly, increasing brittle failure risk at connection stress concentrations. Always verify both limits on the MTR.
Chemical Composition
API 5CT does not specify a full chemistry for P110 — only maximum limits for key elements. Many international project specifications add requirements beyond the API minimums.
| Element | API 5CT Max % | Notes |
|---|---|---|
| Carbon (C) | 0.35 | Lower C preferred by 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) common in project specs |
| Sulphur (S) | 0.030 | Tighter limits (0.010) common in project specs |
| Carbon Equivalent (CE) | Not specified by API | Often ≤ 0.43 in IOC project specifications |
Many IOC project specifications — Shell, TotalEnergies, NNPC — add requirements for Cr, Mo, Ni, V, and CE limits beyond the API minimums. Always check project-specific chemistry requirements before placing a P110 order.
Standard Sizes
| OD (inches) | OD (mm) | Common Weights (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 |
P110 vs T95 vs L80 — Grade Selection
The three most compared OCTG grades in the 80–110 ksi range. Selection is driven by two independent variables: required yield strength from collapse and burst load calculations, and H2S environment from 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 |
| H2S sour service | Yes — mild sour | Yes — moderate sour | Not suitable |
| NACE MR0175 | Yes | Yes (with qualification) | No |
| Collapse resistance | Baseline | Better than L80 | Best of the three |
| Typical well depth | Under 3,500 m | 2,500–5,000 m | 3,000 m+ / HPHT |
Choose L80 when the well contains H2S, depth is shallow to medium, and NACE compliance is the priority.
Choose T95 when moderate H2S is present alongside higher pressure requirements that exceed L80's collapse capacity.
Choose P110 when the well is sweet (no significant H2S), depth is deep to ultra-deep, and maximum collapse and burst capacity is required.
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.
NACE MR0175 / ISO 15156-2 limits carbon and low-alloy steel tubulars in H2S service to a maximum hardness of 22 HRC. P110, with its 758 MPa minimum yield and no hardness ceiling, routinely produces hardness values well above this threshold. High-strength steels above the NACE limit are susceptible to sulphide stress cracking — 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 pressure. The correct grade escalation for wells with both high pressure and H2S:
| Condition | Correct Grade |
|---|---|
| Mild sour, moderate pressure | L80-1 PSL-2 + SR16 (HIC test) |
| Moderate sour, high pressure | T95 PSL-2 with NACE qualification |
| Severe sour, high pressure | C110 or Q125 |
P110 High Collapse Variants
Standard P110 collapse resistance is calculated using the API 5C3 formula, which assumes worst-case dimensional tolerances for wall thickness eccentricity and ovality. A well-made P110 pipe has actual collapse resistance significantly higher than the formula predicts — but standard API tolerances prevent engineers from using that extra capacity in casing design.
P110 High Collapse (HC) addresses this directly. It is produced to tighter dimensional tolerances — wall thickness eccentricity typically under 10% vs the standard 12.5%, and ovality typically under 0.5% vs 1.0% for standard pipe. These tighter dimensions 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.
When HC is worth the premium: The HC cost premium — typically 8–15% over standard P110 — pays off in deepwater and HPHT casing design. The alternative is stepping up to heavier wall standard P110, which costs more in material weight, increases running loads, and adds wellbore volume requiring cement. For collapse-critical sections below 3,000 m TVD, HC grades are often the more economical solution at the system level.
Critical procurement note on HC: There is no single API specification for High Collapse — each mill defines HC tolerances 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 wall thickness eccentricity to the HC spec — not the standard API tolerance. A P110 HC order inspected against standard API dimensional tolerances provides no collapse improvement over standard P110.
PSL-1 vs PSL-2 for P110
| Requirement | P110 PSL-1 | P110 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 API | Tighter — OD, wall, straightness |
| Traceability | Heat number | Full heat + pipe number per joint |
| Charpy impact | Not mandatory | Mandatory per API 5CT 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 — PSL-2 is the practical minimum. Most IOC project specifications require PSL-2 for all P110 and many add supplementary requirements for Charpy testing at low temperature (SR2) and additional hardness surveys (SR13).
HPHT Applications
High Pressure High Temperature wells — generally defined as wellhead pressure above 690 bar (10,000 psi) and bottomhole temperature above 150°C — represent the primary application environment for P110. Key considerations when specifying P110 for HPHT:
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 toward requiring HC grades or heavier wall even when standard P110 appears adequate at ambient conditions.
Thermal cycling loads: HPHT wells with large temperature differentials between production and shut-in generate significant axial thermal loads in the casing string. The connection must be rated for combined axial, bending, and pressure loads — not just burst and collapse in isolation.
Cement integrity: High collapse capacity in P110 is only fully realised with competent cement behind the pipe. Unsupported P110 in a cement void can still fail in collapse if the void coincides with the maximum collapse load depth in the string.
Connection Types for P110
| Connection | Suitability | Notes |
|---|---|---|
| STC | Not recommended | Tensile efficiency too low for deep P110 strings |
| LTC | Limited — surface casing only | Inadequate for HPHT or deep applications |
| BTC | Moderate | Acceptable for non-HPHT P110 at moderate depth |
| Premium | Required for HPHT | Metal-to-metal seal — fully rated to P110 body strength |
For HPHT P110 applications, premium connections are a design requirement — not an optional upgrade. Standard API threads cannot maintain gas-tight integrity under combined thermal, axial, and pressure cycling loads in deep HPHT completions. ZC Steel Pipe supplies premium connections qualified to API 5C5 CAL IV rated to full P110 body yield.
What to Check on a P110 MTR
The Mill Test Report is the primary document for verifying P110 compliance. For a standard P110 PSL-2 order, check these items before accepting any consignment:
| MTR Item | What to Verify | Why It Matters |
|---|---|---|
| Yield strength | 758–965 MPa — both min AND max | Over-yield above 965 MPa is non-conforming — reject it |
| Tensile strength | Min 862 MPa (125 ksi) | Confirms Q+T produced correct microstructure |
| Hardness (if tested) | Record actual values — no API limit, flag values above 32 HRC | Unusually high hardness signals over-quench and brittle risk |
| Heat treatment | Confirm Q+T — reject normalise or N+T records | P110 requires Q+T — other heat treatment cannot achieve the yield band |
| Chemical composition | C ≤ 0.35%, S and P ≤ 0.030% minimum — check project CE limit | High S and P increase susceptibility to brittle fracture |
| NDE records (PSL-2) | Full-length UT or EMI body scan confirmed | Absence means pipe is PSL-1 regardless of labelling |
| Charpy impact (PSL-2) | Values, temperature, specimen size vs project specification | Confirms toughness at operating temperature |
| Dimensional report | OD, wall, straightness per API 5CT — for HC: eccentricity and ovality | HC collapse rating is only valid if HC tolerances were met |
How to Specify P110 on a Purchase Order
A complete P110 casing purchase order must include:
- Standard — API 5CT or ISO 11960
- Grade — P110 (no sub-grades, but specify HC if required)
- OD and nominal weight — e.g. 7 inch × 29.00 lb/ft
- Thread type — BTC or premium connection designation
- Range — R1, R2, or R3 (most strings are R3)
- PSL level — PSL-1 or PSL-2 (PSL-2 for all HPHT applications)
- Supplementary requirements — SR2 (Charpy), SR13 (hardness survey) as required
- HC tolerances — if High Collapse, specify mill's HC tolerance package by name
- 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
For projects in Nigeria, Angola, or Brazil where NOC documentation requirements apply — NNPC, Sonangol, Petrobras — confirm the MTC format and language requirements before mill order placement. Some NOC specifications require additional traceability documentation beyond standard API 5CT PSL-2.
References
- API Specification 5CT — Specification for Casing and Tubing (American Petroleum Institute)
- ISO 11960 — Petroleum and Natural Gas Industries: Steel Pipes for Use as Casing or Tubing
- NACE MR0175 / ISO 15156 — Materials for Use in H2S-Containing Environments in Oil and Gas Production
- API TR 5C3 — Technical Report on Equations and Calculations for Casing, Tubing, and Line Pipe