API 5CT P110 Casing Pipe — Specifications, Grades & HPHT Guide

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.

The most common P110 order error we flag before production begins is a purchase order that does not check H₂S partial pressure — the mill is compliant shipping P110, but the string is non-conforming for the well environment. A question we get regularly from EPC procurement teams ordering P110 for deep HPHT completions is whether standard API tolerances are sufficient for collapse design — the answer depends entirely on the casing design model being used. When we review yield histograms from P110 heats for projects in Nigeria and Angola, we ask for the full distribution rather than just the minimum and maximum values on the MTC.

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.

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

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.

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

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.

Note that API 5CT sets no maximum for carbon or manganese in P110 — those elements are unrestricted at the API level. Project specifications from Shell, TotalEnergies, and NNPC routinely add carbon equivalent limits in addition to the API chemistry requirements. Always check project-specific chemistry requirements before placing a P110 order.

Standard Sizes

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.

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.

Worked Burst and Collapse Calculation

For a 7-inch 26 lb/ft P110 string (wall thickness 0.362 in, OD 7.000 in):

Internal yield pressure (burst), per API 5C3 Formula 31:

P = 0.875 × (2 × Yp × t / D) P = 0.875 × (2 × 110,000 × 0.362 / 7.000) P = 0.875 × 11,377 P = 9,950 psi (68.6 MPa)

The same size and wall in L80-1 (80,000 psi yield) gives 7,240 psi — P110 provides 37% more burst resistance at identical geometry. This is the core reason P110 is specified at depth: the wall thickness needed to reach the same burst capacity in L80 would add significant running weight.

Collapse — plastic regime (per API 5C3):

The D/t ratio for this pipe is 7.000/0.362 = 19.34, placing it in the plastic collapse regime for P110. Minimum plastic collapse pressure at 110,000 psi yield with no axial load is approximately 7,200 psi. Under an axial tensile stress of 11,000 psi (representative of a hanging string above a packer), the modified yield strength Ypa reduces to approximately 104,000 psi and minimum collapse drops to 6,110 psi — a 15% reduction from the unstressed value.

This axial de-rating is significant in deep HPHT wells where the string hangs under its own weight. Casing design must apply the combined-load correction from API 5C3 Section 2.1.5 — designing to the rated collapse pressure at zero axial load will overstate collapse resistance at depth.

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:

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

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.

When Not to Use P110

• Any well with H₂S above trace levels — P110 has no hardness ceiling and routinely tests above 32 HRC in heavy-wall pipe. NACE MR0175 / ISO 15156-2 prohibits carbon steel above 22 HRC in sour service. No exception applies for short exposure or low H₂S concentrations.
• Wells where only surface casing load calculations drive the grade — P110 costs 15–25% more per tonne than N80 or J55 at the same size. If your load calculations are satisfied by a lower grade, the premium buys nothing.
• Connections using only BTC or LTC in gas service — P110 body performance is wasted if the connection cannot hold gas-tight integrity at rated load. Standard API threads leak before P110 yields.
• Projects where lead time is critical and mill inventory is tight — P110 Q+T requires longer mill scheduling than normalised grades. In markets where distribution stock is limited, P110 lead times can be 10–14 weeks from order versus 4–6 weeks for J55 or N80 from stock. If the well programme cannot accommodate this, the grade selection must account for it.
• Shallow, low-pressure surface casing — the collapse and burst capacity of P110 is designed for depth. Using P110 in shallow applications with H40 or J55 loads wastes material and cost without any engineering benefit.

Connection Types for P110

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:

How to Specify P110 on a Purchase Order

A complete P110 casing purchase order must include:

1. Standard — API 5CT or ISO 11960
2. Grade — P110 (no sub-grades, but specify HC if required)
3. OD and nominal weight — e.g. 7 inch × 29.00 lb/ft
4. Thread type — 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 for all HPHT applications)
7. Supplementary requirements — SR2 (Charpy), SR13 (hardness survey) as required
8. HC tolerances — if High Collapse, specify mill's HC tolerance package by name
9. Quantity — in joints or metric tonnes
10. Delivery port — for freight planning and lead time
11. MTC level — EN 10204 3.1 or 3.2
12. 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