API 5CT Casing & Tubing – OCTG for Oil & Gas Wells
API Spec 5CT / ISO 11960 | J55, K55, N80, L80, C90, T95, C95, P110, Q125 | PSL1/PSL2/PSL3 | NACE MR0175 Sour Service Grades
OCTG serves one purpose: wellbore integrity. It is not pipeline pipe. Selection depends on four variables: depth (collapse pressure), pressure (burst rating), temperature (derating, connection sealing), and fluid chemistry (CO₂, H₂S, chlorides).
This page helps you select the right API 5CT grade for your well conditions.
Casing vs. Tubing – The Fundamental Difference
| Parameter | Casing | Tubing |
|---|---|---|
| Function | Supports wellbore walls, isolates formations | Conduit for produced oil/gas to surface |
| Installation | Cemented in place, permanent | Run inside casing, retrievable |
| Diameter | 114.3 mm – 508 mm (4½" – 20") | 48.26 mm – 114.3 mm (1.9" – 4½") |
| Wall thickness | 5.21 – 16.13 mm (typical) | 3.18 – 16 mm (typical) |
| Connection | STC, LTC, BTC, XC | NU, EU, IJ |
| Consumption share | >70% of well tubular cost | 20–25% of well tubular cost |
Casing is structural. Tubing is production-critical.
API 5CT Grade Portfolio – By Application & Environment
| Grade | Yield Strength (MPa) | Heat Treatment | Typical Application | Sour Service | Impact (SR16) |
|---|---|---|---|---|---|
| H40 | 276–552 | As-rolled / Normalized | Shallow wells, low pressure | ❌ No | Optional |
| J55 | 379–552 | Normalized | Shallow–medium wells, general service | ❌ No | Optional |
| K55 | 379–552 | Normalized | Higher tensile strength, moderate pressure | ❌ No | Optional |
| N80-1 | 552–758 | As-rolled / Normalized | Medium–deep wells, non-sour | ❌ No | Optional |
| N80-Q | 552–758 | Quenched & Tempered | Deep wells, improved toughness | ❌ No | Optional |
| L80-1 | 552–655 | Q&T | General sour service, ≤23 HRC | ✅ Yes | Optional |
| L80-9Cr | 552–655 | Q&T | CO₂ corrosion, mild H₂S | ✅ Yes | Optional |
| L80-13Cr | 552–655 | Q&T | Severe CO₂ corrosion, sweet/sour | ✅ Yes | Optional |
| C90 | 621–724 | Q&T | Sour service, deep wells | ✅ Yes | Optional |
| T95 | 655–758 | Q&T | High-strength sour service | ✅ Yes | Optional |
| C95 | 655–758 | Q&T | Non-sour, higher strength than N80 | ❌ No | Optional |
| P110 | 758–965 | Q&T | Deep wells, high pressure, non-sour | ❌ No | Optional |
| Q125 | 862–1034 | Q&T | Ultra-deep, high-pressure, non-sour | ❌ No | Mandatory |
NACE MR0175 / ISO 15156 compliance is not optional for sour wells. If H₂S partial pressure exceeds 0.05 bar, grades without hardness control (J55, N80, P110) will fail by sulfide stress cracking.
How to Select the Right API 5CT Grade – By Well Condition
| Well Condition | Recommended Grade | Key Requirement |
|---|---|---|
| Shallow, low pressure | J55 / K55 | Cost-effective, normalized |
| Medium depth, moderate pressure | N80-1 / N80-Q | Good strength, optional Q&T |
| Deep, high pressure | P110 / Q125 | High strength, Q&T required |
| Sour service (H₂S >0.05 bar) | L80-1, C90, T95 | Hardness ≤22/23 HRC, NACE MR0175 |
| CO₂ corrosion | L80-13Cr | 13% chromium, corrosion resistant |
| Severe CO₂ + H₂S | L80-13Cr | Specialized sour service |
Product Specification Levels (PSL) – API 5CT Table E.1
| Level | Scope | Additional Requirements vs. Lower Level |
|---|---|---|
| PSL-1 | Baseline requirements of API 5CT | — |
| PSL-2 | More stringent tolerances, mandatory CEV reporting, full-body NDT (casing ≥4½") | Restricted chemistry, heat traceability per heat, SR16 optional |
| PSL-3 | Individual heat traceability, 100% UT inspection, mandatory impact testing (SR16) | Each pipe marked with unique heat number, Charpy V-notch @0°C, full documentation |
We supply PSL-1 as standard. PSL-2 / PSL-3 available upon request.
Thread Types – API Connections
| Connection | Series | Application |
|---|---|---|
| STC | Short Round Thread Casing | Standard casing, moderate depth |
| LTC | Long Round Thread Casing | Deeper wells, higher joint strength |
| BTC | Buttress Thread Casing | High tensile strength, large OD |
| XC | Extreme-Line Casing | Flush OD, limited clearance |
| NU | Non-Upset Tubing | Standard tubing, economical |
| EU | External Upset Tubing | Higher joint strength, deep wells |
| IJ | Integral Joint Tubing | Flush OD, workover operations |
Premium connections (VAM, Hydril, Tenaris, etc.) are available on customer‑supplied tooling. We supply plain-end pipes qualified for any OEM premium threading – chemistry, CEV, hardness, and NDT fully documented.
Continue to Detailed Product Pages
| Product | Key Features |
|---|---|
| → J55 / K55 / N80 Casing & Tubing |
Carbon steel, normalized / Q&T. General service. |
| → L80 / P110 Casing & Tubing |
Sour service (L80-13Cr) & high-strength (P110). |
| → C90 / T95 / Q125 Casing |
Deep well, sour service (C90/T95) & ultra-deep (Q125). |
| → Well Screen Pipe |
Wire Wrapped Screen & Slotted Liner. |
Related Case Studies
| Case Study | Project | OCTG Grade Used |
|---|---|---|
| [→ Deep Gas Well – Central Asia] | 15,000 ft gas well – L80 + T95 combination string | L80, T95 |
| [→ Sour Gas Gathering Line – Middle East] | 8" & 10" X52 PSL2 seamless | (line pipe, not OCTG) |
| [→ Refinery Expansion – Thailand] | 6"–12" STPG410 seamless | (pressure pipe) |
Related Technical Resources
| Resource | Link |
|---|---|
| API 5CT Grades Overview | /technical/api5ct-grades-overview |
| Casing vs Tubing – Selection Guide | /technical/casing-vs-tubing |
| PSL1 vs PSL2 vs PSL3 | /technical/api5ct-psl |
| NACE MR0175 / ISO 15156 Guide | /technical/nace-mr0175-guide |
| OCTG Connection Types – API & Premium | /technical/octg-connections |
Quality Assurance – Every API 5CT Pipe Ships With
| Test / Document | Standard / Requirement |
|---|---|
| Mill Test Report | EN 10204 Type 3.1 – heat-specific chemistry, tensile, hardness, flattening, hydrotest |
| Heat treatment records | Actual furnace time/temperature curves (Q&T grades) |
| Hardness survey | Transverse section – ≤22/23 HRC (sour service) |
| Hydrostatic testing | 100% – pressure per API 5CT Table E.4/E.5 |
| Dimensional inspection | OD, WT, straightness, drift test |
| Thread inspection | API 5B gauging, certified by lab |
Optional:
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Charpy V-notch impact testing (SR16) – 0°C, -20°C, -45°C
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HIC / SSC testing per NACE TM0284 / TM0177
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100% ultrasonic testing (UT) – full body, longitudinal + transverse
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Third-party inspection – DNV, BV, LR, SGS, TÜV – no surcharge
Why Choose Shenlong for API 5CT Casing & Tubing?
| Factor | What It Means |
|---|---|
| Full grade range | J55 to Q125 – carbon, alloy, sour service – one source |
| PSL1/PSL2/PSL3 | All product specification levels available |
| NACE qualified | L80, C90, T95 – hardness controlled, certified |
| Threading capability | API connections in-house; premium on customer tooling |
| Full traceability | Every pipe tracked from heat number to your project |
| Third-party inspection | DNV, BV, LR, SGS, TÜV – available on request |
Request for Quotation
Send your inquiry with:
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Grade
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PSL (1/2/3)
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Dimension (OD × WT × length)
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Thread type
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Quantity
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Sour service requirement
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Destination port
? info@pipesl.com
? +86-21-68415587
Technical Review
This technical page was prepared by the Shenlong engineering team and reviewed by Wang Lei, Senior Metallurgical Engineer, 22 years of experience in OCTG manufacturing and oilfield metallurgy. All specifications verified against API 5CT 11th Edition, NACE MR0175/ISO 15156, and API 5B.
For technical inquiries: admin@pipesl.com
API 5CT casing & tubing – engineered for oil & gas wells worldwide.
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