Description
API 5CT Casing & Tubing – OCTG for Oil & Gas Wells
*API Spec 5CT / ISO 11960 – Seamless Steel Pipe for Casing, Tubing, and Accessories – Carbon, Alloy & Sour Service Grades*
What Is API 5CT?
API Specification 5CT (ISO 11960) is the global reference standard for steel pipes used as casing, tubing, and pup joints in oil and gas wells.
API 5CT governs five categories of technical requirements:
| Category | Scope |
|---|---|
| 1. Materials | Chemical composition, mechanical properties, hardness limits |
| 2. Dimensions | OD, WT, mass, length tolerances, drift diameters |
| 3. Manufacturing | Heat treatment (normalized, quenched & tempered), straightening, NDT |
| 4. Threading | API Round, Buttress, Extreme‑Line; gauging per API 5B |
| 5. Supplementary Requirements | SR16 (impact), SR22 (leak resistance), PSL escalation |
OCTG serves one purpose: wellbore integrity.
It is not pipeline pipe.
Selection depends on four variables:
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Depth – collapse pressure
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Pressure – burst rating
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Temperature – derating, connection sealing
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Fluid chemistry – CO₂, H₂S, chlorides
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
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.
We supply PSL-1 as standard. PSL-2 / PSL-3 available upon request.
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.
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