API 5CT Oilfield Casing Coupling
API 5CT Oilfield Casing Coupling is a critical component used in oil and gas drilling operations to connect sections of casing. Its design and manufacture adhere to the API 5CT international standard published by the American Petroleum Institute (API), thereby ensuring structural integrity and sealing reliability within extreme downhole environments.
Essentially, this coupling consists of a short, hollow steel tube featuring internal threads (BOX) machined at both ends. These threads serve to securely join two sections of casing-each fitted with external threads (PIN)-to form a continuous wellbore structure. The coupling must be precisely matched to the corresponding steel grade, thread type, and dimensions of the casing to withstand the complex combination of downhole stresses-including tension, compression, internal pressure, and corrosion-thereby preventing wellbore collapse or fluid leakage.
Contact us immediately to customize an API 5CT casing coupling solution tailored to complex well conditions; our expert team is ready to provide comprehensive support for your drilling project from start to finish!
API 5CT Casing Coupling Specification Table
| Standard | API SPEC 5CT "Specification for Casing and Tubing" |
| Application | Casing connection in oil and gas well drilling |
| Common Grades | H40, J55, K55, N80, L80, P110, Q125 |
| Thread Types | STC (Short Thread Coupling), LTC (Long Thread Coupling), BTC (Buttress Thread Coupling) |
| Outer Diameter Range | 4-1/2″ to 20″ (approximately 114.3mm ~ 508mm) |
| Length Categories | R1 (4.88–7.62m), R2 (7.62–10.36m), R3 (10.36–14.63m) |
| Connection Method | Threaded connection (internal thread coupling + external thread casing) |
| Product Specification Level (PSL) | PSL-1 (basic), PSL-2 (enhanced testing), PSL-3 (for severe service conditions) |
| Manufacturing Process | Hot-rolled/cold-drawn seamless or ERW welded pipe, precision machined and heat-treated |
| Testing Requirements | Tensile, flattening, hydrostatic, and non-destructive testing (NDT) |
Chemical Composition of API 5CT Casing Coupling
| Grade | C (%) | Mn (%) | P (%) | S (%) | Cr (%) | Mo (%) | Others |
|---|---|---|---|---|---|---|---|
| J55/K55 | 0.34–0.39 | 1.25–1.50 | ≤0.020 | ≤0.015 | - | - | V: 0.11–0.16 (N80) |
| N80 | 0.34–0.38 | 1.45–1.70 | ≤0.020 | ≤0.015 | - | - | V: 0.11–0.16 |
| L80-13Cr | 0.15–0.22 | 0.25–1.00 | ≤0.020 | ≤0.010 | 12.0–14.0 | - | - |
| P110 | 0.26–0.35 | 0.40–0.70 | ≤0.020 | ≤0.010 | 0.80–1.10 | 0.15–0.25 | - |
| Q125 | ≤0.35 | ≤1.35 | ≤0.030 | ≤0.030 | Cr/Ni included | Mo included | High-strength, high-toughness design |
Tensile Properties of API 5CT Casing Coupling
| Grade | Yield Strength (MPa) | Tensile Strength (MPa) | Elongation (%) | Hardness Requirement |
|---|---|---|---|---|
| J55 | 379–552 | ≥517 | ≥20 | - |
| K55 | 379–552 | ≥655 | ≥20 | - |
| N80 | 552–758 | ≥689 | ≥20 | - |
| L80 | 552–655 | ≥655 | ≥20 | ≤241 HB |
| P110 | 758–965 | ≥862 | ≥18 | - |
| Q125 | 862–1034 | ≥931 | ≥16 | Transverse impact energy ≥60J at 0°C |
Manufacturing Process of API 5CT Casing Coupling
Raw Material Preparation: High-quality carbon or alloy steel billets (e.g., 37Mn5, 30CrMo) compliant with API 5CT.
Heat Treatment: Normalizing or quenching & tempering to achieve required strength and toughness.
Machining:
Internal threads (BOX) cut to API 5B precision standards;
Deburring and chamfering of ends.
Surface Treatment:
Phosphating or painting for corrosion resistance;
Thread protectors installed to prevent damage during transport.
Quality Inspection:
Dimensional checks (OD ±0.79mm, wall thickness -12.5%);
Mechanical testing (tensile, flattening, hydrostatic);
NDT (ultrasonic, magnetic particle) to detect cracks or defects.
Marking & Packaging:
Laser marking of grade, size, batch number, PSL level;
Bundled with steel straps, palletized for shipping.
API 5CT Coupling test equipment
FAQ
What does API 5CT mean?
API 5CT is the abbreviation of the Specification for Casing and Tubing published by the American Petroleum Institute (API), serving as an international technical standard for oil well casing and tubing in the oil and gas industry.
What are the three types of coupling?
API 5CT specifies three main types of casing couplings: Short Round Thread Coupling (STC), Long Round Thread Coupling (LTC), and Buttress Thread Coupling (BTC). All are designed in accordance with API Spec 5B and are used to connect oil well casing, ensuring downhole sealing integrity and structural strength.
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