An API 5CT Coupling is a short length of pipe used to connect two joints of threaded casing or tubing. These couplings are manufactured according to the API Spec 5CT standard, which is the leading specification for OCTG (Oil Country Tubular Goods).
Couplings must match the grade and thread type of the pipes they connect. Their primary function is to provide a leak-proof, high-strength seal that can withstand the extreme internal and external pressures found in oil and gas wells.
Whether it's Premium connections or standard API threads, our technical team is here to help you choose the right coupling for your well conditions. Chat with us now.
Specifications of API 5CT Couplings
To ensure reliability in deep-well environments, API 5CT couplings follow strict material and dimensional requirements:
Standard: API Spec 5CT (latest edition).
Material Grades: J55, K55, N80-1, N80-Q, L80 (1, 9Cr, 13Cr), C90, T95, P110, Q125.
Connection Types:
For Tubing: NU (Non-upset), EU (External upset).
For Casing: STC (Short Round Thread), LTC (Long Round Thread), BTC (Buttress Thread).
Quality Level: PSL1, PSL2, and PSL3 (Product Specification Levels).
Surface Treatment: Phosphating (standard for anti-galling), Copper plating (optional), or Zinc coating.
Size Chart for API 5CT Tubing and Casing Couplings
Tubing Coupling Size Table (NU & EU)
| Pipe OD (Inches) | Coupling OD - NU (mm) | Coupling OD - EU (mm) | Length (mm) |
| 1.900" | 55.88 | 63.50 | 95.25 / 120.65 |
| 2-3/8" (2.375") | 73.02 | 77.80 | 107.95 / 130.18 |
| 2-7/8" (2.875") | 88.90 | 93.17 | 130.18 / 133.35 |
| 3-1/2" (3.500") | 107.95 | 114.30 | 142.88 / 146.05 |
| 4-1/2" (4.500") | 132.08 | 141.30 | 155.58 / 158.75 |
Casing Coupling Size Table (STC, LTC, BTC)
| Pipe OD (Inches) | Coupling OD (mm) | STC/LTC Length (mm) | BTC Length (mm) |
| 4-1/2" | 127.00 | 158.75 / 177.80 | 225.43 |
| 5-1/2" | 153.67 | 171.45 / 203.20 | 234.95 |
| 7" | 194.46 | 184.15 / 228.60 | 254.00 |
| 9-5/8" | 269.88 | 196.85 / 266.70 | 269.88 |
| 13-3/8" | 365.12 | 203.20 | 269.88 |
| 20" | 533.40 | 203.20 | 269.88 |
Applications of API 5CT Couplings
Casing Connection: BTC and LTC couplings are used to connect large-diameter casing pipes that form the structural wall of the oil well.
Tubing Connection: EU and NU couplings are used for the production tubing that carries oil/gas to the surface.
High-Pressure Wells: P110 grade couplings are used in deep, high-pressure reservoirs.
Corrosive Environments: 13Cr and L80-9Cr couplings are utilized in wells with high CO2 or H2S content to prevent sour service corrosion.
Manufacturing Process of API 5CT Couplings
The production of a coupling is more complex than a standard pipe, as it requires high precision to prevent leaks:
Coupling Stock Selection: We use high-quality seamless coupling stock (thick-walled tubes) that meets or exceeds the grade requirements.
Cutting: The stock is cut into specific lengths based on API standard dimensions.
Heat Treatment: To achieve the required mechanical properties (tensile and yield strength), couplings undergo Quenching & Tempering (Q&T).
Threading: Using high-precision CNC machines to cut NU, EU, STC, LTC, or BTC threads. Thread accuracy is verified using API gauges.
Surface Treatment (Phosphating): A chemical coating is applied to improve corrosion resistance and provide lubrication, preventing "galling" (thread damage) during installation.
Inspection & Marking: Magnetic Particle Inspection (MPI), Hydrostatic testing, and laser marking for full traceability.
API 5CT Seamless Couplings
Contact our sales team today for the latest inventory and pricing on J55, N80, and P110 couplings.
FAQ
What is API coupling
An API coupling is a short, threaded steel pipe component used to connect two lengths of threaded oilfield tubing or casing.
Its primary functions include:
Connection: Joining individual steel pipes to form a continuous pipe string extending thousands of meters deep into an oil or gas well.
Sealing: Ensuring-through high-precision thread engagement-that no leakage of oil or gas occurs, even under high-temperature and high-pressure conditions.
Standardization: Adhering strictly to the API 5CT standard, thereby ensuring perfect compatibility between tubular goods produced by different manufacturers worldwide.
How to choose the right coupling
Match the Steel Grade: The grade of the coupling must be the same as the pipe it connects. For example, a J55 pipe must be paired with a J55 coupling, and a P110 pipe with a P110 coupling.
Match the Thread Type: The threads must be identical to ensure a leak-proof seal:
For Tubing: Choose EU (External Upset) or NU (Non-Upset).
For Casing: Choose BTC (Buttress Thread), LTC (Long Round Thread), or STC (Short Round Thread).
Match the Dimensions: Always select the coupling size based on the pipe's Outer Diameter (OD) according to API 5CT standards.
Consider the Working Environment: If the well environment is corrosive (high CO2 or H2S), you must select specialized corrosion-resistant grades such as 13Cr or L80.
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