Tubing and casing
API 5CT tubing and casing couplings
Couplings join tubing and casing joints. Each is machined from seamless coupling stock in the grade of the string and threaded to API 5B for its connection and size.
An API 5CT coupling is a short internally threaded sleeve that joins two lengths of tubing or casing. Tubing couplings come in NUE and EUE, casing couplings in STC, LTC and BTC, each in regular or special clearance outside diameters. We machine couplings from seamless coupling stock heat treated to the grade, J55 to P110, and cut and gauge the threads to API 5B, with thread protectors fitted for shipment.
Coupling types
| Coupling | Joins | Notes |
|---|---|---|
| NUE | Non-upset tubing | Round thread; simple and low cost |
| EUE | External upset tubing | Round thread on upset pins; the common production tubing joint |
| STC | Casing, short round thread | Shortest casing coupling |
| LTC | Casing, long round thread | Longer engagement, higher joint strength than STC |
| BTC | Casing, buttress thread | Highest tensile strength of the API casing connections |
| Special clearance | Any of the above | Reduced outside diameter for tight clearances |
Dimensions, threads and tolerances per API 5CT and API 5B.
Grades and stock
Couplings are machined from seamless coupling stock, heat treated to the API 5CT grade of the string they join. The grade sets strength and, for L80, C90 and T95, a maximum hardness for sour service; the values are in the grade table on the API 5CT pup joints page. Each coupling is marked with its grade, size and connection and traced to the heat of its stock.
Threads, finish and inspection
Threads are cut to API 5B and checked with thread gauges. Couplings are inspected for dimensions and visual defects, then coated or plated as your order states, fitted with thread protectors and packed by size and grade. Magnetic particle inspection, hardness testing of each coupling for sour-service grades and third-party witness can be added.
For hydrogen sulfide service, use L80 Type 1, C90 or T95 couplings with the hardness limit and testing API 5CT sets for the grade, and the same grade as the pipe.
We make these parts to the API 5CT and API 5B requirements your order calls up: material, dimensions, tests and marking as specified. We do not hold an API license, so the parts do not carry the API Monogram. If your specification requires monogrammed equipment, the quotation says so plainly.
Ordering
Tubing coupling, 2-7/8 in EUE 8 round, regular OD, L80 Type 1, threads to API 5B, phosphated, thread protectors fitted, EN 10204 3.1, 200 pcs
Casing coupling, 7 in BTC, special clearance, P110, threads to API 5B, EN 10204 3.1, 50 pcs
Frequently asked questions
What is a special clearance coupling?
A coupling with a smaller outside diameter than the regular coupling for the same connection, used where the clearance between the string and the casing or hole is tight. Its smaller cross section gives a lower joint strength, so check it against the string design.
Must the coupling grade match the pipe?
Normally yes: an L80 string takes L80 couplings, a P110 string P110 couplings. Some designs use a higher-grade coupling deliberately; follow your string design.
Are couplings supplied with thread protectors?
Yes. Couplings ship with thread protectors fitted and threads coated against corrosion, packed by size and grade.
Do you make couplings for premium connections?
No. Premium connections belong to their license holders, and their couplings are made under license. We make API couplings: NUE, EUE, STC, LTC and BTC.