There are several types covered in API 5CT standard for coupling specifications, classified in regular couplings, special clearance couplings, combination couplings, reducing couplings, seal ring couplings, and special bevel tubing regular couplings.

Regular couplings

Regular couplings diameters complied with API 5CT Tables C.32 to C.35 or Tables E.32 to E.35. Coupling bearing contact face inside and outside edges shall be rounded or broken, but shall not significantly reduce the width of the bearing face (dimension b), since less thickness will not be safe to support the pipe weight. The ends of couplings shall be faced exactly at right angles to the axis.

Special clearance couplings

In the case specified in the contract, special-clearance (reduced outside diameter Wc) couplings for buttress (BTC connection) casing and external upset (EUE connection) tubing shall be furnished. Unless otherwise specified, special-clearance external upset tubing couplings shall have a special bevel on both ends. The inside and outside edges of the bearing face shall be rounded or beveled. The ends (or root face when beveled) of couplings shall be faced at right angles to the axis.

Special-clearance coupling dimensions and tolerances shall comply with as given in Tables C.33 and C.35 or Tables E.33 and E.35 and as shown in Figures D.3 and D.5. Color identification sees clause 11.

Combination couplings

Combination couplings with different types of the thread of the same specified size shall be furnished when specified on the contract. The minimum length and minimum OD of this coupling shall be sufficient to work with the specified size specified threads.

Reducing couplings

Reducing coupling is also a kind of pup joint, used to connect two pipes of different diameters with the same or different types of thread on the two ends. Same with combination coupling, minimum length and minimum diameter of reducing couplings shall be sufficient to support the specified size and threads.

Seal-ring couplings

Sealing-ring couplings conforming to the requirements shall be furnished when specified in the PO. Grooves may be cut before or after threading at the manufacture’s option. Grooves and threads shall be free of fins, wickers, and ribbons that are loose or can become loose and fold into the thread dorm. Couplings shall be inspected after the final machining of the groove.

Special clearance coupling

When specified in the order, special-clearance (reduced outside diameter) couplings for buttress casing and external upset tubing shall be furnished.

Combination coupling

Reducing coupling are used to connect two pipes of different diameter with the same or different types of thread on the two ends, and shall be furnished when specified on the agreements. The minimum length and minimum diameter of reducing couplings shall be sufficient to accommodate the specified size and type of threads.