Threaded Connection Types
Premium Threaded Connection
The strongest OCTG connection, with a metal-to-metal seal and gas-tight sealability
Semi-Premium Threaded Connection
An OCTG connection without a metal-to-metal seal, but higher torque/tensile capabilities than API threads
API Threaded Connection
A basic OCTG connection with minimal torque and strength ratings (LT&C, Buttress, 8rd, etc)
Any threaded connection in which the box end is threaded onto the pipe (no coupling)
Threaded and Coupled (T&C)
A connection which uses a coupling made-up to the pipe to act as a box end
Flush Pipe / Flush Joint
An integral connection in which its Outside Diameter (OD) is the same as the OD of the pipe body
An integral connection in which its Outside Diameter (OD) is slightly larger than the OD of the pipe body
Glossary of Inspection and Connection Terms
Apex of Triangle
On Buttress pipe. Top or tip of stamped 3/8” triangle indicating the point of maximum power-tight makeup
Dimensions specified by the American Petroleum Institute to provide reliable API connections
Base of Triangle
On Buttress pipe. Bottom of stamped 3/8” triangle indicating the point of nominal power-tight makeup
Coupling End/Mill End
End of pipe with coupling installed or if pin x pin with mill identifications. Also may be called collar end or box end.
Top of the thread form
Imperfection deviating outside of tolerances and rejectable
The difference between shoulder torque and final make-up torque amounts.
Perfect/Effective Thread Area
Area of good threads, possible slight imperfections to crest. Full crested.
Side of thread connecting root to crest
Imperfect Thread Area
Area of imperfect threads, also called Run-In/Run-Out threads
A deviation from the specifed product, but within the manufacturer’s published tolerance. Not rejectable.
The void in an API coupled connection between two facing pins made-up inside the coupling. Semi- and Premium connections do not have a J-area.
The power-tight putting together of a coupling or integral box connector to a pin end connector.
The length measurement of the pin end of the connection which will be stabbed into the box end of the preceding joint. Sometimes used as a verification of a particular thread.
Imaginary line running the crest (external threads) and root (internal threads) that is parallel with the pitch diameter line
Dimensions of a connection running at tolerance
Minimum Length Full Crested Threads
The area of the effective/perfect threads free from thread form defects in accordance with API and manufacturer specifications
Imaginary line running at the root (external threads) and crest (internal threads)
Dimensions running right on the specifications
External threads (no coupling). Also called the field end.
The size of a connection at a specified point along the tapered connection
Pitch Diameter Line
An imaginary line running approximately midway between the root and the crest of the threads, along the taper
Connection has been made up with mechanical assistance to at least the minimum published torque
Bottom of thread form
The make-up torque required to achieve shoulder engagement.
Stand In Condition
Pipe at power tight has gone into coupling too far
Stand Off Condition
Pipe at power tight has not made up into coupling far enough
The change in the diameter of the thread, along the minor cone for external threads and the major cone of internal threads, in inches per foot (mm per meter)
The distance from the end of the pipe to the vanishing point of the threads and typically indicates the point of power tight makeup
An inspection that encompasses an overall check for thread defects/damage caused by faulty workmanship, mechanical damage, and black-crested threads. Whenever possible, field technicians will repair the threads without jeopardizing the integrity of the connection.