Page 110 - Well Control for Completions and Interventions

102 Well Control for Completions and Interventions

3.3 TUBULAR CONNECTIONS

Pipe connections for the oilfield use many different thread forms,
but can broadly categorized as either “integral connector” or “threaded
and coupled.” With an integral connector thread, both box and pin con-
nections are cut into the body of the base pipe. In coupled connections,
the pipe body is cut with a pin connection at each end of the joint. The
joints are then connected using a separate box/box coupling. Threaded
and coupled is by far the most common type of connection, as they are
simpler and cheaper to produce, especially where corrosion resistant alloys
are required. Connections are also defined by the sealing mechanism, and
can be divided into two broad categories, API and premium (Fig. 3.12).

3.3.1 American Petroleum Institute connections
API connections are widely used. They are cheap, simple, and readily
available. However, they are not suitable for all wells, having a number of
limitations.
• They are weaker than the tubing when the connection is in tension.
• Axial loads are taken through the threads.
• Because of the thread flank angle, they are prone to “jump-out.”
• The sealing mechanism is thread interference, and sealant (pipe dope) is
needed to prevent liquids escaping through the spiral leak path of the
thread.Timeand differential pressurecanextrudethepipedope, andleaks
will develop. The API connections are not suitable for use in gas wells.

Figure 3.12 Thread and coupled connection (left) and integral connection (right).