There has been some confusion as to our company's
policy regarding the use of seal rings in the ST-L connection. It
is incorrect to state the Grant Prideco does not recommend
the use of the seal ring in ST-L.
Grant Prideco's policy on using a TeflonŽ seal ring in the ST-L liner
connection is:
The seal ring is optional.
Further, the metal-to-metal radial flank seal is the primary internal
pressure seal of the ST-L connection. The connection is fully rated,
equal to the API pipe body internal yield pressure, with the metal-to-metal
seal alone. The Teflon seal ring is offered as an option and is not
required. The seal ring functions as a back-up to the primary seal
thereby providing an extra measure of seal integrity in the event
that the metal seal is damaged during shipping, handling, or makeup.
The use of the seal ring is usually determined by the operators philosophy
and comfort level as opposed to any particular characteristic of the
application. All ST-L is manufactured for use either with or without
the seal ring. (The seal ring groove is machined in all ST-L boxes.)
If a user wants the optional seal ring, he should contact the Grant
Prideco Field Service Department at 713-924-2832 or his local Grant
Prideco Technical Support/Sales Office.
The seal ring should not be used for the following conditions:
The seal ring should not be used for applications above 600* F.
The seal ring should not be used in ST-L for small diameter and light
weight pipes. For these sizes the seal ring can create swaging of
the pin ID to the extent that the connection may not pass drift. Therefore,
we recommend that ST-L be run without the seal ring for the following
sizes:
All sizes and weights of 4-1/2" and smaller
5" 18.00 ppf and lighter
5-1/2" 15.50 ppf and lighter
6-5/6" 20.00 ppf
7" 20.00 ppf and lighter
7-5/8" 24.00 ppf and lighter
8-5/8" 28.00 ppf and lighter
9-5/8" 40.00 ppf
10-3/4" 40.50 ppf
Millions of feet of ST-L have been run successfully both with and
without the seal ring. There are some operators that require the Teflon
seal ring be used 100% of the time. The majority of operators Use
ST-L without the seal ring.
