To have standard tap end stud lengths you must assume
the studded outlet side has a predictable raised face dimension (or no
raised face at all). Does API control the
raised face of a studded outlet?
We assume that your concern involves only
6BX connectors, as most wellhead
manufacturers currently do not make 6B
connectors, either open face flange or studded face flange, with raised
faces.
API does control the raised face dimension on 6BX
connectors, but not within limits that will allow interchangeable tap
end studs in studded face flange connectors.
WOODCO USA and most other manufacturers design
studded face connectors without a raised face as permitted by API Spec
6A. No raised face on studded face connectors permits defacto
standardization of tap end studs.
Note that the face to face make-up design of 6BX
connections requires that at least one face of the two mating connectors
has a raised face. This has resulted in a standard practice of always
having a raised face on 6BX open face flanges, and a defacto standard of
always omitting the raised face on studded face flange connectors (Some
rare exceptions exist, e.g. NOVShaffer uses maximum height raised faces
on studded face connected blowout preventers).
Some persons do not know of this defacto standard, or
that API Spec 6A permits a studded face 6BX connector with raised face
omitted: see API Spec 6A, 19th Edition, page 250, note b. "Q" may be
omitted on studded flanges."
In 1995 AWHEM formed a Task Group to specify
interchangeable flange bolts and tap end studs for API Spec 6A open face
flanges and studded face flanges. You can view the resulting document
at:
http://www.awhem.org/PDFs/TR9501A.pdf .
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