All flanges above
ANSI Class 250 work in a similar fashion. They use the bolts
arraigned in a circle around the flange to pull the faces together with
a gasket in between. The gasket gets compressed by the force exerted by
the bolts, and a seal between the flanges occurs.
Several different flange face and gasket designs use
different mechanics to accomplish a desired, leak tight, connection.
ANSI 16.5 Raised Face (RF)
flanges compress a flat, relatively soft gasket, between two serrated
raised portions located adjacent to the flange bore. The tightness of
the bolts must exert enough pressure on the gasket to compress the
gasket and hold it in place, not allowing the flanges to separate under pressure, thus achieving a seal.
For more information about flanges that seal with a
flat gasket, see
http://www.garlock.eu.com/pdfs/Products-OK/Metallic
Gasketing-OK/Graphonic Series of Gaskets GMG1-11.pdf .
ANSI 16.5 Ring Type Joint (RTJ),
and API 6B
flanges, sealed with an R type gasket, seal in much the same way as
raised face flanges, except they utilize an oval or hexagonal steel ring
gasket contained in a groove machined into the face of the flange
adjacent to the flange bore. Unlike Raised Face flanges of the same size
and pressure rating, the compression does not need to hold the gasket in
place, as the grooves in the flanges accomplish this retention. The
tightening of the bolts compresses the gasket, coining the flanks of the
gasket, and with sufficient tightness prevents flange separation under
pressure, achieving a seal.
ANSI 16.5 Ring Joint Type, and API 6B flanges, sealed
with an RX type gasket, seal in much the
same way as the flanges above, except the steel ring gasket has a
cross-section profile that facilitates coining only on the outside
flanks of the flanges' seal groove. The gasket profile creates a self
sealing feature due to the mechanical force created against the inside
of the gasket by the contained pressure, forcing tighter contact between
the gasket and the outside flanks of the flanges' seal grooves.
API 6BX flanges seal
with a BX hexagonal steel gasket fitting
in machined grooves in raised faces (on at least one of the mating
flanges) on the flanges adjacent to the flange bores. The depth of the
grooves and the size of the gasket allow the gasket to coin and the
raised faces to contact and react in such a manner as to reinforce the
bending strength of the flange connection.
For more information about the actual sealing
characteristics of the various types of steel ring gaskets, see
http://www.woodcousa.com/field_appr.htm .
For more information about connecting all types of
flanges that seal with steel ring gaskets, see
http://www.woodcousa.com/flg_make-up.htm .
Also see Q & A
42, When and Why Have Raised Faces on API Flanges?
For a Catalog for Bolts,
Nuts, Ring Gaskets and Wrenches, Click Here.
