How They Work
Under axial compressive load, ring type joints plastically
deform and flow into the irregularities of the flange
groove. Since the load bearing area of the ring
type joint is relatively small, very high surface
stresses result between the sealing faces of the
ring type joint and the groove. These stresses are
further increased on the Style RX and BX rings which
allows very high internal pressures to be sealed.
Since ring type joints are solid metal, their recovery
characteristics are poor. The seal is maintained
by the action of axial load upon the gasket.
Surface Finish Requirements
With all metal to metal type seals, it is imperative
that the gasket and groove sealing faces are free
from indentations, score marks, tool/chatter marks
and other imperfections. The surface finish of the
gasket and groove sealing faces is also critical
and
should not exceed the following:
|
Style
R and RX
|
63 microinches
RMS maximum (1.6 micrometer Ra)
Ra 1.6 micrometers |
|
Style
BX
|
32 CLA microinches
RMS maximum (0.8 micrometer Ra)
Ra 0.8 micrometers |
Reuse
Ring type joints are designed to have a limited
amount of positive interference, which ensures
that the ring type joint seats correctly
into the groove on compression. Their reuse is
not recommended for two reasons:
--⊙ The initial seating
of the gasket will be impaired.
--⊙ When the gasket
is plastically deformed, work hardening of the
external metal surface occurs.
-- --This
may result in permanent damage to the groove.
Hardness of Materials
On compression of the flange assembly, it is imperative
that the ring type joint be significantly softer
than the flange groove so that the gasket plastically
deforms and not the groove. The use of harder
ring type joints can result in flange groove damage.
For this reason, ring type joints are supplied
with the following maximum hardness values:
Protective Coating
In accordance with API Specifications, soft iron,
low carbon steel, and other ferrous materials
ring type joints are protected from corrosion
with electroplated zinc or cadmium to a maximum
thickness of 0.0005". Alternative material
coatings can be supplied on request.
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