Choosing the Right Gasket
 Correct gasket choice is an important
step in the design of a process system as choosing
the correct gasket from the beginning can result in
significant savings due to longer gasket life,
reduced gasket failure and lower leak rates.
Other Considerations
Limitations in steam
Steam duty is perhaps the most common
and one of the most arduous gasket applications. It
is difficult in part because
1. Steam
is a powerful hydrolyser capable of changing the
nature of many polymers and fibres.
2. An
increase in the pressure of saturated steam results
in a corresponding increase in temperature. Gaskets
under increased stress (ie higher internal pressure)
in general require a reduced operation temperature.
3. Many
materials harden in steam leading, in some cases, to
embrittlement. This is especially applicable to
asbestos free calendered materials.
When discussing temperature limits in
steam only approximate guide-lines can be given due
to considerations such as
-
Flange design (ie spigot and
recess is far better than raised face)
-
Gasket thickness (thinner gaskets
perform better)
-
Required service life
-
Assembly techniques
-
Maintenance procedures
-
Degree of acceptable
embrittlement
-
The use of jointing compounds in
an assembly
Bearing these factors in mind we
suggest that very careful consideration be given to
the above parameters, especially where operation is
near the borderline of the PT diagrams available.
Low Temperature Duty
The following conditions need to be
met before determining suitability of materials at
low temperatures.
-
The gasket is completely dry when
installed
-
The flange is assembled at
ambient temperature
-
The flange and bolt materials are
suitable for low temperature use
Gasket Size
A general rule is that gaskets cut from a sheet can
be successfully used at smaller diameters, lower
pressures and/or lower temperatures. As diameter,
temperature or pressure increase the use of
semi-metallic gaskets are more common. This is
largely due to the effect of hydrostatic end thrust
in reducing stress on the gasket and increasing the
chance of a blow-out.
As a general rule, special care
should be taken for gaskets above 600mm diameter, or
operating above 200°C or 50 bar.>>The
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