Page 11 - Design Criteria.qxd

12 ® Welcome to the Next Generation of Sealing Technology
Flexitallic Flexicarb®
The Flexitallic Flexicarb range of sheet sealing materials is manufactured from high purity exfoliated graphite flake, and
is available with or without a reinforcing metallic core. The “standard” product range is based upon graphite with a min-
imum carbon content of 98% and, for nuclear applications, graphite with a minimum carbon content of 99.85% is avail-
able. The graphite foils can be attached to the reinforcing core by mechanical means or by the use of selected adhesives.
Flexicarb laminates are particularly suited for applications involving moderately high temperatures and pressures in
conjunction with a wide range of media. They are widely used in demanding general industrial applications and in the
petrochemical/refining industries. Because these products do not contain any rubber or polymeric binders they have the
highest levels of stress retention, ensuring that gasket stress applied during assembly is maintained during service.
Graphite based products are resistant to most industrial chemicals but are susceptible to attack by oxidizing agents
such as nitric acid. Sulfuric acid can also attack graphite at certain combinations of concentration and temperature. When
selecting a graphite laminate for use in chemical service, consideration must be given to any possible reaction between the
chemical medium and the reinforcing metallic core.
In air or in services where oxygen is present, graphite can burn away at high temperatures as it is converted to oxides
of carbon. The rate at which this occurs depends on the application temperature and the concentration of oxygen present.
In a well bolted flange only the inner edge of the gasket will be exposed to oxygen in the pipe; the graphite will burn away
very slowly with service life being dictated by the land width of the gasket. In high temperature applications where the
fluid being sealed does not contain oxygen, consideration must be given to possible attack of the graphite by oxygen from
the external atmosphere surrounding the flange.
For long term service, work by independent testing has shown that maximum service temperature should be much
lower than that usually quoted in manufacturers’ literature. This work has been validated by the Tightness Testing Research
Laboratory (TTRL) at Ecole Polytechnique in Montreal on behalf of the Pressure Vessel Research Council (PVRC). The
TTRL report includ-
ed the maximum
service temperatures
for various periods
of service for
graphite sheet gas-
kets as shown in the
table:
Product Range
Flexicarb Laminated Sheet LS (GS 600)* - Homogeneous
Graphite foil. This product is used for the production of graphite
laminates.
Flexicarb SR (RGS4)* - This laminate contains a 0.05mm
(0.002”) thick 316 stainless steel core with adhesively bonded
graphite facing.
Flexicarb ST (RGS 3)* - This laminate contains a tanged 0.1mm
(0.004”) thick 316 stainless steel core onto which the graphite
faces are mechanically attached. This gasket is used where high
pressures have to be contained and is particularly suitable for use
in superheated steam service.
Flexicarb NR (RGS 1)* - Laminate in which the graphite is adhe-
sively bonded onto a 13 micron (0.0005”) thick nickel core using
a chemically resistant nitrile phenolic adhesive.
* Parenthesis UK designation
Required Maximum Service Temperature
Service Life
Years °C °F
1 370 691
3 330 630
5 320 610
10 305 580
Flexicarb
Foil
Metal Core