Page 16 - Design Criteria.qxd

It is also recommended that for complete
electrical insulation protection that self-
adhesive tape is wrapped around the out-
side diameter of the flange to prevent the
ingress of foreign matter.
With style NCA and NCB insulat-
ing sets it is imperative that the bore of
the gasket is equal to that of the pipe.
This will prevent any foreign matter
from accumulating in the annular space
between the bore of the gasket and the
bore of the pipe thus preventing bridg-
ing.
Phenolic laminate provides excellent insulating properties as well as corrosion
resistance. See table for typical properties of 3mm (1/8”) thick phenolic. Other gasket
styles such as Sigma and non-asbestos sheets may also be suitable.
Typical Properties of Phenolic Gaskets
Maximum axial compressive stress 315MPa (45,700 psi)
Axial electric strength in oil @ 90°C (190°F) 23kV/cm (58kV/in)
Maximum operating temperature 120°C (250°F)
Minimum operating temperature -60°C (-76°F)
As standard, Flexitallic insulating kits are dimensioned to suit schedule 80 pipe
suitable for use on standard and non-standard flange assemblies up to and inclusive of
Class 2500.
TYPICAL APPLICATIONS
Offshore installations, sea water environments, hydrocarbon service, chemical instal-
lations, oil refining pipelines requiring galvanic corrosion protection and electrical
insulation.
17 ® Welcome to the Next Generation of Sealing Technology
Insulating Sets
Insulating sets comprise of a phenolic laminate or neoprene faced phe-
nolic laminate gasket (Style NCA and NCB only) which is located
between the flange sealing faces, phenolic laminate bolt sleeves, two
insulating washers per bolt for maximum protection and two plated
mild steel washers per bolt. Stainless steel washers can be supplied
upon request.
Insulating sets are essentially used for pipeline flange corrosion
protection, where a seal is required between dissimilar flange materials.
The use of dissimilar metallic flanges with a conductive gasket materi-
al accompanied with a suitable electrolyte may set up a galvanic cell
which will corrode the anodic metal. Insulating sets are also used to
electrically isolate flange joints, preventing the flow of electrostatic
charge along pipelines.
There are three standard styles of insulating sets available to suit
raised face, flat face, and ring grooved flanges, as illustrated below.
Standard Styles
One 3mm
(1/8”) thick
plated
steel washer
for each nut.
One
Insulating
washer for
each nut
One full
length
insulating
sleeve for
each bolt
3mm (1/8”)
thick
insulating
gasket or
oval ring for
ring joint
flanges
One
insulating
washer for
each nut
One 3mm
(1/8”) thick
plated steel
washer for
each nut
Style NCB
Inside Bolt Location
Gasket Insulating Set
Assembly
Utilizes a central gasket which
locates within the bolts.
Style NCC
Ring Joint Gasket
Insulating Set Assembly
Insulating oval section ring joint
will fit into a standard RTJ flange
ring groove.
Style NCA
Full Face Gasket
Insulating Set Assembly
Suitable for flat face and raised
face flanges. This style mini-
mizes the ingress of conductive
foreign matter between the
portion of the flanges out-
side the raised faces and
reduces the risk of bridging.
1/8” thick steel washer
1/8” thick insulating washer
Insulating sleeve
1/8” thick insulating gasket
1/8” thick insulating washer
1/8” thick steel washer