96
SPECMA SEALS HANDBOOK
SOFT GASKETS
C H O O S I N G
T H E
Choosing the right gasket material
for a specific application is not
always an easy task. All the factors
that affect a gasket in a flange joint
may seem infinite, but nevertheless
they all have to be taken into
account in order to achieve
optimum seal function.
It was sufficient before for the parameters
temperature, application, media and
pressure to provide enough information to
allow the correct gasket to be chosen.
Things are not as simple nowadays, as
factors such as flange design, flange
rotation, sealing surface finish, bolt
utilisation ratio etc. can affect the performance of a gasket. In general, it may be
stated that the definition of a tight flange
joint has dramatically changed over the
years. Leakage values have changed. They
used to count drops per minute, but now
they can be defined using ppm (parts per
million).
Look for soft gaskets according to
their performance:
To quickly and easily find the right product
in our broad range of soft gaskets, we
recommend that you look at our “Quick
guide on choosing the right soft gasket”.
This quick guide states the material
structure, applications and operating
parameters for soft gaskets.
Note that data stated for max. pressure and
max. temp. cannot normally be combined.
Information and values submitted must
always be checked by the customer/
consumer as variation in respect of media,
equipment, installation and operating
conditions can be so great that only the
customer/consumer can fully assess the
circumstances and maintain control over all
data relating to the seal required.
R I G H T
G A S K E T
M A T E R I A L
The correct sequence when choosing the right gasket:
Temperature:
In most cases, the temperature of the media to be sealed
off must be taken into account first. This allows the
number of potential alternatives to be limited considerably,
making your choice easier. When the system's operating
temperature approaches the max. value for a specific
gasket material, it is recommended that you choose a
“better” material instead, with a higher max. temperature
limit, so that you have a greater safety margin.
Applications:
Here, attention must be paid to the flange type and the
design of the bolted joint. Bolt quality, the number of bolts
and the bolt dimensions determine the available force in
the respective flange joints. The gasket's clamped area is
determined by the gasket's contact dimensions. The resulting
seating stress on the gasket is calculated by dividing the
available force by the clamped area expressed in N/
mm2 (MPa). The technical specifications for the respective
products show recommended minimum and maximum
values in order to facilitate your choice of gasket. We would
be happy to recommend the right material with the aid of a
seating stress calculation.
Media:
There are thousands of different liquids and gases in
industry. Fortunately, however, a relatively limited number
of media are actually used in industry. The “Applications:”
section for each gasket type shows the general resistance
to media. Further information on resistance to media for the
various materials is available from the technical department
at Specma Seals.
Pressure:
Finally, the pipe system's internal operating pressure must
be taken into account. The maximum pressure specified for
each soft gasket material must be considered as a guide
value.
If there is a risk of the flange joint being subjected to major
dynamic influence and/or pressure surges, an alternative
product should be selected.
Different types of gasket material:
Material
Product name
Cellulose fibre Cellulose fibre jointing
Max. temp.
Rubber sheeting
Daniel's Ebonite , SBR rubber, NBR
rubber, CR/SBR rubber,Vulcopack®,
Silicone rubber,Viton® rubber
Rubber gaskets with metal core
G-ST-P/S gaskets
+70°C
Rubber bonded cork
NBR rubber bonded cork
+120°C
Rubber bonded aramid fibre
Dixo® 4000, Novapress 815 +120°C
®
Rubber bonded aramid fibre with graphiteDixo 7000 XP
+70°C to +230°C
+120°C to +200°C
+300°C
®
Rubber bonded mineral fibre
70 Service
+250°C
Rubber bonded carbon fibre Garlock Style 9850 Extreme +350°C
Reinforced PTFE
Multiflon® Black, Multiflon® Blue
®
Restructured and reinforced PTFE
Gylon® Style 3501E, Gylon® Style 3504,
Gylon® Style 3510
Glass fibre reinforced PTFE
+180°C
+260°C
UCAR 323-LC®+245°C
Expanded PTFE (ePTFE)
Gore® GR, Gore® UPG Style 800, Gore® DF,
Gore® Series 500, Gore® Series 600, Softseal +270°C
Expanded graphite without reinforcement Grafex® EC, Grafex® Crinkle-Tape,
FlänsMan®, Grafoil® TG-281
+650°C
Expanded graphite with reinforcement Grafex® EX, Grafex® EXP, Elastagraph,
Grafex® SA, Grafex® NR
+650°C
Mineral fibre
Isoplan 1000
MicaMicapac® 1000
+1000°C
+1000°C
The above materials are the most common in the group “Non-metallic soft gaskets” and
essentially cover all normally occurring applications in the process industry. Composite and
metal gaskets are dealt with separately in the following section.
The stated limit values apply under favourable conditions.
Do not utilise more than one maximum value at a time.
If in doubt please contact us, we will be happy to offer advice.
SPECMA SEALS HANDBOOK
SOFT GASKETS
Q U I C K
G U I D E
on choosing the right soft gasket
Designation Base material Used for
Temperature range Pressure pH
Elastagraph
Enclosed, corrugated
core of stainless
steel, faced with
expanded graphite.
Virtually all media including steam, water, petroleum
products, solvents, acids, alkalis and gases, with the
exception of strongly oxidising acids
at high temperature.
-200°C to +650°C, higher
300 bar
in non-oxidising atmosphere.
Grafex® EXP
Expanded graphite
with insert of
acidproof expanded
metal
Virtually all media including steam, water, petroleum
-200°C to +750°C, higher
250 bar,
in non-oxidising atmosphere. higher in
products, solvents, acids, alkalis and gases, with the
exception of strongly oxidising acids at high temperature.
favourable
cases.
0-14
Grafex® EX
Expanded graphite
with insert of
acidproof expanded
metal
Virtually all media including steam, water, petroleum
-200°C to +650°C, higher
250 bar,
in non-oxidising atmosphere. higher in
products, solvents, acids, alkalis and gases, with the
exception of strongly oxidising acids at high temperature.
favourable
cases.
0-14
Grafex® SA
Expanded graphite
with insert of
smooth acidproof
foil.
Steam, water, petroleum products, solvents, acids, alkalis
etc. i.e virtually all media with the exception of strongly
oxidising acids at high temperature.
0-14
Grafex® NR
Expanded graphite
with insert of
smooth nickel foil.
Virtually all media including steam, water, petroleum
-200°C to +650°C, higher
200 bar
in non-oxidising atmosphere.
products, solvents, acids, alkalis and gases, with the
exception of strongly oxidising acids at high temperature.
0-14
Grafex® EC
Expanded graphite
without insert.
100 bar,
Virtually all media including steam, water, petroleum
-200°C to +650°C, higher
in non-oxidising atmosphere. higher in
products, solvents, acids, alkalis and gases, with the
favourable
exception of strongly oxidising acids at high temperature.
cases.
0-14
Grafex®
Crinkle-Tape
Self-adhesive tape
of expanded
graphite.
For sealing of flanges, lids and covers at virtually all
media with the exception of strongly oxidising acids in
combination with high temperature.
-200°C to +650°C, higher
100 bar,
in non-oxidising atmosphere. higher in
favourable
cases.
0-14
FlänsMan®
Self-adhesive tape
of braided expanded
graphite fibre.
For sealing of flanges, lids and covers at virtually all
media with the exception of strongly oxidising acids in
combination with high temperature.
-200°C to +650°C, higher
45 bar
in non-oxidising atmosphere.
0-14
Grafoil® TG-281
Self-adhesive foil
of expanded
graphite.
For sealing of flanges, lids and covers at virtually all
media with the exception of strongly oxidising acids in
combination with high temperature.
-200°C to +650°C, higher
100 bar,
in non-oxidising atmosphere. higher in
favourable
cases.
0-14
Garlock Style
9850
Extreme®
Nitrile rubber
Highly resistant to mineral oils, hot oil, gases,
bonded carbon fibre. hydrocarbons and other petroleum products.Very
suitable as a gasket for gas applications thanks to its
excellent sealing properties to prevent diffuse leaks
-40°C to +350°C,
but +200°C in steam.
100 bar in
favourable
cases.
-
Dixo® 7000 XP
Nitrile rubber
bonded aramid fibre
with graphite.
Ideal for sealing pipe flanges, lids, covers and split casing
flanges. The gasket is resistant to steam, water, petroleum
products, refrigerants, solvents, gases, weak acids and
alkalis etc.
-100°C to +300°C, higher
in certain media, see
product sheet.
100 bar in
favourable
cases.
See
product
sheets
Novapress 815
Nitrile rubber
bonded aramid fibre
with surface facing
of nitrile rubber
Mainly as a seal in flanges where freon and other gases
are present. This gasket is capable of withstanding
most freons and can also be used against oils and fuels.
Extremely gas-tight.
-80°C to +200°C.
50 bar
-
-200°C to +650°C, higher
150 bar,
in non-oxidising atmosphere. higher in
favourable
cases.
0-14
97
98
SPECMA SEALS HANDBOOK
SOFT GASKETS
Designation
Base material Used for
Temperature range Pressure pH
70 Service
Nitrile rubber
bonded mineral
fibre.
Low pressure steam, LPG, oil, petrol, weak acids and
alkalis, solvents and jet fuel
-100°C to +250°C
continuously,
briefly up to +370°C.
70 bar
-
Dixo® 4000
Nitrile rubber
bonded aramid
fibre.
Water, weak acids and alkalis, oils, fuels, solvents, gases
etc.
-100°C to +120°C
continuously,
briefly up to +200°C.
50 bar
-
Gylon® Style 3501E
Gylon® Style 3510E
Restructured
PTFE with
reinforcement.
Flanges, lids, covers and split casing flanges in chemical,
pharmaceutical and food industries, where stringent
demands are made of tightness, safety and cleanliness.
-210°C to +260°C.
80 bar,
higher in
favourable
cases.
0-14
Multiflon® Black
PTFE reinforced
with carbon.
Flanges, lids, covers and split casing flanges Suitable
for a wide spectrum of media, such as acids, alkalis,
solvents, hydrogen peroxide 50%, chlorine dioxide 23 g/l,
petroleum products etc.
-200°C to +180°C.
40 bar,
higher in
favourable
cases.
0-14
Multiflon® Blue
PTFE reinforced
with glass fibre.
Flanges, lids, covers and split casing flanges. Suitable for
a wide spectrum of media, such as acids, alkalis, solvents,
chlorine, chlorine dioxide, petroleum products etc.
-200°C to +180°C.
40 bar,
higher in
favourable
cases.
0-14
Multiflon® White
PTFE without
reinforcement.
Limited application,
see product sheet.
-200°C to +180°C.
6 bar
0-14
UCAR 323-LC®
Glass fibre
reinforced PTFE.
Flanges, lids, covers and split casing flanges.Very suitable
for demanding applications in the process industry,
where conventional PTFE-based soft gaskets with large
cold deformation properties and high compression in
heat tend to cause leakage.
-212°C to +245°C.
40 bar,
higher in
favourable
cases.
0-14
GORE® GR
Biaxially expanded
PTFE.
Specially designed for metal flanges and large flanges, flanges
which are difficult to access and flanges with complex shapes.
Suitable for foods and pharmaceuticals, drinking water, oxygen etc.
-268°C to +270°C, up
to +315°C under
ideal conditions.
max. 40 bar
0-14
GORE® Joint
Sealant DF
Sealing tape
of monoaxially
expanded PTFE.
The majority of types of flange and manhole.
Suitable for foods and pharmaceuticals, drinking water,
oxygen etc.
-268°C to +270°C, up to
+315°C under
ideal conditions.
40 bar
0-14
GORE®
Series 500
Series 600
Sealing tape of
biaxially expanded
PTFE.
Heat exchangers, air coolers, pressure vessels, columns
etc. Suitable for flanges, lids, covers and parting lines.
Suitable for a broad range of media, e.g. acids, alkalis,
solvents etc. (not suitable for molten alkali metals and
fluorine).
-268°C to +270°C, up to
+315°C under
ideal conditions.
max. 40 bar
max. 6 bar
0-14
0-14
GORE® UPG Style
800
Biaxially expanded
PTFE.
Plastic flanges, enamelled flanges, PTFE and rubber-faced
flanges. Particularly well suited to extremely aggressive
solutions or in cases where the flanges are weak.
-268°C to +270°C, up to
+315°C under
ideal conditions.
max. 40 bar
0-14
Softseal
Sealing tape of
monoaxially
expanded PTFE.
Flanges, lids, covers, split casing flanges, also for
enamelled flanges and plastic flanges. Softseal is resistant
to all gases and fluids with the exception of fluorine and
molten alkali metals.
-240°C to +270°C.
40 bar,
higher in
favourable
cases.
0-14
The stated limit values apply under favourable conditions.
Do not utilise more than one maximum value at a time.
If in doubt please contact us, we will be happy to offer advice.
SPECMA SEALS HANDBOOK
SOFT GASKETS
Designation Base material Used for
Temperature range Pressure pH
G-ST-P/S
Rubber/steel
gaskets
Nitrile rubber with
steel core.
Pipe flanges of steel, plastic or rubberised for water, air,
gas, oils, petroleum products etc. Approved by DVGW
for use in gas pipes. Recommended by KTW for drinking
water.
-25°C to +70°C.
40 bar
-
Daniel's
Ebonite®
Synthetic special
rubber without
fabric.
Very good resistance to alkalis, chlorine solutions,
chlorine dioxide, green liquor, saline solutions, solvents,
oils, low pressure steam, water etc.
-60°C to +150°C,
higher in favourable cases.
40 bar
2-14
SBR rubber with
or without
fabric
Styrene butadiene
rubber with or
without fabric.
For general applications where no specific demands
are made, e.g. for water. Not oil resistant.
-15°C to +80°C.
10 bar
-
NBR rubber with
or without
fabric
Nitrile rubber with
or without fabric.
Synthetic NBR rubber for oils, fuels
and non-oxidising acids.
-15°C to +70°C.
10 bar
-
White NBR rubber
without
fabric
White nitrile
rubber without
fabric.
White synthetic NBR rubber for
food applications
-30°C to +85°C.
10 bar
-
CR/SBR rubber
with or
without
fabric
Chloroprene
rubber with or
without fabric.
Synthetic rubber with good resistance to the elements,
ozone, non-oxidising acids. Limited resistance to oil
products.
-25°C to +100°C.
10 bar
-
Vulcopack®
Specially vulcanised
EPDM rubber
without fabric.
Superheated and hot water, low pressure steam, acids
and alkalis.Very good weather/ozone resistance and
wear strength. Excellent gasket for manholes etc.
-40°C to +140°C.
25 bar
-
Silicone rubber
without
fabric
Silicon rubber
without fabric.
Synthetic rubber for high and low temperatures
with good resistance to the elements, ozone. Limited
resistance to oil products and chemicals in general.
-60°C to +230°C.
10 bar
-
Viton®
rubber
Fluoride rubber
without fabric.
Excellent resistance to oils, acids, chemicals. Less suitable
for esters, ketones, water vapour and alkalis at high
temperatures.
-30°C to +200°C.
10 bar
0-14
Rubber
bonded
cork
Fine-granulated
cork bonded
with nitrile rubber.
Primarily suitable for oil, fuels, solvents
and water. Seals at low seating stresses.
-30°C to +120°C.
10 bar
-
Cellulose
fibre
gasket
Glycerineimpregnated
cellulose fibres.
Flanges, lids and covers in cooling machines, air lines,
paper machines, transformers etc. Able to withstand
engine fuels, mineral and diester oils, water and other
media. Not suitable for steam.
-60°C to +120°C.
10 bar
-
Isoplan
1000
Mineral fibres.
The steel and glass industries for furnaces, boilers,
fireproof doors, fireplaces, drying equipment, fire
protection etc.
max. +1000°C.
3 bar
-
Micapac®
1000
Mica.
High temperature applications. Extremely good chemical
resistance . Particularly suitable for aggressive acids at
high temperature.
max. +1000°C.
5 bar
0-14
99
100
SPECMA SEALS HANDBOOK
SOFT GASKETS
F U N C T I O N
P R I N C I P L E
F O R
F L A N G E
J O I N T S
Flange joints are normally divided into two main types
– with a load-bearing gasket and with metal-to-metal contact.
1. Flange with load-bearing gasket
With this type of flange joint, there is no contact between the
flanges: the gasket takes the entire load. It is possible to compress
the gasket further if the system pressure increases, in order to
compensate for the increased seating stress then required by
the gasket. However, you should take into account the fact that
increased prestressing of bolts also increased the risk of flange
rotation (bending). Most commonly occurring in flat flanges with or
without a raised sealing face (type IBC or type FF) and in flanges
with tongue and groove or spigot/recess (type TG or type SR).
2. Flange with metal-to-metal contact
In a flange joint where there is contact between the two flange
faces, it is not possible to further increase the seating stress on
the gasket once contact has been made between the flanges.
The gasket is enclosed in a groove with a well defined depth,
which is determined by the gasket's degree of compression
in relation to its original thickness. This type of flange system
requires careful control over the gasket's compressibility and its
recommended min. seating stress.
Bolt force
The influence of force in a flange joint:
The total force generated by all the bolts in
the bolted joint on tightening is transmitted
to the gasket of the flanges. The force is
distributed across the clamped area of the
gasket, at which point the seating stress
generated compresses the gasket so that it
fills out irregularities and also compensates
for distortion in order to achieve max.
sealing capability. The gasket in the above
example is centred within the bolts, known
as an IBC gasket (“inside bolt circle”).
When the system is pressurised, a
“hydrostatic force” occurs which attempts to
separate the flanges, which in turn results
in reduction of the seating stress on the
gasket. The remaining seating stress on the
gasket is the pressure to which the gasket
is subject during operation and is crucial to
an optimum flange sealing function. Under
“Technical data” for each gasket
type, recommended min. and
max. values are stated for the
seating stress.
Gasket
seating
stress in
service
Flange
rotation
(bending)
It is worth noting that in the case described
above with flanges with a raised sealing face,
there is a risk of the flange potentially being
subject to rotation (bending). The degree of
flange rotation is dependent on bolt forces,
flange geometry and material. In the event
of flange rotation occurring in a flange, the
seating stress on the gasket will be greatest
at the outermost point of the raised sealing
face and smallest in towards the medium
(see diagram). This should be taken into
account when choosing a soft gasket
material as there is a risk of the gasket being
partially subject to excessively high seating
stress and hence potentially being crushed.
Hydrostatic
force
Clamped
area
If you use a flat flange without a raised sealing
face and an FF gasket (“full face”) covering
the entire flange face complete with bolt
holes, this eliminates the chances of flange
rotation. The disadvantage of this design is
that the collective force of all bolts in the joint
is distributed across more or less twice the
area than is the case with an IBC gasket,
which in turn means that the seating stress on
the gasket is essentially half as great.
Seating stress calculation:
To ensure that our gaskets have the best possible chances of working optimally, we help our customers with seating stress calculation for flanges.
The Seating stress calculation enquiry form can be found in section entitled “Questionnaires”, and also on our website at www.specmaseals.se/Products
The stated limit values apply under favourable conditions.
Do not utilise more than one maximum value at a time.
If in doubt please contact us, we will be happy to offer advice.
SPECMA SEALS HANDBOOK
SOFT GASKETS
Summary of sealing surface types
on flanges as per EN 1514 and suitable for soft gaskets.
The most common flange types with regard to sealing surface design:
Type A: Plan flange without raised sealing surface
Type B: Flange with raised sealing surface
Type C: Flange with tongue
Type D: Flange with groove
Type E: Flange with spigot
Type F: Flange with recess
Flat gaskets suitable for the above flange types and sealing surfaces
Flanges type A without raised sealing surface with gasket type FF
o/d
p.c.d.
i/d
The figure illustrates soft gaskets of type FF
(full face) for flat flanges type A. The gaskets
are supplied complete with bolt holes.
Flanges type B with raised sealing surface and gasket type IBC
o/d
i/d
Type FF can also be used for flanges
type B with raised sealing surface.
The figure illustrates soft gaskets of type IBC
(inside bolt circle) for flanges with raised
sealing surface type B.
Type IBC can also be used for flat flanges
type A without raised sealing surface.
bolt hole
dia.
Flanges type C/D with tongue and groove with gasket type TG
o/d
i/d
The figure illustrates soft gaskets of type TG
(tongue and groove) for flanges with tongue
and groove type C/D.
Flanges type E/F with spigot/recess and gasket type SR
o/d
i/d
The figure illustrates soft gaskets of type SR
(spigot and recess) for flanges with spigot
and recess type E/F.
101
102
SPECMA SEALS HANDBOOK
SOFT GASKETS
PROFILE GUIDE FOR SOFT GASKETS
Product description
Profile
Soft gasket of soft
Type 200
material cut out of sheet
Standard
Profile figure
EN 1514-1
DIN 2691
DIN 2692
DIN 7603
Ditto but with inner
Type 106
EN 1514-1
eyelet
DIN 2692
ASME
Soft gasket with PTFE
envelope
Type 301
EN 1514-3
Soft gasket with corrugated
metal core and PTFE
envelope
Type 302
EN 1514-3
Type 303
DIN 2690
Type 304
DIN 2690
Soft gasket with inner
eyelet faced with PTFE
Type 305
DIN 2690
Gasket with partition
bars for heat exchangers,
with either integrated
or welded-in bars
Type VVX
See page 127
Gaskets for threaded joints.
Several of the gasket types mentioned in the section “Soft gaskets” can be used for sealing threaded joints. It is important to remember
to choose a material with sufficient mechanical stability so that it is not destroyed when it is subjected to a twisting motion.
As regards soft gaskets, gaskets of rubber bonded fibre or reinforced PTFE are normally recommended, while gaskets of expanded
graphite should be avoided. At temperatures over +260°C, some type of metal gasket is recommended, see page 112 or 113.
A table showing the most common dimensions for gaskets for threaded joints as per DIN 7603 can be found on page 213.
The stated limit values apply under favourable conditions.
Do not utilise more than one maximum value at a time.
If in doubt please contact us, we will be happy to offer advice.
SPECMA SEALS HANDBOOK
SOFT GASKETS
I N S TA L L AT I O N I N S T R U C T I O N S
Soft gaskets
Dovetail joint gaskets
Lubrication:
Threads and nut faces must be lubricated
unconditionally so as not to lose prestressing
force in the friction faces. Use Grafex® GTL
thread paste made of graphite for best results.
Make sure that the sealing surfaces are
well cleaned and flat, and free of scratches,
irregularities and paint. Remachine them
if necessary. The faces must be free of
grease as the degree of friction between
gasket and flange is crucial in order to
achieve optimum function.
Grafex® GTL thread paste has extremely good lubricating
properties and inhibits corrosion, and it is suitable for use in both
carbon steel and stainless steel bolted joints.
Flange surface finish:
How to tighten the flange:
When machining uneven flanges, the
greatest possible care should be taken
with regard to the presence of any
radial scratches or machining marks.
Such scratches or marks are essentially
impossible to seal off, no matter what type
of soft gasket is used. The flange sealing
surface should not be turned in a spiral
motion: you should attempt to achieve a
sealing surface of concentric grooves.
Actions before installation:
Make sure that the flanges are clean and
parallel. Avoid all forms of sealing paste or
release agent.
Bolts and nuts:
Ideally, use new bolts, nuts and washers to
guarantee optimum installation. Make sure
that the nuts rotate freely into the threads
of the bolts. Use a thread cleaning tool in
the event of the slightest inertia. Also check
that the bolts are straight and undamaged.
The nut face of the flanges must also be
checked. In the event of pitting, machine
or use hardened steel washers or NordLock lock washers to achieve a base with
controlled hardness for every installation
operation.
1) Make sure that the flanges are clean and
parallel.
2) The dovetail joint should be positioned
at or near to a bolt in order to achieve the
greatest possible seating stress on the
gasket at the joint.
3) For gaskets of expanded graphite with
or without reinforcement, the joint has to be
provided with a joint strip of self-adhesive
Grafex® Crinkle-Tape on both sides for
maximum sealing function at the joint face.
Checking flanges:
To achieve an optimum seal, both the
flanges have to have the same surface
finish. In normal cases, 3.2 – 6.4 µm Ra
is recommended. When the gasket is
compressed, the irregularities of the flange
are filled out. The coarser the surface finish
of the flange, the higher the seating stress
required to make the gasket penetrate into
the irregularities.
For the best results, follow the
step-by-step instructions below:
Tightening the flange correctly is crucial
in order to achieve an optimum sealing
function. Use a torque wrench or hydraulic
torque spanner. Impact wrenches or
hammering nut wrenches should be
avoided. It is very important for the bolts
to be tightened in the correct order using
a minimum number of tightening motions
in order to distribute the force as evenly as
possible across the flange.
• Tighten in a minimum of 3 stages. The more
stages, the easier it is to achieve the
recommended prestressing and distribute force
evenly across the flange.
• The first stage should be limited to max.
30% of the recommended max. torque.
• The bolts are tightened diametrically in the
recommended order as shown in the example below.
• During the final tightening stage, the bolts are
then tightened in order around the
circumference to the same torque as the final
diametric tightening process.
Tightening torque:
The recommended tightening torque (or
just “torque”) is dependent on bolt quality,
dimensions, thread pitch and friction in the
bolted joint. These values can be found in
the bolt supplier's recommendation tables.
Different values apply to joints calculated as
per pressure vessel standards.
Examples of
recommended
tightening
sequence in
the case of
diametric
tightening:
4) For other types, the joint should be
supplemented with a sealing material suitable
for the relevant gasket material or a layer of
self-adhesive Grafex® Crinkle-Tape on both
sides. For PTFE gaskets, it is recommended
that the joint should be wrapped with
conventional PTFE thread tape.
5) Then tighten the bolted joint in the usual
sequence.
6) Sealants of all types should be avoided
on the gasket's sealing faces.
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