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Gaskets RELIANCE GROUPTRAINING MODULE
Module No.RG-CM-G - 001
AuthorRSG / MGC
Rev: 0
Approved bySVKR
Date: 12/13/01 Page 1 of 62
GASKET
Gaskets RELIANCE GROUPTRAINING MODULE
Module No.RG-CM-G - 001
AuthorRSG / MGC
Rev: 0
Approved bySVKR
Date: 12/13/01 Page 2 of 62
CONFIDENTIALITY STATEMENT
This Training manual is prepared exclusively for the technical knowledge
enhancement of the personnel of Reliance Group of Industries.
No part of this document may be reproduced in any form, in an electronicretrieval system or otherwise. The document must be returned or when the
recipient has no further use of the same. The document or any part of the
document is not allowed to be taken out of the respective site or to be
shared with any person outside Reliance Group.
Reliance Group of Industries reserves the right to refuse access to the
above document on the grounds of confidentiality.
Authorization for information disclosure is allowed with the written
permission of the respective Site Engineering Head.
Gaskets RELIANCE GROUPTRAINING MODULE
Module No.RG-CM-G - 001
AuthorRSG / MGC
Rev: 0
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Date: 12/13/01 Page 3 of 62
TRAINING MODULE OBJECTIVE
This Training manual is intended to help engineers to understand the basic
fundamentals of a Gasket. It is often said that a gasket is leaking but this is
not strictly correct because truly it is the joint which leaks and Gasket is
only one component of the several that makes one joint. Hence it has been
experienced that for the gaskets, it takes more time to identify the problem
than to solve it. Thus, in this module, an effort has been made to provide
much needed source of information in the field of Gaskets.
To make the module easy to use, contents are divided into short sections
like Gasket introduction, Selection criteria, Installation guide, Trouble
shooting, Types of Gaskets, Do’s & Don’ts etc.
It is hoped that users may suggest improvements in future editions, to
make this module more useful.
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TABLE OF CONTENTSSr. No. Description Page No1.0 Introduction 06
1.1 Why Gaskets Are Use 061.2 How Gasket Seal 071.2.1 Gasket Seating Stress “Y” 091.2.2 Gasket Factor “M” 09
2.0 Type of Gaskets 132.1 Based on Shape 132.2 Based on Material of Construction 152.2.1 Soft Sheet Gaskets 152.2.2 Semi Metallic Gasket 172.2.3 Metallic Gaskets 21
2.3 Spiral Wound Gaskets 233.0 Gasket Materials 27
3.1 Soft Gasket Materials 283.2 Metallic Gasket Materials 33
4.0 Application of Types of Gaskets 385.0 Gasket Selection 40
5.1 Flange Design 405.2 Surface Finish 405.3 Selection of Gasket Materials for different services 43
6.0 Installation 456.1 Installation and Maintenance Tips 456.2 Gasket Installation Procedures 45
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7.0 Trouble Shooting Guide 508.0 Trouble shooting Leaking Joints 549.0 Sealing layer Material and Sealing Stresses 56
9.1 Core Thickness 579.2 Gasket Consist of a Metal Core 58
10 Do’s & Don’ts 5911 Standards 61
11.1 Material Standards 6111.2 Dimension Standards 61
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1.0 Introduction
A gasket is some softer material usually inserted between contact faces to obtain
fluid tight joints. Tightening the bolts causes the gasket material to flow into theminor machining imperfections resulting in a fluid-tight seal.
1.1 Why gaskets are used
Gaskets are used to create a static seal between two stationary members of a
mechanical assembly and to maintain that seal under operating conditions which
may vary dependent upon changes in pressures and temperature. If it were
possible to have perfectly mated flanges and were possible to maintain an
intimate contact of these perfectly mated flanges throughout the extremes of
operating conditions a gasket would not be required. This is virtually impossibilityeither because of:
• The size of the vessel and /or flanges
• The difficulty in maintaining such extremely smooth flange finishes during
handling and assembly
• Corrosion and erosion of the flange surfaces during operations
As a consequence, relatively inexpensive gaskets are used to provide the sealing
element in these mechanical assemblies. In most cases, the gasket provides a
seal by external forces flowing the gasket material into the imperfections
between the mating surfaces. It follows then that in a properly designed gasket
closure, Three major considerations must be taken into account in order for asatisfactory seal to be achieved.
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Sufficient force must be available to initially seat the gasket. Stating this another
way, adequate means must be provided to flow the gasket into imperfections inthe gasket seating surfaces
Sufficient force must be available to maintain a residual stress on the gasket
under operating conditions to ensure that the gasket will be in intimate contactwith the gasket seating surfaces to prevent blow-by or leakage.
The selection of the gasket material must be such that it will withstand the
pressure exerted against the gasket, satisfactorily resist the entire temperature
range to which the closure will be exposed and withstand corrosive attack of theconfined medium.
1.2 How gaskets seal
When closed, a gasket seal is subject to a compressive stress produced by
assembly. Under working conditions this load may be relieved by hydrostatic end
thrust as shown in below fig no1. The gasket is subject to a side load due to
internal pressure tending to extrude it through the flange clearance space. To
resist extrusion the compressive load should be greater than the internal
pressure and remain so. A factor of atleast 2 is usually recommended to allow for
relaxation of gasket compression stress, which is normally inevitable. This in turn
will depend on the material. A material with a low relaxation is preferable as it
can be employed with lower initial compression pressure, or maintain factor ofsafety at the same pressure.
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Gasket creates a static seal between two members of an assembly and maintains
the seal during operating condition that may fluctuate. Seal is provided by the
gasket flowing in to imperfections in the mating surfaces. Force to affect the sealis provided by bolting compressing the gasket.
TYPICAL JOINT DIAGRAM
Hp Total joint-contact-surface compression load in lbs
HHydrostatic end force in lbs
∆F Change in joint load due to the gasket relaxing in lbs
Fbo Initial required tightening force in lbs
WTotal tightening force required to seal joint in lb
FIG NO 1A
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1.2.1 Gasket Seating Stress “Y”
Sufficient force is necessary to deform the gasket in to the imperfections. The
“Y” is defined, as the applied stress required to seat the gasket up on the
flanges. For gasket design, the necessary compressive stress is the function of
flanges surface finish, gasket material, density, thickness, fluid to be sealed andallowable leak rate.
1.2.2 Gasket Factor “M”
Sufficient force must be present during operation to maintain the seal against the
internal pressure to prevent leakage. For gasket design, the required ratio of
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gasket compressive stress to internal pressure depends upon the gasket style
and materials. The “M” is defined, as the residual compressive force exerted
against the gasket contact area must be greater then internal pressure when the
compressive force has been relieved by the hydrostatic end force. It is the ratio
of residual gasket contact pressure to internal pressure and must be greater then
unity otherwise leakage would occur. It follows then; the use of higher value for“M” would result in a closure design with a greater factor of safety.
“Y” and “M” have no theoretical values but are empirical, developed form
experience. Gasket material must be suitable for the temperatures, pressures
and environment to which it is exposed. Filler material is generally Graphite orsome times Teflon or another Non – Asbestos material.
“M” and “Y” values are given below for different types of gaskets
Gasket material Gasket
factor
“M”
Min.
design
seating
stress “Y”
in N/mm2
Rubber without fabric or a high percentage of asbestos ξfiber:
*below 75° BS and IRH
75° BS and IRH or higher
0.5 0
1.0 0
0
1.4
Asbestos ξ with a suitable 3.2 mm thick 2.0 11.0
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binder for the operating 1.6 mm thick
conditions 0.8 mm thick
2.7 5
3.5 0
25.5
44.8
Rubber with cotton fabric insertion 1.2 5 2.8
Rubber with asbestos ξ fabric insertion, 3 – ply
with or without wire reinforcement 2 – ply
1 - ply
2.25
2.50
2.75
15.2
20.0
25.5
Vegetable fiber 1.7 5 7.6
Spiral-wound metal, Carbon
asbestos ξ filled Stainless or monel
2.5 0
3.0 0
To suit
applicant
Corrugated metal, asbestos ξ
inserted or Corrugated metal,
Jacketed asbestos ξ filled
Soft aluminium
Soft copper or brass
Iron or soft steel
Monel or 4 to 6% chrome
Stainless steels
2.50
2.75
3.00
3.25
3.50
20.0
25.5
31.0
37.9
44.8
Corrugated metal
Soft aluminium
Soft copper or brass
Iron or soft steel
Monel or 4 to 6% Chrome
Stainless steels
2.75
3.00
3.25
3.50
3.75
25.5
31.0
37.9
44.8
52.4
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Flat metal jacketed
Asbestos ξ filled
Soft aluminium
Soft copper or brass
Iron or soft steel
Monel
4 to 6% Chrome
Stainless steels
3.25
3.50
3.75
3.50
3.75
3.75
37.9
44.8
52.4
55.1
62.0
62.0
Grooved metal
Soft aluminium
Soft copper or brass
Iron or soft steel
Monel or 4 to 6% Chrome
Stainless steels
3.25
3.50
3.75
3.75
4.25
37.9
44.8
52.4
62.0
69.5
Solid flat metal
Soft aluminium
Soft copper or brass
Iron or soft steel
Monel or 4 to 6% Chrome
Stainless steels
4.00
4.75
5.50
6.00
6.50
60.6
89.5
124
150
179
Ring joint
(for dimensions see BS 1560)
Iron or soft steel
Monel or 4 to 6% Chrome
Stainless steels
5.50
6.00
6.50
124
150
179
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Rubber O- rings :
below 75° BS
between 75° and 85 ° BS and IRH
0 to 0.25 0.7
1.4
Rubber square section rings :
below 75° BS and IRH
between 75° and 85 ° BS and IRH
0 to 0.25 1.0
2.8
Rubber O- rings :
below 75° and IRH
between 75° and 85 ° BS and IRH
0 to 0.25 1.0
2.8
ξ New non-asbestos bonded fiber sheet gaskets are not necessarily direct
substitutes for asbestos-based materials. In particular pressure, temperature andload limitations may be applied.
2.0 TYPE OF GASKETS
Gaskets can be classified based on shapes or based on Material of construction.2.1 Based on shapes
Although shapes and dimensions very enormously there are certain shapes
common to most industries. Chiefs among these are flange gaskets produced to variousstandards. The two most common types of gaskets are:
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FIG NO 2
FIG NO 3
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2.1.1 Inside bolt circle or ring type
Where the periphery of the gasket is generally located by the bolts.
2.1.2 Full Faces type
Where the out side diameter is similar to that of the flange and has a series of
holes corresponding to the number and diameter of the bolts.
These types are illustrated in Fig no 2 & 3.
2.2 Based on Material of Construction
Based on this criteria the gaskets can be classified in to three types
1) Nonmetallic or Soft sheet gaskets
2) Semi-metallic
3) Metallic
2.2.1 Soft Sheet Gaskets :
They are also called non-metallic gaskets. Usually composite sheet materials are
used with flat face flanges and low pressure class application. Non metallic
gaskets are manufactured with nonasbestos material or Compressed Asbestos
Fiber (CAF). Non-asbestos types include arimid fiber, glass fiber, Natural Rubber,
elastomer, Teflon (PTFE), and Flexible Graphite. These types of gaskets can beclassifies in to following categories
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A) Fiber gaskets
• Major advantages:
Ü Low cost
Ü Comfortable surfaces
• Major disadvantages :
Ü Possibility of blowout
Ü Rubber binder /composite
Ü Structure makes chemical compatibility complex
B) PTFE Based gaskets
• Major advantages:
Ü Highly chemically resistant
Ü Extremely soft surfaces
Ü Approved in “clean” operations such as food processing
• Major disadvantages:
Ü Low temp. limit
Ü Creep relaxation notorious
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Ü Blowout failure possible
Ü High cost
C) Graphite based gaskets
• Major advantages:
Ü Highly chemically resistant
Ü Extremely soft surfaces
Ü High temperature limit
Ü Approved in some clean operations such as nuclear industry
• Major disadvantages:
Ü Poor handleability
Ü Possibility of blowout
Ü Oxidation
2.2.2 Semi-metallic:
Semi metallic gaskets are composites of metal and nonmetallic material. The
metal is intended to offer strength and resiliency, while the nonmetallic portion
of a gasket provides conformability and sealability. Commonly used semimetallic
gaskets are Spiral wound, Metal jacketed, Camprofile and variety of metal
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reinforced graphite gaskets. Semimetallic gaskets are designed for wide range ofoperating conditions of temperature and pressure. They can be classified as:
A) Spiral Wound Gasket :
The spiral wound gaskets are used most commonly in Hydrocarbon industries.
They have been described separately below.
B) Jacketed :
Jacketed gaskets are made from non-metallic gasket material enveloped in a
metallic sheet. This inexpensive gasket arrangement is used occasionally on
standard flange assemblies, valves and pumps. Jacketed gaskets are easily
fabricated in a variety of sizes and shapes and are an inexpensive gasket for
heat exchangers, shell, and channel and cover flange joints. Their metal sealmakes them unforgiving to irregular flange finish and cyclic operating conditions.
The main features are as follows:
• Made of a metallic outer shell with either a metallic or non-metallic filler
• Very durable, easy to handle
• Less expensive
• Requires a smooth flange finish (100 rms., max)
• Poor memory (not good for cycling)
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Fig No 5
Fig No 4
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Jacketed heat exchanger gasket
• Made of a metallic outer shell with either a metallic or non-metallic filler
• Very durable, easy to handle
• Less expensive
• Requires a smooth flange finish (100 rms., max)
• Poor memory (not good for cycling)
C) Camprofile :
Camprofile gaskets are made from a solid serrated metal core faced on each side
with a soft nonmetallic material.
The term Camprofile (or Kammprofile) comes from the groove profile found on
each face of the metal core. Two profiles are commonly used: the DIN 2697
profile and the shallow profile. The shallow profile is similar to DIN profile except
that the groove depth is 0.5 mm (versus 0.75mm for DIN). The most common
facing for Camprofile gaskets is graphite. Other facings such as expanded or
sintered PTFE and CAF are also used. The Camprofile gasket combines the
strength, blowout and creep resistance of a metal core with a soft sealingmaterial that conforms to the flange faces providing a seal.
Camprofile gaskets are used on all pressure classes from class 150 to class 2500
in vide variety of service fluids and operating temperatures.
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2.2.3 Metallic:
Metallic gaskets are fabricated from one or a combination of metals to the
desired shape and size. Common metallic gaskets are Ring Joint gaskets and
Lens ring. They are suitable for high temperature and pressure applications andrequire high bolt load to seal.
A) Ring joints:
Standard Ring joint gaskets can be categorized in to three groups: Style R, RX
and BX.
Fig No 6
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Style R gaskets are either oval or octagonal. The style RX is pressure
energized adaptation of the standard style R. The BX pressure
energized are designed for use on pressure systems up to 20,000 psi.
The main features are as follows:
• Initially developed for use in petroleum industry, highpressure/temperature
• No recovery , not good for cycling
• Requires very smooth finish, 63 rms. Max.
• Manufactured in accordance with API 6A 7 ASME B16.20
FIG NO 7
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• Blow out resistant
B) Lens rings:
Lens ring gaskets have a spherical surface and are suited for use with conical
flanges. They are used in specialized high temperature and pressure applications.
Other specialty metallic seals are available, including welded membrane gaskets
and weld ring gaskets. These gaskets come in pairs and are seal welded to theirmating flanges and to each other to provide a zero leakage high integrity seal.
2.3 Spiral wound gaskets
Spiral Wound gaskets are the most common gaskets used, hence they have been
described here specially. They are used in all pressure classes from Class 150 to
Class 2500. The part of the gasket that creates the seal between the flanges
faces is the spiral wound section. It is manufactured by winding a performed
metal strip and a soft filler material around a metal mandrel. The inside and
outside diameters are reinforced by several additional metal windings with nofiller. Please refer Fig no 8 for construction details of Spiral wound gaskets
The features of Spiral Wound gaskets are as follows:
• Well established
• Wide range and combination of materials
• Variable density
• Well suited to cyclical
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• Blow out resistant
• Cryogenics to extremely high temperatures (1100 °c)
• Vacuum to high pressure(175kg/cm 2)
• Ease of flange clean-up
2.3.1 Sizing Spiral wound Gaskets
Fig No 8
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Spiral wound gaskets must be sized to ensure the spiral wound component is
seated between flange surfaces. If it protrudes beyond a raised face or into aflange bore mechanical damage and leakage may occur.
2.3.2 Variable density
Spiral wound gaskets are manufactures by alternately winding strips of metal
and soft fillers on the outer edge of winding mandrels that determine the inside
dimensions of the wound component. In the winding process, the alternating
plies are maintained under pressure. Varying the pressure during the winding
operation and / or the thickness of the soft filler, the density of the gasket can
be controlled over a wide range. As a general rule, low winding pressure and
thick soft fillers are used low-pressure applications. Thin fillers and high-pressure
loads are used for high-pressure applications. This of course would account for
the higher bolt loads that have to be applied to the gasket in high-pressure
applications. In addition to all these advantages of the spiral wound gasket, they
are relatively low cost. When special sizes are required, tooling costs are verynominal.
Gasket confined on I.D. and O.D.
Gasket I.D. = Groove I.D. + 1/16”
Gasket O.D = Groove O.D.+ 1/16”
Gasket confined on O.D. only
Gasket I.D. = Bore + Minimum ¼”
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Gasket O.D.= Recess O.D. –1/16”
Gasket unconfined I.D. and O.D.
Gasket I.D. = Seating surface I.D. + Minimum ¼”
Gasket O.D = Seating surface O.D. - Minimum ¼”
Centering guide = Bolt circle Diameter – Dia of the Bolt
Gasket Unconfined I.D. and O.D.
Gasket Dia I.D. O.D.
Up to 1” +3/64” –0 +0 –1/32”
1” to 24” +1/32” – 0 +0 – 1/32”
24”to 36” +3/64” – 0 +0 – 1/16”
36” to 60” +1/16” – 0 +0 – 1/16”
60” and above +3/32” – 0 +0 – 3/32”
2.3.3 Inner and outer Rings
For application involving raised face flanges, the spiral wound gasket is supplied
with an outer ring, for critical applications it is supplied with both outer and inner
rings. The outer ring provides the centering capability of the gasket as well as
the blow out resistance of the windings and acts as compression stop. The inner
ring provides additional load bearing capability from high bolt loading. This is
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particularly advantageous in high-pressure applications. The inner ring also acts
as barrier to the internal fluids and provides resistance against buckling of thewindings.
Reasons to use them
1. Contains and protects sealing elements
2. Prevents buckling (when properly sized)
3. Required by ASME B 16.20 for PTFE, and recommended where buckling is
a problem
4. Recommended for vacuum service
5. Directs more of the bolt load to the sealing element
6. Prevent erosion of the flange face
Loose or integral rings:
Thermal-shock conditions may damage with integral centering rings (thermal
tension may cause cracks in the core).
3.0 Gasket Materials
Gasket materials can be divided in two-category i. e. Soft or Non metal and other
one is Metal. They are described in detailed below.
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3.1 Soft gasket Materials
A “soft gasket” material is a term used when referring to a gasket material that is
easily compressed under a low bolt load. This term has been used to distinguish
the difference from a metallic gasket. A soft gasket material can be selected from
a large variety of rubbers (neoprene, viton, SBR, EPDM, etc), TFE, graphite, and
compressed non- – asbestos sheet products. Soft gaskets are used in a wide
range of applications from pipe flange, heat exchanger, compressor and bonnet
valve gaskets to name just a few. Soft gasketing material can be purchased in avariety of cut shapes or be provided in sheet or rolls.
3.1.1 Natural Rubber
Natural rubber has good resistance to mild acids and alkalis, salt and chlorine
solutions. It has poor resistance to oils and is not recommended for use with
ozone. Its temperature range is very limited and is suitable only for use from –
56°c to 93°c.
3.1.2 SBR (Styrene- Butadiene)
SBR is a synthetic rubber that has good resistance and has good resistance to
weak organic acids, alcohol’s, moderate chemicals and ketones, It is not good in
ozone, strong acids, fats, oils, greases and most hydrocarbons. Its temperature
limitations are approximately –51°c to 120°c.
3.1.3 CR (Chloroprene)
Chloroprene is a synthetic rubber that is suitable for use against moderate acids,
alkalis and salt solutions. It has good resistance to commercial oils and fuels. It is
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very poor against strong oxidizing acids, aromatic and chlorinated hydrocarbons,
Its temperature range would be from approximately –51 °c 120°c.
3.1.4 Buna-N Rubber (Nitrile, NBR)
Buna-N is a synthetic rubber that has good resistance to oils and solvents,
aromatic and aliphatic hydrocarbons, petroleum oils and gasoline’s over a wide
range of temperature. It also has good resistance to caustic and salts but only
fair acid resistance. It is poor in strong oxidising agents, chlorinated
hydrocarbons, ketones and esters. It is suitable over a temperature range ofapproximately –51°c 120°c.
3.1.5 Fluorocarbon (Viton)
Fluorocarbon elastomer has good resistance to oils, fuel, chlorinated solvents,
aliphatic and aromatic hydrocarbons and strong acids. It is not suitable for use
against amines, esters, ketones or steam. Its normal temperature range wouldbe between -26°c to 232°c.
3.1.6 Hypalon (Chlorosulfonated Polyethylene)
This material has good acid, alkali and salt resistance. It resists weathering
sunlight and ozone, oils and commercial fuels such as diesel and kerosene. It is
not good in aromatics or chlorinated hydrocarbons and has poor resistance
against chromic acid and nitric acid; its normal temperature range would be
between -45°c to 135°c.
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3.1.7 Silicones
Silicon rubbers have good resistance to hot air, they are unaffected by sunlight
and ozone. They are not, however, suitable for use against steam, aliphatic andaromatic hydrocarbons. The temperature range would be between -53 °c to
260°c.
3.1.8 EPDM (Ethylene Propylene-Diene Monomer)
This synthetic material has good resistance to strong acids, alkalis, salts and
chlorine solutions. It is not suitable for use in oils, solvents or aromaticshydrocarbons. Its temperature range would be between -56 °c to 176°c.
3.1.9 Grafoil
This is an all graphite material containing no resins or inorganic fillers. It is
available with or without a metal insertion, and in adhesive-back tape form for
pipe gaskets over 24 inches in diameter. Grafoil has outstanding resistance to
corrosion against a wide variety of acids, alkalis and sail solutions, organic
compounds, and heat transfer fluids, even at high temperatures. Its use against
strong oxidizing agents at elevated temperatures should be investigated very
carefully. In addition to being used as a gasket, grafoil makes an excellentpacking material and is also used as a filler material in spiral-wound gaskets.
3.1.10 Ceramic Fiber
Ceramic fiber is available in sheet or blanket form and makes an excellent gasket
material for hot air duct work with low pressures and light flanges. It is
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satisfactory for service up to approximately 1093 °c. Ceramic material is also used
as a filler material in spiral-wound gaskets.
3.1.11 Plastics
Of all plastics, PTFE (polytetrafluoroethylene) has emerged as the most common
plastic gasket material. PTFE’s out standing properties include resistance totemperature extremes from -95°c to 232°c (for virgin material). PTFE is highly
resistant to chemicals, solvents, caustics and acids except free fluorine and alkali
metals. It has a very low surface energy and does not adhere to the flanges.
PTFE gaskets can be supplied in a variety of filler material such a glass, carbon,
molybdenum disulfide, etc. The principal advantage in adding fillers to PTFE is toinhibit cold flow or creep relaxation.
3.1.12 Compressed non-asbestos sheeting
Early efforts to replace asbestos resulted in the introduction and testing of
compressed non-asbestos products in the 1970’s. Many of these products have
seen extensive use since that period however there have been enough problems
to warrant careful consideration in choosing a replacement material for
compressed asbestos. Most manufactures of non-asbestos sheet materials usesynthetic fibers.
3.1.13 Vegetable fiber sheet
Vegetable fiber sheet is a tough pliable gasket material manufacturer by paper
making techniques utilizing plant fibers and a glue-glycerin impregnation; it is
widely used for sealing petroleum products, gases and wide variety of solvents.
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Its maximum temperature limit is 120°c. If a more compressible material is
required, a combination cork-fiber sheet is available. The cork-fiber sheet has thesame max temperature limitation as the vegetable fiber sheet.
3.1.14 CMG
Corrugated Metal Graphite (CMG) is a high performance gasket for standard
flange or heat exchanger applications. This gasket offers:
• High sealability
• Conformity where low bolt load is available
• Maintain high bolt loads, upon re-tightening, in heat exchanger
applications.
• Heavy gauge corrugated insert for support
• Choice of insert metals
The CMG molds in place by filling in irregularities of the spaces creating a
superior seal. It maintains the seal even in harsh environment including
hydrocarbons and steam applications. You can specify CMG for applicationswhere there is:
• Low bolt loads or high available gasket stresses
• Restricted area for flange separation making it impossible for a spiral
wound type
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• A need to substitute compressed asbestos or non-asbestos gasket for a
variety of applications
3.1.15 CM-PTFE
Corrugated metal faced on both sides with expanded PTFE
(polytetrafluroethylene). The standard construction of a “CM-PTFE” features a
corrugated 316ss metal core. The design of this type gasket allows for a wide
variety of metals to select from to meet special process criteria. The PTFE
selection for the face material gives you the chemical resistance for aggressiveapplications.
CM-PTFE Benefits:
• High creep resistance
• Chemical resistance
• Conforms to the irregularities in flange faces for a tight seal with low
minimum sealing stress
• Superior memory characteristics ensure that bolts remain tight so that retorquing is not necessary
3.2 Metallic gasket Materials
3.2.1CARBON STEEL
Commercial quality sheet steel with an upper temperature limit of approximately
1000°F., particularly if conditions are oxidizing Not suitable for handling crude
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acids or aqueous solutions of salts in the neutral or acid range. A high rate of
failure may be expected in hot water service if the material is highly stressed.
Concentrated acids and most alkalis have little or no action on iron and steel
gaskets, which are used regularly for such services. Brinell hardness isapproximately 120.
3.2.2 STAINLESS STEEL 304
An 18-8 (Chromium 18-20%, Nickel 8-10%) Stainless with a maximum
recommended working temperature of 1400 °F. At least 80% of applications for
non – corrosive services can use type 304 stainless in the temperature range of –320°F to 1000°F. Excellent corrosion resistance to a wide variety of chemicals.
Subject to stress corrosion cracking and intergranular corrosion at temperature
between 8000F to 15000F. In presence of certain media for prolonged periods oftime. Brinell hardness is approximately 160.
3.2.3 Stainless Steel 304L
Carbon content maintained at a maximum of 0.03% recommended maximum
working temperature of 1400°F. Same as excellent corrosion resistance as type
304. This low carbon content tends to reduce the precipitation of carbides along
grain boundaries. Less subjected to intergranular corrosion than type 304. Brinellhardness is about 140.
3.2.4 Stainless Steel 316
An 18-12 Chromium – nickel steel with approximately 2% of molybdenum added
to the straight 18-8 alloy. Which increases its strength at elevated temperatures
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and results in somewhat improved corrosion resistance. Has the highest creep
strength at elevated temperatures of any conventional stainless type. Notsuitable for extended service within the carbide precipitation range of 800 ° to
1650°F. When corrosive conditions are severe. Recommended maximum working
temperature of 1400°F. Brinell hardness is approximately 160.
3.2.5 Stainless Steel 316L
Continuous maximum temperature range of 1400 °- 1500°F. Carbon content held
at a maximum of 0.03%. Subject to a lesser degree of stress corrosion crackingand also intergranular corrosion than type 304. Brinell hardness is about 140.
3.2.6 Stainless Steel 321
An 18-10 chromium- nickel steel with a titanium addition. Type 321 stainless has
the same characteristics as type 347. The recommended working temperature is1400° to 1500°F and in some instances 1600°F. Brinell hardness is about 150.
3.2.7 ALLOY 20
45% Iron, 24% Nickel, 20% Chromium and small amount of molybdenum and
copper. Maximum temperature range of 1400 °- 1500°F. Developed specifically
for applications requiring resistance to corrosion by sulfuric acid. Brinell hardnessis about 160.
3.2.8 ALLOY 1100
Alloy 1100 is commercially pure (99% minimum). Its excellent corrosion
resistance and workability makes it ideal for double-jacketed gaskets. The brinell
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hardness is approximately 35. For solid gaskets, strong alloys like 5052 and 3003
are used. Maximum continuous service temperature of 800 °F.
3.2.9 BRASS
Yellow brass 268 has 66% copper and 34% Zinc. Offers excellent to good
corrosion resistance in most environments, but is not suitable for such materials
as acetic acid, acetylene, ammonia, and salt. Maximum recommended
temperature limit of 500°F. Brinell hardness is 58.
3.2.10 COPPER
Nearly pure copper with trace amounts of silver added to increase its working
temperature. Recommended maximum continuous working temperature of
500°F. Brinell hardness is about 80.
3.2.11CUPRO NICKEL
Contains 69% Copper, 30% Nickel, and small amounts of manganese and iron.
Designed to handle high stresses, it finds its greatest application in areas where
high temperature s and pressures combined with high velocity and destructive
turbulence would rapidly deteriorate many less resistant alloys. Maximum
recommended temperature limit of 500 °F. Brinell hardness is about 70.
3.2.12HASTE ALLOY 276
16-18% Molybdenum, 13-17.5% Chromium, 3.7-5.3% Tungsten, 4.5-7% Iron,
and balance is nickel. Maximum temperature range of 2000 °F. Very good in
handling corrosives. High resistance to cold nitric acid of varying concentrations
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as well as boiling nitric acid up to 70% concentration. Good resistance to
hydrochloric acid. Excellent resistance to stress corrosion cracking. Brinellhardness is about 210.
3.2.13 INCONEL 600
Recommended working temperature of 2000 °F and is some instance 2150°F. Is a
nickel based alloy containing 77% Nickel, 15% Chromium and 7% Iron. Excellent
high temperature strength. Frequently used to overcome the problem of stress
corrosion. Has excellent mechanical properties at the cryogenic temperaturerange Brinell hardness ids about 150.
3.2.14 INCOLOY 800
32.5% Nickel, 46% Iron, 21% Chromium. Resistant to elevated temperatures,
oxidation, and carbonization. Recommended maximum temperature of 1600 °F.
Brine hardness is about 150.
3.2.15 MONEL
Maximum temperature range of 1500 °F. Contains 67% Nickel and 30% Copper.
Excellent resistance to most acids and alkalis, except strong oxidizing acids.
Subject to stress corrosion cracking when exposed to fluorosilic acid, mercuric
chloride and mercury, and should not be used with these media. With PTFE it iswidely used for hydrofluoric acid service. Brinell hardness is about 120.
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3.2.16 TITANIUM
Max temperature range of 2000 °F. Excellent corrosion resistance even at higher
temperatures. Known as the “ Best solution” to chloride iron attack. Resistance
to nitric acid in a wide range of temperatures and concentrations. Most alkaline
solutions have little if any affect upon it. Outstanding in oxidizing environments.Brinell hardness is about 215.
Note: -
Maximum temperature ratings are based upon hot air constant temperatures.
The presence of contaminating fluids and cyclic conditions may drastically affectthe maximum temperature range.
4.0 Application of types of gaskets
Pressure class
Gasket type Low class
150-300
Medium
class
600-900
High class
1500-2500
Max temp ofmaterials ( °C)
Non Metallic
CAF X - - 343 – 538
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Non asbestos
fiber
X - - 288
PTFE X - - 199 – 288
Graphite X - - 399
Semi Metallic
Metal jacketed X X - 399+ *
Metal reinforcedgraphite
X X - 399+ *
Spiral wound X X X 399+ *
Camprofile X X X 399+ *
Metallic
Ring joint
gaskets
- X X 343+ *
Lens ring - X X 343+ *
Machined ring - X X 343+ *
X - Applicable
- - Not applicable
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* - Depends on material
5.0 Gasket selection
The proper selection of gasket is critical to the success of achieving long- term
leaks tightness of flanged joints. Due to their wide spread usage, gaskets are
often taken for granted. Industry demands for reduced flange leakage in
environments of increasing process temperatures and pressures have led gasket
manufacturers to develop a wide variety of gasket types and materials, with new
gaskets being introduced on an ongoing basis. This rapidly changingenvironment makes, and will continue to make, gasket selection difficult.
5.1 Flange design
Flange design details, service environment, and operating performance guide the
gasket selection process. Start with the flange design. Identify the appropriate
flange standard, outlining size, type, facing, pressure rating, and materials (i.e
ASME B16.5, NPS 4, Class 1500, RF, and carbon steel). Identify the service
environment of temperature, pressure, and process fluid. It is useful to highlightgasket –operating performance.
5.2 Surface finish
Surface finish is important as it governs the thickness and compressibility
necessary in the gasket material to complete a physical barrier in the clearance
gap between flanges. However this can govern the type of material which can be
employed, and with it the ultimate performance of the gasket. Thus a resilient
material which could provide good closer with comparatively rough surfaces may
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extrude at the working pressure required, or not to be compatible with the fluid
involved or the temperature of the service, in which case a finer surface finish
may have to be employed in order to accommodate a harder material with high
closer pressure. With thinner materials it becomes necessary to provide a betterquality surface finish on the metal faces.
Table below gives required surface finish for different types of gaskets.
5.3 Selection of Gasket materials for different services
Fluid Application Gasket material
Steam(high
pressure)
Temp up to 538°C Spiral-wound comp. Asbestos or graphite
Steel, corrugated, or plain
Monel, corrugated, or plain
Steam(highpressure)
Stainless steel 12 to 14 % chromium,corrugated
Ingot iron, special ring- type joint
Temp up to 399°C Comp. Asbestos, spiral-wound
Steam(highpressure)
Temp up to 316°C Woven asbestos, metal asbestos
Copper, corrugated or plain
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Steam(low
pressure)
Temp up to 105°C Red rubber, wire inserted
water Hot, medium, and high
pressures
Black rubber, Red rubber, wire inserted
Hot, low pressures Brown rubber, cloth inserted
Hot Comp. asbestos
cold Red rubber, Wire inserted, Black rubber, Soft
rubber, Asbestos, Brown rubber, Cloth
inserted
Oils (hot) Temp up to 399°C Comp. asbestos
Temp up to 538°C Ingot iron, special ring-type joint
Oils (cold) Temp up to 100°C Cork or vegetable fiber
Temp up to 149°C Neoprene comp. asbestos
Air Temp up to 399°C Comp. asbestos
Temp up to 105°C Red rubber
Temp up to 538°C Spiral-wound comp. asbestos
Gas Temp up to 538°C Asbestos, metallic
Temp up to 399°C Comp. asbestos
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Temp up to 316°C Woven asbestos
Temp up to 105°C Red rubber
Acids Hot or cold mineral
acids
Comp. Blue asbestos
Woven blue asbestos
Ammonia Temp up to 538°C Asbestos, metallic
Temp up to 371°C Comp. asbestos
Weak solutions Red rubber
Hot Thin asbestos
Cold Sheet lead
6.0 Installation
6.1 Installation and maintenance Tips for all Gaskets: -
All too often we hear “the gasket is leaking”. This is not strictly true. It is the
joint that leaks and the gasket is one component of several that make up the
joint. Unfortunately, the gasket is expected to make up for any and all
deficiencies in design, improper installation procedures and to compensate for all
flange movement due to thermal changes, pressure changes, vibrations etc. In
many cases the gasket will do these things but only when careful attention isgiven to all the aspects of gasket selection, design and installation.
6.2 Gasket Installation procedures: -
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Step 1 Inspect the gasket seating surfaces. Look for tool mark, cracks, scratches or
pitting by corrosion and make sure that the gasket-seating surface is proper for
the type of gasket being used. Radial tool marks on a gasket-seating surface are
virtually impossible to seal regardless of the type gasket being used; therefore
every attempt must be made to minimize these. If remachining of flanges is not
possible, investigate the use of patching cements such as Devcon that can befairly effective in repairing the gasket seating surfaces.
Step 2 Inspect the gasket. Make sure the material is as specified, look for any possible
defects or damage in the gasket.
Step 3 Inspect and clean each stud or bolt each nut, each washer, and the facing on
the flanges against which the nuts will rotate. Look for severe galling, pitting,
etc. If any of the above mentioned items are damaged beyond repair, replacethat item.
Step 4 Lubricate all thread contact areas and nut facings. The importance of proper
lubrication cannot be overstressed. No joint should be made up without the
proper lubricant being applied to the threaded surfaces and to the nut facings.
When flanges will be subjected to high temperatures, the use of an anti- seize
compound should be considered to facilitate subsequent disassembly. There are
available on the market today a vast variety of an anti-seize compound should be
considered to facilitate subsequent disassembly. The better the lubricant, themore consistent will be the actual achieved bolt stress at installation.
Step 5 With raised face and flat face installation, loosely install the stud bolts on the
lower half of the flange. Insert the gasket between the flange facing to allow the
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bolts and nuts and bring all to a hand – tight or snug condition. (If the gasket is
being installed in a recess or a groove, center the gasket midway into the recessor the groove.)
Step 6 Torque bolts in a minimum of four stages as listed in steps 7,8,9 and 10 below.
Step 7 Torque the bolts up to a maximum of thirty percent of the final torque value
required following the sequence recommended. (See charts for bolting
sequence.) Number bolts so that torquing requirements can be followed. With
any gasket material, it is extremely important to follow a proper bolting
sequence. If this sequence is not followed, the flanges can be cocked. Then,
regardless of the amount of subsequent torquing, they are cocked. Then,
regardless of the amount of subsequent torquing, they cannot be brought back
parallel. This problem, of course, is maximized on metallic gaskets more so thanon nonmetallic.
Step 8 Repeat step 7, increasing the torque to approximately 60 percent of the final
torque required.
Step 9 Repeat step8, increasing the torque to the final torque value.
Step 10 On high-pressure, high-temperature applications, it is suggested that the
flanges be retightened to the required stress after 24 hours at operating
pressures and temperatures to compensate for any relaxation or creep that mayhave occurred.
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7.0 Trouble - shooting Guide
Fault Cause Remedy
Design
Insufficient gasket
stress
Insufficient bolt load Increase number of bolts
Increase Dia of bolts
Change to higher tensile
material
Gasket too thin Fit thicker gasket
Gasket too wide Reduce area of gasket
Wrong gasket type Fit gasket which requires a
lower seating Stress
Excessive gasket stress Excessive bolt load Reduce number of bolts
Change to lower tensile material
Gasket too narrow Increase area of gasket
Wrong gasket type Fit gasket which requires a
higher seating stress
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ASSEMBLY
Lack of compression Bolts insufficiently
tightened
Apply additional torque
Incorrect tighteningprocedure
Bolts should be tightened insequence
Gasket relaxed due to
operating temperature
It is recommended that once
plant reaches operating temp all
gaskets are ‘ followed –up’ to
restore compression
Bad threads Ensure nuts are a good running
fit over entire length of boltthreads
Insufficient length of
thread
Ensure threads sufficiently long
to allow nuts to make contact
with metal faces
METAL FACES
Uneven Flanges too thin Flanges should always be
sufficiently rigid not to bedestroyed by the bolt loads
The use of an IBC gasket With thin flanges and an IBC
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(ring joint) gasket the bolt load could cause
flanges to bow or bend
Flanges should be straightened
and full faced gasket used
Flanges not parallel Flange faces should always be
parallel and bolt load should
never be relied on to pull
flanges together. Please refer to
Fig no --- and no ---below.
Damaged Mechanical damage while
faces exposed
Every attention should be given
to ensure faces are clean, flat
and free from imperfection too
deep for the gasket material tocompletely fill.
Dirty or corroded Previously used jointing
compounds frequently
harden and from anuneven surface
Faces should be wire brushed
right down to clean metal.
Serration’s should also be
perfectly clean and of soundcontour.
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Old gasket not
completely removed
Spigot and recess faces should
be checked for correct fit
Incorrect surface texture Concentric grooving is ideal for
high pressures.
GASKET MATERIAL
Loss of resilience and
interface contact
Re-use of gasket The re-use of gaskets is not
recommended
Metal gaskets work
hardened
Where possible metal gaskets
such as copper should be
annealed prior to use. When
they can give further usefulservice.
Material deteriorates
rapidly
Material incompatibility
with contained fluid /
temperature
Check manufacturer’s material
recommendations and select a
material or gasket type capableof withstanding the conditions
Gasket extrudes from
faces
Too high a seating stress See recommendations under
design faults
Excessive use of jointing
compounds
Unless specified by gasket
manufacturer the use of
compounds and pastes is not
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recommended.
Incorrect dimensions Design or manufacturingerrors
Gasket should always have
clean cut edges with the bore
slightly larger than that of the
vessel or pipe
8.0 Troubleshooting Leaking Joints.
Gasket badly corroded select replacement material with improved
Gasket Extruded
Excessively
select replacement material with better cold flow
Properties, select replacement material with better load
Fig no 14
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carrying capacity - i.e., more dense.
Gasket Grossly Crushed Select replacement material with better load carrying
capacity, provide means to prevent crushing the gasket by
use of a stop ring or re-design of flanges.
Gasket mechanically
damaged due to
overhang of raised face
or flange bore.
Revise gasket dimensions to insure gaskets are proper size.
Make certain gaskets are properly centered in joint.
No apparent gasketcompression achieved
Select softer gasket material. Select thicker gasket material.Reduce gasket area to allow higher unit seating loads.
Gasket Substantially
thinner O.D than I.D.
Indicative of excessive “flange rotation” or bending. Alter
gasket dimensions to move gasket reaction closer to bolts to
minimize bending movement. Provide stiffness to flange by
means of back-up rings. Select soft gasket material to lower
required seating stresses. Reduce gasket area to lower
seating stresses.
Gasket unevenly
compressed around
circumference
Improper bolting up procedures followed. Make certain
proper sequential bolt up procedures are followed.
Gasket thickness varies
periodically around
Indicative of “ flange bridging” between bolts or warped
flanges. Provide reinforcing rings for flanges to better
distribute bolt load. Select gasket material with lower
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circumference. seating stress. Provide additional bolts if possible to obtain
better load distribution. If flanges are warped remachined oruses softer material.
9.0 SEALING LAYER MATERIALS AND SEALING STRESSES
The following table gives information regarding different types of materials
offered as sealing layer materials. Also given is recommended seating stress forreliable sealing purpose.
Fig no 15
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Temp.
(Deg.C)Seating Stress
Materi
al
Min Max
Max.Oper
ating
Pressure(
Bar)
Gas
tightn
ess
Applicatio
n Min
(N/m
m2)
Optimu
m
(N/mm2
)
Max
(N/mm2)
Graphite
-200 550 250 GoodAggressiveMedia
20 90 400
PTFE -200 250 100 GoodAggressiveMedia
20 90 400
CAF -150 450 100Moderate
Liquids 65 161 400
Silver -200 750 250 GoodAggressive
Media125 240 450
9.1 CORE THICKNESS
When a is replacing an existing gasket (eg. spiral wound gasket), It is
recommended that 4mm thick core shall be used to prevent unnecessarystresses on existing pipelines.
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For new systems, it is recommend to use 5mm thick cores. This value should be
taken into account of the design stage.
Pipe system Core thicknessSeated Thickness (Core
+ 2 sealing layers)
Existing
New
4mm
5mm
5.0mm to 5.2mm
6.0mm to 6.2mm
9.2 Gaskets consist of a metal core
(Generally Stainless Steel) with concentric grooves on either side with sealing
materials. The sealing layers (depending on the service duty) can be Graphite,
PTFE (Teflon), CAF or Metal (e.g. Aluminum or Silver). Gaskets used without
sealing layers to provide an excellent seal but there is a risk of flange surfacedamage.
o The very wide seating stress range (minimum to maximum stress) of the
gasket makes it:
§ Highly suitable for varying temperature and pressures.
§ Less sensitive to assembly faults (inaccurate bolt tensioning).
§ Suitable for light and heavily constructed flanges.
o Dependent on layer material gaskets are resistant to temperatures up to1000 o C
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Resistant to media pressures up to 250 bar.
The additional benefits are:
o When assembled the layer thickness of the sealing material is extremely
small (0.5mm) thus reducing leaks, reject rates and environmentpollution.
o The gasket will not damage the flange surface and can be easily removed.
o Reduces maintenance costs
o Emergency sealing of damaged flanges by using 1mm thick sealing layers
until the flange can be re-worked.
o Flange face protection. Gaskets will not damage the flange faces even atextreme seating load.
o Excellent performance when subject to fluctuating temperatures and
pressures.
o Direct replacement for existing gaskets. No special flange finish is
necessary.
o Eco-friendly by significant reducing leakage into the atmosphere.
1.0 Do’s & Don’ts
10.1 Do’s
Gaskets RELIANCE GROUPTRAINING MODULE
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Date: 12/13/01 Page 60 of 62
1. Apply additional torque to improve compression on gasket, which avoids
leakages.
2. Bolts should be tightened in sequence i.e. diametrically opposite and
gradually increasing load on each bolt alternately to distribute uniformload on gasket.
3. Once plant reaches operating temperature all gaskets are “followed-up” torestore compression.
4. Ensure threads sufficiently long to allow nuts to make contact with metal
faces, which gives uniform compression.
5. Check manufacturer’s material recommendations and select a gasket,which is capable of withstanding the conditions.
6. Use better load carrying capacity material.
10.2 Don’ts
1. The re-use of gaskets is not recommended.
2. Do not select the under size gaskets which will protrude into the flow path
of the fluid and could create turbulence.
3. Do not use of pastes or compounds unless specified by manufacturer,
which reduces the friction between the gasket, and thereby load bearingproperties.
4. Do not use of seating surfaces having cracks, scratches, pitting etc.
Gaskets RELIANCE GROUPTRAINING MODULE
Module No.RG-CM-G - 001
AuthorRSG / MGC
Rev: 0
Approved bySVKR
Date: 12/13/01 Page 61 of 62
5. Do not grease the gasket, as it is incompressible.
11.0 Standards
There are variety of standards that govern dimensions, tolerances and
fabrication of gaskets. The more common international standards are:
11.1 Materials
British
BS 1832 – Specification for oil resistant compressed asbestos fiber jointing.
BS 2815 – Specification for compressed asbestos fiber jointing.
Grade A – For water, inert gases, inert liquids or steam up to 64
bar and 510°c
Grade B – For water, inert gases, inert liquids or steam up to 16
bar and 230°c
German
DIN 3754 – Specification for various compressed asbestos fiber grades.
American
ASTM F104 – Classification system for non- – metallic gasket materials.
11.2 Dimensions
Gaskets RELIANCE GROUPTRAINING MODULE
Module No.RG-CM-G - 001
AuthorRSG / MGC
Rev: 0
Approved bySVKR
Date: 12/13/01 Page 62 of 62
British
BS 3063 – Dimensions of gaskets for pipe flanges to BS 10, BS 1770 and BS2035.
BS 4865 – Dimensions of gaskets for pipe flanges to BS 4505, BS 4622 and
BS4722.
Part 1 – Dimensions of non- - metallic gaskets for pressures up to 64bar.
Part 2 – Dimensions of metallic spiral wound gaskets for pressures 10
to 250 bar.
BS 3381 – Design material and dimensions of metallic spiral wound gaskets foruse with flanges to BS 1560.
American
ASME B16.20 – Dimensions of metallic gaskets for pipe flanges, ring joint, spiral
wound and jacketed
ASME B16.21 – Dimensions of non-metallic flat gaskets for pipe flanges
API 601 – Metallic gasket for piping.
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