Gaskets

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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.

TABLE OF CONTENTS

Sr. No. Description Page No

1.0 Introduction 06

1.1 Why Gaskets Are Use 06

1.2 How Gasket Seal 07

1.2.1 Gasket Seating Stress “Y” 09

1.2.2 Gasket Factor “M” 09

2.0 Type of Gaskets 13

2.1 Based on Shape 13

2.2 Based on Material of Construction 15

2.2.1 Soft Sheet Gaskets 15

2.2.2 Semi Metallic Gasket 17

2.2.3 Metallic Gaskets 21

2.3 Spiral Wound Gaskets 23

3.0 Gasket Materials 27

3.1 Soft Gasket Materials 28 3.2 Metallic Gasket Materials 33 4.0 Application of Types of Gaskets 38

5.0 Gasket Selection 40

5.1 Flange Design 40

5.2 Surface Finish 40

5.3 Selection of Gasket Materials for different services 43

6.0 Installation 45

7.0 Trouble Shooting Guide 50 8.0 Trouble shooting Leaking Joints 54 9.0 Sealing layer Material and Sealing Stresses 56

9.1 Core Thickness 57

9.2 Gasket Consist of a Metal Core 58

10 Do’s & Don’ts 59

11 Standards 61

11.1 Material Standards 61 11.2 Dimension Standards 61

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 the minor 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 impossibility either 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 a

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 in the 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 contact with 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 the confined 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 of safety at the same pressure.

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 seal is provided by bolting compressing the gasket.

TYPICAL JOINT DIAGRAM

H

H

Hydrostatic end force in lbs

∆

F

F

W

Total tightening force required to seal joint in lb

FIG NO 1A

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 and allowable 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

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 or some 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 ξ

fiber:

*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

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

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

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 and load 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 various standards. The two most common types of gaskets are:

FIG NO 2

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 be classifies in to following categories

A) Fiber gaskets

•

•

Ü Structure makes chemical compatibility complex

B) PTFE Based gaskets

•

Ü Highly chemically resistant Ü Extremely soft surfaces

Ü Approved in “clean” operations such as food processing

•

Ü Low temp. limit

Ü Blowout failure possible Ü High cost

C) Graphite based gaskets

•

Ü Highly chemically resistant Ü Extremely soft surfaces Ü High temperature limit

Ü Approved in some clean operations such as nuclear industry

•

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

reinforced graphite gaskets. Semimetallic gaskets are designed for wide range of operating 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 seal makes 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)

Fig No 5 Fig No 4

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 sealing material 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.

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 and require high bolt load to seal.

A) Ring joints:

Standard Ring joint gaskets can be categorized in to three groups: Style R, RX and BX.

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, high pressure/temperature

• No recovery , not good for cycling

• Requires very smooth finish, 63 rms. Max. FIG NO 7

• 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 their mating 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 no filler. 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

• Blow out resistant

• Cryogenics to extremely high temperatures (1100°c)

• Vacuum to high pressure(175kg/cm2)

• Ease of flange clean-up 2.3.1 Sizing Spiral wound Gaskets

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 a flange 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 very nominal.

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 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

particularly advantageous in high-pressure applications. The inner ring also acts as barrier to the internal fluids and provides resistance against buckling of the windings.

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.

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 a variety 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)

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 of approximately –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 would be 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.

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 and aromatic 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 aromatics hydrocarbons. 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 excellent packing 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

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 to temperature 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 to inhibit 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 use synthetic 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.

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 the same 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 applications where there is:

• Low bolt loads or high available gasket stresses

• Restricted area for flange separation making it impossible for a spiral wound type

• 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 aggressive applications.

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 re torquing 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

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 is approximately 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 of time. 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. Brinell hardness is about 140.

3.2.4 Stainless Steel 316

and results in somewhat improved corrosion resistance. Has the highest creep strength at elevated temperatures of any conventional stainless type. Not suitable 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 cracking and 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 is 1400° 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 hardness is 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

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

as well as boiling nitric acid up to 70% concentration. Good resistance to hydrochloric acid. Excellent resistance to stress corrosion cracking. Brinell hardness 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 temperature range 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 is widely used for hydrofluoric acid service. Brinell hardness is about 120.

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 affect the 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 of materials ( °C) Non Metallic CAF X - - 343 – 538

Non asbestos fiber X - - 288 PTFE X - - 199 – 288 Graphite X - - 399 Semi Metallic Metal jacketed X X - 399+ * Metal reinforced graphite 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

* - 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 changing environment 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 highlight gasket –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

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 better quality 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(high

pressure)

Stainless steel 12 to 14 % chromium, corrugated

Ingot iron, special ring- type joint Temp up to 399°C Comp. Asbestos, spiral-wound Steam(high

pressure)

Temp up to 316°C Woven asbestos, metal asbestos

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 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 is given to all the aspects of gasket selection, design and installation.

-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 be fairly 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, replace that 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, the more 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

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 recess or 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 than on 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 may have occurred.

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

ASSEMBLY

Lack of compression Bolts insufficiently tightened

Apply additional torque

Incorrect tightening procedure

Bolts should be tightened in sequence

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 bolt threads

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 be destroyed by the bolt loads The use of an IBC gasket With thin flanges and an IBC

(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 to completely fill.

Dirty or corroded Previously used jointing compounds frequently harden and from an uneven surface

Faces should be wire brushed right down to clean metal.

Serration’s should also be perfectly clean and of sound contour.

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 useful service.

Material deteriorates rapidly

Material incompatibility with contained fluid / temperature

Check manufacturer’s material recommendations and select a material or gasket type capable of 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

recommended. Incorrect dimensions Design or manufacturing

errors

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

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 gasket compression 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

circumference. seating stress. Provide additional bolts if possible to obtain better load distribution. If flanges are warped remachined or uses 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 for reliable sealing purpose.

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/mm 2₎ Graphi te -200 550 250 Good Aggressive Media 20 90 400 PTFE -200 250 100 Good Aggressive

Media 20 90 400 CAF -150 450 100 Modera

te Liquids 65 161 400

Silver -200 750 250 Good Aggressive

Media 125 240 450

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 unnecessary stresses on existing pipelines.

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 thickness Seated 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 surface damage.

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 to 1000 o _C

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 environment pollution.

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 at extreme 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

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 uniform load on gasket.

3. Once plant reaches operating temperature all gaskets are “followed-up” to restore 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 bearing properties.

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.

British

BS 3063 – Dimensions of gaskets for pipe flanges to BS 10, BS 1770 and BS 2035.

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 64 bar.

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 for use 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.