GASKET - Seabird Groups surface than non-metallic gaskets. GASKET - Classification • Non-metallic...

GASKET

• A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage while under compression.

• Gaskets allow perfect mating surfaces on machine parts where they can fill irregularities. Gaskets are commonly produced by cutting from sheet materials, such as gasket paper, rubber, silicone, metal, cork, felt, neoprene, nitrile, fiber glass, PTFE or Teflon

GASKET

• It is usually desirable that the gasket be made from a material that is to some degree yielding such that it is able to deform and tightly fills the space it is designed for, including any slight irregularities. A few gaskets require an application of sealant directly to the gasket surface to function properly.

• Gaskets are also made entirely of metal and rely on a seating surface to accomplish the seal.

• Gaskets for high pressure systems may contain asbestos.

GASKET

• Since it is expensive to grind and lap joint faces of flanges to obtain fluid-tight joints, a gasket of some softer material is usually inserted between contact faces.

• Tightening the bolts causes the gasket material to flow into the minor machining imperfections, resulting in a fluid-tight seal.

• Effective gasket widths are given in various sections of the ASME Boiler and Pressure Vessel Code.

GASKET

ASME Standard for Gasket Materials

• ASME B16.20- Metallic Gaskets for Pipe Flanges, Ring Joint, Spiral Wound and Jacketed

• ASME B16.21- Nonmetallic Flat Gaskets for Pipe Flanges

GASKET – ASME Standards

BS & API Standard for Gasket Materials

• BS 4865 Part 1 Flat Ring Gaskets to Suit BS4504 and DIN Flange

• BS 3381 Spiral Wound Gaskets to Suit BS 1560 Flanges

• API 6A Specification for Wellhead and Christmas Tree Equipment

GASKET – BS & API Standards

Requirements for a gasket are:

– Good compressibility and face adaptability

– Good recovery

– Strength

– Limited relaxation

– Chemical resistance

– Temperature resistance

GASKET - Requirements

GASKET - Classification

• Metallic or Semi-metallic Gaskets:

– Consists of metal or a combination of metal parts and

non metal parts.

– Suitable for medium and high pressure applications.

– Metallic gaskets require a much higher quality of the

sealing surface than non-metallic gaskets.


• Non-metallic Gaskets:

– Used in low to medium pressure applications

– Up to nominal pressures of 40 or 63 bars on the

raised face

– Up to 200 bars in tongue grooved flanges.


1. Corrugated Metal Gaskets:

A metallic or semi-metallic gasket system.

High sealing pressure at the metal corrugation

High blow out resistance

In case of metal to metal, a perfect flange surface (Ra < 3,2) is required

GASKET - Metallic or Semi-metallic

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1. Corrugated Metal Gaskets:


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2. Metal Jacketed Gaskets:

A semi-metallic gasket system.

• The gasket consists of a soft filler encapsulated with a metal cover.

• The metal jacket provides compressive strength and blow out resistance.

• The filler provides compressibility and resilience.

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Profile shapes: Profile S6 or S12

Metal cover: Carbon steel, SS, monel, copper, etc.

Fillers: CSF, expanded graphite etc

Dimension: From 250 mm to 3000 mm


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2. Metal Jacketed Gaskets:- Strength & Drawback

Good shelve life

Robust, can be handled and installed without special care

Wide range of shapes

Requires a good flange surface (Ra < 1,6) because of metal to metal sealing


3. Camprofile (Grooved) Gaskets:

A semi-metallic gasket system.

• Centering (outer) ring made of special steel

• Cam-profiled (sealing) ring made of special steel

• Soft covering layer made of graphite, PTFE, ..

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3. Camprofile (Grooved) Gaskets:

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3. Camprofile (Grooved) Gaskets :- Strength & DrawbackThe soft cover adapts flange surfaces with Ra < 6,3

The soft covering layer is trapped in the tread and can not be extruded into the gap

The trapped graphite provides good compressibility and resilience

The cam profiled ring can be re-used again several times

A good quality camprofile gasket can be very expensive

Standard material of core: CS, SS 316L, SS 304, SS 321, other materials-on demand

Material of soft cover: CSF, expanded graphite, PTFE

Dimensions: From 250 mm to 5000 mm


4. Ring Joints:

A metallic gasket system.

• The ring type joint was initially developed for use in the petroleum industry, where high pressure/temperature applications necessitated the need for a high integrity seal.

• They are mainly used in the oil field on drilling and completion equipment.

• Ring type joints are also commonly used on Valves and pipework assemblies, along with some high integrity pressure vessel


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4. Ring Joints :

• Manufactured from a variety of metals and alloys, usually oval or octagonal in cross-section, depending on the flange design.

• Oval and Octagonal RTJ's are designed to seal pressures of up to 6,250 psi in accordance with ASME B16.20 and up to 5,000 psi in accordance with API 6A pressure ratings.

• Most applied type is style R ring that is machined to tight manufacturing tolerances in accordance with the relevant standards, to ensure correct installation in standard API 6B and ASME B16.5 Ring Type Flanges.


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4. Ring Joints:


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R Oval R OctagonalRX

BX

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4. Ring Joints :- Strength & Drawback

Very safe and reliable sealing system; will be always applied,

when aggressive media or explosive gases are involved;

Risk in the choice of ring joint material: the ring joint material

must be softer than the flange material.

Metal to metal sealing; requires therefore good (Ra < 1,6)

flange surface


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4. Ring Joints :- Protective Coating

In accordance with API Specifications, soft iron, low carbon

steel, and other ferrous materials ring type joints are

protected from corrosion with electroplated zinc or cadmium

to a maximum thickness of 0.0005 in.


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4. Ring Joints :-Profile Shapes: R oval, R octagonal, RX, BX

Standard Metals: soft iron, LC carbon, range of SS; other materials on demand


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Dimensions and Tolerances of Type R Ring Gaskets ASME B16.20 to be used with RTJ flanges ASME B16.5 & B16.47 series A


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5. Spiral Wound Gaskets:

A Semi-metallic gasket system.

• Centering (outer) ring made of steel

• A spiral wound V-shaped metal strip filled with graphite, PTFE, ceramic, mica, ....

• Inner ring made of steel


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5. Spiral Wound Gaskets :- Strength & Drawback

Covers a wide pressure and temperature range and is therefore a real multi purpose (universal) gasket

The spiral wound gasket does not stick to the flange surface and can be easy removed

Has a good shelve life and requires no special care during handling and installation

Good resilience because of the V-shaped metal strips

Very popular gasket system and therefore good availability

Needs very parallel flange faces

Quality control difficult, as the quality of winding and the welding cannot be checked


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5. Spiral Wound Gaskets:

Standard Sizes: Acc. to EN, ASME/ANSI, BS, DIN; standard sizes (from 15 mm to 3200 mm are also available)

Standard Fillers: Expanded graphite, PTFE, ceramic, mica

Thickness of Fillers: From 2.5 mm up to 7.2 mm (standard thickness 4.8 mm)

Standard Metals: Low carbon steel (paint or zinc plated finish), SS 316L, SS 304, SS 321, monel and other exotic materials are on demand


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GASKET – Spiral Wound

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Dimensions of Spiral Wound Gaskets ASME B16.20used with Raised Face flanges ASME B16.5


For other pressure class refer ASME B16.20


Suggested Compressed thickness of Gaskets

1. Fibre Reinforced Gaskets:

• Fibre reinforced gaskets are either cut or punched toshape out of fibre reinforced sheet material whichconsisting of fibres, fillers and binders.

• The quality and composition of this components andthe production process determine the gasketproperties.

• NBR is used as a high quality binder

• Commonly used fibres are Aramide Fibre, CarbonFibre, Cellulose Fibre, Glass Fibre, Mineral Fibre

• Aramide is the most important fibre used because ofits outstanding technical properties

GASKET - Non metallic

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1. Fibre Reinforced Gaskets :- Strength & Drawback

Cheap and good availability

Easy to cut/punch to size

Limited in temperature resistance due to the rubberbinder


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1. Fibre Reinforced Gaskets :-


2. Graphite Gaskets:

• Graphite gaskets are made from pure graphite sheetsby means of drilling or cutting.

• It has good corrosion resistance, high / lowtemperature resistance, good compression resilientand high intensity, all kinds of round, complicatedgeometric gaskets.

• Widely used in pipes, valves, pumps, pressurevessels, heat exchangers, condensers, generators, aircompressors, exhaust pipe, refrigerator, etc.


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2. Graphite Gaskets:

Reinforced Graphite (Semi Metallic)

• Graphite gasket are reinforced by metal.

• It has good corrosion resistance, high / low temperature, good compression resilient and high intensity, and a variety of round, complicated geometric gaskets

• Widely used in pipes, valves, pumps, pressure vessels, heat exchangers, condensers, generators, air compressors, exhaust pipe, chillers

GASKET

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2. Graphite Gaskets:- Strength & Drawback

Can follow easy any flange irregularity, Ra < 12,5

No creeping

Graphite is readily damaged, so requires more carein handling and storage

No resistance in oxidizing environments


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2. Graphite Gaskets:- Graphite sheets from which the required diameter can be cut


metal reinforcement

3. PTFE (Poly Tetra Fluoro Ethylene) :-

PTFE is generally used because of its outstandingchemical resistance.

Attacked only by molten alkali metals and fluorinegas

Has excellent anti-stick and dielectric properties.

Usually the leak rates are remarkably low.

Very dense sealing material.

Adapts perfect to the flange.


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3. PTFE :- Drawback

Creeping and poor mechanical properties.

Limited temperature resistance. If PTFE (e.g.

Fluolion) products are heated to elevated

temperatures, fumes will be produced which may

give unpleasant effects, if inhaled.


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3. PTFE :-


4. Rubber Gaskets:

Rubber gaskets are cut or punched to shape from industrial manufactured rubber sheets made from industrially produced rubber.

Adapts very good to the flange

Best resilience

Good sealing material

Very limited temperature resistance

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GASKET - Non-metallic

4. Rubber Gaskets:


Dimensions of Non-Metallic Flat Gaskets ASME B16.21

to be used with Raised Face flanges ASME B16.5

Non Metallic GASKET - Dimensions

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Insulation gasket

• Insulation sets are often used in petrochemical applications electrically isolate two mating flanges to reduce the likelihood of creating a galvanic cell which would result in corrosion of the flanges and pipe work.

• Insulation sets are also used to prevent the flow of electrostatic charge to reduce sparking in hazardous environment.

• Used when two different materials are joined together to prevent corrosion.

GASKET – Insulation

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GASKET – Materials selection

GASKET – Colour Coding

Gaskets are colour coded to help expedite the

selection and identity of the gaskets.

The colour of the outside edge of the centering

ring identifies both the winding and filler materials.

The metallic winding filler materials are

designated by colour stripes at equal intervals on

the outside edge of the centering ring.

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ASME B16.20

Colour Code

Chart

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GASKET - Tightening

• Gaskets should be tightened evenly in at least three or even four stages using an opposed-pattern as illustrated here.

• Final pass around all of the bolts at the end is suggested to ensure that all remain tight.

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GASKET – joint Integrity

Overall joint integrity is essentially a function of three main criteria:

• Correct gasket selection to suit the operating conditions and the overall bolted joint strength / stiffness

• Quality of the joint components – the gasket manufacture, flange and bolt materials etc.

• Installation competence – ensuring that the gasket is fitted correctly, with the design seating stress

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GASKET - Troubleshooting

GASKET - Installation

Do’s and Don’ts:

Mating flanges should be of the same type and correctly aligned.

Fasteners should be selected to ensure that they do not exceed their elastic limit at the required tension.

Do not re-torque elastomer bound compressed non-asbestos gaskets after exposure to elevated temperatures. (They may well have hardened and are at risk of cracking.)

Ensure that fasteners show no signs of corrosion, which might affect their load bearing capacity.



Nuts should have a specified proof load 20% greater than the UTS of the fastener.

Hardened steel washers of the same material as the nuts should always be used.

A thread lubricant or anti-galling compound should be used on bolting as appropriate, but only a thin, uniform coating should be applied. Where stainless steel is used, it should be ensured that such coatings are suitable for use.

Fasteners and/or gaskets should never be re-used.

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Gaskets should be kept as thin as possible.

Gaskets should never be ‘hammered-out’ against the flange. Not only can this cause damage to the flange, it will also damage the gasket material and thereby reduce gasket performance.

When cutting full-face gaskets, the bolt holes should be cut first, followed by the gasket outer and inner diameters. Note that if the bolt holes are fairly close to the gasket O/D, then punching-out the holes last may produce enough stress to crack the gasket at this point.

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Good quality gaskets should always be procured from reputable suppliers only.

Gaskets should be stored in a cool dry place, away from heat, humidity, direct sunlight, ozone sources, water, oil and chemicals. They should also be stored flat (i.e. not hung on hooks).

Avoid the use of Jointing Compounds and pastes –these can lubricate the flange-gasket interface and encourage stress relaxation effects.

Thanks

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GASKET - Seabird Groups surface than non-metallic gaskets. GASKET - Classification • Non-metallic...

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Transcript of GASKET - Seabird Groups surface than non-metallic gaskets. GASKET - Classification • Non-metallic...