Gasket

gasket banner 4A gasket, abbreviated GSK, is a material that is used to seal the face of flanges, valves and equipment.  Gaskets can be made from materials that are soft or hard, but will compress to make a tight seal.  When compressed between two flange faces it will deform to match the surface grooves and irregularities.  A gasket must be installed properly to prevent leakage.  The surface of the flange must be clear of all foreign bodies such as dust, dirt or grease that could prevent a proper seal.  To ensure a seal through out the life of the gasket, sufficient pressure or stress should be maintained to prevent leakage.  It is very important to select the right gasket material to be used.

 

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Gasket Index

 

Gasket Design Classification

Gasket materials can be divided into three basic categories:

  • Non-metallic Gasket  -  or "soft gaskets" are made from materials that are easily compressed under a low bolt load.  They can be used with both flat and raised face flanges in low pressure applications.  Materials used are different types of rubber, PTEF, ceramic fiber, glass fiber and more.  ASME B16.21 - Nonmetallic Flat Gaskets for Pipe Flanges.
    • ring gasketRing Gasket  -
      • Ring gaskets have no bolt holes.
      • These gaskets are positioned inside the flange bolts and around the pipe bore.
      • Ring gaskets are typically used on raised face flanges.
      • When used on a raised face flange, the ring gasket is positioned on top of the raised surface of the flange.
      • An advantage of ring gaskets is that they can be installed without having to fully disassemble the joint.
      • The gasket ID and OD, thickness and the desired pressure tolerance of the gasket should be specified.
      • Used for low pressure, low temperature and noncritical applications.
      • Ring gaskets and spiral wound gaskets are used with raised face flanges.
    • full face gasketFull Face Gasket  -
      • These gasket covers the entire face of the flange.
      • Full-face gaskets are typically used on flat face flanges.
      • Full-face gaskets are cut with bolt holes which allow the insertion of the flange bolts through the gasket.
      • Used for low pressure, low temperature and noncritical applications.
      • Full face gaskets are used with flat face flanges.
      • The ID and OD must be specified together with the bolt circle diameter and the number and spacing of the bolt holes.
      • Gasket thickness and the desired pressure tolerance of the gasket should also be specified.
  • Semi-metallic Gasket  -  Made from both non-metallic and metallic materials and can operate at both high temperature and pressure applications.  They can be used with raised face, male and female, and tongue and groove flanges, and many sizes and styles.  ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed.
  • Metallic Gasket  -  Made from a combination of materials.  These gaskets are used for special applications where a tight fit is needed. Ring joint flanges (RJF) often use these gaskets.  ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed.
    • spiral wound gasketSpiral Wound Gasket  -  Spiral wound gaskets are formed by winding a metallic and nonmetallic material together in a spiral, which enhances flexibility and durability.  These gaskets can also tolerate a greater range of operating conditions, recover quickly, and accommodate flange surface irregularities.  Because they can withstand vibration, shock, and pressure and temperature fluctuations, spiral wound gaskets are ideal for pipes and pump systems.
      • Spiral wound gaskets with no Inner Ring (RW) is engineered for ASME flanges with metal windings, filler material, and a centering ring.  This style offers excellent general purpose performance for raised face flanges.
      • Spiral wound gaskets with Inner Ring (RWI) features an inner ring, spiral winding, filler material, and a centering ring for use in higher pressure applications. 
      • A forged ring that fits into the machined groove of an ring type joint flanges.
      • A metallic sealing ring.
      • Produced to specific tolerances, using using high quality materials and machining processes.
      • Used for heavy duty, high pressure, high temperature and critical applications.
      • Used with high temperatures and/or alternating pressures.
      • Selecting based upon chemical compactibility with the media and hardness of the flange.
      • The flange groove should match the ring gasket style.
      • The groove and ring gasket should be properly aligned in order to create the proper seal.
      • Gasket and flange groove must be free of imperfections and debris.
      • Ring type joint gaskets are used with ring type joint flanges.
      • Gasket Styles:
        • R  -  R type rings are used for the flange rating from Class 150 to 2500.
                • Oval  -  The original design of the R type gasket is Oval.
                • Octagonal  -  The octagonal RTJ is a modification to the oval design and provides better sealing.
        • BX  -  These gaskets are used for the Class rating of 2000 to 20,000 psi. The BX type gasket has a pressure passage hole for pressure equalization on each sealing face sides.
        • RX  -  The flange face-to-face separation will be higher when compared with the R type gasket.  RX type gaskets are normally specified up to Class 5000 flanges.
    • ring joint gasketRing-type-joint Gasket  -  These gaskets provide a high integrity, high temperature seal and are widely used in the petrochemical, oil and gas industries.  RTJ gaskets have a smooth surface finish to provide an optimal metal-to-metal seal.
    • Kammprofile Gasket  -  Kammprofile gaskets consist of a metal core with a nonmetallic outer layer.  The metal provides reinforcement, while the nonmetallic material allows the gasket to form a tight seal.
    • Tanged Graphite Gasket Sheet  -  This gasker is made with high purity flexible graphite reinforced with metallic or non-metallic inserts.  Graphite gasketing provides a reliable seal as it seals easily under moderate bolt load.  It offers superior torque retention, retains dimensional stability in high temperatures and seals tightly, even during pressure fluctuations.
    • Metal Jacketed Gasket  -  A gasket comprised of a soft pliable core inside a metallic jacket.  Almost any metal or alloy can be found in sheet form can be used as a jacket.

 

Gasket Design Consideration

  • Gssket Selection  -  Selection depends on such factors as:

    • Service Pressure
    • Service Temperature
    • Corrosion Resistance
    • Fluid Types
    • Mechanical Load affecting the Gasket
    • Cost
  • Gasket Temperature  -  For higher temperature and pressure systems, thermal stress may cause flanges to loosen which in turn reduces compression on the gasket that may cause for leaks.  It is important to consider the side effects of an elevated temperature system and proceed with the necessary caution such as re torqueing any loosened flanges from system temperature.
  • Gasket Sealing  -  Failure in a gasket may occur if the specified amount of compression between the flanges on the gasket is not maintained.  This may occur from simple loosing over time, irregularities in operation, or even just expected wear from a piping system.  Ensuring the proper compression on the gasket is being met is crucial to maintaining a good seal and seat and to prevent failure.
  • Gasket Poor Sealing  -  If the gasket is under loaded, meaning the compressive force is not enough or un even across the gasket due to poor bolting, leakage and failure may also occur.  Uneven compression leads to uneven wear which also is a major cause for premature failure.  Similarly, over compression of a gasket may cause for failure from cracking or ripping within the gasket.
  • Gasket Permeability  -  The material of the gasket is expected to wear out over time.  It is expected that over the life time of a gasket more and more compression is needed to ensure no leaks occur as the gasket wears out over time and is less able to maintain proper sealing.  Most of the time, replacing the gasket is necessary once the required compression exceeds safe limits.
  • Gasket Reusing  -  Gaskets are expected to be used only once as the wear from a single use heavily deforms the initial shape of a gasket.  It is important to identify and note whether a gasket has already been used and to not use it for more than a single application.

 

Gasket API Stamping

  • Manufacturer
  • Manufactured to standard ASME B16.20 or applicable standard.
  • Inner ring material stamp other than carbon steel.
  • Outer ring material stamp other than carbon steel.
  • Nominal pipe size and pressure class.
  • Winding material and filler material.
  • Stamping Location
    • Metaillac fillers are color coded on full rim of outer ring.
    • Non-metallic fillers are marked with color stripes on the outer ring.
    • Inner ring material stamped on inner of outter ring.

 

Gasket Installation Procedure

  • Verify that the material specified and the contents are not damaged.
  • Visually inspect and clean the pipe flange faces and apply lubrication oil to all threads.
  • Do not use old or multiple gaskets.
  • Install the gasket and align the flanges and gasket so that bolts will be centered.
  • Use alignment pins in two diametrically oposition bolt holes whenever possible to assure alignment of flanges and gasket.
  • Tighten two diametrically oposed bolts to start with remove the two alignment pins as needed.  Following the bolt tightening procedure for the correct flange size.
  • Bolts should be of sufficient length to extend through the nut approximately 1/4".

 

Gasket Datasheets

Gasket TypeDatasheets
Gasket All Gaskets
Gasket Full Face
Gasket Ring Type
Gasket Spiral Wound

 

Gasket Standards

ASME Standards

  • Nonmetallic gasket dimensions and tolerances in accordance with ASME B16.21 for ASME B16.5 and ASME B16.47 flanges.
  • Standard thicknesses are 1/16" and 1/8", but others are available.
  • Spiral wound gaskets for ASME B16.5 1/4" to 24" dimensions and tolerances in accordance with ASME B16.20.
  • Spiral wound gaskets for ASME B16.47 22" to 60" Series A (MSS SP-44) dimensions and tolerances in accordance with ASME B16.20.
  • Spiral wound gaskets for ASME B16.47 26" to 60" Series B (API Std 605) dimensions and tolerances in accordance with ASME B16.20.
  • ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed
  • ASME B16.21 - Nonmetallic Flat Gaskets for Pipe Flanges
  • ASME B16.47 - Large Diameter Steel Flanges: NPS 26 Through NPS 60 Metric/Inch Standard
  • ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through 24

ISO Standards

  • ISO 4709 - Composition cork -- Gasket material -- Classification system, requirements, sampling, packaging and marking
  • ISO 7483 - Dimensions of gaskets for use with flanges to ISO 7005

 

Gasket Glossary

A

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  • Adhesion  -  Sticking of the gasket material to either or both flanges of a mechanical assembly.
  • Adhesive  -  A compound that adheres or bonds two items togeather.
  • Antistick  -  A coating or surface treatment that prevents the gasket material from adhearing to the flange.

B

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  • Barlow's Formula  -  Relates to burst pressure, the point just before or at when a pipe or tubing fails under pressure.
  • Binder  -  The elastomer or rubber used in gasket material.
  • Blowout  -  Occures when internal pressure tends to push the gasket material out from between flanges.
  • Bolt Fracture  -  A type of fastener failure that occures when a fastener is over-tightened and causes the bolt to break.
  • Bolt Hole Distortion  -  The flange is permanently distorted directly beneath the bolt.  Caused by initial bolt torque.
  • Bolt Load  -  The load generated by a bolt when it is tightened.
  • Bolt Tightening Procedure  -  When tightening, always use the correct sequential bolt order for the flange.
  • Bolt Torque  -  A rotational moment. It is a measure of how much twisting is applied to tighten (turn) the nut on a bolt.

C

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  • Cocking  -  When the flange of a mechanical assembly is not parallel to each other.
  • Cold Flow  -  The continued deformation under stress.
  • Compressibility  -  The state of being compressed.  For a gasket, it is the percent loss of thickness when subjected to a given load.
  • Compression Set  -  The residual deformation of a material after removal of the compressive stress.
  • Cork  -  A gasket material manufactured from from the cork tree.  Corke material is typically combined with rubbers to give it greater resistance to chemicals and solvents.
  • Creep  -  Deformation with time when a part is subjected to constant stressMetals creep can occur at elevated temperature however with gasket materials it can occur at normal ambient temperatures.
  • Corrosion Resistance  -  The ability of a material to resist chemical destruction from an environment.
  • Creep Relaxation  -  A transient stress strain condition in which the strain increases concurrently with the decay of stress.
  • Crush Resistance  -  A measure of a gasket's ability to resist initial bolt load and /or extreme stress generated by the expansion of a bolted assembly upon heating.

D

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  • Deformation  -  Is measured by how much an object is deformed from its origional dimensions.
  • Density  -  The ratio of the amount of matter in an object compared to its volume.
  • Ductility  -  The ability of the material to deform before it fractures.

E

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  • Elastic Limit  -  The limiting extent to which a object my be deformed and yet return to its initial shape after removal of the deforming force.
  • Elongation  -  The increase in length expressed numerically as a fraction or percentage of the initial length.
  • Expansion  -  The increase in any linear dimension or volume.
  • Extrusion  -  Permanent displacement of part of a gasket into a gap, under the action of fluid or bolting pressure.

F

G

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  • Gasket Extrusion  -  The tendency of a gasket to flow from between flanges, particularly around bolt holes where stresses are concentrated.
  • Graphite  -  A gasket material commonly used with steam.

H

I

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  • Initial Flange Pressure  -  The stress on a gasket attained when a joint is initially tightened.
  • Isolation Gasket  -  Used to stop the current flow across metallic pipelines by separating two flanges.

J

K

L

M

N

O

P

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  • Permeability  -  The quality or condition of allowing passage of media through a material.
  • Pipe Flange  -  A bolted connection where two pieces of pipe, equipment, fittings or valves are connected together to form a piping system.
  • Preload  -  A load that sufficiently stretches the bolt / screw to give a tight joint and overcome any forces tending to pull the joint apart.
  • Pressure  -  The force exerted perpendicular to the surface of an object and is expressed as force per unit area.
  • Proof Load  -  The amount of stress that the fastener can withstand without experiencing deformation.
  • PTFE  -  A plastic used for making gaskets.  PTFE isd extremely chemically inert, and as such is resistant to chemicals and corrosives.  PTFE also has a low co-efficient friction.

Q

R

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  • Raised Face Flange  -  The most common type of flange facing is the raised face flange.  It is used in almost all applications in high and low pressures and temperatures.
  • Rubber  -  A material that is capable of recovering from large deformations quickly and forcibaly.

S

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  • Seal  -  Any device designed to prevent or control the movement of fluid from one chamber to another to exclude contaminants.
  • Sealing Stress  -  The amount of flange pressure in a flanged joint assembly to compress and seat a gasket material in order to create an effective seal.
  • Shear Strain  -  Opposing forces acting parrallel to the cross-section of a body.
  • Shear Stress  -  Tends to deform the material by breaking rather than stretching without changing the volume by restraining the object.
  • Spiral Wound Gasket  -
  • Strain  -  The deformation, stretched or compressed, of a material compared to its original length.
  • Stress  -  The force per unit area of cross-section.
  • Swelling  -  The increase volume or linear dimension of a specimen immersed in liquid or exposed to vapor.

T

U

V

W

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  • Warp  -  The lengthwise yarns in a woven fabric.
  • Weathering  -  The surface deformation of a rubber object during outdoor exposure, such as cracking, crazing or chalking.
  • Wicking  - Leakage through a gasket.
  • Working Pressure  -  The normal pressure that a system operates at.

X

Y

Z

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Creep
Isolation Gasket
Spiral Wound Gasket

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