Gasket Glossary

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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.

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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 stress.  Metals 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

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• Flange Insulating Kit  -  See Isolation Gasket
• Flat Faced Flange  -  A flange that is machined flat and does not have a ridge like a raised face or ring type joint flange.

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.

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N

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• Nominal Diameter  -  The external size diameter designated of pipe or threads.
• Nominal Pipe Size  -  See Nominal Diameter

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

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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

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• Tensile Strength  -  The maximum stress a material can resist before it starts to elongate.
• Thermal Conductivity  -  The ability to transfer heat within a material without any motion of the material.
• Thermal Expansion  -  The increase in length, area or volume due to the increase (in some cased decrease) in temperature.
• Torque  -  A measure of how much twisting is applied to a fastener.

U

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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.

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