Expansion Joint Terminology

Abrasion Resistance: The ability to withstand the wearing effect of a rubbing surface. In elastomers, abrasion is a complicated process, often affected more by compounding and curing than by the elastomer. Soft, resilient compounds, such as pure gum rubber are frequently specified.

Adhesion: The strength of bond between cured rubber surfaces or cured rubber surface and a non-rubber surface.

Ambient Temperature: The environment temperature surrounding the object under consideration.

Anchor: Terminal point or fixed point in a piping system from which directional movement occurs.

Angular Movement: The movement which occurs when one flange of the expansion joint is moved to an out of parallel position with the other flange. Such movement being measured in degrees.

Arch: That portion of an expansion joint which accommodates the movement of the joint.

ASTM INTERNATIONAL: This organization has developed methods of testing and classifying elastomers as well as setting standards, such as ASTM F 1123-87, Standard Specification for Non-Metallic Expansion Joints.

Atmospheric Cracking: Cracks produced on surface of rubber articles by exposure to atmospheric conditions, especially sunlight, ozone and pollution. Chlorobutyl, EPDM, CSM, Neoprene and Fluorelastomers are all highly resistant compounds.

Average Burst: Used by a manufacturer to determine Maximum Allowable Working Pressure. The average burst pressure is determined from a large number of burst tests on specimens of equal size, construction and grade.

Axial Compression: The dimensional reduction or shortening in the face-to-face parallel length of the joint measured along the longitudinal axis.

Axial Elongation: The dimensional increase or lengthening of face-to-face parallel length of the joint measured along the longitudinal axis.

Axial Extension: The dimensional lengthening of an expansion joint parallel to its longitudinal axis. Such movement being measured in inches or millimeters.

Top of Page

Baffle: A sleeve extending through the bore of the expansion joint with a full face flange on one end. Constructed of hard rubber, metal or Fluoroplastic, it reduces frictional wear of the expansion joint and provides smooth flow, reducing turbulence.

Bellows: See Arch or Expansion Joint.

Bench Test: A modified service test in which the service conditions are approximated, but the equipment is conventional laboratory equipment and not necessarily identical with that in which the product will be employed.

Bending Modululs: A force required to induce bending around a given radius; hence a measure of stiffness.

Blister: A raised spot on the surface or a separation between layers, usually forming a void or air-filled space in the rubber article.

Bloom: A natural discoloration or change in appearance of the surface of a rubber product caused by the migration of a liquid or solid to the surface. Examples: sulphur bloom, wax bloom. Not to be confused with dust on the surface from external sources.

Body: Carcass of the expansion joint.

Body Rings: Wire or solid steel rings embedded in the carcass used as strengthening members of the joint.

Bolt Hole Pattern or Drill Pattern: The systematic location of bolt holes in the expansion joint flanges, where joint is to be bolted to mating flanges.

Bore: A fluid passageway, normally the inside diameter of the expansion joint.

Burst Test: A test to measure the pressure at which an expansion joint bursts.

Capped End: A seal on the end of a sleeve joint or flange to protect internal reinforcement.

Carcass: Body of the expansion joint.

Cemented Edge: An application of cement around the edges of an expansion joint with or without internal reinforcement for protection or adhesion.

Cemented End: A capped end accomplished by means of cement.

Chalking: Formation of a powdery surface condition due to disintegration of surface binder or elastomer, due in turn to weathering or other destructive environments.

Coefficient of Thermal Expansion: Average expansion per degree over a stated temperature range, expressed in a fraction of initial dimension. May be linear or volumetric.

Cold Flow: Continued deformation under stress.

Compensator: See Expansion Joint

Compression Set: The deformation which remains in rubber after it has been subjected to and released from a specific compressive stress for a definite period of time, at a prescribed temperature.

Concurrent Movements: Combination of two or more types (axial or lateral) of movement.

Conductive: A rubber having qualities of conducting or transmitting heat or electricity. Most generally, applied to rubber products capable of conducting static electricity.

Connector: See Flexible Connector.

Control Rods or Units: Devices usually in the form of tie rods, attached to the expansion joint assembly whose primary function is to restrict the bellows axial movement range during normal operation. In the event of a main anchor failure, they are designed to prevent bellows over-extension or over-compensation while absorbing the static pressure thrust at the expansion joint, generated by the anchor failure.

Convolution: See Arch.

Coupling: See Expansion Joint.

Cracking: See Atmospheric

Cracking, Flex Cracking Crazing: See Atmospheric Cracking

Top of Page

Design Pressure: The maximum high temperature that the expansion joint is designed to handle during normal operating conditions. Not to be confused with excursion temperature.

Design Temperature: The maximum high or low temperature that the expansion joint is designed to handle during normal operating conditions. Not to be confused with excursion temperature.

Diameter, Inside: The length of a straight line through the geometric center and terminating at the inner periphery of an expansion joint.

Directional Anchor: A directional or sliding anchor is one which is designed to absorb loading in one direction while permitting motion in another. It may be either a main or intermediate anchor, depending upon the application involved. When designed for the purpose, a directional anchor may also function as a pipe alignment guide.

Drill Pattern: They systematic location of bolt holes on the mating flange to which the expansion joint will be attached. Usually meets a specific specification.

Duck: A durable, closely woven fabric.

Durometer: A measurement of the hardness of rubber. (also see Hardness).

Eccentricity: A condition in which the inside and outside of two diameters deviate from a common center.

EJMA: Expansion Joint Manufacturers Association (Metal Expansion Joints).

Elasticity: The ability to return to the original shape after removal of load without regard to the rate of return.

Electrical Resistivity: The resistance between opposite parallel faces of material having a unit length and unit cross section. Typically measured in Ohms/cm.

Elongation: Increase in length expressed numerically as a fraction or a percentage of initial length.

Enlarged End: An end with inside diameter greater than that of the main body of an expansion joint.

Excursion Temperature: The temperature the system could reach during an equipment failure. Excursion temperature should be defined by maximum temperature and time duration of excursion.

Top of Page

Face-to-Face (F/F): Dimension between the pipe flange faces to which the expansion joint will be bolted. This is also the length of the expansion joint when the system is in the cold position. Also see Pre-Compression and Pre-Set.

Fatigue: The weakening or deterioration of a material caused by a repetition of stress or strain.

Flange: See Integrally Flanged Type Expansion Joint.

Flanged End: Turned up or raised end made so that it can be bolted to an adjacent flange.

Flexible Connector: See Expansion Joint.

Flex Cracking: A surface cracking induced by repeated bending or flexing.

Flex Life: See Cycle Life.

Floating Flange: Metal flange which is grooved to contain the bead on each end of an expansion joint. The flange floats until lined up with mating bolt holes and bolted in place, and is used on spherical expansion joints.

Fluorelastomers: Highly resistant compounds.

Free Length: The linear measurement before being subjected to a load or force.

Friction: A rubber compound applied to an impregnating a fabric, usually by means of a calender with rolls running at different surface speed; hence the name “friction”. The process is called “frictioning”.

Frictioned Fabric: A fabric with a surface treatment which will bond two surfaces together when interposed between the surfaces. Also may be used to adhere to only one surface.

Top of Page

Hardness: Property or extent of being hard. Measured by extent of failure of the indentor point of any one of a number of standard hardness testing instruments to penetrate the product. (Also see Durometer.)

Heat Resistance: The ability of rubber articles to resist the deteriorating effects of elevated temperatures.

Helix: shape formed by spiraling a wire or other reinforcement around the cylindrical body of a rubber pipe.

Hydraulic Pressure: A force exerted through fluids.

Installed Length: See Face-to-Face.

Integrally Flanged Type Expansion Joint: An expansion joint in which the joint flanges are made of the same rubber and fabric as the body of the joint.

Lateral Deflection or Lateral Movement: Movement ore relating displacement of the two ends of the joint perpendicular to its longitudinal axis.

Lateral Offset: Refer to Lateral Deflection or Lateral Movement.

Limit Rods: Rods placed across an expansion joint from flange to flange to minimize possible damage to the expansion joint caused by excessive motion of the pipeline.

Lined Bolt Hole: A method of sealing exposed fabric in a bolt hole.

Liner: A sleeve extending through the bore of the expansion joint with a full face flange on one end. Constructed of hard rubber, metal or Fluoroplastic, it reduces frictional wear of the expansion joint and provides smooth flow, reducing turbulence.

Top of Page

Main Anchor: A main anchor is one which must withstand all of the thrust due to pressure, flow and spring forces of the system.

Mandrel: A form used for sizing and to support the expansion joint during fabrication and/or vulcanization. It may be rigid or flexible.

Mandrel Built: An expansion joint fabricated and/or vulcanized on a mandrel.

Maximum Burst: The theoretical (predetermined) burst pressure of an expansion joint.

Metal Reinforcement: Wire or solid steel rings embedded in the carcass used as strengthening members of the joint.

Misalignment: The out of line condition that exists between the adjacent faces of the flanges.

Movements: The dimensional changes which the expansion joint is designed to absorb, such as those resulting from thermal expansion or contraction. See Angular Movement, Concurrent Movement, Resultant Movement, Lateral Movement, Torsional Movement, Thermal Movement, Transverse Movement.

NMEJ: Non-Metallic Expansion Joint Division, Fluid Sealing Association.

O-A-L: Alternative term for the face-to-face dimension of the overall length of an expansion joint.

Oil Resistant: The ability to withstand the deteriorating effects of oil (generally refers to petroleum) on the physical properties.

Oil Swell: The change in volume of rubber due to absorption of oil.

Open Arch: Rubber face flange of sufficient thickness to form a tight seal against the metal flanges without the use of gaskets.

Operating Temperature: The temperature at which the system will generally operate during normal conditions.

Top of Page

Permeability: The ability of a fluid or gas to pass through an elastomer.

Permanent Set: The deformation remaining after a specimen has been stressed in tension or compression a prescribed amount for a definite period and released for a definite period.

Pipe Alignment Guide: A pipe alignment guide is framework fastened to some rigid part of the installation which permits the pipeline to move freely in only one direction along the axis of the pipe. Pipe alignment guides are designed primarily for use in applications to prevent lateral deflection and angular rotation.

Pipe Sleeve: See Compression Sleeves.

Ply: One concentric layer or ring of material, such as fabric plies in an expansion joint.

Pre-Compression: Compressing the expansion joint (shortening the F/F) so that in the cold position the joint has given amount of compression set into the joint. The purpose of pre-compression is to allow for unexpected or additional axial extension. This is performed at the job site.

Pre-Set: Dimension that joints are deflected to insure that desired movements will take place. See Lateral.

Proof Pressure Test: See Hydrostatic Test.

Pump Connector: See Expansion Joint.

Reducers: Expansion joints used to connect piping of unequal diameters.

Reinforcement: Flexible and supporting member between tube and cover; wire or solid steel rings embedded in the carcass as strengthening members of the joint.

Resultant Movement: The net effect of concurrent movement.

Retaining Rings: Used to distribute the bolting load and assure a pressure tight seal.

RMA: The Rubber Manufacturers Association, Inc. now known as American Rubber Products Manufacturers

Top of Page

SAE: The Society of Automotive Engineers. This organization has developed methods of testing and classifying elastomers.

Service Test: A test in which the expansion joint is operated under service conditions in the actual equipment.

Soft Cuffs: Designed to slip over the straight ends of the open pipe and be held securely in place with clamps.

Soft End: An end in which the rigid reinforcement of the body, usually wire, is omitted.

Specific Gravity: The ratio of the weight of a given substance to the weight of an equal volume of water at a specified temperature.

Static Wire: A wire incorporated in an expansion joint for conducting or transmitting static electricity.

Straight End: An end with inside diameter the same as that of the main body.

Sun Checking: See Atmospheric Cracking

Tapers: Reducing expansion joints used to connect piping of unequal diameters.

Temperature: See Ambient Temperature, Design Temperature, Excursion Temperature, Operating Temperature.

Tensile Strength: the force required to rupture a specimen. “Dumbbell” specimens are cut from flat stock by a die of specified shape. Large elongations require special considerations in holding specimens and measuring the test results.

Testing: See Bench Test, Burst Test, Hydrostatic Test, Service Test.

Thermal Movements: Movements created within the piping system by thermal expansion. Can be axial, lateral or torsional.

Top Hat Liner: Consists of a sleeve extending through the bore of an expansion joint with a full face flange on one end.

Torsional Movement: The twisting of one end of an expansion joint with respect to the other end about its longitudinal axis.

Tube: A protective, leak proof lining made of synthetic or natural rubber as the service dictates.

Under Gauge: Thinner than the thickness specified.

Van Stone Flange: A loose, rotating type flange, sometimes called a lap-joint flange.

Wire Reinforced: A product containing metal wire to give added strength, increased dimensional stability or crush resistance. See Reinforcement.

Wrap Marks: Impressions left on the cover surface by the material used to wrap the expansion joint during vulcanization. Usually shows characteristics of a woven pattern and wrapper with edge marks.

Top of Page