Glossary terms relate to metal bellows, metal expansion joints, ball joints, alignment guides, strut joint and Vibrasnubs, and their related applications.
ANACONDA: A company founded in 1908 known for copper mining and manufactured products made from copper alloys. The manufacturing division was renamed Anamet Industrial and manufactured metal expansion joints, strip wound and corrugated metal hose, Vibration Eliminators®, and OEM products. Anamet Industrial was acquired by Hyspan and these products are manufactured by Hyspan subsidiary, Universal Metal Hose.
ALIGNMENT GUIDE: A devise installed adjacent to expansion joints and along pipe or copper tube runs to maintain alignment. Most alignment guides are a “spider type” which permit axial movement (pipe or tube expansion or contraction) but they are not designed to react the weight of the pipe and media (Support). Refer to Series 9500alignment guides.
ANGLE FLANGES: Flanged connections made by rolling structural angle. Commonly used in low pressure ducting. May be drilled and bolted, or edge welded.
ANGULAR ROTATION: The displacement of the longitudinal centerline of a bellows from a straight line into a circular arc. Sometimes confused with torsional rotational – see Torsion.
ANGULAR SPRING RATE: The moment (in.- lbs) per degree of angular displacement required to rotate the ends of a bellows out of plane with the bellows centerline in a circular arc. Normally measured in in.-lbs./degree. The angle is measured as the included angle between the planes of ends.
AXIAL DEFLECTION: The longitudinal centerline of the bellows remains straight with the ends parallel and the convoluted length compressed or extended.
AXIAL SPRING RATE: The force required to compress or extend the ends of a bellows with the longitudinal centerline straight and the ends parallel. Normally referred to in lbs./in. The spring rate without consideration of axial displacement is the “theoretical axial elastic spring rate”. Bellows may not remain elastic throughout their range of deflection, and as a result the spring rate is reduced for greater deflections. The Working Spring Rate takes deflection into consideration and is commonly used by manufacturers. For a complete discussion see Section C-4 of the Standards of the Expansion Joint Manufacturers Association®
BELLOWS: The bellows is the flexible element of an expansion joint. Formed metal bellows are made from tubing by the application of internal pressure. The convolutions are formed in parallel planes that are perpendicular to the longitudinal centerline of the bellows – referred to as annular. The tubing is normally made from sheet or coil that is rolled into a tube and longitudinally welded.
COLD SPRING: Also referred to as Preset. An expansion joint or ball joint is installed displaced axially, laterally or angulated from the manufactured configuration to increase the movement capability, or if the product is designed to deflect from the installed position to the neutral (manufactured) position in operation.
CONNED: When you are convinced to buy another manufacturer’s product.
CONTROL ROD: Devises normally made from rod or bar installed to limit the travel of each individual bellows in a universal expansion joint to the rated motion. Control rods are not designed to react pressure thrust – see Tie Rods.
CONVOLUTED LENGTH: For practical purposes the convoluted length is measured between the convolution sidewalls at each end of the bellows to allow an actual physical measurement to be made. For analytical purposes the convoluted length is measured between the centers of the radii of the end convolutions.
CONVOLUTED OR CORRUGATED: Each formed shape of the cross section consisting of a root and crest is a convolution or corrugation. With parallel sides the gap at the root and crest are equal, and referred to as “U” shaped. If the inside radii at the root and crest are equal but the gap between the sides is reduced, the cross section has an Ω shape, and is referred to as omega shaped.
CONVOLUTION CREST: The semicircular segment of the convolution at the outside diameter.
COVER: A shield or shroud that covers the outside surface of a bellows to provide protection from mechanical damage or arc strikes. It may also be used to retain external insulation around the bellows, or as a uniform surface for insulation installed on the outside of the cover.
CYCLE LIFE: The cycle life or fatigue life expectancy of a bellows is based on the number of complete pressure and displacement cycles that result in metal failure. The most commonly used method of analysis is included in the Standards of the Expansion Joint Manufacturers Association®; however, when specified there are related methods included in ASME/ANSI B31.3 and ASME Section VIII Division 1.
DESIGN PRESSURE: The pressure specified that is used to design a product. Normally given in conjunction with the design temperature to specify the material properties to be used. The design pressure is normally equal to or greater than the operating or Working Pressure.
DIRECTIONAL ANCHOR: An Anchor that allows movement along one or two axes but provides a structural reaction along the remaining axis (axes).
DOUBLE OR DUAL EXPANSION JOINT: An expansion joint commonly referred to as a Dual Center Anchor Base Expansion Joint consisting of two bellows joined by a (center) spool that includes an Intermediate Anchor. Required for long pipe runs where the axial movement exceeds the capability of a single joint. Sometimes confused with a Universal Expansion Joint that is primarily designed to absorb lateral offset.
DRIP LEG: Also referred to as a drip pot or mud pot is added to the bottom of the body or stationary portion of an expansion joint in the form of a welding saddle or reinforced saddle to collect condensate and sediment.
EFFECTIVE AREA: The cross-sectional area of the bellows based on the Mean Diameter of the convolutions. This area multiplied by the pressure equals the Pressure Thrust Force (Lbs.).
EQUALIZING RINGS: External rings installed between each convolution of a bellows and at the ends with a cross section that approximates the shape of a compressed convolution. They reinforce the bellows against internal pressure, and limit the movement of each convolution to the rated travel.
EXPANSION COMPENSATOR: See Compensator
EXPANSION JOINT MANUFACTURERS ASSOCIATION (EJMA)®: An organization of leading manufacturers of metal bellows expansion joints established in 1958 that publishes the Standards of the Expansion Joint Manufacturers Association, the worldwide standard for metal bellows expansion joint design.
EXPANSION JOINT: When used within the context of this web site, expansion joint refers to a metal bellows expansion joint designed to absorb axial, lateral and angular motions in piping systems.
EXTERNAL PRESSURE: Refers to a condition where the highest pressure is on the outside surface of the bellows. This can result from an internal vacuum or designs where the bellows is enclosed in a pressure vessel and externally pressurized (Series 3500 & Series 8500). All metal bellows rated for a pressure greater than 15 psig are suitable for full vacuum service.
EXTERNALLY PRESSURIZED EXPANSION JOINT: Generally refers to a type of expansion joint designed to absorb axial motion that has an enclosed bellows designed with the fluid external to the bellows. Sometimes referred to as an externally pressurized and guided since the design includes integral guides. Refer to Series 3500 expansion joints.
FLEX TORQUE: Refers to the moment (ft.-lb.) required to angulate a ball joint as the result of the seal resistance. These values are normally for the breakaway condition.
FLOATING FLANGE: A flange that is not welded. Normally a back up flange for a Lap Joint Stub or a Van Stone.
FLOW DIRECTION: The direction of flow of the fluid in a piping system. May be an important consideration in the design of an expansion joint. Some expansion joint configurations (not all) must be oriented in accordance with the flow direction and include external marking indicating the correct orientation. Systems with bi-directional flow require special consideration.
FLOW LINER: A flow liner is sometimes referred to as an internal sleeve and is designed to isolate the internal surface of the bellows from the impingement of the flowing fluid. It eliminates bellows resonance resulting for the flow induced vibration, and provides a thermal barrier as a result of the stagnant flow between the liner and bellows . Most flow is unidirectional and the liner is welded to the upstream end. The direction of the flow is marked on the exterior of the expansion joint. For bi-directional flow a Telescoping Flow Liner may be recommended.
GIMBAL EXPANSION JOINT: Gimbal expansion joints permit angular motion in any plane. They consist of two pairs of hinged connections to a floating ring. They are designed to react the full pressure thrust. When two or three joints are correctly installed in a pipe run they absorb motion in multiple planes by lateral offset.
GRAFOIL®: Name identifying a proprietary formulation consisting of flake graphite and synthetic oil that is used as an injected sealant in Hyspan Perma-Pax Packed Expansion Joints and some Hyspan Barco Ball Joints products.
GROOVED END: A common method of installing expansion joints in fire protection systems and potable water lines. The connection consists of grooved pipe, non-metallic seals and an external clamp. The configuration of the groove is specified by ANSI/AWWA C606-87.
HINGED EXPANSION JOINT: Hinged expansion joints permit angular motion in one plane. The hinges are designed to react the full pressure thrust. When two or three joints are correctly installed in a pipe run they absorb motion in one plane by lateral offset.
HVAC: An abbreviation for Heating Ventilation and Air Conditioning.
IN-LINE PRESSURE BALANCED EXPANSION JOINT: An expansion joint configuration that is Pressure Balanced that does not require a change in flow direction. Primarily designed for axial travel. Configuration can be internally pressurized as shown in the illustration or externally pressurized.
IN-LINE PRESSURE BALANCED HINGED OR GIMBALED EXPANSION JOINT: Proprietary Hyspan designs that are pressure balanced and permit lateral offset – See In-line Pressure Balanced
INTERMEDIATE ANCHOR: An Anchor that reacts the spring force of a metal bellow expansion joint, or the seal resistance force of a packed expansion joint or ball joint. They are not designed to react the Pressure Thrust Force.
INTERNAL SLEEVE: See Flow Liner
INTERNALLY GUIDED EXPANSION JOINT: The inherent design of an externally pressurized expansion joint or a packed expansion joint provides guiding that is integral to the expansion joint. There are other forms of internal guiding such a special flow liner designs. All are suitable for axial travel only.
LAMINATED BELLOWS: Laminated or multi-ply bellows are made by fabricating individual tubes and telescoping them together prior to forming. The maximum pressure, spring rate, and stability pressure are increased in direct proportion to the number of plies. The axial deflection is determined by the individual ply thickness. Multi-ply designs permit a lower spring rate and higher cycle life than a single ply configuration for an equivalent pressure. Multi-ply designs are effective for high pressure bellows, and they are recommended for applications involving vibration or rapid cyclic movement because of the inherent damping provided by the relative movement of the plies.
LAP JOINT END: Consists of a stub end and a lap joint backup flange. The stub end and flange conform to the specifications of ASME/ANSI B16.9 & 16.5 respectively. Normally used when flange hole alignment is an issue or if there is a requirement for a corrosion resistant wetted surface. Bellows or tubing that is flared over a flange face is a Van Stone and normally does not conform to the same specifications.
LATERAL DEFLECTION: The displacement or offset of the ends of the bellows perpendicular to the longitudinal centerline with the ends remaining parallel.
LIMIT ROD: Devises normally made from rod or bar installed to limit the travel of an expansion joint to the rated motion. They are designed to react the full pressure thrust in the event of an anchor failure. See also Control Rods and Tie Rods.
MAIN ANCHOR: An Anchor that reacts the combined Pressure Thrust Force and the spring force of a metal bellow expansion joint (spring rate multiplied by displacement) or the seal resistance force of a packed expansion.
MATERIAL THICKNESS: The original thickness of the tubing used to form the bellows. For multi-ply or laminated bellows it is the thickness of the individual plies.
MEAN DIAMETER: The diameter of the bellows convolutions calculated by adding the convolution inside diameter and outside diameter and dividing by two. Used to calculate the bellows Effective Area.
MITERED CORNER: Corner configuration used for rectangular expansion joints. Convoluted straight sections are meshed together and welded at the 45° intersection – similar to a picture frame.
MOTION INDICATORS: A devise added to an expansion joint that is used to indicate the displacement of the expansion joint from the manufactured position.
MULTI-PLY: See Laminated
NPS: Refers to Nominal Pipe Size. For steel pipe see ANSI B36.10, and ANSI 36.19 for stainless steel pipe. Occasionally referred to as IPS – iron pipe size.
OMEGA SHAPED: Refers to a convolution shape with inside radii at the root and crest are equal but the gap between the sides is reduced – see Convoluted or Corrugated.
OPERATING PRESSURE: See Working Pressure
PACKED EXPANSION JOINT: An expansion joint design that utilizes packing material as a seal – Series 6500. Also referred to as a packed slip expansion joint. Prior to the common usage of metal bellows expansion joints, expansion joints were identified as “packed” and “packless” referring to joints with a bellows seal.
PACKLESS EXPANSION JOINT: Metal bellows expansion joint – See Packed Expansion Joint.
PANTOGRAPH LINKAGE: A scissors like structure installed on a Universal Expansion Joint to equalize the movement of the two bellows elements. The linkage is not designed to react pressure thrust but can be designed to support the weight of the Center Spool that joins the bellows.
PERMA-PAX EXPANSION JOINT: Identifies Hyspan Series 6500 Packed Expansion Joints.
PIPE GUIDE: See Alignment Guide
PLANAR PIPE GUIDE: Limits motion to transverse and angular in one plane. Commonly used in suspended piping systems incorporating ball joints, and hinge and gimbal expansion joints to maintain the piping in plane.
PLATE FLANGES: Bolted flanges made from plate material that generally do not have a hub and are normally flat face (raised face is optional). Commonly made to the inside and outside diameters and drilling of standard flanges such as ASME/ANSI B16.5, DIN and JIS standards. Frequently incorporated into expansion joint designs to save length and incorporate special features such as tie rods.
PLY: Refers to the thickness of the material used to manufacture a bellows. May be a single thickness (one ply) or multi-ply, Laminated.
PRESET: See Cold Spring
PRESSURE BALANCED EXPANSION JOINT: An expansion joint design that incorporates a balancing bellows and linkage to internally react the Pressure Thrust Force. Although the external pressure forces are eliminated, there are spring forces resulting from the bellows that must be reacted. See In-Line Pressure Balanced Expansion Joint, In-Line Pressure Balanced Hinged or Gimbaled Expansion Joints and Pressure Balanced Elbow.
PRESSURE BALANCED ELBOW Expansion Joint: A Pressure Balanced Expansion Joint that incorporates a bellows, an elbow (or tee) and a balancing bellows (not in flow) linked by tie rods. If lateral motion is required two bellows are installed and referred to as a Universal Pressure Balanced Elbow.
PRESSURE THRUST FORCE: When the ends of an expansion joint or system are capped and pressurized, there is a resulting force that is equal to the applied pressure times the Effective Area of the bellows element, or the effective area of a packed expansion joint. The only force (internal to the expansion joint) opposing the pressure thrust results from the axial spring force of the bellows or seal resistance of the packing. Bellows spring forces are generally insignificant compared to the pressure thrust and a reaction must be provided. See Pressure Thrust Technical Notes.
REDUNDANT PLY: As a safety measure, a bellows can be designed with two plies with each ply capable of meeting the service conditions. The outer ply is considered to be redundant (at least if the inner ply doesn’t fail). The technique is normally combined with a method of testing for failure of the inner ply – see Testable Bellows.
REFRIGERATION CONNECTOR: A special type of braided metal hose used for refrigeration service. Must be internally cleaned to refrigeration system standards. Hyspan Anaconda Vibration Eliminators ® are manufactured for this application.
REINFORCED BELLOWS: Metal bellows configurations that have external devises (normally rings) that reinforce the bellows against internal pressure. They can have the added benefit of equalizing the movement of the individual convolutions. Common methods are Equalizing Rings, circular cross section rings and “T” shape fabricated rings.
RETAINER: A component of Hyspan Barco Ball Joints that retains the ball and seals. Threaded design through 2” NPS, flanged design 2-1/2” NPS and over. Allows disassembly of the ball joint for maintenance.
SERVICE PORT: An opening in the body or stationary portion of an expansion joint in the form of a welding saddle or reinforced nozzle to provide a branch connection.
SHIPPING DEVICES: Often referred to as shipping bars. They are installed on most metal bellows expansion joints to maintain the factory configuration during shipping and installation. They must be removed after installation and prior to pressure testing – they are not designed to react pressure thrust. Hyspan shipping bars are painted yellow and labeled. They are not to be confused with Tie Rods or Control Rods which remain installed in service
SHROUD: See Cover
SINGLE EXPANSION JOINT: An expansion joint with a single bellows element.
SLOTTED HINGES: A Hinged Expansion Joint that permits angular motion in one plane but does not react pressure thrust. The purpose of the hinge is to support the weight of the Center Spool in a dual or double hinge arrangement. Tie Rods are commonly added to react the pressure thrust.
SPRING RATE: General reference to the spring constant of a metal bellows – refer to Axial Spring Rate, Lateral Spring Rate and Angular Spring Rate.
SQUIRM PRESSURE: Internally pressurized bellows become unstable at a critical or squirm pressure. Bellows that are long relative to their diameter tend to buckle much like a long column under compression. Another type of squirm referred to as in-plane occurs when the individual convolutions deviate from parallel planes. Either condition represents the maximum pressure capability of the bellows, and failure will occur if the pressure is increased.
STABILITY PRESSURE: See Squirm Pressure
STRUT JOINT: An assembly designed to brace or stabilize tanks, vessels, piping and other equipment against external loading such as wind loads and seismic events. An assembly with two strut joints separated by a spool allows lateral and angular movement but is rigid axially. Also referred to as a flexible strut joint. When used with a Vibrasnub allows gradual axial motion and absorbs shock and vibration.
SWEAT END: Refers to an overlapping or telescoping end connection that is joined by soldering or brazing. Commonly used with copper tube.
TANGENT: See Neck
TELESCOPING FLOW LINER: A Flow Liner that is made in two parts that are telescoped together and welded at both ends of the expansion joint with the free ends in the center. Commonly used for bi-directional flow.
TEST PRESSURE: Expansion joints are leak tested to establish that they are leak tight, and /or proof tested to determined that they can be safely pressurized at the operating conditions. There are many methods of testing but the most common method is a hydrostatic test to 1½ times the Design Pressure. Test conditions should replicate operating conditions and test structural components such as tie rods, hinge and gimbal attachments. In order to be acceptable the expansion joint must be leak tight and not permanently deformed after testing. Expansion joints made the ASME code are tested to a pressure that is adjusted for elevated temperature. Because of the unique properties of a bellows this may not be practical – refer to the applicable code to determine the correct pressure.
TESTABLE BELLOWS: As a safety measure a bellows can be designed with two plies with a test port(s) are installed on the bellows neck that extend into the space between the plies. The pressure is monitored between the plies to detect a leak in the inner ply as an early warning. The most common testable bellows has two ports at opposite ends 180º apart with a screen between the plies. There is a flow test to ensure free flow between the ports.
THINNING: Most bellows are formed by application of internal pressure to a tube with a diameter approximately equal to the final convolution inside diameter. The material is drawn from the length of the tube. As a general rule the original tube length is approximately three times longer than the finished part. Thinning may occur at the Root and Crest of the convolutions depending on the forming method used. The maximum thinning for Hyspan bellows is 5%. Most bellows performance data is based on material parameters in the “as formed” condition.
THERMAL EXPANSION: Most metals expand when they are heated and contract as they are cooled. This is a property that is unique to each metal and metal alloys which varies for different temperature ranges. For piping the ASME has established values for this property, coefficients of thermal expansion, which have been used to calculate the linear expansion of commonly used pipe materials – Thermal Expansion of Materials
TIE ROD: Devises, usually rods or assemblies made from rod and pipe whose primary function is to react the full Pressure Thrust at operating and test conditions, and to allow lateral offset. They can also function as limit stops to prevent over travel of the individual bellows elements of a universal expansion joint, and to stabilize the center spool of a universal expansion joint.
TIED UNIVERSAL EXPANSION JOINT: A Universal Expansion Joint with tie rods that is designed to absorb lateral movement in all planes.
TOROIDAL BELLOWS: A bellows with a toroidal shaped cross section designed primarily for high pressure applications.
TORSION: A moment (in.-lb.) or displacement around the longitudinal centerline of the bellows – twisting. Although bellows can react a limited amount of torsion they are not designed for torsional displacement, or to react torsional moments. Should not be confused with Angular Rotation.
UNIVERSAL EXPANSION JOINT: An expansion joint configuration consisting of two bellows elements joined by a Center Spool. A universal expansion joint will absorb lateral motion in all planes, axial and angular motion but is limited to low pressure because of instability without tie rods or other structural components. Most commonly used as a Tied Universal Expansion Joint.
UNREINFORCED: Refers to a bellows that does not require external Reinforcement for support
V-FLEX: Identifies a Hyspan metal hose product consisting of two flexible hoses at 45º joined by a 90º elbow. Designed primarily for seismic isolation of small diameter piping. See V-Flex.
VIBRASNUB: Identifies a Hyspan product designed to brace large piping, vessels and tanks while absorbing shock and vibration when used in conjunction with Strut Joints. See Hyspan Barco Flexible Strut Joints and Vibrasnubs.
WELDED BELLOWS: Bellows made from flat or shaped disks that are welded together at the root an crest of the convolutions. They are commonly used for scientific and instrumentation applications. Prior to improvements in bellows forming techniques they were used for industrial applications.
WORKING PRESSURE: The system pressure during normal operation. See Design Pressure.