Expansion Joint Glossary of Terms 3

Expansion Joint Glossary of Terms 

PLANAR PIPE GUIDE. A planar pipe guide is one which permits transverse movment and/or bending of the pipeline in one plane.It is commonly used in applications involving lateral deflection or angular ratation resulating from “L” or “Z” shaped piping configurations.

PRESSURE BALANCED EXPANSION JOINT.A pressure balanced expansion joint is designed to absorb axial movement and/or lateral deflection while restraining the pressure thrust by means of tie devices interconnecting the flow bellows with an opposed bellows also subjected to line pressure.This type of expansion joint is normally used where a change of direction occurs in a run of piping but can be designed as a in-line device where no change of direction is necessary.The flow end of a pressure balanced expansion joint sometimes contains two bellows separated by a common connector,in which case it is called a universal presure balanced expansion joint.

 PURGE CONNECTION. Purge connections,where required, are usually installed at the sealed end of each internal sleeve of an expansion joint for the purpose of injecting a liquid or gas between the bellows and the internal sleeve to keep the area clear of erosive and corrosive media and/or solids that could pack the convolutions.Purging may be continuous,intermittent or just on start-up or shut-down,as required.These are sometimes called aeration connections.

 SHIPPING DEVICE. Rigid support devices installed on an expansion joint to maintain the overall length of the assembly for shipment.These devices may also be used to pre-compress,preextend or laterally offset the bellows.

 SINGLE EXPANSION JOINT.The simplest form of expansion joint,of single bellows construction,designed to absorb all the movements of the pipe section in which it is installed.

 SWING EXPANSION JOINT.A swing expansion joint is designed to absorb lateral deflection and/or angular rotation in one plane.Pressure thrust and extraneous forces are restrained by the use of a pair of swing bars,each of which is pinned to the expansion joint ends.

 TANGENT. The straight unconvoluted portions at the end of the bellows.

 TIE ROD. Devices, usually in the form of rods or bars,attached to the expansion joint assembly whose primary function is to continuously restrain the full pressure thrust during normal operation while permitting only lateral deflection.Angular ratation can be accommodated only if two tie rods are used and located 90 degrees opposed to the direction of rotation.

  UNIVERSAL EXPANSION JOINT. A univesal expansion joint is one containing two bellows joined by a common connector for the purpose of absorbing any combination of the three basic movements,i.e.axial movements,lateral deflection,and angular rotation.Universal expansion joints are usually furnished with control rods to distribute the movement between the two bellows of the expansion joint and stabilize the common connector.This definition does not imply that only a universal expansion joint can absorb combined movments.

  WELD ENDS. The ends of an expansion joint equipped with pipe suitably beveled for welding to adjacent equipment or piping.