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Expansion Joint Glossary of Terms
EXPANSION JOINT. Any device containing one or more bellows used to absorb dimensional changes,such as those caused by thermal expansion or contraction of a pipeline,duct,or vessel.
FLANGED ENDS.The ends of an expansion joint equipped with flanges for the purpose of bolting the expansion joint to the mating flanges of adjacent equipment or piping.
GIMBAL EXPANSION JOINT. A gimbal expansion joint is designed to permit angular rotation is any plane by the use of two pairs of hinges affixed to a common floating gimbla ring. The gimbal ring,hinges and pins must be designed to restrain the thrust of the expansion joint due to internal pressure and extraneous forces, where applicable.
HIGNED EXPANSION JOINT. A hinged expansion joint contains one bellows and is designed to permit angular rotation in one plane only, by the use of a pair of pin through hinge plates attached to the expansion joint ends. The hinges and hinge pins must be designed to restain the thrust of the expansion joint due to internal pressure and extraneous forces,where applicable.Hinged expansion joints should be used in sets of two or three to function properly.
INTERNAL SLEEVE. A device which minimizes contact between the inner surface of the bellows of an expansion joint and the fluid flowing through it.These devices have also been referred to as liners,telescoping sleeves,etc.
INTERNALLY GUIDED EXPANSION JOINT. An internally guided expansion joint is designed to provide axial guiding within the expansion joint by incorporating a heavy internal guide sleeves,with or without the use of bearing rings.The use of such expansion joints will assure installation without initial lateral or angular misalignment and can be installed in pipelines where reverse flow will be encountered.
LIMIT ROD. Devices,usually in the form of rods or bars,attached to the expansion joint assembly whose primary function is to restrict the bellows movement range(axial,lateral and angular)during normal operation.They are designed to prevent over-extension or over-compression of the bellows while restaining the full pressure loading and dynamic forces generated by a main anchor failure.
PANTOGRAPH LINKAGE. A scissor-like device.A special form of control rod attached to the expansion joint assembly whose primary function is to positively distribute the movement equally between the two bellows of the universal joint throughout its full range of movement.Pantograph linkages, like control rods, are not designed to restain pressure thrusts.
PIPE ALIGNMENT GUIDE. A pipe alignment guide is a form of framework fastened to some rigid part of the installation which permits the pipeline to move freely along the axis of the pipe. Pipe alignment guides are designed primarily for use in applications involving lateral deflection and angular rotation.
PIPE SECTION. A pipe section is that portion of a pipeline between two anchors.All dimensional changes in a pipe section must be absorbed between these two anchors.