# Axial Expansion Joint (Bellows)

Axial expansion joint looks like the simple bellows without ties. It can be exposed for bending, compressing, tension, lateral, and torsion deformations. But it is designed to work mainly for tension and compression by manufacturer. Also it can have guide rods

To achieve this, the guide supports should be placed to remove any bending and lateral deformations of expansion joint. To prevent buckling of pipes, connected to expansion joint the buckling analysis should be performed. Analysis will give the distance between guide supports to prevent buckling.

Expansion Joint analysis results can be found in Expansion Joint Deformation Table. See also "How to Reduce the Nozzle Loads in START-PROF"

All expansion joint properties can be taken from expansion joints database by pressing the "..." button and selecting the appropriate expansion joint.

#### Properties

 Property Description Name Element name. If checked then it shown in 3D view Effective area1 Expansion joint effective area. Used for calculating thrust force. More.. For bellows, Effective Area Aeff is an area if circle with an Effective mean bellows diameter Deff: Aeff = Pi * (Deff)^2 / 4 Approximately Deff = (Dmin + Dmax)/2 is mean bellows diameter. Value must be obtained from manufacturer For Slip type expansion joint Aeff = Pi * (ID)^2 / 4, ID - internal pipe diameter For pressure balanced expansion joints Aeff=0. Flexibility1 Axial flexibility, (1/Kax) of whole length of expansion joint (all convolutions). Kax = Axial stiffness of the bellows. Value must be obtained from manufacturer Allowable axial expansion movement, Δk1 Allowable axial expansion movement (maximum allowable linear deformation): Δk/2, where Δk - full allowable axial expansion movement. Used for analyzing expansion joint deformation. Value must be obtained from manufacturer Rotational deformation analysis If turned on, there are no rotational restraints in the expansion joint and allowable skewing is analyzed. If turned off, there are rotational restraints and skewing analysis is not run. Frictional force Maximum frictional force. For slip type expansion joints

An axial expansion joint allows linear movement along the axis of connected pipes and restricts rotation of adjoining pipe ends relative to each other, as well as mutual linear displacements perpendicular to the pipe axis. Internal pressure thrust force Fthrust is taken into account. Deleting rotational bending restraints allows the analysis of expansion joint skewing, which will produce the appropriate warning message. Expansion joint model used in START-PROF can be seen on fig. 1.

Fig. 1. START-PROF expansion joint model

The expansion joint's function is due to its special construction (fig. 2) or due to appropriately placed supports to the left and right of the expansion joint (fig. 3).

Fig. 2. Slip type expansion joint model

Fig. 3. Bellows/lens expansion joint model, functioning as an axial expansion joint, with bending and displacement restricted

To add the expansion joint weight see description here.