10/23/2015 How to Specify Slip Joints in Piping Systems

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Figure 1: Specifying the longitudinal stiffness for a slipjoint.

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HOW TO SPECIFY SLIP JOINTS IN PIPING SYSTEMS

Slip joints are connectors in piping systems that allowfor significant axial expansion. A typical application fora slip joint is a pressurized piping system such as aboiler, a wind tunnel or an oil pipeline.

In the PipePak piping design and analysis system, aslip joint is a specifically defined expansion joint,which allows translational movement in the directionof the longitudinal axis but all other directions arerigid. Such an expansion joint can be modeled (ineither PipePlus or Superdraw III) by using a bellowselement as follows:

In the PipePlus spreadsheet, press "b" when thecursor is in the "Extra data" column to specifythe "Bellows" option for the point. The"Expansion Joint Definition" screen will appear.Specify the value for the "Longitudinal stiffness"field (see Figure 1) and then click on the "OK"button.In Superdraw III, use the "FEA Add:PipePakAnalysis:Bellows..." command sequence. The"Bellows" pop-up menu will appear. Click on the"Values..." button to specify the translationalstiffness value in the longitudinal axial direction.Then, click on a line of the model to add a bellows.

A bellows element is a generalized structure element, which can be used to simulate almost any connectorincluding expansion joints. In addition to a slip joint, the following kinds of expansion joints can be simulated:

Gimbal expansion joint - allows rotation in both the horizontal and vertical axes; no translationalmovement is possible.Universal joint - allows deflection in all but the torsional direction.

For more information about slip joints, expansion joints and the bellows element, see the PipePak User's Guide.

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