In a piping system connected to pump suction, a tied Rubber expansion joint was used.


Rubber Expansion joint Vendor has been identified; he has given the following allowable.

Axial compression =17mm, Lateral offset =12mm, Degree of angular movement=2.75, degree of torsional movement=2.

Axial spring rate=38 N/mm, lateral spring rate=46N/mm, Angular spring rate =103 Nm/Deg

Pipe suction axis is X. Tied expansion joint has been as per CAESAR.
With restraints X, RY & RZ.But expansion joint has been modelled with a gap in rotation RY=0.2 & RZ= 0.2

I am sure that we can use stiffness values, but I am not sure using vendor rotation allowable in our Calc.

Please give a suggestion regarding above, is it correct way that, we can make use rotation gap in our calculation.
Regards,

BVKUMAR

Stiffness is value for bellow portion, whereas X Ry Rz are for tie rod symbolic modelling.
So for bellow model use data given by vendor but for tie rod model you can not give any gap for X Ry & Rz for technically correct model.
But some time I take ( small axial or rotational gap ) to get good result say for cooling water line analysis. Considering the fact that total piping with tied bellow can absorbed very small amount axial movement or angular rotation without increasing load in nozzle.
In General we should not model like that.