I am facing a problem with modelling of an existing piping to a Plate Heat Exchanger. It has an expansion bellow installed in the piping to the Plate HX with tie rods attached. The tie rods have nuts on the flange end (outer side) and not the bellow end so as to restrict/work against tension occurring from the bellow pressure thrust force.

I tried modelling it using the method mentioned in the CAESAR Application guide,5-4 using the complex model but this isnt making any difference on the axial force on the Plate HX nozzle. I understand that when the pipe expands and bellow compresses, the pressure thrust force is transferred which opposes the expansion force. This is how the bellow would control expansion and transmission of thrust force, Right?

Please advise me on the matter, if such tied expansion bellows, also known as bellow type pump connectors serve when installed axially before equipment's input. If that being the case, what is wrong with my modelling?

Hi Uzair

If I understand you correctly, you try to model tied expansion bellow with nut only outside of tie rod not inside of tie rod. You are expecting it will take care thrust force as well as thermal contraction of bellow.
However it will not work like that way.

Say bellow contract due to thermal expansion then tie rod will be ineffective & you will find pressure thrust in both end of bellow.

If you are using untied expansion bellow you need to consider only annular portion* pressure to calculate pressure thrust on nozzle, rest portion of pressure thrust will directly go inside equipment.

Regards

Habib