I am working on some modification on existing Line which is having Pressure balance Expansion joint near the turbine nozzle. The existing exp joint vendor is not tracable, but i have the exp joint specification. I have to check whether existing bellow can still be retained with the new modifcation on line.

The Exp. joint has 3 bellow elements( 2 on one side and 1 opposite),
The axial spring rate & lateral spring rate given in the spec., i suppose are for the overall exp. joint. Individual bellow element spring rate /stiffnesses are not available in the spec.

Assuming the bellow elements stiffness, same as overall exp. joint stiffness, since in that case the exp. joint would be more stiffer showing maximum loads on nozzle,
would it be correct way to model?

The pressure balanced is the only expansion joint to provide axial flexibility as well as restrain the pressure thrust.

The stiffness values provided are definitely for the overall stiffness.

The simplest way to model this will be to provide the stiffness values but make the effective ID equal to zero in the input.

Modelling this way, you should not get a high load at the equipment connection.

First, I'm assuming you have a pressure balanced tee/elbow as aposed to an in-line pressure balanced joint. With a PBE where you don't have the shop drawing, the previous response is accurate but I would add to set the operating temperature of the pipe to ambient to account for the fact that the tie rods will be at ambient temperature. You will have to manually add the pipe growth to what ever CAESAR II comes up with for axial growth.

Dan Edgar
Prinicipal Engineer
SF Pathway

I was working with In-line pressure balance expansion bellow. While modelling this bellow I had taken 3 parts of bellow with node no. say 50,60,70,80 and connect 50 to 70 And 60 to 80 with tie rod. ( As tied expansion bellow is modelled in caesar II ). Still pressure thrust was there. So I had entered pressure zero considering the fact that pressure balance will take care of pressure thrust. What is the correct procedure to model in line pressure balance expansion bellow.

Regards

Habib

Habib,

In my opinion to simplify modelling an in-line pressure balanced expansion joint,if you have all the data for expansion joint , model it as zero length expansion joint , put effective ID equal to zero ( this will make the pressure thrust zero).

In line or the elbow type pressure balanced bellow takes care of the axial pressure thrust load ( like a tied bellow ), but do not offer the high axial rigidity ( comparable with the pipe axial stiffness ) of the tied bellow.

So here you need use the true axial stiffness of the bellow and not the rigid stiffness of the tied bellow.

Regards