REPLICATE A PIPE ARRGT. FOR VERTICAL MVMT. ACCOMMODATION

Hi all,

This is my first post related to PIPE STRESS ANALYSIS. I'm a beginner in pipe stress analysis and got a query related to replicating an arrangement used for pipe expansion in CAESAR.

I've a pipe which is connected to an equipment having vertical (downward) expansion. To accommodate the vertical expansion, a horizontal pipe arrangement is used before the vertical pipe which will convert the vertical movement of the pipe into horizontal movement (preset-ed telescopic kind or of a bell & spigot kind of joint - as the vertical pipe moves downwards, the preseted horizontal portion moves down with telescopic movement in the horizontal pipe, thereby relaxing the preseted pipe by moving inside the bell joint). Telescopic movement is provided at both ends of the horizontal pipe arrangement used before the vertical pipe; both ends can have axial movement when the vertical pipe is coming down. The first end of the horizontal pipe have rotational flexibility of upto 4 degrees. Pipe size is 20 inch.

Attached is a sketch of the pipe with displacements.

Can any one please guide me as to how I can replicate this thing in Caesar?

Interesting arrangement. Generally a telescopic movement could be handled with CNodes or perhaps and expansion joint element. I know I modeled a Ball Joint once with an X, Y, and Z restraint using cnodes. I suggest you check out what the expansion joint element can do for you here.

Thanks,
Duncan

http://www.coade.com/Uploads/mechanical-engineering-news/jun99.pdf

See page 17. This almost exactly describes what you're trying to do, although it's not clear whether you're trying to simulate or specify the telescopic movement.

Michael,

I'm trying to specify the movements of the pipe at those two points in the horizontal pipe because of the expansion. I tried to replicate this arrangement with the help of x, y, z, rx, ry and rz restraints to specify the rotational as well as translation flexibility because of the pipe downward expansion.

I provided lateral "rotational restraints with gap" to provide the rotational motion and [b]only"axial translational restraint with gap"[/b] to specify the telescopic movement, on the first end of the telescopic arrangement (Node 20 as per my sketch). Similarly, I provided only "translational restaints with gap" on the second end of the arrangement (Node 30 as per my sketch) for the axial and vertical downward movement of the node because of exapansion.

Before the Node 20 of the arrangement, there is a +Y restaint on the straight pipe piece, which acts as a pivot (fulcrum) for the telescopic arrangement to function.

I think this explains my arrangement completely.

Hi All,

Can we replicate the arrangement as discussed in the problem , using an expansion joint in caesar??

Please help....

The only specification of movement you should have is for node 60. Caesar would then simulate the movement of the joints and rotational piece. I can't conceive offhand of a need to specify rotational movement of the arm segment within CAESAR, but rather you need to simulate it and determine if its path is acceptable.

The method proposed does not allow for thermal growth of the rotating element. As such, you must have an expansion joint between the two ball joints to make thermal stresses go away.

This is what's required to get CAESAR to simulate rotating rigid body physics in piping.

Modeling expansion joints here could be used. I guess the only advantage is the addition of the joint stiffness as it looks like other modeling issues are handled with the restraints (but you could also include this stiffness in your restraint definition).
It looks like you are expecting the telescopic components to carry bending. Can the proposed hardware function?