Trunnion

Hi,

I have general question on Trunnion. In any critical piping system we provide trunnion's and shoe's, my question is why we do only model trunnion in stress analysis but why not shoe and even we do stress calculations on trunnion to check whether it can sustain the piping load on that.


Regards,
Suresh

Trunnion is a pipe piece attached in piping system hence can model in caesar.
Shoe is a complecated structure ( not pipe piece) hence can not model in caesar. Seperate simple local stress check ( or Finite element analysis) may be required to assess intrigrity of shoe in operating/design load for critical system. For general case company standard to follow for pipe shoe.

Regards

Habib

Dear Suresh
We do local stress calculation on trunnion because it is directly connected to our piping system and it is supported at a certain distance on structure. So the load will create bending moment at piping trunnion junction which will cause failure. But in case of shoe that load will be acting as a radial load on shoe( ignoring friction and any other lateral load) and no bending moment at shoe. And the chance of failure when only radial load is acting is minimum.

Thanks for the reply,shr and rajeev.

What you said is may be correct or may not be. i need some technical explanation on this. Previously i just asked the same question to my seniors, they just replied the same. As here lot of experienced people are available, i thought i would get complete picture about this. i am looking for detailed explanation.

Please help me out.

Regards,
Suresh Gupta

Can any one please help me out. I am very much eager to know the detailed concept on this.

Thanks in advance.

please help me out

Suresh,

Regarding modeling Pipe shoes in C-II, which could be done using a rigid element from the center till the BOP of pipe, and then putting the restraint at that node. This could be done for large diameter pipe above 24" because the support will not be at the center. C-2 being a beam element software does not understand the concept of shell. There are various problems associated with this method.
1. When the pipe passes through a reducer to a smaller pipe size, the length of the rigid element will vary and will cause non uniform load distribution on a straight run of pipe. The C-2 results will be different..
2. There will be additional moments due to guide or friction at the center of pipe due to shoe, if the diameters are large i.e say 42"
3. The rigid element will experience thermal expansion, and problems of lift off will be seen in adjacent supports for a high temperature piping.

You will have more problems while analysing a system with large diameters....
I had done this on a system with 90" diameter, temp=500 Deg.C and landed into problems on support load distribution and hence stresses. We do not know about the correct load distribution at site for large diameter piping. We assume the results from C-2 output are accurate. But I am still not confident on this.

The best way to model is to assume the support at the center of pipe and check the shoe for loads using FE software.

Regards,

Suraj