Hi,

Can you clarify for the following.

I wanted to split the calculation into two as it is a big system. So that i have noted down the displacement in thermal and sustain condition at the seperation point(from the combined calculation).The stresses are with in the allowable in both the SUS and EXP condition.

Then I inputed the displacement(for both sustain and thermal case) for one of the splited calculation ( I mean that displacenment given at the point of seperation)..But the stress is failing in sustain case

For clarity I am giving below the load case below

1. W+P+T1+D1 OPE
2. W+P+D2 SUS

(D1 - Displacement taken from the combined system for the thermal case)
(D2 - Displacement taken from the combined system for the sustained case)


Can anyone explain me whether displacement(D2) can be given for sustain conditon?if I don't give, system is safe.I hope that this is understand to you all.IF any additoned information is required, I will send the same

regards

Sha..

When you do this it's a good idea to split the system at an anchor for this very reason. Sometimes, in large systems, you may even want to BUILD an anchor at a convenient point for splitting the analysis. Intermediate anchors in very large piping systems are usually required anyway, simply to provide control points in case of failures.

If you choose to have a big, floppy piping system, then in addition to entering displacements, you also need to enter rotations at your split. Most fatigue problems are caused by bending stresses, and rotations have a lot more to do with that, in most cases, than displacements.

Finally, you need to make sure you have entered the data correctly. If you have messed up units, or switched coordinates, you could easily have created your own mess.

Like CraigB says try to split at anchor. If you do not have any you have a good change that your piping will not behave as you expect. I use a simple rule. If there is a piece of pipe that is not "forced" to move into specific direction then no good. Any movement depending on friction or spring rate is not "forced". One day pipe moves one direction and next some other direction.

I have used sometimes splitting in a way that my two models overlap, e.g. I have same section of the pipe in both models. Calculation results near the ends in both models are wrong but I make this clear in the report. Typical place to use this is when I calculate an existing system, which doesn't have ANC and there are few kilometers of piping.

Sha,

I agree the best way to seperate system is at anchor since the load will not pass from the both side of it. When we specify the DISPCL as the boundary we still miss the stiffness which seperated.

Just for confirm, when you put DISPLC. boundary, did you put zero Rx, Ry, and Rz as boundary? It used to generate fail.