Hello,

We are doing a stress analysis of heater inlet piping, which is having 10” dia main line and 4 Nos. of 6” dia branch connections. The support system for the main line and branch lines are simple resting type with guide (Restraint : +Y and Guide). During operation (Operating case) there is a vertical movement in the support nodes. Ultimately this shows the pipes are not resting on the supports during operating condition. Then what is the use of this support? And also tell me about the basis of stress calculation in these kind supports during operating conditions. We didn't give any Stiffness value on the restraints.

If the supports are lifting in operation, you need to take them out of the model and rerun to verify your sustained stresses are still within allowables. If not, you're likely going to need springs at some of those locations. With a heater, you're movement may even be high enough to warrant constant springs.

If you take the supports out of the model, then the Expansion case will be incorrect. To properly evaluate the "extreme displacement stress range" (the expansion case), you have to be able to evaluate each condition of the piping system. In the shut-down case, if the pipe is sitting on the supports, they must be in the model. The same holds true for these supports in a model where a section is off (spared) for subsequent use.

For primary stress evaluation (sustained), you may want to perform a "hot sustained" evaluation (CAESAR II by default performs a "cold sustained evaluation"). There is a write-up in the Technical Reference Manual on how to do this.

Once you evaluate all of these conditions, you can decide between a "hard support" and a "spring".