Dear all,

I am analyzing a piping system that is connected to a tank. The density of fluid is high. I have to use a variable spring near tank due to settlement. The imposed loads in ope. and sustain case are bellow the allowable but as the density of fluid is high in case that the pipe is out of fluid(WNC+P+H and WNC+P+H+D) due to decrease in weight of the system, that is concern to weight of fluid, the spring moves upward and imposes large load and moment on nozzle. Can I declare the manufacturer of spring to place something like limit stop to restrict the movement of spring to prevent excessive moment on nozzle when there is no fluid in piping system?

I suggest you try using constant load hanger instead of variable spring hanger in the problem area.

Ibrahim Demir

Expansion bellow may be use in this case.

You could also make a design where there is no one load case where the nozzle is completely free. That way you'll have an average of the nozzle loads. Don't know if it works in your particular case. But it can help in some situations.

Hi Rez,

I think constant hanger is not a solution for it, because tank settle.. and sping lock is imposible.

Would it be posible to assemble your spring support in the tank foudation or attach in tank itself? so it would equaly settle? otherwise as suggested above to use bellows.. my opinion*

Regards!

Hi Rez,
I will suggest that please check out the actual settlement value in WNC load case from geotechnical group. This is a long term settlement value and if the value will reduce, it will help.. how much settlement you are considering in this system?

Dear Reza59,

Regarding to settlement, it is usual to use exp. bellow. Consult w/ the vendor the allowable lateral movement, moment on the bellow. Below is my opinion:


I think the software apparently does iteration by moving to related spring FIG table to have variable type based on load variation. If can't find one it will try two. If still can't find it will select the constant type one.


WNC+P+H; What is the internal pressure you have considered for this case?
WNC+P+H+D; What is the displacement you have considered for this case? is it from the settlement predicted by civil/soil guy? Take a close discuss w/ them.


In what case? I'm doubt about this except for the represent of Temperature. But need to see your support configuration there. Sorry if i'm wrong then. Would you please to post the graphic of your model isometric to your next reply? it seems many of us are very interesting w/ this case.


Try using spring travel at pre-spring design? expert may suggest...thx

I agree with Samsul about the CAESAR II selection of hangers. However, you can still select your own suitable hanger (soft spring hanger or constant load hanger) and introduce to your CAESAR II calculations.

In this case you need to externally check the range of the selected spring with maximum and minimum displacements/forces after the analysis. It may not be some cases the economical ones, but it works perfectly.

So, you first need to know the sustain case load on the hanger(s) and start digging the hanger catalogs for this load and find the right range to start with. You may try this more than once to find the most suitable within the working range displacements and forces. I suggest to consider some margin in the displacement/force range for the application. If you can not achieve to fit any one of them you need to change the pipe route to suit your requirement.

Hope it helps,

Ibrahim Demir

Thank you all for your replies.

I do not have any problem with spring selection.I have tried different constant and variable springs.In this case, it makes no difference to use constant or variable type because the problem is due decreasing the weight of system as a result of fluid drainage.This increase the longitudinal moment on nozzle.I know expansion joint will solve the problem but I would like to consider it as a last resort.
I want to know that I can order the manufacturer to provide a lock(other than lock that use for hydro test) so that before system become out of fluid, people at site, could lock the spring in that position then drain the fluid?

THe suggestion to put the spring on the tank foundation is a very good one. In addition to dealing with all possible settlement issues, it also ensures that your moment arm for the spring force in the line empty case is minimized.

You may also find that putting the first support for the line on the tank foundation allows you to use a rigid support. This will eliminate the "line empty" problem temporarily, although you will then have to consider uplift of that support as the tank settles.

If you reflect a bit, you will probably realize that the "line empty" load case is an occasional case and the piping stresses can be dealt with in that fashion. Applications with slurries and other high-density fluids can produce this problem, it is not an easy one to handle analytically.