Dear all,
16" low pressure steam line is connected to nozzle of a steam drum. Line is comming downward from nozzle and then moves horizontaly. first support is given in horizontal line. Sutained load is only 20% of allowable. in operation nozzle moves 13mm upward due to expansion of vessel and vertical pipe expand 11mm if set free. due to this difference nozzle load increases upto 28%. Now I am being advised to use a spring support near nozzle which will decrease loads in operation.
My question is that when loads are in allowable range both on first support and equipemnt, system also passes allowable stress range, then why We need spring support.
I study in "pipe stress engineering" book that we need spring support when displacemnt in vertical direction exceeds 13mm. is this the reason to use spring support?

Thanks for time

Are you saying the pipe lifts off that first support on the horizontal run in the operating state?
While liftoff may be acceptable, it is not the best support situation. The deadweight loads shifts to other supports (and the nozzle). And the system may be less stable in the horizontal direction.
Reread your text. Does it say any nozzle that moves 13 mm requires a spring hanger or does it say if support is necessary, then a spring should be used. My guess is the latter.
My opinion is, if you check stresses and loads and deflections and all are acceptable in the installed and operating conditions without the spring and if there is no stability issue, then no spring is required.

Thanks dave for reply but I think I could not explain my question in a better way. I am attaching its drawing and loads on nozzles for better understanding.
there is on normal support and spool run between two equipments. Without spring max load on nozzles and normal support is well within limits. Piping also pass creteria of maximum allowable stress set by B31.3. Now spring is being propsed at one of nozzle and I have put result in attached file. Attached file will explain my question.
Do I really need spring support in this case.?

hi all
Pls give me some comments on my question.
Am I not able to explain my question?

If you can shorten the run from the vessel nozzle to the Elbow to fitting make-up (fitting-to-fitting) then you should be able to eliminate the proposed spring support.

Probably the design criteria or practice requires two supports for this kind of lines. In this situation, a spring hanger is normally used.

Good luck,
Carter

maybe you could try with support (no spring hanger) attached to the vessel.