hello in my current project i am selecting spring for operating condition
my selection criteria is vartion should be less than 25%
my doubt is as i am checking only in operating condition
in some cases where there is difference between design and operating temperature is more (such as in flare or in regeneration case)
so it may cause problem. so how can this problem be addresed

how much varition i can permit in design condition so there will be no problem in site. i dont know when spring will bottom out ( after how much travel) please put some light on this issue.

Regards
Pinky

The final load on spring ( particularly for big lines) also depends on the pipe support hardware , the exact weight of which is typically will not be known to you.The question is why you are using springs and where.For sensitive equipments, the equipment should be taking near zero load during bthe alignment condition ( WNC Case with the end of the pipe flange fre and the tip displacement <1.6 mm). As, you will not know the exact weight of the pipe support hardware ( and sometime weight of the flanges also, particularly for big lines ), so a good rule of thumb is to talk to the spring vendor to find out the permissible site variation in spring load adjustment and check the sensitivity of your system to pipe support weight and if ( typically 20% but you have o check with the vendor)with these variations, still you can keep the tip displacement to within 1.6 mm , there will not be any major problem at site as dring the alignment there will not be any "additional" load imposed on the equipment.

By big size lines , I mean typically 20 inch and above.

The permissible variation can be even 35% and higher but it depends on the spring vendors limit and what the client wants. I have seen some clients stick to a max. of 5% variability closeto strain sensitive equipments.Although they could not technically justify to me why 5%.

The above points are typically for systems connecetd to strain sensitive equipments like pumps , compressors etc. I am not sure what type of system you hav eand what are the project requirements ad hence no "case specific " recommedations could be provided.

Springs should be seleceted typically for operating conditions , although one has to ensure that there is no bottoming out during transient conditions.For the systems n question, you have to investigate for occasional fluid loads also ( not necessary if the system will be hydrotested)as otherwise the spring will be undersized.

Regards

Dear Anindya
I like to clarify something from you.
“The final load on spring ( particularly for big lines) also depends on the pipe support hardware”
The way I understand spring hardware weight are supported by external steel structure. For piping stress spring act as pre load force with operating variation only. So piping will not affect much because of it’s spring hardware weight.

Dear Pinky
General variable on spring load is permitted upto 25%. Vendor may accept bit more for occasional case.
You can check load variation from restraint summery.
If say spring maximum variation allowed 25% , if piping more beyond that then the spring after moving (to reach 25%) then it will act as rest support.
You may cross check the stress calculation to replace spring with resting support with gap ( movement value that make 25% load variation.)
Check then stress, spring load & nozzle load if that are quite OK then I don’t see any problem in that calculation. In that suggested model nozzle load need not to maintain as vendor ask but obviously should not be too high. Same things valid for spring also.
Regards
Habib

If you want CAESAR II to consider muliple (OPE) load cases during the hanger design, then setup the "multi-load case" design option. You'll find this on the "Hanger Run Control" dialog. You define how many "Hanger Design OPE" cases you have, then pick the selection criteria.

Note, CAESAR II assumes all hanger design cases are first in the load case list.

Shr,

The load on the piping due to weight of pipe shoe or stiffer rings , wts of trunnion end plates etc are some examples.I did not refer to spring hardware.

Regards

Yes, you need to design the spring under "Max load and travel condition" which would be in transient/design case. Use the Hanger control dialog box and specify all temperature cases. Use case-13 in "Multiple load case design options".
This gives you the max variation which should comply as per your project specification.

Regards