Dear all,

I am having the doubt on Cold load spring design.

Normally the CAESAR will do Hot load spring design only. Where we can find the Hot load of spring & Operating load both are same as well as vertical movement.
But If I invoke the cold load design, Operating Load & Hot load of spring is varied as well as vertical movement.

My doubt is, Whether I can directly take the Hanger report for Hot load & vertical movement, or I have to take the operating load as Hot load & its movements as vertical movement of spring while doing cold load design?

Kindly help me.

Thanks in advance.

Regards,
Gobinath

See
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=53893#Post53893
and many other posts in forum.

best regards.

Dear mariog,
Thanks for your link.

I am understanding that spring balanced in any one position. I am trying to balance the spring in cold condition. But in cold condition itself, it is not balanced.Both cold & sustained load at the spring points are getting varied.Vertical movements are totally varied from spring report & operating case.

I can give the spring supplier only two values. i.e). Hot (or) cold load & vertical movement. If I give the preset load & vertical movement from spring report, the spring will not reach this (spring report) vertical movement & hotload in operating condition. If I give the operating condition load as hotload & its vertical movement as spring movement, the preset load will differ with our analysed preset load. So we can't ensure that pipe will move to this vertical movement.

Kindly help me to solve this problem.

Regards,
Gobinath

My understanding, cold load and sustained load can differ due to frictional effect of the system.

check the loads with and without friction.
your sustain load and cold load should match then.

model spring with friction if required.

Gobinath,


I'm not sure I understand what you intend to do, consequently I cannot help you to "solve" the problem.

A spring support is... a spring giving force. The force is not constant because a simple spring cannot give a constant force.
A spring has a Spring Rate (lbs/in or N/mm); for example Anvil supports fig 82, 98, B-268 have different spring rates.
For this reason a spring cannot assure independent "cold load" and "hot load"; the values are correlated with spring rate and pipe line movement from the cold to the hot position.

In order to choose a proper size hanger, it is necessary to know the actual load which the spring is to support and the amount and direction of the pipe line movement from the cold to the hot position. A result of size selection is the spring rate of spring support (and please note cannot be "any" spring rate, there is a certain limitation in what Manufacturer wants to consider as "spring").

As it is desirable to support the actual weight of the pipe when the line is hot, the actual load considered in spring selection is the hot load. The cold load is calculated by adding (for up movement) or subtracting (for down movement) the product of spring rate times movement to or from the hot load.

The above described "procedure" is the basis of Vendor spring selection, however you can proceed in different way if you want; just think to the benefits of your procedure! For example, considering an out of engineering sense behavior, you can choose hot load (or cold load, if you prefer!) complete arbitrary as 1kN for first support, 2kN for second support etc. Is there a benefit doing this?
No, the goal is to properly "balance" piping by spring forces.

As a conclusion, it is nothing to be "solved".
Under normal circumstances "you want the springs balanced in the Operating condition - since that is where you want the piping to be all the time. Therefore if the balanced position is the Operating case, then all other load cases are not balanced."
If you want to do something different, you can do it!

Thankyou for your valuable reply Mr.Ashish.

As per my understanding, Cold load & sustain load wont be same. Due to spring stiffness it will vary. We have to build one more case for actual installed load. This actual installed load & sustain load will may equal. And my analysis is without friction only.

Thankyou for your valuable reply Mr.mariog.

If my understanding is correct, while doing cold load spring design, we should take Operating condition load & movement as Hot load & vertical movement of spring & neglect the CAESAR Hanger report's Hot load & vertical movement. If I calculate the cold load (preset load) with these operating load, movement & spring rate selected by CAESAR, the cold load used for analysis is exactly arrived. Depending on supplier spring rate, this cold load will be slightly varied. These slight variation, any way we have to accept.

Once againg thanks to you all for your valuable replies.

Regards,
Gobinath.S

Mr. Gobinath,

Sorry, i did not get that.
please let me know,what is the difference between installed load and cold load.

thanks in advance.

regards

Dear Mr.Ashish,

Please check the Technical Reference Chapter-3 page-127 & Chapter-6 page-11. There the actual cold load has been explained.

Installed load & cold load are same only. But there is different between calculated theoretical cold load & actual cold load.

Regards,
Gobinath