Why we are limiting variability of

[suren12564]

Why we are limiting variability of spring with in 25 percent. How does it affect if I choose a variable spring with variability exceeding 25 percent. Thanks in advance

 

[XL83NL]

Do the math. What happens if you set the difference in hot and cold to say 35%? I doubt if any reasonably designed piping system could handle such variations.

I’m not sure why the default industry was set to 25%, but it must have been chosen at some point by someone, and after that perhaps was accepted as the de facto.

 

[suren12564]

That is what I couldn't imagine and seeking explanation. How does it effect the piping system??

 

[EngDesServices]

Spring variability is the difference in loading divided by the operating load (typically (HL-CL)/HL).

As your variability increases, your distance of travel increases, altering the load on the pipe as governed by Hooke's Law (F=-kx). If the component being supported was to be designed for excessive travel using variable spring cans, then it is possible that you end up with a very large localized loading due to the spring becoming significantly compressed/tensioned.

From a practical perspective, constraining variability constrains overall spring movement and likely increases the lifetime of the component. A spring can with a large movement will likely fail sooner than one with a shorter movement when factoring in site conditions like temperature and corrosion.

For systems that have large piping displacements that would otherwise become over-stressed by constraining displacement, like cokers, we've always used constant rate spring hangers.

Michael Hall, PE (TX) PMP - President
Engineering Design Services LLC

http://www.engdess.com