There's already a thread about reboiler piping but I made a new one because my case is different...

Our reboiler is spring supported. I designed the spring based on operating condition. Nozzle during sustained case with fluid is also ok but the big problem is when i checked the nozzle loads when the reboiler is empty (during startup), i obtained very big Forces and Moment! What should i do? pls help me. thanks

Problem solved. Wejust do FEA on the nozzle and it is ok. Thanks

Question to the experts. What if FEA is failed? Are there any other solution to this problem? Can we lock the spring during start up to prevent the effect of spring when reboiler is empty? Ive searched all over the net and I can't see a clear solution to this

That depends on where you are in the design. If possible, beef up the reboiler nozzles with repads to handle the extra spring load under the empty condition.

Otherwise, you're going to want to look at using a longer travel (i.e. softer) spring to reduce the variability, or maybe even a constant spring to eliminate the variability. Doing so will leave you with only the differential from the missing liquid weight to contend with.

Failing that, you would have to look at some sort of specialized start up instructions where you may, as you noted, have to leave one of the springs blocked in until the reboiler has been filled to its operating weight. However, I would do everything possible to avoid this. Operations might remember to do this the first time the unit comes up if you are standing next to them while they are doing it. At the next shutdown, the travel stop will probably never get put back in again and the nozzle will see the loads anyway.

Hi,
Sorry if interest has been lost on this post. But.....How do you commission the plat in this case? I am facing the same problem, but the Nozzles are “ok” for both cases (WNC and OPE+H). The difference in weight is about 100 KN @200C –The constant springs allow a variation of 20% of the load.
Would you be able to remove the pins for a 100% variation? - or lines must be flooded?
Thanks for your opinions...

Always, always put in nozzle flexibilities to reduce nozzle loads!

But make sure you define all six degrees of freedom. I made the mistake once of missing the axial degrees of freedom. It showed the Reboiler nozzles passing with flying colors!

But upon further review it was failing miserably...oops. They decided that the temperature differentials I was using were unreasonable in real operating scenarios. They figure the column and reboiler could never operate at too great of a differential temperature, since it is a once through exchanger...the tube side will heat the shell side, if the shell side lost steam.

Not sure if I buy that, but whatever, they signed off on it!

And like Edward said, you always have the option of adding repads to your nozzles, especially if it is new construction.

Threeouts,thanks for your comments. I agreed.Although I like to model nozzle flexibilities only on stream cases.

I will like to know how do you remove the constant spring pins on the empty case if the operating load is 5 times greater? Knowing that we only got 20% to play with.
What has been done in the past? Specialized start ups? If this is the case, what about EXP stresses during start up, if the spring could be acting as a rigid?

What is a stream case, and why would you not model nozzle flexibilities in this case? You will see that your loads will drop dramatically.

It has been my standard operating procedure to model nozzle flexibilities anytime I am dealing with equipment. Once you do a few, it becomes routine. Just don't forget to define all six degrees of freedom!

I meant Extreme....
Generally I like to comply with the vendor allowable loads, ignoring the nozzle flexibilities. Just to be on the safe side. Remember there are a lot of geometrical considerations to be taken into account when using wrc-297.
Also, this bulletin doesn't address pressure stresses or pad reinforcements issues.

Going back to the main question....any opinions?
Thanks,

WRC-297 is perfectly fine as long as it is in the allowable geometrical configuration like you said. I personally prefer using NozzlePro FEA analysis. A very powerful tool that is simple to use, and is very accurate for all geometry configurations. I use NozzlePro to calculate nozzle flexibilities in ALL of my systems, not just in "extreme" cases.

Talk about painting yourself in a corner when you don't use nozzle flexibilities. Conservatism has nothing to do with it.

There are many alternate way out couple of discussed below.

1 ) Firstly i Would recommend to go for rigid support rather than springs by maintaining proper elevation of reboiler with respect to column, so that differential thermal expansion of reboiler process out nozzle & column process inlet nozzle should be minimum. This can be done by adjusting reboiler lug.

2) if at all it is not possible with rigid support then go for spring in that case you can select your spring

a) on average load of your reboiler operating & Empty weight so that column & reboiler nozzle loads will be optimum & will be approximately same in case of empty & operating only sign changes.

b) on operating load of reboiler, but in this case nozzle loads in operating case is minimum but in empty case is exceeds in huge amount. as it happens with "JR Park "

now question about how to reduce these loads if it is exceeding allowable.

3) one way to pass your nozzle loads with WRC -297/nozzle pro/ansys
4) just add down stopper at your lug locations such that these supports should be act only at WNC case & not operating case.
this you can do with your spring also by adjusting lock nut


for detail you can read article named

Column - Reboiler analysis
at
https://docs.google.com/file/d/0B9bzMCku48GPNWxOaDV2YVZXeVk/edit