Dear friends,
why they have put spring at the low point of pipe?
thanks in advance
ozm

According to me possible reasons could be
1. To share the vertical load on trunnion
2. To reduce loads acting on a single cleat in operating case.
3. Column thickness may be less causing piping to distribute the loads

If your question is about the location of support i.e. why rest support is at top and spring support at bottom then according to me this is to avoid differential expansion between first rigid support and vessel nozzle. That's why it is necessary to check pipe flexibility bet. vessel nozzle and first rigid support from vessel.

ozm,

we don't know the configuration of that pipe co'z that picture didn't show the whole pipe. so, maybe after that spring there's a bend and a support. and on that particular support it has a huge vertical force acting on it due to thermal expansion. that's why they put the spring there.

study that configuration and check your loads acting on that area. goodluck.

in this sketch you can see the layout of supports.

Is the + Y at top attached to the tower and if so does the tower grow upwards???


Usually a spring can is a good choice if its questionable whether a + Y would provide to create a restriction to thermal growth. Does the spring spec sheet indicate a travel?

Presumably, if they had the rigid at the bottom, there would be problems at the nozzle. Perhaps the tower design temperature is different than the pipe (not unusual in chem plants).

It looks to me like the rigid support elevation was chosen in order to minimize the in-plane moment load applied to the nozzle.

ozm,

in addition to that, analyse also the behavior around the nozzle of the exchanger if you will put a +Y instead of spring. That's the other reason. As you can see in the configuration there's not enough flexibility on the area of the exchanger. So, in order to minimize the forces and moments on that area they put a spring there.

I would not leave the springs out. Design temperatures may be the same but you can be sure that some operating conditions result in different temperatures. First suspect is shut down. Vessel most probably has a lot of energy stored in internals. Pipe not. Different cooling rates. Check also vessel material. It may be different to pipe. Heat expansion coefficient!

My estimate is 30 m distance between the trunions and spring is designed for 10 to 20 mm movement.

In tower over head, pipe goes a very long vertical distance. For reducing the weight load imposing to nozzle you have to put +y support. As system expand upward in operation it is mandatory to put this +y support as close as possible to nozzle to decrease expand load imposed on it .but sometimes there is a problem. as you know the higher level of tower has thinner thickness then lower parts so there is load restriction acting on +y support. therefore you should put another(or sometimes more) +y support to distribute load between them and decrease imposed weight load but if you put another +y support, in operating condition upper supports lift off and also very huge expand load impose to nozzle in upward direction. Therefore you must use spring in this case.
yours,
reza
mdreza2001@yahoo.com

REZA59,

Can you pl. eleborate on what you mean by the following statements"As system expand upward in operation it is mandatory to put this +y support as close as possible to nozzle to decrease expand load imposed on it" and "as you know the higher level of tower has thinner thickness then lower parts".The second statement is indeed the case for tanks,but for towers?
The first support should be a resting one ( and as close as possible to nozzle)to take care of the dead wt. load on the nozzle and it is irrespective of whether the line is operating or not. In fact in operating condition, because of differential movement b/w pipe and vessel , you may need to use a spring as the first support instead of a rigid one.To take care of the moment that is generated due to differential movement b/w pipe and tower, you may also have to put additional flexibility b/w nozzle and the riser in terms of added pipe lengths.

Regards

My dear anindya
you are right, it is apparent that we should put rest support as close as possible to nozzle to take care of sustain load on nozzle but in some case you can put the support even a bit far from nozzle and there is no problem in sustain case but in operating case as you have increased length of pipe (ΔL=L1άΔӨ) expansion load of pipe may over load the nozzle. If you doubt about it you can try it.
Regarding tower thickness you can ask an equipment professional.
very best regards,
reza

I don't disagree with you and that is precisely what I wrote in my response too.To solve the problem of differential expasion , when we move the first support down, typically we increase the leg b/w the nozzle and the first elbow to reduce the stiffness of this leg and thereby reduce the nozzle loads due to this differential expansion.Sometimes a spring can also be used at the first location.

Regarding the tower thickness, I will definitely talk to an equipment professional as I am not convinved that it should always be like that, the way it is for tanks.

Regards

My observation is that the spring at the bottom has nothing to do with the vessel or nozzle. Rather a deadweight restraint is required to reduce the loads on the exchanger. (Dummy leg supports typically don't take much deadweight load.) A rigid support at the bottom of the riser is not possible since there is significant negative vertical movement coming down from the vertical rigid at the top. A spring on the horizontal run going to the exchanger would be just as effective but that support may not have been possible.