Hi. I've been asked to provide som

[kryanl]

Hi. I've been asked to provide some information to a tank vendor for them to engineer and install pipe supports that will run up the side of their tank.

This particular system/tank is an exact copy of an existing tank system at another one of the clients sites. The tank size, pipe sizes, and everything is identical. Therefore, I was asked to go through the old documentation and find the loads from the previous job, and re-submit them to the tank vendor for them to perform the calculations required for them to provide attachments on their tank for our pipe supports. These attachments, on the existing tank will be simple stubs that our piping engineers will attach their designed supports to. Again, they will be copying the previous job's supports.

My question is this: while looking through the files, I noticed that the previous tank was designed to carry an actual pipe support (vertical) more toward the bottom of the tank, and then guides were used running up the side of the tank, up to the top, where the pipe went over the edge (it is an open top water tank), and filled the tank. To me, it would make more sense to put a pipe support (vertical) at the top of the tank, and guide it toward the bottom.

More specifically, here is what I'm dealing with: the tank is 55' tall.
This is what the existing tank is designed for:
Vertical support at 11'
Guide at 22', 33', 44' and 53'
I would have thought the tank should be designed for:
Vertical support at 44'
Guide at 11', 22', 33' and 53'

I thought it was more appropriate to 'hang' pipe, rather than support it from the bottom, letting it potentially buckle toward the top. Granted, the guides are not loose, there is only a 1/16" of a gap on any side of the pipe for it to move, so I suppose that the guides do somewhat act as a vertical support?

Can anyone clear me up, or at least, point me to a site where I can find a thourough explanation? Thanks so much.

 

[BigInch]

Always better to support things as close to the ground as possible. That's a natural anchor point from which things can easily expand and contract freely, if you let them. That's why the guides are above. Bottom supports also do not relying on the tank wall to support the pipe and any additional stresses. Thermal expansion or contraction stresses can be very high and may subject the tank wall to local buckling if attached directly to the tank. Hanging a riser from the top adds its own weight and the weight of its contents to the tank wall stress.

Hanging pipe is good for the pipe, but bad for whatever you're hanging on to. Pipe is much more rigid than a tank wall, so support pipe risers from the bottom whenever you can.

http://virtualpipeline.spaces.msn.com

 

[StephenA]

If you support it at the top, where is the thermal expansion taken up?

Stephen Argles
Land & Marine

http://www.landandmarine.com

 

[kryanl]

Thanks for the replys. In response to Stephens question, the way the pipe is set up, below the bottom support, the pipe turns at a 90 and travels 8' to the closest piece of steel which we can then support. This 8', I had calculated, was length enough to allow the pipe to grow down without overstressing the elbow.

 

[StressGuy]

With an open top tank, supporting from near the bottom with guides going up to keep the line from buckling sounds like a good idea.

On tall towers, we typically support up high because there is usually a hard connection into the tower. By putting the support up near the nozzle, you reduce the potential for stresses due differential expansion between the support point and the piping connection. You do also get the benefit by "hanging" the pipe of avoiding column buckling in the pipe.

From what you describe, I see the pipe as being free to grow up w/o a nozzle connection to fight against. As long as the guides are close enough, buckling shouldn't be a problem.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[kryanl]

Aha! So, the basic rule of thumb is: for an unattached pipe runing up a tank, you support from the bottom because it basically can grow up as much as it needs, but if there is a nozzle connection (i.e. an overflow) at the top, then you would support from the top, and guide down.

 

[BigInch]

No support at the bottom, with guides up the side. If the vessel is too tall, sometimes you have no choice but to support at a few intermediate points along the way.

http://virtualpipeline.spaces.msn.com