Trapeze Supports 1

[engrpiper]

Which is better and why.

Back to back channels?

"W" i-beams? Why would a spec not allow "W" shapes?

Thanks for your replies!

 

[BigInch]

What's the difference between back to back Cs vs W, except more fabrication cost, more corrosion and more surface to paint?

I would use 1-C where possible, keeping in mind that any axial displacement of the pipe above would tend to twist them useless, and a W section for a heavier load.

I've NEVER seen a spec that prohibited W shapes for pipe supports. Probably a mistake. Ask for a variation.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[MJCronin]

Suggest that you repost in a structural forum..

Big inch...you are not a structural engineer, are you ?

The use of a single channel or "C" in a trapeze support in not recommended because you are not loading the member properly. Twisting (shear) is induced in the single C when loaded in this manner

Back-to-back channels are always preferred because the load is applied to the composite member properly and only bending is induced.

-MJC

 

[BigInch]

Whoooo. I don't recommend second guessing anyone you might find cruising EngTips. I've been doing this for 100 years now. And since you mention it, I seem to remember that actually my first registration was as a Civil/Structural P.E. in Texas, 1981. Even before then I started doing pipe stress for Nuclear Plants, South Texas Project, Matagorda, Texas, I realized that piping is just a space frame with internal pressure that sometimes got very hot. And as for most frames of any kind, Loads => Strain => Stress => Deflection so I don't see a lot of difference. I've designed structures to 200 feet high, multi-story chem process finishing buildings, 100 ton reactor foundations, added decks and helicopter landings to offshore platforms and pipe stress in my spare time. The pipes kept getting longer and longer, until my record got to be a 42" diameter pipeline 1500 miles long going from 0 to 2800 m elevation ... twice over two intervening mountain ranges. I've designed compressor foundations for 5000 HP recip compressors, then changed the cylinders myself to new flow conditions 5 years later, pipe bridges over Tx and La state highways, stone column foundations to 30 m depths for equipment along the Red Sea. Converted a gas line to 2-phase by designing and installing 7 liquid handling piping skids on offshore platforms. Hot heavy oil line hydrauics, to multiproduct pipeline operation design, not to mention developing a national refined product transportation infrastructure for a large mid-east country. Engineering, Purchasing, Construction, Client Rep for 2000 miles of offshore survey, Civil Structural Engineering Dept manager, Engineering Project Manager for pipeline projects up to 500 MM$. OK you tell me. To be honest I really don't know what I'm any more.... structural, petroleum, mechanical or civil? IMO, I'm getting very close to being all four plus some.

Anyway getting back to the "C"s .... If vertical loads were small, such that eccentric loading on the C causes only minimal torsion, and axial pipe loads are minimal to nonexistant, as I would be the case if using a swinging support since they don't resist any to begin with, I would not see anything wrong with using a C. Try specing a back to back C on an offshore platform and the maintenance and operation department will schedule you for some open heart surgury.

And I also note that it is really very difficult to avoid torsion or eccentric bending in some form or another when loading a C in any manner, so are you saying that Cs should always come back to back? I say, check it, feel it, smell it. If it works, use it.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[lilliput1]

Better to use a 1 5/8" square unistrut than a 1" C.

 

[BigInch]

Neither will I argue with that, except I'd say better than a 3" C. And nobody's got to assemble them B/B.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[desertfox]

Hi engrpiper

The suport system you use should be suited to what your supporting in terms of load, convience of mounting etc.
For pipes I see no point in welding 2 channels back to back
unless its just a one off support somewhere as Big Inch stated its just extra fabrication cost.
For supporting long running pipes there must be off the shelf systems you can purchase similar to the site I found
here:-

http://www.lebeaucontracting.com/pdfs/powerstrut.pdf

Further if you use back to back channel which in reality is an "I" beam then they will see a bending load "only" if the supporting threaded rods are mounted evenly about the neutral axis ie you need 4 threaded rods to prevent a torsional load on a back to back channel or "I" beam unless
you decide to put threaded blocks in line with the neutral axis of the "I" beams or back to back channel but again think of the cost.

regards

desertfox

 

[JohnBreen]

Hello,

In light of the discussion thus far, I thought I would mention that the ASME B31 Pressure Piping Codes require that the pipe supports comply with the requirements of MSS SP-58. This being the case, it would be prudent to look at a good pipe support manufacturer's catalog to see what MSS SP-58 pipe supports look like. E.G., I don't think you are going to see unistrut in MSS SP-58.

Just a thought.

Regards, John.

 

[BigInch]

John, Great point, however not every pipe is pressure pipe and not every pressure pipe is designed to B31.X, so its not ususual to see unistruts and many other types of non SP-58/69 compliant supports. Is it not also possible that unistruts or some other structure can be used to support/hang an SP-58 support?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com