Vertical Spacing for Pipe Supports

[NewMechanicalEngr]

I've found plenty guidance on horizontal pipe supporting, but very little to none on vertical.

Can anyone please help me determine how far the following pipe sizes can extend beyond the last support if they are installed VERTICALLY? Basically, how high can I extend a vent pipe after the last support?

1" diam, S/40
1" diam, S/80
1.5" diam, S/40
1.5" diam, S/80
2" diam, S/40
2" diam, S/80

Thanks for your time,
Charles

 

[ApC2Kp]

NewMechanicalEngr,

A suggested maximum vertical extension past support might be half of the maximum horizontal span.

So approx. 6 ft for NPS-1, 8 ft for NPS-1.5, 10 ft for NPS-2

Loads of seismic, wind, equipment vibration, etc will make the stress situation more complicated for support / length.

Avoid putting elbow or angle at exit of vent pipe, as very large bending loads could develop and deform vertical pipe.

 

[DSB123]

NewMechanicalEngr,
You need to consider vortex shedding/resonance on the overhanging length of pipe due to wind. If the natural frequency of the pipe matches the vortex shedding frequency then "problems".

ApC2Kp,
I would not like to think of extending a 2"nb pipe 10 foot upwards past the last support unless its a "solid" pipe.

 

[NewMechanicalEngr]

Thanks for the comments.

There are numerous examples of lights on conduit, vents, cameras, etc at many facilities. However, I was looking for a sound basis.

Any other feedback and information is welcome!!!

Thanks again,
Charles

 

[JohnBreen]

Hi Charles,

Vertical piping seems always to demand a little creativity in its design. The insights above provide you with some things to think about.

Regarding your vent piping, it is a simple cantilever problem. You have cantilevered beam, presumably simply supported on one end and you have to consider all the various loading cases and design for the "worst case". The pipe and any other inline hardware will be important as will the wind loadings. Then as mentioned above you must look at the natural frequency of your cantilevered beam and safeguard it from the oscillations that may occur due to the shedding of air vortices as the wind moves past the circular cross section. As you have a cantilevered end, the thermal expansion and contraction of the piping will not be restrained so that should not be a problem. If you have a vent pipe from a safety relief valve there are other issues to be considered and you should look at ASME B31.1 (Power Piping) in Appendix (Roman numeral) II.

For other considerations in designing vertical piping, you may want to look at this thread:

thread378-210714

Regards, John.

 

[MJCronin]

To all..

This is a little off subject, but not much....

The biggest challenge I have ever faced in supporting a piping system was on a "black liquor boiler" in a papermill.

The piping was large diameter (~14-16 inch NPS), thin walled stainless piping (sch10s), and carried a dense liquid ( SG = 1.5). at ~425F The piping riser went vertically up the side of the boiler some 150 ft with branches.

A detailed CAESAR-II pipe stress analysis was necessary. Because of the large SIFs from the thin walled elbows and the local stress problems, several iterations were necessary to come up with an acceptable scheme.

The client was told that he could either put in three sets of trapeeze spring hangers (with local pad reinforcement of the pipe wall) on his riser. OR...... he could change the riser to schedule 40S piping and have a simpler support scheme.

The 10S piping material had been ordered and the client was totally outraged. He wanted a cheap simple support scheme and he wanted it now.......!!!

I was working as a consultant in Maine at the time and was the only one who had any knowledge of CAESAR-II. I was blamed for my "uncooperation with the client", discharged and vowed not to accept any more positions involving piping stress analysis.

Moral: Risers can be tricky....don't accept a job where you are always the one that gives the client bad news..

-MJC

 

[ApC2Kp]

NewMechanicalEngr,

For comparison, there are specifications for flag poles,
(flagpolewarehouse.com)
that show a residential quality flag pole of 20 ft height, has aluminum tube of 2.25" O.D. , 0.1875" wall thickness, rated for 59 mph wind on 3' x 5' flag, or 79 mph bare pole.

The NPS-2 Sch40 pipe would be roughly similar to this 20 ft flag pole. The flag pole has a tapered geometry for less wind loading, and less mass with aluminum for higher resonant frequency. The strength of the carbon steel pipe would probably be greater than strength of aluminum tube, but then who wants to re-paint a flag pole!

 

[rconner]

Small iron pipe might indeed make a quite effective flagpole, though I guess it might dictate more than one to hoist it for some purposes (fyi see

http://www.sftt.org/cgi-bin/csNews/csNews.cgi?database=DefenseWatch 2005.db&command=viewone&id=88

and more recently

http://www.askthebuilder.com/381_Patriotism_is_Never_Out_of_Style.shtml

).