Piping Loads

[dcw815]

I'm a structural engineer but need some advice. Ive done lots of pipe supports and racks with piping engineers before but in this case we dont have a pipe stress engineer involved. Yet.

We have a 36inch diameter pipe that's 20ft off the ground and about 90ft long before it elbows down into the ground. It has 6 pumps below it that feed it with wastewater effluent. The contractor says the pipe supports dont need any bracing because theres no lateral load in piping.

In my opinion it needs a piping engineer to determine if theres guide or anchor loads. At my past job if we didnt have a pipe stress analysis we assumed 30% pipe weight for friction load at guides and 35N/mm pipe dia for anchors plus seismic.

In your opinion is there obviously lateral load or does it need a piping engineer? What does B31 say about when you need a piping engineer to check it? Is there a minimum requirement? Thanks.

 

[bimr]

The piping load is the sum of multiple loads. You have the dead load of the piping, fluid, and whatever else is attached to the pipe supports.

You also have wind load. You also have earthquake load.

You also have the friction load from the pipe supports. These are the pipe anchor and guide forces caused by restrained dimensional changes caused by thermal expansion or contraction of piping under normal operating conditions (e.g., loads from a pipe stress analysis).

This pipe is large enough that you should have a pipe stress engineer evaluate it.

 

[1503-44]

B31 basically says you always need an experienced pipe stress engineer to do the stress analysis.

 

[MJCronin]

You can always trust the wisdom and honesty of the installation contractor, dcw815 ....

They know more than any engineer plus they will always stand behind what they claim ..... They will never go back on their word ...

My opinion only

MJCronin
Sr. Process Engineer

 

[LittleInch]

DCW815,

An experienced piping engineer, looking at the design, temperatures, other loads like wind and thermal expansion (when empty), snow, ice, seismic, people climbing all over it etc may simplify it down to your simple guide, which is better than the nothing that your construction contractor is telling you. Construction contractors in my experience never hang around long enough to see their constructions fail in operation and therefore their opinions are worth listening to, but ignoring 90% of the time.

You need to design the supports. To design the supports you need loads. Those loads come from the piping engineer / dept after some due analysis and design work.

Now you can forget about this and use figures that worked on the last job, but real life has a habit of not always being the same aa the last job. Might work this time, but if it doesn't and the structure bends / moves / collapses are you going to be sufficiently far away that they can't find you or your company or???

You clearly know what you should be doing so I would suggest that that is exactly what you do - the right thing.

There is very rarely no other loads than vertical weight. If not during operation then construction.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

20ft off the ground obviously needs adequate sideway resistance. Even if it is a moment connection at the baseplate, the effective column buckling length is 2x, i.e. 40ft! It probably also needs longitudinal struts to an X-braced bay to resist the friction forces. Otherwise you only have the pipe holding them upright. It will be a major shape just providing the min kL/r.

 

[dcw815]

Thanks all. That's what I thought. Wanted to make sure I wasn't out of line before I make it a bigger issue.

 

[1503-44]

Make it an even bigger issue.

 

[KevinNZ]

The pipe may not have side loads or need side bracing but the piping designer should be one saying that.

 

[1503-44]

Oh come on. The pipe is holding the support up, right?
The connections look hinged.

 

[racookpe1978]

Sure. At the moment the photo was taken, the pipe may well have been "pulling up" the support. Depends on the pipe temperature expansion/contraction moment, and pressure and load condition (empty, vented, full, etc.)

But you are absolutely right: It is the pipe stress engineer who decides where the pipe is, and where the support is and what its loads actually are, under all reasonable conditions of loading, temperature, and dynamic (weather and ice) loads.

 

[1503-44]

That support looks like not even minimum K*L/r[sub]x[/sub] and K*L/r[sub]y[/sub] are meet, even if it was solid steel.

 

[KevinNZ]

The support in the photo is pinned at both ends and loaded only in compression. The pipe design only requires vertical support at this location. The pinned ends means no frication to consider. The pipe is providing the lateral support to the support.

 

[1503-44]

Thats what I thought. ??? I thought you had earthquakes in NZ. ???

 

[KevinNZ]

Sure do. There are braced supports and anchors near by.

 

[1503-44]

I was hoping that too.

 

[racookpe1978]

The vertical pipe support in the picture is just acting like any of ten thousands suspended supports: But, when the pipe expands or contracts, the "swing" induced will cause the pipe to lower a little bit across the top of its "circle". The arc of support is only one way though, it will kind-of-sort-of act like a pinned support going left-right with respect to axial flow.

 

[1503-44]

Except it is kind-of-sort-of in compression, until the pipe expands. Then maybe becoming a tensile load when bending the pipe down. And adding more bending moment at center span, instead of less. Interesting concept.

 

[KevinNZ]

The concerns above can be checked by including the support steel in the stress model.

If vertical movement of the pipe is concern try this,