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Below Ground Pipeline Supports ("Uniformly" vs "Simply" Supp

Below Ground Pipeline Supports ("Uniformly" vs "Simply" Supp

Below Ground Pipeline Supports ("Uniformly" vs "Simply" Supp

(OP)
Does anyone have experience installing below ground pipe supports at riser locations to prevent lines from settling due to unstable ground conditions?

I'm currently in a situation where we have a low temp (75 deg C), low pres. (ANSI Class 300) below ground line but because of unstable soil conditions, compaction under the line is not an option.  The below ground portion of the line was designed to rest on undisturbed soil (i.e. "Uniformly" loaded support) however we would like to support the pipe using I-Beams resting on driven steel piles to "Simply Support" the below ground line at the riser locations.  Aside from bell holes at each riser location, the remaining below ground sections of the line are all bore sections.

The line is a NPS 16 STD Gr. 359 pipe (which is ample wall thickness for pressure containment/earth load/thermal growth stress considerations) and the support spacing will be 5m.  The line is cathodically protected so a neoprene pad is placed between each support and pipe for electrical isolation.

I would like to evaluate the difference between uniformly supporting the pipe vs simply supporting the pipe (and the stress concentration that would be introduced via the point loads at each support).  Any comments on past experience/reference material/analysis consideration would be much appreciated.  Please let me know if further information is required.

Thanks in advance,

Auzie5
 

RE: Below Ground Pipeline Supports ("Uniformly" vs "Simply" Supp

With a support nearly under the load, the pipe only sees it as a shear load passing through it.  No length to develop moments.  As long as the riser is not a cantilever standing out over the end of the support somewhere, little moment will be developed anywhere.  Maximum moments with more or less continuous supports will be around WL^2/8 to WL^2/12, if there is any spanning, but then its not continuous supports, is it.

Are all these steel supports to be buried underground?  If so, I would expect to have more problems with them (eventual corrosion) then leaving the pipe unsupported between the 5 meters support locations.  A 16" will usually span that distance quite easily.  

We will design everything from now on using only S.I. units ... except for the pipe diameter.  Unk. British engineer

RE: Below Ground Pipeline Supports ("Uniformly" vs "Simply" Supp

And don't forget, the setteling soil means that your pipeline is supporting a substantial soil weight.  I would probably use the assumption that an 8-inch 'ribbon' of soil is being supported, times the burial depth.

Pretty conservative, but your line is essentially uninspectable after installation.  And, like BigInch, I suggest sacrificial anodes be bolted th your pilings.  Buy them at any Marine supply.

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