Pipe manifold concrete support saddles 3

[JohnWeal]

We have a DN1400 Epoxy coated steel (sch10) manifold in a pumping station which receives 9 x DN800 pipes from the 9 canister pumps. From the DN1400 manifold there are 2 x DN1600 pipelines transporting the raw water up to the treatment plant.

The DN1400 manifold is located within the pumphouse building and is supported on 6 x concrete saddles which are positioned between the DN800 connections. The saddles sit on the main floor slab.

What is the correct construction for such a saddle support? Is the pipe positioned / levelled first and then the formwork / rebar positioned around the DN1400 manifold and then the concrete mix poured?

Is any lining required between the pipe and the saddle? Is any room left for 'grouting' similar to installing a pump base for instance?

Best Regards

John

 

[bimr]

One method is to install the pipe first.

 

[JohnWeal]

Many thanks bimr.

I note from the sketch that the saddle contacts the pipe at the 8 O'clock and 4 O'clock positions on the pipe.

Is that also standard design? I do agree with that incidentally, just that the current saddle design shows it with 9 and 3 O'clock!!

Regards
John

 

[bimr]

This design shows contact between 8 O'clock and 4 O'clock positions on the pipe.

Where thrust generated in a pipe surge (power failure) is possible, the saddles should be extended up to the mid point of the pipe.

 

[EdStainless]

The higher on the sides that the saddle comes the more likely that there will be fit and alignment issues.
And the cushion between the steel and concrete is important.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[rconner]

While bimr makes an interesting point concerning lateral loads, so does EdStainless. I would only add I am aware of some research with flexible pipes that fit saddles reasonably well that indicates that at least from the standpoint of vertical (weight induced) loads or accelerations there is likely little, if anything, gained by going from 150 to 180 degree saddle angles.

 

[rconner]

oops meant to say, "...from the standpoint of maximum localized stress due to vertical (weight induced) loads or accelerations there is likely little, if anything, gained by going from 150 to 180 degree saddle angles."

 

[bimr]

Saddles are weight supports and will not provide lateral restraint unless sufficiently deep.

 

[JohnWeal]

Thanks for the detailed replies.
As the DN1400 manifold receives flows from the 9 DN800 feeder pipes from the pumps, it is pliable that we can have a power cut. It has been a common occurrence in northern Iraq so has voltage stability. Another issue!!
The two DN1600 rising mains that discharge from the DN1400 manifold (via 1400/1600 expansion pipe) do include 2 DN400 surge relief valves in each DN1600 pipeline to alleviate surge. (Bermad type 735)
With controlled start /stopping of the pumps, the pressure in the DN1400 manifold I would have thought be fairly stable.
How is it possible to calculate a lateral thrust in the 9 o'clock 3 O'clock direction in order to determine whether the manifold requires additional side supports rather than mass on saddle vertical load?

EdStainless, what do mean by 'cushion between the steel and concrete'?
I assume you are saying that the 25mm epoxy (non-shrink) grout is not sufficient?

Grateful for you help everyone. I'm really looking forward to the construction phase.

 

[bimr]

You would have to do a water hammer analysis on the piping network.

 

[LittleInch]

If the schedule allows then the best method IMO, is to locate the pipe add some temporary supports, wrap it in neoprene and then box it in with formwork and pour the support.

If however you need to get the supports in first you will need a pipe of the next size up to box in as per the drawing from bimr, otherwise you can't pour the curve in the correct line and height. Either that or you pour as much as you can and then leave the last bit when the pipe is there.

Either way you need a good accurate setting out of support line and level.

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

 

[MJCronin]

I think that it is important to point out that you are asking a question where there are many opinions, and no one correct answer.

Pipe support design is, IMHO an area where engineering, science and Voodoo all intersect.....

MJCronin
Sr. Process Engineer

 

[rconner]

As to question concerning "cushions between steel and concrete", Mr. Russell Barnard of ARMCO Steel delivered a paper at the 1946 AWWA Annual Convention on the development of steel water pipe standards (that was reprinted as a stand alone pamphlet in 1948). This paper/reprint referred to "suitably padded concrete saddles" and that the padding consist of "several layers of felt with graphite in between", or instead pipe can be supported with ring girders or flange rings welded to the pipe. In 1970, the "Welded Steel Water Pipe Manual" of the Steel Plate Fabricators Association (SPFA) provided the most elaboration on shape and dimensional information on supports to date, and in one location where axial movement was to be lubricated referred to "two layers" of "sheet packing with graphite grease". It also mentioned "it is good practice to construct the saddles with a radius about 1% larger than that of the outside of the pipe". While the reason(s) for this suggestion was not provided, I have a hunch unstated candidates could well include minimization of the situation mentioned by another on this thread, where a flexible pipe (that by nature often has at least slightly imperfect circularity) might rest predominantly on the upper corners instead of the arc of the cushion (increasing at least some localized stress there) and/or that some designers might not realize the geometric reality that any thickness of "cushion" effectively makes the radius of the cushion contact arc smaller than any at least the underlying pre-formed structural pier or saddle form, and/or also that it may really not hurt even a perfectly shaped flexible pipe when it deflects very slightly under weight reaction load to bear well on a slightly larger radius arc. AWWA manuals M41 Ductile-Iron Pipe and Fittings as well as M11 Steel Water Pipe a Guide to Design and Installation provide similar calculation procedures for determining maximum localized stresses at saddle supported piping locations, and with regard to the former well-instrumented and published research at American Cast Iron Pipe Company found that for pipes that fit the test saddles well that level of maximum localized stress might occur a few degrees above the saddle tips, or instead a short distance axially off the edge of the saddles at the bottom of the pipes. As to cushioning or lubrication means, the verbiage in the fourth edition of AWWA M11 for steel pipe is remarkably similar to that of Barnard nearly six decades earlier, reading "several layers of felt with graphite in between or joint filler material" (with really only the last four words, it appears allowing some alternative, added since). As to rubber sheet (as one responder on this thread has mentioned "neoprene"), it should probably be mentioned (and while it is probably mostly academic) while a layer of graphite is indeed a "lubricant", at least unlubricated rubber is on the other hand a very high coefficient of friction material. In a water pump stations and plants with generally rather short reaches of pipes, legacy materials with very low coefficients of expansion, flanged or other restrained joints, and often also not huge swings in temperature (even well strapped down), this difference may be of little or no consequence as rubber sheets and other methods not mentioned in the manuals are commonly used. [I only mention this in that much greater thermal axial loads might be encountered on piers or supports at long spans and reaches of pipes strapped tightly down on rubber pads than when lubricated saddles or rollers/bracketed rollers etc. are employed.] Other than explaining the effects on maximum localized stress due to varying saddle angles and axial width, and mentioning other considerations and support mechanisms in e.g. bridge crossings etc., AWWA M41 on ductile iron pipe has not really gotten into specific support design and construction, perhaps due to the fact the support field has so greatly expanded, with a huge variety/numbers of support schemes and specialized support schemes/vendors used for insulated and non insulated pipelines it appears with generally good success.