expansion couplings in above grade pipe

[Lesali]

I'm facing a "new to me" problem and I would appreciate peer review on this approach:
I have an irrigation canal that needs to cross a drainage canal - clear spans 70‘. The plan is to pipe the water across with two 42" dia steel pipes. See attached drawing.
I've encorporated a back-span beam w/ cantilever in order to limit deflection and reduce positive bending moment at mid span of the pipe. I want to incorporate expansion joints and plan to do so at the “beam” inflection points creating a hinge 8' from the support. I've thought of using a Dresser Style 63 expansion joint to transfer shear across the joint. I've also have employed a ring girder to stiffen the pipe at the supports.
Is this a common approch to a long pipe span? Can Dressure couplings be used in this manner? Or, is there a better approch? Please comment. Thanks.

 

[civilperson]

Expansion joints are unnecessary. Either the water will maintain a close temperature or the steel will be stressed within the allowable limits for changes of temperature.

 

[bimr]

The Style 63 looks like the correct expansion joint.

Expansion joints typically do not have the capability to transmit large pressure forces. Restraints are usually installed on both sides of the expansion joint to prevent the pressure force from pulling apart the joint.

For a bridge like you have, it would more usual to have one expansion joint instead of two. The pipe should be anchored on one side of the joint with a sliding restraint on the other.

You should submit your application to Dresser for their recommendation. The most effective use of Style 63 expansion joints usually requires an engineering recommendation. For that reason, a complete description of the installation should be submitted, with sketches or working drawings, if possible.

 

[BarryEng]

If you have a look at AWWA M11 (manual for steel pipe design & installation), table 7-1 shows that a 42" pipe can span over 70' if the plate thickness is 5/8". This assumes that you have a 'normal' saddle support of 120 degrees. With a ring girder support, the span could be increased considerably.

I have designed many pipelines of this size spanning this distance even with plate thicknesses less than 5/8". All of these pipelines have spanned the distance without the requirement for any movement joints. These have included pipelines with high (water utility) internal pressures. With a ring girder support, I have designed a DN1800 pipe with an 16 mm wall thickness, to span 40 m.

Remember that AWWA M11 is a manual for water utility operators & hence is conservative. If you are designing many pipelines, you can use the provisions of ASCE 79 (manual for pipe design by pipe designers in the power industry - power penstocks). This manual assumes that you are already a pipeline designer.

If you do not have supervisors that are pipe designers, AWWA M11 is a good starting point (& generally conservative).

 

[rconner]

I agree with others on recommended reference etc. I otherwise don’t have a real strong feeling about this issue from a theoretical standpoint one way or the other, and as different responders have posted I believe pretty much successful pipeline crossings have been made both ways. However, could also be mentioned that couplings or joints can introduce some flexibility into the system, and also depending on location/design of same provision for at least a couple joints or couplings at least somewhere in aboveground piping might allow for access to the pipeline in the future, or for that matter for whatever reason replacement of exposed piping, and without the need for a cutting torch and welder (and whatever is incumbent with use of same, or a welder required to weld it back etc.), if that maintenance etc. flexibility were for whatever reason desired.

 

[nackra]

http://www.civildesignhelp.info/modular-pr.pdf

I am used to pipe rack/bridge for control of deflection (pipe flowing full) and stresses on pipeline (water hammer, expansion/contraction, etc)

 

[BarryEng]

I meant to mention in my earlier thread, that when you weld the pipe together without expansion joints, thermal forces on an empty pipe will generate about 3 to 4 times higher forces (axial) than for the pressure (water utility) forces. If the steel pipe is empty & subject to full solar radiation, an expected (at least for my location - 35 deg south latitude) temperature variation of +/_ 30 deg C can be expected from 'link in' temperatures.

The manual that I listed previously (power penstocks) uses flexible joints because the large diameter pipes used in the power industry generate thermal forces that are far too high & these forces cannot be restrained economically (especially for above ground pipes).

As far as deflection is concerned, I just lay the pipes with a slight upward camber (very large vertical curve). Each pipe can be deflected a small amount within its joint & welded into position. I usually design the pipe (for a single span) so that (under full loading) the pipe still has a slight upward deflection. A flat pipe (single span) sometimes looks as if it is sagging.

If you use DIPRA (do a 'google' on DIPRA, USA) & download their program (for RRJ DI pipes of course) for a designed soil restraint length (your pipes must be welded together of course - not RRJ). Then multiply the restraint length by 3 or 4 to obtain your welded length required either side of the canal (to restrain full thermal forces).

If you want the calcs for the thermal restraint force, just reply to this thread.

The original reason that I started to weld pipes rigidly (ie - not use 'flexible' joints), was the constant problems of leaking flexible joints (on bridge spans) & constant maintenance. Originally we used to have 'dismantling joints' next to a valve in a valve pit, to aid in the removal of the sluice valve. I found that VERY RARELY was a valve removed & the dismantling joint used. We now just use a 'gas axe' (oxy cut) to remove the valve & replace the valve with a welded band. Much simpler, much quicker & no maintenance. The valves are specified to be able to take an axial load.

For any access into the pipeline, we use a 'manhole' (DN600 tee with a flanged joint) located near the above ground section, in a small circular pit.