Above ground pipeline 3

[Joe1001]

Good day,
I am currently designing a steel pump-line(500mm dia.) The pipeline exits the pump station and surfaces after about 20m. From there it runs above ground for approximately 1500m. The first section of pipline (before it goes underneath a road) is approx 100m. The thermal expansion on this piece of pipe is calculated at around 62mm. The induced stress in the pipe if the ends of this 100m pipe is anchored will be approx 130Mpa(with no expansion joint). The pipe will be continuously welded. I've checked the bending stresses, poison stress etc and all seem to be within allowable limits. Maybe someone can give me some pointers regarding:

1)Can one leave the expansion joint out? If so, will the pipe not fatigue after a period of time due to continuous expansion & contraction.
2)If one does opt for the expansion joint will one locate it approx in the middle (the pipe gradient is flat)? Does one need to anchor the pipe at all, as at one end it will go into the ground(22.5 deg bend), and the other end it will be enchased in concrete underneath a road?

Thank you for your time.

 

[BigInch]

Leave out the expansion joint and the pipe will last for 50 years. Put in the expansion joint and you'll be fixing that every 6 months.

You will have an anchor at the concrete encased road crossing, whether you want it or not.

Your above ground pipe will snake a bit to accomodate that expansion, if you don't guide it. Let it snake a little. DO NOT PUT IN AN EXPANSION JOINT.

Be more concerned about expansion going into the pump station where it might affect pump and equipment alignments. If more flexibility is required, put in bends. DO NOT put in an expansion joint... never, ever, if there is any alternative.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[fortmceng]

joe1001:

did you try putting expansion loops. avoid expansion joints if possible.

 

[Joe1001]

Thank you for the information.

At the pump station we catered for expansion with flexible couplings direct to the pump suction and pump discharge sides. Thrusts at bends and check valves are taken up by anchor blocks to ensure that no loads are transferred to the pumps.

On the pipeline, if one add bends to accommodate the expansion, won't one create problems with the thrust generated at theses bends, i.e large bending moments on the pipe? We are designing for 2.5MPa max surge pressures. If that is not a problem, where would one put bends on a long gradually sloping pipeline. At the moment i'm looking to do it every 150m (expansion approx. 95mm)

 

[BigInch]

Axial force is the typical killer, because it is large in magnitude and coming right at you. Yes, bends add bending moment, but greatly reduce axial forces in the process, so its a good trade-off, as long as you can allow lateral displacement in the middle of the pipe segment. That's usually not so much of a problem as trying to allow movements at the ends of the pipe where the equipment connects.

You really don't have much expansion, as that's only a strain of 0.00004, representing 1240 psi about 8500 kPa. That's nothing for axial stress, but X a big cross section of metal area its a big anchor force. So, add some flexibility to reduce both and allow some of that big section modulus to resist some moment, instead of trying to carry it all in axial load. Note that the above ground section will bow, if it is not laterally guided. It will not buckle, since the total end displacement of 62 mm is so small, therefore you do not need any expansion joints or expansion loops either. What's the arc formed by a 1500 m long pipeline when you move the ends together by 62 mm? Nothing.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rconner]

I have been following this thread with some interest, and I will first issue a response to the question in Mr. BigInch’s last post. Actually I believe a pivot end-restrained lateral bow in a theoretically, totally unfettered or frictionless welded (though that is in reality probably not possible) pipeline due to an “arc length” growth of only 62 mm could be nearly an entire meter off an original straight line at mid-length, if it were assumed the entire line bows in one direction. I would however suspect with such a long line (and while I don’t have direct experience), that the bowing perhaps more likely be somewhat broken up, more or less in rebating or “snaking” fashion, with local bowing starting where the line was advertently or inadvertently installed even slightly off-line.

Available mensuration formulas in this regard for circular geometry are available including
C = 2[2HR-H2]1/2 , A = ?RB/180, and H = 2Rsin2 (B/4) where, “C” is equal to the chord length (defined in the post as 1500 m), “A” is equal to the arc length (1500+0.062 = 1500.062 m), “B” is the angle subtended by the arc, “H” is in effect the mid-arc “bow”, and “R” of course is the radius of the circle defined by the bowed arc. There are thus three equations with three unknowns to solve (and would invite anyone who enjoys a good, hairy algebraic challenge to check my guesstimate).

Now of course if you were using e.g. hdpe pipe with near 15-20 times the expansion coefficient of steel, you could really see some squirming!

While you did not note your specific required service, another arguable way (at least for normal water or sewer etc. service) to deal with expansion, and I will note also some normal levels of imperfect support surfeying/construction, relative ground movements (due to some imperfect beddings/settlements etc.), and all basically without rebating stressing or fatiguing of the pipe walls/welds, coatings, or connections etc. is to use e.g. push-on joint bell and spigot ductile iron pipes with quite large rubber gaskets, suitable lateral tie-downs or other lateral restraint, and external anchorages for major thrust foci like thrust blocking, batter piles with tie-downs etc. Such a system will result in only a total range of VERY few millimeters thermal movement with even VERY high levels of delta T that is basically confined with such design to discrete e.g. 6 meter lengths of pipe (see the table at

http://www.acipco.com/international/engineeringlibrary/engineering-data/linear.cfm

), and this movement is in practice most likely accommodated for “50 years” or more service by slight flexing of the large gasket bulb. [I believe incidentally some particularly surface origin water sources at least in temperate regions can undergo quite a bit of temperature variation every year.]

 

[CarlB]

rconner, like you I questioned that the arc offset would be minimal. I used CAD and came up with 5.9 meters vs your about 1 meter. Radius of arc is 47670 m. Using 2 arcs versus 1 gave about half the offset for half the growth per arc. Break the length into 15 (100 m lengths); each arc offset is about 0.4 m, radius is about 3170. So almost linear relationship. It takes a lot of snaking absorb a little length change!

 

[BigInch]

My point is that, even if its 10 meters, the deflection would have a d/L ratio of 10/1500 and remember the axial stress without bending is 1200 psi. Nothing guys. What are you worried about. If it doesn't catastrophically buckle, which is highly unlikely, please sleep peacefully.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[cvg]

a six meter deflection might put your pipeline outside ot it's easement and in my opinion would be unacceptable. Why not just put the line underground?

 

[BigInch]

Why are you analyzing pinned end bending?
"So, add some flexibility" ... allows some axial movement to reduce lateral deflection so it does not force the entire 6 m bow-out, just as you guys have found out, a little movement albeit in the other direction would reduce that 6 m deflection considerably, and the 6 m is not considering any lateral restraint from contact friction with sleepers or any other frictional resistance in the lateral direction even from resting on the ground. Its the worse case with full anchors at each end. If you want two smaller bends, put a guide in the middle, or 3 or n. Even if he fully guides it, there's only 1200 psi no problem compressive axial stress and he's got flexible couplings at the station no problem if there is axial expansion into the station. If he doesn't guide it, so what. If he puts in a bend, it reduces axial stress. If he does it right, little moment is added. So what. Now tell me why he needs an expansion joint.

cvg, I did warn him, "as long as you can allow lateral displacement in the middle of the pipe segment". Let's let let the OP decide what he can handle and how much flexibility he needs to allow for to keep him within his RoW.

Personally, I've never seen an expansion joint needed or installed in ANY pipeline transmission system of any kind, inside or outside of a station, above or below ground. That includes a heck of a lot of installed pipe from GOM to Canada, Tx to NY, Europe the mideast, Russia to Turkey, not to mention South America. I promise he don't need one here.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rconner]

I used the assumption of a pinned connection simply due to my suspicion that assumed circular arc geometry in that case would be statically determinate (and thus I could solve with a pencil, paper and simple calculator in the admittedly quite quick and dirty fashion that I did, and that admittedly probably does exaggerate the bow some as I explained). Now, I do feel that pressure and thermal expansion/contraction etc. of welded pipelines, and what movement/growth etc. can result when same occurs, may evertheless be something quite helpful for folks to know.

In this regard, I do know incidentally of a paper by Ulrich Luscher et all of Woodward-Clyde and James Maple of Exxon entitled "Pipe-Soil Interaction, Trans-Alaska Pipeline" I think presented at an ASCE Pipeline Division Conference in San Diego 1983, wherein some details of an actual gas pipeline bowing occurrence in Russia more than 40 years ago were included.

In that case, a reportedly initially buried 40" (~1000 mm) diameter welded steel pipeline that was installed apparently with loose sand in cold weather (and that backfill may have been eroded some) reportedly bucked roughly ten feet (~3 m) up out of the ground and into the air, and over a 213 feet (65 m) unsupported span, in sort of "Nessie" fashion when under operating pressure and warmer operating temperature (that was reportedly only 118 degrees F. or 48 degrees C.)!! In that case I suspect more footage of pipe was however likely operative, and where the upheaval occurred may also have been at a location of at least a slight down slope of the pipeline.

While I suspect all parties know much more now than they did then (and one would hope as a result of at least natural evolution that designs/installation conditions etc. are likely at least some improved over what they were in Western Siberia more than 40 years ago!), this would appear to be at least one example of at least uncomfortable occurrences that can occur due to at least unanticipated behaviors.

Luscher et al concluded, "To prevent excessive (and possibly damaging) pipe movements from occurring during early operation, lateral and longitudinal stability and restraint in straight sections, in bends, and at transisitons to elevated pipeline must be considered in design."

Everyone have a good weekend.

 

[rconner]

Oops, I pulled down my book to double-check and the paper I remembered is not from the 1983 San Diego ASCE conference with the title, "Pipelines in Adverse Environments II", but I suspect from an earlier conference with the same name (as far as I know though everything else is as reported).

 

[Hansito]

Joe,
Your presentation shows (civil/Environment). Don't get me wrong but this is a Piping Stress Specific problem, if is possible have a word with one, besides valuable information I saw you have already received here.
For a pump system you should have a Piping Stress Study made with some specific software like Caesar II.
A main rule in piping is never have 2 anchors (or something similar) in a strait run. Do not count with lateral deformation for that case, mainly with such big diameter as 500 mm. Besides you need guides on the run, remember you may have other loads like seismic. I agree with some previous responses which mention a possible loop, I agree that expansion joint should be avoided.
Regards,
Hansito

 

[BigInch]

rconner,

Yes they buckle in that type of installation. There was no anchor at a road crossing within 1500 meters and probably at least another 3000 m before that 48" diameter formed a virtual soil anchor, and without any additional flexibility at the point where it was reburied, plus a much greater temperature change than is being discussed here, it is possible. Yes, its very possible to experience a pipeline buckle. Happens in cold places like the FSU quite often actually. The thermal stress here is 1200 psi. Not quite the same as a 50ºC temperature change.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[RoyJoy]

Greetings all. I was wondering if anyone would be able to answer a question for me with regard to flow over a backward facing step. Is there anyway to characterize the ratio H/X for the reattachment of flow at some downstream point given only the H and without the use of numerical modeling? Thank you so much for your help.

 

[BigInch]

RoyJoy, Please start a new thread and in that thread please do try harder to explain what you mean by "backward facing step" and "H/X".

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/