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Aerial Crossing of Natural Gas Pipeline
2

Aerial Crossing of Natural Gas Pipeline

Aerial Crossing of Natural Gas Pipeline

(OP)
What forces must be considered when attaching a pipeline to an existing bridge?  How do you mitigate thermal expansion of the pipe?  Are thrust forces a factor?  The span is 1200' long.  Any help is appreciated.

Thanks

RE: Aerial Crossing of Natural Gas Pipeline

2
Anchor at the ends and install enough guides along the span to allow the pipe to snake, but still keeping lateral deflections within the width of the route allowed.  Increase the number of guides until lateral deflections are restricted to be within the available lateral clearance.

Alternately, expansion loops could be added, if space is available.  

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

Unless there are differences in temperature between the bridge itself and the pipe, both elements will contract and expand at the same rate, so you have to provide expansion loops only at those locations in which the bridge is allowed to move (expansion joints).

If there are differences in temperature, there will be differences in the expansion/contraction rate and you will have to account for those, either by allowing the movement in a controlled manner without affecting the stability of the pipe or by restraining the pipe enought o account for the strain generated by the thermal expansion.
 

RE: Aerial Crossing of Natural Gas Pipeline

Comment:
I assumed (maybe incorrectly) that you were talking about a steel pipe. If it is steel, what I said is correct. If it is PVC or other material, the rate of expansion/contraction does not necessarily have to be the same as that of the bridge structure.

 

RE: Aerial Crossing of Natural Gas Pipeline

If you put expansion joints between the anchors you have to consider a force Ftot which is equal to the contribution of several factors:

Ftot = Fp + Fs + Ff + Fc

Where:

Fp = p * A
Thrust due to inside pressure (p = pressure in N/m2 and A = transverse area of the expansion joint bellow in m2)

Fs = K*dL

Spring force of the bellows (K = spring constant of the bellow in N/m and dL = length variation due to thermal expansion in m)

Fa = F*M

Friction force (F = friction factor and M total weight of the pipeline between anchors)

Fc = (2*At*w * v^2)*sin (ang/2)

Centrifugal force (At = transverse area of the pipe in m2, w = specific weight of the fluid inside the pipe in kg/m3, v = fluid velocity in m/s and ang = angle of the pipe).

Usually the last term Fc has to be taken into account for high pipe diameter and fluid with an high specific weight.
 

RE: Aerial Crossing of Natural Gas Pipeline

I said expansion LOOPS.

NO EXPANSION JOINTS SHOULD BE USED HERE!

 

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

The forces you must consider according to most design codes are as follows:

1) Dead Loads, weight of the pipe acting on supports

2) Dynamic Loads, any vibratory excitations from the bridge structure (may be quite nasty for a bridge) or pulsations in you gas flow causing shaking of the pipe (not likely).

3) Thermal growth loads, Loads imparted to the structure from the thermal growths of the pipe. These growths are calculated from the temperature of the fluid in the pipe and the thermal growth properties of your pipe material. Follow BigInche's advice on the control of thermal expansions. These expansions will also produce thrust loads on your intermediate supports due to the normal force from dead loads multiplied by the appropriate friction factor (0.4 for steel on steel) for your pipe and support materials. This must be taken into account for all sliding supports.

4) Wind Loads, load on the supports due to wind on the pipes cross sectional area, likely to be significant for a bridge with the pipe exposed
.
5) Earthquake loads, Dead load accelerated in the lateral directions by earthquake, size in accordance with you local requirements.

Just my two cents worth.
 

Always remember, free advice is worth exactly what you pay for it!   

RE: Aerial Crossing of Natural Gas Pipeline

The pipe temperature will be primarily governed by its fluid temperature - not solar heating nor ambient conditions. The bridge temp will be governed by ambient temperature comnditions and solar heating. The daily expansion and contraction of the bridge will prove greater than the daily expansion/contraction of the pipe which will be moderated by its fluid temp. You will nedd to perform a thermal analysis of both systems to determine appropriate support design    

RE: Aerial Crossing of Natural Gas Pipeline

Disagree. The lateral and vertical plane should have no relative differential displacements between pipe and bridge.  The pipe is not anchored to the bridge in the axial direction, so consequently the pipe on slide plates when moving will have at first static frictional loads, then dynamic frictional loads and lastly the final static friction load from the supports through the plate to the pipe. Those loads are equal to pipe sum of dead and live loads x friction factor of 0.4 (if steel on steel).  Only the static frictional loads need be considered.  As the movement is relative, it doesn't matter if the pipe is considered static and the bridge moves, or if the bridge is considered static and the pipe moves.  The result is the same frictional loads on the pipe in either case.  Just looking at the pipe alone, with the static frictional loads is all that is required.  The pipeline engineer can leave the bridge analysis to the highway engineers responsible for the approving the permit.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

Usefull for ductile iron pipe crossings, but OP says this is a steel - gas pipeline.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

BigInch,

What are the "cons" of using expansion joints when dealing with steel pipes instead of ductile iron pipes?

RE: Aerial Crossing of Natural Gas Pipeline

Firstly, they are simply not needed for continuous steel pipelines away from critical equipment.  They can usually be avoided entirely in steel pipelines anywhere, including next to compressor flanges, simply by the addition of adequate flexibility.  

Maintenance, maintenance, maintenance, maintenance.  Did I mention maintenance (in an often far away location)? smile

Not to mention the typically higher pressure, leaks, with the added potential of endangering the public by a flamable gas being released into an area with no lack of ignition sources.

 

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

I would never allow a bellows joint for this application, just as BigInch states "maintanence"

All it will take is a minor change to the support during maintance 5 years from now by a road crew who never should have touch it and BAM, blown bellows.

I avoid a bellows unless its absolutly needed, usually only due to a lack of arrangment space to get the needed flexibility or extremely tight pressure drop requirements.

Always remember, free advice is worth exactly what you pay for it!   

RE: Aerial Crossing of Natural Gas Pipeline

BigInch,

Thanks for your explanation: a good display of skills and competence.

RE: Aerial Crossing of Natural Gas Pipeline

Thanks to you as well for posting paper on the "net"-NPSHA pressure paper the other day.  Very enlightening.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

BigInch, can you put a thread reference for the compliment paid above?

rmw

RE: Aerial Crossing of Natural Gas Pipeline

Link to ione's doc post is,
http://files.engineering.com/getfile.aspx?folder=b4584563-0a1d-4566-babc-c5a12c45dbb1&file=DissolvedGasAndCavitation.pdf

Thread header was in the pumps forum, "DissolvedGasAndCavitation"

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

I got to clowning around too much in the other thread and realized I wound up not giving ione enough credits for his post.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

Thanks again BigInch. I don't deserve such a compliment: I always have much more to learn than to teach from people like you.

RE: Aerial Crossing of Natural Gas Pipeline

Is there any concern for needing to calculate thrust on the bridge or supports in the event of a pipe failure?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Aerial Crossing of Natural Gas Pipeline

Good question Keith.

While it is true that thermal loads are routinely considered, I have designed some pipe restraints in nuclear facilities for whip loads from pipe breaks, but never have I done that for refinery, pipeline stations, or offshore platforms, except at specific blowdown and relief valve locations.  Some specific pipe supports or underground "thrust blocks" may be installed and designed for loads due to change-of-direction of fluid flow thrusts at elbows, tees and blowdown points where the pipe itself may not carry those loads, but for outright pipe breaks, I can't say its typical practice.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

In 1996 a task committee of the former "Crossings Committee" of the ASCE Pipeline Division (or "PLD", at the time composed of professionals in oil and gas etc. as well as water/wastewater) presented a then new MOP # 89, "Pipeline Crossings" at the annual PLD conference that year in Burlington, VT.  This manual may be of some interest to you.  While I don't think purporting to address all regulatory and design issues of all kinds of pipeline "crossings", aerial crossings via "host" and "dedicated" or "self-spanning" pipe bridges are discussed in an ~10 page section of this manual.  With regard to all the various host bridges, this MOP makes the opening statement, "The most important concept regarding the use of host bridges is to recognize and accept the primacy of host agency standards and guidelines."  
Also, about the only other thing I would add seeing others responses already to this thread is that under the heading "Combustable Fluids" (not my spelling, but you can tell Engineers did it!) MOP #89 says, "A casing extending the length of the bridge and a sufficient distance beyond is usually recommended."  While not purporting to know all the reasons for such casing (or in effect double pipe) recommendation, I would think it could be argued that casings might reduce the vulnerability or increase the security of such crossings in perhaps multiple respects.     

RE: Aerial Crossing of Natural Gas Pipeline

Whether casing would be used would typically be determined by the owner's specifications contained in the crossing permit.  There is no requirement for casing crossings in CFRs, B31.3, B31.4 or B31.8, or (I believe) in any recently adopted utility infrastructure security regulations.  It can also be argued that casing collects moisture and facilitates hidden corrosion, making leaks and breaks more probable.  That would have to be evaluated against the probability of an attack by other factors.  Assuming that an attack by other factors would be directed primarily at the bridge, I don't think the casing and pipeline would be left untouched, so there would be considerable doubt in my mind as to what true value that requirement might add to overall security of the pipeline.  If it was indeed a strategic pipeline which might be the prime target, it would be far better to seek another route, possibly a horizontally drilled crossing well away from a highly traveled route mounted on a bridge, which would also offer the additional advantage of not having to subject the bridge to possible collateral damage by a specific attack on a strategic pipeline.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

(OP)
Thanks everyone.  rconner - How can I get a copy of this manual.  It appears to be out of print.

RE: Aerial Crossing of Natural Gas Pipeline

Be sure it wasn't withdrawn for the above reasons.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Aerial Crossing of Natural Gas Pipeline

(OP)
Thanks again.  The client is opposed to anchoring the pipeline using anchor blocks.  They suggested we use flowable fill.  Have you heard of/done this before?  Also, is there a way to calculate the effects on the pipe if no anchors are used at all?

RE: Aerial Crossing of Natural Gas Pipeline

I guess there can be a healthy debate with regard to pipeline "casings" for any application and specific design including bridge crossings (and I will not necessarily come down on any particular side of same), although of course it does not appear the ASCE MOP referred to this as a "requirement.  This particular manual I see also now at least partially accessible for reading at http://books.google.com/books?id=X8iawQ2IdKgC&pg=PA56&lpg=PA56&dq=cased+combustible+pipeline+bridge+crossings&;source=bl&ots=_VAHN5aJBn&sig=8iwHrblKJGKov3U6eQQsQuphfUU&hl=en&ei=Bh4MS5iQG8GXtgeTmvHpAg&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAkQ6AEwAA#v=onepage&q=cased%20combustible%20pipeline%20bridge%20crossings&f=false incidentally also defines many pros and cons of different means of making "crossings" and also with and without casings in general.  I have not heard that same has been "withdrawn".   

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