Aerial Crossing of Natural Gas Pipeline 2

[zsiga]

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

 

[BigInch]

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/

 

[kelowna]

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.

 

[kelowna]

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.

 

[ione]

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.

 

[BigInch]

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/

 

[ColonelSanders83]

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!

 

[stanweld]

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

 

[BigInch]

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/

 

[ione]

Maybe this can help

 

[BigInch]

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/

 

[ione]

BigInch,

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

 

[BigInch]

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)?

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/

 

[ColonelSanders83]

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!

 

[ione]

BigInch,

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

 

[BigInch]

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/

 

[rmw]

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

rmw

 

[BigInch]

Link to ione's doc post is,

http://files.engineering.com/getfil...a12c45dbb1&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/

 

[BigInch]

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/

 

[ione]

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