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

 

[itsmoked]

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

 

[BigInch]

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.

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"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/

 

[rconner]

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.

 

[BigInch]

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/

 

[zsiga]

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

 

[BigInch]

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/

 

[rconner]

I did not know (or for that matter why?) this MOP might be "out of print"; however, it appears it is still accessible from e.g. Linda Hall Library at

http://leonardo.lindahall.org/ipac2...open&index=.GW&term=Pipeline Crossings#focus.

 

[zsiga]

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?

 

[rconner]

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=X8...combustible pipeline bridge crossings&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”.