3" Steel Pipeline on Bridge - Allowing for expansion 1

[ross59]

Hi,

I've got a natural gas distribution line replacement project due to bridge reconstruction. The old bridge is coming down, a new one is going up, and I have to move the gas line.

The bridge designer has provided a location to install the gas line, near the edge of the bridge under a removable steel grating, above the deck supports. Rollers will be placed on the deck supports. This will support the pipe about every 15'.

Over a 200-foot span, I calculate 1.75" of contraction/expansion of the steel given 100-degree F temperature variations from winter to summer.

Where we exit the bridge, it should be possible to include a 10-foot section of exposed pipe running vertically, at a 90-degree angle to the span. This should allow for some contraction/expansion, but I'm wondering if that is sufficient and if anyone has a recommendation for methods to anchor the pipe at the base of the vertical leg, to prevent a transfer of forces (movement) to the underground section of the pipline. The pipe is .188 wall steel, with a max operating pressure of 60 psi.

Thanks for any thoughts!

 

[ColonelSanders83]

You seem to be asking someone to do your design for you, rather then asking how to do it yourself.

Perhaps you should consult your design code (which you didn't list) and purchase a copy of Pipe Stress Engineering by L.C. Peng. This will anable you to evaluate it yourself.

Your other alternative is to hire an expert.

Just my 2 cents worth.

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

 

[CRG]

ross59, why the rollers? Do rollers that are subjected to rain, wind, ice, and snow become maintenance items?

 

[ross59]

Didn't mean to offend you Col.

And, as a matter of fact, I was on Amazon checking out the Peng book when you posted.

Phil

 

[ross59]

CRG,

You ask an interesting question.

The current bridge crossing does not use rollers and has been in service since about 1968 with no issues.

However, most of the other bridge crossings I operate and maintain (note I did not "design any of them"...they predate me) do incorporate rollers. The advantages I see with the rollers are:

1. non-conductive rollers will allow for electrical isolation from the bridge structure, possibly allowing me to avoid other means of electrical isolation necessary for cathodic protection in the connected underground section of this piping system.

2. Rollers will allow for the transmission of pipe motion due to expansion/contraction.

Maintenance is of course always a concern. That being said, I've been doing this for 17 years and I've never had any issues with a pipe roller. They seem pretty bullet proof. CFR192 will make this section of piping subject to inspection at a minimum frequency of once every 3 months. Routine maintenance can be incorporated on the same frequency, as (or if) required.

 

[CountOlaf]

Are you exiting the bridge vertically on both sides? If so, perhaps you could anchor the center point, and then each "L" would only have to acount for 7/8" expansion.

As far as anchoring at the base, why not concrete? If you don't want the gas pipe to contact the concrete, a "sleeve" could be embedded in the concrete and then the gas pipe could be anchored to that sleeve...

 

[CRG]

You may want to reconsider the pipe wall thickness for any exposed piping to ensure no damage occurs from external sources. The worst case may may turn out to be rifle fire.

Let me guess that the rollers that you have seen used in other bridge construction were accompanied with expansion joints. My experience is that expansion joints and rollers are, all to often, specified as a substitute for making a detailed pipe stress analysis.

 

[BigInch]

No expansion joints should be needed. Besides they are a maintenance headache in a plant, never mind somewhere out on a bridge. I'd guess a 10 ft leg on a 3" pipe is going to be enough to allow expansion, if the operating pressure is not too high. Anchor in the center as adivsed above to distribute expansion to both ends. Rollers or slide plates could be used. Slide plates should be clamped on the pipe side, with neoprene vulcanized to the inside of the clamp for isolation. You might suggest that the pipe be placed under the beams using hanger supports. The hangers could be isolated from the bridge at point of attachment, or the pipe encirclements be provided with wraparound neoprene pads. Hangers would also allow for some lateral displacement and provide some additional flexibility.

**********************
"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/

 

[ross59]

Thanks a lot Big Inch.

The clearance between the bridge and the river isn't going to allow me to hang. I need to be as high as possible.

I'm waiting on the bridge engineer to get me the latest version of the bridge plans, then I'm going to start working it out.

I wish my Grandfather were still alive. He designed the current crossing. I always wondered why he used 600# flanges on a pipeline that only carried 45 PSI. Once I started in with a calculator...it starts to make sense.
Thanks for the responses guys. I'm going to order that Peng book too. I've got a few months before any decissions are due.

Phil

 

[BigInch]

No I wouldn't want to hang anything below bottom of bridge steel either. Hanging inside a protected area would be OK.

Not wanting to say anything bad about anybody's grandfather, I think there were probably some 600# flanges in company surplus that he had to use first. Even though large stresses can develop at times, I wouldn't expect to see a 600# anything on a 45 psi line. There would have to be a severe lack of flexibility, an appropriate amount of which should always be provided in any piping installation.

**********************
"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/

 

[racookpe1978]

At least the bridge (if all steel construction) should expand and contract at the same rate as the pipe.

This leaves you with an anchor needed at both ends (?) or center (?) to account for the movement of the pipe's relative motion against the "earth" at both ends: So look at the fixed points where you bury the pipe back underground over to the bridge, across the bridge (see recommendatins for a center fixed point) and across, then off the bridge, then back underground.

Keep things symmetric and you only have to do one side for the calc.