Pipeline River Xing Valve Placement 1

[justhavinfun]

I'm trying to find specific information as to the valve installation requirements, per 49 CFR 195.260. I am aware that valves are required, but would like to place them away from the river crossing and would like to know the constraints of placement in relationship to high water marks or banks. (Major River - 20" Gas Transmission Line - Rural)

 

[Ashereng]

I just read 49 CFR 195.260. It is not perscriptive. It states if you have a body of water more than 100 ft wide at high water mark, you need valves on both sides. It does not give specifics as to maximum/minimun distances, which I think is what you are looking for.

Is this a new install? How long is your pipeline? What is the size? How are you crossing?

In our pipeline system, for new installatins, we now use HDD. So, we locate our valves at the entry and exit sites of the drill. We build a riser, and then go back down.

If you are doing an open cut, I would suggest at least a couple of hundred feet back from the high water mark (to allow for erosion of bank, river meander, etc).

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[Ashereng]

Sorry, didn't read the 20" Gas Transmission line part. My bad.



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[justhavinfun]

I'm aware of the API limitations and valve requirements, I am looking for any other code or construction issues that would prevent me from installing the valves well, well away from the crossing, as in 1/4 to 1/2 mile from the banks.

 

[Ashereng]

I think 1/4 mile might be okay. 1/2 mile might be too much.

The valves are needed in case of leakage. They don't want stuff in the waterway.

Talkt to the department that governs the water way. They will have to okay your final plan anyways.

I think my valves are about 1/4 mile away.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[BigInch]

Depends only on how much product you're willing to spill WHEN the river washes out the pipeline. Put them just as far away as you need to guarantee that the river will not wash out the valve stations and where you can get some access.

 

[Ashereng]

What do you mean by the "river washes out the pipeline"?

River crossings typically have the pipeline 100 ft below the river bottom.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[BigInch]

Well, I guess I mean "WHEN". That's what rivers do... wash out pipelines. I hope you're not trying to say that pipeline washouts don't happen. 3 major product pipelines were washed out on the Trinity River just north of Houston, Texas. (Colonial Pipeline, for one.) Rivers are not static systems and constantly seek lower levels. You just hope they do not do reach the level of your pipeline during the design lifetime of your particular project. What usually happens is that most pipelines are generally well maintained and easily outlast their design lifetime. This is when washouts usually occur, unless the river cross section is monitored and the line is lowered to levels below any new scour depths that fall within the river's new potentials.

Did you hit the zero too many times? Unless the the crossing is installed using some horizontal directional drilling technique, you will NEVER EVER have 100 ft below the river bottom (I assume you mean scour depth). At least in the 30 years I've been doing this, that has been the case. I mean do you have the time and money to dig a 120 foot deep pit to place the thrust boring machine on one side of a river and another 100 foot deep pit on the other side to receive the cutting head??? That doesn't sound reasonable to me. I was construction engineering manager for 750 miles of the BTC Pipeline Project and we did not have any such design (at least one that was not horizontally drilled (ie. not thrust bored) for any of our river crossings.
In fact, I give you a challange. I do not believe you can show me any AFC drawing of a crossing, river, canal, railroad, highway or anything else, where the pipeline is/was/to be/ installed using, lay-in, drop in, cut and cover, or horizontal thrust boring, (or any method other than the relatively very expensive and horizontal drilling method) 100 ft below any level marker. Most pipeline river crossings are placed across rivers by overtrenching to 10 ft below scour depth and pulling them in place, then sinking them to the required level. If you can show me such a drawing, I will show you a company that will go broke within the next 1 to 2 years.

OK back to actual river crossing design. Rivers are not always static systems. Rivers may temporarily reach a static or steady state where the bottom profile is in equilibrium with the current energy level of its particle transport dynamic. River "bottoms", as I think you use the term, are never the critical design case, as a river bottom profile at any given instant in time is dependent on the actual flow state at that instant in time only. Maximum Scour depth for the design lifetime of your pipeline is the design condition. When rivers are flowing at a low flow state, sand particles, pebbles and rocks are deposited, positioned and transported to and from and around the river bottom according the velocity prevalent at that flow state and an equilibrium condition is/can be achieved if an identical flow condition is/will be prevalent for a sufficient length of time. That will be the "river bottom" at the low flow state. Of course, when the river reaches the high flow state, the particle transportation dynamics is usually much different and a new equilibrium state becomes the target river profile, which will be reached, if the new flow condition prevails for the necessary length of time. Hence there is a given scour depth, usually defining a different depth profile, for each given state of flow of any given river. The only time they are (usually) the same is when the river has a sufficiently "hard" bottom in relation to any given flow state the river is likely to achieve. That condition usually means the current state of the river is that it is flowing on bedrock, or some other material that is not likely to change during the design lifetime of the pipeline. The Stokes particle settling velocities will determine the scour depth at your design storm condition, so unless your river is not at bedrock, or some other particle flow insensitive material, you will be able to determine your scour depth for any given flow state prevalent.

So, don't think of rivers as static systems.

 

[Ashereng]

BigInch,

Nope. Hit the zero button the correct number of times. I did round up a bit though. We are typically about 60-70 feet below the bed. 100 sounds more impressive though - sorry about that. And yes, we HDD for crossing large bodies of water. The current climate with most environmental agencies is against open trench. Hence, HDD.

If you want examples of large crossing using HDD, Mears has a good web site with examples of their work:

http://64.66.190.43/hdd_projects.html

4500 feet is about 1.5 km.

Yes, rivers are dynamic systems. Not only the "scour depth", can change, but the banks erode, and the river will also "move". I guess that is sort of like the banks eroding. We have seen rivers move back and forth, over 1/2 to 3/4 of a mile, over the last 50-100 years.

So I guess yes, we are trying to keep our pipelines from getting washed out, by spending a bit more money.





"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[BigInch]

60-70 Maybe, maybe I could believe... that's only 70% deeper than 40. We basically won't do any pit deeper than 40 to max of 50. The rest of the world doesn't care about what the EPA says and the routine is open trenching. For open trenching, 10 ft clear below max scour depth is pretty much std. When we do HDDs, depths below the river bottoms are usually controlled by the geometry of the minimum bend radius that you can make from the minimum drill site setback and still keep within the directional mobility and bending stress limits of the pipe.