# Why will a pipe pulled around a curve rotate no torque

1. Apr 22, 2015

### Shane Smith

Hello everyone, I am not a physicist nor do I know that much about physics. I do however have a physics question and this seemed like a great place to get an answer. I will present my situation the best I can. I work in the Horizontal Directional Drilling industry. This industry installs pipelines of various sizes underneath obstacles.
My question is this these drills are designed on a radius design. Will enter the ground at a determined angle hold a tangential line then curve along a designed radius then back to a tangential length then back to a curve along a designed radius to a determined angle then back to a tangential length then exit the ground. Will then pull the product pipe back through these vertical curves underneath the obstacle. There can also sometimes be horizontal curves designed into these crossings. I hope this part made sense.
A pipe is then pulled back through the bore path through the vertical and horizontal curves.
My question is this why does the pipe being pulled rotate somewhat, normally less than 150 degrees but it does rotate with no torsional forces being applied.
Could someone with some physics knowledge try to explain this to a physics layman. It would be greatly appreciated because several instances have come up in the past where I was not able to explain why this occurred other than "physics I guess."
Thanks for any responses.

2. Apr 22, 2015

### rumborak

I think this would benefit from a picture

3. Apr 22, 2015

### Shane Smith

Ok I will post one soon

4. Apr 22, 2015

### Shane Smith

Hope this can help in the understanding of the process. My thinking is this and correct me if I am totally off here. The pull may not always be in the exact center of the product being pulled. There is large amounts of pull being applied to the product, there is friction also involved. Then after the product is pulled approximately 30' it is then relaxed while you can prepare to pull another 30' usally less than a minute or two. Then these forces are applied over and over until the product is pulled from point A to point B.
Again I am not an expert in the field of physics but am an expert in the field of Horizontal Directional Drilling. And am about to pull a product and the client wants me to guarantee there will be no twist of there product even though it is being pulled through two vertical curves and one horizontal with no torque being applied to the product.

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• ###### HDD explanation.jpg
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5. Apr 22, 2015

### Shane Smith

They are thinking that adding weight to the front of the pulled product will prevent twisting. My thinking is, it could cause more.

6. Apr 22, 2015

### rumborak

Frankly, I don't have a good theory as to why the pipe would twist while being pulled. Does it have a preferred direction in rotation?

7. Apr 23, 2015

### CWatters

The pipe is delivered on a drum and has a natural curve in it. I'm guessing that when it's put into the ground it is taken off the drum in such a way that the curve of the pipe is the opposite way to the curve of the tunnel in the ground. The pipe therefore has a tendency to rotate 180 degrees so the curves match and stress in the pipe is reduced.

Haven't time just now to do a diagram sorry.

8. Apr 23, 2015

### CWatters

Ok here is a sketch..

9. Apr 23, 2015

### Shane Smith

It is not on a drum it is welded into one solid piece. Then laid out as straight as possible in the direction of the pull. But it is being pulled through a hole that has a curve. Can the pull forces being applied when pulled through the ground around the curve when relaxed and the pipe is in a relaxed state cause the pipe to rotated ever so slightly. Then this pull then relax process is repeated over and over until the pipe is pulled all the way from point A to point B. Resulting in a rotation of the pulled product. Sometimes it rotates only a few degrees sometimes as much as 180 degrees. These pull forces can be as high as 600000 lbs. depending on the size and length of the pipe. The most recent one was 2700' of 36" steel pipe that averaged close to 380000 lbs of pull to pull it through the hole.

10. Apr 23, 2015

### 256bits

Well, what type of manufactured process goes into making the pipe?
Is it seamles pipe, sections rolled plate longtitudinal welded and then welded together, or spiral coil welded? That could make a difference. I can envision a spiral coil welded pipe acting somewhat similar as a spring that will twist when an axial load is applied. But don't quote that as being the actual reason.

In any event, I suspect it has something to do with the interplay of stresses within the pipe itself. The curves in the bore hole may or may not have anything to do with it.

11. Apr 23, 2015

### CWatters

Only other thing I can think of is the draw wire... Perhaps it twists/untwists when under tension?

12. Apr 23, 2015

### sophiecentaur

If the bore is made with a rotating drill then won't there be helical grooves along the length of the hole? That suggests to me that there will be a rotational force on anything dragged through. Is that too simple an explanation?
Would it be possible to run through the bore with a reamer with the opposite sense of rotation to counter this effect? Or could you put a straight groove along the length, to act as a guide?
In the light of the scale of these things, those suggestions could well be laughable - I realise.

13. Apr 23, 2015

### Shane Smith

I appreciate all the input from minds with more physics knowledge than that of my own. But let me ask this. Say the pipe is above ground on level ground and stretches for 2700' around a curve. Pull is applied to it to move it another 2700'. Would it rotate just from the pull being placed on it to move it along the path around the curve? In my experience the pipe will rotate. I am looking for an explanation from an expert in the field of physics as to why this occurs. I am always trying to broaden my knowledge in all fields. Thanks for all the input and look forward to reading more input. No responses are considered laughable I appreciate each one. It is always good to get a perspective from more than one mind.

14. Apr 23, 2015

### OldEngr63

How is the pull rope attached to the pipe? Is it symmetric on the pipe center line, or is it in any way eccentric?

15. Apr 23, 2015

### rumborak

Shane, I don't think you will find a clear cut answer like "this is a physical law, when you pull a tube around the corner it will twist.".
This will likely come down to how the tube was manufactured, or how exactly it is being pulled etc

16. Apr 24, 2015

### bahamagreen

This sounds like an excellent hypothesis - the drill bit leaves rifling on the inner walls of the hole.

17. Apr 24, 2015

### Shane Smith

That sound like an excellent hypothesis, but on occasion one pipe will be pulled into place as a casing, and then another pipe pulled into it and it will rotate also inside a smooth
pipe. I think it is just the nature of the beast, a round pipe pulled through a curve wants to naturally rotate.

18. Apr 24, 2015

### sophiecentaur

Haha. Good hypothesis but doesn't fit the facts as a theory. H O W E V E R .. . . if ever it starts to turn, it could sustain that turn because of the rifling it makes for itself. Once started, it would get more and more torque. Question - is there any preferred direction or is it random?

19. Apr 28, 2015

### Cecil Tomlinson

I believe the problem is that you are pulling the pipe through more than one curve. A pipe pulled through one curve will be stressed by the curve and experience some strain in the direction of the curve. When it comes to the second curve (which is in a different direction) the pipe will rotate in the shorter direction to align its strain from the first curve with the second curve, else the pipe will be strained in a different direction and could be weakened or might even break from experiencing opposite strains.