Threaded bolt in a pipe

[FC2008]

Hi,
lets say I have a pipe section with a threaded bolt screwed into it. The bolt is now perpendicular to the length of pipe.

I then pressurize the fluid/gas inside of the pipe. If the pressure inside is, lets say 10 000psi how much pretension is recommended?

I have a copy of Machinery's Handbook and have found some equations that enables me to calculate the axial force due to torque. I know this isn't very precise due to the friction factors, I just want to get an overview.

With a M60x1,5 bolt and a torque of 300Nm I get something like 28 200N axial force, which is considerably less than the force generated on the bolt by the pressure inside of the pipe.

So, how much axial force should I have so that I can be sure this thing will not become an missile?

Fortunately, I am not the designer on this project, I'm just trying to get some idea of how this works.

Thank you.

 

[MintJulep]

It doesn't matter in this case.

The point of developing preload in a bolt is to clamp parts together. As your describe your application, you're not clamping anything.

You need to look at the pull-out or stripping strength of the threads.

 

[unclesyd]

As you describe it the bolt acts just like a straight thread pipe plug.
The only little problem I see is determining the hydraulic force act on the bolt from the inside. I would use the nominal diameter for the area and consider it like you would a jack screw.

 

[FC2008]

What if I intend to use the plug to compress a O-ring, C seal or other seal? Then I would like the pretension to have a certain value?
I should have written this in my first post..

Thanks!

 

[rb1957]

you're trying to seal under the head of the bolt ? how much leakage are you expecting to see along the thread ? is the bolt removable ? does the bolt thread into the opposite side of the pipe ?

 

[rconner]

I am some curious about the wording you used in your quite brief inquiry -- you said that you have a bolt that I suspect at least initial readers have assumed is threaded completely through the wall of the pipe so that the inside end face of the bolt is exposed to the pressurization (hence your question re effect of internal pressure). Also, when most of readers hear "bolt" they most often think of straight threads ("NC" or "UNC" etc.) on same, instead of e.g. tapered pipe threads (e.g. "NPT") as are present on most common threaded "taps" through pipe walls e.g. to which smaller pipes or instruments etc. are connected.
What I am reading into all of this but is certainly not confirmed is that you are for some reason tapping a straight threaded hole and passing a bolt through the wall of a tube or pipe, but what could then be some confusing is your ensuing specific question "how much pretension is recommended" (it would appear just screwing a bolt freely though a straight tapped hole from the inside or outside would require no pretension)? Is it possible you really mean "how much clamping force (required for some unstated reason e.g. clamping or pressing something against the outside of the pipe ?) can be tolerated" (assuming you can somehow develop an effective seal to begin with at the penetration) before the thing blows out under th eeffects of that pull as well as outward internal pressure?

In any case, unless you thread an inner nut and/or washers etc. on the bolt end, it would appear how hard e.g. you could pull on the bolt from the outside with the pipe section under pressure would be primarily a function of the shear strength of effective straight threads through the pipe wall, which in turn of course is a function of the size of the bolt and the thickness and curvature etc. of th etube/pipe wall.

If this doesn't smoke out something helpful for you, you may want to provide some more information.

 

[unclesyd]

As posted by rb1957 you need to give a little more information.

Can you post a drawing or sketch?

Is the compression of the seal at atmospheric or at operating pressure?
I ask this as the seating of either type seal is only a matter of distance the bolt travels after contact with the seal, not torque.

 

[FC2008]

http://i163.photobucket.com/albums/t282/Calc_photos/Plug.jpg

I want to make sure that there is a certain amount of pressure between the nut and pipe.

If I for example placed an o-ring under that nut, how can I make sure there is enough compression going on even when the internal pressure is very high? I
can estimate the pressure on that surface to some degree using the equations given in Machinerys Handbook.

I would like to know at what internal pressure, torque value, bolt and nut diameter there is a good chance that there will be leakage past that o-ring, c seal or something else..

( I know that I should not place an o-ring there )

Is this any clearer?

Thank you for your time.

 

[unclesyd]

Place you Oring, just pick your size.
Take a look at Sealtight fasteners, aside from possibly having a fastener that may be suitable for your application there is some good information available.

http://www.self-sealing-fasteners.com/html/socketheadcaps.htm

The information you ask for can only be determined with a lot more dimensional information and enviromental conditions,

Normally with a properly designed restraint for your sealing method like the Oring or C-ring only a flat gasket will require a minimum torque value. For the O and C route all required is a very minimum value to compress the sealing element which will be based on size, etc. Generally you design such a joint were the driving element for the sealing element is self evident, in your case the head of the fastener seats on the pipe, the bottom of the counterbore.

Do you really mean this statement about leakage?

" I would like to know at what internal pressure, torque value, bolt and nut diameter there is a good chance that there will be leakage past that o-ring, c seal or something else.."

 

[FC2008]

unclesyd: thanks a lot for the link! That statement is a mess

 

[unclesyd]

Appreciate the acknowledgement. If possible keep the forum up to date.

If conditions warrant you may want to look at Vibrseal for you application.
This will give you two approaches to your problem.

http://www.longloklocking.com/products_vibraseal.htm

 

[rb1957]

i'd install the bolt/plug with loctite on the threads.