required material around bolts 1

[dramarc]

Hi!

In a cylindrical reactor with a inside diamter of 100mm with wall thickness of 35 mm a flat lid 40 mm thick will attached by 8 bolts,each 10 mm diamter. The bolts will be screwed into the shell wall. The construction in stainless steel.

How many mm of material (Shell wall) is required Radially "outside" the bolts?
The internal reactor pressure is 100-150 Bars.

THe most stress will be in the shell closest to the flat lid (as I understand it) but if the thickness of shell, radially outside the bolts where sufficently small it would nont be able to hold the bolts.
What do you suggest? Are there any general rules for this?

 

[SnTMan]

I don't know of definitive answers, but:

I would leave at least one bolt dia. margin either inside or outside. I assume you are using some type of gasket to seal a flat cover. Locating the bolts closer to the inside wall would tend to minimize the applied moment on the cover.

After locating the bolt circle you might check the hoop stress on whatever margin you have left.

I assume you have checked the bolt tensile stress due to pressure and it is OK, with some margin left to seat the gasket.

I wouldn't call that a big vessel, but I would call that a high pressure. Be careful.

Hope this is helpful.

 

[dramarc]

I can´t find what rules to apply for this in the code. As far as the internal pressure the further out the holes in the shell wall are placed the better. what forces does the shell wall outside the bolts have to withstand?

 

[prex]

You are really trying to have the beast designed onto this forum, and this doesn't sound OK to me.
First of all your 8xM10 bolts cannot be OK for your data: keep in mind that a 4" flange class 900, with a pressure rating close to yours, has 8 bolts 1 1/8" diameter (M27!). So please don't try to have a confirmation here of something that is clearly out of reason, unless you can justify your choices in detail.
Concerning your question of the space left around the bolt tappings, no special calculation is required: the minimum for pressure design would be that the sum of metal left inside AND outside the bolt hole is higher than the minimum required thickness of the cylindrical shell.

prex

http://www.xcalcs.com

Online tools for structural design

 

[StoneCold]

Dramarc
Maybe you should go with a Parr reactor. That is probably cheaper in the long run. You can look them up at

http://www.parrinst.com

 

[EdStainless]

Even when we built our own units we used metal "C"s to hold the lid on with jack screws for taking up the slack. I don't like bolting into the wall since you now have two 'weak points' together.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[dramarc]

Thanks for the answers!

Prex: This reactor is for personal learning use only and as you problably already have figured out by the means of the construction, it´s not for commercial use!

The reactor will be calculated upon and results minimum results of bolts, thickness etc will be compared with those stated in the code (european and american)

If it will be built, it will be examined under pressure testing with water what happens to it.

regarding bolts there is a company called bulten-stainless that sell bolts with a certificate for pressure vessels that states that up to 640 MPa (before the bolt starts getting longer) can be used for pressure vessels. That´s why i can go down in dimension of bolts instead of using 1/3 or 1/4 of that value that´´s normally done.

Anyway I´m happy for all the answers to my "stupid questions" And I´ve learned alot.

/Andy

 

[JStephen]

I wonder if minimum metal thickness around the threads would be limited by the tapping operation- anyone have experience with that?

 

[SnTMan]

I don't have my refs handy, but it seems to me there is a reference to allowance for tapped holes in ASME Sec. 1.

Confirm/deny anybody?