Thread design help

[Ahmed Zeid]

Hello all,
I am working on a project where I am designing a thick walled pressure vessel (7000 psi internal pressure) that is closed from the bottom and open from the top. The top is to be covered with a threaded cap (kind of a short bolt 3.8 inch diameter). I need help to design the thread. I am not sure where to start. All I know for now is that a buttress thread is probably most suitable for this application. Any tips would be helpful.
Thank you.

 

[506818]

Are you looking to seal on the threads only, or will you be using an o-ring of some kind? O-ring will be a standard groove (see Parker handbook or ISO 3601). Sealing on the threads requires an NPT (i.e. tapered thread). Have a look at Swagelok pressure ratings for tapered fittings as they give pressure ratings based on materials and temperature.

If you're asking about the loads the threads can take, there are some simple calcs (Google bolt load calculation or something along those lines). You'll need to ensure a minimum number of threads to prevent shearing before tensile failure. Also, if using dissimilar materials, you'll need a multiplication factor for the weaker of the two.