Tapped axial holes on tube

[sleepdrifter]

I have to design a fixture that is a roughly a 23" ID tube w/ a 1" WT that will have a tapped bolt pattern around the flat base portion of the tube. I've been trying to find how I can calculate what kind of stress would cause the part to fail. My biggest concern is that I'm aligning with 1/2" clearance hole BP so I'm aiming to use 1/2"-13 tapped holes and the slimmest margin I have from major diam of tapped hole to my part OD is roughly .175".

What sort of equations should I be looking at to confirm that I'm not going to shear the threads off since I don't have much material between the tapped hole and OD of the part? Less worried about shearing threads off and more so a major deformation of the thread area due to a thin wall thickness. I've abided by the rule of thumb 1.5D of wall thickness for steel but how can I mathematically determine if my design is prone for issues?

 

[sleepdrifter]

@MintJulep

With a 1/2-13 bolt, using a lubricant with a k-factor of 0.18 and a torque of 80 ft-lbs I'm looking at a clamping load of about 10,698.76 lbs. I'd risk pullout at any thread engagement length less than 0.75in. Ontop of this, I need to factor in the load on the bolts from the pressure vessel, right? Which is roughly 1,000lbs. Can you enlighten me on any concerns with the fasteners having such a high strength for their application? Aside from being able to cut cost on less strong fasteners, what am I missing

Thanks for pointing this out.. up to this point in my career I've been so used to just pulling torque from a torque table and calling it a day (working on extremely overengineered things where failure wasn't much a concern). I'm now engineering things that if they fail could cause serious damage which is why I'm trying to learn how to properly conduct analysis on these designs.

@goutam_freelance @Stress_Eng

Thank you both for the detailed analysis. I'm going to digest this as I have time to so I can understand exactly what's going on in this analysis. I'll also conduct a simple FEA to the best of my ability to see how it lines up with what you two have provided.