Min Thickness at bottom of blind tapped hole 1

[MrBTU]

My machine shop drilled too deep on some blind tapped holes, so that only .15" of thickness is remaining on the flange at the bottom of the hole (flg thickness is 1.5")

They want to know if they can still use the flange.

The only thing I can think of to justify this to my Code AI is to calc the thickness based on UG-34(c)(2) flat head calc. When I do I get .06 so it passes, and no corr allowance. Also, UG-16 min thickness is .0625 so it passes there too.
I'm inclined to say it is OK.

If it were in the shell I would use App 30, but that is not the case.

Does anyone agree or have a better idea?
Thanks

 

[SnTMan]

MrBTU, have you seen this thread? thread794-278708

Regards,

Mike

 

[MrBTU]

SnTMan - thank you - UG-43(d) gives me what I need - 1/4 of the required thickness of the flange needs to remain.

 

[SnTMan]

MrBTU, you're welcome, you can perhaps finesse the situation along the lines you had suggested or similar, but if you can live with something straightforward out of the Code, much easier to support to other parties.

Regards,

Mike

 

[MrBTU]

My AI now says that UG-43(d) does not apply to my situation because mine is not a studded flange welded to a shell, it is rather an end flange exposed only to end load (which was not clear from my original post). So he's accepting my flat plate calc for now but sending the question back to the home office for "further review"

 

[SnTMan]

Ah, well, there's always the AI to condsider...

Good luck

 

[racookpe1978]

"it is rather an end flange exposed only to end load (which was not clear from my original post). So he's accepting my flat plate calc for now but sending the question back to the home office for "further review" "

Seems that is a more critical situation - A loading directly on the plate.

That is, it seems you would need more than 1/4 plate thickness to be safe.

1) How big a flange - you mentioned it was 1.50 inch thick but not hole dia (1/4 inch? 1 inch? 1-1/2 inch?) The larger the hole diameter, the more the "flat plate" across the thin hole will be stressed at its center.

2) Is it a "drilled hole" with a 118/132 degree "point" at the tip? Or a milled hole with a flat bottom? A drilled hole will be stronger (as long as the hole was actually done with a sharp drill bit that didn't tear up the steel) since the angled hole makes a kind of a truss shape that is stronger than a simple flat plate. On the other hand, a drilled hole will concentrate corrosive material at the extreme tip - which IS where you actually measured the hole, right????)

Do NOT accept the mechanic's "assumed" length/depth of the hole, measure the thing! You have almost no margin already, assuming a depth isn't wise.

3) What pressure service? A 1.5 thick flange implies a very high pressure to be held internally against a theoretical "flat plate" only 1/16 inch thick (after corrosion allowance removed) holding all of your liquid/gas inside the pipe.

4) Is your "(circular) flat plate" assumption for your calc using the whole flange or just the dia of the "plate" at the bottom of the hole? A large dia hole in a small dia flange plate is very different than a 1/4 dia hole in a 24 inch dia flange plate.

 

[MrBTU]

RacookPE - here are answers to your questions:
This is a reversing flange (loose type to appendix 2). OD 14.063", ID - 10.125", w/ 12, 5/8-11 UNC tapped holed on a 11.75" bolt circle. It is a drilled hole with a point at the tip. Pressure is 300 psi.
The AI now says to calc the stress from the UG-34 calc and add it to the stress calculated in the Appendix 2 calc for the hole.

 

[racookpe1978]

OK.

Then you actually have this configuration for the 12x holes, not just one. (I think. Please verify my assumptions.)

Effective Circumf @ 11.75 = 11.75*3.14 = 36.8 inch - 12x.625
Stress is on (36.8 - 7.5 (area where the holes are)) x 1.5 = 43.95 sq inches

Force @ 11.75 = 300 x 3.14 x 11.75^2 /4 = 32,500 lbf

32,500 lbf/43.95 = 740 psi (No margins)

Force at bottom of each of 12x 0.625 dia holes over a 0.15 thick wall looks like the bigger threat. Why not cover the inside of the flange with a 1/4 or 3/16 plate 13 inches in diameter, welded around the outside to seal off pressure from the bottom of the holes?