Putting a partial penetration tap in a blind flange
Putting a partial penetration tap in a blind flange
(OP)
Hey Everyone:
Had a question come across my desk the other day I was hoping to get some input on! We are using a 16" bolted blind flange wiht a 1.5" hole drilled in it as the head of a pressure vessel. On the inside of the vessel, I need to attach a 150# 1.5" flange to the opening but my Engineer wants to drill out roughly 50" of the flange thickness and tap it to screw in some studs for the 1.5" flange. My question is does the code consider this reduction in the flange thickness or not because your fill it in with the stud? I recommended that he only drill and tap 25" for the studs and weld the studs into place, but I was hoping to get some more opinions on this. If you need other details let me know!
2) When you choose your allowable stress from Div II, part D for a flange head, can you use 1.5 x the given amount because your are really dealing with a bending stress and not a membrane stress when it is bolted on? Or is that logic faulted cause it is going against a value given by the Code?
Had a question come across my desk the other day I was hoping to get some input on! We are using a 16" bolted blind flange wiht a 1.5" hole drilled in it as the head of a pressure vessel. On the inside of the vessel, I need to attach a 150# 1.5" flange to the opening but my Engineer wants to drill out roughly 50" of the flange thickness and tap it to screw in some studs for the 1.5" flange. My question is does the code consider this reduction in the flange thickness or not because your fill it in with the stud? I recommended that he only drill and tap 25" for the studs and weld the studs into place, but I was hoping to get some more opinions on this. If you need other details let me know!
2) When you choose your allowable stress from Div II, part D for a flange head, can you use 1.5 x the given amount because your are really dealing with a bending stress and not a membrane stress when it is bolted on? Or is that logic faulted cause it is going against a value given by the Code?





RE: Putting a partial penetration tap in a blind flange
You need to consider the reduction in thickness if you're drilling holes - removing thickness.
No, you canot use 1.5S for the equations even though you recognize that there is a bending stress involved:
How 'bout a compromise solution: Weld some studs (check with matl's / welding engineer) to the blind flange rather than threading them in.
But... your approach of welding a standard flange on the inside is probably cheaper and easier and likely more reliable. That's the solution I'd choose.
jt
RE: Putting a partial penetration tap in a blind flange
Also, the gasket that is being called out is a spiral wound gasket with a y of 10,000 and m of 3. With this gasket I am not getting the blind flange to pass the UG-34 equation for thickness. Are there any other gaskets out there you could recommend that are made of 304 and can be used with liquid nitrogen temperatures?
RE: Putting a partial penetration tap in a blind flange
Regards,
Mike
RE: Putting a partial penetration tap in a blind flange
"Drilled holes to be tapped shall
not penetrate within one-fourth of the wall thickness from
the inside surface of the vessel after deducting corrosion
allowance, unless at least the minimum thickness required
as above is maintained by adding metal to the inside surface
of the vessel."
So does that mean you can only take away 1/4" of the material of you were starting from the outside surface of the shell? In my case I am actually taking away material from the internal surface so it seems like it slightly complicates this, unless I am over thinking it.
RE: Putting a partial penetration tap in a blind flange
RE: Putting a partial penetration tap in a blind flange
Does the Code mean you can tap up to 1/4" of the total thickness?
RE: Putting a partial penetration tap in a blind flange
I would not recommend welding of stud bolts because it may alter the mechanical properties of the bolt. Ask a material specialist before proceeding with this option.
Can you give more detail as to what component is attached to the inside of the blind flange? Why does it have to be bolted? Are there space limitations?
RE: Putting a partial penetration tap in a blind flange
RE: Putting a partial penetration tap in a blind flange
Personally, if I understand the construction and assuming you engineer wants to drill 50 percent of the thickness, I wouldn't have any problem with it.
Metallurgy aside you definitely don't want to weld the studs. What if you wipe one out?
Regards,
Mike
RE: Putting a partial penetration tap in a blind flange
RE: Putting a partial penetration tap in a blind flange
This paragraph assumes tapping a hole from the outside, but it means that if the minimum thickness of your plate is 1" + 1/16" of corrosion allowance, you must have 5/16" of thickness left after you drill your pilot hole. Also, check UG-43(g) for required minimum engagement of your 1/2" studs. The engagement needs to be at least 1/2", but no more than 3/4" (and these values don't account for the metal lost due to drilling a pilot hole).
-TJ Orlowski
RE: Putting a partial penetration tap in a blind flange
If that isn't an option, solve for m & y values using your ANSI flange, then consult your gasket supplier for a suitable gasket for your application with the m & y values you need.
-TJ Orlowski
RE: Putting a partial penetration tap in a blind flange
On further reflection, you are no doubt right, you don't have a B16.5 part anymore, in which case you would have to prove it. So calculate it and make one, if necessary, can't be that big a deal.
You could either treat it as a loose ring per Appendix 2, or a flat head with opening per UG-34, either way I would disregard the stud holes in these calculations, but make them to comply with UG-43.
Regards,
Mike
RE: Putting a partial penetration tap in a blind flange
but question: will that void the B16.5?
RE: Putting a partial penetration tap in a blind flange
As I had worries about, and I believe someone in the string confirmed, you can not just take a 16,5 flange and modify it out of the scope of 16.5, and then still say I dont need to check the thickness because it is a 16.5 flange....
I could probably add pad, but at that point I am probably going to just make a new part, just really hoping I could work with what I have!
Thank you all for the great responses!!!
RE: Putting a partial penetration tap in a blind flange
RE: Putting a partial penetration tap in a blind flange
if lower pressure and temp design, you may have extra T. on the flange.
you may now void B16 and calculate the flange as a flg made of
plate.'hope that will fix your problem. genblr