UG-37 when no nozzle is welded (female thread instead)

[nachocivicoseng]

Hi,

I am dealing with circular flat unstayed covers that include a female-threaded hole and I am a bit puzzled about application of UG-39(b)(1) & UG-37 rules to check without reinforcemente element added when no welded nozzle is expected: for E1=1 and F=1, these paragraphs always lead to the available "A1=d(t-tr)" balancing the required "A = 0,5 d tr" REGARDLESS OF THE HOLE SIZE d; say, you can simply deduce from both equations:

A1 >= A1 => t>=1,5 tr

and thus, a very little hole seems to need as much reinforcement thickness in the cover as a much bigger one: isn't it quite a nonsense? Am I wrong in any of my assumptions?

Thank you very much in advance for your comments!

 

[trottiey]

First, check if I understood correctly: you've discovered that if your flat head thickness is 1.5 X the required thickness, then no additional reinforcement is required for openings that meet UG-39(b)(1), without a nozzle. Did I get that right?

I think the part you're missing is that you are not obligated to make the entire plate thicker. If you look at Fig. U37.1, you'll notice that area A1 only extends to the limits of reinforcement, which is a circle twice the diameter of your opening.

So yes, a large hole could be reinforced with the same extra thickness as a small one, but that reinforced thickness would have to extend further radially away from the hole. Make sense?

 

[nachocivicoseng]

Hi trottiey, thanks again!

Yes, you got it totally right. The economic reason behind this concern is that for my quite short-d, low-pressure vessels, it is much cheaper to take a thicker plate than adding and welding reinforcement pads. Now I understand better the situation and of course it makes sense - since a higher d requires a higher required total reinforcing area. Best regards,

JIGC
ChemEng