Dear forum members,

I have calculated a 24" circular head, considering the internal pressure and the edge moment from the bolts.
Now I need to place a single small central opening (net opening (corroded) less than 60 mm).

Question: do I need to calculate a reinforcing for this opening or may use the paragraph which allows not to calculate nozzles smaller than 60 mm?

notes:
the requirements of UG-45 are fully implemented.
There are no fluctuations in the pressure or special loads on the nozzle

The text of the Code is a bit tricky here, but the conclusion is that the size exemption limits of UG-36(c)(3) apply.

It is tricky how UG-36(c)(2)(a) for cylinders, cones, and formed heads refers to "except as given in (3) below" but UG-36(c)(2)(b) says "openings in flat heads shall be reinforced as required by UG-39." It almost sounds like we've lost that exemption for nozzles located in the flat covers! Otherwise, they surely would have said something.

But refer to UG-39(a). It says that the subsequent rules in UG-39 do not apply to openings that do not exceed the size and spacing limits of UG-36(c)(3) and meet the further restrictions of UG-39(a). Phew, we get our exemption back!

Confirm your dimensions but it appears that 60 mm should be exempted (assuming it meets the additional restrictions in UG-36(a)).

Dear Oded,

You mean 24" is circular flat head?, as per code UG-39(a), reinforcement calcualtion not required for opening smaller than 1/4 the head diameter meaning that 1/4 x 24" =152.4mm.

your opening diameter is only 60mm, so reinforcemnt not required because opening size under or below 1/4 OD.

Thank you.

Regards,
Faizol

As per code UG 39;

"The rule in this paragraph applies to all openings in flat heads except opening(s) that do not exceed the size and space limit in UG 36 (c-3) and do not exceed one fourth the head diameter or the shortest span"

In such case exemption is allowed only if both the conditions are fulfilled.

Regards