ASME I PG-29 DISHED HEADS

[xgiorg]

HELLO,

AS IT'S EXPOSED FROM ANOTHER POST, I HAVE THE SAME DOUBT, I ADD A PDF:

"M1Can (Mechanical) 23 Nov 06 9:51
I am looking for some help interpreting the required thickness of a semielipsoidal head with a manway. In the past we sized the head thickness based on a blank unstayed head and provided reinforcement for the manway opening ( Re PG-29-4)

But we were recently reviewing a new customers calculations and they size the thickness of the head per PG-29.3 which results in a head thickness of almost double that required for a blank unstayed head ( although no reinforcement is required).

I think it comes down to what is considered "a flanged in manway" , is this an opening integral to the head ie pressed in. The frames for the manways we have experience with are bar rolled and welded into the head , which we check to ensure that they provide adequate reinforcement for the opening.

Any help on this will be greatly appreciated"

PG-29.7 FORCE TO USE FOR A ELLIPSOIDAL HEAD (2:1 KORBOGGEN) THE EQUATION T=5PL/4.8Sw.



THANKS

 

[prex]

I think that both approaches may be correct from the code point of view, though different from an economic perspective.
Which is your question?

prex

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[xgiorg]

I mean, PG-29.7 says that the thickness of a ellipsoidal dished head shall be at least as thick as the required thickness of a seamless shell. In the next paragraph it is write that "If a flanged-in manhole... is placed in an ellipsoidal head" the thickness shall be at least t=5PL/4.8Sw.
Then, if I apply this, I have a head thickness of almost double that required for a blank unstayed head, independant on the reinforcement.
Thats why I ask about what is a flanged-in manhole exactly. Is a little bit amazing, because in asme VIII div.1 this case haven't this difference between a head with manhole and without it.

 

[prex]

A flanged-in opening is an opening where a hole smaller than the opening is first cut, then the perimeter of the opening is hot formed (extruded) in order to form the nozzle neck.
This is not your case, so you don't need to use the second half of UG-29.7, and your approach (per PG-29.4) appears correct to me.

prex

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads

 

[xgiorg]

Prex, thank you, I have some problems with the vocabulary of ASME, do you know if it exist a book where are explained all the terms? the next I have to understand is "flanged opening supported by an attached flue".
I add a image in wich you can see what I think it is. Is it correct?

 

[vesselfab]

A flued opening is illustrated in UG-38. it is where the opening is formed/pulled from the head itself instead of welding in like your first picture.

I have seen nothing in this post that says the manway is actually flued.

I see a standard weld in manway, which is drawn incorrectly by the way.

 

[prex]

Well, my problems for understanding all the terms are not far from yours...
The point to be understood first is that boilers were the very first types of pressure vessel built, and the code maintains rules for fabrication procedures that are obsolete in industry, as are many related terms.
Anyway I wouldn't worry too much with the attached flue, as PG-29.3 is for a dished head (typically a 6% crown radius, see 29.13) and you are dealing with an ellipsoidal head. For sure the flanged opening supported by an attached flue does not resemble your photo: I think it has to do, like the flanged-in type, with the so called autoclave closures, where an oval cover is on inside of vessel and is kept into position by the internal pressure, not by bolting. Whether attached means welded or else I don't know, but who cares, it's something we'll never see anymore...

prex

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads

 

[xgiorg]

Maybe is something like in this photo?

vesselfab, why is it incorrectly draw in the first add?

 

[vesselfab]

NO

that is a ringed elliptical manway

a flue is formed in the head

the neck is not welded in

see ug-38 in code for a picture

 

[xgiorg]

Thanks vesselfab, it was my intention to show in the last picture an attached flue (are you agree?), as you explained UG-38 shows the shape of a flanged-in opening.

 

[vesselfab]

no it is not a flued opening, for the second time

not my job to teach drafting technique...sorry

find a qualified engineer somewhere near you and pay him to tutor you