Dished End Minimum Straight Flange

[roca]

Is there a code requirement (ASME, BS, EN, AS) for the minimum length required for a dished end straight flange or can you in effect have no straight flange and weld the shell directly to the head tan line?
This would mean that you are applying weld in the overstressed knuckle area.

 

[SnTMan]

roca, ASME SecVIII, Div 1 does NOT require a st. flange (skirt) when the head is equal to or thinner than the cylinder to which it is butt-welded. See UG-32(l) and UG-33(i).

Cannot help with the other Codes.

Regards,

Mike

 

[athomas236]

Not aware of any code requirement but back in the days when I was a pressure vessel designer woe used a minimum of 3" between the tangent line and the weld.

regards,

athomas236

 

[MJCronin]

roca,

It is my understanding that there must be a minimum "straight flange" for a rolling machine to grasp the piece when as it is formed.

Fabricated heads, of course, can be made without an SF.

The SF length is typically between 1.5 and 3.5 inches.

Why is the SF a problem and why are you asking this question ?

Is this a real world application or just an idle question ?

-MJC

 

[Shmulik]

UW-13 (2): "Formed heads concave or convex to pressure, shall have a skirt length not less than shown in Fig. UW-13.1, using the applicable sketch."

UG-32 (l): "All formed heads thicker than the shell and concave to pressure, intended for butt welded attachment, shall have a skirt length sufficient to meet the requirement of Fig. UW-13.1 when a taper transition is required."

One additional point for rethought or interpretation: UW-3 (1) defines Category A for a circumferential welded joint as: "connecting hemispherical heads to main shell".
UW-3 (2) defines Category B for a circumferential welded joint as: "… connecting formed heads other than hemispherical to main shell".

How about a spherical / torispherical head with no skirt?
Is it going to stand under category A or B ?

 

[vesselfab]

our hemispherical heads have no straight flange...or should I say....a negative straight flange...as the head is actually shortened by use of cut-back to say 3"-6" short of reaching tangent line.

On f&d & elliptical heads, the straight flange is there during manufacturing and trimmed by head manufacturer to maintain the proper depth. It also allows the head manufacturer to have an area to adjust to maintain strapping as the "dished" portion of the head is not perfectly concentric or located correctly due to pressing operations.

 

[roca]

MJCronin
I have always seen / used dished 2:1 and torispherical heads with a SF of approx 50 - 75 mm dependent on wall thickness.

I have just recently seen a head on a vendor drawing with a thickness of circa 100mm and a SF of 50mm.
The SF just seemed a little small to me on first inspection

Thanks to all for all the replies

 

[OwaisGillani]

IMHO, the 2:1 elliptical and torispherical heads always looks better when this rule is followed.

SF= 2 x shell thickness but not less than 50mm.

I dont know where (if ever) I read it but I always find the results visually appealing.

For hemispherical heads, there should not be any straight flange.

 

[MJCronin]

roca..

The industry standard SF is 1.5 inches, but the fabricators can be flexable.

For common types and finshes, see this website:

http://www.brightontruedge.com/types.htm

Contact the fine folks at Brighton in Cincinatti, OH(formerly ENERFAB)with specific questions.

-MJC

 

[vesselfab]

we use 2" as a standard

haven't seen a 1 1/2" called in years except on standard manufactured tanks that are not custom.

 

[athomas236]

gosh guys we are just talking milimeters here

 

[SnTMan]

Engineering. It's just one d#mn detail after another

Regards,

Mike