min thinning allowance in formed heads 2

[Sergio76]

When we are designing heads (ellip 2:1 or F & D) the result in code formulas give us the min required after forming, i know the thinning allowance depends of many factors from the fabricator, also the knucle radious could no be lower than 6% of OD (for F & D), so somebody could give some safe porcentage or value to add into my calcs in order to get the purchase thickness or thickness before forming.

 

[weldtek]

Since thinning is dependent on many factors, the head manufacturer normally specifies that.

 

[innovation2]

For a F and D use 15-20% thinning, but it may be different for a 2:1.

 

[SnTMan]

Sergio76, reasonably good rule of thumb for 2:1 heads:

1/16" thinning for 7/8" thickness or less
1/8" for over 7/8" to 2"
1/4" over 2"

I would probably feel OK to use these for F&D heads as well.

Again, confirm with the vendor.

Regards,

Mike

 

[PMCap]

While head manufacturer has final responsibility to satisfy the specified minimum thickness after forming, I use the following data to determine nominal (before forming) head thickness requirements when preparing pressure vessel cost estimates:

ASME Flanged and Dished Head: 16" to 72" add 0.032" when trequired is 0.25" or less, add 0.0625" when trequired is 0.500 or less, when trequired is 0.500" or greater - add 15%

2;1 Elliptical Head: 20" to 216" - add 15%