ASME Fig UW 16.1 (p) attachment

[Cluain]

I was looking through ASME VIII-1 and was amazed at the weld sizing for a pad flange attachment.
If one attachs a pad flange 1" thick to a flat head 1.5 " thick, then the resulting throat dimension is based on a t(min) of .75". Therefore, one would end up with a fillet leg dimension on the interior of approx .75" and an exterior leg dimension of approx .5625"s.
My weld strengths pass with a .375" inside and out. Can anyone tell me why the sizings per Fig UW 16.1 (p) are so excessive and, can one merely base weld sizes per U2(g) utilizing UW18, UW15 and UG41 for the service load etc..

 

[JoeTank]

Sorry, U-2(g) can not be used to waiver other specific requirements of the Code.

Joe Tank

 

[vesselfab]

because that's the way it is. Early days of code made things stronger than required for safety margins before we had all these new fangled computers to spit every type of report you can imagine. Now after pulling my tongue out of my cheek, it also helps with stress discontinuities.

 

[Cluain]

OK, so lets say my design for the head thickness meets the criteria for U2(g). Am I now able to use U2(g) for construction; ie, attachment of pad flanges. One has to agree that these weld sizes are massive not to mention uneconomic. What about UW-18(d) and common sense.

 

[vesselfab]

well, it's a wonderful thing, our ASME Code, it makes Vessels strong safe and have a very long expected service life.

One thing you have not considered. You have to have enough weld to make sure the pad is ""anchored"" enough to do it's job, to act as a localized thickening of shell or head to reinforce the opening. Weld strength calcs just consider the strsses in the weld caused by pressure. The increased weld sizes in the attachment figures are there to simulate what the attachments would look like if you had actual thickened portions of shell at localized area with sloping transitions to lessen stresses at corners.

Yes, the ASME code is somewhat conservative in some some areas, but our vessels are safe. You have to remember these rules are set up after years of practical experience and are based upon really basic calculations that provide a good design that can be perfomed with limited resources (think before PC's)

Just be thankful that you vessel is not for one of the users that require pad attachment welds to have a leg that is full size of the pad or t pad minus an eigth. If the little 3/4" weld bothers you....that would drive you nuts.

 

[JoeTank]

The conservativeness of the Code has permitted total idiots to design and build safe vessels for a long time. I guess that's not a bad track record. Yeah, some parts defy logic and imagination, but it works.

Joe Tank

 

[vesselfab]

yep, it was hard doing those calcs by hand with a monroe or marchant mechanical calculator, long before the first powerful TI SR-10 (which I paid a hundred bucks for long ago just because it did square roots) was on the market.

 

[JoeTank]

vesselfab,
Do you remember the HP-35 and SR-50 (or was it SR-51?)?

Joe Tank

 

[vesselfab]

oh sure do

I programmed the little strips for the 50 to run calculations and printed out answers on the little thermal printer stand.

then i taped the answer print out to forms I had make to show the formulas used.

after copying, the form look well done

early copy paste before pc's LOL