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Re: Seismic load combinations and ASME Section VIII pressure ve

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>I think
>that pressure vessels full of hazardous/flammable fluids should be
>considered as part of life safety issues.
Actually a vessel full of pressurized air will behave like a bomb under 
the right circumstances. An 8 foot tank I was testing which was as full 
of water as we could get it took out a wall I was standing behind when it 
ruptured. There's enough energy in the vessel wall and in the residual 
air to ruin your whole evening if there's a big enough weld defect. 

>What is the 'grunt' engineer to do? Look at this both way? allow the
>stress increase and then check again without it? (hmm, does that make
Part of the problem is that the grunt engineer is apparently trying to 
satisfy the ASME Code requirements with UBC loading rules. You're going 
to have to decide what the seismic or wind loading actually is and use 

Figure all the applicable Code details so that it satisfies the 
applicable sections of the Code for pressure only. That'll take care of 
all the times when the vessel is under pressure and there's no 
earthquake. When there's an earthquake, calculate the seismic stress as 
you normally would, add it to the pressure stress and make sure it 
satisfies UG-23(d). That will take care of the times when there's an 
earthquake and the vessel is pressurised. If the wall doesn't satisfy 
UG-23(d) you can either change the wall thickness or the material so that 
it does. The 20% increase in allowable stress mandated by UG-23(d) isn't 
mandatory, it's just the upper limit. If you want to use a lower margin, 
you certainly can. 

I confess I don't see the issue here--the code seems straightforward 

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw(--nospam--at)        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)

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