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Re: tank cracking

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>My problem 
>is  how to calculate this pressure variation required for the analysis.
I think your problem may be corrosion or fatigue aggravated by corrosion. 
The pressure created by the raker moving at 0.1 rpm can't be all that 
great, and whatever pressure there is would certainly equalize over the 
tank bottom unless there was a great deal of sloshing. Is there a great 
deal of sloshing? 

Where exactly are the cracks? In the tank shell welds or the welds 
attaching the supporting structure to the tank. You description of the 
tank structure isn't very clear. 

A 46 meter (diameter presumably) tank is one helluva big tank to sit on 
columns. Have you taken a careful look at the local loading imposed on 
the tank shell by the suppot structure. Random gust loads, cyclic 
stresses due to filling and draining over a 20 year period and lots of 
other things seem more significant than the raker pressure variation.

The repair welds, unless they're carried out with the greatest care, will 
only aggravate matters. Weld repairs are very tricky and usually end up 
doing more damage from local heating and sloppy workmanship than they fix.

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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