API 650 11TH EDITION APPENDIX V

[dmobley01]

Has anyone else had problems with unstiffened shell section of appendix V? We have a tank that passes due to wind with no indermediate stiffeners but when appendix V is applied it no longer passes for just the wind "W". Also the thicker the top shell course gets the more HTS becomes which increases the min shell thickness. Any explainations you guys could give?

 

[JStephen]

First off, note that the shell is good with no additional calcs if the vacuum is only 1".

Secondly, note that you can reduce the factor of safety under certain conditions.

 

[dmobley01]

Vacume = .0625psi. Yeah we have reduced the FOS but it still does not pass due to "W" alone. We reduced by taking the tsmin equation and multipliing it by 2/3.

Do you know why they calculate a different wind pressure in appendix V that is greater than than the wind pressure calculated fore section 5?

So you have not run into anything wrong with these equations?

This is a stainless steel tank so any shell thickness increass is $$$$.

 

[JoeTank]

dmobley01,
The increased $$$$ for a properly designed stainless steel tank is but a fraction of the $$$$ to fix or replace a vacuum damaged tank.

The Section 5 wind forces include a drag coeffioient of 0.6 for wind loads on projected area of the tank sidewall. The Appendix V method uses a coeffiecient of 1.0.

Joe Tank

 

[dmobley01]

Thanks for you responses!

Very true about the money, which is why we are trying to figure this out since it does not make since to us.

Do you know why Appendix V uses 1.0 instead of .6?

It just doesn't seem logical for it to not need an intermidate wind girder for wind in section 5 but does need one (or more) for appendix V for wind alone not even including external pressure yet. Thats using FOS of 2 too.

Also, does it make since that the thinner the top shell course is the lower tsmin becomes per appendix V?

 

[JoeTank]

The 1.0 factor represents the true value of maximum external pressure on the windward side of the shell. The 0.6 factor is an average factor for wind on the entire projected area of the shell and accounts for variation of external pressure.

Joe Tank