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[PSUBS-MAILIST] Pressure hull



To all,
 
I would like some reactions on a drawing i made a while ago. You can find it at:  http://www.prismnet.com/~moki/20030126.073208/doubleXendXcapX.jpg .
The idea is to construct a very simple pressure hull out of two torispherical endcaps. The conning "tower" is made out of a standard line pipe with a little overdimensioned wallthickness and the smallest possible diameter. The endcaps are made with a small cilindrical section on it but i am afraid that the tower will intersect with the torispherical part.     
In order to keep it simple i chose a very common steel for the endcaps. It is P265GH (yield strenght 265 n/mm^2, 38500 psi, tensile strenght 410 n/mm^2, 59500 psi). This is an "off the shelf" material at Afflerbach, the german manufacturer. I think you could call it soft boiler steel.
To calculate the strenght of it (apart from the conningtower and viewports) one can use the formulas for a sphere, using the dishing radius of the endcap (in this case 1040 mm). Maybe it is my age, to much alcohol or lack of intelligence but watever method i use (ABS, Lloyd's or an old pressure vessel codebook) i get different outcommings. Can anyone of you say something sensible on this? I am considdering a wallthickness of 12 mm, divingdepth 100 mtr?  
If it is ever going to be build it will be tested unmanned to a depth 50% more than its safe working depth. Should it collapse i will hold no one responsible for that. So please be free to give your advise.       
 
Thank you very much,
 
Thijs Struijs