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Re: [PSUBS-MAILIST] Calculations

Very good point. Logically, if it thick enough steel to be able withstand internal pressure, it should mean that it is thick enough to withstand an equal amount of external pressure.
----- Original Message -----
From: steve
To: personal_submersibles@psubs.org
Sent: Tuesday, July 08, 2003 4:52 PM
Subject: Re: [PSUBS-MAILIST] Calculations

Hi All
 
i noticed a lot of talk recently about propane tanks, the thread was a bit dead but i gathered that the question of 'Is it worth using that old propane tank in the garden', was dumped because the work would probably be more involved to convert a tank than to just buy the tube and end caps.
 
My question though is, how does it compare with cost?  If the cost of the tank is say 1/2 the price would it be a viable option?
 
I had the opportunity to check a propane tank up close recently; i keep seeing psubs in all types of pressure tanks now...i think it's called obsessive compulsive disorder. 
Anyway, thinking as you do, that it would be a great size for a psub i checked out the plate attached to one end.
 
The plate read:
Manf: Robert Bros
BS1500 Class 2
210psi and Full Vacuum
TP 310psi
310 Gals
 
A thought came to me, i remember on previous posts, a lot of talk about the pressure vessel only being rated for internal pressure.  If it states that it can also withstand a FULL VACUUM, how does that affect its suitability as a psub hull?
 
I may be completely wrong here but, can vacuum stresses be compared with external pressure stresses?
It seems to me that if the internal pressure was reduced to 1/2 ATM then wouldn't that be the same as applying 2 ATM pressure to the outside of a hull?
 
i understand that once the pressure vessel used for a purpose it is not intended for (ie. cut / welded etc.) the figures wouldn't be valid anyway, but it makes me think
 
anybody got any ideas???
 
Regards
 
Steve Bosworh
UK
 
 
P.S.    I did check out the manufacturer but they apparently don't exist anymore and the BS number is now obsolete and doesn't say much.
 
----- Original Message -----
From: Chris Jackson
To: personal_submersibles@psubs.org
Sent: Tuesday, July 08, 2003 9:10 PM
Subject: Re: [PSUBS-MAILIST] Calculations

After futher research and sudgestions, I have found that at 100 meters the water exerts a pressure of about 162psi, but what I am not sure of is whether an air tank (decided on an air tank instead of a propane tank due to price and comments I have read about propane tanks) with a 165psi rating would hold up to that kind of EXTERNAL force, since I assume the rating aplies to the INTNERAL force rating.
----- Original Message -----
From: Chris Jackson
To: personal_submersibles@psubs.org
Sent: Tuesday, July 08, 2003 1:12 PM
Subject: Re: [PSUBS-MAILIST] Calculations

I have recently aquired more information, however I still uncertain of several things. I found this link: http://hotconnect.com/tank/vertair.htm and I am considering the 36" by 98" tank made with carbon steel, but I am unsure which pressure rating to use, the depths I am considering will be in the 50-100 meter range, but possibly shallower since this will mainly be used in freshwater
----- Original Message -----
From: Chris Jackson
To: personal_submersibles@psubs.org
Sent: Tuesday, July 08, 2003 11:12 AM
Subject: [PSUBS-MAILIST] Calculations

I am trying to do some calculations to figure out such things as crush depth and required hull thickness. The constants are that the pressure hull will be 36 inches in internal diameter and 100 inches long, and what I need to know is the relationship of hull thickness versus crush-depth with these parameters. If anyone can provide me results or information of a simple calculation program, I would be much appreciative.
 
Thank you,
Chris Jackson