Re: [PSUBS-MAILIST] Gathering Material to build mini sub

["Mark Steed" <plutomark@mail.astate.edu>]

What a great web site and resource. Thanks, Mark Steed


---------- Original Message ----------------------------------
From: "Greg Cotton" <gregc02@attglobal.net>
Reply-To: personal_submersibles@psubs.org
Date: Sun, 21 Apr 2002 17:43:56 -0500

>Here is the results of a quick search for vapor pressure of 
propane (working pressure of the tank) at 
>various temps.
>
>http://www.gasplants.com/property.htm
>
>In other word that tank in your yard is at 109 psi during normal 
summer weather (70 degrees) and 172 psi 
>at 100 degrees. Of course the temp. of the propane usually 
doesn't hit the peak air temps unless they 
>persist for days and use of propane lowers the temp somewhat. The 
tanks are designed to take worst 
>case temps. Bear in mind that this is internal pressure, the 
ratings for extenal pressure (pressure hull) are 
>considerably less and you have no reliable way to figure what 
that is. Used tanks will almost certainly be 
>weaker than new.
>
>I'm not taking any position on propane tanks as pressure hulls, 
pro or con. I've considered them in the 
>past and they may even have a place for limited depth Psubs, but 
I also tend to agree with the point that 
>you can build something you know for about the same price.
>
>Greg
>
>
>
>Date sent:      	Sun, 21 Apr 2002 15:29:58 -0500
>To:             	personal_submersibles@psubs.org
>From:           	David Buchner <buchner@wcta.net>
>Subject:        	Re: [PSUBS-MAILIST] Gathering  Material to 
build mini sub
>Send reply to:  	personal_submersibles@psubs.org
>
>> At 10:17 -0500 4/21/02, Mark Steed wrote:
>> >I don't know if it has been mentioned here before, but I will
>> >include an experience I had with propane tanks. While 
converting
>> >one for use in an entirely different manner than 
submersibles,it
>> >was discovered that the propane literally seeps into the pores 
of
>> >the metal itself and is almost impossible to remove. The 
amount of
>> >seepage varies with the condition of the interior metal 
surface.
>> >The only way to effectively remove the stuff is to make a large
>> >enough opening in the tank (without sparks!) and once in a safe
>> >location, burn the stuff out. I was totally amazed by the 
force of
>> >the burning residue left in an "empty" propane tank. Any
>> >conversion,or for that matter,any work on propane tanks should
>> >proceed with extreme caution. I do not recommend it.  Mark 
Steed
>> 
>> My dad converted a smaller (100 lb; the tall narrow ones) 
propane tank into a low-pressure air tank for a
>> cannon to fire potatoes and stuff. I think what he did was 
remove the valve and fill up the tank with water
>> all the way to the top before cutting the hole bigger and 
welding his 2" pipe to it.
>> 
>> Also, he's got a lifetime of experience with welding and 
inspecting high-pressure stuff - steam pipes and
>> boilers and whatnot - and he doesn't fill his formerly-propane 
tank with any more than 40 psi air. I don't
>> know what pressure a full propane tank usually holds, but I'm 
sure it's more than that. He's sometimes kinda
>> reckless, so I take this as some measure of how serious this 
is. Something about how this tank was figured by
>> engineers to do a certain thing and ANY use of it other than 
that is a whole 'nother unknown thing. Also, an
>> old tank has been cycled lots of times: full, empty, full, 
empty - and cold, warm, cold warm - and there's no
>> guarantee how much of even that original strength it still 
has. -- 
>> 
>> David
>> buchner@wcta.net - MN, USA
>> http://customer.wcta.net/buchner
>
>
>