[PSUBS-MAILIST] O2

Thu Jan 30 14:09:23 EST 2020

 I use medical O2 tanks that are filled from a big tank, so they will never be at full capacity, so little chance of the venting off.Hank
    On Thursday, January 30, 2020, 11:47:52 AM MST, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Wow, I've never had that happen. How weird, I would have been sure it would happen only if the tank was left in strong sunlight or something like that. Have to say that would not be a good event. I guess one would switch off the electrical power breaker immediately and surface using only ballast to try not to have any sparks.

On Thu, Jan 30, 2020 at 1:06 PM Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Alec,I have seen one tank empty out. The burst disk went on one of a bunchof tanks we had for a dive trip. It was about 8am so no heat from sunlight to increase pressure.A really loud hisssss for ages. Would sure get you panicking.Alan

On 31/01/2020, at 3:33 AM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Yes, fire as in the Apollo 1 scenario. It's really a hard ABS requirement to meet, because you're already at 21% O2 under normal conditions so any one tank can't contain more than 2% of the cabin volume in O2. I think you'll find that implies the tanks need to be absolutely minuscule. On the plus side, as you say it would take a really, really unusual failure to empty a tank. Make sure the tank valves are readily accessible and not hidden behind anything, and make it a documented SOP for them all to be closed except the one currently discharging.
On Thu, Jan 30, 2020 at 9:22 AM hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Alec, good point, so the risk with that is fire?  In my case, with separate bottles not inter-connected the tank would have to fail or the regulator.  I love simpleHank
    On Thursday, January 30, 2020, 7:02:22 AM MST, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hank,
In addition to the 1 atm rule Sean mentioned, there is a second requirement. The uncontrolled release of the contents of one tank of O2 should not raise the cabin O2 content above 23 percent. This second condition I suspect you will find more onerous than the first.
Best,Alec

On Thu, Jan 30, 2020 at 8:31 AM Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Plumbing all of your oxygen cylinders into a manifold using check valves should suffice. The idea being that any single failure should not empty the entire bank, and the individual cylinders need to be small enough to keep the total pressure increase below 1 atm if you do happen to lose one. 

Examine your entire plumbing system, identifying every connection and the consequences of it failing. Either the consequences need to be acceptable, or you have to have a response plan for that failure. 

As far as corrosion protection for through hull fittings, if you overlooked something in design, plating or cladding with corrosion resistant materials can be an option. At work, I have some vessels that I designed in A105 steel (similar to A516 gr 70, but forgings), that I am sending out to have the fluid exposed surfaces clad with Inconel 625 for corrosion resistance. Of course, I'm dealing with much worse stuff than seawater: hydrogen sulphide-saturated acidified high salt brines at elevated temperature. Still, it's always worth a look at costs of such processes versus the lifetime cost of maintenance. I was expecting the cost of cladding to be far higher than the quote I received. On the other side of the coin, I have some parts in the same system with deep holes that can't possibly be clad or painted, so I had to have them machined out of Hastelloy C276. One 8" end cap is worth more than my truck.

Sean

-------- Original Message --------
On Jan. 30, 2020, 06:04, hank pronk via Personal_Submersibles < personal_submersibles at psubs.org> wrote:

 Sean, okay that is where I missed the boat.  I know about the do not exceed 1 atm rule but did not realize it meant a single tank.  If I lost all my O2 it would be a problem.  I am using multiple tanks so all is good.   I do not have room to drill out the steel plus changing an O2 tank would really suck with this new body. Forget about a change if the sub is in the water.Hank
    On Thursday, January 30, 2020, 5:12:49 AM MST, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Nothing wrong with internal tanks as long as you can prove by calculation that the unintended release of the contents of any single cylinder (provided they are individually valved - hard plumbed manifolded cylinders where a single failure would empty them all would need to be considered together as one) will not raise the pressure of the occupied space by more than 1 atm.

Through hull shouldn't be a big deal either. Drill larger if necessary, and use a stainless insert.

Sean
-------- Original Message --------
On Jan. 30, 2020, 04:58, hank pronk via Personal_Submersibles < personal_submersibles at psubs.org> wrote:

Hi All, here is an interior picture of Limiting Factor that shows what appears to be O2 tanks.  I thought it was not an approved practice to have that much compressed gas onboard.  My original design in E3000 was to have external O2 supply but I prefer internal.  I messed up in two ways.  First off I provided a steel penetrator opening for O2.  The other screw up is when I built the new body I completely neglected access to change out the tank.  So I am going with internal tanks unless someone can talk me out of it.  Hank
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