Re: [PSUBS-MAILIST] Compressed Air Quality

[CWall@swri.edu]

What initially failed on the Thresher was a silver soldered joint- not a welded
 joint.  The quality control and inspection procedure was the real culprit, and
 the Navy completely revamped the protocols for silver soldered joints after
that. (It's a "sweat-soldering" procedure, and the joints weren't "wetting"
completely- the capillary action wasn't pulling the solder into the gap.)

The MBT emergency blow valves did ice up, for the reasons you state- and those
valves were also re-designed.

You are correct when you state that the drop from 2000 psi to 500 psi will
cause the temperature of the gas to drop by 3/4ths- but the reader should be
cautioned: that is *absolute* temperature- so if the air is equilibrated with
the surrounding water at, say, 0 degrees C (which is 273 degrees Kelvin), it
will drop to a quarter of that, or 68 degrees Kelvin- which is minus 205
degrees C, or 337 degrees below zero Fahrenheit.   And while heat flow into the
 air from the water will mitigate that somewhat, it shouldn't be any wonder
that rime ice would form at the lip of the valve.

 In any case, it's not the moisture in the compressed air that is the problem-
the valve gets chilled and the splashing of water in the tank throws up liquid,
 and that is what freezes and causes blockage.  You can get around that with
good design.  Slow introduction of the air also helps, because the heat flow as
 the valve chills has more time to work, maintaining a higher temperature (or
rather, lessening the drop).

( I had a buddy that was on a sub in the same class as the Thresher, and when
the final report on the valves was issued, they were at sea.  He told me that
the skipper stopped the sub and yanked the valves and had the onboard machine
shop modify them before they dove again- I don't know if that is true or not,
but I think the solution was obvious once they knew what the problem was.)

Craig Wall
---------- Original Text ----------

From: "Robert Carlson" <rob.carlson@gte.net>, on 11/15/00 12:49 AM:
To: Incognito2@CTC@SwRI26[<personal_submersibles@psubs.org>]

Joe,

You are probably correct that there is little danger of creating ice cubes
unless one was to use some form of orifice to restrict flow (why, I'm not
sure).  However if you calculate the tempature change in your example (2000 psi

to 500 psi) your gas tempature will drop to 1/4 of the original tempature.
Consequently, your nozzle tempature will be below freezing tempature for water
(assuming that you started around room temp).  If there is sufficient moisture
in the air then you will form ice - how much is the question.  If your piping
is large enough then I would guess it would be hard to turn it into an ice cube

machine.

As for the Thresher (I'm no expert here): I had heard that there were two
things that compounded the sinking. First, there was a steam line rupture in
the piping (weld problem, perhaps).  As it turns out the procedure at that time

was to SCRAM the reactor (steam ruptures cool down the reactor too quick and
there was a fear of loss of control of the nuetron reaction) and shut the main
steam stops.  Unfortunately, they were not able to perform a fast startup and
so once the leak was isolated they had to start up the reactor the old fashion
way (which takes longer than 30 min).

So in the meantime they start losing nuetral bouyancy with no propulsion.
Emergency Blow was ordered when they began sinking faster than they had time to

pump.  When they blew the MBTs the lines froze and so no air got into the MBTs.


So here they are: heavy, no propulsion (except a 150 HP retractable outboard)
and now no Emergency blow!!

The US Navy made a few changes in submarine operations as a result:  a means to

recover the reactor quickly, and stringent HP air standards i.e. dry air.

Just some food for thought,
Regards,
Rob Carlson
Seattle. WA

Marsee Skidmore wrote:

> Rob,
>
> I was hoping that someone who knew would answer your question. Since no one
> has, I'll say, "I dunno, but I think so." I concur with all of your
> suppositions. I don't intend to blow ballast at depth, since I'm kinda
> partial to droppable ballast. In the event that I do, I intend to have 2,000
> psi (min) in the high pressure air bank competing with 500 psi (max)
> ambient. With big lines, that would take a mighty long ice cube to block.
>
> I'm curious about your Thresher reference. I thought that Thresher's
> plumbing problem was due to a defective weld. - Joe
>