[PSUBS-MAILIST] Propane tanks

[Coalbunny <coalbunny@onewest.net>]

Earlier I was chatting with a friend tht served on a sub for a few years
in the 70's and 80's.  He gave me the following information to give to
you guys-

-The odoriferous stuff isn't H2S as I thought, it's Mercaptin.  It has
two purposes- give the propane an odor and to separate the water from
the propane.  Yes, propane has a certain amount of water vapor in it,
and the mercaptin removes it by encapsulating/capturing it (or something
like that).  In the bigger tanks (500 gallon+) they also insert methanol
to remove the majority of it.  They do that after purging the tanks. 
They do that periodically for inspection and certification, which they
do every few years.  

-You must have some kind of additional support inside if using a tank
for a submarine.  You can cut the tank open, but you must be very
careful in doing such.  hen you cut the tank, do it LENGTHWISE.  This
should prevent compromising the tank's integrity.  

-The mercaptin will leave a smell long after the propane is gone.  Even
though the steel tank doesn't "leak" water or gas, it is still porous,
on the atomic scale.  The mercaptin will absorb into the pores.  But you
can dilute the odor by doing the following-
1. Flush the tank with water.  Fill the tank 100% with water and leave
it sit for 3-4 days.  drain the water out and refill it again.  Do this
for a minimum of three times.  The mercaptin will attack the water and
the quantity of water will remove a good deal of the mercaptin.
2. After the water treatment hook a hose from your car exhaust and run
it to the tank.  Keep the car running and make sure you fill the tank
with the Carbon Monoxide.  this should help remove the remainder. 
You will still have some odor in the tank after you do all of this.  But
it should be around 1-5% of what it was before.  The remainder will
dissipitate over time and should not be any problem.

-When welding on a tank, purge the propane from the tank and inject
Carbon Dioxide.  Proceed with caution.

-A 100 pound propane tank is designed for an interior pressure of 350
psi and a bursting pressure of 700 psi.  While the tanks are designed
for this, many different factors come into play.  But a 20 pound tank
sealed up could crush as shallow as 100'.
1. Corrosion.  While the mercaptin and methanol are used to keep the
water "tame", the tanks will still corrode.  Good reason for a yearly
purge.
2. Physical damage.  Dents promote tank bursts.  Count on it doing
similar stuff when under pressure.
3. Age.  Age and damage both promote metal fatigue.  Metal fatigue
promotes faliure under pressure.

If you guys have any more questions on this stuff, let me know and I'll
see if I can get the answers.
Carl

-- 
"The plain meaning of the right of the people to keep arms is that it is
an individual, rather than a collective, right and is not limited to
keeping arms while engaged in active military service or as a member of
a select militia such as the National Guard." - U.S. vs. Emerson, 5th
Circuit Federal Court- published October 16, 2001