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> Date: Wed, 12 Mar 1997 18:21:26 -0800 (PST)
> From: Bob Favorite <rwfavorite@uc*.ed*>
> To: Dave Mabry <dmabry@mi*.co*>
> Cc: jthomas@ca*.co*, Techdiver List <techdiver@aquanaut.com>
> Subject: Re: epoxy coatings
> I am also a PSI inspector and I don't recall epoxy linings being illegal.
> If they are in good shape then there is nothing wrong with leaving them
> although I recommend removing them. If they appear at all damaged the
> lining should be removed using a shot blaster and then the cylinder can be
> VIP'ed.
> As far as steel vs. Al for O2 the increased O2 content can cause
> rusting and the rusting uses up the O2 resulting in decreased pO2. Al
> will stop rusting once a surface layer of oxidation has formed but this is
> not true for steel it will continue to rust until all the metal present is
> oxidized.
>
> ooooO Bob
> ( ) Ooooo Favorite
> \ ( ( ) RVT
> \ ) ) /
> ( /
>
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>
Bob,
You are a little off base reguarding oxygen causing
rusting and lowering the po2. Moisture causes rust an is accelerated
in a high oxygen environment. If a tank is clean inside and is filled
with dry oxygen it will not rust in twenty years. Medical oxygen tanks
are given a lot number and expiration date when they are filled. The
large tanks ( 225 - 330 cuft.) are almost all made of steel, and
there expiration date is 5 years from when they were filled. It is
generally assumed there will be 95% or more oxygen in these tanks
after five years even if the tanks have some rust in them. Whether
you have 95% or 100% Oxygen is insignificant for decompression stops.
The problem is that when rusting occurs, it uses up a small
amount of oxygen and converts it into co2 ( carbon dioxide ). In this
situation it shouldn't be significant since you are generally at rest
when you decompress and are not generating a lot of co2 to start
with.
Finally from your post, if you lower the percentage of o2 in the
tank, it is the fo2 not the po2 that changes. 95% oxygen in 20 fsw
still yields a po2 of 1.6 ata.
Ted
Ted Green (owner)
Tidewater Aquatics (Dive Store)
Salisbury Maryland USA
TDI IT #029
SSI MI #178
The world contains but three types of people:
1. Thoose who make things happen.
2. Thoose who watch things happen.
3. Thoose who wonder what happened.
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