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> Date: Tue, 11 Mar 1997 20:44:12 -0500
> From: Dave Mabry <dmabry@mi*.co*>
> Reply-to: dmabry@mi*.co*
> Organization: Great Lakes Maritime Institute
> To: Trey Irvine <gmirvine@sa*.ne*>
> Cc: Techdiver List <techdiver@aquanaut.com>
> Subject: epoxy coatings
> Are there any problems associated with older steel tanks that have been
> epoxy coated on the inside? I may have a chance to buy some 71.2 cu ft
> that have the coating. Can they be used for O2?
>
> Thanks.
> --
> Dave Mabry dmabry@mi*.co*
> Great Lakes Maritime Institute Underwater Research Team
> NACD NSS-CDS #42872
> --
> Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
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>
>
Dave,
Let me set you and the "stroke technicians of the techdiver
mailing list" straight regarding steel 72's with epoxy coatings.
First, tanks that have epoxy coatings on the outside may or may
not be galvanized under the epoxy. Externally epoxy coated galvanized
tanks are all but impervious to external corrosion and will last far longer
externally than any other type of tank in the same environment period!
Almost all the tanks that were not galvanized under the external
coating have died. Eventually the coating on these tanks got nicked
and water migrated under the epoxy and the tank started to rust
because the tank never dried under the epoxy. By the time the owner
realized there was a problem, it was usually to late because to much
of the wall had rusted away.
Internally coated epoxy tanks are a whole other subject.
Internally coated epoxy tanks that have a completely intact lining
and show no signs of rust under the coating ( large bubbles in the
coating may indicate rusting occurring under the coating ) are ok to
use in the USA as long as they are not exposed to oxygen percentages
higher than 40%. The epoxy coating is PROBABLY not compatible with
oxygen, even if it has been oxygen cleaned. The solution to this
problem and tanks that have a perforated lining is to have the lining
removed. This is done with an internal steel shot blaster that strips
the lining out of the tank. I have had a number of tanks done this
way. When done correctly no trace of the coating remains, the tank
can be oxygen cleaned and used for any gas mixture.
Low pressure steel 72's make great wing tanks! They have
better buoyancy characteristics, and are smaller in physical size
compared to aluminium 80's. Also, if your filling al 80's and st 72's off an
oxygen bank without the benefit of a booster pump, the st 72 will
hold more cuft. at the same pressure. An al 80 holds about 52 cuft.
at 2,000 psi.. A st 72 holds about 58 cuft. at 2,000 psi..
Finally, if you think steel 72's are a tank of the past, take a
long hard look at an OMS st 85. It is almost exactly the same
physical size as a st 72, but the working pressure is 2,400 psi.. They
also make great wing tanks and hold more gas than an al 80!
Ted Green
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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