Internal rust & flash rust in steel tanks

[padiscubapro]

I get it from my ANDI distributor, but its available in many places.. here is a link to the manufacturer's web site

http://www.bluegoldcleaner.com/

 

[Compressor]

I need some help here. Upon VIPing my 6 steel PST tanks by a scuba shop, I discovered taht all tanks have rust in them (no visible water). These were VIPed in the past by a diff scuba shop. Tanks never emptied in the past except for Hydros. And I never filled them.

My question gang:
1. If the tanks get tumbled, will this expose the inner bare metal even more and get more rust potential? ie: it is the outer (now rusted) layer that is galvanized only.

2. Is it possible to protect the inner bare metal now in any manner besides filling at a reputable dive store?

3. Should the tanks be written off?

Currently the tanks were "brushed" and the shop VIPed them. But I am not really satisfied with this situation.

Thank you for your potential help.

 

[The Chairman]

and figure out where you got the water... someone filled your tanks with moisture laden air. There is no other way for all 6 to have gotten rust... question your lds about this, but tumble the tanks ASAP.

 

[Compressor]

But it does not answer my questions. Yes I will tumble them but what happens next?? Am I going to have bare metal succeptible to rust or get to galvanized metal.

 

[The Chairman]

All steel tanks can rust IF there is water present. The "brushing" does not get rid of the rust completely which can be self perpetuating. PST tanks have no inner coating to prevent rust from the factory.

The bare metal will ONLY be susceptible to rust if you put moisture laden air back in... find out that source!!!

moisture+air+steel = rust

The only thing YOU can remove from that equation is moisture.

 

[Compressor]

Ok. Thank you.

 

[FredT]

Flash rust is what forms if a steel tank is "slow dried" following hydro or cleaning. Although it can plug ythe filter in your reg if it's excessive enoug to break free fromthe tank wall it does little structural damage to the tank.

A phosphoric acid rinse will remove it even without a tumbler, but do the final rinse with boiling water, and immediately dry the hot tank with dry nitrogen or Scuba air.

FT

 

[oxyhacker]

No. Your tanks will not rust more/faster as a result of tumbling. Tumbling will leave them bare metal, and that's the best thing for them.

In the early days, manufacturers (USD especially) tried to come up with anti-rust coatings, using various plastic and epoxy coatings inside. None worked. They'd crack or pinhole, and water would get trapped underneath, concentrating, in effect, all the rusting action in one place. It was found that if the entire tank was left bare metal, any rust would occur over the whole surface, with negilible effects in any one place. Flash rust - light rust over large areas - is inesthetic but not very harmful to the tank. If there's water puddling in the tank, and the tanks are left in the same position for long periods of time, all bets are off, since deep pits can develop where the water is.

This sort of answers your second question too: no there is no coating or treatment that will prevent rusting, and you don't really need one anyhow if your tanks are being filled with dry air meeting accepted SCUBA standards. Every once in a while some idiot posts about spraying WD40 inside, but please don't. I would look into where you've been getting your air, as it is necessary to remove most of the moisture in order for the filters to function correctly, and wet air is often a sing of other, much more serious, air quality problems.

 

[oxyhacker]

I should have said, if the entire INSIDE of the tank was left bare metal.

Originally posted by me

It was found that if the entire tank was left bare metal, any rust would occur over the whole surface, with negilible effects in any one place.

 

[The Chairman]

and ask HIM how you should get rid of rust... :tease: He has been working on a set all day... (snicker, snicker)