Internal rust & flash rust in steel tanks

[Rick Murchison]

As for how the rust gets in there, the most common cause is the dive shop taking the tank and filling it without first blasting the orifice clear with the air in the tank - a single drop of salt water here, a single drop there and you have enough sprayed inside to cause considerable rust - and any tank that's ridden in the open with an uncovered valve in even light seas will get salt water spray on and in the valve orifice.
Blast 'em out yourself after you get the tank off the boat and before it gets to the shop and the rust problem will most likely disappear.
Rick

 

[jsloo]

Sorry to bother everyone. I was just hoping to get one question answered.
One of my tanks is a faber scubapro LP steel, about 78 cu. ft.
It is fairly new, used about 5 times.
At the end of a dive, I used up ALL of my air. From that point, the tank simply had a routine air fill.
I had heard that I should be very concerned regarding the possibility of having introduced small droplets of salt water into the tank. (By basically "sucking the regulator dry." Therefore, starting a corrosion process.
Should there be cause for concern??
Should this tank undergo a subsequent inspection process??
Thank you for your time.
jsloo

 

[The Chairman]

yearly, or if the tank has been completely emptied for any reason. Catch any corrosion NOW before it can ruin a tank.

 

[FredT]

It's easy to yank the valve and check NOW.

It can be a real PITA to deal with if you let it set a week.:hithead:

FT

 

[Iguana Don]

And don't worry about bothering us, that is what we are all here for.

OBTW - Welcome to the Board--------------Ask Away

ID

 

[DameDykker]

Hi jsloo

You can easily do that your self. Empty the tank completly. Take of the valve (a light tap on the valve body should get it unstuck if it was screwed in tight). A mini mag-light is enough to vis inspect it. Small rust stains is not a problem, but if you see water let the tank dry completly (might take days) before you re-attach the valve and refil the tank. If you are in a hurry drain as much as possible add alcohol and drain again. The remaining liquid will contain a high percentace of alkohol and therefore evaporate much quicker. Alkohol does not in any way damage the tank just get it all out before refilling.

Don't forget alwas to relase a small blast of air before refilling to ensure that moisture trapped in the seal area is not carried into the tank.

And by the way: How did you end up with a complety empty tank?

 

[nickjb]

Given the the way a 1st stage regulator works (pressure acting against a spring) is it possible to completely empty a tank by sucking through the regulator? Will there always be a small amout of air pressure in the tank unless the valve is opened without a reg in place?

 

[FredT]

Originally posted by nickjb
Given the the way a 1st stage regulator works (pressure acting against a spring) is it possible to completely empty a tank by sucking through the regulator? Will there always be a small amout of air pressure in the tank unless the valve is opened without a reg in place?

Not only is it possible, it's easy to do without realizing it if breathing slow while hunting fish or photos. The pressure closes the valve, not opens it. Once the tank pressure is below IP setting that first stage is simply an open pipe!

FT

 

[The Chairman]

down to the ambient pressure you are in. At 99 feet that would be 58.8 psi (absolute). At the surface you could reduce tank pressure to 14.7 psi (absolute). This is why you keep trying to breath every now and then during an ESA. You may not get much but you should get a little.

 

[jsloo]

Thanks guys for your responses....

I ended up bringing the tank to the LDS.
A quick visual inspection inside, confirmed no evidence of rust.
Before this at home, with the valve off, I propped it up about 30 degrees, in front of a dehumifier for awhile.
I'm probably a little too "anal."
Thanks again.