Rust inside steel tanks failing visual inspection

[Odo]

Thanks all for weighing in on this. I don't think the dive shop is being unscrupulous about the rust existing. I'm sure there is rust of some sort, flash or otherwise (It's a nitrox tank, so I don't know how to make that call). Most of my fills have been at Jensen since they closed the Stuart store. They are a good bunch of guys that work there. The explanation of how the moisture may have gotten in the tank pissed me off. I doubt, however, that they would volunteer that, well, there was that time they maybe couldn't get filters or driers replaced on the compressor and perhaps were giving wet fills.... Maybe I will just make a tumbler and do it myself.

 

[drbill]

Bill, think about that for a second.....the IP is created by tank pressure, so it can never be higher than tank pressure, at most it can be equal to tank pressure. Once the tank pressure reaches the IP of the reg, the first stage will go full and stay that way, keeping tank pressure and IP equal. And even it it did, were is the water going to get in from?? The ambient wate pressure would have to be higher than either the tank pressure or the IP and even then, one of the second stages would have to be open.....if that were the case, you have much bigger problems than a little rust in the tank.

Thanks for the clarification. I'm a marine biologist who SCUBA dives rather than a dive professional. I know I've been told that if my tank pressure drops too low there is a chance that water will be drawn into the tank through the reg... but thinking about that, shouldn't it only occur (if it doers at all) at depth where ambient pressure is higher (and with a tank that low, OOA may be a much more serious consideration than any possibility of water intake).

 

[herman]

Exactly. Pulling a tank too low allows water to get in is one of those old diving wives tales. For water to enter the tank due to low pressure, 2 things MUST happen at the same time, the ambient pressure containing sufficient moisture must be higher than the tank pressure AND the tank must be unsealed -the valve open or removed. Even a competely empty tank with the valve shut will not allow moisture to enter.....unless you believe that water can somehow enter a tank/valve that has been holding back over 3000 psi with no problem. A tank with the valve off or open for long periods of time can allow moist air to enter and eventually rust the interior of the tank but that requires a long time (unless its setting out in the rain).

 

[merxlin]

I agree that venting the valve and making sure the whip is dry can limit the amount of water able to get in the tank. But on aboat with 20-30 divers and a crew trying to get all the tanks refilled in a normal surface interval, things will happen. I also agree the filters may not get changed/drained as frequently as they should. But my worst experience was with an LDS that is no longer in business. They were pumping so much water in the lines and therefore the tanks that after 3 dives I had rust in my first stage!

 

[KD8NPB]

We charge $6.50 for a visual tank inspection.

For that awesome price, you get an eddy current test (if required), or if it's a crusty steel tank, we have a wire whip. 5-10 minutes with that, then I blow it out with Grade E air. If I still see pits still, THEN I'll whip out the pitting gauge. If it doesn't pass the gauge, then I get to have a chat with you in regards to the condition of your tank. We don't own a tank tumbler, but we will gladly point you in the right direction towards somebody who does if that's the case. I have yet to have to take that route.

$45 for tank tumbling is ridiculous. There is no materials cost other than electricity. It takes a tech maybe 10 minutes to empty your tank, pull the valve, fill it with media + cleaning solution, put a plug in the end, then throw it on the tumbler overnight. It's also extremely abrasive & overzealous if the tank simply has a thin later of flash rust. Coupled with the fact as well, that you're supposed to re-hydro after a good tumbling.

Weird facts : Out of all the VTIs I do, about 25% are "bad alloy" aluminum tanks. In the past 30 years, we have only had to reject about 3 "bad alloy" aluminum tanks. Two with obvious cracking, one with a failed Eddy.

 

[Odo]

I agree it's rediculous. That doesn't include the vis+ either, which I think is $30 now. That is the 3rd tank I've had to do in about the past year. I'm going to inspect prior to taking in for vis from now on and do the tumble myself (after I McGiver me one together). I saw one on here that was made from a washing machine motor...genius! I just replaced my regs with HOGs so I could do the maintenance myself. I might as well handle the tanks as well. My friends with steel tanks won't mind either, I'm sure.

 

[GROBIOG]

I have seen in numerous threads about water in tanks, and always comes up the lower pressure allows water to get in, then some says it is basically impossible to happen that way, let me ask...

How does water get in the tank(fact, about as much as 4 FLOZ), there is no fill water tank, this is a tank in a batch of a 100 tanks, all always filled from the same compressor?

 

[redacted]

I have seen in numerous threads about water in tanks, and always comes up the lower pressure allows water to get in, then some says it is basically impossible to happen that way, let me ask...

How does water get in the tank(fact, about as much as 4 FLOZ), there is no fill water tank, this is a tank in a batch of a 100 tanks, all always filled from the same compressor?

It could happen if the user essentially empties it and then descends with that empty tank. Or someone does it while filling or servicing the tank - usually done by a "dive professional".

What is your explanation?

 

[halocline]

Unless the tank was submerged with the valve open and empty, water comes in one way; through the filling process. 4 fl oz means you're getting one hell of a wet fill. Oh yeah, as awap's post reminded me, there is another way. Someone could fail to dry it out after hydro, slap a valve on.

 

[fire_diver]

If I was finding that much water in a tank, only filled from a single compressor, then the compressor is lacking some serious maintenance. I would never fill my tanks there again.