external corrosion / pitting on aluminium cylinders - how bad?

[afieldofblue]

Hello all,

I've come across barely used but corroded aluminium tanks (luxfer AL80s) that were stored improperly for a few years (read sitting in a not so dry area by the sea).
We just washed them to see, but it's clear that there is a lot of alumium oxyde (white dust), and advanced pitting on the exterior. The pitting is especially concentrated on areas that seemed to have been covered with a nitrox sticker that was removed. We haven't looked inside yet (some have never been used), but will.

This is a rather remote area, meaning the tanks would need to be sent abroad for inspection / hydro testing, which is quite an expense (read it might be cheaper to buy new ones).

I was wondering if I could have some opinions on this type of external corrosion - would you say these are recoverable, or too corroded to service / inspect and use?

Thanks for your help!

-

 

[Tracy]

They look fine from here. I would use them

 

[LanceRiley]

hi im curious about this as well...
i have similar tanks not as much as those... but there seems to be pitting... bad storage during the pandemic.

but they passed hydro.

 

[afieldofblue]

hi im curious about this as well...
i have similar tanks not as much as those... but there seems to be pitting... bad storage during the pandemic.

but they passed hydro.

Yeah, exactly the same - we ended up sending them for hydro and they all passed, so we were just used them.
I'm a little afraid this will accelerate tank breakdown in the future though

 

[LanceRiley]

Yeah, exactly the same - we ended up sending them for hydro and they all passed, so we were just used them.
I'm a little afraid this will accelerate tank breakdown in the future though

to be honest i bought the tank pretty cheap. maybe 30$ a piece

one of those pandemic finds. i hope when it breaks it will just hiss slowly? and not empty right away?

ive been thinking of selling em after 3-4yrs… i assume by that time i would have ROI

 

[afieldofblue]

I think the main risk is the pitting digging into to the tank structure and weakening it, which might be a risk when filling. But if they passed hydro, it should be fine.

 

[LanceRiley]

I think the main risk is the pitting digging into to the tank structure and weakening it, which might be a risk when filling. But if they passed hydro, it should be fine.

yes but in my country next hydro is 5years. we dive mainly saltwater.

it could be eating away in 5years time. i do wash the tanks with fresh water. but you cant’t really manuall rub the tank with your hands while spraying with fresh water. need an old tooth brush to brush the pittings. sometimes i can see salt build up if i dont brush

 

[Eric Sedletzky]

As @Tracy said, they look good from my house!
Clean them up and send them to hydro. If they pass, great!
Aluminum tanks are THICK. It would take a very deep pit to make one fail. Something I’ve done with aluminum tanks in the past is to polish them out and leave bare open aluminum. That seems to be the best thing so it can breathe. As soon as your cover up aluminum you’re trapping salt water and corrosion begins. If they are left bare they dry and the metal forms a ‘patina’ that will not really continue to corrode if moisture is not allowed to remain.
Just dive them. The uglier they get the better because it has that “seasoned vet” look.

 

[rjack321]

How deep are the pits? You can estimate in mm using a pin or needle

 

[SlugLife]

Do they do Visual Inspections in your area? My guess is these tanks would pass a VIP, but since I'm not there I can't really inspect the tanks myself.

As others suggested, first we need to know how deep the pits are. The Visual Inspection training covers things like pit depth and clusters. For isolated pits on 3AL Luxfer, they should be more more than 3.7mm deep, and for line-corrosion, 3-inch long, it should be no more than 1.1mm deep.

The other thing to look at is any possible internal corrosion. Depressurize the tank, remove the valve, and ideally insert a light into the tank. See if there is any corrosion or pitting inside the tank. Also check for any cracks or damage to the threads on the tank-neck.