Hot Dip Galvanized Cylinders - Damage or Normal Mottling?

[Scorpaenichthys]

I recently bought 3 brand new Faber hot dip galvanized steel HP 100s and I was hoping someone could give me insight into what happened here...

I understand that HDG tanks develop a dull silver mottling, but what seems to have happened to one of my tanks seems in excess of this. I have zero problems if this is purely aesthetic - my concern is if this represents corrosion to the exterior/coating of the cylinder that can result in functional damage.

I loaded the tanks in my car one night to prep for their first dive day; I had a slightly damp but well-rinsed weight harness up against them to prevent movement. The next day I found dark spots on the tank and a silver coating on the harness (zinc?). Obviously gave me a serious scare as this tank hadn't even touched sea water. After the next dive I gave the cylinders extra care - rinsed extra well, completely dried with a clean towel, and loaded in the car on a dry towel. The next morning again I found the same cylinder with fresh dark spots and a silvery coating on the towel where it had rested - pictures attached. I have loaded tanks like this for years and never had a problem, never would have expected an issue.

It seems that only one of the tanks is developing this very dark mottling; the others have light marks after resting against a damp spot that I assume are normal (visible in the first pic on the bottom tank). I don't know if this is due to the individual cylinder itself or if it just repeatedly ended up in an unlucky position.

If anyone has insight or experience with this it would be greatly appreciated it... I don't know if I'm being paranoid as I'm obsessively careful with my equipment, or if this is legitimate damage either from my own mistakes or a poor coating.

Thanks in advance!

 

[lowviz]

Them babies are just waking up to saltwater. You want to see seasoned? See pic.

"If it ain't red, it ain't dead." Iron rust is your enemy, this is all good...

 

[Bob DBF]

Looks more like you picked up dye from the cloth, but it could just be the picture. I'm with @lowviz, if you you use the tanks they won't look new for long.


Bob

 

[JamesBon92007]

To me it looks like some kind of reaction took place between the zinc and the towel. From the pictures I don't see anything that would likely prevent it from passing a visual.

 

[tbone1004]

that's dye leaching from the towel. Not something you should be worried about

 

[Scorpaenichthys]

Thank you all for your replies! It's a relief to hear it's likely just the tanks learning to love sea water!

As for the towel, while it may look in the photo like dye leaching, it most definitely isn't - it's a physical silvery layer on the surface you can feel with your fingers. The same silvery coating ended up on my weight harness (the result being the first two photos), which too was a layer and not dye leaching. I can only think maybe there's a top layer of zinc that isn't fully bonded to the steel and vulnerable? I'm not quite sure how the process works and if that may be the case.

 

[guruboy]

What happens if you wipe it down with a wet cloth? Does the silver stuff come off?

 

[JamesBon92007]

Perhaps they used methylene blue to dye the towel

 

[lowviz]

...//... I'm not quite sure how the process works ...

The zinc on the exterior of your tank is a sacrificial anode. The idea is to form an electrochemical cell using zinc, iron, and water. The iron won't rust until the zinc is gone. Don't stress, all is well.


The inside of the tank is another matter. There is no protective zinc to form a cell if you get a little puddle of water inside. Thus, get good clean fills and never drain a tank completely down.

The link below may help explain the process and save you a lot of money too.

 

[Scorpaenichthys]

Haha, that was informative. Thanks for all the feedback - sounds like the cylinders will be a-ok despite my paranoia.

The silvery coating is pretty persistent on the towel, almost... bonded. It does come off but not without effort; after a full cycle in the wash half is still there well attached. I guess the towel is now also a bit corrosion-resistant...