Is this 72 galvanized?

[JahJahwarrior]

No inner liner, yellow paint on the outside, from the mid 70's PST. Under the paint is this whitish, grayish layer. I can kind of scrape underneath and it's shiny, but some dull brown rust spots.

I think it's galvanized and the whitish layer is some paint primer or the some discoloration left behind after peeling off the yellow paint with a chemical stripper.

But before I send it for a hydro, let me know if you think it's ungalvanized and I'll paint it with ZrC. If galvanized ill leave it alone.

 

[Mr Carcharodon]

Yep that looks like galvanized steel. The whitish layer is zinc oxide which is OK. Once you start to see (orange) iron oxide, and worse pitting, it is time to get it hot dipped again. 72's are nice tanks for short dives or shallow dives. I doubt there are any uncoated steel tanks out there. The higher strength steels are not corrosion resistant on their own.

 

[JahJahwarrior]

I read some posts here which mentioned early 72's might be ungalvanized, hence the concern.

These will probably never see salt water, they are dedicated now to exploring shallow sidemount caves

Thanks for the info, I never expected to see white under the paint!

 

[AfterDark]

I read some posts here which mentioned early 72's might be ungalvanized, hence the concern.

These will probably never see salt water, they are dedicated now to exploring shallow sidemount caves

Thanks for the info, I never expected to see white under the paint!

If it doesn't rust in a day or so it's galvinized, if it does rust well it's steel. If so just paint'em. I painted my steel PST with Rustoleum primer, paint, clear coat. 5-5 and 5 coats of each. Wet sand the the yellow paint with 600 grit, it makes a good base for the primer to adhere.

I like 72's grew up diving them and still use'em as ID's.

 

[halocline]

it is time to get it hot dipped again.

No it's not, at least if you ever want to get a fill....that kind of heat would disqualify the tank, I believe.

It is galvanized, but I would still remove all the paint on top of the galvanizing, lightly prep the surface with fine sandpaper, and put a few coats of ZRC right over the old galvanizing. It's designed to repair existing galvanized finishes. Let it cure for a week or so; it really hardens up slowly. It'll look better and stand up to getting knocked around more.

 

[Gilldiver]

Hot dip galvanizing is done between 850-900F, you don't get into trouble with most steels till you reach stress relief temps of 1100-1200+F

After all, it was hot dipped once already.

Not many modern tanks get hot dipped anymore due to the costs of hot dipping vs a spray application or zinc electroplate. Hot dip is much better as it is way thicker and can last many decades if not centuries, spray and electroplate is good for maybe a decade or two at most, many times much less. In other words, that tank can be used by your grand children if you take basic care of it.

 

[JahJahwarrior]

Honestly i think the tanks will be fine. They are joining a family of many other tanks and I'll treat them well. If I do anything it will be a coat of ZRC but they are fresh water only sidemount cave tanks... They'll get scratched up so no sense painting over the zinc.

 

[halocline]

Hot dip galvanizing is done between 850-900F, you don't get into trouble with most steels till you reach stress relief temps of 1100-1200+F

I don't have the metallurgy knowledge to doubt you, but I am pretty confident that, at least around here, you'd never be able to get a tank that had been re hot-dipped filled or even qualified.

 

[Boiler_81]

Gilldiver is correct. The hot dipping of a tank will not have any impact on it's strength. On what basis do you think the tanks would be rejected?

I don't have the metallurgy knowledge to doubt you, but I am pretty confident that, at least around here, you'd never be able to get a tank that had been re hot-dipped filled or even qualified.

 

[Gilldiver]

Gilldiver is correct. The hot dipping of a tank will not have any impact on it's strength. On what basis do you think the tanks would be rejected?

If you have only the shops that don't fill anything older than 20 years etc. Lots of shops have rules that they makeup without any info - always try to avoid these if you can. But that may mean getting your own compressor, everything else can be done over the internet of by mail. Even reg rebuilding, I can ship a reg by FedEx Ground to a friend 5 states away cheaper than driving to some shops.