Plastic coated steel 72's

[ew1usnr]

It's called "Savogran Heavy Duty SuperStrip"
"Removes paint varnish, polyurethane and marine finishes"
"Fast acting. Approximate stripping time for epoxy, polyurethane and marine finishes 25 minutes"

I bought a one quart can for about $8 from the paint section at Lowe's hardware. One can will do at least four, maybe six tanks. The stuff is like a loose gel and can be painted on vertical surfaces. I painted it on, waited 20 minutes, and scraped it of with a razor blade scraper. It came off really easy. Make sure that you don't have any stickers on the tank because the stripper may not dissolve the plastic of the sticker. It took a couple of repeats to get the tank entirely clean. Wear rubber gloves when you are doing this. Then I rinsed it with water, washed it with detergent and rinsed again. You want to get this stuff off the tank afterwards so that you don't have to handle any residue.

 

[Genesis]

Officially, DOT rules say if you expose them to heat then they're junk.

Might you get away with it? I don't know. But I sure as hell wouldn't attempt it without an immediate hydro after I did the galvanizing! If the tank goes "boom" when filled you're going to be unhappy!

BTW, while metallizing sounds attractive, as it doesn't require the same amount of heat, that STILL is potentially questonable, as the localized heat levels can reach 300-400F or thereabouts. The other thing you might do is call PST - they made most of these, and could probably tell you what is and is not acceptable. I suspect they're going to say "no way" to a hot dip, and probably "no way" to a metallize process, but I might be wrong.

Cold galv won't last NEARLY as long (its basically a paint) and you'll have to watch out for incipient corrosion on a regular basis, but I'd go that way anyway, as so long as you use nothing that can physically remove base metal on the tanks to strip them (e.g. no grinders!) and no heat there is no risk of rendering them unsafe from the stripping and painting operation.

In fact, I am. I just picked up 4 older Steel 72s that I'm going to make into doubles. The galvanizing under the boot area was trashed on all 4, but the rest of the galvanizing is in good shape. A quick (exterior) dip to get the mess off the bottom showed that what appeared to possibly be some pitting on the cylinder indeed was just the galvanizing "sacrificial" byproducts and the base metal itself is perfectly fine - but the galvanizing on that part of the tanks is shot with base metal clearly visible in several places.

They're getting recoated with cold galv and will then be banded and put in service. No re-hydro necessary as they were just done a couple of years ago, and the insides are absolutely spotless. (They were passed on a VIS just before I picked them up; since I'm applying neither mechanical abrasion nor heat, I'm not changing a thing in that regard... besides, I fill my own tanks )

The only thing I'll have to watch out for is the cold galv wearing through, and touch up as required. I suspect it will require fairly frequent touch-ups, but the cold galv compound in a spray bottle is cheap - and really, only the bottoms of the tanks are going to need close attention, as that's the only place where the original hot dip is compromised.

You can't beat the overall deal on these older 72s; they have a nice price, work well as singles, have GREAT buoyancy characteristics and total weight compared to AL80s (identical "land" weight but you can take 6lbs or so off your belt with them!) and work well as light doubles for many diving configurations as well. The only downside is that they can be a bit negative in a wetsuit as doubles, depending on how heavy of a wetsuit you use and whether you dive an AL or SS plate. Lots of people think you need something bigger for a single - you don't most of the time if your air consumption rate is reasonable. If you're doing dives where the air in a 72 isn't enough you might want to take doubles anyway for the redundancy.... so pair up a couple of those and you've got 140cf of gas - enough for two moderate dives or one fairly significant one.

 

[Dryglove]

I did a ton of research on this subject and found ZRC cold galvanizing compound to be the best on the market. I have coated 4 steel 72's with this stuff and it is amazingly tough stuff. It is way better than paint could ever be.

Do some research and you will see it is good stuff. Also ask fredt what he thinks about it if you dont want to take my word for it.

 

[ew1usnr]

This looks like good stuff. See: http://www.zincrich.com/galds.htm

But, I want to paint my tank yellow. The ZRC site says "TOPCOATING: After 24-48 hours, ZRC may be topcoated with acrylic, chlorinated rubber, epoxy, urethane or vinyl type products. DO NOT TOPCOAT WITH ALKYD, ALKYD-MODIFIED ACRYLIC, OR LACQUER TYPE PRODUCTS."

I looked at the Rustoleum site and they say: "What product should I use to paint galvanized steel? Any of the water-based acrylics, such as Painter's Touch brush products or the American Accents brush products. 8781 Aluminum Primer may also be used."

The "Painters Touch" says: "Indoor/outdoor, Smooth, durable Finish , Great for wood, metal, Quarts and half-pints are acrylic latex (soap and water clean-up)"

Or, I could skip the ZRC and instead use metal primer and Rustoleum "Protective Enamel" that says
"Superior coverage and durability, Indoor/Outdoor,
Protects against rust & corrosion on interior & exterior metal"

It appears to boil down to deciding which it is more important. The top coat or base coat. With this being a scuba tank I suppose that it is a given that the paint will be scratched (this is for use, not display). Given that scenario, the ZRC would continue to protect even when scratched and would be therfore better. I called ZRC at 1-800-831-3275. They said that they do not sell their stuff through Home Depot or Lowes, but that in Tampa I can pick it up at Hughes Building supply. It comes in spray cans and quart cans. A spray can should work for one tank.

 

[Genesis]

You'll be SORRY!

One scratch in the topcoat and without the galvanic action to protect the tank it will begin to rust under the paint! That's death to the tank, because you won't see it until the pitting gets bad enough to hose you.

The corrosion limit for a steel tank is 0.5mm pit depth. That's not much! Surpass that and the tank is condemned on a VIS.

 

[ew1usnr]

Genesis once bubbled...
The corrosion limit for a steel tank is 0.5mm pit depth. That's not much! Surpass that and the tank is condemned on a VIS.

Your advise is duly noted. I will use the cold galvanizing compound.

Question: My tank looks fine. But, you're right. A 0.5 mm pit isn't much. If there was a pit like that, wouldn't a coat of primer and a coat of paint fill it up and smooth it over? How would anyone know it was there? Even if the tank were bare steel, how would a dive shop tell a difference between a 0.4 and a 0.5 mm pit? That's almost microscopic.

 

[Genesis]

You need a surface-reading micrometer to do this accurately, and its a problem on a tank because the surface isn't flat.

Bottom line is that any significant corrosion damage will simply fail the tank, as an inspector is going to err on the side of caution and fail a tank that is questionable. Line corrosion (all in a line) is even worse; that's how you get an explosion (the entire "ring" or "line" fails, and the tank ruptures rather than leaks.)

Galvanized tanks can have an amazing amount of crap under the boot area and still be ok. I just cleaned up 4 of them and one looked like it was going to fail MY VIS originally (and since I fill my own, its my butt if I'm wrong!) but after a dip in Ospho to get rid of the corrosion (this will also remove a SMALL amount of intact galvanizing, but not much if you don't keep it in there for very long) I found that what appeared to be pitting was actually the galvanizing that was totally wasted under the (now removed!) boot - the base metal was fine. Above the boot line the galvanizing was unharmed by the dip - galvanizing is pretty tough stuff - but below it all that was left was the galvanic product (a white powder, and under that, a black mess) on a significant part of the metal.

Fortunately, the base metal was intact and the tanks are fine - they were just fugly. They're getting coats of cold-galv now and will be in the water by the weekend.

Had those tanks NOT been galvanized they would have been dead for sure. The anodic protection of the zinc kept the steel from corroding, and the remaining hot-dip on the rest of the tank will continue to do so - with the cold galv providing even more protection.

Just expect to need to recoat the cold-galv fairly frequently, because you will need to. I'm not going to topcoat mine, as I want easy access to the cold galv for touch-up purposes.

Oh, and beware boots. The newer ones on steels drain well, but the older non-ribbed boots are WHY the galvanizing gets trashed in the first place. If that boot design had never existed virtually ALL of these galv tanks would be like new - 20 or even 30 years after manufacture - provided that the inside didn't succumb to water intrusion.

A bigger problem is using boots on a cold-galv'd tank. If you can avoid it do so. Cold Galv is effectively a paint, and the boot ridges will score the paint, probably back to the base metal. If water gets trapped in THERE, you're asking for crevice corrosion which is especially ugly and dangerous. If you CAN'T avoid it then you need to make very certain that you remove those boots after EVERY use, rinse well with fresh water, and watch CAREFULLY for any rusting that starts to develop.

 

[ew1usnr]

I had to look to see what "ospho" was (http://www.foreandaftmarine.com/201-osphoq.htm). It looks about the same as Naval Jelly (http://www.shorechemical.com/Section 7 Tech Sheets/naval_jelly.htm) . It dissolves rust and leaves a clean surface for painting.

I think that you are right about not bothering with a top coat of colored paint. It would greatly magnify the complexity of maintaining cold zinc undercoat. Without a top coat there would be no problem at all. And, my other 72 has a bare galvanized finish anyways, so both the tanks would match (roughly).

The boot is a necessary evil. The new boots are a whole lot better that the cup shaped old ones. I don't put boots on my 80's, but the 72 would be tough to live with if I couldn't stand it up. I'll use this tank in fresh water so every dive will be rinsing it.

What do they do to a tank when they "oxygen clean" it. A friend suggested that I do this just to be safe after having glopped the paint stripper all over the tank. I washed off the exterior with detergent and water. I don't think that any of this stuff got inside the tank, but it will be rinsed out anyways when they do the hydro.

 

[Genesis]

The most common ways are with a degreaser (e.g. Simple Green) and a tumbling media. With a steel the trick is not to get flash rust in the tank when you're done and go to dry it. The easiest way is to use Nitrogen for the drying (no oxygen, no rust)

Another option is to use HOT (as in almost boiling) water for the final rinse, and then to stick a scuba LP hose up in there and turn it on. The tank will dry VERY quickly inside from the residual heat in the steel and the very dry air. You might get some flash rusting this way though.

The latter works REAL well for aluminum tanks though; its bone-dry inside in less than 5 minutes.

The entire trick with O2 cleaning is to get any residue that might burn (e.g. oils, etc) out of the tank. In truth the bigger problem is the VALVE, which must be torn down and cleaned as well. I typically use a simple green solution for the valve in an ultrasonic cleaner (torn down to parts, of course), because the valve is where you have all the twisty gas passages and where adiabatic heating is a concern.

Remember, to get a fire you need fuel, oxygen and heat. Take any one away and there is no fire. The point of O2 cleaning is to remove the fuel to the best of your ability. Proper procedure takes are of the heat concern. The Oxygen concern you can't do anything about

In truth ALL valves will have some fuel available (O-rings and seats), so what you're really after here is lowering, rather than eliminating, the risk.

 

[pasley]

Another opotion is to paint the tank with plastic coating. The hardware stores sell cans of a plastic that you can apply like paint, or dip the tank into. It is the same rubberized coating that plier handles are dipped in.

I really don't recommend it as once you start using the tanks, you will not be able to spot any rust. But it should make a good seal. But it is another option.