Cold galvanized / Hot-dipped = Difference?

[Packhorse]

My understanding is cold galvanising is just paint with a high zinc content.
There is also a method called flame spray galvanising. Im unsure if it is used on tanks though.

 

[oxyhacker]

You missed something. Go to Mike's post at the beginning of this thread. "Cold Galvanizing" is paint. Admittedly , very good, zinc-rich paint, but still paint. Actually not a bad choice, for a lower cost steel tank, since while it may not hold up as well as hot dip, it is very easily touched up in the field.

Oh someone else asked about flame spraying. That process, or very similar one, is used on Faber tanks. It results in a very thin zinc layer, not nearly well as bonded to the base metal as hot dip. but quite a bit better bonded than paint. However the layer is thin enough that it scratches or abrades off easily, so it is often used as a base coat and covered with a protective layer of paint, as it is on Faber.

I would rate cold galvanizing and flame sprayed zinc/paint as pretty much comparable.

Is this "cold galvanized" finish a paint? Are we being coy about this or did I miss something? What happened to metallizing, the use of a hot, plasma jet to deposit zinc? I have some surplus tanks that were flame sprayed thirty years ago and they are holding up with one having some minor rust bleed. The metallized finish is porous and holds paint tightly. So, a touch up with galvalite works well. Problem solved.

PS, the hot dip process is impressive. It takes a lot of force to ram those cylinders into molten metal, buoyancy and all.

 

[SparticleBrane]

To the best of my knowledge PST added aluminium to their zinc to make it "shinier". We made an inquiry to Worthington's applicator and the response came back that they would not contaminate their one million pound zinc bath to make it look "prettier". If you look at properly coated galvanized surfaces around you, lightpoles,sheet metal, etc., you will see the "spangle"

Thanks for the info! Not that it really matters anyway, since PST cylinders are only that shiny for a few dives (if that many), then they turn the standard mottled grey.

Then again, if you don't take the original stickers off the cylinder...
I have a friend who recently picked up a HP100 from 1989 (?) that was COVERED in stickers, one of which was the halfway beat-up huge round PST sticker. After peeling it off, there were several areas underneath that still looked brand new -- the sticker was waterproof and didn't let anything touch the original hot-dip finish for almost 20 years. :11:

 

[BradEllis]

Mike, that's a fantastic picture. Got any more? I'd love to see how they're made!!

Check out this video on our site that shows the manufacturing process of Worthington Tanks!

Making a Worthing Steel Scuba Cylinder

Brad Ellis
DiveSports.com

 

[SparticleBrane]

Seen it many times. Thanks for the video though.

 

[pescador775]

I went back a page and read his post but could not find the info. I found some hype about "cold galvanizing" and zinc rich spray which means nothing to me. However, after triangulating the various comments I agree that the LP77 appears to be painted. Some of these new products appear to be very durable but I have to know what it is beforehand in order to discuss it.

You missed something. Go to Mike's post at the beginning of this thread. "Cold Galvanizing" is paint. Admittedly , very good, zinc-rich paint, but still paint. Actually not a bad choice, for a lower cost steel tank, since while it may not hold up as well as hot dip, it is very easily touched up in the field.

 

[tep]

Here's a question for the steel cylinder experts.

Regarding the issue of corrosion resistance in steel cylinders, has any manufacturer considered or attempted to produce cylinders with a carbonitride surface treatment? The extreme hardness and corrosion resistance imparted by carbonitriding appears to be an ideal solution to the corrosion problem that afflicts steel in marine environments.

There's nothing in that article or any other on carbonitride that I could find that addresses rust and corrosion, it's all about creating a 0.5mm-0.75mm layer that is much harder than the original steel. It also does increase brittleness, and if there's too much nitrogen in the process, you get austenite, which is rather brittle, if I recall correctly.

Because of the flexing that you get in fill/empty cycles in a cylinder, I'd expect the nitride layer to "crackle", creating microcracks which could serve as source points for much deeper cracks that would spread throughout the cylinder walls.

 

[Sadamune]

There's nothing in that article or any other on carbonitride that I could find that addresses rust and corrosion, it's all about creating a 0.5mm-0.75mm layer that is much harder than the original steel. It also does increase brittleness, and if there's too much nitrogen in the process, you get austenite, which is rather brittle, if I recall correctly.

While carbonitriding is primarily used to increase the surface hardness of a ferrous substrate, it also has the added benefit of conferring corrosion resisitance, though to various degrees depending on the process and specific alloy. GLOCK's carbonitriding process, which they call 'Tenifer', does protect the various steel components of their pistols from corrosion.

Because of the flexing that you get in fill/empty cycles in a cylinder, I'd expect the nitride layer to "crackle", creating microcracks which could serve as source points for much deeper cracks that would spread throughout the cylinder walls.

Ah. Well, that explains why carbonitriding isn't employed in pressure vessles. Thanks for pointing that out.

Sadamune