hot dip zinc coating 4 steel cylinders
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FredT
Guest
You'll kill them as far as DOT is concerned.
This method is what I use to boat proof ungalvanized O2 bottles. It works _almost_ as well as hot dip.
--From an old post on another board-
Sandblasting works on a tank that is not galvanized, and most E bottles won't be. Be wise to check to be sure on a small point though. From the numbers that should be a steel flat to slightly recessed bottom tank and a 1/2" NGT thread valve. If there is ANY hot dip galvanizing on the tank take care to leave it intact. There isn't any better corrosion protection to be had.
A few things to keep in mind. First off use a "soft" abrasive for blasting. Calcium carbonate or walnut shells would be my first choices. You want something that will remove the paint and not work the steel. A wire brush on an angle grinder would work well if the tank is not galvanized. Once you can see bare steel it's time for a phosphoric acid rinse, clean boiling water rinse, and thorough drying to kill any microscopic corrosion followed by a good grade of cold galv. Since you intend to keep the tank on a boat anything less is just an excuse to repaint the tank in a year or so. ZRC is about the best cold Galv on the market but there are several much cheaper alternatives. Be sure it's a true cold galv coating, not just a "zinc rich" paint. You should have well over 90% of the dry film be powdered zinc for a true cold galv. Under a cold galv no primer is necessary or wanted. A second coat of cold galv will prevent any holidays in the coating but is not absolutely necessary, as a true galv will heal over any micro porosity.
Another thing is to be careful not to obliterate the original marking on the tank with too thick a coating on the shoulder. Obliterate or mask those and you get to start over as nobody will fill it. A good even single coat on the numbers is all you need. You'll be retouching that area after each hydro anyway.
If you want it green, go ahead and paint it with Rustoleum or something similar ON TOP of the galv coating. Dont go overboard with the topcoat, as some porosity is needed for the galv to work properly, and plan on redoing it in a couple of years. A hint of color from a spray can 12 to 18" from the tank is enough to identify it in an emergency. The cold galv is providing your corrosion protection, more paint simply adds weight and may actually hurt your corrosion protection. As far as decals go most fill stations will have the shoulder stickers to identify the tank as O2, and they be free most places. Might as well take advantage of it.
Wrapping the tank in an old weight belt web before putting it in the vise to tighten the valve will help protect your new finish. Be sure to prefit the valve hand tight with no tape or compound on it. Count the turns going in and mark the valve outlet location on a piece of tape on the shoulder. This is your "zero point" When doing the final tightening after applying sealer tape or compound you want 3 turns on the valve from this point. (Hint: Without a good vise and an 18" wrench you won't get there.) Maximum Teflon tape is 1 to 1.25 turns of 1/2" wide tape applied 2 threads from the tank end of the valve. Do not expose Teflon to the O2 in the main tank, and torque means nothing on those valve fit ups. More is NOT better on the tape or the turns. 1 to 1.25 turns on the tape and 2.75 to 3.25 on the turns to tight! If it leaks after that get a new valve. The thread is damaged on the old one!
FT
This method is what I use to boat proof ungalvanized O2 bottles. It works _almost_ as well as hot dip.
--From an old post on another board-
Sandblasting works on a tank that is not galvanized, and most E bottles won't be. Be wise to check to be sure on a small point though. From the numbers that should be a steel flat to slightly recessed bottom tank and a 1/2" NGT thread valve. If there is ANY hot dip galvanizing on the tank take care to leave it intact. There isn't any better corrosion protection to be had.
A few things to keep in mind. First off use a "soft" abrasive for blasting. Calcium carbonate or walnut shells would be my first choices. You want something that will remove the paint and not work the steel. A wire brush on an angle grinder would work well if the tank is not galvanized. Once you can see bare steel it's time for a phosphoric acid rinse, clean boiling water rinse, and thorough drying to kill any microscopic corrosion followed by a good grade of cold galv. Since you intend to keep the tank on a boat anything less is just an excuse to repaint the tank in a year or so. ZRC is about the best cold Galv on the market but there are several much cheaper alternatives. Be sure it's a true cold galv coating, not just a "zinc rich" paint. You should have well over 90% of the dry film be powdered zinc for a true cold galv. Under a cold galv no primer is necessary or wanted. A second coat of cold galv will prevent any holidays in the coating but is not absolutely necessary, as a true galv will heal over any micro porosity.
Another thing is to be careful not to obliterate the original marking on the tank with too thick a coating on the shoulder. Obliterate or mask those and you get to start over as nobody will fill it. A good even single coat on the numbers is all you need. You'll be retouching that area after each hydro anyway.
If you want it green, go ahead and paint it with Rustoleum or something similar ON TOP of the galv coating. Dont go overboard with the topcoat, as some porosity is needed for the galv to work properly, and plan on redoing it in a couple of years. A hint of color from a spray can 12 to 18" from the tank is enough to identify it in an emergency. The cold galv is providing your corrosion protection, more paint simply adds weight and may actually hurt your corrosion protection. As far as decals go most fill stations will have the shoulder stickers to identify the tank as O2, and they be free most places. Might as well take advantage of it.
Wrapping the tank in an old weight belt web before putting it in the vise to tighten the valve will help protect your new finish. Be sure to prefit the valve hand tight with no tape or compound on it. Count the turns going in and mark the valve outlet location on a piece of tape on the shoulder. This is your "zero point" When doing the final tightening after applying sealer tape or compound you want 3 turns on the valve from this point. (Hint: Without a good vise and an 18" wrench you won't get there.) Maximum Teflon tape is 1 to 1.25 turns of 1/2" wide tape applied 2 threads from the tank end of the valve. Do not expose Teflon to the O2 in the main tank, and torque means nothing on those valve fit ups. More is NOT better on the tape or the turns. 1 to 1.25 turns on the tape and 2.75 to 3.25 on the turns to tight! If it leaks after that get a new valve. The thread is damaged on the old one!
FT
FredT
Guest
It does look like you caught it in time. Looks like a soft blast and acid treatment is in order for sure. If the abrasive roughens the sound steel surfaces you need a "softer" abrasive. That means going to either a smaller particle size or a less hard material.
Be sure to route the tank past your local PSI trained inspector (who will likely be seeing the tanks yearly) after the blast and before the acid wash so he can evaluate the damage. That'll eliminate his questions about what you did later on. If he kills the tanks at that point you're only out the cost of the abrasive work.
FT
Be sure to route the tank past your local PSI trained inspector (who will likely be seeing the tanks yearly) after the blast and before the acid wash so he can evaluate the damage. That'll eliminate his questions about what you did later on. If he kills the tanks at that point you're only out the cost of the abrasive work.
FT
i am very unhappy with the slow responses from the oms folks in ny. when they finally answered my e-mails all i got was the 30 or 90 day warranty was up and the hot dip program was on hold.
i realize that the bozos in italy are responsible for the poor job of coating the cylinders...however the us distributer(oms) should back the us consumer a bit more here.
as u can see i have several oms tanks...i also bought the iq pack and a O2 analyzer from them. u would think i'm a fairly decent customer and deserve better treatment than this.
oh well...typical dive industry who gives a schit attitude i suppose.
mr:upset:
i realize that the bozos in italy are responsible for the poor job of coating the cylinders...however the us distributer(oms) should back the us consumer a bit more here.
as u can see i have several oms tanks...i also bought the iq pack and a O2 analyzer from them. u would think i'm a fairly decent customer and deserve better treatment than this.
oh well...typical dive industry who gives a schit attitude i suppose.
mr:upset:
At least they answered your email. I had questions on their 21w hid light I bought, I send several email and a letter, never got a response. I have several OMS products, tanks, IQ Pak, STA,Wing, and HID light. I have since sold my OMS hid light, and will not buy another OMS product again. With products from Oxycheq and Koplin, who needs OMS, they can kiss my backside. I may dump all of my OMS gear.
Good thing you caught it in time. Tought luck about the mfg not backing it better.
Attached is a link about a tank that did not get caught in time and the bottom rusted and became a missle.
http://www.diveshop-pr.com/pages.dir/engl.dir/tankexplosion.html
In other post I have read, it appears that some dive shops will kill the tanks if you take any type of mechanical grinder or sander to them. I would discuss with your planned tank inspector your proposed plan of action before you do anything. Find out what he thinks is acceptable and what is not.
Let us know how it all comes out.
oxyhacker
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Neat pics. I hope the VIP sticker wasn't damaged when it let go!
Seriously though, it would be interesting to know about the circumstances, especially who put that tank on the whip and what they ever were thinking when they did - no way that much rust could not have been visible to a casual inspection from the outside, and those old plastic-coated USD steels are notorious for corrosion probs, as any good shop knows).
Re galvanizing. I ran into a guy some years back who had several steel O2 tanks he was using for deco, which he'd had hotdipped. So it can be done. Looked great - he said it hadn't been particularly expensive. Most galvanizers are into quantity and have fairly high minimums though. Oh and if you can't find one set up to do tanks you may have to supply hanger/plugs for the tanks.
I've been looking for a place that will do them, but haven't managed to find one - if anyone does, please let me know.
Seriously though, it would be interesting to know about the circumstances, especially who put that tank on the whip and what they ever were thinking when they did - no way that much rust could not have been visible to a casual inspection from the outside, and those old plastic-coated USD steels are notorious for corrosion probs, as any good shop knows).
Re galvanizing. I ran into a guy some years back who had several steel O2 tanks he was using for deco, which he'd had hotdipped. So it can be done. Looked great - he said it hadn't been particularly expensive. Most galvanizers are into quantity and have fairly high minimums though. Oh and if you can't find one set up to do tanks you may have to supply hanger/plugs for the tanks.
I've been looking for a place that will do them, but haven't managed to find one - if anyone does, please let me know.
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