Properly Refinishing Steel Tanks?

[Thalassamania]

Please do, and please report back. I took the PSI course many years ago, my notebooks are in transit and my once photographic memory is fading a little. My memory is that PSI objected to epoxy because even a tiny pinhole could result in a pit which could grow, undetected, under the coating, into a serious structural flaw. It that has changed, or if there are new materials that would prevent this or if the old grey cells, they ain't what the used to be ... I'd like to know.

 

[oxyhacker]

POR-15 is a moisture cured urethane, that is to say, it uses moisture as a catalyst so it can be a one-part paint, but still offer performance comparable to a two-part. If you use it on a damp day, it will set up very quickly. This is what, according to the manufacturer, makes it work so well over rust - in will, to a degree, suck the moisture out of the rust as it cures.

You go to be real careful these days about generalizing about how different finishes perform based on tags like "urethane" or "epoxy" since there can be huge differences in how they are made and perform. For example, the one-part rattle can epoxy appliance paints have almost nothing in common with a real industrial-strength two part marine expoxy, nor does one-part "urethane" rattle can mag wheel paint have much in common with a moisture cured product like POR-15.

We've use POR-15 (the same stuff is sold by several different companies) on tanks, and it seems to hold up very well. The only thing is, it is intended to be used as a primer, since the resin discolors in sunlight. But anything you can topcoat it with is not going to be nearly as durable as the POR-15 so while you will get good protection the cosmetics may not be all that great. The other thing is, it is quite expensive, even more so because once a can is opened and exposed to the air it tends to start curing and has often set up solid by the next time you need some, making it especially uneconomical to do small jobs or touch up.
POR-15 also goes on fairly heavy, and is very difficult to remove, which can make inpecting the exterior of the tank difficult, the way powder coating does. For these reasons, we tend to use ZRC these day which, while not as bullet proof, is much cheaper and easier to use, and especially, to touch up.


QUOTE=MSDT Mark;3283812]Thalassamania, thanks for the solid advice. PSI does not recommend the use of epoxy because epoxy is a porous coating.

The website for POR-15 states the following. POR-15® chemically bonds to steel to form a rock-hard, nonporous coating that won't crack, chip, or peel. It works by isolating metal from moisture; without moisture present, steel can't rust. I will continue to research this product and post my findings. I would much rather be safe than sorry...

Thanks again,
Mark[/QUOTE]

 

[MSDT Mark]

Oxyhacker, you have provided the missing piece of the puzzle in my decision. I have used POR-15 in other applications with outstanding results. I wasn’t sure if this was my best choice for refinishing steel cylinders. I understand now that ZRC is the best choice, and why. I once read that science wins over bull sh** every time.

I appreciate you taking the time to explain the comparison of these two products as opposed to just an opinion.

Respectfully,
Mark

Dive buddy helping with the final touches, now off for hydro testing. FYI one thing I noticed with these cylinders is that rust forms under the bands, not just under boots…

When applying the finial exterior coating it is paramount not to cover the stamped information too heavy. If the cylinder inspector or Hydro facility cannot read all information the cylinder will not be passed. The coating will have to be removed.

 

[scubaskipper]

Just another reason for changing to the hot dip galv. I'll have people drop by the boat to try and sell me tanks that look like the ones in the photo. "All they need is alittle paint." ZKY has it right. As you can see, there is alot of work involved, especially if you don't have the proper tools ( sprayers, etc...) . I found sometimes it was hard to find these products in small amounts. Figure anything you don't use is wasted. The best stuff is not cheap, you get what you pay for. In the end, it was just too much of a pain for me to do myself.

 

[MSDT Mark]

Just another reason for changing to the hot dip galv. I'll have people drop by the boat to try and sell me tanks that look like the ones in the photo. "All they need is alittle paint." ZKY has it right. As you can see, there is alot of work involved, especially if you don't have the proper tools ( sprayers, etc...) . I found sometimes it was hard to find these products in small amounts. Figure anything you don't use is wasted. The best stuff is not cheap, you get what you pay for. In the end, it was just too much of a pain for me to do myself.

Having access to the proper equipment makes the job go much easier. With that being said this was a labor of love. I’ll enjoy diving these doubles even more, if that’s possible…

 

[Colliam7]

Someone needs to get a hold of the folks at P.S.I. As I stated earlier, if memory serves (and granted, times change and memory fails) epoxy coating on a steel tank, internal or external, means failure for the visual inspection.

Two quotes from my PSI 'manual' (Bill High's book): 'Paint, epoxy and molten zinc have been found erratically adhering to interior walls. Altered cylinders should be rejected because the possible damage may be difficult to assess.' If you put epoxy on the interior of a tank (or exterior for that matter), you may find it difficult to get a VIP done. The cylinder won't be condemned, it just won't be passed, because the inspector may not be able to adequately assess the corrosion on the surface. You may not have any problem, because inspectors have latitude - it is a judgement process in part. But, be forewarned. AND, owner painting in general is considered cause for increased suspicion during VIP. Another quote from the 'manual': 'Be warned, visual cylinder inspectors, expecially those trained at PSI Visual Cylinder Inspection Training seminars, are alert to, and most wary of, cylinders repainted by owners.' This text is in the section dealing with repainting of AL cylinders, where there may be additional issues of metal compatibility, high temperatures possibly used in repainting, etc. But, it is applicable to all cylinders, in terms of the suspicion an inspector might have. So, if you choose to have the surface refinished, have it done by a commercial shop, and make sure the condition of the surface immediately prior to application of zinc, paint, whatever is thoroughly documented. Do-it-yourself refinishing of scuba cylinders is generally not recommended.

 

[oxyhacker]

Treating the inside of tanks with the impression you will do anything beneficial is of course a fool's errand. You won't stop the tank from rusting or oxidizing, and you just might get it condemned.

Treating the outside is sometimes unavoidable. Sure some clueless dive store may hassle you about it but if you've got an old steel tank that is starting to rust, you don't really have any choice but to either let it rust to hell, and eventually fail inspection, or paint it and have a usable tank.

Two quotes from my PSI 'manual' (Bill High's book): 'Paint, epoxy and molten zinc have been found erratically adhering to interior walls. Altered cylinders should be rejected because the possible damage may be difficult to assess.' If you put epoxy on the interior of a tank (or exterior for that matter), you may find it difficult to get a VIP done. The cylinder won't be condemned, it just won't be passed, because the inspector may not be able to adequately assess the corrosion on the surface. You may not have any problem, because inspectors have latitude - it is a judgement process in part. But, be forewarned. AND, owner painting in general is considered cause for increased suspicion during VIP. Another quote from the 'manual': 'Be warned, visual cylinder inspectors, expecially those trained at PSI Visual Cylinder Inspection Training seminars, are alert to, and most wary of, cylinders repainted by owners.' This text is in the section dealing with repainting of AL cylinders, where there may be additional issues of metal compatibility, high temperatures possibly used in repainting, etc. But, it is applicable to all cylinders, in terms of the suspicion an inspector might have. So, if you choose to have the surface refinished, have it done by a commercial shop, and make sure the condition of the surface immediately prior to application of zinc, paint, whatever is thoroughly documented. Do-it-yourself refinishing of scuba cylinders is generally not recommended.

 

[jim T.]

Can we get our tanks Re-hot dip galvanized? Is that possible and if so
where can we get it done? I imagine it's an expensive process though...?
Thanks.

 

[MSDT Mark]

Two quotes from my PSI 'manual' (Bill High's book): 'Paint, epoxy and molten zinc have been found erratically adhering to interior walls. Altered cylinders should be rejected because the possible damage may be difficult to assess.' If you put epoxy on the interior of a tank (or exterior for that matter), you may find it difficult to get a VIP done. The cylinder won't be condemned, it just won't be passed, because the inspector may not be able to adequately assess the corrosion on the surface. You may not have any problem, because inspectors have latitude - it is a judgement process in part. But, be forewarned. AND, owner painting in general is considered cause for increased suspicion during VIP. Another quote from the 'manual': 'Be warned, visual cylinder inspectors, expecially those trained at PSI Visual Cylinder Inspection Training seminars, are alert to, and most wary of, cylinders repainted by owners.' This text is in the section dealing with repainting of AL cylinders, where there may be additional issues of metal compatibility, high temperatures possibly used in repainting, etc. But, it is applicable to all cylinders, in terms of the suspicion an inspector might have. So, if you choose to have the surface refinished, have it done by a commercial shop, and make sure the condition of the surface immediately prior to application of zinc, paint, whatever is thoroughly documented. Do-it-yourself refinishing of scuba cylinders is generally not recommended.

Colliam7
Thanks for the accurate information from Professional Scuba Inspectors. I am very familiar with this company and greatly value their training and standards of inspection. Your comments are greatly appreciated. However, taking my cylinder to anyone other than a high pressure cylinder manufacturer concerns me. If I refinish the cylinder myself, I know for a fact that no heat has been used, no metal has been removed from the cylinder, (none). I know exactly what was under the original finish. As you have mentioned inspectors have latitude - it is a judgment process in part. That is true as well for the person refinishing the cylinder.

I would have no confidence taking a cylinder to anyone else for refinishing. That is why I do it myself…

Respectfully,
Mark

 

[jim T.]

Are cylinder manufacturers (Worthington, etc.) the only ones who can renew a hot dip galvanized
tank? Do they even provide that service? Are there local places in larger cities that do this properly?