Properly Refinishing Steel Tanks?

[crlavoie]

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?

The number of galvanizing shops has steadily declined for a number of years due to the overhead and risk associated with running them. There's as much need as ever, just fewer of them.

As of 5 or 6 years ago, one of the largest hot dip tanks in the world was here in Boston. Not sure what's available in your area but even if there is someone, it's very possible that they might not do tanks. Tanks pose a different challenge in that they are not vented. The air has to have a place to escape during the heating and assuming that you don't want the inside to be galvanized, it poses a problem. It can obviously be overcome but I would imagine it's more trouble than it's worth for a small shop. In your case it might be more feasible to find someone capable of painting them (properly).

 

[jim T.]

Thanks. I know that anchor chain re-galvanizing companies have steadily vanished in the Seattle are over the last few years. I guess when the time comes, I'll contact Worthington and ask if they know of anyone in my region. I have new-ish tanks so I'm a long way off barring any surprises. It's just always nice to know who can do things ahead of time.

I just thought...maybe PSI tank inspectors/company in the Seattle area might know of someone. I'll check that out.

 

[WD8CDH]

I don't think it is even possable to re galvanize a tank without ruining it's heat treating. If it could be done, I would suspect that the tank would have to be re-heat treated and recertafied by the manufacturer.

Hot dip galvanizing way exceeds the maximum temperature rating of a tank.

 

[FredT]

Hot dipping as done by the manufacturer is part of the "approved" process done before hydro. The "approval" process mandated by DOT requires destructive testing of a minimum percentage of each "lot." The lot size cannot exceed ~200 tanks manufactured from the same "heat" (the term used for the batch of steel produced in one crucible or ladle depending on when alloying elements are added) of material.

Since the consumer has no idea if the tanks he has comes from the same heat, and the approval process requires the destruction of several tanks in the lot redipping lot sizes of 1 starts to be pretty much a non-starter once the tanks leave the manufacturer's facility.

A re-dipped tank is pretty certain evidence that the bottle has been exposed to "heat" in excess of 1000F, thus legally killing the tank as far as DOT is concerned.

The tank my be fine structurally, but legally in the US it's dead.

A rusted tank has some simple steps to repair, that aren't always so simple to do.

1. Clean gross external rust with a non-abrasive blast process or manual wire brush.
2. Treat remaining rust on the surface with a phosphoric acid compound to stop the rusting process, then rinse with hot water and flash dry. Do not remove sound hot dip coatings if that can be avoided. If it comes off with a pressure wash at the car wash it's not "sound."
3. INSPECT! The default answer is "trash it" unless ALL irregularities are checked and found to be within spec.
4. Apply 2 or more coats of a cold galvanizing compound. I prefer ZRC but I have used cold galvanizing compounds from Grainger and CRC with mixed results. Please not I did not say PAINT! The end dry film has to have a continuous phase of zinc to work properly. A "paint" won't have this property.

The application of an extra coat or three on the base and shoulder of the tank will delay the job repetition significantly. "Excess" material can be used to treat fresh hydro stamps.


Internal rust is addressed the same way, less step 4.

FT

 

[jim T.]

Thanks Fred.

 

[jac11819]

Everyone thanks for all the valuelable info. This is awesome!

 

[MSDT Mark]

Where can ZRC® Cold Galvanizing Compound be purchased?

 

[pescador775]

It is kind of weird to read this stuff. Of course, ZRC is the cheapest way to go and is the most practical in a kind of logic applicable to third world countries. However, decades ago, we used to galvanize military surplus tanks at various places (like San Diego Sandblasting). The zinc coating was applied by "metalizing", a kind of plasma jet which applied zinc metal to steel. The result was good for about 5-10 years of heavy use. They would probably last forever if touched up with "zinc rich" which we had never heard of back then. During metalizing, the surface of the steel is heated slightly but not enough to hurt anything. Prior to applying the zinc, the tank was sand blasted. I was told that not even a finger print on the tank was acceptable. I still have some old tanks around with these zinc coatings.I don't know what happened to this practice. Thirty years ago, it cost 10 bucks per tank. SDS told me they did not make any money on it but did it as a kind of 'favor" for divers. I believe it.

 

[FredT]

Where can ZRC® Cold Galvanizing Compound be purchased?

ZRC Worldwide

 

[crpntr133]

The fine folks at XS Scuba will sell you a can. I think it was $15 shipped. Most other places that I found would only sell by the case. I'm pretty sure I even called ZRC.