Steel Tank Exterior (can it be redone)

[A. Boyette]

Yes, you can repaint cylinders if it's done right. I've also condemned cylinders that weren't done right. Some guy brought one in one time very proud of his repaint job (which looked like a hack). When I questioned the abraded surface he said the took the old paint off with a sanding disk attached to his drill.

Sanding removes metal. There' a whole chapter on repainting cylinders in the PSI manual, 5th Edition, but I can't post it here due to copyright. But the gist of the story is use aluminum-compatible gel strippers and steel wool to remove old paint. Home Depot and Lowe's sells a product called "Zip Strip" which Luxfer approves of and says is fine to use on their cylinders.

Both Imron auto paint, a poly enamel, and Centari, an acrylic enamel (by DuPont) are approved by Luxfer to use on their cylinders IF they are not forced-heat cured. Any heat curing must be done at temps below 250* F. Allow the cylinder(s) to sit in a clean, warm, dust free room for two days to dry.

With Imron paint, use 225S cleaner followed by 226S conversion coating, then apply Corlar Epoxy Primer. After the primer dries, Imron should be applied in two light coats.

Any Cylinder inspector is going to question you if your cylinder looks repainted, and some will automatically reject a repainted cylinder "for safety concerns" and will probably tell you it isn't permitted.

Luxfer and PSI clearly says it is permitted IF it's done correctly. I have a regular customer with about 50 cylinders who constantly repaints his cylinders but I know he does it without heat curing and sanding. The only thing that bugs me is he tapes over the VIP sticker like he's masking up a car to paint. So the next year when I remove the old VIP sticker there's a big gray rectangle there with a ridge around it.

 

[JamesBon92007]

Yes, you can repaint cylinders if it's done right. I've also condemned cylinders that weren't done right. Some guy brought one in one time very proud of his repaint job (which looked like a hack). When I questioned the abraded surface he said the took the old paint off with a sanding disk attached to his drill.
.

Just for the record, earlier in the thread when I said "I sanded" the tank it was very gently, by hand, with #400, just to insure a good bond.

I suppose it's somewhat of a conundrum to have a steel tank that is not galvanized and needs to be painted. Fortunately all of my other steel tanks are galvanized

 

[NAM001]

Yes, you can repaint cylinders if it's done right. I've also condemned cylinders that weren't done right. Some guy brought one in one time very proud of his repaint job (which looked like a hack). When I questioned the abraded surface he said the took the old paint off with a sanding disk attached to his drill.

Sanding removes metal. There' a whole chapter on repainting cylinders in the PSI manual, 5th Edition, but I can't post it here due to copyright. But the gist of the story is use aluminum-compatible gel strippers and steel wool to remove old paint. Home Depot and Lowe's sells a product called "Zip Strip" which Luxfer approves of and says is fine to use on their cylinders.

Both Imron auto paint, a poly enamel, and Centari, an acrylic enamel (by DuPont) are approved by Luxfer to use on their cylinders IF they are not forced-heat cured. Any heat curing must be done at temps below 250* F. Allow the cylinder(s) to sit in a clean, warm, dust free room for two days to dry.

With Imron paint, use 225S cleaner followed by 226S conversion coating, then apply Corlar Epoxy Primer. After the primer dries, Imron should be applied in two light coats.

Any Cylinder inspector is going to question you if your cylinder looks repainted, and some will automatically reject a repainted cylinder "for safety concerns" and will probably tell you it isn't permitted.

Luxfer and PSI clearly says it is permitted IF it's done correctly. I have a regular customer with about 50 cylinders who constantly repaints his cylinders but I know he does it without heat curing and sanding. The only thing that bugs me is he tapes over the VIP sticker like he's masking up a car to paint. So the next year when I remove the old VIP sticker there's a big gray rectangle there with a ridge around it.

Of course this is all out to lunch if a filler was used to fill in gouges. If an inspector can not tell if a filler was used under the paint then he is well with in his rights not to accept the tank for vis. I am; more than willing to take a tank that is factory painted with chips in it than a repainted tank for that reason.

Thanks for the 250 degree figure. Great post though and valuable info for those that want to re surface their dinged tanks.

 

[A. Boyette]

Of course this is all out to lunch if a filler was used to fill in gouges. If an inspector can not tell if a filler was used under the paint then he is well with in his rights not to accept the tank for vis. I am; more than willing to take a tank that is factory painted with chips in it than a repainted tank for that reason.

Thanks for the 250 degree figure. Great post though and valuable info for those that want to re surface their dinged tanks.

All true.
I'd personally be real suspicious of a repainted cylinder that came in more than a couple years old and the paint on it looked like a new car finish with no dings or scrapes underneath. Dings and scrapes just happen. If it was old enough to repaint but yet it doesn't have dings or scratches under the new paint that's a reg flag.

A couple of years ago I bought a nice new Faber steel cylinder. It sure was pretty. Then I took it to a LDS to be filled after the first dive. The little short guy puts it in the cement water tank, fills it, then grabs it by the valve and drags it up the cement side of the tank to take it out. I was pissed. A scrape all the way from the crown to the bottom.

I went from "pretty painted" tanks to plain old bare aluminum for just that reason. Now I don't have to worry about dings and scratches.

 

[A. Boyette]

Just for the record, earlier in the thread when I said "I sanded" the tank it was very gently, by hand, with #400, just to insure a good bond.

I suppose it's somewhat of a conundrum to have a steel tank that is not galvanized and needs to be painted. Fortunately all of my other steel tanks are galvanized

I gotcha. The cylinder this guy brought in was obviously hacked. It wasn't even round anymore. It had flat spots on it where he had run his sanding disk on the drill. PSI says "light sanding" is permissible.

"Initially, the tripped cylinders are scuffed using a fine sandpaper, then prep-sol, a paint thinner, may be wiped over the metal to remove particles."

I can't see "light sanding" being any more destructive than tumbling. Tumbling probably removes more metal than "light sanding". Especially if it's one of the guys who puts a cylinder on the tumbler and leaves it all day long.

 

[Eric Sedletzky]

Zinc is the best long term solution for steel tanks. Painted tanks are were /are originally painted with a true polyester urethane AKA linear polyurethane. Brands like Awl Grip, Sterling, Alexseal are true linear polyester urethanes. Imron by Exalta (formerly DuPont) is not a true polyurethane. A true linear polyurethane consists of 1 part paint: 1 part catalyst: 25% <> reducer.
Imron is 3:1 and 10%, it’s badically a glorified acrylic enamel. True polyurethanes are generally not available to the general public. I had a marine business so I have access to those paints. They also use linear polyurethanes in aviation. LP is not designated as a car paint, it’s an extremely tough and durable industrial product. It’s very high VOC and falls under a different designation.

The problem with paint on scuba tanks in general is that rust can begin in a chip or scratch and begin an invisible corrosion crawl which sometimes is not immediately apparent. Sometimes after popping blisters or scraping away blistered paint you will find that the rust damage is way worse than you thought. A zinc rich cold galvanizing material painted directly on bare steel is the best bet because zinc acts as a sacrificial metal which will corrode first before the steel underneath will, even if there is a scratch in the zinc and exposing bare steel to salt water. Zinc will heal itself and the rust will not continue further out under the zinc layer causing rust creep.
However, zinc must be applied over CLEAN BARE STEEL. Putting some other primer down first will make the sacrificial action and benefit of zinc worthless unless it is applied directly to bare steel and is also used as a final topcoat. Don’t put anything over it, there is no need.
I have several tanks that I de rusted/ sand blasted, and zinced, and they all are holding up great. I don’t mind the dull grey finish. If you strip tanks to bare steel and or sandblast them, it’s mandatory that you get them re-hydroed.

 

[A. Boyette]

If you strip tanks to bare steel and or sandblast them, it’s mandatory that you get them re-hydroed.

I think "mandatory" is stretching it a bit. I found an "unless" in the Bible which would imply to me that it was optional in at least some cases.

"HOLD all cylinders with fresh paint for a hydrostatic retest, unless the inspector
is sure the fresh paint doesn’t hide an imperfection."

 

[NAM001]

I think "mandatory" is stretching it a bit. I found an "unless" in the Bible which would imply to me that it was optional in at least some cases.

"HOLD all cylinders with fresh paint for a hydrostatic retest, unless the inspector
is sure the fresh paint doesn’t hide an imperfection."

That sounds like a (process wise) a silly exemption. first first i could have painted tha tank 2 years ago and then took it o a dive trip and had it filled at a new shop. That shop knows nothing of the tank history and can say they fear it. there is no identification on a tank that says the tank under the paint is good, so its up to the whim of that shop owners. now we are back to the old if its an AL tank it will not be filled unless that shop did the vis on it. or they question the origin of the vis sticker ect. I hve seen painted tanks that are colored but see through at the same time. Process wise i do not see any complications with those tanks as far as the inspection goes. Tank failure happens with a .060 deep scratch in it. ANY I repeat ANY repaint will cover that up. From the inspectors view that tank can not be properly certified to be in a usable condition once repainted.

 

[JamesBon92007]

I think we are very fortunate to have all this information available to us now. Anyone who is interested can download the Luxfer Visual Inspection Guide plus learn about various coatings on tanks (i.e, paint) and the buoyancy characteristics and air volumes of various tanks are readily available. When I bought my first aluminum tanks I took their word for it that they were "better" but wasn't immediately aware that not only did they weigh more than my steel 72s but were more buoyant so my beach dives now entailed carrying about 8 more pounds for only a few minutes more of air. Thanks to the very knowledgeable and intelligent people who are now online and are generous enough to share their knowledge and insights I have formulas for determining the exact capacity of my tanks and can determine how much air they hold at various pressures. When I first painted my steel tank the tank fillers were only concerned with heat-treating because they had been informed about that particular danger. If I had Bondoed over deep scratches and dings I doubt if it would have occurred to them to ask.

 

[Eric Sedletzky]

I think "mandatory" is stretching it a bit. I found an "unless" in the Bible which would imply to me that it was optional in at least some cases.

"HOLD all cylinders with fresh paint for a hydrostatic retest, unless the inspector
is sure the fresh paint doesn’t hide an imperfection."

CYA
Brand new painted or zinced tanks with a current hydro buried under the finish, or fresh stamp and hydro shop brush touch with color of the day like it was done after the fact.
Which one rings alarm bells?