ArthurGerla
Contributor
I've found several remarks on the web on the dangers of powder coating aluminum scuba tanks because of the temperatures involved. Apparently the heat alters the properties of the metal. Does the same apply to steel tanks?
Powder coating a steel tank
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Boogie711
Guest
Yes
As someone who fills and vips tanks, I'd like to reiterate that I wish people would stop painting their tanks. The nicks and scratches are scars earned through use and should be worn with pride, repainted tanks beg the question: what are you hiding under there? We found one awhile back that had been condemned with a hole drilled through the side, some idiot plugged the hole and repainted the tank to hide the plug. Same thing for stickers - they belong on your luggage, not your tanks.
FredT
Guest
ArthurGerla:
According to DOT rules ANY evidence of applicaiton of heat to a pressure vessel kills the vessel. A retester is required to condem any tank that hsa seen temperature extreems, no matter what the metal construction.
BTW when considering coating any tank also consider how you'll get it off. Chipped or damaged coatings that may hide a defect in the metal under the coating have to be removed before the tank can be retested. Applying a coating like Rhino truck bed lining (A cold process) to your tank may seem like a neat idea, until you have to either remove it for inspection or scrap the tank!
FT
DennisW
Contributor
I just finished a cylinder inspection course and, what they all said. Don't paint your tanks. When you go through the PSI or
Diving Technlogies International training, the instructor will warn you to be suspicious of painted tanks, especially ones that are newly painted and are not new tanks. Powder Coating is just a bad idea for any tank, especially aluminum. I would condemn any aluminum tank for sure if it had been powder coated. The baking may not damage a steel tank, I would have to check on that because steel will not lose its properties at lower temperatures like aluminum. But I would be extremely careful and may refuse to inspect it if I could not find out what the temperature was that it was baked. Maybe I'll call my instructor and see what he has to say about it and then make a post about this next week.
Diving Technlogies International training, the instructor will warn you to be suspicious of painted tanks, especially ones that are newly painted and are not new tanks. Powder Coating is just a bad idea for any tank, especially aluminum. I would condemn any aluminum tank for sure if it had been powder coated. The baking may not damage a steel tank, I would have to check on that because steel will not lose its properties at lower temperatures like aluminum. But I would be extremely careful and may refuse to inspect it if I could not find out what the temperature was that it was baked. Maybe I'll call my instructor and see what he has to say about it and then make a post about this next week.
DennisW:
The powder coating process uses temperatures between 250 and 450 deg F. The temperature required to cause a phase change in steel occur at temperatures in excess of 1100 deg F so the powder coating process would not affect the properties of the steel in anyway.
Having said that I would treat every scrape and scratch on a tank as a badge of honor except bare steel corrodes very quickly in salt water. If your tank starts to show orange streaks it is time to consider repaint or protecting it somehow.
Aluminum corrosion tends to be self limiting whereas steel can develope deep pits that will result in the tank failing a hydro/vis.
I have heard of/but never used a cold zinc process to stop exposed steel from corroding. May not be as pretty but seems to be the most accepted way to stop corrosion.
wedivebc:
You don't need to heat steel up to its melting point to affect the integrity of the tank, wedivebc.
Yes but the the tempurature required for any phase change is far below the temperature involved in powder coating. Steel is not like water and ice it goes through many changes before it actually melts but the first change (that affects the chrystaline structure) occurs at greater than 1100 degrees F. Far higher than any powder coating process. Aluminum is an entirely different story.jonnythan:
Not that I know what I'm talking about here, but let me ask some questions:wedivebc:
- At what temperatures are most steel alloys tempered? I was under the impression that this process occured at temperatures as low as maybe 450F - yes? Again, my understanding is that tempering counts as a phase change and, even if it doesn't, wouldn't a process that could potentially render a tank more brittle than it was be of great concern?
- What temperatures does powder coating require? Not the low-temp UV stuff, but the old fashioned, hard-as-nails stuff. I was under the impression that a minmum temperature might be 350F but that many of the ovens actually heat to substantially higher than that.
WarmWaterDiver
Contributor
It should be considered that dive tank "steel" isn't just generic steel. For steel alloys containing chromium & molybdenum in piping and other other industrial pressure vessel services, post weld heat treating is actually required to remove residual stresses in the heat affected zones near the welds, to mitigate stress cracking. I personally wouldn't monkey with my dive tanks like this thread discusses without getting the consultation of a good metallurgist.
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