Fritz - 3/22/2009 12:56 PM
I wonder how it is that manufacturers of tanks will paint them if it is to never be done. They must be breaking the law by what you are saying here.
If you have ever seen how they make scuba tanks, then you will know that they sand each tank at the end of the manufacturing process after hydro testing and before painting. They [the manufacturers] don’t want to be liable for your work, that is what it all comes down to, someone getting hurt or killed by their product.
The reason tanks should not be sanded afterward is there is no guarantee that the sanding has not done damage to the structural integrity of the tank. All tanks will eventually fail. It may take a thousand or more cycles of filling, but when they do fail, they go boom! When the tank is filled, the flexing of the tank wall causes the metal to work harden and crack, this crack can start at an existing crevice made by sanding.
For those that have never seen metal work harden and fail, try bending a metal clothes hanger back and forth until it breaks. That is work hardening and failure.
I have a dive buddy that paints his tanks, he is a marine tech and uses Imron paint. He lightly scuffs the surface of the tank finish with a scuff pad, just enough to dull the finish and give the new paint a "tooth". He also is experienced in this process and has the proper equipment. All the difference in the world.
Any of the certifying bodies will tell you not to because they don’t want to be responsible for personal injury either.
With proper care and testing your tanks will last a long time and if you want them a different color, pay someone with the experience to do it, then have the tank hydro tested if they don’t do it themselves. Testing should be after the paint is done, not before like the manufacturers do. (Strange procedure to me.)
Although I have painting experience in the automotive field, I doubt that I will ever paint my own tanks. I do wish they were all yellow, though.
Have fun and dive safe.