SD...
Under no circumstances heat the cylinder...
Retailers like Home Depot sell a wide range of very effective paint strippers...
The new strippers work very fast...albeit a little messy...spread lots of news papers out...make sure you have good ventilation in the room where you're working...gloves/respiratory mask/goggles should be used...
Make sure the tank is properly capped...do not allow any stripper to get inside the tank use an old valve with proper ''O'' ring...also keep the stripper away from any plastics...you won't need scrapers...you can wipe of the old coating material with a rag...
Once stripped verify the outside of the cylinder is actually galvanized...the steel hidden under layers of coating may be shiny and appear to be zinc...but may be unprotected steel...
This method works very well...cylinders will look like new when completed...
Having said all this...depending on age...you may have trouble getting fills no matter how nice the tank looks...
Finally...discount any and all bad advise regarding having the tank ''overfilled''...if you're interested in more volume...source another 72...a set of bands...a manifold and double them up...
Best...
Warren
I quite agree that strippers work well on LP72s. They'll even remove some of the plastic coatings! The plastic caps used to ship tanks protect them well from strippers if you don't have a spare junk valve handy. Your LDS probably has a bucket full. Ask nice and you might get one for free.
As for heating the tank, how hot you can safely get it depends on the alloy. One common alloy for steel scuba tanks is 4130. After heat treating, it's annealed at 1550F and then tempered at 1050F+ according to
AISI 4130 Alloy Steel (UNS G41300). If you are concerned about this, find the material it's made from, look up the alloy, and form your own conclusions.
Aluminum tanks and steel tanks are chalk and cheese. Heating 6160, the most prevalent alloy for aluminum cylinders, beyond 350F or so causes a substantial loss of strength and can lead to a ruptured tank. Don't do that.
Heating an LP72 to 150F, on the other hand, is not going to hurt it in the slightest bit. Even an AL tank can get this hot in a closed car in the summer.
Warren seems to be the only poster so far advising that it can be hard to get fills for LP72s. It can be hard to get anyone to do anything with the *really* old ones that have pipe threads, but even those are fine as long as the pipe threads are OK. Most dive shops only deal in straight threads and have no expertise with pipe threads, but tapered threads are still used in larger commercial cylinders. They're OK as long as they have the right number of threads engaged when (a) hand tight and (b) torqued to spec.
[Edit: Fix tupo.]
