-Oh yes. I don't know exactly what kind of heat treating is done, but I recall one spec noting that some 40% of the tank's strength comes from the heat treat. Or to put it another way, the heat-treated tank is 40% stronger than the same tank, annealed.Originally Posted by boslab
But then, the same is true for steel tanks as well- maybe not the same ratio, but the material is still definitely heat-treated.
DOT regulations, in fact, require the destruction of any tank that's been exposed to more than X temperature for a given time period, though I can't recall if that spec was 150 or 200 degrees.
Many years ago, a few people were killed trying to fill some SCUBA tanks that the owners had had powder coated. The heat of the baking process annealed the tanks, which then exploded when filled. As noted earlier, the tank wall had become weaker than the burst disc, so the relief couldn't save them.
Personally, I had one customer seriously pissed off with me when I "destroyed"- I drilled a hole- in a tank he'd had powder coated to match his paintball gun. I don't know who did the actual work, but he sent it to me (along with the gun) for assembly and tuning. There was no way I was going to return the tank, knowing, as I did, it was horribly unsafe to use. If I refused to assemble it, he'd have just found some other doofus to do it- or done it himself- and wound up dead or injured for it.
I replaced the tank, but I doubt the customer really knew what I saved him from, and probably never forgave me.