This is the problem. People don't listen, they take delivery and just light a big fire and complain the paint blisters.They mostly cure once subjected to heat
if its direct heat,ie you painted a fire bowl or bbq and lite a fire on it,some paints wont last that long,if like on a stove where the heats not direct,for eg painted on the outside fire on the inside,it'll last ages,or should.
In my experience a lot of heat/stove paint will take heat yes,but dont like actual flame.
If your building a stove/wood burner its good practice to line the inside with either firebrick or vermiculite,then again,if its a fire pit etc dont bother painting it let it rust
Question now then, is what do I do with the tank?