A: I am not aware of any standard that will tell you when the drums have rusted to the point of being dangerous. You might want to call some drum reconditioning companies which will almost surely have methods to determine when they will no longer recondition as drum. They receive old used drums from suppliers and then wash them, abrasive blast clean the inside and outside surfaces, take out all the dents, etc., and then repaint both the inside and outside. I must believe that there are drums that they will refuse to recondition on account of corrosion.