I'm likely going to say something stupid here, as my memory isn't great, but 7018 is critical of its environment. It should be stored in a hot box once opened, and used within a few hours (something like four of them) after being removed. Simply placing such rod back in a hot box isn't enough if the welds are certified. It's a wonderful rod, but it has stringent requirements. It is referenced as a low hydrogen rod, thus is must be moisture free, unlike some of the other rods.
7018 was the basic rod we used in the welding class I pursued. My purpose was to learn to weld a boiler. I learned the necessary techniques, but there is NO substitute for experience, and one gets that by welding. And welding. And welding, ad nauseam. That's the part I still need in order for me to proclaim myself a weldor.
H