It appears that you must be working in a facility that has tanks of some sort. (designed to some standard)
I would also ass-u-me (I hate that word) that those tanks were built to a specification / Code and that construction, was in compliance with those Codes &
performed welding to a Qualified Welding Procedure (using Qualified Welders). Qualified welding Procedures (WPS's) dictate the type of filler metal in relation to
base-metal compatability etc.
Look for the history/information on the Tank, research the construction/fabrication method and the Procedure used.
I doubt that you have a Welding Procedure for just E6010 w/out E7018 cover, ( but you may ). I seriously doubt that E6013 is addressed in your
Welding Procedure. (but it could be)
Either way, Don't guess, match the original design or latest edition of that same standard..
Good Luck
There is no shortcut, to anyplace WORTH going!
Tom