A professional welder told me how to weld plugs without blow thru that work very well. You use a non-ferrous metal on the back side, (aluminum, brass, copper) and it vastly lessens that chance of blow thru. The non-ferrous backing will not weld to the steel. A lot easier if you have a helper hold the non-ferrous backing in place. Use a pair of pliers or screwdriver to hold the backing metal as the heat does transfer.
