I'm trying to braze a 2" thick X 5.44 dia. ring to a 1.5" sch 40 type 304 S.S. pipe. I'm using propane & oxy. with a #6 tip, the rod is Harris flux coated low fuming bronze, AWS spec. A5.8 RBCuZn-C. I can't seem to get this to work, the brass is just turning black & the Stainless gets a white...