I was going to type out a long, detailed reply, but Al had already replied to this question over in your duplicate thread.
In short: verify the preheat @ a minimum of 6" from point of welding on the thickest part(See D1.1:2010 Clause 5.6).(check on the bottom of your base plate while heat is being applied at the joint where the baseplate meets the column shaft)...psst, you're going to need a large rose bud or it's going to take you a long time to soak through that base plate.