Yep, I agree, racer, I too noticed the good looking welds. In what I read from Jose, I think he knows a thing or two about welding...
Goog looking forge, by the way; it seems very efficient.
May I suggest a little modification? I know that Yamaha, for one, has found that inducing air into an exhaust was helping the hot gases complete their combustion and eliminate some more pollution. Maybe you could divert a little of your air going up through the pipe; this little air stream would point upward and toward the center of the chimney. The extra oxygen is supposed to complete the burning process. In a time when global warming is on every lips, I think it would be wise to do what we can to reduce our environmental footprint.