Is a backing gas required if I am welding P1 to P8 with GTAW ER309? Even though this is a dissimilar weld, I am assuming that the root pass will still have some sugaring without the backing gas? Thank you very much!
I agree with js55. While there are GTAW rods that have a flux which supposedly eliminates the need for purge gas there has been much discussion on that matter with (in my opinion) no true consensus. Purging should be the route you take. Argon is usually the gas of choice.