I have been welding gtaw roots in many different alloys over the past 10 years.
For er70,80,and 90 no purge. Works good( as long as the tube has no draft through it and it clean).
The place I am working at now wants me to tryout there stt Lincoln machine(similar to millers RMD.)
I have a really hard time believing that any stainless root beads can be put in without a back purge.
Anytime molten stainless is exposed to oxygen it will sugar.
I understand what miller and Lincoln say about there processes. It makes sense to me.
If anyone has been using either of these processes could they post a pic of one of these open root beads.
I still think these processes are snake oil.