If I deciphered your post correctly...
The welds you are making are stainless lap joints and T joints for the bushing "shelf" (lap joint) and T joint (stand-offs)?
If the lap joint is tube-in-tube (like a socket weld) then stuff one end of the inner tube with foil, cover the inlet side with foil and tape, poke an argon hose in it. Flow argon and then weld with a decent sized cup, enough CFM and post flow to weld the "socket".
If the T joint is open to both sides, purging the backside (depending upon whether its fixed to a plate, etc) might be better done with SolarFlux versus a purge chamber. I'd have to see it to make that decision or recommendation.
I'll say this, if the inner tube is going to be PVC inside a 316 tube, I don't get the application. From a materials mixture, I can't envision why 316 if PVC is also used? They are not conducive materials for any sanitary application that I have witnessed. And thus purging becomes more of a "best practice" versus a "code requirement".
I'm probably missing something...
The welds you are making are stainless lap joints and T joints for the bushing "shelf" (lap joint) and T joint (stand-offs)?
If the lap joint is tube-in-tube (like a socket weld) then stuff one end of the inner tube with foil, cover the inlet side with foil and tape, poke an argon hose in it. Flow argon and then weld with a decent sized cup, enough CFM and post flow to weld the "socket".
If the T joint is open to both sides, purging the backside (depending upon whether its fixed to a plate, etc) might be better done with SolarFlux versus a purge chamber. I'd have to see it to make that decision or recommendation.
I'll say this, if the inner tube is going to be PVC inside a 316 tube, I don't get the application. From a materials mixture, I can't envision why 316 if PVC is also used? They are not conducive materials for any sanitary application that I have witnessed. And thus purging becomes more of a "best practice" versus a "code requirement".
I'm probably missing something...