Carbon to SS Welding

Don't do anything. You can passivate the weld, or brush it with a SS wire brush and coat the weld with something to keep it dry.

You may get some localized rust but it will be on the outside of the pipe.

Anonymous Poster #1-

Hope you used SS rod to weld the steel pipe supports to the SS pipe! Best to use SS rod and not steel rods for welding of SS to steel. Except in a few cases always the rods of the better metal to weld dissimilar metals. This also holds true for different grades of SS. For 304 and 316 use 316, etc. Even better to TIG weld it with the appropriate wire/rod grade and size.

Wire brush or grind the surfaces to be welded to get them as clean as possible. Then weld. Chip any slag off if rods were used, no chipping if TIG was used. Wire brush all joints to remove any residuals. Paint with a suitable paint for the metals and the atmosphere.

Good Luck, Old Salt