Welding Tips and Tricks

I have a little project on my hands where I need to weld a SS bung for a back pressure sensor to a down pipe. The pipe looks to be plain steel or a low quality SS. it has traces of surface rust so I'm not sure. So is this the case where I would use a 3xxL filler rod?

Sometimes SS will have rust on it from carbon steel contamination Either from tooling or steel that is around it. That would mostly show up on the surface. Try putting a magnet on it. Most SS isnt magnetic, that is not 100% cause some SS is magnetic.

Im pretty sure you could use almost any SS rods to weld it.

Use a 309L stainless rod.