Can we weld on aluminized or stainless tubing?

We weld stainless pipes all the time. In the food service industry. I honestly don't know if there's a difference in the grade of stainless used for muffler pipes or not but our plumbing spends years in a wet environment with no hint of rust. We tig with a stainless filler rod and polish with a scotchbrite wheel. From past experience I've seen rust on stainless caused by impurities in the grinding/sanding wheels used to clean up the weld.