Rust Protection Paint

how to weld stainless steel to mild steel?

i have a mig welder and want to weld grade 304 stainless steel tube to a mild steel tube (at a 90degree angle). the weld joint is critical and needs to be fairly strong, it will also be exposed outdoors (the mild steel is already painted to ensure rust protection). i think both tubes are 1mm thick.
would welding the two tubes together be a problem if so could i reinforce it with something (like a 3mm mild steel plate) and what welding wire would you suggest
could anyone help me since i have tons of mild steel lying around and do not want to purchase any more.
thanks

1) The wire must always match the higher grade of steel. So you would need 304 stainless wire to make the welds.

2) Both pieces must be clean and free of paint, oil, grease, etc.

3) What are you doing with it? 1mm is about 22ga. Not thick enough to support anything. How much pressure? It should be good for 150 psig.

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