Welding Rusty Exhaust. As a general rule steel surfaces should be cleaned of any oil grease rust and mill scale before using any type of filler metal or consumable for any arc welding process. So first thoroughly clean the.
However one of the most common things that welded on a car is the exhaust pipe. This is possible because the measuring and alignment that was done earlier ensured that once the new piece of pipe was welded in the whole exhaust system would maintain its original orientation and once done appear as if it was never. Water vapour from exhaust - petrol if burnt properly produces water vapour also.
Are done with mild steel welding wire and are not treated to resist corrosion.
These are all surface contaminants which can potentially adversely affect weld. If the damage is too deep to weld and repair then you shouldnt think about the welding. In a recent article I talked about welding on a car frame and what that all entails. If there are any other rust holes or spots that you missed while welding you will be able to feel the air from the exhaust.