I think the factory exhaust is just plain old carbon steel mild.

You can get exhaust any way that you want in either 304 or 409. 304 is more expensive and 409 is cheaper because it is a stainless it has less nickel content and more iron. 304 has high nickel so is more corrosion resistant.

If in doubt about what your pipe is and you want to weld it with wire, heli-arc (tig) or mig (wire) use Inco 182 rods or inco 82 wire.

In the refineries we use the term " IN DOUBT INCO IT OUT". Inco is a good catch all for most carbon steel to chrome or ss or vice versa.

 

I thought the factory pipe was zirconium?
Or maybe aluminized steel?