The mild steel pipes made by Yamaha (they should know) are perfectly fine if you maintain them, I do.
You can do 3 things first keep them clean.
Second, and i plan to do this over the winter, is to take them off and respray with high temp paint.
What i have been doing up to now, is to rub grate polish onto them. This is high temp black polish for wood burners etc, they look lovely and black and shiny after a coat of that, and last a couple of months.
Of course like everyone else has suggested you can buy some stainless ones.
GET POLISHING FIRST!