Polished Stainless Steel for Tractor Exhaust??

Not a tractor, but these stacks are around 3 years old and have between 600-700C exhaust flow thru them. They donīt stay shiny very long after new.

Taking T_Bone's temperature values as a guide, I'd say you might be borderline as to whether or not the pipe will "blue". I've got a Ford with a pyro in the pipe off the turbo, and it consistently runs 900+ under load, and up to 1150 on a hard pull. That pump is turned up a lot though. Dunno where the exhaust temp will be on yours.... There would be several factors involved including the length of the pipe, and whether or not it's all exposed to moving air. If it's contained under a lot of hood, then the air circulation potential is not there. On my Ford, I just have a length of aluminised exhaust pipe. Below the hoodline it's going to hell. Above the hood is new (muffler just fell off), but so far it's holding.
If you do go with a straight pipe, be sure to get the outlet above the cab, or you'll not enjoy the sound too much. This old Ford barks like a junkyard dog... but with the pipe above the cab, most of the rasp is gone. Do notice a bit more racket on a hard pull. Bystanders might notice more noise, but in cab, there's little difference. I would also keep th epipe straight. Any bend is likely to run higher temps, or at least discolor more quickly. Look at most any tractor with a curved top in th eexhaust rather than a rain cap. They almost always rust through in the bend. Something to consider anyway.

Rod

In order for the SS to color fast on the outside of the pipe, the pipe would have to be held at a certian temperature for a specific time for a given exhaust temperature and will be dependant on the pipe wall thickness.

On the common 300series SS that temperature should be about 900š too 1100š for about 10min on a sch10 pipe. On a sch40 pipe that may well be 30min or longer.

Sch10 pipe is about .120" wall thickness and Sch40 pipe is about .188 wall thickness.

And then there's the surrounding ambient tempature to consider as well the front of the pipe or the heal of the pipe. The heal will color fix much faster as it's protected from the cooling air of forward movement.

And then there's the velocity of the exhaust gas to consider.

As you can see alot of unpredictables to consider but generally the thicker the pipe wall the less problem with the pipe becoming color fast.

Also my tempatures and heat soak times are ball park numbers.

T_Bone