Replacement materials for burn tubes and baffles?

[DiscoInferno]

The burn tubes on my BIS Ultima are on their last legs, they've been slowly sagging over the years which I think accelerated two years ago when I hammered them flat again. At this point they are hopelessly deformed and corroded. The official replacements from Security/Lennox run about $70 each (I need at least 3), which is a little absurd for a pipe with holes. I can buy stainless tubing online for a fraction of that and drill my own holes, but which alloy? 304? 316? 310? H or L? So many choices.

The baffle boards that sit on the tubes run $200 for the set, they're intact but fragile. Anyone know what that material is and if it can be more-cheaply sourced?

 

[WES999]

I made burn tubes for my Fisher, As I remember I used 304 welded tubing, as it was cheaper than the 316 stainless. My tubes seem to be holding up fine under moderate use. The 316 is more resistant to corrosion and may last longer. I purchased my tubing form online metals,
the 316 is about $7 more per 4' length.

304
T-304 is the most commonly used stainless in the world. You can find it in everything from forks and knives to backsplashes. It is weldable, machinable with the right techniques, and has good corrosion resistance, but is not for use in salt water environments. This material is hardenable by cold work.

316
Also known as marine-grade stainless steel, T-316 is similar in machinability and weldability to T-304, but has far superior corrosion resistance. It has a far higher yield strength than both 303 and 304, meaning that it will not bend as easily. This material is hardenable by cold work.

Try Mcmaster carr http://www.mcmaster.com/#thermal-insulation/=qlppqb
They have some
Extra High Temperature Rigid Ceramic Insulation that looks like it should work.