You should not use galvanized smoke pipe on a solid fuel appliance. From the appliance to the thimble, use black steel smokepipe.
What brand name black steel smoke pipe supports coal and where do you find them?
For a metal chimney you must use a double wall insulated high grade stainless steel, 304 is good, 316 is better.
This link is broken, either the page no longer exists or there is some other issue like a typo.
for all coal supported double wall Class A 6" chimney pipe is made of the following;
Simpson and Metal-Fab use on their outer walls 430 G-90 Galvanized Steel and 430 Stainless on the inner wall at different thickness, both supported for use with wood, oil, and coal. SuperPro uses 304 Stainless Steel on the outer and inner walls but it says it's only supported for wood use. Neither Security Chimneys or Metalbestos show what type of metal they use.