The homemade triple wall chimney pipe you are considering could work for a while in principle but i strongly advise against your trying it.
Diy double wall stove pipe.
The double wall allows a clearance of 6 from the wall and 8 from the ceiling.
The stove pipe is connected to the stove and goes through the ceiling or back of the home to redirect smoke outside of the home.
This foam can be added to concreate to make.
The pipe should fit the outlet or exhaust of your wood burning stove.
A major issue with these is a loss of heat or having it misdirected.
Darwin invented the foam mate which is a machine that creates a nice thick foam the consistency of shaving cream.
Single and double wall single wall pipes are used when there s a gap of at least 18 between the combustibles and the chimney system.
Your worries about the durability of galvanized steel.
In this measurement reduce the length at least by two inches as the 90 degree elbow is about 8 inches tall.
The double wall pipe is used if the gap is less than 18.