It's Boiler tubes/Flues/Superheater tubes. Basically allows the gas to go from the back to the front producing steam along the way. Superheater does the same bu

It's Boiler tubes/Flues/Superheater tubes. Basically allows the gas to go from the back to the front producing steam along the way. Superheater does the same but with the steam. https://en.wikipedia.org/wiki/Steam_locomotive_components https://en.wikipedia.org/wiki/Steam_locomotive_components https://en.wikipedia.org/wiki/Superheater#Locomotives https://en.wikipedia.org/wiki/Superheater#Locomotives