RUST & CORROSION ARE THEIR WORST ENEMY!
The main problems with Cast Iron pipe are rust and corrosion.
Rust - the interior of the pipe will rust over time, which not only constricts the interior diameter of the pipe but it also creates a rough surface which slows down the rate of flow.
Corrosion – over time wastewater (or highly corrosive fluids i.e. soda, etc.) will erode through the bottom of the pipe weakening the structure and leading to exfiltration into the environment.