Cast iron DWV (drain, waste, vent) pipes are not rust proof and over time corrode, perforate or crack allowing effluent (sewage) and dangerous sewer gas (methane) to enter a building. If you saw a cast iron pipe in a home your are considering buying or already own home with them, take note.
Commonly, these pipes rust from the inside out. Most frequently it occurs first with “horizontal” and low sloped pipes first as they do not drain well / completely compared to pipes with are vertical. In the end, ultimately, these pipes will need to be replaced as they have a life span of about 50 to 100 years when new. To complicate matters leaks go undetected initially as they are often buried underground, encased in concrete floors or within wall cavities. In some cases, only visible portions of the cast iron pipes have been replaced making their detection unknown during an inspection.
You may be surprised to learn that this is also one of the alarm bells with insurance companies. As such, they may refuse coverage on these homes or require, for example, additional premiums, and or repair / replacement.
If you are about to buy a home or own a home that has cast iron pipe, protect yourself…get it inspected.