How long do iron pipes last?

[Left-is-Hot]

How long do iron sewer pipes last before they corrode through?
I don't have any issues with my sewer pipes under my house now, but I was curious about this. My place was built in 1956. I assume that it's iron pipes that run under the house? I already replaced the clay pipes that ran outside.

 

[Chris]

You are probably on borrowed time already. 50 years is a good life for them. If you keep acidic waste to a minimum you will get a little more time but I would start saving soon for the day they start giving you problems.