Cast Iron Sewer Line failure

It would be interesting to see an area farther down the line from where the actual failure occured. This may tell you whether or not the failure was internal or external. What was the condition of the ground it was removed from. I understand it would be saturated due to the leakage but if you could keep it uncovered for a while you could see if it is due to ground water. Since you are replacing it with PVC it should fair a lot better. I would inspect as much of the line as possible and consider replacing it all. I've seen conditions like this in areas where the ground water was high around leach fields. PVC took care of those situations. Gotta love that stuff!

Nice pic! Much better than trying to explain in words.

What I forgot to say was this pipe is "above ground" between floors. I have other lovely pictures.

Is the pipe in a location where it might have frozen (while plugged enough to be full of water)?

You never know what the janitorial staff has been throwing down there all these years to keep the pipe open. They could be using causting drain "uncloging" mixtures rather than just getting a snake and doing the job the right way.

Hmmmm......

If the issue is what is on the inside of the pipe, then why is the corrosion on the outside?

As I indicated before, That crack sure looks to me like the result of freezing, which allowed water to leak through the crack, causing the corrosion. And, as you indirectly point out, that leak appears to have been there for some considerable time, perhaps years...

Thought I would sweeting the pot right before lunch. this does show general locations of failure better.

What was the orientation of the crack? was it on the top,or sides, or bottom? Could the pipe have filled with water before the building was hooked up to sewer line, cracked from the freezing. When the temperature rose again the problem remained hidden until the volume of fluids overflowed the crack. If the crack was at the top, or near the top this would be possible. Of course if the installation was in Florida, then never mind.