Condensate and Copper pipes

About 10 years ago we had a heating system installed in an unheated attic. They ran the condensate drain (heater, AC, and runoff from the humidifier) into a 1.5 copper vent pipe close by.

This weekend we discovered the vertical portion of the vent pipe immediately under the insertion point has eroded out. It is not a major problem to replace the copper with PVC, however my pipes underground are CI.

Any problems with the CI and condensate? Sadly, I don't have any other options.

Depending on the system, the pH can be quite acidic (in the 3 range, where it goes 1-14 and 7 is neutral). Suggest you look into the manufacturer's neutralization kit. If you don't, you'll continue to eat up your metal pipes. How often the sacrificial materials need to be replenished will depend on the system design.