I have an old but functioning oil burner located in the garage. The system vents via chimney attached to garage. The chimney is badly damaged and would need extensive repairs. Is there a way that I can eliminate the chimney and use an alternate(aluminum or steel pipe) method of venting the unit? Where can I find requirements related to this?

Find the model number and brand of your oil heater. Than maybe you or we can look it up and try to get you the information you need. Usually the instal manuals have flue piping and sizing in them...

Being it is old it may be hard to look up. You could also call your local hvac company to come do it for you. They would be able to see the unit and develop as to what would work with your system and local codes.

Oil burners require a type L vent or better known as metalbestos all fuel type. IT is expensive. You could rebuild the chimny as another option.