My iron toilet flange appears to have been soldered to a 4 inch cast iron pipe. The flange is loose and and still good, but broke off part of the 4 pipe just below where the flange rested on it. This is pipe is now jagged. By moving it, I can get it to fit back on, but there is no seal. I will be raising the floor and need to raise the flange height and would like to replace the old flange with an ABS one. Can the new flange be place over the 4 pipe and then secured to the new floor or does it have to be secured to the cast iron pipe too? Any ideas? Thank you, Bob