10dlkr Essentially, you have damaged and split the hard rubber (Ebonite ??) on the flange face. Patch repair the split with any good epoxy or polyester repair paste and if possible also use a soft rubber gasket when making up the joint. But what is flowing in the pipe - - will it attack the epoxy and soft rubber. Hard rubber is often specified when nasty acids are in the pipe and usually these attack the epoxy and sometimes soft rubber also. however even if the soft rubber gasket is not ideally suitable it will last many years and be replaced as and when found to be in need of replacement
regards
corrosionman.