What is the span for stiffener ring for each pipe size?
Do we have a table for this?

A Stiffener Ring normally is a ring of metal (same material as the pipe or vessel) that goes completely around the pipe or vessel.
Are you asking how apart (i.e.: distance from one ring to the next) should the stiffener Rings be?

Yes, I am asking for the distance from one ring to the next. Does the span depends on pipe size and project specifications? Do we have table for this for use in global practice?