There are two flanges at each end of the pipe, one of which is marked as below. What is the standard flange?
In the middle, the center ring should be standard with the outside caliper. At least the manufacturer has its own standard. Specific not clear, have not seen so big
This kind of flange is used in high pressure pipes
This is an international standard flange. Nominal diameter DN100 of the back of the F is convex meaning
