Flange rating also named flange pressure or flange class, flange rating class or pressure are for flanges application, low pressure medium pressure and high pressure will have different flanges class using. EU flanges pressure for PN6 PN10 PN16 PN25 PN40, Japanese and Korean flanges pressure for 5K 10K 16K 20K 30K and US flanges rating class for 150 300 600 900 1500 2500.