Flange type: 1 According to the material,It can be divided into carbon steel, cast steel,alloy steel,stainless steel, copper,  aluminum alloy
                    2 In accordance to production methods, It can be divided into the forgeable flanges, casting flanges, welding flanges.
                    3 According to the creation criteria It can be divided into national standard (GB) (Ministry of  chemical industry standard    petroleum standard, electric power standard), American Standard (ASTM), German standard (DIN), Japanese standard (JB).

Steel pipe flange in China national standard system (GB)

1 Nominal pressure of flange: 0.25Mpa-42.0Mpa    Series 1:PN1.0, PN1.6, PN2.0, PN5.0, PN10.0,PN15.0  PN25.0, PN42 (main series)  Series 2:PN0.25, PN0.6, PN2.5, PN4.0
2 Structure:flat welding flange PL; welding neck flange SO; WN; socket welding flange SW loose flange PJ/SE integral pipe threaded flangeIF; Th; BL lining cover flange, flange cover BL (S).
3 flange seal type: flat FF, RF, FM raised face concave the convex tongue and groove face, MF, TG,ring joint face RJ

The application of the flange

1 flat steel flange: suitable for carbon steel pipe in the nominal pressure is not more than 2.5Mpa. Flat welding flange sealing surface can be made into smooth type, concave type and tenon slot three. Flat welding flange smooth application of the largest, used for mild medium conditions, such as low non clean air, low pressure circulating water, it has the advantage of cheaper prices.
2 welded steel flange: for the corresponding flange and pipe welding, reasonable structure, strength and stiffness is bigger, can withstand the high temperature and high pressure and cyclic bending and temperature fluctuations, reliable seal. Nominal pressure 0.25-2.5Mpa's butt flange sealing surface uneven.
3 socket weld flange: commonly used with PN ≤ 10.0Mpa, DN ≤ 40 pipe;
4 loose flange: loose flange commonly known as loose flange, divided into ring loose flange, flange looper flange and butt loose flange. Commonly used in the medium whose temperature and pressure are not high and medium corrosive condition. When the corrosive medium, the flange contact with  the medium part (flanging short) high-grade corrosion-resistant materials such as stainless steel and other materials,and the external is the use of inferior materials such as carbon steel flange ring clamp it in order to achieve sealing;
5 integral flanges: often the flange and the equipment, pipes, valves etc. as a whole, this type of flange are  usually used in equipment and valves.