The main factors affecting flange sealing are: bolt preload, sealing surface form, gasket performance, flange stiffness and operating conditions.
1.Form of sealing surface
1)Flat type: simple structure, convenient processing, convenient for anti-corrosion or lining. However, the gasket is easy to extrude and not easy to be compressed. It is used in low pressure, small size, non-toxic, and low sealing requirements.
2)Concave-convex type: good neutrality and good sealing performance, suitable for medium pressure and high temperature occasions.
3)Tongue and groove type: good neutrality, reliable sealing, small gasket width, and small pressing force. It is suitable for flammable, explosive, toxic and high pressure occasions. It is more difficult to process and repair.
In flanged connections, the sealing effect largely depends on the sealing performance of the gasket.
1)Material requirements: corrosion-resistant, non-polluting products, with certain elasticity, appropriate mechanical strength and flexibility, not easy to deteriorate, harden or soften when temperature changes.
a) Non-metallic: Non-metallic flanges are mainly divided into rubber (used for low pressure and non-corrosive media such as water and steam with temperature < 100 °C), asbestos rubber (widely used in occasions with temperature ≤ 350 °C and lower pressure) , PTFE, etc. (mainly used in equipment with corrosive media)
b) Metal: aluminum, copper, mild steel, chrome steel, used for high temperature and high pressure
c) Non-metal and metal combination: metal clad gaskets and spiral wound gaskets, used for high temperature and pressure, large fluctuations
3.Three important parameters in flange standards
The nominal diameter of the flange refers to the nominal diameter of the container or pipe that is matched with the flange, and refers to the inner diameter of the container (except for the container that uses the pipe as the cylinder). Some value between the diameters, most of which are close to the inner diameter of the pipe. Steel pipes with the same nominal diameter have the same outer diameter, and since the thickness varies, the inner diameter also varies.
Nominal pressure is a pressure rating for the purpose of making a standard.
3) Maximum allowable working pressure:
The nominal pressure in the pressure vessel flange standard is determined according to the flange material 16Mn (or 16MnR) and the design temperature 200oC. When the flange material and temperature change, the maximum allowable working pressure of the flange will increase or decrease.