1. The design temperature and pressure of the container;

2. The connection standards for valves, fittings, temperature, pressure, and level gauges connected to it;

3. The influence of thermal stress on the flange of the connecting pipe in process pipelines (high-temperature, thermal pipelines);

4. Process and operating medium characteristics:

For containers under vacuum conditions, when the vacuum degree is less than 600mmHg, the pressure rating of the connecting flange should not be less than 0.6Mpa; When the vacuum degree is (600mmHg~759mmHg), the pressure level of the connecting flange should not be less than 1.0MPa;

For containers containing explosive hazardous media and medium toxic hazardous media, the nominal pressure level of the container connecting flange should not be less than 1.6MPa;

For containers containing extremely and highly toxic hazardous media, as well as highly permeable media, the nominal pressure rating of the container connecting flange should not be lower than 2.0MPa.

It should be noted that when the sealing surface of the connecting flange of the container is selected as concave convex or tenon groove surface, the connecting pipes located on the top and side of the container should be selected as concave or groove surface flanges; The connecting pipe located at the bottom of the container should use a raised or tenon faced flange.