1. Flange connection is a more common and main method for connecting instruments and process equipment and pipelines. Because there are many standards for flanges, complex sealing surface forms, various pressure-temperature grades, and various steel grades, it makes the reasonable application of flanges more difficult. The flange standards used in instruments and equipment imported from China are all foreign standards, which adds to the complexity of flange applications. In order to compile a comprehensive material table, automatic control designers often have to spend a lot of time to consult flange standards, compare them, and find alternative domestic flange products. Even so, some errors will inevitably occur, and the temperature and pressure levels are not correct, which will cause problems in principle. When the instrument is installed, the flange cannot be matched, resulting in waste, so the correct choice of flange is a necessary link for the selection of various instruments.
Correct and reasonable selection and application of instrument flanges need to grasp several key aspects, that is, the correspondence between flange standards, flange standard numbers, temperature and pressure, and the comparison of materials in various countries to achieve a multiplier effect.
2. Flange standard number and specifications
The main application standards in China are chemical flange standards. The standard is divided into two systems (European system and American system), the flange standard number is different, and the flange is also different. Although it is the same as the chemical flange standard, it cannot be interchanged. The HG flange standard number must be clearly marked to avoid errors.
3. Universal comparison of flange installation
If different standards from different countries are used, the flange standard number should also be noted. In fact, after careful comparison, various standards are different. Some standards, such as the European system of chemical flanges, have flanges with the same outer diameter, the number of screw holes, and the same size under the same DN when the flange is less than 100mm. Therefore, it can be used universally for the major of automatic control. If the project pressure level is PN1.6MPa and the instrument pressure level is PN2.0MPa, if the HG20592-97 European system is adopted, as long as the pressure resistance level allows, it can be completely matched. The general parameters of flanges under common pressure levels need to consult relevant literature.
4. Chemical flange standard American system
After careful comparison, the American standard system for chemical flanges has no versatility at pressure levels below 5.0 MPa. This is different from the European system and should be noted when applying.
5. Temperature considerations
The flanges of various standards have different pressure resistances at different temperatures, so they cannot be easily matched. Such as ANSI-150, if the pressing force corresponds to 4.448N/inch 2=6.895kPa (l pound force=0.4536kgf), then 667.2N/inch, 2=1.034MPa (150 pound force), but different standards at different temperatures The pressure resistance is different. For flanges of different standards such as HG, JIS, ANSI, DIN, etc. can not only correspond to the pressure resistance, but also consider the temperature grade. Even if the same material has different pressure resistance at different temperatures, please refer to the reference for details.
6. Problems related to materials
With the same standard flange, different materials have different pressure resistance at different temperatures. Under the HG20604-97 standard temperature and material and pressure relationship. Due to the wide variety of steel grades in various countries in the world, the literature groups commonly used steel grades according to their characteristics. Among them, the nominal pressure rating belongs to the flange of the European system, and the material group number is 1.0-14.0 (a total of 11 files); the nominal pressure rating belongs to the American system. Flange, the material group number is 1.0~2.4 (a total of 12 files), the same standard number under the same temperature conditions, if the material group number is different, the flange's pressure resistance (high non-impact pressure) is also different.
