Pressure rating of flange
Pressure rating of flange
Does the steel pipe have a pressure rating, and does the flange also have a pressure rating? Answer: Yes! Let's take a look at the pressure rating of the flange together:
According to ASME B16.5, steel flanges have 7 pressure levels: Class150-300-400-600-900-1500-2500
The pressure rating of the flange is very clear. The flange of Class300 can withstand greater pressure than Class150, because the flange of Class300 needs to be made of more materials to withstand greater pressure. However, the pressure capacity of the flange is affected by many factors. The pressure rating of the flange is expressed in pounds, and there are different ways to express a pressure rating. For example: 150Lb, 150Lbs, 150# and Class150 have the same meaning.
Examples of pressure levels
The pressure capacity of the flange is also different at different temperatures. As the temperature rises, the pressure bearing capacity of the flange decreases. For example, the flange of Class150 has a pressure bearing capacity of 270 PSIG at room temperature, a pressure bearing capacity of 180 PSIG at 400°F, a pressure bearing capacity of 150 PSIG at 600°F, and a pressure bearing capacity of 75 PSIG at 800°F.
In other words, when the pressure drops, the temperature is allowed to rise, and vice versa. Since flanges can be made of different materials, such as stainless steel, cast iron, ductile iron, carbon steel, etc., each material has a different pressure rating.
The following figure is an example of an NPS12 flange. As you can see, the diameter of the flange inner hole and the raised surface are the same. However, the outer diameter of the flange, the diameter of the bolt hole center circle, and the diameter of the bolt hole become larger as the pressure level increases.
The number and diameter of bolt holes are:
CL 150-12 x 25.4 CL 300-16 x 28.6 CL 400-16 x 34.9 CL 600-20 x 34.9 CL 900-20 x 38.1 CL 1500-16 x 54 CL 2500-12 x 73
Pressure and temperature ratings-example
The pressure-temperature rating refers to the maximum allowable working gauge pressure (pressure unit is Bar) of the material and grade at the rated temperature (degrees Celsius). For the intermediate temperature, the linear interpolation method is allowed to determine. But it is not allowed to insert between flange levels.
If the bolts and gaskets of the flange joint meet the relevant restrictions, and the alignment and assembly of the flange joint comply with good regulations, then such a flange joint can be suitable for pressure-temperature ratings. If the latter is used for flange joints that do not meet these restrictions, the user is responsible.
The rated temperature corresponding to the rated pressure refers to the shell temperature of the pressure vessel of the flange and flange pipe fittings. Generally, this temperature is the same as the temperature of the storage fluid. The user shall bear the responsibility for selecting the pressure rating not based on the temperature of the stored fluid. When the temperature is below -29℃ (-20℉), the rated value should not be greater than the rated value at -29℃ (-20℉).
As an example, the following are two sets of materials classified according to ASTM and their pressure-temperature ratings according to ASME B16.5.
2. Not to be used above 455℃.
3. Do not use above 370℃.
4. Do not use above 260℃.
5. Do not use above 425°C.
