Question: What is the relationship between the design pressure of the pipeline and the flange pressure rating, and the valve pressure rating?
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I have a design: the pipeline is designed for a pressure of 4.2 Mpa and a temperature of 200 degrees, with a flange pressure class of CL.600； However, for various reasons, the valve pressure class chosen is (CL.300). In the piping field, it is considered that pipes of (CL.600) cannot be equipped with valves of (CL.300), which prevents the completion of the piping work. May I ask: what is the relationship between the pressure rating of pipeline design and the pressure rating of valves? Do they have to be identical? This post was last edited by zyucao on 2009-3-23 09:58]
I often do piping design, with the same pressure rating for the pipes and the same rating for the valves. Your pipeline is rated at 4.2 Mpa, which falls under the medium-pressure category, and the temperature is also high; for safety reasons, the valve rating cannot be reduced.
The pressure rating of the valve fittings must be greater than or equal to the pressure rating of the pipeline.
Your fittings and valves rated for CL.600 need to have their pressure ratings adjusted to correspond to the operating conditions; the temperature-pressure values of the flanges must meet the required specifications before they can be used.
Yes, generally the design pressure of the fittings should be the same as that of the pipeline
Depending on the material used, there are different temperature and pressure ratings. The pressure rating of pipes and valves should be the same; otherwise, it may be possible that the flange holes of the standard flanges do not match those of the valves (with some exceptions). Please confirm the material, and then, based on temperature and pressure, you can find the corresponding pound rating in the temperature and pressure rating table. In the case of LZ, the material of the valve might be of better quality, allowing it to meet the requirements regarding working temperature and pressure. However, the material of the flange is of lower quality, so a CL600 flange is necessary. For sizes under 2”, it may be possible to match the requirements, but for sizes over 2”, it might be more difficult. The pressure rating usually needs to be consistent. If it isn’t, as described in LZ, please check whether the eye distance, working temperature, pressure, bolt diameter, etc., are feasible; if they are, then there’s no problem, and it can be handled as a special case. This post was last edited by Albertlu on 2009-3-23 at 12:06
Valves and fittings are available in pressure series for easy selection; the design pressure of pipelines is determined with economic considerations in mind, by rounding values based on the pressure source. The design pressure of pipe fittings is generally greater than or equal to the design pressure of the pipes. Regarding the operating conditions you are using, as mentioned on the 4th floor, temperature-pressure calibration of the flanges is necessary. In China, the pressure rating for valves is generally based on a value of 20 degrees; for ISO low-carbon steel, it is based on 100 degrees, while for stainless steel, it is based on 20 degrees. It is recommended to determine this by verifying temperature and pressure in accordance with the manufacturing standards applied to the valve.
One additional point: if the flange pressure rating selected for the pipeline design differs from that of the valve, it can easily lead to differences in the connection dimensions between the pipeline flange and the valve flange. In other words, differences in bolt hole sizes, the number of bolts, and bolt dimensions can prevent proper connection. It is recommended that LZ check the relevant standards adopted in the design to see whether the connection dimensions for flange bolts of different pressure grades are the same. For reference! This post was last edited by clguan on 2009-3-23 13:26.]
Under normal circumstances, the pressure rating of valve fittings should be equal to that of the pipeline. Two-piece flanges of 600LB and 300LB with the same diameter cannot be connected due to mismatched connection dimensions, and using 300LB-grade equipment in conditions of 4.2 MPa and 200 degrees Celsius poses risks. It should be replaced with 600LB.
Flange pressure rating: It is possible to consult the temperature and pressure curve for the flange; the maximum allowable operating pressure for a 600-pound flange at 200°C. For different materials, the relationship between temperature and allowable pressure varies. You can look up the allowable pressure for a 300-pound flange at 200°C by yourself. It is possible that the grade chosen for the pipe is on the conservative side; 300-pound flanges can also be used.
The pipeline pressure must be consistent with the flange pressure rating! !