I would like to ask how the pressure rating of valves in pressure pipelines is determined?
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Our company and the client prefer to use a design pressure of 1.6 MPa or 2.5 MPa. Recently, when we were involved in the process of obtaining permits for the design of pressure pipelines, we found that for pipelines with a design pressure of 1.6 MPa and a design temperature of 70°C or 80°C, valves of PN16 grade were used. The equipment specifications did not indicate the material from which the components were made. I brought this up with our company’s approval officers, who said that this has always been the practice – since the temperatures never exceed 100°C, a PN16 valve is used when the design pressure is 1.6 MPa, and a PN25 valve is used when the design pressure is 2.5 MPa, and so on. The temperature-pressure ratings for the common materials used in valve bodies, such as WCB, A105 forged, and 16Mn forged, are below 1.6 MPa; WCC can handle up to 1.6 MPa, but it is not clear which forged alloy is equivalent to WCC. Was the temperature-pressure rating not taken into account when selecting this valve? Moreover, the temperature-pressure ratings of the valves seem to be lower than those of the flanges; I wonder why they aren’t set to be the same
The selection of the pressure rating for valves in pressure pipelines requires taking into account various factors such as the design pressure and temperature of the pipeline, the properties of the medium, flow characteristics, and the operating environment of the valve. Generally, the rated pressure of a valve should be greater than or equal to the design pressure of the pipeline, and attention should also be paid to the temperature range for which the valve is suitable. The temperature-pressure ratings of the valve must meet the requirements specified in relevant standards, to ensure that the valve does not experience failures or leaks during operation. Regarding the situation you mentioned, if the rated pressure of the valve is lower than the design pressure of the pipeline, it is possible for the valve to fail or leak, posing a safety risk. Furthermore, the choice of valve material, manufacturing process, and sealing material also affects the service life and reliability of the valve. Therefore, it is recommended to take various factors fully into consideration when selecting valves, and to carry out the selection and design in strict accordance with standards and specifications, so as to ensure that the valves function properly during use and maintain the safety and stability of pipeline operation. .
Are there any valve temperature-pressure ratings that are lower than those of flanges? The temperature-pressure ratings of HG standard flanges are usually lower than those of the valves; it is sufficient to select them based on the flange parameters.
It mainly depends on your specific operating conditions. In chemical plants, the pressure rating chosen for valves is generally one level higher than that of the pipelines; for example, if a pipeline is designed to operate at 1.6 Mpa, valves with a pressure rating of 2.5 Mpa are used, and so on.