In the valve temperature and pressure gauge, does the pressure correspond to the design pressure and design temperature, or to the operating pressure and operating temperature?
Thread Content
The pipeline grade specified in the design documents defines the design pressure as 1.6 MPa. At present, with an inlet working pressure of 1.4 MPa and a working temperature of 75°C, PN16 valves are selected. However, some believe that according to the pressure-temperature rating values for valve pressure classes specified in GB/T12224-2015, valves of PN16 class have a maximum operating pressure of 1.46 MPa at a design temperature of 75°C (see figure below). Is it correct to say that the valve does not meet the strength requirements of a design pressure of 1.6 MPa, and that its grade needs to be upgraded to PN25?
The pressure shown on the valve temperature and pressure gauge corresponds to the operating pressure and operating temperature, rather than the design pressure and design temperature. Based on the described conditions, with an inlet working pressure of 1.4 MPa and a working temperature of 75°C, a PN16 valve is sufficient to meet the requirements. According to the pressure-temperature rating values for valve pressure classes specified in GB/T12224-2015, valves of PN16 class have a maximum operating pressure of 1.46 MPa at a design temperature of 75°C. This pressure exceeds the operating pressure of 1.4 MPa required for air intake; therefore, using PN16 valves meets the strength requirements, and there is no need to upgrade the valve class to PN25. .
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The design pressure and design temperature are set higher than the operating pressure and operating temperature in order to provide a safety margin when selecting pipe fittings; therefore, the nominal pressure of the pipe fittings (including valves) must meet the pressure-temperature rating at the design pressure.
A safety factor must be maintained, choosing a higher grade
Normally, the higher level is chosen, and a safety factor is also maintained when there are abnormalities in pressure and temperature in the pipelines
The actual operating pressure and temperature of the pipeline are close to those specified for the valve; to allow for a safety margin, valves of a higher grade are generally chosen.
The temperature and pressure value is 1.46; although this is higher than the operating pressure of 1.4, the valve operates in a critical condition for an extended period of time, which theoretically poses safety risks. Therefore, a certain safety factor should be maintained
Design pressure, operating pressure, and nominal pressure are three distinct concepts; it is necessary to select an appropriate safety margin for pressure resistance from the perspective of pipeline risk assessment.