Issues regarding the design pressure and design temperature of steam ejectors
Thread Content
According to SH/T3118, for steam ejectors: the driving steam pressure ranges from 0.3 to 1.6 MPa, while the testing pressure is 0.4 MPa. In actual use, the inlet pressure of the ejector is -25 KPa, and the outlet pressure is at saturation level, ranging from 0.05 to 0.1 MPa. The driving steam is at a saturated pressure of 0.8 to 1.2 MPa. . So, which value should be used to determine the design pressure of the jet pump? Can we simply set the standard pressure testing pressure equal to the design pressure at 0.32 MPa? If it is designed based on the driving steam pressure, the design pressure has to be very high. For the design temperature, should it be based on the saturated temperature of the driving steam plus 20, or on the saturated temperature at the outlet plus 20? Personally, I prefer a design pressure of 0.32 MPA, which matches the pressure specified in the standards for pressure testing. The design temperature is set at the saturated temperature of the driving steam plus 20°C. Everyone is welcome to discuss.
It is divided into two chambers, with the design pressure determined accordingly; the power chamber is set at a maximum of 1.2 MPaG, while the design pressure for the other chamber ranges from 1.3 to 1.5 MPaG； The process side is determined based on the maximum possible operating pressure; if there are shut-off valves at the inlet and outlet, it is advisable to consider the highest pressure of the power steam. The temperature can generally be set based on the highest possible temperature that may occur.
What is the basis for choosing this value?
The test pressure is already this high; setting the design pressure higher would be inappropriate. Of course, under these design pressure conditions, no valves are installed between the injector and the subsequent equipment. Consider a safety valve for subsequent equipment.
Regarding injectors, it was said everywhere that they do not fall under the category of pressure vessels; however, according to the new regulations, injectors are not considered exceptions – meaning they should be evaluated based on their PV value. Many of them actually need to be treated as pressure vessels, or even classified in a higher category. In that case, the design pressure and design temperature should both be specified. I don’t know what the future of equipment management will hold.
Design pressure and design temperature of steam ejectors