Operating pressure of PN40-304 ball valve
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I’m facing a problem right now. The system operates at a pressure of 3 MPa and a temperature of 300°. However, the system needs to undergo a steam test at 5 Mpa and 350° for a duration of 1 minute. At present, the process engineer and one valve supplier believe that PN40 is sufficient for the 304 flanged ball valves in the system, while I and another supplier think PN63 is required. Of course, the price difference is quite large. That’s what I think; according to HG/T 20592, a 304 flange allows a stress of 2.27 Mpa at 300°, so PN40 does not meet the requirements. PN63 should be selected. Additionally, according to the process description, this test does not fall under normal operating conditions. I’m not sure if this statement is correct... If it’s not, then with 5MPA and 350°, should the flange be PN100? I earnestly ask for everyone’s advice
Why is a steam test at 5 Mpa and 350° required?
Voltage tolerance of the test system. In a certain extreme condition, steam at 5 MPA and 350° will penetrate in.
This means that values of 5 MPa and 350° may occur during the operation of the system, and such conditions should be taken into account as design parameters.
This post was last edited by dennyg on 2018-6-12 22:07. Well, this is another question... I think it should be counted; according to the manufacturing process, it’s not considered normal operating conditions but rather an accident. To test the accident condition, the probability of it occurring is extremely low. What worries me is the pressure rating of the ball valve
Personally, it is recommended to choose according to the standard of increasing the design pressure; for example, if the design pressure is 2 MPa, the pressure rating of the valve selected should be at least PN25 or higher.
They are all calculated at the next higher level. Since pressures of up to 5MPA are possible. Then it needs to be designed to meet the 6.4MPA requirement. Otherwise, you’ll regret it when problems arise~~
From an economic perspective, valves rated at 64 pressure would be sufficient, but from a safety standpoint, the system needs to undergo a steam test at 5 Mpa and 350° for a duration of 1 minute; in such cases, valves rated at 100 pressure should be used. However, the additional cost associated with this one-minute test may make the boss reluctant to go ahead with it. If the prices of small-diameter valves 64 at pressures of 100 are similar, there is a significant price difference for large-diameter valves; therefore, the selection should be made based on the actual circumstances.
Thank you all for your generous help; I look forward to more teachers stepping in to assist...
It can be selected according to PN63 pressure. Can the valve be removed during testing and temporarily connected using a bypass?