How to eliminate the impact of temperature on pressure during the pressurization of a heat exchanger?
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These past couple of days I’ve been working on pressurizing the heat exchangers in the workshop, and I encountered this issue: the equipment requires a pressure retention time of over 10 hours. The large temperature differences between day and night in Xinjiang have a significant impact on the pressure. For example, the pressure of one heat exchanger was 1.10 MPa at 7 p.m. yesterday, while it dropped to 1.02 MPa at 9:10 a.m. today. The specification states that the pressure drop over 10 hours should not exceed 0.02 MPa; otherwise, it’s considered unacceptable. By 10:30, the pressure rose to 1.065 MPA, which was still not within the acceptable range. By 11:00, the pressure increased to 1.11 MPA, and this time it met the requirements, though it was still above the specified limit. I wonder if anyone else has encountered such a problem – how did you resolve it?
You can use the gas equation of state for correction, but it still feels a bit uncertain in this way. We generally use liquid pressure, such as water or other incompressible media, to apply pressure in order to minimize the impact of temperature factors.
I forgot to mention that we use tap water here. Normally, if a liquid doesn’t vaporize, its volume changes very little; but under high pressure, it becomes quite sensitive to such changes
If it is felt that temperature conditions have a significant impact, then 24 hours or more later, two time points with similar conditions should be selected (with a time difference of over 10 hours between them) to record the changes in pressure differential.
This method is acceptable, but in today’s society, time is money. In our workshop alone, there are 69 heat exchangers that need to be pressurized, which consumes a lot of time. Additionally, keeping the heat exchangers under a pressure higher than their rated value for extended periods is also harmful to the equipment
Safety remains the top priority; the frequent occurrence of accidents in today’s society is closely linked to a focus on utilitarianism. However, safety awareness should be of utmost importance.
When testing equipment under pressure, the longer the time the pressure is maintained at the same level, the lower the safety level. What you said seems to be incorrect; feel free to continue the discussion. . .
This post was last edited by rjs999 on 2012-5-11 08:50. Pressuring a pressure vessel is a way to test the device’s tolerance for pressure as well as its resistance to pressure shocks; the longer the device is exposed to extreme pressures, the greater the stress on it, which may cause damage to the device. According to you, can we think of it and do it this way? “If the device could cause damage, we need not apply pressure; testing can be carried out only at operating pressure! ”Your device can only handle a pressure of 10 Kgf/cm2 – what about those devices that operate at pressures of dozens or hundreds of megapascals? In my opinion, safety regulations are like laws that must not be violated. Most safety accidents are caused by violations of procedures. Of course, a single violation may not lead to a safety accident, but one can’t be that lucky all the time!
Our \"safety regulations\" require that the pressure retention time be ten hours. I think there should be some formula that can calculate the volume expansion of water, so that the impact of temperature changes can be determined through calculations. Is this approach feasible?
Your idea is correct in principle and makes sense theoretically; it can be corrected by referring to the water density-temperature chart. However, without multiple calibration curves as evidence (or approval from the local boiler inspection agency), it is likely that the local technical supervision department will not give consent. Furthermore, if calculated in this way, it becomes complicated as to whether the temperature expansion factor of the metal material should also be excluded. When dealing with such issues, we usually conduct selective comparative tests under the same conditions, or simply find a warehouse to handle them inside.
If we ignore the temperature expansion of the metal material and consider only water, this method works. But there is still a problem: I don’t know how to determine the temperature of the water. Under high pressure, it’s not possible to insert a thermometer inside, and measuring through the wall of the casing also doesn’t work. I tried it – the temperature on the sunny side is higher than that on the shaded side, which can be felt by hand. Additionally, changing the location as you suggested is even less feasible, as the equipment is already installed in place. . .