Who is right and who is wrong about "hydraulic test pressure"
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This post was last edited by Dou Man on 2023-5-23 11:16 A few days ago, there was such a discussion in the QQ technology discussion group. A group of friends posted a message: “The design pressure of the inner cylinder is 0.1, and the design pressure of the jacket is 0.6. The hydraulic test pressure of the inner cylinder is 1.25 * 0.1 or 1.25 * 0.6? ” First: “0.125”A: “Is there any standard or basis in the book? I'm going to argue with our review! ” B: “When the inner cylinder is under internal pressure, the water pressure is 0.125 ； When the inner cylinder is under external pressure, the water pressure is 0.75 da again. Then to be on the safe side, take the high value of 0.75” C: “You want to ask the audit, if the inner cylinder has a normal pressure flat cover and the jacket is under positive pressure, what is the test pressure of the inner cylinder?" D: “The definition of hydrostatic test is the design pressure” E: “The inner cylinder is designed for two pressures. Of course, take the higher value for the test pressure. There is absolutely nothing wrong with the review” F: “The inner cylinder is called the design pressure, and the value of the jacket can only be called the calculated pressure." G directly posted the picture: Finally the dust settled. Finally, guessing, the situation should be like this. The reviewer considered the most dangerous working conditions of the "public components", so he rashly increased the test pressure of the inner cylinder. However, the bigger problem it brought was that the head of the inner cylinder and the non-public component parts. In the words of another netizen, "It is unfair to press the jacket to the head, and it bears an unbearable weight." Regarding this discussion, there should be no controversy. The test pressure of the inner cylinder should not be increased because the stress of the common components will be checked during the hydraulic pressure test of the jacket, and GB/T 150.1-2011 4.6.1.7 Regulation: “For multi-cavity vessels composed of two or more pressure chambers, the test pressure of each pressure chamber is determined according to its design pressure, and each pressure chamber is subjected to a pressure test separately." But when I saw this discussion, I accidentally discovered that in the example in Wang Fei's reference book, the hydraulic pressure test calculation of a negative pressure in the inner cylinder (-0.1MPa) and a positive pressure in the jacket (+0.6Mpa), the jacket pressure test pressure is 1.25 * 0.6=0.75Mpa, there are actually different opinions here, because the calculation of the pressure test pressure in the standard is the "minimum value", and in the above 4.6.1.7 (c) is described as follows: "If it is necessary to increase the test pressure of a certain chamber, the provisions of 4.6.3 should be met." The implication is that the designer needs to consider the circumstances under which the test pressure needs to be increased. When increasing the test pressure, the necessary pressure test stress verification should be performed. Let's look at Chapter 4 of Li Shiyu's 2019 version of the tutorial (1), which gives an example of increasing the pressure test pressure (4) with such a description: “For a two-chamber pressure vessel, if one chamber is under positive pressure and the other chamber next door is under vacuum, the test pressure of a certain chamber should be at least 1.25 times the calculated pressure of the 'common component' when the two chambers of the vessel are under superimposed hazardous conditions (the static pressure of the liquid column should also be taken into account if necessary). ” Therefore, I personally think that whether the test pressure needs to be increased cannot be generalized. It may not be appropriate to strictly follow the examples in Teacher Wang Fei's book. After all, the authors (experts) also represent their personal opinions. The so-called benevolent people have different opinions. However, after the pressure test stress verification has been passed, it is not a bad idea to use the "calculated pressure" for the jacket test pressure. In this case, I personally think it is necessary to consider increasing the test pressure. Dear friends, what do you think are the appropriate values for the negative pressure of the inner cylinder (-0.1MPa), the positive pressure of the jacket (0.6MPa), and the hydraulic test pressure of the two chambers?
According to the provisions of GB/T 150.1-2011, for multi-cavity vessels composed of two or more pressure chambers, the test pressure of each pressure chamber should be determined according to its design pressure. Therefore, the hydraulic test pressure of the inner cylinder should be calculated based on the design pressure of 0.1, which is 0.125MPa. As for the pressure test pressure of the jacket, the stress should be checked before deciding whether the test pressure needs to be increased. .
The jacketed container is obviously a double-chamber container, and each cavity is designed separately. Of course, the common part is calculated according to strict conditions. As for the hydraulic pressure test, everyone must calculate it according to their own design pressure. As for the lower head being under high pressure, some people say it is unsafe. But were the inner cylinder and lower head inspected during the hydraulic pressure test of the jacket? Therefore, there should be no controversy and there is no need to increase the inner cylinder hydraulic test pressure.
The stipulations in GB150 are very clear. The hydraulic pressure test is based on the design pressure. It can be done in one sentence. I wonder if you have bothered with it.
Try the inner cylinder first and then the jacket, and calculate them separately. However, the design must take into account external pressure loads. Not only that, but wind loads, gravity, etc. also need to be considered. The maximum pressure difference between adjacent chambers must be considered for the jacketed vessel. The design needs to check the stability of the common components under the test pressure. Those that can be satisfied need to be carried out separately. Those that cannot be satisfied need to be checked for leakage first, and then the pressure resistance test is conducted at the same pressure at the same time. The pressure difference cannot exceed the allowable value for verification. Increased pressure must also be calibrated.
The main screenshot mentioned tightness, the pressure test is to verify the strength, the leakage test is to verify the sealing, and there is also a sealing test to verify the leakage rate. It seems that the old man confused the three.
That makes perfect sense. What you described is exactly what is included in GB150.1. 4.6.1.7 Those 3 items.
The test pressure of each cavity is determined according to the design pressure of each cavity. This standard has made it very clear. It has nothing to do with whether the design pressure in the cavity is positive pressure or negative pressure. What should be paid attention to is the stability of the common components during the test.
“The "minimum value of the pressure test pressure" is determined according to the formula. The formula is based on the design pressure as the parameter, but it does not mean that the lowest value is taken in all cases.
You said you don't consider the situation of each cavity, just press 4.6.2.2 It’s just the calculated “lowest value”. It’s not necessarily true whether the pressure in the real pressure test is the lowest value! If the minimum value is taken, there is no need to put forward the statement 4.6.3 "Stress Calibration of Each Pressure Component When the Test Pressure Is Greater than the Specified Test Pressure" in the standard. There are many situations to increase the pressure test pressure. 150 lists the two situations where the vertical container is lying horizontally and the medium density is greater than water. The training tutorial written by Teacher Li Shiyu lists other situations besides those described in 150.
The determination of the minimum value is based on the design pressure but the final pressure test pressure. It does not necessarily take the minimum value. The designer can increase the pressure test pressure, provided that stress verification is performed.