Discussion on "Stress Calibration of Hydraulic Test"
Thread Content
Regarding the stress verification of hydraulic tests, many designers use SW6 software in their designs and ignore how to perform verification of hydraulic tests. If you haven’t seen the following content, many friends will say: What else needs to be checked? GB150 has stipulated the verification conditions for hydraulic testing, but it is ≤0.9Relφ! No. First, let’s talk about the calibration of hydraulic tests. GB150 regulations: If using greater than 4.6.2.2 , 4.6.2.3 For the specified test pressure, the stress level of each pressure component under the test conditions should be checked before the pressure test. This is a change in the standard. It is no longer mandatory to conduct strength verification before the pressure test. Instead, verification is required when the test pressure is greater than the formula calculation. Secondly, for SW6, which components have been verified by hydraulic tests? If careful friends read the calculation books, they will find that there are many components whose strength calculation books are not verified by hydraulic tests, such as tube sheets, flat covers, flanges, etc. So how should they be checked? There is another situation that is more common in shell and tube heat exchangers. For example, when the design pressure on the pipe side is greater than the design pressure on the shell side, there are two methods to consider in order to check the tightness of the connection between the pipe and the tube sheet.: 1. Increase the shell side test pressure to be equal to the tube side test pressure. When using this method, the stress situation during the shell internal pressure test must be checked. It is required that the calculated value of the primary film stress at any point on the shell shall not exceed 0.9 times the yield limit of the material used at the experimental temperature. At the same time, the pipes, flanges, etc. can meet the strength requirements of the pressure test. 2, the leakage test method is used to check the tightness of the pipe and tube sheet. For the first situation, there is a need to improve the stress calibration during hydraulic testing. How should it be done? Different units have different practices and opinions. Some think that the hydraulic test pressure is directly used as the design pressure. I personally think this method is not reasonable. Let’s see what you do first, and then I’ll talk about what I do.
Alas, no one commented again. Demotivates me.
It is clear that we are doing engineering design, and we need to classify the importance of equipment. Important equipment for high voltage can be carefully considered. If every equipment is considered in this way, it will not make people exhausted. Moreover, the pressure test is a short-term load, which can also be covered by the safety factor of the material. If every piece of equipment is like this, wouldn’t you feel tired? What's more, neither the flange nor the tube sheet itself is strength-controlled, so what's the point of checking the hydraulic pressure test? Of course, special equipment such as particularly large vertical heat exchangers still need to be fully considered. For general equipment in engineering, your leisurely company can consider it.
It's great to be part of the discussion, first of all you're very welcome. First of all, let me state that the following is only a technical discussion and has no specific purpose. I cannot agree with your statement of "discussing these issues" and distinguishing between high pressure and low pressure. First of all, the standard does not make such a requirement out of thin air. You can say that you did not do this, but it does not mean that what you did is right. Secondly, there is no word in the standard that states that "high-voltage equipment needs to be calibrated with a voltage test, or that low-voltage equipment can be exempted from the voltage test." Finally, you are right to say that the withstand voltage test is a short-term load, but when you use the safety factor as a margin, I don't know what your understanding of the safety factor is. If you want to obtain or replace certificates, you should talk to the expert teacher about this, haha. When it comes to engineering design, you need to be literal and have a basis for everything, and you can't be pat on the head or think too highly of yourself. There is no single cause for any accident. Accidents in which equipment was damaged due to the pressure test alone have also occurred. Therefore, the responsibility for designing is your own. You don’t have to do this, but there is no reason to blame others, right?
Are flanges and tube sheets not strength controlled? Please tell me, what is the control? What is the purpose of checking the axial stress, hoop stress and circumferential stress of the flange? Why does the tube sheet need stress calculation? Thanks for your guidance
The purpose of the pressure test is not only to test the strength, stiffness and stability of the equipment, but also to test the tightness of the welded joints and the sealing performance of the sealing structure. For example, for a fixed tube sheet heat exchanger, the shell side design pressure is 0.8MPa and the tube side design pressure is 1.0MPa. According to the standard, the pressure design pressures are 1.1MPa and 1.35MPa respectively. If the shell side pressure test pressure is increased to 1.35MPa, how to check the stress of each component?
For example, for a fixed tube sheet heat exchanger, the shell side design pressure is 0.8MPa and the tube side design pressure is 1.0MPa. According to the standard, the pressure design pressures are 1.1MPa and 1.35MPa respectively. If the shell side pressure test pressure is increased to 1.35MPa, how to check the stress of each component? Some personal practices: 1. The input of the shell is 1.35MPa, and the allowable stress is 0.9ψσs; 2. Pipe flange: Maximum non-impact working pressure at 20℃ 1.5 times >1.35MPa ； 3. Container flange: Maximum allowable working pressure 1.25 times>1.35MPa ； 4. Hole reinforcement: When calculating thickness, the allowable stress is 0.9ψσs ； 5.Tube sheet: Take 1.35/1.25=1.08 as the design pressure, and check the allowable stress against the hydraulic pressure test temperature.
My approach is actually basically the same as yours. It uses "virtual design pressure" to check each component. The only difference is that I directly use the last item, taking 1.35/1.25=1.08 as the design pressure, taking the water pressure test temperature as the design temperature, and then checking each component.
The poster raised a question that no one understands. 150 only gives the control requirements for the stress of the shell film during the pressure test. No control index is given for bending stress.
SW6 has a test pressure input field. If no input is made, the normal test pressure will be used. If it is input, the input pressure will be used for verification.
Hello, can you explain "5. Tube sheet": Take 1.35/1.25=1.08 as the design pressure, and check the allowable stress against the hydraulic pressure test temperature. ”