Why does the pressure-volume hydraulic test reach the test pressure first and then reduce it to the design pressure?
Thread Content
According to GB150.4 "Pressure Vessels Part 4 Manufacturing, Inspection and Acceptance", when a pressure vessel is subjected to a hydraulic test, the pressure is first raised to the design pressure. After confirming that there is no leakage, the pressure is raised to the test pressure and maintained for 30 minutes, and then the design pressure is maintained for a period of time. My question is, since there is no leakage after maintaining the test pressure for 30 minutes, why does it need to be lowered to the design pressure and maintained for a period of time? What's the point of doing this?
I still have some doubts. Inspection should be carried out during the test pressure maintenance process. Why should it be lowered to the design pressure for inspection? Is it for safety reasons that people should stay as far away from the test container as possible during the pressure test?
The inspection is relatively rough during the test pressure. Because the test pressure is high for safety reasons, inspection is not required during this period. Inspection is only allowed when the design pressure is approaching. Many units do not follow the regulations. It is okay if there is no problem, but it will be troublesome if there is a problem. Many accidents occur during the testing phase, so it is recommended that you follow the regulations and conduct inspections after the design pressure is approaching to ensure safety on site. The first consideration when establishing regulations is safety. This person understands
That's it, thank you for your answer. However, I am a user and am not a mechanical major. When I went to the manufacturer to supervise the production of equipment, I explained this process to the manufacturer. The manufacturer said that the test pressure is fine, why should the pressure be maintained until the design pressure? I don’t know how to answer. I feel that the actual operation is also difficult. If the workers are rushing to meet the deadline, it will be difficult to ensure such operation.
The test pressure of the container should be a verification of the overpressure limit of the container. For safety reasons, when designing things, you should always design things a little higher than the requirements when the equipment is working normally. If it is accidentally exceeded, it will not be easy to cause problems. It is not safe under overpressure, so try not to go to the pressure test station. Personal understanding.
After the test pressure is reduced to the design pressure, the performance of the gasket and fasteners can be checked. If the test pressure damages the gasket or fasteners (which can be understood as plastic deformation), the nozzle will leak when the design pressure is reduced.
As for the pressure test regulations mentioned above for safety reasons, it is not important.
The test pressure is calculated, and it is not artificially determined or increased. In the industry, the calculation is basically passed, and then the pressure test is basically no problem (except for special circumstances, such as fraud in materials or welds)
It turns out there are still such considerations, thanks for the answer! The possibility you mentioned is mainly due to the consideration during the pressure test of the pipeline. During the pressure test of the container, blind plates are temporarily added and there should be relatively few fasteners.
The main things to check during the pressure test are the tightness of the weld and the sealing of the pipe mouth, which can be seen intuitively.； Under test pressure (short-term overpressure), it can also redistribute stress on the container, refine some small cracks, etc.