What to check during the pressure vessel pressure test?

It’s specified in the fixed-volume regulations and GB150

I’ve seen it; the standard specifications only state that the outer wall of the container must be kept dry during pressure holding. Can I assume that? ； If, during the pressure testing, the pressure reaches the specified test pressure and remains at that level for a sufficient amount of time, as long as the pressure indicated by the gauge does not change, I can consider that the pressure testing of this container is complete and that it has passed the testing? What else should be considered besides pressure during pressure holding? For example, check whether there are any fluctuations in pressure; if there are, it indicates a leak. How do you locate that spot? In what order should I look?

Sections 4.7.6.2 and 4.7.7.1 of the fixed-volume gauge specifications mention the acceptance criteria: no leakage, no visible deformation, and no abnormal noises. As for pressure fluctuations or leaks in the equipment, a preliminary judgment can be made based on experience, followed by further investigation. As for determining the location of the leak, it seems that only experience and step-by-step inspection are available; there don’t seem to be any instruments for this purpose. The above are purely my personal opinions

To find leaks, you can apply soapy water to areas such as the surface of the container, the flange joints, and welds where leaks are suspected

Check for leaks, deformation, or abnormal noises, and verify if there is a pressure drop on the pressure gauge. These are the main aspects that a pressure test should check. A pressure test is a test to evaluate the strength of a product.

External inspection of pressure vessels Also known as inspection during operation, the main aspects of this inspection include checking for any abnormalities on the external surface of the pressure vessel, such as cracks, deformation, leaks, or localized overheating； Are the safety accessories complete, sensitive, and reliable? ； Are the fastening bolts in good condition and fully tightened? ； Check for any abnormalities such as foundation settlement, tilting, or damage to the anti-corrosion layer. External inspection is both the task of inspectors and part of the routine patrol checks carried out by operators. If any safety-threatening conditions are detected (such as cracks, deformation, or severe leakage in the stressed components), the operation should be stopped and the relevant personnel should be informed promptly. Internal and external inspection of pressure vessels This type of inspection must be carried out after the vessel has been shut down and its interior cleaned thoroughly. In addition to all the items covered in the external inspection, the main aspects of the inspection also include checking for corrosion and wear on the inner and outer surfaces ； Inspect all welds, head transition areas, and other stress concentration zones for cracks using the naked eye and a magnifying glass; if necessary, use ultrasonic or radiographic testing to examine the internal quality of the welds ； Measure the wall thickness. If the measured wall thickness is less than the minimum wall thickness of the container, a strength check must be conducted again, and measures such as operating at reduced pressure or carrying out repairs should be proposed ； Containers that may cause changes in the microstructure of metal materials should be subjected to metallographic inspection when necessary ； The main bolts of high-pressure and ultra-high-pressure vessels should be inspected using magnetic particle or dye penetrant testing

Sometimes, when the volume of the container is large, it is not possible to determine whether there is a leak just by looking at the reading on the pressure gauge. Based on experience, leaks in the main body of tanks are almost non-existent; instead, leakage points are mainly found at the fillet welds of various connections, the circumferential welds between connections and flanges, as well as the reinforcement rings.

During a hydrostatic test, first check whether there is a pressure drop on the pressure gauge; it is also necessary to consider both the upper and lower readings to determine the magnitude of the fluctuations. For example, in summer the temperature is high, and under normal conditions the pressure also increases. Therefore, it is necessary to check areas such as the welds, especially the fillet welds at the joints of the pipes, the circumferential welds between the pipes and the flanges, as well as reinforcement rings and manhole gaskets, to ensure that there is no leakage. If no signs of leakage are observed after maintaining the pressure for a specified period of time, then it is considered qualified

The fixed-volume gauge states that during pressure holding, the outer wall of the container must be kept dry, which is used to determine the location of leaks. During pressure holding, as long as water seeps in and wetts the weld point, it is possible to determine the location of the leak.