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1. Submersion test: Used for small containers or pipes subjected to low internal pressure. Before testing, the container or pipeline is filled with compressed air at a certain pressure (0.4–0.5 MPa). Then submerge it to check for leaks, such as leakage on the right side ； Bubbles must form in water. This is also a common method for checking whether a bicycle tire is leaking. II. Water filling test: Use the static pressure generated by the weight of water to check for any leaks in the structure. Based mainly on visual inspection, it is suitable for general welded structures that are not under pressure but require sealing. 3. Ammonia leakage test: It has the same purpose as the kerosene leakage test, and its sensitivity is higher than that of the kerosene leakage test. Before the experiment, a piece of white paper or bandage soaked in an HgNO3 solution with a mass fraction of 5% or phenolphthalein reagent is attached to the side of the weld where it is easy to observe; thereafter, ammonia gas is introduced into the container or compressed air containing 1% by volume of nitrogen is used. In the event of a leak, color spots will appear on the white paper strip or bandage. Those soaked in an aqueous solution of 5% HgNO3 show black spots, while those soaked in phenolphthalein reagent show red spots. 4. Kerosene penetration test: Used for welded structures subjected to low internal pressure and requiring a certain level of sealing. Kerosene has strong penetration, making it very suitable for testing the sealability of welds. Before inspection, apply lime water to the side of the weld where it is easy to observe; after it dries, apply kerosene to the other side of the weld. If there are penetrating defects, spots or strips of kerosene will appear on the lime layer. The observation period is 15-30 minutes. 5. Helium mass spectrometry test: The helium mass spectrometry test is currently the most effective method for checking sealing integrity. Helium mass spectrometers have extremely high sensitivity, enabling them to detect helium at a volume fraction of 10-6. Before the test, helium is filled into the container first, followed by leak detection on the outside of the container’s welds. The disadvantages are the high cost of helium and the long inspection period. Although helium has extremely strong penetrative power, it still takes a considerable amount of time to penetrate extremely small gaps (which cannot be detected by other methods); the leak detection of some thick-walled containers often takes dozens of hours. Appropriate heating can speed up the leak detection process. 6. Airtightness Test: The airtightness test is a standard inspection method for boilers, pressure vessels, and other welded structures where airtightness is of critical importance. The medium is clean air, and the test pressure is generally equal to the design pressure. During the test, the pressure should be increased in stages. After reaching the design pressure, apply soapy water to the outside of the weld or seal surface, and use whether bubbles form as an indicator for testing. Due to the explosion risk associated with airtightness testing, it should be carried out after the hydrostatic test is successful.