How should gas-liquid mixing tests be conducted for large containers such as spherical tanks?

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Preface: As a type of pressure vessel, spherical tanks have three methods for pressure testing. The most commonly used method is a hydraulic test, which basically involves using water for pressure testing ； Next is the pressure test, which involves using compressed air ； The gas-liquid mixed pressure test combines the characteristics of the first two types of tests, and it is a relatively new method for pressure resistance testing. Since gas-liquid mixing tests are used less frequently, and their use has only started to increase in recent years, many people are not yet fully aware of the specific procedures and precautions involved. Therefore, an overview is provided here first. I. Procedure for the gas-liquid mixture pressure test: This test typically involves the use of both water and air; only after a certain amount of water has been added can pressure be gradually increased through the gas phase, allowing for step-by-step observation of the spherical tank’s apparent condition and its sealing performance. The specific process is as follows: 1. Safety inspection: The safety department of the testing unit should send personnel to supervise on-site to ensure the safety of the testing process. 2. Segmented liquid filling: When filling large containers such as spherical tanks, it is necessary to do so in stages in order to conduct foundation settlement tests simultaneously. Generally, the liquid is added in 3 stages; the amount of liquid added in the first stage is equivalent to 1/3 of the weight of the medium when the system is at full capacity ； The final total water volume should exceed 1.2 times that of the medium when the system is operating at full load. After the water inflow is completed, the foundation settlement data should be carefully monitored to ensure that there is no excessive uneven settlement. 3. Temperature requirements: The minimum temperature for testing is determined based on the material of the spherical tank; generally, the temperature of the medium inside the tank should not be lower than 5°C ； In special cases, it shall be evaluated by the designer and clearly specified. 4. Slow pressure increase: Pressure can be applied to the gas phase only after the liquid has reached the set volume and the temperature meets the requirements. The pressure should first be increased slowly to 10% of the specified test pressure, and held at that level for 5 minutes. A preliminary inspection of all welded joints and connections is carried out; once no leaks are detected, the pressure is then increased further to 50% of the test pressure. 5. Gradual pressure increase: If no abnormal phenomena occur, the pressure is increased gradually by 10% of the specified test pressure at each step, until the test pressure is reached, after which the pressure is maintained for 10 minutes. The test pressure is generally not less than 1.1 times the design pressure, with the specific value to be specified by the designer. 6. Pressure reduction test: Then reduce the pressure to the design value and maintain it for a sufficient period of time for testing; the pressure must remain constant during this period. 7. Leak detection: For the gas-liquid mixed pressure test, the outer wall of the tank should be kept dry. After checking to ensure there is no liquid leakage, soap solution or other leak detection fluids should be used for further inspection; no air leaks, no abnormal noises, and no visible deformation indicate that the test is successful. II. Precautions for the gas-liquid mixture pressure test 1. Due to differences in the medium, type of equipment, specifications, and safety standards, the specific requirements and acceptance criteria for the gas-liquid mixture pressure test vary. Therefore, designers should determine personalized testing requirements in accordance with relevant **standards and industry regulations**, and then testers shall develop testing procedures and operational guidelines based on these requirements to ensure the safety and effectiveness of the tests. 2. During the testing process, operations must be carried out strictly in accordance with the established procedure to ensure the accuracy and reliability of the tests. 3. Before the test, a thorough inspection of the testing equipment should be carried out to ensure its integrity and safety. 4. During the experiment, safety precautions should be observed, such as wearing protective glasses and gloves. 5. During the test, if any abnormal conditions are detected, the test should be stopped immediately, and inspections and repairs should be carried out. III. Conclusion The gas-liquid mixture pressure test is an important testing method that can effectively evaluate the pressure resistance of equipment or structures in a gas-liquid mixed environment. When conducting such tests, it is necessary to follow the test procedures strictly and pay attention to safety measures in order to ensure the safety and effectiveness of the tests.