How to conduct a hydraulic test on a spherical tank?

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After the installation of the spherical tank is completed, pressure tests and airtightness tests shall be carried out in accordance with the specifications in the drawings. During pressure testing, a pressure gauge with the same range and calibrated properly must be installed at both the top and bottom of the spherical tank. It is advisable to choose a pressure gauge with a range of about 2 times the test pressure, but it should not be less than 1.5 times or more than 4 times the test pressure. It is advisable that the diameter of the pressure gauge be no less than 150 mm. The test pressure is based on the reading of the pressure gauge at the top of the spherical tank. Before the pressure test, compressed air at a pressure of 0.4–0.5 MPa should be introduced into the opening reinforcement rings of the spherical tank to check the quality of the welds. The first version of the hydraulic test uses water; other liquids that do not pose a risk can also be used if necessary. The test pressure is in accordance with standard specifications. During the test, the temperature of the liquid should be below its flash point or boiling point. During hydraulic testing of spherical tanks made of carbon steel, Q345R, and normalized 15MnVR steel, the liquid temperature must not be lower than 5℃ ； For other low-alloy steel spherical tanks (excluding cryogenic spherical tanks), the liquid temperature during the hydrostatic test must not be lower than 15°C. If factors such as steel grade and plate thickness cause an increase in the material’s ductile transition temperature, the temperature of the testing liquid must be increased accordingly. An exhaust port should be provided at the top of the spherical tank during testing. The air inside the spherical tank must be completely removed during filling. During the test, the outer surface of the spherical tank should be kept dry. During the experiment, the pressure should be increased gradually; once it reaches 50% of the test pressure, it should be held at that level for 15 minutes. Afterward, penetrant testing should be conducted on all welds and joints of the spherical tank, and once no leaks are detected, the pressure can be increased further. When the pressure rises to 90% of the test pressure, hold it for 15 minutes, then conduct another leak check; only after confirming no leaks are present should the pressure be increased further. When the pressure rises to the test pressure, it is maintained for 30 minutes, after which the pressure is reduced to the design pressure for inspection; no leakage is considered acceptable. After the hydraulic test is completed, the liquid should be drained, and the tank should be dried out using compressed air. During drainage, it is strictly prohibited to discharge it on-site. During the refilling and draining of spherical tanks, the settlement of the foundation should be monitored during the following stages: before filling ； When the liquid level reaches 1/3 of the sphere shell diameter ； When the liquid level reaches 2/3 of the sphere shell diameter ； 24 hours after filling with liquid ； After draining the liquid. The settlement of each pillar foundation should be measured, and the foundations of all pillars should settle evenly. After fluid discharge, the differential settlement of the foundation shall not exceed Db/1000 (where Db is the diameter of the base circle, in mm), and the differential settlement between adjacent pillar foundations shall not exceed 2 mm. When exceeded, measures should be taken to address it.