Introduction to hydraulic testing, pneumatic testing, and leak testing of pressure vessels

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I. Hydrostatic Testing 1. Clean water is generally used; when conducting hydrostatic testing on austenitic stainless steel pipes, or on pipes that are connected to such pipes or equipment, the chloride content in the water must not exceed 0.005%. If this level poses a negative impact on the pipes or the process, other suitable non-toxic liquids can be used. When flammable substances are used for testing, their flash point must be at least 50℃； 2. The liquid temperature during testing must be no lower than 5°C, and higher than the brittle transition temperature of the corresponding metal material ； 3. For pipes subjected to internal pressure, in addition to the requirements specified in item (5) of this section, the hydrostatic test pressure at any point in the system shall be not less than 1.5 times the design pressure. When the design temperature of the pipe is higher than the test temperature, the test pressure shall not be lower than the value calculated using equation (1). If the stress generated in the pipe at the test temperature exceeds the yield strength of the pipe material, the test pressure shall be reduced to the maximum pressure that does not exceed the yield strength. 4. For pipes subjected to external pressure, the test pressure shall be 1.5 times the difference between the design internal and external pressures, and shall not be less than 0.2 MPa ； 5. When the pipeline and the container are subjected to a hydraulic test as a single system, and the test pressure for the pipeline is less than or equal to that of the container, the test shall be conducted at the pressure specified for the pipeline. If the test pressure for the pipeline is greater than that of the container, and it is not possible to separate the pipeline from the container, while the test pressure for the container is greater than or equal to 77% of the pipeline’s test pressure calculated in accordance with item (3) of this clause, then, with the approval of the design unit, the test may be carried out at the pressure specified for the container ； 6. The test pressure for the inner tube of the jacketed tube shall be determined as the higher of the internal or external design pressure, while the test pressure for the outer tube of the jacketed tube shall be determined in accordance with item (3) of this clause ； 7. The pressure is increased slowly during the test; once the test pressure is reached, it is maintained for 10 minutes. Then the pressure is reduced to the design value, and this level is held for 30 minutes. The test is considered successful if the pressure does not drop and there are no leaks ； 8. During testing, the gas in the pipes must be completely removed. If a leak is detected during the test, it must not be repaired while under pressure; when draining the liquid after the test, care must be taken to prevent the creation of negative pressure. II. Pressure test 1. The gas used for the test shall be dry and clean air, nitrogen, or other non-flammable and non-toxic gases ； 2. It is strictly prohibited to bring the test temperature close to the metal’s brittle transition temperature ； 3. During testing, an overpressure relief device shall be installed, and its set pressure shall not be higher than 1.1 times the test pressure or the test pressure plus 0.34 MPa (whichever is lower) ； 4. The test pressure for steel pipes and non-ferrous metal pipes subjected to internal pressure is 1.15 times the design pressure ； 5. A pre-test must be conducted using the test gas before the actual test, with a test pressure of 0.2 MPa ； 6. During the test, the pressure should be increased gradually and slowly. When the pressure reaches 50% of the test pressure, if no abnormalities or leaks are detected, the pressure should be increased in steps of 10% of the test pressure until it reaches the test pressure. Afterwards, the pressure should be reduced to the design pressure for inspection; a pass is considered to be achieved if no leakage is detected using a foam detector. It is strictly prohibited to tighten bolts while the pressure is still high during the test. III. Leakage Test The leakage test must meet the following requirements: Pipelines transporting extremely hazardous, highly hazardous fluids, as well as flammable fluids, shall undergo a leakage test. 1. The test is carried out after the pressure resistance test is successful; air is preferably used as the testing medium, but according to the provisions in the design documents or relevant standards, halogens, ammonia, or other sensitive gases may be used for a leakage test at lower pressures to assess sensitivity ； 2. The key areas to check during the leakage test are the valve stuffing box, flange or threaded connections, as well as the vent valve, exhaust valve, drain valve, etc ； 3. For the leak test, the pressure is increased gradually step by step. Once the test pressure is reached and the pressure is held constant for 10 minutes, all sealing points are inspected by applying a neutral foaming agent; no leaks being detected constitutes a pass.