Hydraulic test, pneumatic test, leak test
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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 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 formula (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 carried out 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 conducted 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 the test, all gas in the pipeline must be completely evacuated. In case of any leaks during the test, they must not be addressed while the pipeline is under pressure. When draining the fluid after the test, care must be taken to prevent the formation 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 ； (II) It is strictly prohibited to set the test temperature close to the brittle transition temperature of the metal ； (III) The test setup shall be equipped with an overpressure relief device, the set pressure of which shall not be higher than 1.1 times the test pressure or the test pressure plus 0.34 MPa (whichever is lower) ； (IV) The test pressure for steel pipes subjected to internal pressure as well as non-ferrous metal pipes 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 observed, the pressure should be increased in increments of 10% of the test pressure until it reaches the test pressure. Thereafter, the pressure should be reduced to the design pressure for inspection; the test is considered successful if no leaks are detected using a foaming agent. During the test, it is strictly prohibited to tighten bolts while pressure is still applied. III. Leak Test The leak test must meet the following requirements: Pipelines transporting extremely hazardous, highly hazardous fluids, as well as flammable fluids, shall undergo a leak test. (1) The test shall be 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 leak test at lower pressures to assess sensitivity ； (II) The key points of inspection for the leakage test include the valve stuffing box, flange or threaded connections, vent valves, exhaust valves, drain valves, etc ； (III) For the leakage 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 leakage is considered acceptable.
Hydraulic testing, pneumatic testing, and leak testing are the three main methods for pressure testing pipelines and equipment. The following is a brief overview of each test: 1. Hydrostatic test: 1. The test is carried out using clean water; for austenitic stainless steel materials, the chloride content in the water should be kept below 0.005%. If there are special requirements, other suitable non-toxic liquids can be used for testing. 2. The temperature of the test liquid should be no lower than 5°C and higher than the material’s brittle transition temperature. 3. The test pressure for internally pressurized pipes shall be at least 1.5 times the design pressure. If the design temperature is higher than the test temperature, the test pressure must be adjusted according to the calculated value. 4. The test pressure for externally pressurized pipes shall be 1.5 times the difference between the internal and external pressures, and shall not be less than 0.2 MPa. 5. When testing pipes and containers together, use the lower of the two test pressures ； If the pipeline pressure is high and cannot be isolated, and the container pressure is not less than 77% of the pipeline pressure, testing can be conducted based on the container pressure. 6. The test pressure for the inner tube of the sleeve pipe is determined based on the design pressure, while that for the outer tube is determined in accordance with the hydraulic testing standards. 7. Increase the pressure slowly; once the target value is reached, maintain that pressure for 10 minutes, and then keep it at the designed pressure for another 30 minutes. No drop in pressure or leakage is considered acceptable. 8. Remove air from the pipeline; when a leak is detected, pressure must be reduced first. Prevent negative pressure from occurring at the end of the test. II. Pneumatic pressure test 1. Use dry and clean air, nitrogen, or other non-flammable and non-toxic gases. 2. Avoid testing at temperatures close to the metal’s brittle transition temperature. 3. Equipped with an overpressure relief device, the set pressure shall not exceed 1.1 times the test pressure or the lower of these values plus 0.34 MPa. 4. The test pressure for steel pipes and non-ferrous metal pipes is 1.15 times the design pressure. 5. Conduct a pre-test at 0.2 MPa before the actual test. 6. During the test, increase the pressure gradually; after confirming that there are no abnormalities at 50% of the test pressure, raise the pressure in stages to the test pressure, and then reduce it to the design pressure to check for leaks. III. Leak Test 1. Conduct leak tests on pipelines carrying extremely hazardous, highly hazardous, and flammable fluids. 2. It is carried out after the withstand voltage test is passed; air is commonly used as the testing medium, or halogens, ammonia, etc. are used as needed for sensitivity testing. 3. Pay special attention to checking the sealing points such as valves, flange connections, and exhaust/drain valves. 4. The pressure is increased slowly to the test pressure; after maintaining this pressure for 10 minutes, a neutral foaming agent is used to check all sealing points – no leaks indicate compliance. .
I. Pressure resistance tests 1.1 Hydraulic test 1.2 Pneumatic test 1.3 Combined gas-liquid pressure test II. Leakage tests 2.1 Airtightness test 2.2 Ammonia leak detection test 2.3 Halogen leak detection test 2.4 Helium leak detection test 2.5 Others