Airtightness and nitrogen purging

It seems like everyone isn’t interested in this question. :L

Gas-tightness plan for hydrogen production units. Purpose of gas-tightness: The purpose of ensuring the gas-tightness of a system is to use a certain gas medium, at a specified pressure, to test for leaks at all sealing points within the system using soapy water. This allows for further evaluation of the quality of valves, pipelines, flanges, equipment, and welds within the system, as well as assessment of the pressure drop within it. It helps to ensure the system’s airtightness, identify any existing problems, eliminate potential hazards, and guarantee the safety of the system during trial operations. The airtightness testing of process pipeline systems is divided into the following test pressure levels: 0.6 MPa, 2.0 MPa, 2.1 MPa, 2.35 MPa, 2.8 MPa, and 3.2 MPa. The utility system only needs to be tested using nitrogen at its operating pressure. For pipelines and equipment operating at pressures above 2.0 MPa, the airtightness test must be carried out in stages: first, pressurize to 0.5 MPa for a thorough inspection; if leaks are found, reduce the pressure to address them, and only after no leaks are detected should the pressure be increased further. A comprehensive inspection is also required when the pressure is raised to 1.0 MPa and to 1.5 MPa, before raising it any further. Pipelines and equipment rated for high pressures must also be tested for leaks at lower pressure levels; any leaks found must be addressed before increasing the pressure to higher levels. 4.2 Operational requirements for the airtightness of the unit: a. The airtightness test must be carried out after the purging of the unit is completed; all fittings such as flanges and blind flanges that were removed during purging must have been reinstalled, any issues identified must have been resolved, and all safety valves within the unit must have been adjusted at low temperatures and put into operation. b. Contact the dispatch team to arrange a nitrogen source for airtightness testing, ensure an adequate supply of nitrogen, and inform the instrumentation team so that the instrumentation system can also be made airtight. c. Prepare airtight testing tools such as pressure gauges and soapy water, and organize the personnel responsible for conducting airtightness tests. d. Perform leak testing in stages: first ensure leak-tightness at low pressure, then proceed with high-pressure leak testing, making rational use of nitrogen. e. In the event of a leak, contact the pressure relief team immediately; it is strictly prohibited to attempt repairs while under pressure to prevent personal injury accidents. f. The acceptable standard for airtightness is: pressure test level ≤ 1.5 MPa, ΔP ≯ 0.02 MPa/4h ； Pressure testing grade ≥ 1.5 MPa, ΔP ≯ 0.05 MPa/4h. g. The airtightness test of the device must be conducted before and after catalyst loading to ensure the integrity of the system. When hermetically sealing, nitrogen is used as the sealing medium, with a raw gas compressor used to increase the pressure. h. The pressure increase rate should be slow; during the airtightness testing, someone should monitor the pressure gauge, and the pressure under airtight conditions must not exceed the equipment’s design pressure to prevent accidents caused by overpressure or the leakage of high pressure to lower pressure areas. i. The airtightness inspection points should include flanges on equipment and pipelines, valves, pressure gauges, level gauge connections, vent valves, drain valves, union joints, as well as the pressure and flow leads for instruments, thermometers, and thermocouples. j. Inspect the airtight areas by brushing them with soapy water to check for bubbles; for areas that cannot be reached with a brush, use a bulb syringe. Small gaps can be inspected by inserting paper strips there. The drain end can also be dipped in soapy water to check for internal leaks in the valve. k. For airtightness inspections, it is necessary to assign specific personnel to each area and to conduct inspections at designated locations. The workshop can use bulletin boards and posters to make the inspection results public, and records should be kept to ensure that no airtightness issue or bubble goes unnoticed. l. Before pipeline pressure testing, insulation or painting shall not be applied within a range of 50–100 millimeters on either side of the weld joint. m. The hermetic medium must be free of visible water, and the oxygen content in N2 must be less than 0.5%. n. Before airtight sealing, it is necessary to confirm that the pipelines connecting the device to external sources such as gas, oil field gas, compressed natural gas, and hydrogen-rich light gas have been isolated using blind flanges.

Are there any unified standards or industry guidelines for airtightness and nitrogen purging? The nitrogen purging of equipment requires that the oxygen and combustible gas levels inside the equipment be both below 0. 5% ； Different devices have their own specific requirements.

Thank you for the answer from the third floor! :handshake