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This post was last edited by qy576100527 on 2017-6-1 23:15. System Startup (VII) – Airtightness Testing and Nitrogen Purging. 1. The airtightness testing of the unit is carried out after the process system has been purged, but before the chemical plant is put into operation. 2. The airtightness test and nitrogen purging can be carried out simultaneously. The purpose of the airtightness test is to eliminate any major potential hazards and quality issues, ensuring the successful initiation of chemical processing. It also prevents leaks at flange connections due to poor system airtightness after operation, which could lead to shutdowns or other accidents. 3. It is recommended to conduct airtightness tests in segments; the test pressure for each segment should, in principle, be based on the operating pressure, but it must not be lower than the pressures specified for each segment in the table below. The actual segmentation can also be determined based on factory experience. 4. During the airtightness test, care should be taken to ensure that the pressures on both sides of the heat exchanger, which features a differential pressure design, remain within the allowable range. 5. For the airtightness test, air can be used as the medium, with the test pressure being 1.05 times the operating pressure. In a gas-tightness test, all valves, flanges, and welds should be coated with soapy water to check for leaks. Generally, the pressure is stabilized for 30 minutes; if the pressure remains within the specified range, the airtightness test is considered successful, and normal operation can be resumed. 6. Since the process systems within the device contain flammable and explosive materials, in order to prevent the formation of explosive mixtures due to the mixing of these materials with air, the air inside the system must be replaced with nitrogen after the airtightness test, so as to reduce the oxygen content in the system below the specified levels and ensure safe operation.