Summary of work on device airtightness

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Summary of the airtightness testing for the unit: Airtightness checks were conducted on the ether synthesis reaction, reaction separation, washing, and methanol recovery systems. To ensure the successful commissioning of the MTBE unit in just one attempt, we carried out thorough airtightness tests on all these systems. The summary is as follows: I. Basic information on the airtightness task: Conditions to be met prior to achieving airtightness: 1. The process pipelines and equipment have been installed, pressure-tested, and purged, and proper gaskets have been installed. 2. All safety accessories for the equipment and pipelines have been properly installed. 3. All drain valves, vent valves, instrument transmitters, online analyzers, and control valves have been installed and successfully commissioned. 4. All temporary facilities such as temporary short pipes for purging, valves, temporary filters and baffles at each suction inlet have been removed. 5. Replace all overpressure range instruments (mainly vacuum gauges). 6. Ensure that the media required for airtightness, such as nitrogen and air, are readily available. 7. Prepare the tools needed for leak detection: airtightness-specific tools (water guns, etc.), foam water, brushes, small buckets, markers, test records, etc. 8. Prepare the necessary gaskets, packing, and removal tools for replacement. 9. The testers are familiar with the process flow as well as the plans for airtightness and leakage rate testing. The airtight equipment required includes: 5 material tanks ； 3 reactors ； 2 protection reactors ； 4 towers ； 13 heat exchangers ； Static sealing points for 20 pumps: 1,106; Airtight materials: 12 airtight spray bottles ； 2 barrels of water-soluble foaming agent ； 4 tool backpacks ； 2 boxes of marker pens ； 2 boxes of chalk pencils ； 1 small bucket for soap solution ； 8 F wrenches ； Various related sizes of metal wound gaskets ； There are a total of 6 pressure gauges of various grades for the related equipment. II. Airtightness requirements: The materials used within the device are flammable, explosive, volatile, toxic, and harmful chemical substances; therefore, strict requirements are imposed on the safety and airtightness of the equipment. The airtightness testing process takes one month in total, from the preparations before airtightness testing to its completion. (1) Airtightness principle: 1. Airtightness tests need to divide the equipment and pipelines into appropriate systems according to their pressure ratings. 2. To prevent airtight media from the high-pressure system from entering the low-pressure system, the airtightness test should be started from the low-pressure system. 3. When the system operating pressure is lower than the air-tightness pressure of the device, the air-tightness pressure is 1.1 times the operating pressure ； When the system pressure is greater than the pressure of the air-sealing medium in the device, sealing is carried out in two stages: low-pressure sealing and high-pressure sealing. The low-pressure airtight pressure is the pressure of the airtight medium, while the high-pressure airtight pressure is set at 1.1 times the operating pressure. 4. For flammable, toxic, high-temperature equipment and pipelines, this plan must be strictly followed ； For non-toxic and harmless equipment and pipelines (such as desalinated water, circulating water, plant air, etc.), when the pressure is higher than that of the airtight medium, it is sufficient to check for leaks at the pressure of the airtight medium. 5. Piping between systems is separated by valves, and blind plates are used when necessary. 6. The airtightness can be divided into two pressure ranges (0–0.5 Mpa, 0.5–1.5 Mpa). The pressurization should be carried out slowly, starting from lower pressures; once the pressure for each range is reached, the process of increasing pressure should be stopped to check for leaks. If there are no leaks or abnormalities, increase the pressure to the test pressure. 7. For airtightness testing and displacement, at least two pressure gauges must be used for monitoring, and the range of these pressure gauges should be 1.1 times or more of the test pressure. 8. For the orifice differential pressure gauge in the system, during testing, the valves of both pressure lead pipes should be fully opened to equalize the pressure. 9. The flanges fitted with blind plates to isolate the system should be tested for leaks using the working medium during the initial stage of commissioning; the locations where the blind plates are installed should be recorded, and a dedicated person should be assigned to inspect them during operation. 10. During airtight pressure relief, discharge should be carried out via drain valves located at low points or dead ends whenever possible, to prevent fluid accumulation ； When sealing or displacing with nitrogen, try to direct the nitrogen to the flare system; in special cases where it is not possible to send the nitrogen to the flare and on-site discharge is necessary, safety measures must be taken. 11. The pipelines of the material inlet and outlet devices must also undergo a gas-tightness test. 12. The atmospheric pressure system does not require a gas-tightness test. 13. The pipelines of the utility system should be tested for airtightness as much as possible using the medium contained within them. 14. Safety must be observed during the experiment; uninvolved personnel should stay away from the site to prevent accidents. 15. Under normal circumstances, industrial air is used as the medium for airtightness testing; in some special cases, nitrogen can also be used to achieve airtightness in the system. (II) Airtightness testing method: Apply foam solution or spray it using a spray gun to check whether there are any leaks at the joints of flanges, valves (including flanges, valve bodies, and gland packs), pressure gauges, transmitters (including instrument leads and connectors), level gauges, and pump casings that are being inspected. If the flange is large, seal its opening with sealant while leaving a small gap, which can be checked using soapy water. (III) Airtight medium: The airtight air source is 0.6 MPa of utility air. (IV) Placement of pressure testing blind plates: 1) Determination of the thickness of blind plates used for pipeline pressure testing ① Formula for calculating the thickness of welded or flanged blind plates: δ = 1.2A(P/)^1/2 ② Formula for calculating the thickness of plug-in blind plates: δ = 0.85A(P/)^1/2 Where: δ represents the thickness of the blind plate, in mm; A represents the radius of the temporary blind plate, in mm; P represents the test pressure, in MPa; σ represents the allowable stress of the steel plate. 2) Location where pressure testing blind plates are installed: ① Between the pipeline under pressure testing and the equipment that is not involved in the testing. ②Various instrument ports on the pressure testing pipeline. ③Between pipeline systems with different test pressure ratings. 3) Requirements for installing temporary blind plates: ① A label indicating the blind plate must be attached to the location where it is installed (the label should include the name of the person who installed it and the installation date), and this information must be recorded on the test system diagram to prevent it from being overlooked during removal. ②The thickness of the temporary blind plate must be determined through strength calculations to meet the experimental requirements. ③The installation and removal of temporary blind plates must be carried out by designated personnel; temporary gaskets must always be used at those locations. Once the system has been pressure-tested and the entire system is back in operation, proper gaskets shall be installed. (5) Airtightness standard: Calculated using the formula for airtightness leakage rate: Leakage rate = (1 – P2T1/P1T2)/h × 100%. P1, T1, P2, and T2 represent the absolute pressure and absolute temperature before and after the test, with the test duration being 24 hours in principle. A leakage rate of ≤0.2% per hour is considered acceptable. III. Sealing completion status: 1. In the initial stage of sealing, after the purging work was completed, the proper gaskets were installed, and the process was essentially finished within the estimated 10 days. 2. Since all safety valves have been removed for inspection and cannot be installed in time, they are unable to participate in the airtightness testing for now; instead, the upstream and downstream shut-off valves are used to seal off the leakage points of the safety valves. 3. The equipment drain valves, vent valves, instrument transmitters, on-line analyzers, and control valves have been basically installed in place and have passed calibration. 4. All temporary facilities such as the short pipes and valves used during purging, the temporary filter screens and baffles at each suction inlet, etc., shall be removed. 5. The work to seal air leaks is generally completed within 15 days. 6. Since catalysts have not yet been installed in the reactors and reaction towers, these manholes are sealed using temporary gaskets; as a result, there is some leakage, but it remains within the acceptable range for low-pressure sealing. The leakage rate of those devices with higher pressures will be tested again after the catalysts are installed and the required operating pressure is achieved, to ensure the proper operation of the equipment. 7. The entire airtightness work was basically completed within the planned time. IV. Take airtight operation as an opportunity to enhance new employees’ practical independent operational skills and awareness. Master the key points of airtight work, and gain a practical understanding of the technical requirements and characteristics related to airtightness through actual work. Through this airtightness testing, everyone’s familiarity and understanding of the various static and dynamic sealing points in the equipment were improved, enabling them to identify and become familiar with potential leakage points that might arise during normal production in the future. V. Existing shortcomings: Due to the hasty preparation for the purging work, some airtight materials were not prepared in sufficient quantity, which affected the progress of certain tasks during the entire airtightness testing process. For example, the actual amount of gaskets replaced exceeded the planned amount by quite a bit. Part of the additional gasket is intended to ensure the safety of the installation; we propose using more reliable metal wound gaskets ； There are also some gaskets that, due to various preliminary tasks, had been reused multiple times at certain locations; during the airtightness testing, we determined that they must be replaced. This also resulted in an additional number of gaskets being needed.