How to ensure complete replacement

Welding can only be carried out after passing the instrument analysis

It can be pressurized with nitrogen, held at that pressure for a while, then depressurized to normal pressure; repeating this process three times should be fine. But the gas must be analyzed.

First, a large amount of steam should be used for cooking, or washing with water, in order to completely remove any residual chemical substances. Second, after purging with nitrogen for a certain period of time, instruments are used to determine the explosion limit in order to confirm whether the purging was complete

First, rinse the equipment to ensure that all impurities inside it are completely removed； The equipment is purged with nitrogen once again; after maintaining the pressure for the specified time, the pressure is released. An instrument is then used to detect the remaining amount of gas until it meets the required standards. A dedicated person must be present to supervise hot work.

Perform multiple charge and discharge cycles; if the analysis shows satisfactory results, carry out one or two more cycles just to be sure!

Safety precautions for displacement operations: 1. The equipment and pipes to be displaced must be reliably isolated from the system. 2. A displacement plan should be developed prior to the displacement process, and a displacement flow diagram should be created. Depending on the differences in density between the medium being displaced and the displacement medium, the inlet for the displacement medium, the outlet for the medium being displaced, and the sampling points should be selected appropriately to avoid the formation of dead zones. When the density of the displacing medium is greater than that of the medium to be displaced, the displacing medium should be introduced at the lowest point of the equipment or pipeline, while the medium to be displaced should be removed from the highest point. Sampling points should be located at the top and in areas where dead zones may form ； Conversely, when the density of the replacement medium is lower than that of the medium to be replaced, the replacement medium is fed in from the highest point of the equipment, while the medium to be replaced is discharged from the lowest point. Sampling points should be placed at the bottom of the equipment as well as in areas that may become dead zones, to ensure thorough replacement. 3. Replacement requirements. When using water as the displacement medium, it is essential to ensure that the equipment is completely filled with water, and that water flows out from the overflow port at the highest point of the equipment for a sustained period of time; it is strictly prohibited to have the equipment not fully filled with water. When using an inert gas as a displacement medium, it is necessary to ensure that the amount of inert gas used is sufficient (generally at least 3 times the volume of the medium to be displaced). However, to determine whether the displacement is thorough and whether the displacement process meets safety requirements, one should not rely solely on the duration of the displacement or the amount of displacement medium used; instead, it is necessary to base the judgment on whether the sampling analysis results are satisfactory. The gases emitted during the displacement operation should be directed to a safe location. For maintenance work involving open flames, the oxygen content in the inert gas used for purging is generally less than 1%–2% (by volume). 4. Samples shall be taken and analyzed at the sampling points specified in the displacement flowchart, and the results must meet the required standards. 5. Flammability analysis standard: When using a gas detector, the concentration of gases or vapors in the area being tested should be less than or equal to 20% of the lower explosive limit (on a volume basis) ； When other chemical analysis methods are used, if the lower explosive limit of the gas or vapor being analyzed is 10% or higher, its concentration should be less than 1% ； When the lower explosion limit is less than 10% and greater than or equal to 4%, its concentration should be less than 0.5% ； When the lower explosion limit is less than 4% and greater than or equal to 1%, its concentration should be less than 0.2%. If there are two or more types of mixed flammable gases, the one with the lower lower explosive limit shall apply. 6. When performing welding or other fire-related operations inside equipment, it is also necessary to analyze and measure the levels of toxic and harmful gases as well as the oxygen content in the air. The concentration of toxic and harmful gases must not exceed the maximum allowable levels specified in the \"Hygienic Standards for Industrial Enterprise Design\" (GBZ 1—2002), while the oxygen content should be between 18% and 22%.