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Precautions for shutdown purging: Oil remaining in pipelines and equipment must not be discharged on-site; it must be poured into an oil waste tank. Moreover, the oil temperature must be below 50°C before it can be discharged into such a tank. In gasoline and condensed oil systems, the oil should first be removed using water, and then purging should be carried out with steam. Before purging, remove the installed blind flanges, introduce steam to all steam supply points, and drain any remaining water from the vent lines to prevent water hammer; in addition, it is strictly prohibited to introduce steam containing water into the hot oil pipes. The pipelines of the gasoline and condensed oil equipment are first purged with water followed by steam. Before starting the pipeline purging, shut down the meter, safety valve, instrument lead valves, etc. in advance; during purging, the meter and control valves should be connected to bypass lines to prevent debris from blocking or damaging the instruments. Before purging, adjust the process properly; it must be checked by the workshop staff, technical personnel, team leaders, etc., before steam purging is carried out. Ventilation should be carried out slowly, with the steam pressure controlled appropriately based on the pressure gauge on site. All equipment and pipelines must be thoroughly cleaned to ensure no dead corners remain; a dedicated person should be responsible for this process, and records should be kept. The operating procedures must be strictly followed, and safety must be prioritized. The purging of the pipeline should be carried out in sections; drain the condensate at the control valves and meters, and once it is clean, proceed further along the auxiliary lines. When purging towers and vessels, the upper and lower vent valves of the towers and vessels should be opened to allow steam to escape from the higher points and condensate to drain from the lower points. It is important not to cause the trays inside the towers and vessels to be overturned due to excessive pressure, and strict precautions must be taken to prevent overpressure in them. During purging, start with the main equipment and then proceed from near to far, purging in sequence; at the farthest points, open the vent valves or remove the valve glands for venting. For pipelines with numerous branches, purging should be carried out step by step, and records should be kept to avoid omissions. All vents and drain valves must be opened to ensure thorough purging with no dead corners left. For mechanical pumps, first close the pump’s inlet valve, drain all debris from the inlet side of the pump, and then briefly circulate fluid through the pump. Whenever possible, use the pipelines connected to the inlet and outlet for this purpose. Before purging the heat exchange equipment, all residual water must be drained and the drain valves opened to prevent water hammer or damage to the equipment. When purging a heat exchanger where the tube side and shell side are purged at different times, steam should be supplied to one side while the inlet and outlet valves of the other side are opened, and the low-point vent valve should also be opened to avoid pressure buildup that could damage the equipment. Disengage the safety valve before purging; when purging the low-pressure gas system, it is not allowed to use large amounts of steam for purging the gas holder. First, replace the air with nitrogen twice, and then disconnect the flange for steam purging. Try not to use steam to purge underground pipelines. At the end of the line cleaning process, the relevant connection valves should be closed first, followed by turning off the steam supply, to prevent cross-contamination. Once the equipment has cooled to room temperature, the drain valves and vent valves should be closed, and steam blind flanges should be reinstalled. For nitrogen purging of hydrogen-handling reaction systems and pipeline equipment, steam purging is not used; if hot work is to be carried out on the pipelines or equipment, isolation is employed to purge the area where the work is being done in order to reduce water accumulation in the system. For other small pipelines that are not covered, tape should be used for purging; during the purging process, someone needs to coordinate the operations in the common areas, otherwise oil will be forced back and forth and the purging will not be thorough. During the system pipeline purging, strengthen communication with external parties, as well as coordination and cooperation between different systems. For the areas where flanges need to be removed for purging, it is advisable to choose those locations where blind plates can be installed, in order to reduce the need for repeated airtightness checks. After removing the flanges, controls should be in place to prevent too rapid pressure release, which could affect the purging of other pipelines. During shutdown purging, it is strictly prohibited for motor vehicles to enter the plant area, and all fire-related activities are forbidden. Towers, containers, and pipelines are purged for 24 hours, while equipment where welding will be performed is purged for 48 hours. An explosion analysis is conducted before welding, and work may proceed only if the results are satisfactory. Equipment and systems prone to the formation of ferrous sulfide must take measures to prevent its spontaneous combustion after purging: areas that require ventilation for maintenance should be wetted with water, while areas where ventilation is not necessary should be sealed with nitrogen to prevent spontaneous combustion of ferrous sulfide, in addition to strengthening monitoring of critical areas. Pipelines that have been purged with steam need to be protected against freezing and condensation before winter arrives. Any necessary repairs should be carried out before operations resume, in order to prevent the pipelines from freezing and damaging the equipment or disrupting production during winter. It may not be suitable for heavy oil plants; please share more suggestions