Key safety points for the maintenance of chemical processing equipment

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　　The characteristics of chemical production mean that the maintenance of chemical equipment involves complex tasks, high technical requirements, and significant risks. Only by carrying out a series of safety and technical measures on the chemical plants prior to maintenance, in order to eliminate any potential dangers, can maintenance work be carried out smoothly, the quality of such work be ensured, and favorable conditions for safe production be created. 　　Today, DeviceBang will share with you the safety procedures and behavioral guidelines to follow when maintaining chemical processing equipment. We hope that everyone will keep these in mind at work to ensure their own safety! 　　First, please enjoy the “Variations on Chemical Plant Maintenance” – images that won the silver award in the “Dream Exploration” category of the 360° Beautiful Shaanxi: Beautiful Weinan Photography Contest; they are truly beautiful pictures. 　　Achieving safe maintenance in the chemical industry not only ensures the safety of maintenance operations, prevents major accidents, and protects the safety and health of workers; it also facilitates the completion of maintenance tasks on time, to the required quality, and in accordance with planned quantities. This ensures high-quality maintenance of equipment, resulting in stable operation and high efficiency once the equipment is put back into use. It helps to prevent accidents and environmental pollution, thereby creating favorable conditions for safe production. To this end, it is essential to carry out the necessary safety and technical procedures before stopping the machine for maintenance, as well as those procedures after the stoppage. 　　Preparations before maintenance The main tasks include: establishing a maintenance command post ； Develop a maintenance plan ； Conduct safety education before maintenance ； Inspection before maintenance. 　　Safety technical procedures for shutting down the plant before maintenance: Once the shutdown plan is established, it must be carried out in an organized and systematic manner, in strict accordance with the shutdown time, steps, extent of process changes specified in the plan, as well as the approved sequence of shutdown operations. Whether the shutdown phase of the unit proceeds smoothly affects safety in production on one hand, and it also influences whether the maintenance work on the unit can be carried out on schedule and safely, as well as the quality of such maintenance. The main safety measures for shutting down the equipment are as follows: 1. Shut down the equipment in strict accordance with the predetermined shutdown plan. Follow the maintenance schedule, maintain close communication with adjacent processes and relevant sections (such as the boiler room, power distribution room, etc.), and stop the operation of the equipment strictly according to the procedures specified in the shutdown plan. 　　2. Pressure release should be slow and moderate. The pressure release process must be carried out slowly, and the equipment must not be disassembled until the pressure has been completely released. 　　3. The materials inside the device must be completely emptied and disposed of. Before discharging any residual materials, it is necessary to check the condition of the discharge outlets. Flammable, explosive, toxic, or corrosive materials should not be discharged into sewers or onto the ground; instead, the residual materials in the equipment or pipelines should be released at designated safe locations or storage tanks, in order to prevent accidents or pollution. At the same time, the materials inside the equipment and pipelines should be emptied and pumped out as much as possible; any flammable or toxic gases that cannot be collected and utilized should be sent to a flare for combustion or subjected to other forms of treatment. 　　4. Control an appropriate rate of temperature and volume reduction. The rate of temperature and volume reduction should be adjusted in accordance with the requirements of the manufacturing process, in order to prevent accidents such as deformation or damage to high-temperature equipment. For cooling high-temperature equipment, it is not advisable to use cold water or similar methods for immediate cooling; instead, after cutting off the heat source, proper ventilation or natural cooling should be employed. The rate of temperature and precipitation reduction should not be too fast; especially under high-temperature conditions, sudden changes in temperature and the amount of material can cause deformation or rupture of equipment and pipelines, leading to leaks of flammable, explosive, or toxic substances, as well as fires, explosions, or poisoning incidents. 　　5. The valve should not be opened too quickly. When opening the valve, pause after turning it two notches to allow a small amount of material to pass through, so as to check whether the flow is smooth; then gradually increase the valve opening until the desired level is reached. When opening the steam valve, attention should be paid to pipeline preheating, condensate drainage, and protection against water hammer. 　　6. Shutdown procedures for high-temperature vacuum equipment To shut down high-temperature vacuum equipment, it is necessary to first eliminate the vacuum condition; only after the temperature of the medium inside the equipment drops below its auto-ignition point can it be connected to the atmosphere, in order to prevent air from entering and causing combustion or explosion accidents. 　　7. Shutdown operations must be carried out in strict accordance with the process specifications. The shutdown process should follow the cooling curve specified in the process guidelines, with attention paid to the impact of the extinguishing of flames in various areas on the uniformity of temperature reduction within the furnace. Draining and low-point condensate removal must not be carried out when the burners have not been completely extinguished or when the furnace temperature is high, to prevent combustible gases from entering the furnace and causing accidents. 　　At the same time, when the unit is shut down, operators must open and close numerous valves and instruments within a short period of time; to avoid errors, it is essential to closely monitor changes in parameters such as temperature, pressure, flow rate, and liquid level in various areas. 　　Device shutdown and safety procedures after shutdown The main steps for safety procedures after shutdown include: isolation, displacement, purging and cleaning, removal of access holes, proper use of personal protective equipment, as well as the necessary handover procedures between the production department and the maintenance department prior to carrying out repairs. 　　Isolation: Completely cut off the source of media within the equipment. To carry out work inside chemical processing equipment, it is necessary to shut down the equipment; when shutting down a single unit of equipment, it is essential to ensure that no leakage of any media occurs. Due to long-term use of the equipment, many of the pipe valves connected to it are not in the proper position, which can lead to internal leaks, especially with gas valves. After maintenance workers enter the equipment to carry out their tasks, if they do not inspect the pipes carefully, any leakage of gas or liquid – especially of flammable, explosive, high-temperature, or high-pressure substances such as gas, ammonia, acids, high-pressure gases, and crude benzene – can lead to serious accidents such as fires, explosions, burns, and poisoning, with consequences that are unimaginable. 　　Due to unreliable isolation, toxic, flammable, explosive, corrosive, asphyxiating, and high-temperature media often enter maintenance equipment, leading to frequent serious accidents. Therefore, the equipment to be maintained must be reliably isolated, and the safest and most reliable method of isolation is to disconnect the pipelines or install blind flanges. Process engineers must carefully verify all pipes connected to the equipment; for pipes carrying flammable, explosive, toxic, high-temperature, or high-pressure media, blind plates should be installed behind the valves (near the tower end). Removing and installing blind flanges is a hazardous task; a \"Work Permit for Removing and Installing Blind Flanges\" must be obtained, and all necessary safety measures must be implemented. 　　⑴A diagram for the insertion and removal of blind flanges should be drawn, and the operations should be carried out in accordance with this diagram. 　　⑵Blind plates must meet safety requirements and be numbered. 　　⑶On-site safety measures for inserting and removing blind flanges: Ensure that all materials in the system have been removed, and that the pressure and temperature are reduced to the specified levels ； When installing or removing blind flanges on equipment or pipelines that handle flammable and explosive materials in no-fire zones, explosion-proof tools must be used, and there should be dedicated personnel to carry out inspections and supervision ； When inserting or removing blind flanges indoors, it is necessary to open windows or use ventilation equipment to ensure adequate airflow ； When removing or installing blind flanges on pipes carrying toxic substances, workers must wear appropriate personal protective equipment as required to prevent poisoning ； When inserting or removing blind flanges at heights, the safety requirements for working at heights must be met, and a safety helmet and safety belt must be worn ； For tasks with particularly high risks, emergency rescue measures should be in place, along with gas protection stations, medical staff, and ambulances on site. During continuous operations of inserting and removing blind flanges, the operator should not work for too long and should take turns to rest. 　　Displacement, Purging, and Cleaning 　　(1) Displacement. To ensure the safety of work involving hot work during maintenance and operations inside equipment, flammable, explosive, toxic, and harmful gases in all equipment and pipelines within the maintenance area must be removed. Gases commonly used for displacement include nitrogen and steam, with nitrogen being the preferred choice for this purpose. Since steam has a higher temperature, it is necessary to use a cooling tower after displacement to reduce the temperature inside the equipment to normal levels. For the displacement of flammable and toxic gases, inert gases such as steam and nitrogen are commonly used as displacement media; the water injection method can also be employed to expel these flammable and toxic gases. For equipment handling some high-temperature liquids, venting should be considered first, followed by using chilled material or adding cold water to bring the equipment back to normal temperature. For devices under pressure, pressure relief methods should be used to reduce the gas pressure inside the device to atmospheric pressure. After the equipment has been replaced, if it is necessary to work inside it, the inert gas must be replaced with fresh air again to prevent suffocation due to lack of oxygen. 　　⑵Purge. For flammable and toxic liquids that have not been completely removed from equipment and pipelines, purging with steam or inert gas is generally used to eliminate them. 　　⑶Cleaning and removal. For deposits and scale of flammable and toxic substances adhered to the inner walls of equipment that cannot be removed by displacement or purging, cleaning and removal methods must also be employed. 　　Cleaning generally involves two methods: steaming and chemical cleaning. ① Steaming. 　　②Chemical cleaning. Common methods include alkali washing, acid washing, and alternating between alkali washing and acid washing. 　　Proper removal of the access hole: After carrying out procedures such as isolating the medium, replacing it, cooling down the equipment, and reducing its pressure in order to perform maintenance, strict verification and testing must be conducted. The access hole should only be removed once safety is ensured. In the case of equipment containing liquids, the diagonal bolts should be removed; when removing the last four diagonal bolts, this process should be done slowly, and care should be taken to stay away from the sides of the access hole to prevent liquids from spraying out and causing injury. For equipment containing flammable and explosive materials, it is strictly prohibited to use gas welding or cutting to remove bolts. Bolts that are severely corroded must be cut with a hand saw. When creating new access holes in devices such as crude benzene tanks, it is strictly prohibited to use gas welding or grinding discs; instead, sulfuric acid of a specific concentration must be used, along with wax sealing around the area, to create the new access holes. 　　Proper personal protective equipment 　　Labor protection isn’t simply about putting on work clothes; when entering the interior of chemical processing equipment to work ； Personal protective equipment must provide protection and meet certain safety requirements. 　　In areas with flammable and explosive equipment, anti-static work clothes should be worn, and they must be worn properly with all buttons fastened to prevent the generation of static sparks or contact between corrosive substances and the skin. Sharp objects or metal tools should not be kept in the pockets of the work clothes; small tools such as protractors should be placed in dedicated tool bags. 　　The safety helmet must have its straps securely fastened, and it must fit properly on the head. Due to the limited space inside the equipment where work is carried out, there is a high risk of collisions with the head. It is also necessary to ensure that there is a certain gap between the inner lining of the helmet and its outer shell, so that in the event of objects falling and hitting the helmet, the inner lining can still separate the helmet from the head, preventing the outer shell from pressing directly against the head and causing injury. Therefore, sufficient buffer distance must be left inside the cap core. 　　Wear protective gloves properly; when working in equipment that is highly corrosive, such as those exposed to acids or bases, it is necessary to use gloves that provide protection against these substances. Damaged gloves should be replaced promptly. Especially during summer, when hands sweat a lot, this can reduce the insulating properties of the gloves and cause them to slip, so it is advisable to have several extra pairs of gloves on hand. 　　Safety shoes should be anti-static and designed to resist impact. For the large leather boots worn, the soles should be sewn rather than nailed, and slip resistance must be taken into account; the laces should be tied tightly to ensure easy walking. When working inside a tower under suitable conditions, it is advisable to lay some asbestos sheets or rubber on the bottom of the tower within the area of operation; this helps to prevent slipping and also prevents direct contact between people and the equipment. Other: ⑴ Clean the maintenance site and pathways. 　　⑵Cut off the power to the equipment to be inspected, hang a “Do Not Start” warning sign, and lock it. 　　⑶Contact the utility systems (water, electricity, gas, steam) promptly and handle the situation appropriately. 　　⑷Safe handover. Before the maintenance work, the production department and the maintenance department go through strict safety handover procedures; after both parties have inspected and confirmed everything, they sign the \"Safety Handover Form\" to confirm it. 　　Safety requirements during the maintenance phase The maintenance phase often involves electrical work, demolition tasks, hot work, earthwork, work at heights, welding, lifting operations, and entry into equipment. It is necessary to strictly adhere to relevant regulations in order to ensure the smooth progress of maintenance work. 　　Hot work 　　⑴ Designate hot work areas and no-hot-work areas. Based on work requirements, an application shall be submitted by the using unit; after registration and approval by the factory’s safety and fire prevention departments, a \"designated hot work area\" shall be established. All areas outside this designated area are considered no-fire zones. 　　⑵Hot work and classification. Welding and cutting operations in no-fire zones, as well as temporary operations that generate flames, sparks, or hot surfaces such as the use of blowtorches, electric drills, and grinders in flammable and explosive areas, are all considered hot work. 　　Hot work is divided into three categories: special hot work, level 1 hot work, and level 2 hot work. 　　⑶System for Fire Safety Permits for Hot Work 　① Hot work must be carried out in areas where fire is prohibited by obtaining a \"Fire Safety Permit for Hot Work,\" with strict adherence to the procedures for application, review, and approval. 　　“The \"Hot Work Safety Permit\" should clearly indicate the level of hot work, its valid date, the exact location where the work will be carried out, the details of the work to be done, safety measures related to fire prevention, the responsibilities of the person overseeing the hot work, as well as the results of the hot work analysis. The person authorized to approve and sign the permit must confirm that all information is correct before signing it. 　　②Personnel carrying out hot work must carefully verify all relevant details; if any violations of safety regulations are found, they have the right to refuse to carry out the work and report it to the company’s fire safety department. 　　③Before starting the hot work, the person carrying out the work must submit the hot work permit to the site supervisor for inspection; only after it is confirmed that all safety measures have been properly implemented can the work be carried out at the specified time, place, and according to the prescribed procedures. 　　④When the location or scope of hot work changes, the approval procedures must be renewed ； Otherwise, welding is not permitted. 　　⑤When performing hot work at heights or inside equipment, it is also necessary to obtain a \"High-Place Safety Work Permit\" and an \"Equipment Interior Safety Work Permit\". 　　⑷Flame analysis and standards ① Sampling must be representative. 　　②The time between sampling and hot work shall not exceed 30 minutes. 　　③Standards for fire hazard analysis: When using an explosive detector, the concentration of the gas or vapor being tested should be less than or equal to 20% of its lower explosive limit in volume terms. If other chemical analysis methods are used, when the lower explosive limit of the gas or vapor being tested 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%, the concentration should be less than 0.5% ； When the lower explosion limit is less than 4%, the concentration should be below 0.2%. ④ When performing hot work 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 level, while the oxygen content should be between 18% and 22%. 　　Work inside equipment 　　⑴ Work inside equipment and its hazards. Work carried out inside tanks, towers, kettles, vats, spheres, furnaces, boiler drums, pipelines, containers, etc., as well as in basements, manholes, pits, sewers, or other enclosed areas that are part of the petroleum and chemical production facilities, is referred to as work inside equipment. 　　⑵Key safety points for working inside equipment: ① A “Safety Permit for Working Inside Equipment” must be obtained before working inside the equipment, and the approval procedures must be followed strictly. 　　②Before working inside the equipment, it must be safely isolated from other equipment (by installing blind flanges or removing a section of pipeline), and cleaned and purged thoroughly. 　　③Sampling and analysis must be conducted 30 minutes before entering the equipment; the concentrations of flammable gases, toxic gases, and oxygen levels must be strictly kept within safe limits. Work inside the equipment is only permitted after the analysis results are satisfactory. If working inside the equipment for a long period of time, conduct analyses at least once every 2 hours. 　　④Implement appropriate ventilation measures to ensure good air circulation inside the equipment. 　　⑤There should be sufficient lighting; the lighting voltage inside equipment should not exceed 36V, and in humid or confined spaces it should be 12V or less. Lighting fixtures and power tools must meet safety requirements regarding moisture resistance and explosion prevention. 　　⑥When entering equipment containing corrosive, asphyxiating, flammable, explosive, or toxic materials to carry out work, it is necessary to wear appropriate personal protective equipment and devices as required. 　　⑦When performing hot work inside equipment, it is necessary to obtain a hot work permit as required and go through the prescribed procedures. 　　⑧Operations inside the equipment must be supervised by a dedicated person, who must maintain effective communication with the personnel working inside the equipment. 　　⑨When the conditions under which maintenance work is carried out change and may pose a risk to the safety of the workers, it is necessary to evacuate them immediately ； If work needs to continue, the approval process for entering the equipment to work must be carried out again. 　　⑩After the work is completed, the interior of the equipment must be inspected jointly by the maintenance personnel, the supervisor, and the person in charge of the using department. Only after it is confirmed that there are no people, tools, or debris inside the equipment can the openings in it be sealed. 　　Processing after maintenance completion 　After the maintenance is finished, a thorough inspection should be carried out. Once everything is confirmed to be in order, pressure testing, leak testing should be performed on the equipment, safety valves should be adjusted, and instruments as well as interlock devices should be calibrated. The maintained equipment should then undergo individual and combined tests before it is accepted and handed over. 　　By carrying out the above safety and technical measures on chemical processing equipment prior to maintenance, a favorable working environment can be created, which ensures the smooth progress of the maintenance work and provides a reliable guarantee for the safety of such operations as well as the proper operation of the equipment after maintenance.