Basic safety knowledge for on-site maintenance

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The nature of oil and chemical production dictates that maintenance work is characterized by frequent occurrences, complexity, and high risks. 　　I. Preparations before maintenance
The preparatory work mainly includes:
(1) Establishing a maintenance command center ； 　　(2) Develop a maintenance plan ； 　　(3) Conduct safety education before maintenance ； 　　(4) Inspection before maintenance. 　　II. Shutdown of the equipment and safety measures after shutdown
1. Shutdown procedures and precautions
Once the shutdown plan has been determined, the shutdown must be carried out in an orderly manner according to the specified shutdown time, procedures, and all safety measures outlined in the plan. The parking procedures and precautions are as follows: (1) Depressurize. The system should be depressurized slowly, from high pressure to low pressure; care must be taken to ensure that the pressure does not drop to zero, nor should negative pressure be created. It is generally required that a slight positive pressure be maintained within the system. Do not disassemble the equipment until pressure relief has been completed. 　　(2) Cooling. The cooling process should be carried out at the specified cooling rate, ensuring that the required standards are met. High-temperature equipment should not be cooled down rapidly to avoid damage to the equipment; it is advisable to use forced ventilation or natural cooling after cutting off the heat source, with the temperature of the medium inside the equipment generally needing to be below 60°C. 　　(3) Drain completely. Drain the gas, liquid, and solid materials stored within the production system (equipment, pipelines). Should it be impossible to completely drain all materials, this must be documented in detail in the “Safety Maintenance Handover Document”. Additional safety measures should then be taken. The disposal of any residues must be carried out strictly at designated locations and in accordance with prescribed methods; they must not be released indiscriminately or discharged into sewers, so as to prevent environmental pollution or accidents. 　　During parking operations, all sources of fire must be kept away from the device. 　　During the parking process, it is necessary to keep records at all times of any abnormalities that occur and the methods used to address them ； A supervision system must be implemented for critical operations on key devices and vital areas. 　　2. Safety procedures after parking The main steps include isolation, displacement, purging and cleaning, as well as the requirement that the production department and the maintenance department carry out proper safety handover procedures before carrying out maintenance work. 　　1) Isolation 　　Major accidents occur from time to time due to the unreliability of isolation, which allows toxic, flammable, explosive, corrosive, asphyxiating, and high-temperature substances to enter the equipment being maintained ； Therefore, the equipment under maintenance must be reliably isolated. 　　Depending on the specific circumstances, the safest and most reliable method of isolation is to remove the pipeline or install a blind flange. Dismantling pipelines involves removing the pipes connected to the equipment under maintenance, as well as any detachable parts such as valves and expansion joints on those pipes. Then, a blind flange is installed on the flange on the pipeline side. If there are no detachable parts or if detachment is extremely difficult, the valve should be tightly closed, and a blind flange should be inserted at the pipe flange connection linked to the equipment under maintenance. This method is easy to implement, safe, and reliable, and is widely used. Installing and removing blind flanges is a hazardous task; therefore, a \"Work Permit for Installing and Removing Blind Flanges\" must be obtained, along with the implementation of various safety measures: (1) A work plan for installing and removing blind flanges should be drawn up, the tasks should be carried out in accordance with this plan, and records as well as inspections must be kept. The area where the blind plate is installed must have clear labeling to prevent it from being omitted when installed or removed. When removing flange bolts, loosen them gradually and slowly to prevent any residual pressure or remaining materials in the pipeline from spraying out, thus avoiding accidents. The location for installing the blind plate is generally at the flange behind the incoming material valve; gaskets should be placed on both sides of the blind plate and secured with bolts to ensure no leakage. 　　(2) Blind plates must meet safety requirements and be numbered. Prepare appropriate blind flanges based on the actual conditions on site: the size of the blind flanges should match the diameter of the valve or pipe ； The thickness of the blind plate must be determined through calculation; in principle, its thickness shall not be less than that of the pipe wall. The material of blind plates and gaskets should be selected based on the properties of the medium, as well as temperature and pressure. Blind plates should have large lugs and be painted in a special color for labeling and identification. 　　(3) On-site safety measures for inserting and removing blind flanges: Ensure that all materials in the system have been removed, and that pressure and temperature have dropped to the specified levels ； Attention must be paid to fire and explosion prevention. In areas where lighting is prohibited, or when working on windows or pipe blind flanges that handle flammable and explosive materials, explosion-proof tools and lighting fixtures must be used. Lighting is strictly forbidden within the designated areas, and someone should be assigned to conduct regular inspections and supervision during the operations ； When inserting or removing blind flanges indoors, windows must be opened or ventilation equipment that meets safety requirements must be used to ensure adequate ventilation ； When removing or installing blind flanges on pipelines carrying toxic substances, operators must wear appropriate personal protective equipment as required to prevent poisoning ； When performing blind plate operations at heights, the safety requirements for working at heights must be met simultaneously, and safety helmets and safety belts must be worn ； For operations involving particularly high risks, backup rescue measures and a gas protection station must be available; medical personnel and ambulances should be on site ； During continuous operations involving the insertion and removal of blind flanges, operators should not work for too long a period; they must take turns to rest. 　　2) Purging, blowdown, and cleaning (1) Purging. To ensure the safety of maintenance work involving open flames and operations inside equipment, flammable, explosive, toxic, and harmful gases in all equipment and pipelines within the maintenance area must be displaced. For the displacement of flammable and toxic gases, inert gases such as steam and nitrogen are mostly used as displacing media; the water-injection and venting method can also be employed. Vent flammable and toxic gases. 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. 　　Safety precautions for displacement operations: ① The equipment, pipes, etc. to be displaced must be reliably isolated from the system. 　　②Before the displacement, a displacement plan should be developed and a displacement flowchart drawn. Depending on the differences in density between the displacing medium and the medium to be displaced, the inlet for the displacing medium, the outlet for the medium to be 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. 　　③Replacement 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 (usually at least 3 times the volume of the medium to be displaced). However, whether the displacement is thorough and whether the displacement operation meets safety requirements cannot be determined solely based on the duration of the displacement or the amount of displacement medium used; rather, it should be judged by 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 displacement is generally less than 1%–2% (by volume). 　　④Sampling and analysis shall be carried out at the sampling points specified in the permutation flowchart, and the results must meet the required standards. 　　(2) Purging. 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. 　　Safety precautions for purging operations: ①. Purging operations should be carried out one by one according to the pipe section numbers and equipment identifiers, following the purging procedure outlined in the shutdown plan, and a registration form should be filled out. Indicate on the registration form the pipe section number, equipment tag number, purging pressure, air inlet point, air outlet point, responsible person, etc. 　　②. At the end of the purging process, the material valve should be closed first, followed by turning off the gas supply, to prevent backflow of the medium in the piping system. 　　③After the purging is completed, samples should be taken for analysis; upon passing the test, it must be promptly isolated from the operating system. 　　(3) Cleaning 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. Prevent combustion, explosion, or poisoning accidents caused by a **rise in the concentration** of flammable, toxic, or harmful substances in the air, which may occur when deposits or scale rapidly decompose or volatilize due to high temperatures during hot work. 　　Generally, there are two types of cleaning: steaming and chemical cleaning. 　　①Steaming. Generally speaking, after removing the material from larger equipment and containers, they should be cleaned using steam, high-pressure hot water, or by introducing an alkaline solution (sodium hydroxide solution) and boiling them; low-pressure saturated steam is preferred when using steam ； The spraying equipment should be electrically grounded to prevent static electricity sparks from causing fires or explosions, as well as to avoid burns from hot surfaces or alkaline liquids. 　　②Chemical cleaning. Common methods include alkali washing, acid washing, and alternating between alkali washing and acid washing. 　　The alternating use of alkali cleaning and acid cleaning is suitable for simply removing iron oxide deposits inside equipment. If there is oil residue in the equipment, first use alkali cleaning to remove the oil, then wash with clean water, and subsequently carry out acid cleaning – the iron oxide deposits will then dissolve. If the deposit contains substances such as copper and copper oxide in addition to iron oxide, acid washing alone cannot remove them. In such cases, an ammonia solution should be used first to remove the copper components from the deposit, followed by acid washing. Since the copper and copper oxide deposits, as well as the iron oxide deposits, mostly accumulate in layers, ammonia and acids are used alternately for cleaning ； If there is a significant amount of copper and copper oxide fouling, a copper ion sealer must be added during pickling to prevent corrosion caused by the electrode deposition of copper ions. 　　Wastewater resulting from chemical cleaning must be treated before it can be discharged. Typically, waste liquids are diluted and precipitated, filtered, or treated using chemical methods such as neutralization, oxidation, reduction, coagulation, adsorption, and ion exchange, so as to meet discharge standards before being released. 　　For deposits inside certain equipment, they can also be removed by manual scraping. When carrying out this task, the safety regulations for working with equipment must be followed. In particular, it is important to use tools such as copper or wooden ones that do not generate sparks when scraping away combustible deposits, and to handle the scraped deposits properly. 　　3) Others
(1) Clearing the maintenance site and pathways
In accordance with the provisions of “Safety Signs” GB 2894, appropriate safety signs must be posted at the maintenance site. Additionally, there should be a designated person responsible for supervising the maintenance site ； Persons unrelated to maintenance are prohibited from entering ； No temporary repair offices, rest rooms, warehouses, construction sheds, or other buildings shall be erected near pipelines transporting flammable, explosive, or toxic substances ； Pits, wells, depressions, ditches, steep slopes, and other elements that pose a risk to safety during maintenance work should be filled in or covered with covers that are at the same level as the ground; fences and hazard signs should also be installed. Hazard lights should be placed in use at night ； The maintenance site must have unobstructed drainage to prevent water accumulation; the roads at the site should be clear, the surface should be level, the foundation should be solid, and there should be adequate lighting ； Traffic safety signs should be installed on the roads at the maintenance site, and their location, shape, size, and color shall comply with the provisions of GB 5768 on Road Traffic Signs and Markings ； When road use is required for maintenance or construction and it affects fire access routes, approval procedures must be obtained, among other things. In summary, the maintenance site and passages must meet safety requirements. 　　(2) Cut off the power supply to the equipment to be inspected; after verifying through a start-up check that there is no electricity, hang a “Do Not Start” safety sign at the power switch and lock it. 　　(3) Timely contact the utility systems (water, electricity, gas, steam) and handle the situation properly. 　　(4) Safe handover. Before maintenance, the production department and the maintenance department must strictly carry out the safety maintenance handover procedures. The transferring and receiving parties shall conduct thorough inspections and verifications in accordance with the above requirements; once the conditions for safe maintenance handover are met, the responsible persons of both parties shall sign the \"Safety Handover Form\" to confirm this. Even when maintenance or emergency repairs are carried out in the production workshop without shutting down the operation, the \"Safety Handover Form\" must still be filled out in detail. 　　III. Safety requirements during the maintenance phase During the maintenance phase, tasks such as electrical work, demolition work, hot work, earthwork, work at heights, welding, lifting, and working inside equipment are often carried out, along with the use of various work permits. All relevant regulations must be strictly followed to ensure the smooth progress of maintenance work. The following describes hot work and work inside equipment. 　　(I) Hot work
1. Hot work and its classification
Hot work refers to welding and cutting operations carried out in no-fire zones, as well as any temporary operations conducted in areas where flammable or explosive materials are present, involving the use of blowtorches, electric drills, grinding wheels, etc., which may generate flames, sparks, or red-hot surfaces. 　　Hot work is divided into three categories: special hot work, category 1 hot work, and category 2 hot work. 　　Hot work must undergo a hot work analysis, and it can only be carried out upon passing the assessment. 　　2. System for work permits for hot work. 　　①When carrying out hot work in a no-fire zone, a \"Hot Work Safety Permit\" must be obtained, and the procedures for application, review, and approval must be strictly followed. “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 (including the methods used), safety measures to prevent fires, the responsibilities of the person overseeing the hot work, as well as the time and place where samples were taken for hot work analysis and the results thereof. The person authorized to approve the permit must confirm that all information is correct before signing it. 　　②After receiving the fire work permit, the personnel carrying out the fire work must carefully check all the details. If they find any violations of the fire safety regulations, they have the right to refuse to carry out the work and report it to the company’s fire safety department. The person performing hot work must carry the hot work permit with them at all times; working without a permit or with incomplete procedures is strictly prohibited. 　　③Before starting 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 specified 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, in addition to obtaining a \"Hot Work Safety Permit,\" it is also necessary to obtain a \"Height Work Safety Permit\" and a \"Work Inside Equipment Safety Permit.\" 　　3. Hot work analysis and standards. 　　Hot work must undergo a hot work analysis, and it can only be carried out upon passing the assessment. Flame testing analysis shall comply with the following requirements: ① The samples taken must be representative, and the analysis samples for special flame testing operations shall be retained until the completion of such operations. 　　②The sampling time and the duration of hot work must not exceed 30 minutes; if this interval is exceeded or if the hot work is interrupted for more than 30 minutes, re-sampling and analysis are required. 　　③Flame detection analysis standard: When using a flame 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 explosion limit of the gas or vapor being analyzed is 10% or higher, its concentration should be less than 1% ； When the explosion threshold is less than 10% and greater than or equal to 4%, its concentration should be less than 0.5% ； When the explosion lower 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 combustible gases, the one with the lower explosion lower limit shall prevail. 　　④When performing welding or other fire-related operations inside equipment, it is also necessary to analyze and measure the levels of toxic and harmful gases in the air, as well as the oxygen content. 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%. 　　(II) Work inside equipment 　　1. Work inside equipment and its hazards 　　Any 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 spaces within petroleum and chemical production areas, is referred to as work inside equipment. 　　2. Key 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 strictly followed. 　　②Before working inside the equipment, it must be safely isolated from other equipment (by installing blind flanges or removing a section of pipeline; no other methods are permitted), and it must be 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 shows satisfactory results. If work is carried out inside the equipment for an extended period, analyses should be conducted at least every 2 hours. If levels exceed the specified limits, work must be stopped immediately and personnel should be evacuated promptly. 　　④Implement appropriate ventilation measures to ensure good air circulation inside the equipment. 　　⑤There should be sufficient lighting; the voltage for lighting inside equipment should not exceed 36 V, and it should be 12 V or less when working in humid or confined spaces. Lighting fixtures and power tools must meet safety requirements such as being moisture-resistant and explosion-proof. 　　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. 　　⑧When working inside equipment, a dedicated supervisor must be assigned to oversee the operation and maintain effective communication with the workers 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 ； To continue working, it is necessary to reapply for approval to work inside the equipment. 　　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 department using it. Only after it is confirmed that there are no people, tools, or debris inside the equipment can the openings in it be sealed. 　　IV. Handling after maintenance is completed 　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.