Protection and inspection of shut-down and idle equipment

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Petrochemical plants often have some equipment that needs to be shut down and left idle due to process, production, or other reasons. Proper measures should be taken promptly to protect equipment that is out of use or idle. If it is out of use for an extended period, regular inspections should also be carried out to ensure it remains in good condition, preventing corrosion, damage, and rapid deterioration, so that it can be put back into operation when production resumes and does not fail to function, thus avoiding losses to the factory’s assets. Section 1: Causes of Deterioration in Shut-down and Idle Equipment. Equipment that is shut down tends to deteriorate more easily than that which is in operation, usually due to environmental conditions that are completely different from those during operation. The main reasons for shutdowns and the deterioration of idle equipment are as follows: First, the impact of the shutdown process. Whenever a piece of equipment is shut down, its operating conditions during normal operation inevitably change, and it is then subjected to various physical changes such as temperature and pressure. The rate of temperature and pressure reduction during shutdown must be carefully considered regarding its impact on each type of equipment. The specified rates of cooling and pressure reduction in the process operating procedures are necessary measures to protect thick-walled and multi-layered containers and equipment from damage. If these regulations are ignored and the cooling occurs too rapidly, it will lead to increased stress, causing the equipment structure to deform or crack. Even if a cooling rate is not specified for a certain device, the presence of catalysts, coke, or other deposits inside the device often significantly alters the temperature profile. Therefore, special consideration must also be given to the start-up and shutdown of such equipment. For large, thick-walled hydrogen-handling equipment, it is necessary to cool and degas it slowly during shutdown in order to reduce the risk of metal delamination and pore overpressure. Similarly, when reducing the pressure on equipment equipped with linings and protective coatings, a proper rate of pressure reduction can minimize the risk of expansion and bubbling caused by uneven pressure on the back side of such equipment. Some materials undergo brittle degradation when used at high temperatures, and they are highly sensitive to cracks at normal ambient temperatures; this brittleness sensitivity is particularly severe in low cold temperatures. Therefore, during shutdown for maintenance or hydrotesting, it is necessary to supply appropriate heat to raise its temperature. When shutting down operations in cold climates, additional protective measures should be taken, such as completely draining all equipment of low freezing point fluids, to prevent freezing and other forms of damage. II. Corrosion of deposits: The deposits formed during operation can often become corrosive media when the system is shut down. Exposing the equipment to a corrosive environment causes it to deteriorate. This is more harmful to the device materials than in an operating environment. It is most effective to remove some of the sediment before the device is turned on. 　Some sediments should be removed immediately once the equipment is opened, especially self-igniting iron sulfide and other corrosive substances, which must be removed right away. Equipment that comes into contact with acid during operation should be thoroughly emptied, and further protected by neutralization and cleaning with a solution. Austenitic stainless steel can suffer from stress corrosion cracking and pitting in certain aqueous or ionic solutions. During the production process, deposits of iron rust in the form of chlorides and sulfides are formed. If these deposits are not cleaned or neutralized before they come into contact with moisture and oxygen, chloride solutions or polyoxysulfates can cause severe cracking and pitting. Austenitic stainless steel equipment that does not need to be opened or is difficult to purge and clean (such as vertical heating furnaces and U-shaped bends) can be relatively easily purged with nitrogen to drive out moisture and oxygen. This type of equipment can maintain a certain temperature during shutdowns, and can be protected under positive pressure using nitrogen. Before operation, austenitic stainless steel equipment must be pressure-tested using water with a chloride content of no more than 25 ppm. If the equipment can be thoroughly emptied and dried, the chloride level in the water can be allowed to reach 50 ppm. Sulfur deposits can form in the convection sections of heating furnaces and boilers, as well as in flues and chimneys. Corrosion becomes particularly active during periods of downtime; these areas should be thoroughly cleaned to prevent water vapor from condensing. III. The hazards of humidity Humidity is often one of the causes of equipment degradation when it is not in use. Lower temperatures encountered during shutdowns often cause condensation. The moisture caused by condensation, when combined with oxygen, can lead to severe pitting and oxidation/rusting of the equipment. Moisture can also penetrate into cracks and gaps in the equipment’s insulation, causing rusting on the surface of the equipment. Therefore, the process operations during shutdown should maintain a high temperature to prevent condensation. Equipment that has been taken out of service should be protected and kept as dry as possible. IV. Other environmental factors Other environmental factors that affect equipment that is out of service, such as atmospheric humidity, excessively high or low temperatures, the rainy season, as well as the presence of nearby chemical plants, industrial facilities, or large amounts of saltwater in the vicinity, should all be taken into consideration. Section 2: Protection and Inspection Measures for Shut-down and Idle Equipment I. Decision-making on Protection It is essential to provide appropriate protection for shut-down and idle equipment. Choosing the appropriate protection methods and measures is the primary issue that needs to be considered. Generally, it is necessary to take a comprehensive and overall consideration of the following factors before making a decision. 1. Downtime or idle time. How long has the equipment been out of use or idle? The duration of time is directly related to determining which protective measures are most appropriate. 2. The value of the equipment. What is the residual value of this equipment after deducting the depreciation from its fixed asset cost? 3. Nature of protection. Should measures be taken for protection on-site, or should it be removed and stored in a warehouse for idle equipment to be protected there? What kind of deterioration occurs if no protective measures are taken? 4. Methods of protection. What protective methods and measures are most appropriate? This is closely related to downtime or idle time, protection costs, etc. 5. Number of protective equipment. How many devices require protective measures? How many of the same type are there? Each one should be registered individually to keep track of them. 6. Costs for protection. Based on the methods and measures adopted, what is the total cost after calculation? A budget for the costs should be created to see if it is cost-effective The cost of protection should not be close to the cost required to update the equipment. It is even less desirable if it is equal to or greater than the cost required for the update. 7. Possibility of reapplication. Will this device be used again after being out of service for a while, or will it remain unused for an extended period? After responding to the above factors and conducting a comprehensive consideration and thorough evaluation, a decision is made, a specific protection plan is formulated, and protection measures are carried out in accordance with that plan. II. Protection and inspection measures for general equipment: For equipment that is not in use, methods such as external protection, internal protection, overall protection, environmental protection, as well as periodic inspections can be employed. (1) External protection 1. Organic coatings. The most commonly used external protective coatings are paints, varnishes, nitrocellulose paints, and similar materials. When using paints or other organic coatings to protect the surface of equipment, it is necessary to carefully inspect the quality of the coating applied. If any areas of looseness or bubbling are found, they must be removed and repainted ； If the surface has large cracks and fissures, it needs to be completely reworked and repainted. 2. Heavy-duty lubricating oil. Bearings and sliding surfaces, as well as other surfaces that cannot be protected with organic coatings for certain reasons, can be protected by applying heavy-duty lubricants. 3. Encapsulation. There are some items that can be wrapped in heavy-duty waterproof paper or plastic film. In some cases, waterproof paper can also be treated with a vapor-phase preservative. Abroad, vapor-phase preservatives are patented materials that are supplied by manufacturers according to the requirements provided by customers. 4. Metal coating. Applying a metal coating to the exterior of equipment is also a form of protection. The quality of the coating is very important and should be carefully inspected. All defective areas must be thoroughly cleaned and replated with the same metal as the original coating. Great care and attention should be paid when selecting the material for re-plating. 5. Fire and insulation layer. For equipment that is out of service and has a fireproof and insulating layer on the outside, it must be carefully inspected and repaired to ensure its integrity. For equipment that has been out of use for a long time or is idle, if there are cracks or gaps, rainwater or moisture can enter, which will inevitably accelerate corrosion on the metal surface. In areas with high humidity, the best protective measure is to remove the insulation layer from the outside of the equipment and paint the metal surface. (II) Internal protection 1. Oiling. All shut-down and idle containers, heat exchangers, pipelines, furnace tubes and headers of heating furnaces, pistons and valve chambers of compressors and pumps, casings of steam turbines, as well as the inner surfaces of other enclosed equipment, can be protected by applying light oil with sufficient viscosity to adhere to the inner walls. For larger devices that can be taken inside to carry out work, light oil can be sprayed on all accessible internal surfaces. Special attention must be paid to carefully checking the quality; all surfaces should be sprayed thoroughly, evenly, and completely ； For smaller devices and pipes that cannot be accessed for cleaning, light oil can be poured in and then drained, leaving a layer of oil film on all internal surfaces. For protective light oil, a type with low viscosity that does not evaporate rapidly should be used. Light oil with anti-corrosive agents covered by useful foreign patents is used to enhance anti-corrosion efficiency. 2. Fill with oil. All closed containers and equipment can be protected by filling them with a lightweight, non-corrosive oil. In this way, the entire interior of the device can be in contact with oil, preventing corrosion from occurring. 3. Vapor-phase preservatives. The interior of containers and equipment can be protected using a gas-phase preservative. This vapor-phase preservative is a patented product abroad. Customers can order from the manufacturer when needed. The manufacturer supplies as needed and provides construction methods. 4. Inert gases. All closed containers and equipment can be protected by filling them with a dry inert gas, such as nitrogen or carbon dioxide, to displace the air inside. 5. Desiccant. In enclosed containers and equipment, desiccants can be placed to absorb moisture as a form of protection. The desiccant should contain an indicator that can show when the saturation point is reached. With this method, it is necessary to open the container regularly to check the desiccant and replace it when needed. (III) Overall protection 1. Powder coating for sealing. Spray coating sealing is a protective process that involves applying a layer of plastic to completely enclose the equipment. Abroad, this technology is already widely used and successfully applied in **and civilian industries to protect equipment that is no longer in use or is idle, regardless of its size or shape. Desiccants or gas-phase preservatives can be placed inside sealed equipment to help prevent the effects of atmospheric moisture. When the equipment is sealed for an extended period, periodically inspecting the surface of the sealed equipment is also a necessary preventive measure. If the powder coating is applied properly, the plastic coating will protect against the effects of rain, snow, moisture, acids, salts, and mold, providing protection that can last up to 10 years. Before starting the powder coating process for sealing, it is advisable to consult a powder coating factory and those with experience in this field. They can provide valuable advice on selecting appropriate materials and ensuring proper application. Although the application of this process is not very complex, it still requires certain knowledge and specialized equipment. For example, a compressor, a tank with a stirrer, a regulator, a spray gun, and a hose are required, among other things. It is also necessary to decide whether to use regular maintenance staff or qualified contractors for the work. 2. Packaging and soaking. Smaller accessories and instruments can be placed in moisture-proof plastic bags, paper boxes, or containers for comprehensive protection; desiccants can also be added inside. Some small items can also be protected by immersing them entirely in oil or other protective liquids. (IV) Environmental protection: Equipment can be protected by methods such as adjusting the air and removing moisture to change the environment. 1. Adjust the air. If the equipment is placed in a sealed warehouse, the warehouse can be equipped with air conditioners to maintain a uniform temperature and low humidity, thereby protecting the equipment. 2. Remove moisture. In some cases, the equipment is stored in a sealed room dehumidified by mechanical means or with desiccants. An indicator can be placed inside the room; if the saturation point has been reached, the indicator can show this. In a room dehumidified with desiccants, the indicator can be placed in a visible location by the window to prevent anyone from entering, unless the saturation point has been reached and the desiccants need to be replaced. (5) Periodic inspections: The entire set of protective measures requires periodic inspections to ensure their long-term effectiveness. Regular and thorough inspections should be carried out on the external protection measures for decommissioned and idle equipment, such as powder coating, fire and heat insulation, painting, oil coatings, packaging, etc.; repairs or corrective actions should be taken promptly when necessary ； For internal desiccants, preservatives, liquid filling, gas protection, oil rust prevention, and so on, periodic inspections must be carried out, and corrective actions or replacements must be taken as necessary to improve the situation. The relevant departments must provide the conditions for inspections and for making corrections. III. Protection and Inspection Measures for Key Equipment Here, some protection and inspection measures for key petrochemical equipment are introduced, along with specific steps for carrying out these protection tasks. The main aim is to assist those responsible for equipment protection and inspection in formulating plans for such activities. 1. Protection of compressors (1) Centrifugal compressors. The protection scope and level of a centrifugal compressor depend on its type, size, and operating conditions. There are two commonly used protective methods and measures. One method is: to lift the large cover of the superhousing, thoroughly clean the housing and rotor and apply oil, as well as clean the entire lubrication and sealing oil system ； Another approach is to simply fill the casing cooling system, as well as the lubrication and sealing oil systems, with the appropriate type of oil. The following outlines the specific steps for protective measures that can be adopted for a centrifugal compressor: 1) Remove the motor, bearings, seals, and other related components ； 2) Pack the components coated with protective grease in paper or small boxes for internal storage. Carefully support the rotor to prevent the shaft from bending or deforming, or store it in an upright position ； 3) Seal all fuel inlets and exhaust outlets ； 4) Fill the entire compressor system with oil through an outlet, and displace all air inside via the housing vent ； 5) Seal all pipeline connections completely and fill the seal oil system with oil. For the protective measures of complex units such as compressors, a comprehensive and detailed plan is necessary. For decommissioned compressors, whether to leave them in their original installation location on site or transport them to a warehouse away from the site for storage, an environmental impact assessment must be conducted and careful consideration given. It is obviously very difficult to transport a compressor driven by a large steam turbine to the installation site, and the cost is extremely high. For decommissioned compressors, it is important to protect them from the effects of the climate. It can be covered with waterproof canvas on the spot, or placed in a closed room or warehouse, which provides the best protection. In some cases, simple movable enclosures can be assembled for each unit, which helps to reduce the high costs associated with dehumidification in large buildings. A oil mist protection system can also be installed on the compressor to ensure continuous operation without oil mist, which is much more economical than regularly rotating the compressor’s rotor. (2) Reciprocating compressors: Due to the high initial investment cost of these compressors, the scope of protection for large reciprocating compressors should be expanded, and the protective measures should be more detailed. This describes the protective measures and specific steps for a large reciprocating compressor: 1) Drain all the water from the cylinder jackets, intercooler, and water-gas separator ； 2) During drainage, the outlets may sometimes become blocked; therefore, after drainage is complete, all outlets should be checked to ensure that all water has been completely drained (consider using a non-corrosive fluid to displace the water or introducing an anti-corrosive agent in gaseous form) ； 3) Fill all lubrication devices with oil to prevent components from rusting ； 4) Remove all piston rod seal rings and wiper rings, soak them in an appropriate solution for cleaning, then apply a layer of rust-proof grease, wrap the rings in waterproof paper, and place them in a plastic box. Rust prevention can be achieved using grease, high-viscosity oil, or some proprietary material. If patent materials are to be used, the manufacturer should be consulted to select the most suitable one. The packaged ring should be labeled to indicate the part it is for. So that it can be restored to its original position during reassembly ； 5) Remove the intake and exhaust valves from the compressor cylinder block, clean them, and apply a layer of rust-proof grease. After removing the air valve, a layer of oil film can be applied to the valve hole and piston rod using spray or other appropriate methods. Then, store the intake and exhaust valves properly indoors or in a safe location at the bottom of the compressor crankcase to make it easy to find them again. If the piston rod is not made of stainless steel, it should be considered to disassemble the piston and tie rod, apply oil, package them, and put them in a box. The tie rod must be properly supported to prevent bending deformation ； 6) Rotate the drive motor to apply a layer of lubricant or appropriate rust inhibitor to all surfaces of the compressor cylinder bores ； 7) Seal the inlet and outlet with flanged blind plates. The aforementioned protective measures and steps can be appropriately modified for compressors that are shut down for a short period of time. According to foreign sources, in normal climate conditions and factory atmospheres, if a compressor is shut down for more than 4–6 weeks, it is necessary to take appropriate measures to protect both the interior and exterior of the unit. In areas where freezing occurs, the water in the cylinder jackets and the cooling water system must be drained promptly. If it is noticed that the drainage from the outlets has stopped, an immediate inspection must be carried out to ensure that all water has been completely removed. 2. Protection of pumps: Commonly used in petroleum chemical plants are ordinary centrifugal pumps, reciprocating pumps, and plunger pumps. Due to their simple mechanical structure, they are relatively easy to protect, and the costs associated with such protection are not high. Generally, aside from the drive unit, the pump only needs to be protected as a whole; even if all pumps are to remain idle for an extended period, there is no need to disassemble them carefully. If an oil mist protection system is installed, it is much more economical to maintain the operation with oil mist under protection rather than continuously rotating the rotor part. For pumps handling corrosive media, the protective measures taken for both short-term idle periods (3–4 months) and longer-term idle periods are largely the same. The only difference lies in the method and extent to which the pump is cleaned. (1) Centrifugal pump. Here are the protective measures and steps for a vertical split-case centrifugal pump. 1) Open all ventilation and exhaust openings on the pump casing and bearing housing, and clean the casing and housing with a suitable solvent or cleaner. 2) If the pump is to be moved and stored in a warehouse, all connecting pipelines must be removed, and the inlet and outlet flanges must be sealed off with blind plates ； If the pump is to be protected at its original installation site, the suction and discharge valves must be closed and isolated with blind flanges. 3) If a single mechanical seal is used, the seal gland can be loosened to inspect the seal in order to determine whether the sealing surface can still be used ； Then fill the seal with light lubricating oil and gently compress the seal gland. 4) If dual mechanical seals are used, the packing box can be emptied and cleaned with a cleaning agent; thereafter, the outlet at the bottom of the packing box should be sealed and filled with light lubricating oil or grease. 5) If a conventional packing is being used, the packing gland can be loosened to remove the packing. Light lubricating grease should be applied inside the packing box, after which the packing is reinserted and the packing gland is tightened again. Use a label that says, “The packing previously used in operation has been removed.” 6) Seal the discharge ports of the bearing housings, fill them with oil, and close all the ventilation ports of the bearing housings. 7) Disassemble the coupling, apply lubricant or an appropriate rust inhibitor, and cover it with plastic. 8) Close all exhaust outlets. Fill the entire pump casing with light oil, and slowly turn the pump shaft to ensure that all the inner surfaces are coated with oil. 9) During periods of shutdown and inactivity, the pump shaft should be manually rotated from time to time to ensure that a protective oil film is always maintained. 10) If a single mechanical seal is used, the seal should be pressed gently to ensure that oil flows into the stuffing box and covers the seal; the seal should then be tightened again to prevent leakage. 11) Wrap the exposed part of the pump shaft with plastic tape. Make sure that the shafts entering the pump casing and bearing housings are properly wrapped to ensure a tight seal. 12) All other external surfaces must be coated with paint or a suitable preservative. The protective measures and procedures for horizontally split centrifugal pumps are roughly the same as those for vertically split centrifugal pumps; only minor adjustments need to be made according to the actual conditions. (2) Reciprocating pump. Various types of steam reciprocating pumps, such as single-stroke or double-stroke pumps, can be protected through the following measures and steps. 1) Open all vent and discharge ports at both the liquid and steam sides of the reciprocating pump. 2) Disconnect all pipelines at the connection points, seal the inlet, outlet, and steam flanges with blind plates, and close the outlet. 3) Remove the valve cover at the liquid side of the pump and the slide valve cover at the steam side. 4) Remove one valve from each end of each cylinder on the liquid side, inject an appropriate rust inhibitor into all cylinders, and introduce the rust inhibitor into the steam cylinders through the slide valve opened on the steam side. Slowly rotate each piston forward and backward. 5) Apply an appropriate rust inhibitor to all valves and valve components, drain excess rust inhibitor from the cylinder, and close all ventilation and exhaust ports. 6) Reset the valve and valve cover. 7) Remove the packing from the packing box, apply a suitable protective coating to the packing and the rods inside it, put the gasket back in place, and tighten the gland. 8) Wrap the exposed part of the pull rod with plastic. 9) Spray or brush all external surfaces with a suitable rust inhibitor. 10) Apply oil to all lubricated parts. (3) Plunger pumps: Ordinary plunger pumps or metering pumps can be protected using the same measures as mentioned above, with the steps adjusted according to the characteristics of the pump. Special attention should be paid to the pump’s gear system during protection. 3. Protection of steam turbines: Steam turbines are high-speed rotating drives with reliable design, making it relatively easy to carry out protection measures after they are shut down. There is no need to disassemble it or take any other special measures. Below are the protective measures and steps for a steam turbine. For other types of turbines, only minor modifications based on the actual conditions are required to make them applicable. 1) Use compressed air to dry the steam chamber. 2) Use compressed air to blow a gas-phase preservative powder into the steam chamber through appropriate small holes in the body. Approximately 1g of gaseous preservative powder is required per cubic foot of internal volume, depending on the specific conditions. 3) When blowing in the powder, the rotor should be rotated simultaneously to ensure as even a distribution of the powder as possible. 4) Seal the large cover and close the passages of all small holes. 5) Whether it is a single-stage or multi-stage turbine, protection can be achieved by following the aforementioned measures and steps. 6) When the turbine is put back into use, all gaseous corrosion inhibitors must be removed, and steam should be introduced through the turbine to discharge the condensate into the waste water pipeline. If the steam condensate returns to the boiler, the presence of corrosion inhibitors can be checked by analyzing the nitrite content in the condensate. 7) Fill the bearing housing with light grease. 8) Close all vents and discharge ports on the bearing housing. 9) Steps 7 and 8 above can also be replaced by the following method. In other words, the extended part of the shaft end in the bearing housing is sealed using plastic materials or fillers, and then light lubricating oil is poured into the bearing housing until it reaches the top; the oil level should be checked regularly. When it is used again after being driven, the plastic or packing seal on the protruding part of the shaft end can be removed, and the oil in the bearing housing can be drained. Then, inject the appropriate amount of lubricating oil into the bearing housing to the proper level. This method is much more convenient than steps 7) and 8), which involve removing the bearing housing, taking out the grease, and then injecting new lubricant. 10) Remove the governor box. 11) Coat the over-speed jumping mechanism with light oil and package it. 12) Remove the packing from the control valve and inject light grease into the packing box. 13) Spray appropriate rust inhibitor on all exposed moving parts of the governor. 14) Replace the governor box cover in its original position. 15) Clean all external surfaces with a wire brush, then spray them with paint or rust inhibitor. 16) Secure the exposed drive shaft with plastic tape. 17) Inject grease into the coupling or apply a rust inhibitor for protection. When a turbine is shut down and stored for an extended period in a place that is neither hot nor dry, foreign sources recommend applying spray coating to the entire turbine as an effective protective measure, with good results. 4. Protection of cooling and heat exchange equipment (1) Cooling towers: For cooling towers, protective measures must be taken during periods when they are not in use. Because the impact of the environment on cooling towers during periods of inactivity is even more severe than when they are in use. It is not very difficult to take measures and develop plans for the protection of cooling towers. Special attention usually needs to be paid to its mechanical equipment and metal components. The following describes the protective measures and steps for a mechanically ventilated cooling tower with a water storage tank and mahogany structure: 1) Open all external pipeline valves and empty them. 2) Drain all the water from the reservoir and clean it out. 3) Close the open reservoir discharge valve. 4) Repair or replace all damaged structures, and substitute and replenish the bent or missing slats. 5) Tighten all fasteners on the tower frame. 6) Remove the drive motor of the fan and protect it. 7) Remove the gear reducer and drain the oil from it. Replace it with high-quality mineral oil again ； Clean the outer surface of the gear reducer and paint it ； Wrap all exposed shafts with plastic tape ； Store the gearbox in a warm and dry place. 8) Clean the fan using appropriate cleaning tools. 9) Apply light lubricating grease to the fan drive gear and cover it with waterproof paper. 10) Spray paint on the fan or apply metal plating. 11) Protect the fan blades to prevent rotation and provide support. In situations where it is not desired or necessary to remove the fan drive components, regular preventive maintenance can be carried out, but the fan should be rotated every 3–4 weeks. The dried wooden structure of the cooling tower after it was taken out of service poses a serious fire hazard. Therefore, if the shutdown period is around 2 months, a porous hose should be placed around the tower to spray water regularly. If the shutdown period is longer, spraying should be carried out regularly to fill the space with fire-retardant chemicals and insecticides. (2) Spray cooler: The operating conditions of a spray cooler are very similar to those of a cooling tower. Of course, the structural materials of the two are very different. Spray coolers are typically made of steel structural concrete components and coil pipes. For spray coolers, the following protective measures and steps can be followed: 1) Close the inlet valve in the water tank to cut off the water supply. 2) Drain the water from the sink. 3) Cut off the pipeline through which the product is flowing. 4) Flush the product pipeline, then drain it. 5) Cut off the product pipeline of the cooler. 6) Brush the cooler exhaust pipes and water tanks with a wire brush and paint them. 7) Clean the steel structural components and paint them. 8) Cover the sink with a metal cover. 9) Drain the water from the concrete water tank. 10) Close the drain valve of the open collection tank. (3) Finned air coolers: The fans, fan motors, and gear reducers can be protected following the same steps as those for the cooling tower 6)----11). Additional notes regarding the finned air cooler: 1) Open the air cooler, thoroughly clean the tube bundle, and then close it. 2) Use a pump to inject light oil into the pipe, then drain the oil, and finally seal the tube bundle. 3) Spray a suitable rust inhibitor on the external components. 4) Steel structural components shall be protected in accordance with the protective measures for steel structures. (4) Heat exchangers: The protection of shell-and-tube heat exchangers is essentially an extension of the regular cleaning and maintenance tasks carried out during normal shutdowns. Conventional rinsing, chemical cleaning, or mechanical cleaning still needs to be continued. After the heat exchanger is taken out of service, it can be protected on-site or stored in a warehouse for protection. The protective measures and steps described below can be applied either for on-site protection or in a warehouse: 1) Open the heat exchanger, remove the tube bundle, and disassemble all components. 2) Thoroughly clean all components, and remove all chemicals, rust scales, deposits, and other corrosive agents. It is quite effective to perform flushing or chemical cleaning before disassembling the heat exchanger. All chemicals (such as ammonium salts, chlorides, and sulfides) must be completely removed. Because some chemicals have an effect on many common metal materials used in heat exchangers. Erosion of carbon steel and copper alloys by ammonium salts and chlorides ； Chlorides and sulfides are particularly harmful to austenitic stainless steels. 3) Thoroughly coat all interior surfaces of the casing with a protective oil, including the flange surfaces with bolts and the surfaces of other gaskets. The cleaned tube bundle should be immersed in the oil tank for about 30 minutes to ensure complete coating. 4) Reassemble all components, disconnect all connecting pipelines, and seal all vents and discharge ports. 5) When sealing, coat all exposed bolts and flanges with light oil or heavy grease. For heat exchangers that have been out of use for a short period, the flanges can be wrapped with thick waterproof paper or polyethylene plastic. 6) Take appropriate protective measures against the external environment as required by local conditions. In most areas, no additional protective measures are generally required, but in some areas the insulation layer must be completely removed and the metal surface painted. If the tubes need to be stored separately. The following additional measures can be adopted, depending mainly on the local environmental conditions and the materials used for the tubes. 1) Cover the tube bundle with wooden plates and secure them with bolts. 2) Wrap the entire tube bundle with polyethylene plastic, or provide overall protection using methods such as powder coating or applying a protective coating. 3) Although the above measures are designed for shell-and-tube floating-head heat exchangers, they can also be applied to other types of heat exchangers. 5. Protection of storage tanks and pressure vessels: In storage tanks and pressure vessels, corrosion is typically found to affect all components to varying degrees. Atmospheric corrosion occurs on the outer surface, and its severity depends on the temperature and humidity conditions of the surrounding environment. Since external corrosion is easy to detect, necessary measures are generally taken in a timely manner to prevent corrosion. Most cases show that internal corrosion is latent and often difficult to detect; sometimes it is only discovered after damage has occurred or when the storage tanks and pressure vessels are thoroughly cleaned for inspection. By the time corrosion is identified, the repair costs have already become very high. When the downtime is prolonged, special consideration should be given to the protective measures taken. (1) Storage tanks: Before entering any storage tank, certain special protective measures must be taken. Safety measures should be taken when performing various tasks on storage tanks. Before entering the storage tank, it is first necessary to use the naked eye to inspect the interior of the tank through the manhole on its surface, to check for any loose struts, large pieces of scale about to fall off, pillars or brackets that are about to collapse, or any other objects that could fall and cause injury. Once it has been confirmed that the storage tank can be entered safely for work, all loose debris and scale inside must be removed completely, and any areas that require repair must be fixed thoroughly. If necessary, the tank walls should be thoroughly dried; a vent pipe can be used to remove the humid air from within the storage tank. For storage tanks of any type that are no longer in use, the following measures and steps can be taken to prevent deterioration: 1) Spray or brush protective oil onto the internal components and tank walls to create a layer of oil film on the inner surface of the tank. 2) Seal all manholes with padding covers. 3) Open the floating roof discharge outlet. 4) Paint the exterior of the storage tank in accordance with the factory’s maintenance plan. For insulated storage tanks, repair the insulation to prevent rainwater and moisture from entering. 5) If the storage tank is located in an area with strong winds or rising water levels, it should be considered to fill the tank with anti-corrosion water at pH 8–9. Filling the tank with water will enhance the material’s resistance to strong winds and prevent it from floating. Adding preservative water can also increase resistance to counterforces and stability. As a general rule, after a storage tank is taken out of use, a special inspection should be conducted at least once a year. (2) Pressure vessels: Safety precautions must be taken before entering a pressure vessel. Once it is confirmed that the pressure vessel can be safely entered for work, its interior should be cleaned and inspected, and repairs should be carried out if necessary. The following protective measures and steps can be used for any type of pressure vessel that is no longer in service: 1) Seal all manholes using blanking plates. 2) Seal all the remaining openings as well. 3) Perform a leak test using an inert gas at the specified sealing leak test pressure. Care must be taken during pneumatic testing, as there is a risk of the stored energy in compressed air being released; extra caution is required to prevent brittle fracture of metals. The temperature of the experiment is very important and should be given attention. 4) Close the inert gas inlet to fill the container with inert gas. 5) Coat all exposed bolts and flanges with a layer of light oil or heavy grease. 6) Determine appropriate measures to protect the outside of the container based on local conditions. In most areas, additional protective measures are generally not required. However, in some areas, the insulation layer must be completely removed, and the metal surface must be painted. 6. Protection of heating furnaces and chimneys: Here, only some of the protection measures and procedures for the furnace tubes, external steel structures, and auxiliary equipment of heating furnaces during periods of shutdown are discussed. No information is provided on refractory bricks, refractory concrete linings, and insulation. Because under normal circumstances, before the device is put back into operation, these items are inspected and any necessary repairs are carried out. If defects present in the equipment during its downtime cause a weakening of the structure, it should be repaired immediately. (1) Heating furnace ① All metal components of the heating furnace’s header and furnace body are protected in the same manner as the protective steel structure. All shafts on the header doors, sight holes, manholes, and access doors should be coated with heavy-duty lubricant to ensure that they can move immediately when the system is put back into operation. Since rainwater or moisture can cause rust to form on the surfaces of the joints at various openings on the furnace, it is recommended to seal these doors with removable mortar or waterproof compounds. ② The protection of the burner depends on the type of burner used. Extra care must be taken when protecting certain burners. Its moving parts should be coated with heavy-duty grease to keep the threads and adjustment mechanisms flexible and functional. ③ The chipped paint on the flues and pipes with existing paint should be repaired ； All exterior surfaces of chimneys and pipes that were previously unpainted must be derusted and sprayed or painted with an anti-rust agent or paint. Applying rust inhibitor is less costly than painting; however, it must be reapplied repeatedly throughout the downtime period. When heating is resumed after shutdown, the rust inhibitor will also be quickly burned off. ④ If there are no insulating bricks inside the flues and pipes, all deposits inside should be removed completely. During the shutdown period, regular checks should be carried out to ensure that no moisture absorption occurs. ⑤ The flue damper adjustment mechanism should be coated with heavy-duty grease to ensure smooth operation when it is put back into use. ⑥ The maintenance of gauge instruments, such as air pressure gauges, carbon dioxide indicators, fuel control valves, and flame controllers, depends on their level of use and the complexity of their design. Instruments such as anemometers can be completely taken out of their packaging and placed in plastic bags, while more complex instruments should be maintained in accordance with the protective measures specified for them. ⑦ Special protection should be provided for the fuel automatic shut-off valve; this can be achieved by removing the cover, spraying all components with light oil, then reattaching the cover, and sealing the entire unit or applying powder coating as a form of protection. The inspection plate at the lower part of the valve body should also be sealed. ⑧ Refractory materials should be kept dry regularly to avoid moisture. Moisture in the atmosphere can be removed by covering the openings of chimneys and pipes, as well as sealing off any areas where rainwater or moisture can enter. If necessary, appropriate heating or the use of desiccants can be employed to remove moisture. ⑨ All furnace tubes must have their interiors thoroughly cleaned. The junction box should be sealed. If cleaning alone cannot ensure the complete removal of harmful substances, the furnace tubes should be rinsed with a neutral solution or paraffin oil. All pipes that can be cleaned from the outside should have their exterior surfaces cleaned thoroughly to remove harmful deposits; if sulfur or other harmful deposits are present, moisture must be removed completely, which is especially important for austenitic stainless steel pipes. If necessary, it can be dried by appropriate heating or by using desiccants. (2) Chimney ① If an external inspection reveals that the paint on the chimney is peeling, repairs should be scheduled. Areas of the chimney where condensation can accumulate, such as joints, iron straps, and tie rods, must be painted, even if repainting the entire chimney is not necessary. The chimney must be covered to keep out rain. Snow and sand get in. The sulfur deposits must be completely removed from inside the chimney. ② A non-hardening resin material is used for chimney guy wires to protect the accessible wire brushes from corrosion, and practical experience is used to determine whether it is time to replace the chimney guy wires. ③ Ladders on any chimney must be regularly painted for corrosion protection at regular intervals as part of maintenance. 7. Protection of pipelines, valves, and fittings: For small pipelines that are not in use and are exposed to corrosive environments, they should be painted or covered with plastic tape. In climates where freezing occurs, all pipelines must be thoroughly flushed, and the flange joints as well as all low-point drain valves must be opened to ensure the pipes are completely emptied. For decommissioned large pipelines, it is recommended to adopt the following protective measures and procedures for maintenance: ① Thoroughly flush the pipeline. ② Disconnect the flange and open the low-point valve to ensure complete drainage. ③ Dry the pipeline, or circulate oil through it. ④ Check the insulation of the pipeline; suspecting damage in certain areas, open the insulation for inspection. ⑤ Repair all parts damaged by heat insulation. The exposed pipes should be cleaned with a wire brush and then painted. ⑥ Lubricate all valves. ⑦ Spray the outer surfaces of all valves with medium-quality oil, and coat the exposed valve stems with grease. The safety valve should be separated from its manifold. The discharge side should be sprayed with light oil and wrapped with waterproof paper or plastic. ⑧ Tighten all pipeline flange connections. Spray the flange joint with an appropriate light oil. Wrap the flanges with waterproof paper or plastic to prevent crevice corrosion between them. 8. Protection of steel structures: All exposed steel components, such as columns, beams, pipe racks, supports, frames, bases, ladders, walkways, platforms, railings, etc., are subject to atmospheric corrosion. Even though this erosion is usually not severe, necessary protection measures must still be taken. Because people often tend to overlook these steel structural components. It is recommended that the paint be repaired immediately after work is stopped. In areas with severe corrosion, visual inspections of the paint degradation should be carried out regularly, and paint protection measures should be applied in a timely manner as planned. 9. Protection of instruments: After the plant is shut down, it is very important to take timely measures to protect the instruments that are no longer in use. For primary and secondary instruments, although they are usually in different environments, the protective measures remain roughly the same. Primary instruments are widely distributed near the measurement lines and containers in the field, and they are often exposed to harmful environmental conditions; therefore, they usually need to be treated separately and protected. Since the secondary instruments are located away from the field, often in enclosed operation and control rooms, and also involve certain electrical equipment with a certain degree of complexity, they need to be treated as a whole in order to ensure proper protection. If the device is out of service for an extended period, it is recommended to remove all primary instruments and other dispersed instruments, store them in a dry, sealed room, to provide centralized protection. If research indicates that it is not cost-effective to remove and relocate the centralized protection, simple measures can also be taken for on-site protection. The following provides an example of the maintenance measures and steps for an air-operated differential pressure flow meter and its receiving recorder; other instruments can also follow these as a guide. (1) Pneumatic pressure flow meter ① Disconnect the flange of the orifice plate from the pipeline connected to the differential pressure element. ② Seal the connection of the orifice plate flange. ③ Inject light oil into the two chambers of the flowmeter body. ④ Block the inlet of the flow meter chamber. ⑤ Disconnect the air line from the pneumatic conveyor housing. ⑥ Block the air inlets, outlets, and all openings. ⑦ Spray lightweight oil inside the pneumatic conveyor housing and on all its components. ⑧ Spray or brush the protective oil onto the outer surface of the components. ⑨ Wrap the entire component in a thick black plastic bag, and tie the bottom of the bag shut with plastic tape. Another protective measure can also be adopted. That is, after completing steps ① to ⑦, the components are coated with spray paint for overall protection. ⑩ Seal all joints of the metal box with plastic tape. (2) Receiving recorder ① Disconnect all pipelines entering the receiving recorder box. ② Block all vents and openings. ③ Seal all joints of the thin metal box with plastic tape. ④ Insert a desiccant. ⑤ Seal the box lid with plastic tape. ⑥ Spray light oil on the outside of the box. One of the following protective measures can also be considered: that is, placing an electric light bulb in the box to generate heat and prevent moisture from forming ； Use instrument air to introduce it into the box to maintain a positive pressure ； Or the entire structure can be coated with plastic for protection. When the secondary instruments are packaged in a cabinet protected from climatic conditions, it is recommended to adopt protective measures similar to those used for electrical equipment. 10. Protection of electrical equipment: It is very important to provide timely protection for electrical equipment that is no longer in use. Electrical equipment is most sensitive to environmental conditions such as water, dust, and excessively high or low temperatures. The protection of electrical equipment depends on reducing environmental impacts. The measures and steps taken depend on the size of the equipment, its location, and the length of time it remains unused. Various specialized devices have their own specific requirements, but generally speaking, to keep electrical equipment free from faults, it is necessary to keep it clean, dry, sealed, and free from friction. It is also very important to be familiar with the cleaning, maintenance, and preventive techniques provided by the manufacturer. Apart from spare equipment, the nature of electrical equipment insulation dictates that protection on-site should be provided whenever possible. For most electrical equipment, the cost associated with removing it, transporting it, and storing it in a warehouse far from the site of operation is quite high. For the circuits of the shutdown devices, they must be disconnected except for lighting requirements, as well as those related to emergency power supplies or special heating. The following provides a brief introduction to the protective measures and procedures for motors, transformers, power distribution devices, as well as overhead and buried power lines. (1) Electric motors: The electric motors in petrochemical plants often operate in environments and conditions that are detrimental to the lifespan of the equipment. In most devices, they are often exposed to acidic gases, water vapor, and harmful dusts and substances. Although these factors are taken into account in the design of electric motors, given their large number and widespread use throughout the plant, along with some extremely harsh operating conditions, it is impossible to consider all scenarios in the design. The protective measures and steps for removing the motor from the site, transporting it, and storing it in a warehouse are described as follows: ① Disconnect the circuit. ② Clean the outer surface of the motor with a wire brush, and wash it using an appropriate solvent ； When motors are used under particularly harsh conditions with a layer of hard residue covering their surface, it is often necessary to subject them to sandblasting. Before sandblasting, the shaft should be wrapped with plastic tape or protected by other means. For open-type motors, it is necessary to protect their coils from damage caused by sand ； For fully enclosed motors, the openings of the air passages must be blocked or covered. ③ Disassemble the motor. ④ All components except the coil need to be cleaned with steam and detergent. ⑤ Blow away the loose dust on the coil with low-pressure dry air. Use a non-fibrous cleaning cloth, dampened with an appropriate solvent, to gently scrub the surface. If necessary, the coil can be immersed in an approved solvent. If the coil is dirty, it can also be soaked in warm water at 50–60°C along with a detergent solution. Before wet cleaning, the values of insulation resistance and polarization index should be recorded and controlled through the drying process. When cleaning, special care should be taken to prevent dust from getting into areas that are difficult to reach. ⑥ Place the disassembled motor in a drying oven for drying. Raise the temperature at a rate of 2–3°C per hour to prevent the insulation from melting. ⑦ Use a megohmmeter to check whether the motor has a short circuit, and repair it if necessary. ⑧ Apply a layer of air-dried insulating varnish to the motor coil. ⑨ Inspect the bearings and replace them if necessary. Apply the appropriate grease to the bearing. Apply more grease every 12 months. When adding grease, inject twice the required amount to force out the old grease. ⑩ Assemble the electric motor. ⑪ Wrap the motor shaft with plastic tape, and rotate the bearing once a week. If the motor is to be protected on-site, the following measures and steps can be followed: ① Disconnect the circuit. ② If oil lubrication is used, drain the oil from the bearing housing and refill it with the appropriate oil or protective fluid. Manually rotate the motor about 20 times to lubricate the working parts. In the future, rotate the rotor once every 2 weeks. ③ Remove the outer end cover. ④ Install an electric wire heater that extends into the motor, near the coils. The heater should be large enough to maintain a temperature a few degrees higher than the ambient temperature, thereby keeping the motor dry. If it is not possible to use a wire heater that can be inserted inside, a heater or electric lamp can be installed right outside. ⑤ Put the outer end cover back in place. ⑥ Fill the bearing housing with an adequate amount of grease. ⑦ Seal all vents and openings. ⑧ Brush the outer surface clean with a wire brush, then paint it. ⑨ Connect the power supply to the electric heating wire heater. ⑩ Rotate the bearing once a week. If the motor remains on site and continues to be exposed to corrosive and harmful environmental conditions, or when the power supply is unable to operate the electric wire heater, it should be considered to use powder coating for protection or to provide other protective measures to cover it. (2) Transformers: Ordinary-power transformers require only minimal protection during periods of inactivity. Due to the nature of its design and structure, it is relatively insensitive to degradation. Generally, protection should be focused on its outer surface and power connections. Below are the protective measures and steps to take when a transformer is out of service for several months, or even longer: ① Disconnect the circuit. ② Clean all power insulation sleeves with a brush or cloth using a suitable, non-corrosive cleaning solution. ③ Check the porcelain bushing for cracks or breaks, and repair or replace it if necessary. ④ Check the liquid level in the oil and gas filling casing. ⑤ Clean the metal parts, paint them, and apply grease. ⑥ Check the oil level, insulation strength, and impurity content of the transformer oil, and replace it if necessary. ⑦ Clean the outer surface of the fuel tank and check for leaks. ⑧ Install a small air dehumidifier at the breathing outlet or ventilation opening. ⑨ Check all valves and discharge ports to ensure they are closed and leak-free. ⑩ Blow the gas space above the oil surface with dry nitrogen to reduce the oxygen content. ⑪ Clean all external surfaces and coat them with appropriate paint. If the transformer is an unused spare unit, it may remain idle for a long time, and coating it with spray paint as a protective measure should be considered. (3) Power distribution units ① Larger power distribution units are usually enclosed in frames made of thin metal sheets to protect the electrical components from environmental influences. Many power distribution units have a secondary enclosure within the frame of the primary enclosure, to provide further protection for the necessary instruments and control and protection devices. This combination of two outer covers is sufficient to meet the highest demands. For the protective measures required for decommissioned power distribution equipment, only some necessary additions to the conventional protective design are needed. Typically, an electric heater is installed inside a cover to maintain a dry environment, and the external surface is cleaned and painted. If it is impossible to install a wire heater due to a lack of power supply, desiccants can be used for drying. ② Smaller power distribution devices, such as relays, push-button switches, circuit breakers, etc., can be protected by enclosing them in plastic bags. If the cost is not high, powder coating for protection can also be used. The usual maintenance measures such as cleaning, painting, and regular inspections are sufficient for these smaller, inactive devices. An additional measure to take is to place small amounts of chemical desiccants in various packaging bags to keep the devices dry at all times. ③ Many electrical control devices in petrochemical plants are placed inside enclosed enclosures, and the most effective way to maintain these devices is to control the atmosphere within the enclosures to ensure that no corrosive vapors are present. Consider using vapor-phase preservatives placed in a box for protection. An effective and inexpensive method is to use an industrial air-conditioning dehumidifier. The investment in such facilities is minimal, yet their effectiveness and reliability are highly significant. Another approach that could be considered is to install a ventilator to supply air at a slight positive pressure into the enclosed box. The inlet of the ventilator should be equipped with a dehumidifier and a filter. A slight positive pressure can prevent external air from entering, providing safe protection for the equipment. (4) Power lines: It is difficult and time-consuming to maintain decommissioned overhead power lines. Because it is at a high altitude, it is difficult to approach, and it has many components. Inspecting or repairing a single wire or a section of circuit often requires the use of scaffolding or specialized equipment. For overhead power lines, careful consideration must be given to the selection of materials from the initial design stage. Once installed, there are often few longitudinal measures that can be taken for the cable itself. The usual maintenance measures focus on the fittings, stay cables, grounding facilities, poles and brackets, as well as tensioning and suspension components of overhead lines. After metal-clad buried power lines are taken out of use, enhanced inspection and maintenance should be carried out to prevent damage. Once the line is decommissioned, cathodic protection measures should continue to be in use if possible. When a circuit stops operating for a period of time and then resumes operation, an ohmmeter should be used to test its degree of dryness. The test results should be compared with the factory’s specified data to determine the reliability of the circuit. 11. Periodic inspections: For major equipment that is shut down and not in use, in addition to taking necessary measures for protection, periodic inspections must also be carried out to regularly check the condition of these protective measures. The interval for regular inspections is recommended to be between 3 months and 1 year, depending on the type of equipment and the specific operating conditions. To this end, specific inspection intervals should be established for particular equipment through investigations, an inspection plan should be devised, and it should be put into practice. During inspection, it is recommended to clean the protective coatings on the main components of the equipment (such as the compressor’s cylinders, crankshaft, bearings, journal, piston rods, crossheads, etc.) in order to carefully examine their surface condition. If the protection level is satisfactory, the original protective coating can be reapplied to the exposed surfaces as it was before. If the equipment is protected with powder coating, the inspection interval can be appropriately extended based on experience. If rust is found on the device components, they should be wiped clean and dried thoroughly, after which an anti-corrosion coating should be applied again. Periodic inspections of the main equipment must be carried out regularly, so as to detect corrosion and damage to the equipment at an early stage, take timely protective measures to prevent rapid deterioration, and ensure that it remains in good condition at all times.