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In boilers that have been shut down, moisture and water accumulate inside the boiler, while the exterior of the boiler is subject to erosion and rusting caused by soot and slag. If proper maintenance is not carried out, corrosion during the shutdown period is often more severe than when the boiler is in operation. So how should a boiler be maintained after it is taken out of service? According to the technical staff at Mingyuan Petrochemical, the maintenance work after a boiler is shut down involves anti-corrosion measures for both the outside of the boiler unit and its interior. For the anti-corrosion maintenance of the boiler, there are two methods: dry maintenance and wet maintenance, depending on the duration of shutdown. When a boiler is not in use for an extended period, special attention should be paid to the anti-corrosion maintenance of the outside of the boiler. First, after the boiler is shut down and cooled, it is necessary to thoroughly remove the ash accumulated on the heating surfaces, as well as the ash and slag from above the grate and below the boiler body. Then, it is necessary to maintain a certain level of natural ventilation in the flue. Under normal circumstances, desiccants should be placed in the furnace and flue to prevent moisture. If quicklime is used as a desiccant, approximately 3 kg should be placed per cubic meter of the furnace or flue. All ventilation doors should be tightly closed after placement. Quicklime needs to be replaced once it turns powdery. If the boiler room is located in a low-lying area and the floor becomes severely damp during shutdown, a combination of regular low-heat drying and the use of desiccants should be employed. If the boiler is out of service for a long time, after thoroughly removing the soot, apply red lead oil or other anti-corrosion paint to the outer surface of the boiler’s metal. As for the anti-corrosion maintenance methods for the furnace when it is shut down inside, they depend on the length of time the furnace remains shut down. Under normal circumstances, wet maintenance can be used when the shutdown lasts no more than a month; dry maintenance should be employed if the shutdown exceeds one month. When performing dry maintenance, the following points should be noted: The desiccant should not come into direct contact with the metal surface of the boiler; it can be placed in containers such as iron trays ； After placing the desiccant, seal the handholes and other coverings tightly; the valves on the steam and water pipes must be closed ； Quicklime that turns to powder should be replaced promptly. When using wet maintenance methods, it is important to note that condensate water is the best choice for the boiler water; followed by the existing boiler water, with softened water being an alternative option ； After adding alkali, the boiler water is heated to 80–100°C using a low heat source; once the pressure rises to 2–3 bar gauge, it is maintained at this level for 2–3 hours to allow the alkalinity of the boiler water to become uniform. When the pressure drops, the boiler water is refilled to achieve a pressure of 1.5–4 bar gauge, and this pressure is maintained throughout the maintenance period. The alkalinity should be tested regularly, and if it decreases, it must be replenished promptly ； In winter, when using wet maintenance methods, it is important to take precautions against freezing, especially in the waste discharge channels and the economizer sections ； Before the boiler is reused, all the alkaline water inside it must be drained; it is advisable to have a storage tank available for reuse. It must also be rinsed with clean water.