Regardless of whether it is a steam boiler or a hot water boiler, when the boiler is in a normal state, the water inside the boiler should be cleaned. If the inner surface of the tube is wet, especially the outside air enters, it will cause the oxidation and corrosion of the metal on the inner surface. In order to prevent the occurrence of this kind of corrosion, the boiler must be maintained after shutting down. If maintenance and corrosion protection are not done after the boiler is shut down, it will cause metal corrosion, accelerate the oxidation speed, destroy the material of the metal lattice, reduce the service life of the boiler, and easily cause the boiler to burst.
1. The steam pressure method can be used for anti-corrosion and shutdown backup time of no more than 5 days. After the boiler stops supplying steam, all holes and doors should be closed tightly to reduce heat loss, slow down the drop in steam pressure, and maintain the drum pressure above 0.5MPa. When the pressure of the steam drum is lower than 0.5MPa, it should be ignited to increase the pressure, or the steam pressure of the adjacent furnace should be used to maintain the steam pressure.
2. Feed water overflow method anticorrosion after shutting down the furnace, transfer to standby or deal with non-pressure parts defects, and the shutdown time is about 30 days. This method can be used. After stopping the furnace, wait for the steam pressure to drop to 0.5.
3. Within 1 week of normal shutdown of the furnace, use an autoclave furnace to drain water and dry by residual heat. The cost is low.
4. Nitrogen protection. After stopping the furnace, replace the working fluid (water or steam) with nitrogen to maintain the pressure. Disadvantages: difficult to operate and difficult to maintain pressure.
5. Intermittent ignition to maintain pressure and temperature to prevent corrosion. Restricted by conditions, the waste is large.
6. Local antiseptic with medicine. (The water wall and superheater can be filled with water, and the medicine can be added according to the requirements.) The anti-corrosion time is long and difficult to control.
We can also start maintenance according to the maintenance method proposed by each boiler manufacturer
1, pressure maintenance
When the furnace is shut down for less than one week, pressure maintenance can be used. That is, before the shutdown process is terminated, the steam and water system is filled with water, the residual pressure is maintained at (0.05~0.1) MPa, and the boiler water temperature is maintained above 100 ℃, which can prevent air from entering the boiler. The measures to maintain the pressure and temperature of the boiler are: heating by steam from an adjacent furnace, or heating by this furnace on a regular basis.
2, wet maintenance
When the boiler is out of service for less than one month, wet maintenance can be used. Wet maintenance is to fill the boiler's steam and water system with soft water containing lye, leaving no steam space. Because the aqueous solution with appropriate alkalinity can form a stable oxide film with the metal surface, thereby preventing the corrosion from continuing. During the wet maintenance process, a micro-fire oven should be used regularly to keep the outside of the heated surface dry. Turn on the pump regularly to circulate the water. Regularly test the alkalinity of the water. If the alkalinity decreases, add lye appropriately.
3, dry maintenance
When the boiler is out of service for a long time, dry maintenance can be used. Dry maintenance refers to the method of putting desiccant in the pot and furnace for protection. The specific method is: after stopping the boiler, drain the pot water, use the residual temperature of the furnace to dry the boiler, remove the scale and slag in the pot in time, then put the tray with desiccant into the drum and on the grate, and finally close all Valves and manholes, hand-hole doors. Regularly check the maintenance status and replace the failed desiccant in time.
4, inflation maintenance
Air charging maintenance can be used for long-term shutdown maintenance. After the boiler is shut down, do not release water, keep the water level at the high water level, take measures to deoxidize the boiler, and then isolate the boiler water from the outside world. Blow in nitrogen or ammonia to maintain the pressure after inflation at (0.2~0.3) MPa. Since nitrogen can generate nitrogen oxide with oxygen, oxygen cannot contact the steel plate. Ammonia dissolves in water to make the water alkaline.
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