Maintenance during Steam Boiler Shutdown

Hazards of unmaintained or improperly maintained steam boilers during the shutdown period

1. The corrosion area is extensive and the amount of corrosion products (iron oxide) is large. Corrosion during this period will thin the metal wall, reduce its strength and shorten the service life of the boiler.
2. Aggravate the corrosion of the boiler during operation, resulting in a vicious cycle of corrosion. Due to the large amount of iron oxide produced by corrosion when the boiler is stopped, when the boiler is used again, the above-mentioned iron oxide will all react with the cathode, causing more serious corrosion of the boiler.

Maintenance during the out-of-service period of the boiler

1. The lye method. Fill the pot with a certain concentration of lye and keep the pH above 10.
2. Hydrazine method. The pot is filled with hydrazine (a mixture of H2N2 and ammonia (NH3)). The anti-corrosion principle is to use the strong reducibility of hydrazine to remove oxygen in the water and polarize the cathode. However, the use of hydrazine is restricted due to its toxicity.
3. Organic corrosion and scale inhibitor method. When the organic corrosion and scale inhibitor is used as a maintenance agent for deactivation, the organic phosphorus component in the agent can also dissolve some components in the scale and iron scale of the boiler and the soda system, so that the hard scale becomes a porous and loose structure. At the same time, the agent can penetrate under the scale to form a protective film, which destroys the combination of the metal surface layer and the scale, and makes the scale fall off.
4. Dry maintenance. This method is to drain the water and keep the metal surface dry after the boiler is out of use, or fill with some kind of gas to prevent the intrusion of air, so as to achieve the purpose of deactivation and maintenance. 1) Inflatable method. Generally, nitrogen or ammonia gas in the steel cylinder is charged from the height of the boiler, and the pressure of 0.05-0.1MPa is maintained to force the air with higher density to be discharged from the lowest part of the boiler, so that the metal does not come into contact with oxygen. The maintenance effect of this method is good, but the conditions are strict and the operation process is complicated, which limits the use. 2) Desiccant method. This method uses the characteristics of moisture absorption of desiccant to fully dry the metal surface of the pot, so as to achieve the purpose of anti-corrosion.

Selection principles of three maintenance methods

1. According to the stoppage time, you can refer to the following methods: 1 to 3 months to choose the lye method; more than 3 months to choose the desiccant method, the organic corrosion and scale inhibitor method, and the gas phase corrosion inhibitor method (TH2901), coating method.
2. According to the maintenance object, you can refer to the following methods: long-term maintenance of steam boilers can choose desiccant method, gas phase corrosion inhibitor method (TH2901), lye method, organic corrosion and scale inhibitor method; hot water boiler and water circulation system maintenance can choose the lye method and the organic corrosion inhibitor method, and the hot water boiler should not use the desiccant method.

Maintenance requirements

In principle, the ash, slag, and scale should be removed immediately after the furnace is shut down, and the inspection time should be submitted to the technical supervision department in time, so as to strive for early inspection, early maintenance and early maintenance. Under the premise of conditions permitting, the boiler should be maintained immediately after it is out of use. The advantages are: the water resources in the system and the perfect operation facilities can be used to save manpower and material resources; good water quality and perfect operation system can make the maintenance measures fail. In practice, it achieves the purpose of small dosage, uniform dosage, wide shoe cover, no dead corners, and easy monitoring and adjustment; the maintenance effect is guaranteed, no water is released to prevent the entry of air, and the addition of medicine improves the metal corrosion resistance. In addition, maintenance and inspections should be strengthened, especially in the rainy season.