The occurrence of boiler tube burst seriously affects the safety of the boiler and the economy of the unit operation. Very likely to cause injury to operators, the following Shandong Gas Boiler Factory will summarize the causes of the boiler tube burst, I hope you pay more attention to it, to help you all!
(1) The operation of the boiler is improper, and the heating or cooling of the furnace tube is not uniform, resulting in greater stress.
1) When the cooling furnace feeds water, the water temperature or feeding speed does not conform to the regulations; when starting, the speed of temperature and pressure rise or load increase is too fast; when stopping the furnace, the cooling rate is too fast.
2) The cyclical change of working pressure leads to the cyclical change of mechanical stress during start-up, shut-down or off-design operation of units; meanwhile, the thermal stress of high-temperature steam pipes and components due to temperature alternation causes the fatigue damage of pressure components.
(2) In operation, the steam temperature exceeds the limit, which makes the pipe overheated and the creep speed accelerated.
1) Overheating and overheating.
Overheating can be divided into two categories: long-term overheating and short-term overheating. Long-term overheating tube explosion refers to metal explosion under long-term stress and overheating temperature. Its temperature level is much lower than that of short-term overheating, and usually does not exceed the critical temperature of steel.
Overtemperature refers to the operation of metals above rated temperature. Overtemperature can be divided into long-term overtemperature and short-term overtemperature. Long-term overtemperature and short-term overtemperature are relative concepts without strict time limit. Overheating refers to operation, and overheating refers to explosion.
Short-term superheated tube blasting refers to the high temperature level of tube blasting under stress in a short time due to the increase of tube temperature, which usually exceeds the critical point temperature of steel, leading to the transformation of metal structure.
2) thermal deviation
The main factors affecting thermal deviation are uneven thermal stress and hydraulic pressure.
3) Deterioration of heat transfer
The first type of heat transfer deterioration, also known as membrane boiling, refers to the deterioration of boiling heat transfer caused by the excessive heat load outside the tube and the formation of vapor film on the tube wall.
The critical heat load corresponding to the deterioration of the first type of heat transfer is very large, and large utility boilers generally do not occur.
The second type of heat transfer deterioration is that the annular flow of water film in the tube is torn or "steamed dry". The heat load of type II heat transfer deterioration is lower than that of type I heat transfer deterioration. Because there is no obvious boundary point in three stages of heating, evaporation and overheating, the vapor content x of working medium gradually rises from 0 to 1, and the second type of heat transfer deterioration is inevitable.
The deterioration of boiling heat transfer on evaporative heating surface of once-through boiler is mainly related to mass flow rate, working pressure, vapor content and heat load outside the tube.
(3) Wear of heating surface
The wear of the heating surface is caused by the erosion and impact of the ash-containing air flow on the heating surface. The wear rate of heating surface is directly proportional to the cubic power of air velocity and fly ash concentration. It is related to the arrangement of pipes and the wear resistance of pipes. At the same time, the hardness, shape and diameter of fly ash are also factors affecting the wear rate of heating surface.
Wear of heating surface is the main cause of tube burst of economizer.
(4) Corrosion of heating surface.
1) High temperature oxidation corrosion in furnace tube. The oxidation rate of iron ions in heating surface tubes is accelerated with the increase of heating surface temperature at a certain temperature. When the temperature is higher than 580 C, the oxide layer of inner metal wall of furnace tubes is composed of three oxides: FeO, Fe2O3 and Fe3O4, and the oxide FeO near the metal is the main part of the oxide layer.
2) Scaling and corrosion in furnace tubes. The poor quality of feed water and the poor quality of furnace water cause scaling in the furnace tube, and corrosion under scaling easily occurs after scaling. At the same time, scaling increases heat transfer resistance, increases wall temperature, weakens strength and bursts occur.
3) High temperature bonding ash and high temperature corrosion of heating surface. In high temperature flue gas environment, fly ash deposits on the surface of heating surface pipes. The harmful components (compound sulfate) in flue gas and fly ash will react with the metallic elements of pipes, making the pipe wall thinner and the strength lower, which is called high temperature corrosion.
4) The quality of manufacture, installation and overhaul is poor. If the pipe or pipe steel number is wrong, the quality of the pipe weld is not qualified, and the pipe wall at the elbow is seriously thinned.
This is the content of the pure dry goods introduced to you today. I believe that today's content can bring some help to the crackdown. If you still don't understand the content of this article, you are welcome to click on our official website to discuss: Shandong Gas Boiler http://www.mjingoma.com.