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The surface of the boiler is subject to long-term operation under the action of high temperature, pressure and corrosive media. When the steel of the boiler tube cannot bear the load of its working state, different forms of damage will occur and cause accidents. The common accidents of the heating surface tubes of boilers in thermal power plants are mainly the following types:
1. Long time over temperature burst tube
Over-temperature refers to the operation of metal materials at temperatures exceeding the rated temperature. Rated temperature refers to the maximum allowable temperature of the steel during its design life, and it can also refer to the rated temperature during work. As long as one of the above temperatures is exceeded, it is over temperature operation.
2. Short-time over-temperature burst
During the operation, the heating conditions of the boiler's pipes deteriorated due to cooling conditions and dry burning, which caused the tube wall temperature to rise suddenly in a short period of time, the temperature reached above the critical point, the tensile strength of the steel dropped sharply, the pipe stress exceeded the yield limit, and shear fracture occurred and burst This type of tube is called a short-time over-temperature tube.
3. Tube burst caused by poor material
Blasting of poor material refers to the early damage to the pipe caused by the wrong steel or the use of defective steel. If the material itself has defects such as cracks, severe decarburization, or inclusions, or when steel pipes with folds, scars, and cracks are used during installation and maintenance, the strength of the pipe will be severely weakened, and the defect parts are prone to stress during high temperature operation. Concentration, which causes cracks to expand and defects to expand, leading to tube bursts.
4. Corrosive thermal fatigue crack damage
The vapor layer of the boiler heating surface tube, the economizer tube steam plug, the super-heater with water, and the temperature-reducing and pressure-reducing valve gap opening will cause temperature fluctuations, cause alternating thermal stress and thermal fatigue cracks. In addition, under the action of corrosive media, fatigue cracks on these pipes are particularly easy to occur in notched areas with high corrosion rates such as rough surfaces, scratches, and corrosion pits, so they are called corrosive thermal fatigue cracks.