Reason and repair method of TRT blade damage

1、 Cause of damage
TRT (furnace top pressure recovery turbine) works in a lot of harsh environment such as smoke, corrosive gas and washing water. In addition, the gas directly discharged from the furnace top contains untreated clean dust, which will cause sharp wear and corrosion on rolling blades and stationary blades. At the root of blades, losses and cracks are often caused by erosion and corrosion.
1. Scour effect of airflow
Because of the erosion effect of smoke and dust on rolling blades, with the increase of the working time of the unit, the moving blades on the rotor and the static blades on the stator will be gradually lost. Finally, the mechanical function of the blade will be reduced (the thickness of the blade will be reduced by more than 4%), and the decline of the function can be determined by analyzing the working data.
2. Corrosion of media
In the vicinity of the blade root, along with the loss caused by gas, water vapor corrosion and corrosion, if the blade strength decreases and the dynamic and static natural oscillation frequency changes lead to resonance, cracks may also occur at the stress convergence part of the blade root and continue to expand.
Corrosion of embedded part of rolling blade. The rolling blade and the embedded part of the blade are fixed by the method of axial penetration in a triangular shape.
In design, there is a gap between the root piercing part of the rolling blade and the embedded part of the rotor. Therefore, during the working process, the gas will enter into the gap, causing partial corrosion and further cracking. In this case, if the blade works for a long time, the blade will have the risk of cracking and causing major accidents.
In order to check the blade loss and whether there are cracks, it is necessary to carry out sufficient inspection and anti-corrosion treatment, about 30 days of construction period is required, but the general annual regular maintenance period is only about 20 days. Therefore, the actual situation is that the inspection on the cracks that may cause major accidents in the future is not complete. The general method is to check the magnetic particle inspection and the frequency of blade device after cleaning the blade surface by the rotor.
2、 Repair method
1. Wear resistant treatment of cermet coating was carried out on the surface of TRT rolling blade and stator blade, and then dried, demagnetization, electrical error test and correction were carried out, and dynamic balance test was carried out.
2. The embedded part of moving blade. In the parts with pitting corrosion, there is the possibility of cracking at the stress concentration part at the bottom of pitting corrosion, which needs to be removed by grinding. After removing the pitting corrosion, magnetic particle inspection and ultrasonic testing are carried out. Therefore, the rolling blades should be pulled out regularly and coated from the beginning.
However, the dry TRT should be coated with silicone resin at the gap to avoid the invasion of smoke and dust. There are two ways of coating, one is to brush the film, the other is to bury the whole gap by filling. As for the invasion of smoke and dust, although the filling coating has a better avoidance effect, it needs a longer repair period than the film method.
3. Spare blades. The TRT can be restored by replacing the spare blades when problems are found in the inspection, which has the advantages of shortening the maintenance period. Moreover, the disassembled blades can be free from the constraints of regular maintenance period, so they can spend time on fine correction and coating treatment with outstanding anti-corrosion effect.

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