1 The cause of the crack is caused by the material problem. The first, second and third stages of the desuperheater cylinder are 12CrMV, 12CrlMoV and 12CrlMoV respectively; the bolts of the first, second and third stage desuperheaters are 25 steel, 12CrlMoV and 12CrlMoV respectively, and the bolts are used for the thread of the desuperheater cylinder. Fix and support the mixing cylinder inside the desuperheater. In order to prevent the bolt from falling off, a welding process is applied between the bolt and the outside of the barrel. Since the desuperheater barrel is made of alloy steel, its welding performance is poor.
Welds such as chips, rust, and slag inclusions are not cleaned.
The quality is not strictly controlled during the welding process.
The heat treatment was not performed before and after welding according to the drawings.
The bolts were not assembled according to the process required by the drawings, resulting in uneven force on individual bolts. In addition, the mixing cylinder inside the desuperheater is subjected to the impact of the desuperheating water, so that the bolt fillet weld with uneven force is prone to crack.
The design of the bolts is not reasonable after welding.
The bolt fillet welds were not color tested before leaving the factory. The defects in the welding were not treated in time (the infrastructure installation unit found that the individual bolt fillet welds on the desuperheater leaked when the water was pressed against the boiler in the cold state, and only the repair work was performed on the leak).
2 Treatment Process and Method Use a grinding wheel or other tool to remove the scale of the leaky fillet weld surface. And iron filings, rust, slag, etc. between the bolt and the thread until the metallic color is exposed.
Use magnetic particle inspection or color inspection to check the cracks in the fillet welds of the bolts to determine the number of leaks. During the first pass of the welding process, the welds at the threaded joints should be thoroughly cleaned before the second pass of welding. Don't be too fast.
3 Treatment results and existing hazards After the treatment by the above-mentioned processes and methods, the hydrostatic test was carried out to check the spot welds of the desuperheater bolts and no leak points were found. The effect of the treatment is satisfactory.
If this defect is not handled in time, over time, the fixing bolts, fastening bolts and support bolts will change from leaking to falling off, which poses a hidden danger for the safe operation of the desuperheater.
At present, our factory has welded the 77 bolts on the furnace desuperheater and the 22 bolt fillet weld cracks on the 3 furnace desuperheaters. Temporarily avoiding the potential hazard of the desuperheater due to the cracks in the fillet welds on the desuperheater (the design of the structure is difficult to change). In the future, it is necessary to strengthen supervision and inspection of the desuperheater of the superheater to ensure the safe operation of the desuperheater and prevent accidents from desuperheating.
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