The enclosure wall superheater of a power plant leaked during operation.In order to find out the reason,the leakage pipe samples were examined by macroscopic morphology,metallographic analysis,scanning electron microscopy energy spectrum analysis and hardness test.The test results show that the average hardness of sample No.1,No.2 and No.3 are higher than the upper limit required by the standard.There are clear fatigue stripes parallel to each other on the crack section,and the crack extends from the outer wall to the inner wall.The analysis shows that the pipe sample expands to the base material of the tube after the fin weld cracks.Under the long-term action of pipe vibration,boiler start and stop,load change and other factors,the base material of the tube was fatigued and cracked until the leakage occurred.
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