Fracture Failure Analysis of Drain Pipe Elbow in Reheating Section of Ultra Supercritical Unit
In order to study the cause of fracture of the drain pipe elbow in the reheating section,the drain pipe in the reheating section of the B side of a 1000 MW ultra-supercritical unit in a thermal power plant is taken as the research object,and the macroscopic morphology,microstructure,hardness and mechanical properties of the fracture site of the bend and its nearby locations are analyzed(drainpipe material:P92,specifications:φ38.1 mm×5 mm,the working temperature:603℃,the working pressure:4.79 MPa).The results show that:on the one hand,the temperature of the drain pipe changes repeatedly,the expansion and contraction of the drain pipe wall are constrained to a certain extent,resulting in thermal stress cycle,fatigue damage of the drain pipe elbow,thermal fatigue cracks.On the other hand,there are pits on the outer wall of the elbow,and where cracks are easy to occur.At the same time,the hardness value of the elbow position exceeds the standard upper limit,which reduces the deformation resistance of the elbow.In the process of discharging the condensate water,the load change of the unit and the intermittency of discharging the condensate water lead to the change of the medium velocity,and the obvious vibration at the elbow leads to the further development of cracks at the elbow until the fracture.
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