超临界机组汽轮机中压主汽门螺栓断裂原因分析

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Abstract： Asystematic study wasconducted onthefracture accident of Inconel Alloy783 bolts in the intermediatepressure main steam valve of a 66oMW ultra-supercritical unit.During the operation of the unit，29 intermediatepressre main steam valve bolts fractured，with the fractures mainly concentrated at the thread root of the stud end.Through research methods including macroscopic morphology observation， metallographic structure analysis，scanning electron microscope （SEM） detection，and mechanical property testing，the folowing findings were obtained： Bolt No.16 exhibited intergranular fracture characteristics，with a "rock candy-like" fracture morphology，a microhardnessof 370-375HBW （exceeding the relevant standard limits），and obvious oxidation in the crack propagation zone; Bolt No.18 showed transganular-intergranular mixed fracture，initiating at the stressconcentrationzoneof thethreadroot，withatransitioncharacteristicoffragmented grainzones duringcrack propagation.Finite element analysis showed thatthe stressconcentration factoratthe thread root reached3.2，and excesive preload was the keyfactor inducing crack initiation.Basedontheresearchresults，improvement measures were proposed，including optimizing the preloading process，modifyingthe thread structure，and prioritizing the use of new materials such as 1Cr11Co3W3NiMoVNbNB.These measures provide important experimental basis for the selection design and service life evaluation of high-temperature fasteners in ultra-supercritical units.

Keywords：ultra-supercritical;steam turbine;intermediate pressuremainsteamvalve;bolt fracture;failureanalysis

1 序言

某电厂3号机组容量为660MW，汽轮机型号为N660-25.0/600/600 。（剩余4365字）