| The parameter of intermediate-pressure module of the ultra supercritical steam turbine unit in design has been elevated to 3.286MPa/620℃ which is much higher than that in operation. To satisfy the increased steam temperature and flux, the new lifting intermediate pressure valve will be casted by new high-temperature-tolerated alloy material and its diameter will be enlarged, which will influence the valve’s transient stress in start-up, steady operation and shut-down conditions, fatigue and creep lifespan. Thus, it is in urgent demand to assess the new valve’s fatigue and creep strength and optimize the structure in order to ensure the safe operation of the unit in service period.In the dissertation, high temperature creep strength and fatigue strength of the new large-diameter lifting ultra supercritical steam valve in start-up, steady operation and shut-down conditions is analyzed based on the finite element analysis(FEA) software Abaqus.By introducing the Norton-Bailey creep constitutive equations and multiaxial toughness factor, the temperature, stress and creep strain field during 200000 hours’ steady operation under rated condition is analyzed. The result demonstrates that: stress field will redistribute during steady operation; creep equivalent strain meets the code; contact force between the main valve seat and casing decreases drastically during the later period of the steady operation as a result the main valve should be redesigned; the steam tightness performs well.Low-fatigue field is obtained by following the strain-based MansonCoffin equation and Miner rule. The result shows that: temperature and stress field fluctuates significantly; the contact between the seats and casing is reliable; the new valve’s fatigue strength meets the requirement. Finally, calculation of the coupled damage field is finished by redeveloping in the programming language Python on Abaqus in order to check the valve’s reliability and ensure the safety in service period. |
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