Numerical Study Of Strength Of Creep And Impact Behavior In A Steam Valve

Structure of the present steam valve is scaled by a steam valve of 660 MW supercritical steam turbine according to a ratio.Thus,the steam valve is compact and the curvature of inside surface of the valve is much higher than the 660 MW steam valve;furthermore,the inlet steam temperature and pressure is higher than those of the steam valve with the same capacity.In order to reduce the manufacture cost,the material of the steam valve is not changed and the wall thickness is reduced to meet the requirement of quick startup.The creep and impact behavior become the main factors in the design of the steam valve.In the present study,creep behavior and impact behavior in the high temperature are numerically studied by using commercial software ABAQUS.Norton-Bailey equations and multi-axial toughness factor are used to analyze the strength.For three conditions(pressure,pressure and temperature,and 200,000 hours creep),the numerical calculation is performed.The results show that stress concentrates the location at the valve seat,valve disc,and area between diffuser and valvebody.Due to the temperature and temperature difference,stress decreases;further decrease in the stress is caused by the 200,000 hour creep behavior.The contact stress at these locations could causes the failure in the component and reduce the efficiency due to the steam leakage at the area between diffuser and valve body.Especially,assessment on the performance of sealing at diffuser shows the sealing performance decreases to the dangerous level.The calculated results for the impact behavior display that the contact stress suddenly increase to the peak at the contact point and decreases to the low value along the contact surface.Especially,closer the distance of the location to the contact point is,quicker the decrease in the contact stress is.Most of impact energy,in fact,is absorbed by the contact area.The impact between the rod and the valve disc shows that the stress concentrates the part between the rod head and the rod,and it would cause the premature failure.In addition,in the present study,in order to improve the design efficiency,simplified design method is necessary needed.Thus,2D and 3D models are used to describe the impact behavior.The results show that the difference between two models under the normal impact speed is small,and as the impact speed exceeds the normal speed,the difference is significant.The discrepancy is further enlarged as the impact speed further increases.Finally,the comparison of the impact behavior between theoretical method and numerical method is carried out.The results that the calculated results by the theoretical method reaches good agreement with that by numerical method under the low impact speed.For the higher impact speed,the safety margin should further studied.