Estimation of creep of the turbine control valve body at increased steam temperature

Abstract

The influence of the temperature of the supplied steam on the operating and strength characteristics during creep of the control valve body of the steam turbine K-325 is considered. Currently, the valves are operated with steam supply with a pressure of 24 MPa and a temperature of 540°C. The analysis of the effect of increasing the temperature of the supplied steam up to 565°C. The study was carried out in connection with a possible increase in steam temperature to increase the power of the turbine. The temperature and pressure of steam on the walls of the vessel are determined based on the numerical solution of the Navier-Stokes equations in a three-dimensional setting. It was found that an increase in the temperature of the supplied steam has little effect on the nature of the distribution of temperature and pressure on the walls of the valve body. Temperature fields and steam pressure on the walls of the valve body are used to further solve the problems of the strength of the control valve bodies of the K-325 turbine in a stationary mode of operation. The stress-strain state of the valve body of a steam turbine in a stationary mode of robots is numerically determined. The problem was solved by the finite element method in a three-dimensional setting. The results showed that the maximum elastic stresses on the outer surfaces are observed in the region of the upper transition of the inlet pipe. On the inner surfaces, the maximum values of elastic stresses are observed in the area of the branch pipes in front of the control valves. It was determined that an increase in the temperature of the supplied steam up to 565°C insignificantly affects the stress state of the valve body. The creep of the body was calculated using a model of implicit creep with hardening, taking into account the variable and constant creep components. The influence of the temperature of the supplied steam on the creep of the valve body is estimated. The results indicate that an increase in the temperature of the supplied steam by 25°C leads to an increase in creep deformation by a factor of 2.3 after 200 thousand hours of operation. Temperatures, pressures, and equivalent stresses are plotted at the body surfaces and creep curves are plotted at 540°C and 565°C.