Research On The Sealing Performance Of The Middle Flange Of Gate Valve In The Primary Circuit Of Nuclear Reactor

The gate valve is an important equipment in the primary circuit,which is widely used in nuclear power and marine nuclear power plant.The working environment of the primary circuit is high-temperature,high-pressure and radioactive.Influenced by various factors,the changed material properties will bring stress relaxation to the middle flange sealing pair in the gate valve,which will lead to leakage accidents.Thus,to avoid leakage accidents,take reasonable optimum measurements on the middle flange sealing pair in the gate valve is an important research direction in present nuclear industry.In this paper studied the sealing performance of nuclear grade valve through the preloading methods and preloading force of gasket-free flange sealing structure,experimented to get the test date of bolts to guarantee the correctness of finite element analysis in factory,proposed the best preloading method of flange bolt on strain electrical measurement and elastic interaction,established the scope of preloading force which guarantee the middle flange sealing performance through the analysis of steady-state thermodynamic and transient-state thermodynamic.The paper’s main tasks are as follows:(1)Summarized the current situation of flange sealing researches and introduced several factors which influenced flange sealing performance.Aimed at the high-temperature and high-pressure environment which gate valve middle flange were in and combined with flange sealing measurements which usually take at home and abroad these years,this paper used preloading force and preloading methods as main influence factors to improving the sealing performance of the middle flange.(2)An experimental apparatus of bolt pretension is built up,based on strain electrical measurement and elastic interaction principle,to test three different preloading methods of mini gasket-free middle flange sample.By comparison of three experimental data,the best preloading method of middle flange is obtained.(3)Through the experiment to the prototype of middle flange in factory,tested the date of the stress of bolt in different torque and in working pressure,provided the experimental basis for the validity of the finite element results.(4)Trough the steady-state thermal analysis and steady-state coupled-physics analysis(which based on ANSYS)of theoretical-calculated preloading force of bolt,this paper verified whether the theoretical preloading force can guarantee the sealing performance under the steady working environment and concluded the temperature influence on sealing performance.(5)Based on the transient thermal analysis,this paper concluded the leakage reason and optimized preloading force through making transient thermal analysis and transient coupled-field analysis on middle flange sealing pair with theoretical preloading force.This paper also used allowable sealing pressure and the allowable stress as of bolts optimizing condition to conclude the minimum and maximum preloading force to guarantee sealing and verify sealing performance and strength requirements.