Study On Leakage Monitoring Methods For Bolted Flanged Joint Based On Fiber Grating Technology

Bolted flanged joint,as the dismountable static sealing connection,is widely applied in petrochemical appliances.However,it is also the main source of leakage in petrochemical appliances.In a typical chemical industry,bolted flanged joint takes up about 1/3 of places of highest leakage rate.Therefore,it is necessary to build up an effective method of leakage monitoring for bolted flanged joint.Gasket stress has a great influence on sealing performance of bolted flanged joint.There exist a number of researches on predicting the leakage rate of the joint by means of gasket stress.However,it is difficult to measure the gasket stress during the operation of the joint,which causes that there exists difficulties in monitoring the leakage condition based on gasket stress.On the contrary,it is convenient to measure the bolt force.Hence it is of great engineering importance that research is done about predicting the leakage rate of the joint by means of monitoring the change of bolt force.This paper primarily discusses and analyzes the leakage model of bolted flanged joint.And it also does research on the mathematical model between leakage rate and gasket stress as well as bolt force based on porous medium leakage model,therefore building up the predicting model of the joint.Then aiming at the bolted flanged joint of DN40,this paper carries out mechanical property experiments of gasket and sealing performance experiments,which obtain the mechanical property under ambient temperature and high temperature as well as the data of gasket leakage rate.In addition,it does research on the factors influencing changes of gasket stress and bolt force through analogue simulation.Meanwhile,the simulation results and experiment results are compared.Finally,this paper does the research on the fabrication principle of Fiber Bragg Grating Sensor.In order to verify the feasibility of smart bolt measuring bolt force based on fiber sensor technology,the leakage experiments based on the fiber sensor technology are performed.It also finds out that measuring bolt force through fiber sensor technology has higher sensibility and higher resolution by comparison with measuring bolt force by measuring the elongation of bolt.Meanwhile,the relation model between leakage rate and bolt force satisfies the requirement of predicting leakage rate after verification.This proves that it is feasible to take use of fiber sensor technology to measure or monitor whether the leakage rate of bolted flanged joint is over proof or not.