Research On Digital Test Technology Of Sealing Performance Of Safety Valve

The safety valve is a safety protection device for overpressure and automatic discharge.It is widely installed in various types of pressure equipment.The stability of the mechanical structure and the reliability of the seal are directly related to the normal operation of the equipment.According to the requirements of safety valve safety technical supervision regulations formulated by our special equipment industry,all safety valves must be checked at least once every year at the check station of the safety valve.The purpose of the safety valve seal performance test is to detect the leakage.And the leakage rate is expressed by the number or volume of the bubble per minute.At present,the air bubble method and test device recommended by API Std527 are commonly used.This method is simple in structure,but is poor in operation,easily affected by actual conditions,easy to produce error and low working efficiency.In view of these problems,a new type of digital test system for sealing test of safety valve is put forward in this paper,which combines sensing technology,microcomputer control technology and computer technology.The main contents and innovations of this paper are as follows:(1)The test mechanism of the bubble method for the seal test of the safety valve is studied,and the relationship between the size of the bubble and the flow of the gas is theoretically analyzed.In addition,the influence of different factors(gas flow rate,inner diameter and water temperature of pipe)on the accuracy of bubble method is further studied through comparative experiments.Through theoretical analysis and experimental verification,it is found that under the condition of the"bubble method"of the safety valve seal test,the size of the bubble generated in the water is very weak by the gas flow rate(0-30cm~3/min),but is greatly influenced by the inner diameter of the pipe and the water temperature.This indicates that the bubble method is feasible,but it is easy to be influenced by the test conditions and the actual working conditions.(2)According to the technical requirements and performance indexes of the safety valve seal test in the relevant standards,the whole scheme of the digital test system for the seal test of the safety valve is put forward,that is to use the direct measurement of the leakage gas flow method instead of the indirect number bubble method,and to build the whole body frame.On this basis,the main hardware is designed.a special cover for safety valve seal test,which is used to block the outlet of the safety valve and collect the leaking gas.(3)Based on the modern sensing technology and the microcomputer measurement and control technology,a data acquisition system of the lower computer is studied.The signal measured by the gas flow sensor is collected by the single chip microcomputer,and the signal is converted to a digital signal,and then it is sent to the computer management system by RS-232 serial communication.The hardware part of SCM system is mainly composed of power supply circuit,basic circuit,data acquisition circuit,serial communication circuit and emergency circuit.(4)A computer management system for sealing test of safety valve is studied,including database and management software.A special safety valve seal test database has been set up in the SQL Server 2008 database system,which is used to store basic information and test data.The developed management software can realize the functions of information entry of the security valve,the generation of check tasks,automatic test and real-time display,automatic preservation of the result data,task audit and report generation.(5)The digital test system of the safety valve seal test in this paper can realize the automatic detection of the leakage gas.It can directly measure the volume flow of the leakage gas and turn it into the numerical value under the condition of the standard,eliminating the influence of the different working conditions on the measurement accuracy.After the test,the data of the test results are automatically stored in the database of the seal test,which is convenient for the later task audit and report generation,thus realizing the digitalization,automation and paperless of the seal test of the safety valve,reducing the manual error and greatly improving the efficiency of the check personnel.