Leak Detection Research Based On Infrared Thermal Imaging Technology

Pressure vessel, boiler, special valve and pressure piping all need to bear extreme conditions of temperature and pressure, which can be classified as pressure-bearing equipment. The hidden danger of leak may lead to a huge threat of economy and property safety of people, so there is no doubt that the importance of pressure leak detection of pressure-bearing equipment before delivery. The current leak detection ways are crude that rely on human eyes and pressure gage, not only the poor safety and low efficiency, but the process of high-pressure gas leak detection may happen safety accidents. Besides, present testing instruments and systems could not achieve automation and parallel leak detections. Thus, it is urgent to pursue a new convenient, economical and safe method for leak detection. This paper is based on the infrared thermal imaging technology for guidance, probing the leak positions through infrared thermal imager, analyzing the unique infrared characteristics of leak positions, and researching the system design method and feasibility of the infrared thermal imaging technology applied to leak detection. Special works contain the following points:1) According to the basic theory of infrared radiation and the temperature measuring principle of infrared thermal imaging, this paper derived the temperature measurement model of uncooled infrared thermal imager, pursued the temperature measurement problems of infrared thermal imaging, and established relations between emissivity and radiation temperature, real temperature.2) This paper established steam leakage physical model, on the basis of wet-steam model paper introduced porous media in leak path to simulate temperature distribution of outer wall when wet-steam leakage. Changing the resistance coefficient value of porous media to conduct the leakage, paper researched the outer wall temperature distribution under different leakages. And we pursued flow and heat transfer method when steam leakage via unsteady numerical analysis.3) Based on the temperature measurement model, we set the leak detection model. Radiation temperature was regarded as the research object, paper raised the method of radiation temperature dot matrix subtraction under the condition of two different heating mode in approximate real temperature. Paper has validated the feasibility of infrared thermal imaging technology applied to leak detection. We also proved the leak detection model through processing the real leak point and false leak point of high emissivity. With the help of MATLAB to draw temperature distribution isothermal figure, we can accurately judge the location of the leak point compared with visible light image.4) According to engineering practice, we have optimized and improved the testing principle of leak detection system, putting forward two heating processes of the high temperature and pressure steam. And the technological process system was established. Experiment has proved the improved system testing principle, and concluded half quantitative leakage analysis. Paper established the object-oriented data post-processing system, achieved VB to call MATLAB based on ActiveX technique, and completed the data processing and pseudo color mapping.