Analysis On Infrared Detection Of Low Temperature Pressure Vessels Defect And Influence Of External Thermal Excitation

Low temperature pressure vessel is one common form of pressure vessel, it has beenwidely used in process unit of oilfield, natural gas producing and petrochemical process. Lowtemperature pressure vessel is pressure equipment involved in life safety and quite dangerous,dressed with inflammable, explosive, toxic or corrosive media. It also produced the defect ofcorrosion, erosion, wear and tear, stress corrosion cracking, fatigue cracking, materialdegradation with the effect of media, load, temperature and environmental factors in thecourse of using. Therefore, quickly diagnosed pressure vessels defects in the course of usingand timely maintenance of equipment is a key factor to ensure the safety of equipment andpersonnel.In this paper, the heat transfer model of not considering the defects of phase transition incontainer was established according to the principle of infrared imaging nondestructivetesting, heat transfer theory. At the same time numerical simulation analysis was used at theseconditions for different thermal excitation intensity, different heat incentive time, differentenvironmental factors and different parameters of defects which based on control volumemethod. On this basis, the heat transfer model of considering the defects of phase transition incontainer was established according to the basic theory of phase change heat transfer. Thevaporization process of fluid flow in the vessel was simulated under the effect of thermalexcitation and the influence of fluid phase changes for pressure vessel wall surface'stemperatures was studied by using the mixture model of multiphase flow model. The resultsshow that:(1) with the increasing intensity of thermal excitation, the reduced temperature ofpressure vessel surface was increased gradually.(2) with increased excitation time, themaximum reduced temperature trend to rises first and fall later and eventually reduced in thecorresponding reduced temperature of stable state.(3) The wind speed and emissivity inenvironmental factors are of the great influence for the precision of infrared testing. Theinfluence of the environmental temperature can be ignored when detecting the infrareddefects of pressure vessel in atmospheric environment.(4) with the increasing of the defects,the reduced temperature of pressure vessel surface increased gradually, scilicet the bigger ofthe defects area the more likely to be detected.(5) with the increasing of the depth of thedefects, the maximum reduced temperature of pressure vessel surface is decreasing. In otherwords, the shallower depth of the defects to heating surface the more obvious of surface temperature anomaly and the easier to detect. Phase was changed when t=10s of the fluid incontainer and the gas volume fraction increase with increase of the thermal excitation time.Infrared detection to a certain extent was affected when the phase of the fluid in containerchanged.The conclusions of this paper have some reference for defects rapid diagnosis of byinfrared imaging technology the course of pressure vessel using.