| In the thermal power industry,the safety of heating surface tube is very important.According to the statistics,the accidents caused by the explosion of tube heating surface and the failure of other metal materials were accounted for more than 50% of all the non-planned outage.Non-planned outage and failure will result in huge economic losses and personnel damage,and also have a huge impact on social production.In the long-term servicing environment,the organization of steel will inevitably degrade which will lead to the change of its macroscopic properties and microstructure.And the probability of explosion will increase with serving time.Due to lacking the fast and effective monitoring technology,the heating surface tubes were often replaced to reduce the explosion accident rate.The existing heating surface failure detection technology has its own limitations.These limitations include high requirements of the testing environment and cannot predict the failure state of heating surface.Laser-induced breakdown spectroscopy(LIBS)is based on atomic emission spectroscopy and developed in recent years.It can analyze the content and composition of the object.This analysis technique has a plenty of advantages such as slight destruction,rapid speed,multielement synchronous detection,long-distance and non-contact analysis.Meanwhile,LIBS exists obvious matrix effect.Therefore,the matrix effect is unfavorable factors for the traditional quantitative analysis.However,the existence of matrix effects can reflect the characteristics of the substrate material to a certain extent.In this paper,we try to introduce the LIBS technology into the detection of boiler heating surface in power plant by the matrix effect.To provide theoretical basis for the development of high temperature failure trend prediction and analysis technology of boiler heating surface,LIBS is used to detect the heating surface tube of the power plant,and the characteristics of the object can be reflected by the plasma characteristics.In this paper,the failure trends of heating surface were reviewed.The background and significance of this paper were expounded.And commonly nondestructive testing methods which used in heating surface failure analysis were introduced.The development of LIBS was expounded.And the research contents of this thesis were expounded in detail based on the research of LIBS in metal materials and the study of matrix effect.The principle of LIBS and the physical properties of plasma were described.A set of LIBS experimental device which can be applied to heating surface with different diameters was set up.At the same time,in order to understand the main research object of 12Cr1 MoV and T91 steel,the characteristics and failure mechanisms of 12Cr1 MoV and T91 steel are described in detail.The plasma characteristics of 12Cr1 MoV with different microstructure were analyzed by using monochromator and oscilloscope.Some characteristic lines which were selected by the contents of 12Cr1 MoV steel were used for comparative analysis.The plasma time evolution characteristics of ion and atomic lines in the same element were compared.The plasma time evolution characteristics of different microstructure 12Cr1 MoV steels were also analyzed.The relationships between the plasma strength and the microstructure were also analyzed.Meanwhile,the relationship between the intensity ratio of the ion and the atomic lines and tensile strengths were established.The plasma time evolutions of T91 with different carbide particles were analyzed.The plasma characteristics of T91 with different tensile strengths were analyzed.PCA analysis method was used to distinguish T91 steels with tensile strengths.The relationship between the line intensity and tensile strengths were established.At last,T91 steels with different aging grades were studied by LIBS.The relationship between the plasma characteristics(the plasma temperature,the electron density,and the plasma spectral intensity)and the aging grade were analyzed.The relationship between the intensity ratio of the ion and the atomic lines and the aging grade were established.Meanwhile,the peak intensity ratio of the alloying element to the matrix element was used to build the relationship with aging grade and hardness.There was a good linear relationship between the intensity ratio of Cr/Fe,Mo/Fe and the aging grade was found.A theoretical foundation was built for predicting the failure development trend of heating surface by using LIBS technology as a new way. |
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