Welding Seam Of Unequal Thickness Drum Of Utility Boiler Based On TOFD Research On Detection Technology

As power plant boiler drum is one of the core components,and constantly under complex stress,and various alternating stress on drum quality put forward the stringent requirements,in reality,because of the drum is extremely high,volume is very large,the cost of a hoisting process difficult factors,such as drum,once installed,basically no longer be replaced,until it is retired.Therefore requires the drum as far as possible,no case of damage or failure during the service,otherwise,once the damage or failure,A series of serious accident will happen,caused heavy loss of the social economy of our country,How to adapt to the requirements of the new era,it is very necessary to improve the existing method of detecting the weld quality of pot barrel,especially the drum welding of different thickness,most of the conventional type A test method of the traditional ultrasonic testing,not only spend time is long,affect the economic benefit of power plant,the main disadvantages is due to the different thickness of structure more restrictions,inspection blind area and even unable to detect problems,as well as to the defects of qualitative is difficult,defect detection rate is not high.Ultrasonic time difference diffraction method in Europe,America,Japan and other developed countries has been widely used,was introduced into our country in recent years,at present,the domestic well-known professional journals published papers,most of the diffraction of ultrasonic jet lag detection technology in the application of drum manufacturing stage,while TOFD in drum with different thickness during the battle of little actual detection application of articles.To this end,this paper mainly studies the following contents:(1)TOFD detection mechanism of large thick wall workpiece with irregular geometric shapes,such as welding seams of unequal thickness pot barrel,was studied,and new reference echoes related to characteristic structures were extracted to achieve the localization and quantitative characterization of defects.(2)Study the mechanism and general principles of ultrasonic time difference diffraction detection,clarify the key parameters of TOFD detection,and elaborate the detection process and error analysis;Comparison test blocks,weld simulation test blocks and blind spot test blocks were designed and processed.The TOFD detector was used to detect the defects of these test blocks,and the collected experimental data were analyzed to further study the influence law of probe frequency,Angle,wafer size and probe spacing on the TOFD test defect.(3)The finite element method is used to establish the numerical calculation model of the workpiece with special structure.The reflection,diffraction and waveform conversion of TOFD probe pulse in workpiece are analyzed by finite element method.FEM was used to simulate the sound field propagation of the butt joint between the pot barrel and the spherical head,the butt weld of the plate and the thicker workpiece,so as to conduct in-depth analysis and research on the propagation mechanism of TOFD pulse in the workpiece with unequal thinkness.(4)During the maintenance of a large thermal power plant,TOFD technology is used to detect and apply the pot.