Ultrasonic Phased Array Testing Technology On Thick-Wall Weld Of Ladle Trunnion

Ladle is widely used in steelmaking industry, due to the severe load, theroot weld area is easier to resultant defects which would leading to accidents. In orderto ensure the safe operation of the ladle, it is necessary to strengthen the detection ofthe weld.The root weld area is only28mm height and less than20mm width which isrelatively smaller to the entire trunnion area, but it located more than150mm awayfrom the detection surface that required higher penetration for the testing technologies,and the narrow width of the detection surface limits the movement of the contactprobe. Ultrasonic phased array testing technology can perform a wide range of sectorscan by changing the delay law, which result in strong penetration, resolution andhigh detection efficiency, by these features, ultrasonic phased array testing technologycan achieve the detection of the root weld area efficiently. In this paper, simulationand detection experiments was carried out to the root weld area based on the beamfocusing and beam deflection characteristics of ultrasonic phased array testing.Specific work of this paper includes:(1) Based on sound field theory and array signal processing theory, combinedwith simulation analysis, phased array probe that have5MHz center frequency,16array elements, d1/2was suitable to be used for the testing of the root weld areaof ladle trunnion.(2) Beam computation and defect response simulation was taken out on CIVAsoftware. Beam computation shows the sound field characteristics of transverse wavesand longitudinal waves. Defect response simulation shows that both transverse andlongitudinal detection have high resolution, the deviation is less than1mm.(3) The root weld area of ladle trunnion test block was detected and analyzed byusing Omniscan. The optimal detection parameters of testing were identified, bothtransverse waves and longitudinal waves can get better detection results. The highestSNR(Signal to Noise Ratio) of the defects can be more than18dB. Finally, ultrasonicphased array testing technology were applied on an in service ladle.(4) Against to the low SNR during the actual detection, Wavelet threshold de-noising method and MP(Matching Pursuit) were employed to the de-noising of theA-scan imaging results and the effects of the two methods were compared, it revealthat when using Gabor dictionary,5layer iteration, MP method had better adaptabilityto the signals with different SNR, while wavelet threshold de-noising method waspoor to the low SNR signals. Based on the A-scan imaging MP de-noising results, thispaper realized the application of MP on S-scan imaging results which is the uniqueimaging mode of ultrasonic phased array, greatly improved the imaging quality.