不锈钢焊缝中超声传播特性及TOFD检测方法研究

为提高对不锈钢焊缝内部缺陷的超声检测能力,开展了关于焊缝超声波传播特性及其超声衍射时差法(TOFD)的研究工作。通过调整探头间距(PCS)改变检测声束方向,分析检测声束与柱状晶夹角对检测信号信噪比的影响,提出基于超声TOFD技术的焊缝一次波、二次波检测方法;鉴于二次波检测中特征波结构的复杂性,建立了特征波传播模型以识别二次波特征信号。研究结果表明,焊缝中传播的超声波声束呈现明显的各向异性特征,柱状晶与检测声束的夹角是检测信噪比的关键影响因素;与探头置于焊缝根部侧和余高侧相对应,需分别采用一次波和二次波检测方法进行TOFD检测;当检测声束与柱状晶夹角在35°~48°且检测区域具有较高声压时,可有效提高对焊缝缺陷的检测能力。基于声波传播的各向异性特征提出的超声TOFD一次波和二次波检测方法对于提高奥氏体不锈钢焊缝的超声检测能力具有重要作用。

Research on wave propagation characteristics in austenite stainless steel weld andultrasonic TOFD testing technique

In order to improveultrasonic testing capability on austenitic stainless steel weld, ultrasonic propagation characters and related ultrasonic time of flight diffraction method (TOFD) were investigated.The direction of detection beam was changed through adjusting the probes center spacing (PCS) to analyze the signal to noise ratio (SNR) varies with the angle between testing beam and columnar grain.And then, the probe distribution method of primary wave and secondary wave based on ultrasonic TOFD techniquewere proposed.Moreover,the model of wave propagation was constructedtoidentifythe characteristic signal of defect in the light of complex wave structure in secondary wave method.The research indicates that the ultrasonic propagated in the stainless steel weld reflects obvious anisotropy characters, and the angle between columnar grain and detection beam is the main influencing factor to SNR of testing signal.Primary wave method and secondary wave method is respectively adopted for testing, when theprobe is located on the side of weld root and reinforcement.The testing capability on stainless steel weldcan be effectively improved when the angle between detection beam and columnar grain is within the range of 35°~48°and high beam amplitude is obtained.The primary and secondary wave methods of ultrasonic TOFD based on anisotropic characteristic of wave propagation are very important to improve the ultrasonic testing capability on inner defect of austenitic stainless steel weld.