核电铁磁管道磁饱和脉冲涡流/电磁超声混合定量无损评价方法研究

In nuclear power plants (NPP), local wall thinning is a typical pipe defect caused by liquid droplet impingement (LDI) of the coolant inside the pipes during service. It seriously threatens the structural integrity of the key pipes of NPP. Therefore periodic quantitative non-destructive testing (QNDT) of the piping is mandated to guarantee the safety of NPP. The carbon steel is a typical structural material used in the piping of NPPs. Due to large permeability, the pulsed eddy current testing method (PECT), which is suitable for the QNDT of multi-layer pipe structure and with insulated layer of nonmagnetic stainless steel, can not be employed directly for pipes of carbon steel.. Concerning that the magnetic saturation strategy can reduce permeability of carbon steel, therefore a magnetic saturation PECT method is a promising way to overcome the above difficulty. In addition, in magnetic saturation PECT system, the interaction of strong static magnetic field and pulsed eddy current will stimulate electromagnetic acoustic signal, therefore, there should be electromagnetic acoustic testing (EMAT) signal accompany with PECT signal. Due to the complementarity of eddy current testing method and ultrasonic testing method, the hybrid magnetic saturation PECT/EMAT method is expected to be a powerful tool for the QNDT of local wall thinning defects in ferromagnetic pipes of complex structure.. In this project, the hybrid magnetic saturation PECT/EMAT method is proposed to realize the QNDT of defects in pipes with high permeability. The corresponding theoretical analysis method and experimental inspection technique will be developed. The main works planned to be carried out includes: 1) To develop the efficient simulation method for magnetic saturation PECT and EMAT signals prediction, investigation of the magnetic saturation mechanism and optimization of the probe structure; 2) To establish experimental system of hybrid magnetic saturation PECT/EMAT method, develop dual probe and signal separation/extraction methods, evaluate the feasibility of the proposed hybrid method for QNDT of local wall thinning in ferromagnetic piping; 3) To efficiently combine dual PECT and EMAT signals and develop inversion algorithm, the quantitative evaluation of local wall thinning defects in ferromagnetic piping is to be carried out.

核电管道管壁局部减薄是服役过程中液滴冲蚀等造成的体积缺陷，严重威胁核电结构完整性，必须对其进行定量无损检测。脉冲涡流检测方法对多层结构和含保温层不锈钢管具有良好检测性能，但对核电管道主体-碳素钢管由于强磁特性无法有效检测。由于磁饱和可降低铁磁材料磁导率，同时饱和磁场与脉冲涡流相互作用会激发电磁超声，由于涡流与超声检测的互补性，磁饱和脉冲涡流/电磁超声混合检测法有望成为碳素钢管道局部缺陷定量检测的有力手段。本项目主要研究这一创新混合检测法对核级强磁管道局部缺陷定量无损评价的有效性，开发相应的理论分析方法和实验检测技术。拟开展主要研究包括：1）开发磁饱和脉冲涡流和电磁超声信号模拟方法，探究磁饱和机理、优化探头结构；2）建立磁饱和脉冲涡流/电磁超声混合法实验系统，开发复合探头和信号分离方法，实验验证所提方法的可行性；3）有效结合混合检测信号，开发信号反演方法实现铁磁管道局部减薄缺陷的定量重构。

管道管壁局部减薄是服役过程中液滴冲蚀等造成的体积缺陷，严重威胁管道安全， 必须对其进行定量无损检测。脉冲涡流检测方法对多层结构和含保温层不锈钢管具有良好检测性能，但对碳素钢管由于强磁特性无法有效检测。由于磁饱和可降低铁磁材料磁导率，同时饱和磁场与脉冲涡流相互作用会激发电磁超声，由于涡流与超声检测的互补性， 磁饱和脉冲涡流/电磁超声混合检测法有望成为管道局部缺陷定量检测的有力手段。本项目主要研究这一创新混合检测法对管道局部缺陷定量无损评价的有效性，开发相应的理论分析方法和实验检测技术，主要的工作分为两个部分，第一部分提出了脉冲涡流/电磁超声复合检测方法，具体分为：1）提出并发开基于PECT/EMAT复合方法的信号分离算法，验证了该复合方法的可行性；2）开发基于PECT/EMAT复合方法的数值模拟程序，验证了复合方法的有效性；3）构建了存在复杂缺陷的铝&不锈钢平板模型，实验验证了复合方法检测该复杂缺陷的优越性和有效性；4）建立了脉冲涡流/电磁超声复合检测方法的逆问题。第二部分针对磁性材料，提出了磁饱和脉冲涡流方法，具体包括：1）提出并发开磁饱和下的脉冲涡流方法，探究了磁导率的变化对于脉冲涡流有效检出的重要性，证明了该方法的可行性；2）开发基于COMSOL软件，计算模拟了不同磁导率的脉冲涡流的检出电压信号，发现降低磁导率有效地提高了脉冲涡流的检出灵敏度，验证了该方法的有效性；3）构建了不同减薄缺陷的平板模型，通过搭建实验系统实现了对试件饱和磁场的施加，同时也验证了磁饱和对脉冲涡流检测存在重要影响，一定程度上提高了脉冲涡流检测的灵敏度。4）验证了磁饱和的方向对脉冲涡流检测的影响，提出了最佳的饱和磁场方向。