## 1 Introduction  
Nondestructive testing is useful in industry and scientific research to inspect materials without damaging them. While there are more than 50 nondestructive techniques, in many cases, they must be used in combination to obtain more accurate results. The six major nondestructive testing methods are: visual testing (VT), liquid penetrant testing (PT), magnetic particle testing (MT), radiographic testing (RT), ultrasonic testing (UT), and eddy-current testing (ECT). ECT is widely used in industrial applications, including the inspection of heat-exchanger tubing, aerospace structures and craft parts, and weld build-up, and in other applications [1, 2, 3]. In the nuclear industry, steam generator tubes are periodically inspected using ECT to prevent leakage. Because the steam generator consists of thousands of tubes, ECT inspection is carried out using a bobbin probe that can be used at high speed.  
If the bobbin signal shows that defects and foreign objects are present, an inspection is performed using an MRPC(Motorized Rotating Pancake Coil) probe. The object is assessed for risks using the foreign object search and retrieval (FOSAR) method and removed if necessary [4; 5; 6]. The integrity of the steam generator tube is determined using the analysis of the shape and size of the eddy-current signal. Therefore, the objective reliability of the signal is still low, and there is a possibility of misinterpretation. For example, the U-shaped heat-transfer tubes installed in the steam generators at the Korean Standard Nuclear Plant (OPR-1000) generate a noisy signal during the eddy-current test, which makes it difficult to objectively determine the defect signal. The noise signal in U-bend tubes can be caused by a change in the position of the coil probe, a change in the shape of the heat pipe, or foreign objects. However, it is difficult to acquire an accurate eddy-current signal by implementing the desired condition in the mock-up test. To solve this problem, research on the analysis of noise signals using programs such as CIVA and OPERA has been actively conducted [3; 4; 5; 6; 7; 8]. However, this method has limitations because accurately simulating the conditions that can occur in the actual field and obtaining data affected by all of the various causes of noise are difficult. Previous studies of U-shaped heat pipes used in nuclear power plants in the Republic of Korea have confirmed that the distribution of current density can vary due to the influence of ovality, as the cross-sectional area changes depending on the location of the flexion in the manufacturing process. It is therefore necessary to further analyze the eddy-current signals in complex shapes with cross-sectional changes and curvature.  
In this study, a mock-up of the steam generator tube was produced, and the cross-sectional area according to the curvature position of the bend was obtained using CT (Computed Tomography) analysis. Using COMSOL Multiphysics, a commercial numerical analysis program based on the finite element method (FEM), the distance of contact between coils and pipes was seen to vary depending on the change in cross section. The curvature was modeled in three dimensions, and the electromagnetic analysis was performed at each location to analyze the noise caused by structural problems in the curved pipe.