Study on Electromagnetic Characteristic Compensation in Remote Field Eddy Current Testing

[[abstract]]遙場渦電流(Remote Field Eddy Current，RFEC)檢測技術已被廣泛的應用於換熱器管束的檢測，依據從RFEC檢測換熱器管束的經驗中，發現碳鋼管常會因製造與處理過程的不同，以及使用環境的改變，導致本身材質發生變化並使得管子的電磁特性隨之改變。所以在檢測時若沒有對此材料的電磁特性進行補償，就會產生評估誤差。本文利用RFEC的集膚深度理論(skin-depth theory)及RFEC訊號在電壓平面(voltage plane)上的幾何關係，推導出一個數學理論模式，依此數學理論模式建立的新評估曲線(evaluation curve)來補償因管子的電磁特性改變所造成的誤差。經由理論的推導及實驗驗證結果得知此種方法具可行性，所以除了使用頻率調整方式來進行補償外，此數學理論模式對現場檢測之技術人員而言是另一種新的選擇。此方法亦可以提供手邊沒有適當之標準管材時的另一種解決方式。[[abstract]]The Remote Field Eddy Current (RFEC) has been comprehensively applied to detect the wall loss of ferromagnetic tube. According to our experience, we found the problem of variation of material electromagnetic characteristics occurred on the carbon steel tube was often occurred in practice. Therefore, if we fail to compensate the change of electromagnetic characteristics during inspection, the error of evaluation will be generated. This study applied the skin-depth theory of RFEC and geometric relationship on voltage plane for deriving a compensatory model of mathematical methodology. The new evaluation curve established on the basis of this mathematical methodology is to compensate the error contributed by the change of electromagnetic characteristics in the tube. The method offered by this study has been proved to be reasonable, feasible and acceptable through the process of derivation and testing result