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安秉完,任彰宰,具吉謨 韓國非破壞檢査學會 1988 한국비파괴검사학회지 Vol.8 No.1
In the in-service inspections for the steam generator tubing of the nuclear power plants by the Eddy Current Testing. the ECT signals are evaluated by their phase. If oxidized copper sludge is piled up in the secondary side, however, big sludge signals occur in large quantities which originate from copper layers forming in the sludge piles due to the pitting mechanism of the steam generator tubing by Cu²+ and modulate the defect signals, causing the difficulty in the defect detection. In this research, sludge specimens were prepared considering the formations of the sludge signal sources and multifrequency ECT mixing experiments by different choices of the mixing standards were performed. The results were found to bo 5 to 30% of the tube wall thickness over-estimated. Experiments using the ring-type mixing standards showed the least errors of all. while those with the mixing standards nearing the sludge conditions brought larger errors as a result of influence of the interference between the defect and the copper layers.