The Japanese Society for Non-Destructive Inspection (JSNDI) published general rule of method for measurement of thickness and crack size by Electric Potential Drop Technique as the Standard of JSNDI (NDIS3426) in January, 2008. NDIS3426 was established based on the researches for many years including the round robin tests conducted as the academic activities in JSNDI, and the previous technical guideline and standard ASTM E-647-05 ANNEX A6 and BS ISO 12108:2002 established for the measurement of fatigue crack growth in specimens. In this paper, the outline and the background of NDIS3426 was described. The electric potential drop technique is one of the promising methods to monitor or measure the thickness and crack size for the practical use in many industries. For the inspection of the surface deep fatigue crack in the steam turbine casing, the advanced crack depth indicator based on the potential drop technique has been applied. For the monitoring the creep damage accumulated in the seam-welded power piping, the commercialized tool based on the pulsed direct current potential drop technique has been used. For the pipe wall thinning measurement in the operating thermal power plant, the pulsed direct current potential drop technique was applied. This paper shows the present condition of the practical use and the future prospect of the potential drop technique.

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