In recent years, glass fiber reinforced plastics (GFRPs) have been used as structural materials in tanks due to its potential of weight saving, high strength, cheapness and corrosion resistance. Moisture absorption is one of the causes of the serious accidents since some of them are used for more than 30 years. Moisture absorption is known to decrease compressive, bending and fatigue strength of GFRP structures drastically. Although visual inspection is usually performed to detect moisture absorption, it is difficult to detect internal strength degradation. Therefore, nondestructive testing method based on electromagnetic induction test is newly proposed to measure moisture absorption in this paper. In the previous research, a probe capable of measuring permittivity was developed. In this research, we improved it in order to evaluate change in mechanical properties more easily and developed the testing probe which is able to measure moisture absorption. The testing probe was configured by two pickup coils and one driver coil. In order to cancel mutual induction effect from driver coil, two pickup coils were wound conversely and their differential voltage was measured. Experimental study on woven GFRP showed that absorbing moisture can be measured by using the nondestructive testing method based on electromagnetic induction.
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