Abstract
Bidimensional analysis of paint degradation and steel corrosion was carried out on cross-arms used in an electric transmission tower on the Pacific coast of Japan by electrochemical impedance and terahertz wave measurements. Visual observation indicates that underfilm corrosion is intense on the surfaces facing the sea breeze. Electrochemical impedance shows that paint degradation is severe in materials installed at large height. However, the impedance measurement at times indicates good electrical insulating values even when the presence of underfilm corrosion is indicated by terahertz imaging. This suggests that rust expands under the film while showing no apparent signs of paint degradation, and that impedance measurements mainly focus on paint degradation. The new "see-through" technology brought about by terahertz imaging also demonstrates that corrosion is severe near mountain-folded regions of the angle steels and expands towards the edge.
