Norikazu Fuse

Underfilm Corrosion of Transmission Tower Cross-Arms Service-Used in a Pacific Coast Area

Degradation is revealed for cross-arms used in an electric transmission tower on the Pacific coast of Japan by evaluating both paint degradation and steel corrosion. The angled steels exhibit various levels of degradation according to their face orientation and the installation height. The corrosion states are provided as maps with a special resolution of sub-mm order, using the terahertz wave nondestructive measurement. Rust fluid appears to transfuse along the steel/coating interface and induces underfilm corrosion on the nearest faces. The skyward face does not show clear corrosion, indicating the washing effect of rainfall. Electrochemical impedance shows that paint degradation is severe in faces that get a direct sea breeze, whereas the opposite faces show good integrity. The degradation also becomes more severe with increasing installation height. The two analytical techniques show that underfilm corrosion shows rapid progress when the electrical receptivity of the coating is on the order of 107 Ω·cm2.

Detection of rust in coated steel plates using terahertz waves

The applicability of terahertz (THz) waves to the detection of rust in coated steel plates has been examined. Spectral intensity measurements of reflected light from a sample coated with epoxy resin show that optical coherence tomography using near-infrared light and THz waves can detect the hidden rest region. This region can be reproduced by so-called THz imaging without contact. Since rust exhibits strong absorption in the frequency range from 1 to 5 THz, the absorption coefficient can be used to estimate the rust state with high sensitivity. In contrast, neither X-ray fluorescence nor Fourier transform infrared spectroscopy can detect the rust, because of the strong X-ray and IR peaks of the coating. Electro-chemical impedance measurement, which is one of the promising diagnostic methods, judges the water blocking ability of the coating. The impedance value and THz absorption due to rust shows good correlation until the amount of water in the film reaches its maximum.

Relationship between remaining antioxidant content and radiation-thermal degradation in crosslinked polyethylene

To clarify the deterioration mechanism of cables installed in nuclear power plants, three kinds of XLPE sheets with various antioxidant contents were aged by 100 Gy/h γ-ray irradiation at room temperature, 60, and 100°C. The remaining antioxidant content estimated from an oxidation induction time of a differential calorimetric thermogram as well as the elongation at break decreases faster as the initial antioxidant content decreases. On the other hand, an evaluation parameter called oxidation degree, which is the absorbance ratio of the carbonyl group to the methylene group obtained by infrared spectroscopy, increases with aging time. The oxidation degree increases with an increase in the elongation at break, and the relationship of these two parameters can be plotted around a sigmoid curve. Furthermore, the elongation at break and oxidation degree show reasonably stable transitions until the antioxidant content decreases to a certain value. After such a period, the elongation at break starts to change drastically and becomes sufficiently low value. It is clarified from these experimental results that there exists a certain antioxidant content that effectively inhibits oxidation.

Development of Nondestructive Testing Method for Examining Thermal Resistance of Thermal Barrier Coatings on Gas Turbine Blades

In order to improve the efficiency of electric power generation with gas turbines, the turbine inlet gas temperature needs to be increased. Hence, it is necessary to apply thermal barrier coatings (TBCs) to various hot gas path components. Although TBCs protect the substrate of hot gas path components from high-temperature gas, their thermal resistance degrades over time because of erosion and sintering of the topcoat. When the thermal resistance of TBCs degrades, the surface temperature of the substrate becomes higher, and this temperature increase affects the durability of the hot gas path components. Therefore, to understand the performance of serviced TBCs, the thermal resistance of TBCs needs to be examined by the nondestructive testing (NDT) method. This method has already been reported for TBCs applied to a combustion liner. However, recently, TBCs have been applied to gas turbine blades that have complex three-dimensional shapes, and therefore, an NDT method for examining the thermal resistance of TBCs on blades was developed. This method is based on active thermography using carbon dioxide laser heating and surface temperature measurement of the topcoat by using an infrared camera. The thermal resistance of TBCs is calculated from the topcoat surface temperature when the laser beam heats the surface. In this study, the developed method was applied to a cylindrical TBC sample that simulated curvature on the suction side of a blade, and the results showed the appropriate laser heating condition for this method. Under the appropriate condition, this method could also examine the thermal resistance of TBCs present at 70% of the height of the blade. With these results, this method could determine the thermal resistance within an error range of 4%, as compared to destructive testing.Copyright