腐食部材劣化度の非破壊評価技術に関する基礎的研究

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In order to develop new non-destructive techniques for measuring corroded steel plate thickness, we investigated on an electro-magnetic measuring technique and an electro-magnetic acoustic measuring technique. The fluctuation of voltage in a detection coil by magnetic flux transmission through a steel plate was recorded by a personal computer when a excitation coil is driven by a step current. The 2nd peak of the waveforms was found to be correlated with steel plate thickness. We extracted 3 parameters of the peak, namely amplitude, half value breadth and delay time, and examined those quantitative dependence on steel thickness. The delay time is the best parameter for thickness measurement because it is the most stable to a change of coil lift-off and magnetization current. We also conducted electro-magnetic simulations with FEM analyses and measurements of magnetic permeability and chemical composition of the steel plates, and made clear the effect of material parameter deviation to the thickness evaluated. An another thickness measuring technique was investigated by using an electro-magnetic acoustic resonant measuring apparatus (0.2〜17MHz) and a sensor composed of a transmitter coil, a receiving coil and a permanent magnet. Measurements with this system were carried out on a rolled steel plate under tensile load or no load, and the effects of acoustic anisotropy and stress of steel plate to resonant frequency were verified to be small enough for thickness measurement. In the measurement of steel plates with machined rough surfaces (maximum difference of thickness=0〜1mm), it was confirmed that the resonant peak amplitude goes down rapidly to small with roughness growing large over 1MHz, and thickness measurement is difficult in this region. In the region of 100KHz〜1MHz, the amplitude still remain large with the rough surface plates, but unfortunately noises generated at the sensor and the apparatus becomes large. Development of an electro-magnetic acoustic resonant measuring system with low noise in the region of 100KHz〜1MHz is essential for thickness measurement of corroded steel plates.
独立行政法人海上技術安全研究所の論文
2000-02-04

腐食部材劣化度の非破壊評価技術に関する基礎的研究

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