| 摘要 |
PURPOSE:To detect non-destructively local destruction of a protective coating in an early stage by detecting <=10KHz alternating current signal portion of natural electric potential of a sample metal in a corrosive liquid. CONSTITUTION:The difference of electric potential between a sample metal 7 and a reference electrode 8 is detected by using a differential amplifier 14 and <=10KHz alternating current signal is detected by using a frequency analyzing apparatus 24 after eliminating a direct current portion of its output by an electric potential compensation circuit 22. A carbon steel plate is used for the sample metal 7 and a spectrum on the occasion of immersing this plate in city water containing 200ppm sodium nitrite, is shown by a curve (a). Next, 2,000ppm salt is added to said solution and the spectrum after five hours has attained a higher level in <=10KHz domain, especially <=1KHz domain as shown by a curve (b). |
