METHOD FOR MONITORING STATE OF PROTECTING FILM FOR SUBMERGED OR EMBEDDED PIPE LINE OR OTHER METAL STRUCTURE ANDMETHOD FOR POSITIONING SEPARATION OF PROTECING FILM

摘要

PURPOSE: To monitor the state and locate a protective coating by applying sine wave exciting currents of different frequency to a pipe line and determining presence of separated coating based on a corresponding voltage response. CONSTITUTION: Sine wave exciting currents of different frequency are applied from a signal generator 10 in a measuring unit 9 through a protrusion to a pipe line 1. A meter 13 detects a voltage response induced by the exciting current. A decision is made whether a defect 3 or a separation 5 is present in the protective coating 2 of the pipe line 1 based on the response of different amplitude to the sine wave of different frequency. In case of a defect 3, a significant variation can be recognized in the amplitude of voltage response when the frequency is varied in the range of 10-1Hz, for example. In case of a separation 5 due to corrosion, substantially invariant amplitude of voltage response is recognized. More specifically, application of sine wave of different frequency causes to spread the voltage response for the defect 3 and produces a substantially matched response for the separation 5.