In this study, the Electrochemical Impedance Spectroscopy (EIS) technique was used to
identify damage to asphalt coating on carbon steel pipelines in a soil box filled with water-saturated
sand. Four pipe segments with different asphalt coating conditions, i.e., good asphalt coating with
two difference sizes of holiday and no holiday, and degraded coating, were used. Significant
differences were observed from the EIS data monitored on these four segments. For the segments
covered with the good asphalt coating, the impedances measured from the segments with a
holiday were consistently smaller than those obtained from the segment without a holiday, and the
larger the holiday, the smaller the impedance was. Degraded coating showed very low impedances
because of the high porosity and large cracks in the coating. The value of the sand resistance,
Rsand, derived from the EIS data showed a dependence on the relative location of the holiday, which
indicated that the EIS-based above-ground technique might be able to identify the location of the
holiday.
KEY WORDS: EIS measurement, above ground technique, sand, cathodic protection, asphalt coating, holiday,
degraded asphalt coating, coating condition