If the difference in the structure to soil potential for the structures being tested is 100mV or higher, what does this indicate?

A difference in the structure to soil potential of 100mV or higher is indicative of effective isolation. In pipeline corrosion control, effective isolation is important as it shows that the structure is adequately protected from electrical currents that could lead to corrosion.

When the potential difference exceeds this threshold, it typically indicates that there are no significant pathways for current to flow from the pipeline to the surrounding soil, which would otherwise promote corrosion. This suggests that isolation measures, such as the installation of insulating joints or coatings, are functioning as intended, effectively minimizing the possibility of corrosion through electrical means.

In contrast, other scenarios such as a faulty meter or a lightning strike would not necessarily explain a consistent and significant measurement across multiple tests. Further testing might be warranted in some cases, but a consistent reading of 100mV or more in potential difference generally supports the conclusion of effective isolation rather than indicating the need for additional investigation or implying equipment malfunction.