Comparison of Two Electromagnetic Techniques to Determine the Physical Condition of PCCP

The use of electromagnetic techniques for the inspection and determination of distress (broken wires) for Prestressed Concrete Cylinder Pipe (PCCP) has greatly increased over the past 7 years. There are two primary providers of these services that use generically similar methods. Individually the results from each provider have been investigated with mixed results. Direct comparison of results between the two providers and confirmation of the results by excavation had not been performed before. As part of an AWWA Research Foundation study (Romer, 2004), comparisons of the results between the two electromagnetic inspection providers were made on several PCCP pipelines. Correlation between the two electromagnetic inspection results was modest. However, excavation for direct physical examination of the pipes to verify the predicted distress, or lack of distress, was not possible at the time of the electromagnetic inspections. The opportunity to directly compare and confirm the accuracy of inferred prestressing wire damage was finally possible on one of the San Diego County Water Authority's (Water Authority) pipelines. Both providers of electromagnetic inspection services had surveyed the same segment of the pipeline with differing results. Direct comparison of electromagnetic results with actual observed distress has been determined at several locations. This paper reviews the results and documents the predicted electromagnetic results along with the observed physical condition of the pipe sections and emphasizes the importance of proper records and the utilization of other impact factors that affect the performance.