Ask the Experts
Q: I was at the ASCE Pipelines conference and I heard a lot of talk about "false positives" with respect to electromagnetic inspections. What are these and why do they happen?
A false positive is used when comparing estimated results to actual results. In the case of electromagnetic inspection, a false positive refers to when a pipe has been identified to have wire breaks but actually has none. Similarly, a false negative refers to when a pipe is identified to have no wire breaks, but actually has. Since the whole purpose of an RFTC inspection is to identify which pipes are distressed so that only the distressed ones are strategically rehabilitated, the problem with false positives is that they could lead to decisions to rehabilitate pipes that aren’t distressed, which certainly isn’t strategic, or cheap.
After 9+ years of experience, I can shed some light on why a false positive could happen. At PPIC, our electromagnetic technology is called RFTC and the analysis process is extremely detailed and meticulous. I remember when I first joined PPIC and learnt the 'analysis basics' I thought it seemed quite simple - just look for the characteristics of distress, measure the signal change and voila, you’re an analyst. It didn’t take long to realize how much more complex it truly is. There are factors that can make the data look like it has wire breaks when it actually doesn't, but a trained eye can tell the difference. Each pipeline has its own signal, and each pipe has its own subtle variation. So it’s not just analysis training that makes a good analyst, experience and a proven methodology play a key role.
The PPIC analysis methodology is based on over a decade of intensive research and development, and commercial application. Our analysts have a high awareness of the factors that affect analysis, access to the top RFTC experts in the world, and a wealth of inspection and test data. For these reasons, we are able to prevent reporting false positives with our RFTC technology as noted in several papers presented at the conference, which were likely the root of some of the discussions you heard.
Here are the papers that were presented at ASCE that discussed false positives:
- Comparison of RFTC and P-Wave Tests Performed on the Rampart 54” PCCP Raw Water Pipeline
- Condition Assessment and Repair of a 40-Year Old Aqueduct
- Continuity Testing of the Rampart and Homestake Pipeline
- Allison Biggar, Solutions Manager
Allison Biggar has nearly a decade of experience with PCCP condition assessment. Specializing in the RFTC technology, Allison has worked on projects with some of the largest water utilities in North America. For more information, contact Allison at Allison.Biggar@ppic.com.
More Questions » Submit Question »
Disclaimer: The answers provided in the PPIC "Ask the Experts" column should be considered general opinions and should not be taken as formal engineering advice. Site visits are recommended to provide answers to specific challenges that a client may be facing. PPIC does not assume any responsibility for action taken by readers based on the opinions provided in this column.