Both Laser & CCTV for Large Pipe Inspection?

As any World War I Ace will tell you, pilots rely on their vision (among other physical and mental traits) to be the best at what they do. Today’s aircraft are full of instrumentation, computers, and advanced sensors- yet in critical situations they don’t fly themselves: there will always be some need for human observation. The best pilots are those who rely on a combination of vision, instrumentation, and experience to make decisions.

In the same way that instrumentation can make a pilot better, a camera operator’s ability to interpret CCTV is greatly enhanced by laser information. At the same time, no matter how perfectly a laser maps the environment, what the operator sees with his own eyes is “worth a thousand words.” Laser and CCTV complement one another, providing a better evaluation of pipe condition and enabling you to spend less money if rehabilitation is required.

Many companies use CCTV to evaluate their pipe loss. And other technologies, like laser, can do pipe inspection. However, don’t think that laser is “better” than CCTV. CCTV and laser complement one another – CCTV picks up on the defects the laser is likely to miss, and laser picks up the defects that CCTV operators can’t detect or directly measure. Laser can also be used to verify defects observed via CCTV and provide specific physical information on the size and shape of those defects. The net result is an inspection that provides a more accurate and comprehensive description of a pipe, which greatly increases the chances of discovering all defects.

A major problem with CCTV is the effect that lighting and perspective can have on the appearance of a defect. The quality and angle of lighting provided during the inspection directly impacts the operator’s ability to accurately diagnose pipe defects. In one case, a well-qualified CCTV operator noted a number of structural problems in a pipe – including multiple fractures and a single hole. The corresponding laser data showed that these problems were induced by the effects of lighting. In the case of the fracture, direct lighting amplifies the operator’s perception of pipe wall cracks causing him to misclassify them as fractures. Inversely, the located hole was really a mirage created by shadows. Laser data saved the asset owner hundreds of thousands of dollars that they would have spent on a costly and unnecessary rehabilitation program.

In another case, a municipality performed an inspection to assess the quality of a cured-in-place liner they had installed. CCTV inspection revealed a number of blisters – a known installation defect with these liners. However, the corresponding laser inspection was able to provide the exact height, width, and length of each blister – information the municipality used to analyze the severity of the situation, and ultimately obtain repairs from the installation contractor. It was easy for the contractor to dismiss ‘big’ blisters as acceptable, but it was very difficult for him to refute the fact that some of them were 3 feet in diameter!

Finally, on another project, laser scans showed inches of material loss along the walls of the pipe, near the flow line. The pattern indicated in the laser scan showed a distinct pattern – clearly resembling rebar present in reinforced concrete pipes. However, upon closer analysis with the CCTV camera, it became apparent that the grid pattern was caused by an exposed layer of brickwork. Ultimately, it was discovered that the ‘reinforced’ concrete pipe was really a brick pipe with a layer of mortar installed later, that nobody retained documentation for. The addition of the CCTV information helped the asset owner prepare a much more intelligent rehabilitation program.

Both sensors have distinct strengths and weakness that when used together provide a superior inspection. For example, the laser can detect minute changes in pipe geometry such as ovality that are impossible for even a skilled operator to discern. CCTV data can be used to detect fine cracks and other non-geometric defects that do not register in the laser data.

In a recent case study from four projects and about 10,000 feet of video, the laser observed, on average, about 3 defects every 100 feet, while CCTV observed about 2 defects in the same distance. Interestingly, in almost all cases, the observations were of different conditions, or provided unique supporting information. This effectively doubles the defect detection rate that one would obtain using either inspection sensor in isolation. Ultimately, a combined inspection using CCTV and laser data provides a truer, clearer picture of pipe conditions, increases the value of inspections, and provides a more useful assessment of assets when compared to other traditional inspections.

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