By Richard Lindner, Envirosight LLC
Since the advent of miniature cameras, plant and utility personnel have used them to assess pipe condition and troubleshoot problems.
Over the years, new delivery mechanisms have emerged to carry cameras deeper into pipes, while capturing increasingly better images. Among the most sophisticated of these is the video inspection crawler, which can transport a robotically articulated camera hundredseven thousandsof feet into pipes to identify corrosion, deposits, foreign matter, cracks, deformations, offsets and erosion.
As successful and widespread as crawler inspection has become, however, its main drawback remains the issue of operation versus analysis. Under normal conditions, an operator is simply too preoccupied driving a crawler to properly analyze the video it captures. In many instances, the operator isn’t even the person most qualified to make the analysis. Furthermore, those who are best qualifiedmetallurgists, chemists and structural engineersseldom have time to review hours of video footage; footage which may still fail to deliver sufficient detail of problem areas.
Ultimately, the dilemma is one of presentation: crawlers need to capture rich visual data in a manner independent of operator judgment and then present it in a way that allows efficient review by those best qualified to make an analysis.
Manufacturers of video pipeline inspection equipment have responded to this need by developing digital visual sidewall scanning (DVSS) technology. DVSS provides a reliable method for gathering visual data from within a pipe using the crawler platform. But unlike traditional video inspection, DVSS uses digital image processing to deliver information in a format that is easy to analyze.
DVSS relies on software to manipulate video frames into a flat digital scan. The scan resembles a long mural or scroll and it bears an image whose length corresponds to the length of the pipe and whose height represents the pipe’s full circumference, from zero to 360 degrees. These scans show more detail than conventional video and the images are presented in a format that is often easier to review and analyze. Rather than sitting through hours of inspection video, an analyst can review an entire length of pipe at one time, quickly pinpointing problem areas, then making annotations and measurements on the scan itself.
A DVSS scan captures the entire pipe wall interior at high resolution. Scan length corresponds to the pipe length, while scan height represents the full pipe circumference (zero to 360 degrees).
Software that presents a thumbnail version of the entire scan (resembling a film strip) is often included with this technology. The software allows the person reviewing the images to quickly investigate specific scan regions. When an area of the thumbnail is clicked, a detailed view of that region appears in the analysis pane. A corresponding down-pipe view appears alongside it. In these panes, the analyst can scroll the view in either direction and zoom in on specific regions. Often, the system provides drawing and annotation tools that the analyst can use to mark-up the scan, identify pipe features, highlight regions of concern and pose questions to subsequent reviewers.
Ideally, digital visual sidewall scans are created in real time by a quick-moving crawler. The crawler itself requires only three special features:
- A fish-eye camera lens that provides a field of view greater than 180 degrees
- Diffuse wide-angle lighting, and
- A wheel encoder for exact measurement of camera movement.
As the crawler advances down a line, the reel encoder fires a signal corresponding to one predefined interval of forward motion. With each signal from the encoder, the video camera captures a single video frame and transmits it back to the crawler’s central control unit (CCU). The CCU then relays this frame to a back-end computer, which digitizes it and extracts a ring of pixels corresponding to a section of the pipe wall. Using a mathematical algorithm, the computer slices this ring at the bottom and unfolds it into a rectangle. As these rectangles are created from each subsequent video frame, they are stitched together into a complete sidewall scan. Building a good scan in this manner requires ample and even illumination, a camera whose view is centered in the pipe and minimal terrain variation.
Typical DVSS Workflow
Because it captures data automatically and relieves the crawler operator from having to analyze footage on the fly, DVSS allows inspections to be performed quickly. It allows an operator to concentrate on piloting the crawler through the line, leaving visual data analysis to the appropriately trained professionals. For this reason, there is no need to slow down at problem areas or adjust the camera to gain a better view. Likewise, there is no need to stop and backtrack when a potential problem flashes by onscreen, or even to second-guess perceived anomalies. This is because all observations are captured in detail for post-inspection analysis.
This same productivity carries over to the analysis phase, where professionals representing multiple disciplines can quickly survey scans. With adequate software, a single scan of the entire pipe interior is available to the analyst, who can search for areas of interest, zoom in for greater scrutiny and annotate the scan directly. Because the scan is dimensionally accurate, measurement tools also allow the analyst precisely quantify observationscrack length, tap diameter and corrosion surface area, to name just a few examples. In most cases, other inspection data gathered by the crawler, such as inclination, elevation and temperature, also can be plotted.
Consider, for example, a 200-foot-long segment of pipe in fair condition. A DVSS review can be completed in just a few minutes. Compare that to the 10 minutes of video a crawler traveling at 20 feet per minute would generate, plus the time the operator takes to investigate problem areas and the additional time a reviewer spends cueing, jogging and pausing the footage. Factor in the risk of the crawler operator failing to adequately inspect a particular problem area and the benefits of DVSS become apparent.
Digitization of the visual data not only enables rapid analysis and robust annotation, it also allows an analyst to overlay archival scans to determine the speed at which pipe condition is deteriorating. Knowing that an area of corrosion is stable, for example, rather than spreading rapidly or varying as flow composition varies, provides information crucial to making maintenance decisions. Many higher-end DVSS packages take advantage of the digital format to perform machine vision tasks, such as automatic identification of common pipe features like joints and taps. Finally, digitization improves storage density; a DVD-R using DVSS allows documentation of 7 to 10 times more pipe than with traditional digital video.
DVSS technology is comparatively affordable, requires no extensive training and delivers robust, digestible data to professionals involved in all aspects of plant maintenance and operation.
Newcomers who are evaluating DVSS solutions should consider the following key differentiators among systems currently on the market:
• “Real-time” DVSS systems build scans instantly as wall segments are extracted from individual video frames. “Offline” DVSS systems unwrap much longer segments captured by a higher-resolution charge-coupled device, but only after the inspection has been completed.
Real-time DVSS allows the viewer to view the scan as it is built. Upon completion of the line inspection the entire scan is immediately available for review by others, immediately freeing up the equipment and operator to move to the next job.
Offline scanning can deliver a higher-resolution scan, but typically requires extensive post-processing, which means the scan cannot be viewed as it’s created, nor is it immediately available for review by others. Offline systems typically require a second computer (or occupy the primary computer) to perform the image-flattening computations.
- Storage bandwidth. With digital cameras, more resolution is better, but within practical limits. By analogy, is it important to discern every pore on your subject’s face, only to have an image file too big to share by e-mail? The same is true of DVSSmore resolution can be better, but a scan big enough to resolve insignificantly small features wastes computer, network and archival media capacity. Ideally, scans should be viewable on a standard computer terminal with a standard video card, easily transmitted via wireless LAN and readily archived in batches onto CD-R or DVD-R.
- Equipment investment. Some DVSS systems are standalone, which means the DVSS camera, computer and software, as well as a crawler, cable reel and CCU, plus a vehicle in which to haul everything are purchased together in one package.
Other systems are modular, which means the DVSS camera, computer and software can be purchased to retrofit an existing crawler system. These modular systems usually require less investment. They also offer the versatility of switching between DVSS and standard video inspection, and they are easier to upgrade.
- Ease of integration. DVSS should complement a facility’s current inspection program, not upend it. The DVSS system should integrate well with the inspection and asset-tracking software already in use. Plant personnel should be able to link databased observations to regions of the scan, correlate scans to GIS/GPS data, and easily integrate those scans into reports.
Ultimately, DVSS allows plant and utility personnel to focus on what they do best. Crawler operators can dedicate their full attention to navigating inspection equipment through pipes, while other professionals can review pipe scans more efficiently, pinpoint problems, zoom in for greater scrutiny and make annotations that are easy to share and archive. The net benefits are greater productivity, more robust data and better intelligence upon which to base critical maintenance decisions.
Author: Richard Lindner is president of Envirosight LLC, a Randolph, N.J.-based company that specializes in video pipeline inspection. The company serves industry, municipalities, contractors, departments of transportation and civil/environmental engineers.