PROCESSING COMBINED LASER, SONAR AND HD IMAGING FOR BETTER EVALUATION DECISIONS

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1 North American Society for Trenchless Technology (NASTT) No-Dig Show 2011 Washington, D.C. March 27-31, 2011 Paper F-3-05 PROCESSING COMBINED LASER, SONAR AND HD IMAGING FOR BETTER EVALUATION DECISIONS Jeff Griffiths 1, and Jeff Graham, P.E. 2 1 Hydromax USA, Newport News, VA 2 Hydromax USA, Louisville, KY ABSTRACT: From California to Massachusetts, from Ohio to Oklahoma, from 30-inch to 120-inch, round, oddshaped, concrete and brick sewers, with and without flow and with inspection runs as long as 7,500-feet, new inspection technology providing data for condition assessments was considered impossible only a few short years ago. Although millions of feet of sewer lines are televised in the United States each year, larger interceptors that carry significant flow are often ignored because of accessibility issues, lack of redundancy, safety concerns, illumination, cost, clarity of information and the difficulty and cost of dewatering. Since mid-2008, multi-sensor technology has provided the tools to finally overcome many of the obstacles that were encountered in the past. More and more municipalities are using this type of technology to inspect sewers and make more appropriate rehabilitation decisions, which continually proves the cost effectiveness of this value-added tool. Currently more than one million feet of large diameter sewers have been inspected using multi-sensor technology. Using a combination of a high definition camera and various combinations of laser technologies above the water surface, observations of corrosion, deflection, ovality, missing brick courses, damaged pipes, poor bedding, etc. are recorded. Below the water surface, sonar technology identifies the depth and volume of debris and major structural anomalies without the need for expensive dewatering systems. When all of these data collectors are contained on a single delivery system, the inspections can be economically performed in a single inspection run. The collected data is processed into a single submittal with videos simultaneously presenting the laser above the water surface and the sonar below the water surface. The HD camera data is submitted in a video with PACP coding that can be incorporated into most municipal databases. Data reports with still photographs, computergenerated drawings and findings at their specific locations supplement the videos. 1. INTRODUCTION In one western US city, the local wastewater utility provides sanitary sewer service to a population of over 180,000 residents and a transient workforce of nearly 250,000 within the City s municipal boundaries. The City s collection system extends to a service area of approximately 70 square miles and includes nearly 700 miles of sewer main pipelines in diameters up to 78-inch. The utility services commercial, residential, industrial, and institutional entities within its service area boundaries. Paper F

2 During the summer of 2008, the City initiated a master plan to study their sewer collection system. One important component of the master plan was a condition assessment of the City s existing large diameter pipelines. The City has long recognized that operations and maintenance costs account for a significant portion of annual operating budgets. Maintaining assets, monitoring their performance, and planning for their replacement are very important to the City. The goal of the master plan was to identify and adopt best management practices in the industry to create a cost-effective approach to protect capital investments, prolong asset life, and improve performance. The importance of this task was realized during the earliest stages of the study when a 48-inch portion of a main trunk line failed. The collapse was successfully repaired but highlighted the criticality of understanding the structural condition of their sewers. Evidence at the collapsed site appeared to indicate that the failure was the result of corrosion associated with hydrogen sulfide. The existing trunk line was constructed of reinforced concrete pipe. The original wall thickness of this pipe was estimated to be 5 inches. However, in some sections of the failed pipe, thicknesses of less than one inch at the crown were measured. Steel reinforcement in these sections was completely missing. This corrosion appears to be confined to the area of pipe above the normal water depth in the pipe, consistent with a failure pattern normally associated with hydrogen sulfide corrosion. The City prioritized the order in which sewers were to be inspected, but they were still challenged with how to collect meaningful data. While the City was aware that some corrosion was occurring in its system, past CCTV inspection techniques did not provide adequate information to indicate the magnitude of the corrosion and the impending problem. The desire to better quantify corrosion information led the City to utilize the CleanFlow HD Profiler system a new inspection technology from New Zealand that incorporates high definition (HD) imaging, laser profiling, and sonar data collection. The scenario presented above is not unique. In many cases, accessibility issues, significant debris and surcharging, coupled with the fact that it is often not practical to take large interceptors out of service, require innovative inspection technologies. Many utility owners and engineers are challenged with making appropriate rehabilitation decisions on limited budgets. One of the most important steps in this evaluation process is to sufficiently understand the condition of their collection systems. One of the most cost-effective condition assessment technologies is the use of multiple sensors to collect meaningful data on a single inspection run. This paper will highlight how one multi-sensor technology works and the present results from several different inspections. 2. DISCUSSION In the case presented with the 48-inch trunk line failure, the City began investigating available inspection technologies to be used in the master plan condition assessment activity. In evaluating the available technologies, the City considered a number of issues: Image Quality in Large Diameter Pipelines While the City s existing CCTV inspection equipment works well for small diameter collection pipelines, it has been less successful when used on large diameter trunk lines. To be successful, the selected technology needed to have adequate lighting and an image with high enough resolution to capture the details associated with a larger diameter pipeline. Quantification of Corrosion Magnitude To avoid another situation similar to the failure noted above, the City needed a technology that could not only identify where corrosion was occurring, but could also quantify how much corrosion had occurred at each section of pipe. Estimate of Sediment Depths Many of the City s large diameter trunk lines have been installed at a relatively flat grade and can incur some accumulation of sediment. To provide guidance for future cleaning activities, the City needed a technology that would identify sediment depth. Distance Between Manholes A few sections of the City s large diameter trunk lines were installed before the development of modern standards for manhole spacing. As a result, one of the trunk lines to be inspected included a section of pipe with approximately 2,500 feet between manholes. Thus, the City needed a technology that could run significant distances between manholes. Paper F

3 Based on a review of these issues, the City contracted with Hydromax USA (HUSA) to utilize the CleanFlow HD Profiler system for its condition assessment activities. CleanFlow HD Profiler System Using a multi-sensor technology (CCTV, sonar and laser) system is a great way to get thorough understanding of large diameter brick and concrete sewers. Sonar data (below the water surface) will enable the owner to understand how much debris is in the pipes. This is important because by knowing the precise amount of debris, cleaning contractors will provide better quotes since they will not be paying for risk with unknown debris quantities. In addition this information can help provide a modeler a better understanding of their model results. The laser (above the water surface) is critical because it will identify the amount of pipe wall that has corroded away. While CCTV cameras (above the water surface) might give the viewer information that there is sediment or corrosion, it cannot sufficiently quantify the magnitude of either. The CleanFlow HD Profiler system is capable of collecting data on sewers ranging from 24 inches to 120 inches in diameter and is currently configured to inspect as much as 7,500 linear feet in a single deployment. It also has the capability to inspect odd shaped sewers. Typically, the equipment floats through sewers with flow, but it can also be mounted to a skid or tractor. The floating apparatus enables the sonar data to be collected without disturbing the material. This allows the engineer to view how the debris is actually building up in the line. In order for the sonar and laser to both collect data there needs to be a minimum of 12 inches of flow (for the sonar) and at least 16 inches between the water line and the crown of the pipe. The system collects data continuously as it floats through the sewer. Above the water line, pictures are taken by a HD camera six times a second. During a typical inspection an image is taken approximately every 0.5 to 1.0 inch of length. The frequency is based on the float moving through the pipe at a rate of fifteen (15) to thirty (30) feet per minute. The images have approximately three times the clarity of a traditional CCTV camera. In addition the lighting used to illuminate the pipe is done with a strobing mechanism. This is important because the lights never get hot and thus decreases the likelihood of generating steam in the pipe during the inspection. After the inspection is completed the images are stitched together to create a video file. This file enables the pipe to be PACP (Pipeline Assessment and Certification Program) coded and imported into a municipality s CCTV database. The National Association of Sewer Service Companies (NASSCO) is committed to setting industry standards for the assessment and rehabilitation of underground pipelines, which has resulted in the PACP standard. During the entire inspection, a 2-D laser ring, comprised of 180 points, is projected onto the inner wall of the pipe. Four HD cameras are taking pictures of the laser every 0.25 to 0.5 inch. The image frequency is based on the rate the float moves through the pipe. The rapid frequency of the collected images insures that any deflection (flexible pipes) and corrosion or missing materials are being accurately documented. Sonar signals are also being collected every second, which corresponds to data collection at a rate of 0.5 to 1.0 feet. With the voluminous amount of collected data, it is vitally important to present the findings in a meaningful way and simplify the evaluation process. Typical deliverables include a comprehensive multi-sensor report, a four-in-one combined video file, and a PACP exchange database. Upon request, a special viewer is available that allows engineers and owners to pan, tilt and zoom post-processed videos. The capability can be particularly beneficial to the engineer making the rehabilitation decisions. The report contains tabular information highlighting debris levels and corrosion throughout the pipe, total debris in the sewer, a colored flat of the pipe being inspected, and cross sections every 50 feet and at places of interest. The flat is a color-coded unwrapped view of the pipe from manhole to manhole. The top and bottom of the flat represent the data collected below the water line while the middle portion of the flat provides the data collected by the laser. The various colors identify the amount of corrosion and debris as well as the location. Each cross section identifies the amount of debris as well as the amount of corrosion. This deliverable enables the engineer or owner to have the information from all three sensors incorporated in one location, thus helping to making the data easy to understand. In addition to the cross sections and flats, three-dimensional views are also provided. Paper F

4 3. RESULTS By utilizing the HD Profiler inspection technology, the City was able to collect a significant amount of data that had not been previously available via standard CCTV inspection. Two of the more useful data categories newly available to the City were quantifiable measurements of sediment and corrosion: Pipe Sediment Depth of sediment as measured using the sonar results. These results are based on the average sediment depth measured in each pipeline segment. It will be noted that there were several pipeline segments for which no sediment data is available. This is primarily the result of too little flow in the pipelines to collect accurate sonar data. In these areas, flow was inadequate to provide the clearance needed for the sonar equipment between the water surface and the bottom of the pipe. For the areas for which data was collected, it can be seen that most of the pipeline segments have sediment depths of less than 10 percent of the total pipe diameter, meeting the City s current minimum cleaning goal. This was generally good news for the City. It should be remembered that the pipelines selected for inspection consist primarily of large diameter pipelines near the City s treatment plant. Because of their relatively flat slope and location at the bottom of the system, it is believed that these pipelines are the more prone to sediment accumulation than most other pipes in the system. Because of their size and flow rates, these pipelines are also the most costly and difficult pipelines to clean in the system. Using the data available through the inspection, the City will be able to focus its cleaning efforts only on those pipelines that exceed the City s goal. Corrosion Corrosion measurements as estimated from laser profiling. These results are based on the maximum corrosion measured at individual cross sections taken in each pipeline at intervals of approximately 50 feet. The majority of the pipeline segments have relatively little corrosion. This was generally good news and less observed corrosion than might typically be expected given the average age of the pipelines and their location at the bottom of the system. However, there were a small number of segments with measured corrosion that would suggest the need for immediate action. There was also a significant amount of pipe with enough corrosion to suggest that measures should be implemented to protect the pipe from further corrosion. Quantification of corrosion has been a very useful tool to the City in terms of prioritizing repair and rehabilitation projects on its major trunk lines. While consisting of a relatively small portion of the total pipe inspected, a few areas of severe corrosion were identified that will be replaced or rehabilitated immediately. This pipeline was located at the transition of a long flat section of pipe to a short steep section that resulted in hydraulic turbulence. It appears that the turbulence has resulted in the release of hydrogen sulfide at high levels at this location. The turbulence may also be adding to the humidity in this pipeline which has resulted in prime conditions for the formation of sulfuric acid and corrosion of the pipe. While a few dramatic instances of corrosion were identified as described above, these occurrences were rare and would have been identified as problems through typical CCTV inspection activities. Of greater use to the City was the quantification of more modest amounts of corrosion. In these instances, CCTV inspection would have noted some corrosion, but the extent would have been difficult to quantify. Correspondingly, it would have been difficult to make a decision on what type of action would be necessary for each pipeline segment and prioritize the actions without the detailed corrosion measurements. Based on the results of the inspection, the City had identified a number of specific actions it will pursue over the next several years: Seeing the Unknown With the combination of above-water and below-water inspection technologies, it is now possible to see the entire cross section of the pipe. In several instances, the sonar identified major structure flaws and significant offset joints. In brick sewers, the laser data identified the number of brick courses missing from the crown of the pipe. In other cases, the laser data quantifies deflection (ovality), which enables life cycle analysis with successive inspections. Pipeline Rehabilitation and Replacement Using the inspection results, a group of the City s pipelines have been identified for rehabilitation or replacement. The worst sections of pipeline inspected have been identified for Paper F

5 immediate rehabilitation, while pipelines in a little better condition will be rehabilitated within the next few years. While only consisting of a small percentage of the total system, the inspection provided several benefits relative to identifying these pipelines: Understanding of Severity The pipes identified for immediate rehabilitation are those that were deemed to represent immediate concern and require rapid attention. Without the inspection, these pipelines would have been identified as problems, but the importance of quickly attending to the problems may not have been as apparent. Efficient Use of Funding Understanding which pipes need rehabilitation is as important as understanding which pipes do not need rehabilitation. Based on the inspection, the City can confidently conclude that the majority of the pipes inspected are in good condition and do not need immediate attention. This minimizes the total cost of rehabilitation for the City. Prioritization of Rehabilitation Within the list of pipelines identified for rehabilitation is a range of condition severity. Some pipelines are in need of immediate attention, while others may still be serviceable for a period of time. Having detailed data from the inspection has allowed the City to prioritize its rehabilitation projects to make sure those pipelines with the greatest need are addressed first. Pipeline Monitoring All pipelines that were not identified for rehabilitation will continue to be monitored. Those showing some signs of corrosion will be monitored more frequently than those that do not exhibit any corrosion. The benefit of the inspection for this group of pipes is that it provides a baseline for all future inspection activities. As pipelines are inspected in the future, the corrosion measured during the inspection can be compared against the corrosion measured during this initial inspection to calculate the ongoing rate of corrosion. This will help the City be able to better understand where its corrosion issues are the most severe and estimate the remaining service life for each of its pipelines. Additional Inspection Based on the results of this initial inspection, the City plans to complete inspection of all the remaining sections of its major trunk lines to help continue its understanding of the condition of its large diameter pipelines. Pipeline Cleaning Using the data available through the inspection, the City has identified a number of its large diameter pipelines for cleaning. The ability of the inspection to measure sediment in the pipelines, will allow the City to focus its cleaning efforts only on those pipelines with sediment that exceeds the City s allowable limit. 4. CONCLUSIONS Throughout the United States, there are countless combinations of collection system materials, sizes, shapes, and conditions that require innovative inspection technologies. Although millions of feet of sewer lines are televised each year, larger interceptors that carry significant flow are often ignored for a variety of reasons. Access, safety, illumination, cost, lack of redundancy, clarity of information and the difficulty and cost of dewatering are some of the reasons that prevent inspection of these important collection system components. Not only are inspection technologies becoming more available, but also the combined processing of multi-sensor data allows for more accurate condition assessments that were not even practical a few short years ago. The real power of the collection of multi-sensor data is the ability to process the data into a single, comprehensive, easily interpreted submittal. Cities and municipalities understand that one of their most valuable assets is their sewer system. Today more than ever, communities realize the importance of knowing not only where their buried sewer infrastructure is but also the condition of these assets. They also understand that it is more cost effective to be proactive with rehabilitation or replacement of a sewer that is structurally unsound prior to a problem than after a catastrophic failure has occurred. Paper F