Developments in Pipeline Condition Assessment Using Remotely Operated Vehicles

Editor's Notes

• #4: INTRODUCTION Over the past few years, through its research and development programme, the Water Corporation has developed a remotely operated inspection vehicle (Challenger™) capable of operating over long distances within large-diameter pressurised pipelines. The Challenger utilises fibre-optic and computer technology to inspect pipes over distances not achievable using conventional equipment. Due to its unique articulated construction, the Challenger can be deployed through standard manholes into empty or flooded pipes. Some capabilities of the Challenger vehicle are: Suitable for pipes 600mm to 1400mm in diameter Long-range inspection capability of more than 3,000 metres Can be fitted with various instruments, manipulators and tooling Can be deployed through standard manholes Multiple digital video and/or photographic cameras Pressure rating of more than 150 metres Digital image and condition assessment data recording Can be operated in remote areas with minimal technical support Most importantly, the Challenger eliminates the hazards involved with personnel entry into “live” mains.
• #5: EARLY DEVELOPMENT The original impetus to develop a long-range inspection capability came from the planning for the refurbishment of the 640km Perth to Kalgoorlie pipeline sections of which are more than 100 years old. Because the manholes on this pipeline are located between 2 and 4 km apart, an inspection vehicle with a range capability of at least 2 kilometres was required. Apart from the Perth to Kalgoorlie pipeline, the Water Corporation operates some 42,000km of large diameter pipes throughout Western Australia. It was obvious that the inspection equipment would have wide application. To minimise the technical risk, the development of the Challenger system was staged over a number of years. Work completed in 2000 focussed on the development of a basic system capable of inspecting at least 1,500 metres of flooded or dry pipe. Further development resulted in an integrated, containerised system with 5,500 metres of a light-weight optical fibre umbilical, umbilical reel and deployment equipment. In 2005 a digital recording system was developed to replace the array of VCR’s that was previously used. In 2006, a prototype fully digital system was completed. In the context of the inspection equipment commonly in use throughout the water industry, the project was ambitious requiring a number of challenging technical issues to be addressed. Not the least of these was the acquisition of a purpose designed, high-strength, lightweight optical fibre cable capable of both transmitting images and data between the inspection crawler and the control console and of hauling the crawler back to its insertion point at the completion of each inspection run. The high strength of the umbilical allows the crawler to be recovered in the event of a vehicle breakdown. Some other technical issues encountered during the project were: The requirement for a fail-safe drive system Development of energy management strategies to enable the range target to be achieved Development of software to handle the 300,000 images and data collected during a typical survey
• #6: Sonar In May 2007, sonar profiling equipment was fitted to the Challenger vehicle enabling detailed profile surveys to be performed within flooded large diameter trunk mains. Figure 4 is a screen capture of the sonar’s operating software. The calliper function accurately indicates the diameter as 735mm. A piece of 70mm x 80mm rough sawn timber placed in the tank has been clearly imaged. Other features that can be identified in this image are: Increased cement lining thickness over the locking bars at 1 o’clock and 7 o’clock. Variations in the surface texture of the cement lining - smooth trowelled surface between 4 and 5 o’clock and an un-trowelled “orange-peel” finish elsewhere. Using a combination of cameras and sonar fitted to the vehicle, the quality of the condition assessment data from flooded and partially flooded mains is greatly enhanced.
• #7: RECENT DEVELOPMENTS Recent system development has concentrated on enhancing the quality and scope of the data collected by using better camera technology, improved software and by incorporating non-visual inspection instruments such as pulsed eddy-current steel thickness measurement. Digital Cameras As video is primarily an entertainment medium, its wide-screen format and compression algorithms are not generally appropriate for inspection work within pipelines. Also, as the video format produces 25 or 30 images per second per camera, large amounts of redundant data and wasted data storage capacity results. For this reason, the Challenger’s original video cameras have now been replaced with digital photographic cameras which take several high-quality image sets per second.
• #8: Software Applications The move away from a video based inspection system has required the development of suitable software to enable the inspection images and associated data to be stored, processed and disseminated. Several specialised software applications have been developed to capture, process and archive this data, and to produce electronic reports. With this software, the inspection data can be presented to the client in the form of a compact mass-storage device. This electronic report includes all images and the details of defects and can be viewed using an intuitive browsing application. This removes the tedium associated with viewing multiple videotapes or DVD’s and allows the asset condition to be easily reviewed by the asset manager at her work station.
• #9: On-board Instrumentation The design of the Challenger inspection vehicle incorporates data channels intended to enable manipulators and instruments to be installed. This facility has been used to perform Incotest® pulsed eddy-current steel thickness surveys within trunk mains. The Incotest® system can measure the average steel wall thickness beneath the internal cement lining providing valuable information relating to the external condition of the pipe-wall not normally detectable using visual survey methods alone. The Incotest® data presented in figure 4 was captured during a survey of a sewer pressure main that had suffered external corrosion caused by acid-sulphate soil conditions. Although not visible internally, the extra steel thickness of the welded band joints at each end of the elbow and the corrosion perforation at the 7:30 o’clock position were clearly detected. The use of such non-destructive testing (NDT) instruments and sensors can provide valuable inspection data and improves the condition assessment process.
• #10: Instrument Manipulator With increased emphasis on non-visual inspection techniques, it became necessary to develop a manipulator to facilitate the deployment of various sensors. As the manipulators commonly available proved to be unsuitable for work in the confined space of a pipe, a 2-function manipulator was designed and fitted to the vehicle. Radial position sensors allow NDT instruments to be accurately deployed anywhere on the internal pipe surface.
• #11: CHALLENGER OPERATION Traditionally, the approach to pipeline inspection work, whether manned or remotely operated, has been to travel along the pipe pausing, to record in detail, defects and areas of interest along the way. This approach is very time consuming and severely limits the length of pipeline that can be inspected in a given time. It also requires that an experienced condition assessment technician is on-hand to determine what should be inspected and what can be safely ignored. The Challenger inspection system now allows a fundamentally different approach to pipeline condition assessment. By utilizing an array of cameras, all of the visual data can be captured in one rapid continuous inspection run. Although the operator can flag areas of interest to assist the condition assessment engineer, he does not need to play any part in the assessment process. This allows the field crew to concentrate on equipment operation and data collection and to not to be distracted and delayed by condition assessment tasks. Following each inspection run, the field data can be sent to the condition assessment engineer for detailed analysis. A data processing software application developed for the Challenger system provides the tools needed to enable the condition assessment report to be prepared.
• #12: OPERATING COST The cost to inspect a pipeline using the Challenger system is dependent on a number of factors. These include: Remoteness of the pipeline Excavation requirements Traffic control issues Location and size of manholes Nature of the terrain along the pipeline Ease of vehicle access to the pipe Environmental issues relating to the release of water Bushfire risk considerations Although in some circumstances, dealing with these issues can result in considerable fixed cost, the long-range capability of the inspection system ensures that the marginal cost of the inspection is low, typically $2 to $4 per metre. Even with short inspections, the advantages of using an underwater remotely operated vehicle rather than manned entry into the pipe are significant. Some of these advantages are: Simplified OS&H requirements and reduced risk exposure for personnel; Better and more comprehensive data and image capture from multiple on-board cameras and sensors; Minimal scouring and re-charging of the pipe is required; the asset can be returned to service faster and with less environmental impact.
• #13: RECENT INSPECTION CASE HISTORIES Although many long-range pipeline inspections confirm the asset manager’s expectations of the pipe condition, it is the unexpected discoveries that can be of value in the condition assessment process. Here are some examples of unexpected discoveries during what would otherwise have been routine inspections. Case 1 - DN760 MSCL Perth to Kalgoorlie Water Supply Pipeline In May 2002, during an internal inspection of the pipeline near the town of Southern Cross, Western Australia, an unusual off-take was discovered. After considerable external searching, the operators eventually found that the off-take had been concealed within a concrete support bolster. They had discovered the water supply to a large scale hidden cannabis plantation located some distance from the pipe. The discovery of the illicit off-take would have been unlikely without the long-range inspection technology.
• #14: Case 2 – DN1400 MSCL Serpentine During a survey of the Serpentine DN1220 main in 2003, the inspection vehicle encountered several trout (probably Salmo trutta) of good eating size swimming inside the pipe approximately 12 kilometres downstream from the Serpentine pipe-head dam. This unexpected find lead to further investigations of the effectiveness of the intake screens and associated equipment at the dam.
• #15: Case 3 - DN600 MSCL Ophthalmia Dam to Mt. Whaleback Iron Ore Mine Pipeline In May 2006, the Water Corporation was engaged by BHP Billiton Iron Ore to inspect the process-water pipeline to the BHP Billiton iron ore mine at Mount Whaleback, Western Australia. A 2.5km section of this pipe was to be replaced as severe internal corrosion was suspected. However, the remote inspection revealed that although the cement lining of the pipe had deteriorated significantly, the steel shell was still in excellent condition. That result meant that the pipe could be refurbished by renewing the cement lining at a fraction of the cost of pipe replacement.
• #16: Case 4 – DN900 MSCL Perth to Kalgoorlie Water Supply Pipeline The Perth to Kalgoorlie pipeline is buried where it passes through the town of Kelleberrin, 165km east of Perth, Western Australia. In July 2006, this pipe was inspected using the Challenger and what had been thought by the asset manager to be a 40-year-old DN900 MSCL pipe with a substantial remaining life was found to be in fact a 100-year-old DN760 locking bar pipe in very poor condition and liable to imminent failure.
• #17: FUTURE DEVELOPMENT The Challenger long-range inspection system has now been in operation for several years providing effective condition assessment of the Water Corporation’s large diameter, pressurized pipeline assets. Future development will further enhance the quality and broaden the scope of the data produced and will also reduce operating costs. Some of the areas for further development presently under consideration are: Better software with further enhanced functionality More NDT condition assessment instrumentation Hot-tap deployment into live mains Longer range to reduce the number of entry points required Higher speed to reduce survey time Improved reporting and on-line client access to the condition assessment data Higher resolution cameras Improved manipulators
• #18: CONCLUSION The Challenger long-range remotely operated inspection system has proven to be a versatile inspection tool. It has now been developed to the stage where a continuing programme of asset condition assessment work is in place with approximately 50 kilometres of large diameter pipe inspected annually throughout Western Australia. Although it has been instrumental in the discovery of a number of anomalies that would otherwise have remained undetected, the confirmation that a critical asset is in good condition is of equal importance to the asset manager.