Pipeline inspection techniques

May 23, 2007

Thorough surveys are essential for all pipeline infrastructure to avoid unforeseen problems, and there is a considerable range of techniques and methods for inspection and condition reporting that assist in catching major surprises before they happen.

The early detection and identification of cracks, leakage points, blockages or intrusions allows for the adequate repair or replacement of pipeline to be undertaken.
With pipeline infrastructure ageing, the urban sprawl widening and the population growing, demand is continually increasing on our water and sewer mains.
The development of teleinspection technology equipment has opened up a new world for the maintenance, repair, replacement and construction of pipelines, allowing greater consultation ahead of any excavation work.
Teleinspection technology allows pipe inspection without any digging, allowing inspectors to save the unnecessary cost of excavation around a pipe which might still be in a robust and safe condition and not in need of replacement or even repair.
Major developments and improvements over the years in the design of equipment now allows for improved results when determining the most appropriate method or product equipment to be used to complete any scheduled work.
Robotic CCTV crawlers, pushrod portable systems, laser profiling and sonar profiling are just some of the inspection technology systems now being utilised during regular inspection of water and sewer mains. These systems allow for comprehensive information on the condition of the underground infrastructure to be collated, allowing a planned maintenance program to be developed.
CCTV robotic crawlers/tractors and pushrod manual systems allow for condition reporting and surveying of an asset, giving early warning of failures and allowing for economical repair under no-crisis conditions.
CCTV is used in a variety of methods. The camera is placed in the pipeline and is either winched through or self propelled. Crawlers are electronically powered, with the power supply for the camera coming from a connection at the rear. The picture and control signals are transferred to a monitor control centre managed by an operator working to detect and determine what condition work or repairs are recommended.
Robotic crawlers
Robotic crawlers first appeared in the 1950s and the 1990s saw the coming of the age of this equipment in Australia. A greater range of products and equipment now allows inspections to be completed in areas once deemed inaccessible, providing vision that could previously not be seen in small, large or restrictive locations.
Specialist robotic crawling tractor systems are now produced to inspect pipes ranging from 100 mm up to larger pipes in excess of 2 m in diameter.
Crawler systems can be fitted with a fixed forward view camera head, a pan and tilt camera head, or even a zoom pan and tilt camera head fitted with laser for crack width measurement detection. Some crawlers are fitted with an elevator lift to allow greater camera height and vision while working in a larger size pipe. Others are steerable to give directional control if working in larger pipes or box culvert pipe.
Recent developments have led to the introduction of lateral inspection systems, with the system entering the service connection line from the main using remote control functions and allowing vision from a pan & tilt camera head. Lateral inspection systems can be deployed in 150 mm mainline pipe upwards. Introduction of the camera into laterals is aided by a motorised driven guide device and monitoring camera.
The new 3D Optoscanner, Panoramo, is the latest inspection system to be released to the Australian market, capturing images of the pipeline and its condition through the use of two high resolution digital photo cameras. The two 186° wide-angled camera lenses are integrated in the front and rear section of the housing. Pipes are inspected at a speed of 35 cm (14 inches) per second.
During inspection, xenon flashing lights are triggered at the same position in the pipe. The hemispherical pictures are scanned together to form 360° spherical images. During the scanning process, which is possible in both forward and reverse direction, the data is transferred digitally to the inspection vehicle and is immediately available to the operator for orientation purposes and to locate any obstructions.
The data is stored in the form of film and removable onto hard disks or DVDs as storage media. This unique method of inspection captures a complete inspection of the pipe surface allowing you to rotate and also pan & tilt the camera image at any position in the pipe whilst reviewing the data film.
An unfolded 2D view of the inner pipe surface allows rapid viewing of the pipe condition and permits computer-aided measurement of the position and size of objects. For further analysis and data processing, survey software is recommended to complement pipeline inspections.
Veolia is currently using the Panoramo in Australia and will shortly commence a fiveyear contract with Yarra Valley Water for inspection of mains with the system.
Veolia Environmental Services Operations Manager Michael Kelly is particularly pleased with the results the Panoramo has delivered. “The Panoramo system is truly a remarkable advancement into the CCTV market - no question,” said Michael. “To be able to take a true 360 degree virtual reality tour of an underground asset from the comfort of an office is something that can never be matched in quality, speed or accuracy. We can’t wait to get the next one!”
Laser profiling
The ability to detect and measure changes in pipe shape or bore clearance, be it due to deformation, siltation, corrosion or erosion, is difficult at the best of times, especially when using conventional CCTV camera systems.
This is further exasperated by the fact that the video footage produced by the camera is without calibration or a reference point from which to take accurate measurements of any kind – it is all guesswork. Any conventional CCTV survey thereby runs the risk of missing subtle, but relevant, changes in the pipe’s shape as observations are dependent on the keenness of the operator’s eye.
Rigid pipes, such as vitrified clay, present less of a problem as these tend to crack or collapse rather than deform and the results are rather obvious. However, even in circumstances where deformation is obvious it can still be difficult to determine the exact extent of the deformation or if the deformation has got worse over time.
To address this problem, recent advances in pipeline inspection technology have seen the refinement and development of state-of-the-art profiling systems that have enabled the range of applications and degree of accuracy of traditional survey delivery systems to be enhanced dramatically. These new systems are all geared towards the elimination of human error, increased reliability of technology and, ultimately, accuracy of information.
Laser profiling incorporates cutting edge, split laser technology that allows for pipe profiling to be carried out under normal light conditions. This means that profiling and conventional CCTV imaging can be carried out in tandem without interfering with the quality of the survey results. The laser profiler allows you accurately determination of amount of damage contained within a pipe asset. The attachment shows the actual shape of the pipe while the software can predetermine the correct pipe shape and calculate the difference between the two.
The aim of projecting a bright line onto the internal pipe wall is to define a plane on the video image where measurements on the image can be translated in the real dimensions of objects observed through the camera.
The system is calibrated by using two fixed points with a known separation on the radial light plane, established with small marker pins that are illuminated by the laser light. These act as calibration points on the video image to identify the scale of the image where it is illuminated by the red laser light. The laser intensity is sufficient to make the generated red line on the pipe bright enough to see clearly on the video image under normal light conditions. Calibrating the video image allows measurement to be carried out after the video has been recorded and does not slow the rate at which the video can be recorded.
The software measurement tools provide the ability to accurately determine the amount of flow loss caused by a wide variety of pipe faults. Combining the laser profiler and the measurement tools makes obtaining the actual degradation of the pipe a reality. Analysing this data determines whether pipe refurbishment is necessary.
Sonar pipe profiling
The sonar system was specifically designed for the inspection of submerged and semi-submerged pipelines. It uses high resolution/short range sonar and only works underwater. The system itself is capable of inspecting pipelines from 225 mm in diameter to conduits in excess of 5 m in diameter.
The head of the sonar, its transducer, looks sideways at right angles to the direction of the motion through the pipe, resulting in a cross sectional view of the pipe in real time.
As the speed of inspection is critical for the longitudinal resolution, the general guideline for the speed of inspection is approximately 100 mm per second. The sonar uses a colour display to indicate the type of surface the sonar is sweeping, denoted by red for a hard surface and blue for a softer surface. As with the CCTV system, the method of propulsion would either be self propelled or floated, dependent upon known circumstances in the pipeline or the size of the pipe. If heavy silt is expected then pipelines above 600 mm would be surveyed by floating the sonar along the crown of the pipe. If the pipeline were less than 600 mm then either the self-propelled or winch assisted self-propelled method would be used. The level of deformation and/or silt levels can easily and accurately be measured by the site software.



This article was first published in Trenchless Australasia.

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