- +27 (0) 10 446 5706
- gp@orsco.co.za
- Plot 13, RD 5, Brentwoood Park, Gauteng, 1501
What is Pipeline Condition Assessment you ask, well when it is evident that a pipeline is suffering from multiple leaks, but the number, location, size, and severity of pipe wall perforations are unknown. What the root cause of the wall perforations are, and whether it is caused by internal or external corrosion factors.
Deciding on the most appropriate strategy to address the leaks and deteriorating pipeline condition will require a thorough understanding of the current pipe condition as well as the factors contributing to its deterioration. The ultimate strategy should strive to address the evident mode of failure (leaks), but also to understand what is causing the leaks and consider options to prevent or reduce the risk of further pipeline deterioration to ensure that the asset life is extended at minimal cost to the owner.
Pipeline Condition Assessment is not a single activity but rather a process whereby multiple technologies and skills need to be applied selectively and sequentially, resulting in an informed conclusion being reached as to the condition of a pipeline and its components.
The cost of data acquisition is actually initially getting someone to the site and then coding & recording it “Peter Henley, WRc”
The actual cost of coding is insignificant in comparison to what it costs to get the manpower and equipment there during the maintenance of pipes.
This study deals with training programs developed for a stepped Condition Assessment approach which documents symptoms as they appear.
We must urgently develop skilled professionals to meet the national trenchless industry’s needs. In South Africa, trenchless proficiencies are developed informally (mostly with on-the-job training). This training lacks a proper curriculum and programme structure while trainees only become exposed to the specific elements required to complete a specific project or task.
Zafar Khan observes ‘The overall state of municipal infrastructure systems worldwide is not satisfactory.’1 As much as this is true for developed nations, it is even truer for developing nations where urbanization has seriously impacted existing (and ageing) infrastructure to cope with the population influx. There is an urgent need to develop a legacy of passing down invaluable condition assessment (CA) data about our pipe networks – looking at the past and capturing what we have at present so as to plan for the future. We are pipeline detectives – as if in a legal case about pipes.
In South Africa there is constitutional protection of a person’s right to be tried in their own language (The Bill of Rights (1996)). However, the Chief Justice has determined that all written court records must be kept in English. The implications of this is that most South Africans do not have full access to justice in their home language since only 8.1% of South Africans speak English at home (English is only the country’s sixth most common home language). Statistically, then, there is a 91.9% chance that a South African will be at a disadvantage during a court case because they cannot properly understand the proceedings, documents, and records. In our industry, this language barrier makes training of competent technicians just that much more challenging. For this reason, it is essential to use as much imagery (photographs and illustrations) as possible.
We cannot influence the South African legal record keeping system, but we can simplify processes for harvesting trenchless CA. For technicians maintaining the pipe network to be able to identify anomalies they need to understand how a pipeline should function according to its design. Increasing urbanization is putting systems under stresses they were never designed to handle. Without international language conventions for reporting on CA, that is as familiar as a person’s mother tongue, CA reporting will be compromised. In gravity systems there is already a long-standing standardized coding in use by the Water Research Centre (WRc) in Britain and NASSCO in the US yet there is no similar system for pressure pipes.
It is not possible to cover all the technologies available today, but we are going to look at some of the most accessible technologies for everyday CA.
Before in-pipe inspection, there are several procedures that might be utilized to determine what level of the survey should be recommended.
Smoke testing is a fast and effective method for establishing points of in- and exfiltration cause by breakage or illegal connections. A smoke generating blower is placed on a manhole opening and the smoke will blow through the system and rise to the surface wherever there are breaks or leaks. On large sites a technician might use a drone to get a bird’s eye view and quickly locate places where the smoke is escaping.
Fluorescent dyes (dyes that light up brightly in the presence of an ultraviolet light source) help technicians determine where a flow of fluid is going. Adding dyes to the flow and observing possible outflow points will quickly reveal if there is in- or exfiltration on the system. One might use different color dyes simultaneously in a sewer and nearby stormwater drain to confirm the existence and direction of flow from one to the other. By generating a sound at one manhole and measuring the sound at a second manhole an acoustic blockage detection system can establish whether the pipe is blocked or not without having to insert a camera. This is not a high-skill operation and so can often be a cost- effective early test when looking for blocked pipe sections.
By generating a sound at one manhole and measuring the sound at a second manhole an acoustic blockage detection system can establish whether the pipe is blocked or not without having to insert a camera. This is not a high-skill operation and so can often be a cost- effective early test when looking for blocked pipe sections.
This instrument will be covered in detail in the next section. Suffice it to say that this camera can be deployed into a manhole very quickly to acquire high-quality in-pipe images.
If it is deemed necessary for a man to climb down into the sewer manhole, then it is mandatory that he carry a gas detector to test the quality of air inside the confined space. Failure to properly follow this safety precaution could result in death. The detector should be able to measure H2S, CH4, and O2.
Imaging is useful for both preliminary site inspections and in-pipe visual condition assessment. Images should be made of site conditions, manhole chambers, and any excavations made for assessment purposes.
In-pipe observations should include:
Before looking inside the pipes contractors must understand the conditions on site. A mobile phone camera is a perfect instrument for this and information about the location and direction of the photographs taken can be extracted from the resulting photographs. This data can be extracted for inclusion in final reports. Technicians should also take detailed observation notes of the site conditions.
The modern pole camera offers many benefits for level 1 surveys. Recommended pole cameras include a camera that can tilt and zoom to get close-up images of any faults observed. They will have powerful LED flood lights to illuminate the inside of the pipe. There should also be an integrated laser range finder. With this range finder the operator can focus the laser on the point on the pipe where the observation is located and a distance to this point can then be recorded.
The camera should have a wifi connection to a tablet or mobile phone to record images as they are taken. Future software will enable observations to be included in the camera images using exif data formatting. With this capability, even after an image has been sent to another computer the information will still be available for reporting purposes.
Our experience with these cameras has shown that it is useful to have a stabilizing clamp to minimize vibrations in videos and still images.
Every plumber doing drain work today should have a push camera. These vary greatly in size, length of the reel, and camera features. It is best to have a self-leveling camera head as this makes images easier for clients to understand. Centering skids to keep the camera centered in the pipe are also highly recommended. More advanced push cameras might also include a tilt and pan head enabling operators to get even better images of pipe observations. Modern push cameras usually include a distance counter for measuring the distance to observations inside the pipe. When the system includes a keyboard, the technician can make annotations on the images during the survey process. These systems usually save the images to a memory stick enabling the transfer of images to a desktop or laptop computer for reporting. Push cameras are limited in the distance they can survey in a single pass. Depending on the pipe being surveyed a survey cannot extend further than about 120 meters. Typical cameras have cables anywhere from 30 to 120 meters in length.
Crawler cameras are like push cameras, but the camera is mounted on a motorized tractor unit that pulls the control cable through the pipe. Because of this, they can survey much greater distances. Crawler cameras usually have an inclinometer that records the angle of the unit within the pipe and so can clearly show the horizontal pipe profile between manholes. The head height of the camera can be adjusted to center the camera in the diameter of the pipe. These cameras also often have multiple wheels or tractor options to best fit the pipe being surveyed.
Other options include the attachment of laser or lidar pipe profiling devices for obtaining cross-sections of pipes at given locations. These profiles can highlight dimensional differences in the pipe. In concrete sewers, for example, corrosion due to the formation of sulphuric acid resulting from the presence of the gas hydrogen sulfide will result in a mushroom-shaped profile where the acid has eaten away the alkaline concrete above the liquid level. On the other hand, pipes carrying corrosive fluids might have the opposite profile (typical in mine drain conditions) where the invert is corroded away. For larger crawlers, technicians will need hoisting equipment to safely lower and lift the camera from manholes.
Figure: Crawler Camera
These cameras float in, or on, the fluids in the pipe.
Tethered versions are self-propelling (figure 4). The version depicted here uses a spiral screw that can move it over even very thick sludge. These can be equipped with a camera for above-surface visual inspection, lidar for above-surface profiling, and sonar for sub-surface profiling
Free-swimming units are lowered into the sewer and move through the system at the speed of the flow. In good visibility clear water they have neutral buoyancy so that they float in the middle of the flow, whereas in high turbidity the free swimming and tethered units must be positively buoyant for above the water line HD cctv inspection, with sonar under the water level. These units are preferred for long surveys of up to 50km. Furthermore, they are small enough to navigate even 90˚ bends in the system. Options available in these instruments might include, video, sonar, Doppler radar (for accurate speed and distance measurement), acoustic leak detection (in pressure systems), temperature, and pressure.
Before beginning any inspection process, operators should conduct a visual inspection of the site. Notes and related photographs should be taken of on-site conditions. Special attention should be given to manholes and chambers. Observations can include information not available purely from a photographic survey. Technicians can use a clipboard, notepad, tablet, or smartphone to record their observations. They should look for evidence of subsidence, waterlogging, foul odors, or other indicators of problems relating to the drainage or sewerage network on the site.
Whenever a person has to enter a chamber or confined space it is mandatory that the space is safe. At least look to see if there are any cockroaches – our sewer canaries. If cockroaches are present there are not too many noxious gasses. For health and safety purposes, though, technicians should use a gas detector to measure levels of noxious gasses – hydrogen sulfide (H2S) and methane (CH4), and whether there is sufficient oxygen. Instruments capable of measuring all of these simultaneously are readily available. If you want to measure gasses at the bottom of a chamber an instrument with integrated suction pump can suck gasses up through a tube dropped into the manhole. In this case make sure that the tube itself does not give false readings.
GPR systems use radar to create an image of objects underground. New systems can even create a 3D image of the instrument, especially when connected to a GPS system. GPR can reveal voids around a pipe though the pipe itself will prevent it from imaging a void beneath the pipe. GPR works by transmitting a radio signal into the ground and using the reflected signal to establish the depth of objects below the ground. GPR does have some limitations, though. For example, it does not operate very well in wet or salty conditions or in soil that is very rocky. Solid objects have a parabolic shadow cast by the GPR and so voids below a pipe might not be visible. Multi-frequency GPR systems can produce much more detail than earlier single-frequency devices were capable of.
In addition to a survey of the pipeline itself, GPR is also used to perform a geotechnical survey of the environment. It can reveal cut lines, bedrock, and other underground structures that can affect the proper operation of the sewer being investigated.
Figure: A ground penetrating radar unit with integrated 3D imaging capability (CENTRE). GPR use in the field (LEFT), GPR parabolic shadow area (RIGHT)
PPR systems use the same technology as GPR but the units have been re-designed specifically for use inside pipes. The antenna of the PPR points down through the pipe and can reveal voids under the pipe. The PPR also provides information about the pipe itself. In concrete pipes, for example, it can locate the rebar in the pipe structure. A PPR can be towed down the line behind a crawler camera.
Where live flow inspection is required, for example for free-swimming instruments, operators need to know the flow rate of the fluids in the pipe. Available technologies for flow logging include ultrasonic and electromagnetic systems.
Soil chemistry can affect the durability and condition of a pipe. A basic analysis will just test the pH of the soil and can be done with a simple pH kit. When required, soil samples can be sent to a lab for further analysis.
With steel pipelines, the electrical environment can affect the corrosion rates of the steel. Cathodic protection systems are often implemented to mitigate this situation. Using geophysical test equipment condition assessment technicians can determine whether such protection is required. These instruments analyze electromagnetic and resistivity/induced polarization to determine the electrical properties of the soil.
You can use Google Earth to add a plot of the pipeline section with manhole positions and specific fault locations. The resulting map may then be included in your report for output. The fault position could be mapped with a sub-centimeter GPS or simply by measuring the distance from the manhole. If you have a push camera in the pipe you can use a utility locator to pinpoint its location on your map.
Figure: Google Earth site map with GIS data overlaid
For an engineer to properly specify a repair or rehabilitation program he needs accurate data regarding the inclines inside the pipes (the long section). This applies not only to the section to be repaired but also to sections before and after it as flow velocities can affect the efficiency of an installed system. A simplified surveying system using a pole camera pole to replace a surveyor’s staff and a laser level to replace the dumpy level can be used to get levels for a long-section plot. By combining this data with distances between manholes and distances to faults you should be able to plot the full long section of the pipeline showing the position of faults, laterals, and other features.
A utility locator can be used to mark the position above the ground of a camera head fitted with a sonde. You can use a GPS device to plot this position on a Google Earth map.
With a tethered electromagnetic leak detector, it is possible to pinpoint the location of a leak in a live pipeline. The test can be run in both directions to cross-check the accuracy of the location – you should get similar results in both directions.
Figure: Tethered in-stream electro-magnetic leak detection.Pro
Figure: Pipe structure showing wall thickness, rebar, and invert.
PPR, in addition to identifying voids under the pipe, can also locate reinforcing withing the pipe walls.
Length is often measured using the camera encoder while the camera is moving through the pipe system. Where such an encoder does not exist, or where there is a question about its accuracy, there are several alternatives available. Operators can mark the camera cable with electrical tape as it enters the pipe and as it arrives at each point requiring observation information to be recorded. Then, when the cable is retrieved, the operator can use a measuring wheel or tape measure to make note of the marked measurements on the cable. Some crawler cameras, and certainly pole cameras, have an integrated laser measure that can also be used to establish distances to observations within the pipe.
To do any pipe rehab, Hydraulic modeling, or even calculate flow rates through a pipe engineers or technicians will require an inside diameter (ID) measurement. A simple pair of calipers, of suitable size for the pipe being measured, can be employed. A cross-measure attached to the front of the camera can also be used to establish the ID. Such a device can easily be made up using a plastic rod and an old metallic tape measure. ID is especially important where the pipe might be relined to ensure the correct fit of the lining inside the pipe.
The actual shape of a pipe can affect its efficiency. However, a misshaped pipe points to a problem with the pipe. Most pipes are circular, but the pipe profile will affect flow rates through the pipes.
To measure the wall thickness of a pipe a technician will need access to the outside surface of the pipe. When this is exposed an ultrasound device can be employed to establish this thickness.
CA by means of CCTV has been around for a long time, but new technologies are constantly being developed to supplement data captured from the camera. Light detection and ranging (lidar) is one such development and has considerably improved in-pipe CA. Lidar works by transmitting light pulses radially at the walls of the pipe and analyzing the reflected beam to create a three-dimensional image of the inside of the pipe. The same technology as face recognition on a modern phone. Laser-equipped cameras produce similar results from a spinning laser beam projected onto the inside of the pipe.
A lidar-equipped crawler camera can map an entire section of pipe while simultaneously recording CCTV video. Post-processing with the lidar system software can plot cross-sections anything that shows up orange or red in the chromatographs highlights potentially serious problems – the hotter the color the more serious the damage.
While Lidar gives an excellent profile above the water line it does not work for portions of a pipeline filled with water or effluent. In these conditions, a floating sonar device can give a detailed picture of the profile below the water surface and map the level of sedimentation on the invert. The cross-section image produced is similar to that produced by lidar but it only images sub-surface profiles.
Sonar emits sound wave pulses and analyzes the echo to create an image of the surrounding environment much like the way bats and dolphins locate their prey.
Lidar, laser, and sonar all give a cross-section of the internal pipe shape at any given point in the pipe. They can give the actual depth of the damage detected.
Pipeline Condition Assessment is not a single activity but rather a process whereby multiple technologies and skills need to be applied selectively and sequentially, resulting in an informed conclusion being reached as to the condition of a pipeline and its components. (JF Prinsloo Pr Eng PMP)
In South Africa the education threshold is, sadly, very low. As a result, training in this environment is often very challenging. Our mission is to make our processes as simple as possible without compromising outcomes.
It is also important to note that there have been significant advances in artificial intelligence systems generally and this includes pipeline condition assessment. As higher quantities and more detailed data are acquired and fed into these machine learning systems so will their accuracy and usefulness improve. There is a brave new world of condition assessment in the foreseeable future.
With regard to training the onus is on us to equip technicians, not only in specific technologies, but with an understanding of how and when a specific project demands a higher inspection level. For this purpose we have created the following matrix as a quick guide for selecting the most appropriate technologies for your projects.
Thank you for your assistance with the above – Mr. Alaster Goyns
