Condition assessments: Finding the Weak Link
Condition assessments are vital for safeguarding pipeline assets, and there are a number of new technologies that can help
by Leo Carswell, head of technology, WRc and Zachary Alexander, consultant, WRc
It might be stating the obvious, but one of the biggest problems of managing water and wastewater pipes is that they are almost always underground. So they don’t draw attention to themselves, and there tends to be a lot of soil in the way to stop you from seeing them. We do know some things about them. For instance, we can usually tell whether they are doing their job – if the water stops, or the sewage backs up, there’s a problem. Beyond that, though, much of the time utilities aren’t even 100% sure where they are, let alone what condition they are in.
Fire-fighting is no way to manage valuable assets. Would you allow your car, or your phone, or even a ball-point pen to completely fall to pieces before you did something about it? If not, why would you allow a £10M water main to fail before you took some action? The answer, usually, is because nobody knew the asset was going to fail. Nobody knew it would fail because nobody could see what condition it was in. Pipeline asset condition is a product of many factors, a complex mix of ground conditions, manufacture, installation, previous replacement, weight loadings and so on, which although extensively modelled, the industry doesn’t fully understand as each below ground environment is subtly unique. Hence the need for physical condition inspection.
The key to sustainable asset management is having the right information. In this article we will look at some of the inspection technologies that are currently available, when they should be used, and how they can help water utilities to manage their pipelines and sewers.
Right tool for the job
As an asset manager, you want to deploy your resources as efficiently as possible. Therefore the first question to ask is what sort of survey needs to be accomplished. Do you know there is a problem? Do you suspect there is a problem? Asset inspection is all about investing the right budget in the right place at the right time. Before considering inspection techniques, understanding the risks associated with the asset sets the priority of the pipeline for inspection. Then there is a need to select the most appropriate technique, as no one solution fits all needs. Techniques can be selected using a decision matrix based on resolution, reliability and cost.
Resolution is the level of condition detail the technique is capable of identifying, and it increases with increasing technology capability.
Reliability is the level of certainty in identifying the condition. Generally, uncertainty decreases with increasing technology capability.
Cost, in £ per metre or km, increases with technology capability.
Other considerations are the pipe material and the purpose of the inspection. There is a solution for every diameter and material of pipe, and different equipment for leak detection and condition assessment.
The water industry in the UK has for several decades looked enviously over the fence at the oil and gas industry and the techniques they have developed for inspection of critical pipeline assets in extremely challenging environments. Although technology transfer to water has been mooted, cost and logistical challenges created seemingly insurmountable barriers. That was until very recently. Now some of these techniques are being used in the UK and the advantages these techniques offer are being realised by the water industry.
First, we’ll look at systems for inspection of pressure pipes.
One technique which has been extensively used in United States and Canada (over 10,000km of pipeline inspected in water, sewer, oil and gas networks) and is now being used in the UK is a technology called SmartBall. SmartBall is a low-resolution inspection technology. It’s also free-swimming, which means that it can be released into a live water main and allowed to roll along, gathering data all day, until it is trapped and removed from the pipe up to 40km downstream. SmartBall has on-board military-grade gyroscopes, so it knows where it is at all times and can plot the course of the pipeline.
There are two versions. One type uses acoustics to detect leaks down to the size of a pinhole, even at 1 bar (of pressure). The other type uses electromagnetic waves to carry out condition assessment by determining the level of stress in the pipe wall. Because damaged pipe is more stressed than undamaged pipe, this shows up where problems lie. SmartBall condition assessment also reveals the position of pipe joints. This means that each individual length of pipe can be compared to other lengths of pipe and any anomalies can be located.
Where higher resolution is required, alternative tools are available, these again originating from the oil and gas industry. PipeDiver is a free-swimming inspection technology for condition assessment of pipes from 400–3000mm diameter. It carries an array of petals, on which a variety of sensors can be mounted. These provide high-resolution electromagnetic scanning capabilities. The PipeDiver can identify broken metal wires in reinforced concrete pipes, as well as cracking, corrosion, excessive stress, and other defects on a variety of pipe materials. It can autonomously negotiate butterfly valves and bends.
As an alternative to free swimming techniques the WRc Sahara platform offers the potential to introduce tethered sensors into a live water main. In addition to the established acoustic sensors used for leak location Gross Metal Loss inspection offers an alternative low-resolution option. It plots the relative thickness of the walls of ferrous pipes. This allows it to detect internal and external corrosion and gives the information needed to determine whether a pipe is in need of further attention. For plastic pipes an alternative approach can be used based on Conductivity Assessment and the same Sahara platform giving a maximum range of 2000m from the point of insertion. The plastic pipe conductivity assessment technique can find and size leaks, identify old repairs, and find ‘lost’ fittings. It also plots the course of the pipeline, which is traditionally challenging for plastic pipes.
Other techniques offer specific advantages. Sonar inspection on the Sahara platform gives an image of the cross-section of the pipe. It has the advantage that it can be used in turbid water. It is often used for quantifying the extent of sedimentation and build-up of zebra mussels in raw water mains and can be used in tanks as well as pipes. For some tasks the human eye is unbeatable. Identifying an obstruction, inspecting blocked connections and determining the extent of epoxy lining failure are some of the tasks the CCTV survey has been used for. The Sahara CCTV system is capable of sending back live images up to 2000m from the insertion point, and does not interrupt flow.
We’ll now turn our attention to systems for inspecting gravity-flow pipes.
WRc quite literally wrote the manual on benchmarking gravity sewer inspection. In that original manual, we identified that current CCTV procedures fall short. Limited field of view, inability to see below the water level, and – the elephant in the room – operator subjectivity all combine to make CCTV surveys somewhat unreliable. Electro Scan doesn’t have any of those problems, because it simultaneously scans every point of the clock using electrical currents – which are completely objective. Electro Scan can ‘see’ defects because any defect that leaks water must also leak electrical current. It can assess their length, height, and infiltration rate – valuable information that cannot be reliably obtained by CCTV methods. As a recent example, in a UK sewer inspection in May 2015, a CCTV survey identified no defects at all. A 15-minute Electro Scan survey identified 11 defects and prioritised them by infiltration capacity – the worst being capable of passing 24,000 litres of groundwater per day.
CCTV surveys provide a huge amount of information but trying to identify the specific important details is challenging without dedicating lots of time and resource. There is also the issue of bad lighting obscuring detail and the ever-present possibility that the operator will simply drive past a defect while pointing the camera the wrong way.
However, using panoramic vision, it is possible to effectively ‘take a photograph’ of the entire inner surface of a sewer. This photograph lays the whole sewer flat before your eyes, so you can easily tell the parts that need attention and have no need to scroll through seemingly-endless video footage of the inside of a sewer. This eliminates the problems associated with 1970s CCTV technology.
Laser and sonar
The same robot that carries panoramic vision can also carry laser and sonar sensors. These both perform the same task of accurately mapping the internal surface of the sewer in 3D – laser above the waterline and sonar below it. Areas where the circumference of the sewer appears larger or smaller than it should be are highlighted, since these are good indicators of potential problems.
Deep Pipe Locator
Applicable to any type of pipe, this method can locate pipes at a depth of over 20m within centimetres. While not strictly an inspection technology, it is invaluable in cases where construction, and especially piling, is going to be undertaken in the vicinity of a water main or sewer whose location is not precisely known. This can enormously increase the value of the land above the pipe.
So much for our overview of pipeline inspection technologies. It’s well known that UK water companies are currently working to a 1,000 year replacement cycle. In the UK there isn’t enough money to do all the replacement we need to and this situation is not going to change. We therefore need to use the technologies which are now available to assess and address the ‘weak links’ and ensure pipeline assets remain fit for purpose and deliver for customers.
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