Water leaks and the ‘jaws of death’17 September 2020

Water demand in the UK will exceed supply in just 25 years, the head of the Environment Agency has warned – with part of the blame falling on leaking pipework. What can be done to avert this? By Adam Offord

We will not have enough water to supply our needs in 20 to 25 years from now, unless we take urgent action to change things, according to Sir James Bevan, chief executive of the Environment Agency, who has singled out climate change and population growth as the two major contributing factors. “And that, ladies and gentlemen, is the jaws of death,” he told those present at the 2019 Waterwise Conference (www.is.gd/evafig).

Whatever the reality of that deliberately attention-grabbing, cataclysmic statement, the solutions needed to remedy the situation are complex, diverse and far from instant. Yet there is something that can be done right now to preserve this most precious resource – namely to tackle the huge quantity of leakages that continue to plague our pressurised water networks.

Take the length of water pipes (mains) owned by water companies in the UK, for example. This stretches to a massive 345,034km – equivalent to a distance of 8.5 times around the equator (www.is.gd/tehuya). It will come as no surprise that some of the water passing through this pressurised network leaks out. The daily loss is calculated to be around 3,170 million litres, which equates to 1,268 Olympic-sized swimming pools.

Reasons why this happens can vary: from ground movement, especially in weather extremes when the ground expands and contracts around pipes, to natural wear and tear, especially in older pipes; from soil corrosion that can literally eat away at some pipe materials, to vibration damage from heavy traffic. The stresses and strains result in holes, cracks or weak seals in the pipework that lead to a constant battle to detect and mend the leak sites – a battle that admittedly can never be entirely won, but where every victory is critical.

And the primary weapon when it comes to determining if an object, product or system functions within a specified leak limit – whether that be for water companies or industry at large – is widely hailed as non-destructive testing (NDT). Its unique selling point? Using a host of testing and analysis techniques to evaluate the properties of a material, component, structure or system for characteristic differences, or welding defects and discontinuities, without causing damage to the original part.

“Of all the problems facing water companies, leaks remain high up on the league table of headaches,” says Alan Hunt, ABB product manager UK & Ireland – electromagnetic flow. “Despite high rainfall in the UK, we have no cause for complacency about our use of water. Much of the water distributed to consumers, a staggering 3.2 million cubic metres of water a day, escapes through leaks. These enormous water losses must be replaced, treated and pumped again to maintain supplies to customers. This, in turn, uses more energy and resources, cutting the sustainability of water operations and leading to higher operating costs.”

Utilities take three general approaches to leakage management, he states: passive control, regular survey and leakage monitoring (in zones or sectors). “Passive control is the least sophisticated strategy and, in practice, is a reaction to visible leaks reported by customers or spotted by the company’s staff. The second strategy of regular surveys involves listening for leaks on pipework and fittings or taking readings of flow rates to identify high-volume night flows. High water consumption at night would suggest a burst or leak. Leakage monitoring is a strategy of monitoring the flows into defined zones or districts to measure leakage and prioritise maintenance.”

Traditional mechanical meters do not offer the accuracy needed and cannot cope with the low flows seen at night, he argues. By contrast, electromagnetic flowmeters offer improved accuracy over a far superior range of flows. “In fact, modern meters could even detect a toilet flushing.”

ABB’s AquaMaster4 is said to be one electromagnetic flow meter designed to help utilities get a handle on water leaks. “Its built-in data logger runs at high speed, giving the user total flexibility to download logged data frequently – every 15 minutes if needed,” adds Hunt. “The user can then investigate, in precise detail, flow and pressure activity during a period of interest, at even higher time resolution. Such high-resolution data aids step testing, leakage detection and water network analysis.”

COOL APPROACH

Testing and engineering company Applus+ also specialises in leak detection, using helium as a tracer gas. In doing so, leakages of cooling water inside condensers within power plants and other process facilities can be identified rapidly and quantified. Andre de Jonge, leak detection department manager, Applus+ RTD, explains that its method of finding a leak is a process of elimination. He says: “Locating a cooling water leak can be done in several ways; which locating method is used is mainly determined by the construction of the condenser(s). Once the condenser half to be tested is taken out of operation, the cooling water input and output valves are closed, keeping the cooling water chamber filled. After this, a controlled [lowering] of the cooling water level takes place, while the space above the cooling water in the water chamber is filled with a helium/air mixture [at atmospheric pressure].”

As soon as the cooling water level falls below a leaking tube, the gas mixture is sucked through the leak into the vacuum system, causing the partial pressure of helium to rise. When the water chamber has been emptied completely, either a leak is present and registered as a marked horizontal band or no leak is present in the examined condenser half. “Eventually, a fast integral test can be performed, without determining the level of the leak,” adds de Jonge. “Where the presence of a leak in the condenser half to be tested is in doubt, a quick integral test will suffice. In this case, the water chamber is emptied immediately, followed by injecting this space with helium.”

The manholes in the water chambers at both sides of the tubes are opened. On one side, extracting ventilators are mounted, giving a continuous airflow through the condenser. On the other side, helium is injected through selected tubes by means of special hoods. “In this way, the entire marked band is tested until a leak is detected via a rise of the partial pressure of helium in the condenser vacuum,” he states. “This implies that the sought leak tube or rolling is located beneath the hood at its last position. By using a smaller hood, the field in which the leak itself exists is discriminated from all other possible locations.” After plugging off the leak, the entire field is tested once more.

TESTING TIMES

Another organisation providing non-destructive testing (NDT) services for a range of industry sectors is TWI (The Welding Institute). This it achieves through a variety of leak testing techniques, such as bubble leak testing, pressure change testing, halogen diode testing and mass spectrometer testing, which uses helium or a helium-and-air mix inside a test chamber, with a 'sniffer' to detect any changes in the air sample that would indicate a leak. Alternatively, a vacuum can be used, in which case the mass spectrometer will sample the vacuum chamber to detect ionised helium, the telltale signature of a leak.

Whatever the means, the Environment Agency’s chief executive Sir James Bevan is clear that water companies “need to redouble their efforts to fix leakage”, as part of a much wider remit to build long-term water resilience. The good news is that, as they are for industry at large, the tools and technology to do so are already there.

Adam Offord

Related Companies
ABB
Applus RTD UK Ltd

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