The UK has no spare water to lose,
according to the Environment Agency
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 sta . The
second strategy of regular surveys
involves listening for leaks on pipework
and ttings or taking readings of ow
rates to identify high-volume night
ows. High water consumption at night
would suggest a burst or leak. Leakage
monitoring is a strategy of monitoring
the ows into de ned zones or districts
to measure leakage and prioritise
maintenance.”
Traditional mechanical meters do not
o er the accuracy needed and cannot
cope with the low ows seen at night,
he argues. By contrast, electromagnetic
owmeters o er improved accuracy over
a far superior range of ows. “In fact,
modern meters could even detect a toilet
ushing.”
ABB’s AquaMaster4 (pictured left)
is said to be one electromagnetic ow
meter designed to help utilities get a
handle on water leaks. “Its built-in data
logger runs at high speed, giving the
user total exibility to download logged
data frequently – every 15 minutes
if needed,” adds Hunt. “The user can
then investigate, in precise detail, ow
TEST & MEASUREMENT – LEAK TESTING
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 identi ed rapidly
and quanti ed. Andre de Jonge, leak
detection department manager, Applus+
RTD (pictured above), explains that its
method of nding 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 lled.
After this, a controlled lowering of
the cooling water level takes place, while
the space above the cooling water in the
water chamber is lled 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 su ce.
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 air ow
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 eld in which the
leak itself exists is discriminated from all
other possible locations.” After plugging
o the leak, the entire eld 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 'sni er'
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 e orts to x leakage”, as
part of a much wider remit to build longterm
water resilience. The good news is
that, as they are for industry at large, the
tools and technology to do so are already
there.
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