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needle in a haystack

Like a semiconductor sensor, it is
unable to differentiate between organic
gases, although it is considerably more
sensitive and robust.
Network maintenance
There are two ways of maintaining gas
networks, by reactive or preventive
maintenance. With reactive
maintenance, the gas utility relies on
the general public to act as the canary
in the coal mine. Not to stop singing,
but to make a phone call to say that they
can smell gas (or, more correctly, the
odorant additive in natural gas).
With preventive maintenance, the
operator undertakes network surveys,
using staff or contractors to walk the
route of the pipelines with detection
equipment. The sensors in the
equipment can detect gas at far lower
concentrations than a human nose
can detect gas odorant. This approach
generally results in less leakage overall.
One of the greatest benefits of more
accurate detection is that it reduces the
need for bar hole drilling, the practice of
drilling a series of holes in the surfacing
material to pinpoint the source of
the leak. If the location can be more
accurately located, fewer holes, if any,
need to be drilled. This saves time and
reduces damage to road surfaces, cutting
the cost for reinstatement (councils can
levy substantial fines if road surfaces are
not reinstated properly).
Surveying the network
Once gas has been detected, the next
step is to verify that this is actually
natural gas. Here, a gas chromatograph
is normally used. Again, some models
of detectors have this built in, but
standalone instruments are also used.
Alternatively, samples of gas can be
collected in test tubes and sent to a lab
for analysis, but this will take at least
eight hours.
Some instruments can draw gas
through the natural porosity of the road A VACUUM BELL PROBE CAN BE USED TO DRAW GAS THROUGH
surfacing material, eliminating the need THE ROAD SURFACE, ELIMINATING THE NEED FOR BAR HOLES
for drilling bar holes. If bar holes are
needed for regulatory reasons, these can If the location can be more With the right equipment and
then be kept to an absolute minimum. accurately located, fewer holes, methods, operators can return home
When drawing gas through the after a long day’s surveying, safe in
road surface, a bell probe attached if any, need to be drilled. This the knowledge that any gas leaks have
to the instrument is pressed against saves time and reduces damage been correctly identified and that areas
the surface to form an airtight seal. to road surfaces, cutting the declared leak free are actually safe.
A pump in the instrument creates a cost for reinstatement
vacuum sufficiently powerful to pull INFICON is a leading provider of
the gas through the road surface and innovative instrumentation, critical
deliver it to the gas sensor. This whole Finally, the location needs to be sensor technologies, and advanced
process takes 10 to 20 seconds – far documented. Traditionally, this is done process control software that enhance
quicker than drilling a hole through with pencil marks on a map, but some productivity and quality in sophisticated
the pavement and without damaging models of detectors have built in or industrial vacuum processes. For more
the road surface. externally fitted GPS to track the route. information, visit www.inficon.com

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