Detection system tracks
minutest pipeline leaks
Co.L.Mar's Acoustic
Leak Detector (ALD) technology has pinpointed defects this year on three subsea
pipelines in a variety of settings.
ALD installed on a work class ROV.
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Leaks in pipelines
stem from transition of the transported fluid from the internal pressure to the
lower external pressure. The resultant turbulence and sudden expansion of the
fluid mass generate acoustic signals which the ALD processes to extract from
the ambient noise to indicate leakage.
The system's main
components are an underwater acoustic sensor that acquires data along the
pipeline; a transmission line that relays data to the surface vessel; and
PC-based software that evaluates the acquired signal in real time, and its
development along the pipeline track. This signal is converted by the ALD's
receiver to an audible lower frequency. Depending on the application
(inspection or monitoring), different sensors can be deployed by divers, towed
fish, ROVs, or lowered vertically over the side of a surface vessel.
One recent project
was on a newly installed pipeline offshore in the Middle East. Co.L.Mar was
called out following the hydrotest reporting a leak of just 0.21 liter/min
which divers had been unable to locate. At the time, according to Managing
Director Luigi Barbagelata, the line was filled with water and colorant.
"We found the
leak at our first attempt on a valve flange – this was the smallest leak we had
ever dealt with and proves the effectiveness and sensitivity of our system,"
he said. "We used an equipment spread deployed by divers and an ROV."
Another job was in
the Indian Ocean, where Co.L.Mar used an ROV configuration to detect a leak in
an umbilical in 200 m (656 ft.) water depth. Leakage was reported during tests
following installation of the umbilical, which at the time was filled with air.
Leak generated by corrosion and its ALD image.
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"Even though
conditions were not ideal – a combination of air and pressure of just a few bar
- we were still able to find the leak easily," said Barbagelata.
The third job was
Co.L.Mar's first-ever assignment in the Americans. The location was a lagoon in
very shallow water (1 m or 3 ¼ ft. deep). To work in this awkward environment,
an ALD sensor, similar to that used with towed fish for tracking purposes, was
mounted on the side of a small aluminum vessel with a very limited draft.
"The leak [the
pipeline was water-filled] turned out to be in an area where the pipeline was
covered by over 10 ft. (3 m) of sand," Barbagelata said. "I believe
the reason it was buried by so much sand was not due to backfilling, but the
dynamics of the seafloor in that area."
In June, Co.L.Mar
was also commissioned to perform monitoring of the status of a subsea pipeline
during a pigging operation.
"The contractor
was concerned about potential stress that would be imposed on the pipeline. We
monitored the pipeline using a towed fish continuously over the 10-day
campaign, night and day, to ensure that if there were a leak, we could deal
with it. The pigging team was working from the platform, while our specialists
were based on the survey vessel with equipment ready for a repair if a leak
were found."
Over the past two
years. Co.L.Mar has been working on a new monitoring system for leak detection
on subsea structures such as christmas trees, manifolds, or valves. Currently a
basic prototype version is undergoing tests in a 6 x 10-m (20 x 33-ft.) indoor
tank in 8 m (26 ft.) water depth: the sensor is designed to give an indication
of the presence of a leak and the direction of the leakage.
"It comprises
an array of four elements, which have so far given good results in the pool.
Our next step is to repeat and optimize the test in the pool, then perform
further tests out at sea with real leak detection equipment."
11/01/2012
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