Leak detection system
extended to AUV inspections
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Schematic shows an ALD in action on an offshore pipeline.
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Co.L.Mar is
developing new applications for its Acoustic Leak Detector (ALD) technology on
subsea pipelines.
Leaks in pipelines
are generally caused by the transition of the transported fluid from the
internal pressure to the lower external pressure. The resulting turbulence and
sudden expansion of the fluid mass generate acoustic (ultrasound) signals. The
ALD system extracts these signals from the ambient noise, even when they are
very weak. Due to this sensitivity, the system has located leaks down to 0.2
liter/min on an offshore installation.
The system's main
components are an underwater acoustic sensor, which acquires data along the
pipeline; a transmission line that relays the data to the surface vessel; a
hardware receiver; and PC-based software that evaluates the acquired signal in
real time and its development along the pipeline track.
Depending on the application,
the ambient conditions, and the means available on site, the inspection
equipment may be hand-held by divers to check flanges, deployed in a towfish
version, ROV-installed, or lowered vertically over the side of the surface
control/support vessel.
This year Co.L.Mar
has used the technology intensively for leak inspections offshore West Africa.
According to managing director Luigi Barbagelata, one assignment involved a
pipeline with numerous flanges.
"Using our
equipment, the divers were able to detect which flange was leaking," he
said. "Following tightening of the flange bolts, they reapplied the ALD
and verified that a smaller flow was still present, which meant that further
tightening was needed. They could also identify which flange sector was leaking
and which bolts had to be tightened. Without our equipment they would have
probably assumed that the first repair was fine and the leak controlled, but
the resultant hydrotest would have revealed that this was not the case."
In May, Co.L.Mar
used the ALD in vertical mode installed for the first time with multi-beam
sonar and an underwater camera. These items were used to verify the positioning
of the sensor against the pipeline, the as-laid chart for which was not
accurate. Another project was a leak inspection on a pipeline offshore Japan
operated by a major oil company. Scope of the four-day inspection was to verify
the integrity of the pipeline.
This spring, the
company completed the first ALD prototype for installation on an autonomous
underwater vehicle (AUV), with successful trials in a test pool and at sea. The
system can be adapted to different kinds of AUVs to be used for inspecting and
checking the integrity of pipelines. "The advantage of using an AUV for
inspecting pipelines is significant, if the vehicle is equipped with a
navigation system for automatically tracking and following the pipeline. In
that case there is no need for an acoustic beacon for navigation of the
AUV," Barbagelata said.
The checking
capability is applicable to "resident" AUVs, which are deployed to
permanently monitor the conditions of a subsea installation, periodically
returning to a subsea base to recharge batteries and download data.
"The ALD
version we have developed at the moment is recording inspection data, but that
needs to be played back to check if there is a leak," he said. "We
are now working on software that processes the data automatically and in real
time, and decides autonomously if there is a leak. Once this is determined, the
ALD can interface with the AUV's navigation system, modifying the mission in
case of leak detection. We hope to have this solution ready within six
months."
Another ongoing
Co.L.Mar development is a monitoring system for detecting leaks on subsea
structures such as christmas trees and manifolds. The company has completed
work on an omnidirectional prototype following extensive tests in an indoor
tank. Sea trials are scheduled before the end of the year, simulating different
leaks and pressures. Assuming these are successful, the next step will be to
test the equipment on a real subsea installation. Additionally, the company is
working on a more sophisticated directive sensor.
11/12/2013
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