An array of leak detection methods are available for assessing the integrity of subsea oil and gas pipeline systems. These methods include (but are not limited to) the use of acoustic, fiberoptic, sensor-based, fluorescent, and internal leak detec- tion systems and technologies.
A recent case study of leak detection and rectification on a 110-km,
4-in. piggy back pipeline in 80 meters of water highlights some of the
challenges and possibilities associated with these types of operations.
In this case, acoustic pipeline leak detection methods were deployed,
along with fluorescent technologies and optical cameras.
A leak was detected during a hydrostatic test operation. The first
option to identify the leak point with fluorescent technology, and so
a pertinent marker was added into the fluid.
To save the cost and time, the leak detection operation started
from the points which were more susceptible to leak, particularly
the flanges. Unfortunately, after five days of continuous monitoring,
the leak point had still not been detected.
So, the next step was to deploy an ROV that had been outfitted with
an optical camera, which had been designed to detect the fluorescent
dye. But, due to the current on the seabed and a lower flowrate, the
ROV and its mounted camera was not able to detect a leak. Thus a
decision was made to deploy acoustic leak detection (ALD) technologies on a small vessel, a DP- 2 vessel, and also on an ROV.
Leak detection operations were performed on three portions of the
pipeline system: from landfall point to KP 1; from KP 1 to the end of
pipeline KP 110; and on spool pieces along with riser.
During the time of the survey, the pipeline was placed under
pressure at about 200 bar. In the case of the ROV, its speed was set
to a minimum of 0.3~0.4 knots. If noise was received, speed would
be reduced to 0.1 knot. So the speed of the vessels and ROVs were
important parameters in this case.
Inspection on subsea pipeline with the ALD system was performed
• Vertical mode survey from platform end
(KP110) to about 40-m depth (KP 8.00)
• Diver survey to inspect spools, flange, valves
and risers at platform end
• Tow fish mode to cover the shallow-water
section from landfall to 40-m depth
• ROV acoustic sensors were available as an
• Dye detection systems were also available as
an optional method.
Acoustic leak detection technologies can be
deployed in the vertical mode, tow fish mode,
diver mode and/or with an ROV acoustic sensor.
These modes are described below.
ALD vertical mode. Multi-beam sonars are
installed on the clump weight to monitor the
pipeline position. Inspection speed will be about
Iranian Offshore Engineering
and Construction Co.
Acoustic leak detection—vertical mode.
ALD technology proves
effective for finding leaks
Acoustic leak detection deployed
on small diameter system
Images courtesy Iranian Offshore Engineering and Construction Co.