Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TEST-FLUID COMPOSITION AND METHOD FOR DETECTING
LEA~S IN PIPELINES AND ASSOCIATED FACILITIES
Field of the Invention
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This invention relates to a method of locating leaks in
pipelines and associated facilities. More particularly, this
invention concerns a novel test-~luid useful in accurately
locating such leaks.
Back~round of the Invention
; A major and ongoing problem for petroleum and chemical
industries is the inability of present-day technology to
precisely find leaks in transportation and storage facilities.
The problem has two major components: the first challenge is to
establish that a Eacility is in fact leaking; the second
challenge relates to accurately locating the source of a leak.
It is the second of these two issues that the present invention
addresses.
More than thirty different techniques are known in the
art for leak-detection. These methods can be grouped into
several categories depending on the technology used. Some of
these categories are systems based on: odorants, radioactive
or chemical tracers, acoustic signals, dyes, smart pigs,
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electromagnetics, computer product mass-balance, hydrostatic
testing, transient pressure-wave monitoring, reflectometry,
thermal and infrared, and diffusion.
Although these conventional methodologies have enjoyed
some degree of success in finding leaks, none has shown a
10 capability to consistently and precisely locate pin-hole leaks,
particularly in subsurface pipelines and associated facilities.
In many cases, underground facilities are determined to be
leaking only after material mass-balance has indicated that
substantial loss of product has occurred, or when material
15 escaping from a leak rises to the soil surface and is visually
detected. In both cases, such lack of precision can result in
appreciable pollution, as well as in high economic costs
incurred through direct loss of product.
One strategy traditionally used to locate leaks in
pipelines involves the addition of an odorant to a pipeline
hydrostatic test-fluid, followed by attempts to detect the
odorant at ground level. This technique has generally been
unsuccessful for several reasons. Firstly, conventional
instrumentation such as gas detectors ("sniffers") or gas
chromatographs lack the sensitivity and/or field-portability
required to detect the low concentrations of odorant which
typically reach the surface. Secondly, and of critical
importance, is that the mercaptan odorants usually employed in
this technique are water-soluble, and migrate with the aqueous
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phase of the standard test-fluid, to give imprecise or erroneous
5 locations for leaks. Even when such odorant-based techniques
are partially "successful", their overall lack of precision may
impose substantial economic penalties via the increased costs in
equipment and manpower required to excavate over a generalized
area to pinpoint the precise source of a leak.
Therefore, there exists an industry need for a
leak-detection system capable of consistently and accurately
locating leaks in underground, and/or above ground, facilities.
The present invention constitutes a novel leak-detection
test-fluid which has shown to be capable of very accurately
locating leaks in either above-ground facilities, or in buried
?ipelines or associated facilities.
SUMMARY OF THE INVENTION
The present invention relates to a method of detecting
leaks in pipelines and other structures and facilities and, more
particularly, to a leak-detection test-fluid which can be used
co accurately locate such leaks. In accordance with this
invention, a process is provided for accurately detecting leaks
in pipelines and associated facilities wherein a novel
test-fluid is injected into a pipeline or facility so that the
test-fluid escapes through said leak, and an odorant which, by
virtue of its chemical and physical properties, is released from
other test fluid components to be detected in the immediate
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vicinity of the leak site, irrespective of whether or not the
5 leak is above or below the ground surface. A preferred
embodiment of the novel test-fluid is comprised of a solution of
dimethylsulphide, and a mutual ~iolvent, and in some
~pplications, water in varying ratios depending on ambient
conditions (eg. temperature) and according to specific technical
10 requirements.
DETAILED DESCRIPTION OF THE INVENTION
The benefits and advantages that can be obtained in the
15 ?ractice of this invention are achieved through the use of the
test-fluid, a preferred embodiment of which is composed of a
solution of dimethylsulphide, a mutual solvent and, depending on
the technical requirements, water.
This new, test-fluid-based procedure is distinguishable
from other odorant-based leak-detection systems by a number of
specific attributes. Firstly, unlike other odorant-based
systems, this invention operates within the liquid~phase realm
as opposed to the gaseous-phase realm. Secondly, the use of the
25 new te6t-fluid allows for the precise location of very small,
pin-hole leaks in either subsurface or above-ground facilities.
In the new system, an odorant serves to precisely pinpoint the
location of a leak, whereas in conventional gaseous-phase
systems, odorants act within a safety context only to "inform"
or warn operators that a potential hazard exists. The
physical/chemical characteristics of the test-fluid components
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described below, combine to procluce a product with unique
5 properties which in turn enable the accurate location of very
small leaks, even in structures buried to a depth of four meters
or more.
Dimethylsulphide is known in the art as an odorant. It
10 has a vapor pressure high enough to permit percolation from a
leak in a buried structure, through the soil to the surface,
without being appreciably absorbed by the soil. It has a strong
identifiable odor, is relatively insoluble in water, is
non-toxic in the concentrations used in this application, is
15 readily available, and is relatively inexpensive.
In one embodiment of this inventlon, dimethylsulphide
is combined with other fluids which act as carriers. The
dimethylsulphide should remain dispersed throughout the
20 test-fluid for the duration of the test to achieve the best
results. The dimethylsulphide should therefore be at least
partially soluble in the mutual solvent. Since dimethylsulphide
is relatively insoluble in an aqueous medium, the mutual solvent
prevents partitioning of the dimethylsulphide from other
test-fluid constituents. Depending on certain other
requirements, such as use of the test-fluid at ambient
temperatures below the free~ing point of water, the ~ost
appropriat:e mutual solvent, or combination of solvents is
chosen. Suitable mutual solvents incLude alcohols and glycols.
.~lethanol is the preferred mutual solvent.
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The physical characteristics of dimethylsulphide assure
that a detectable mixture of test-fluid components can rise
above a leak and be detected in the immediate vicinity of the
leak, whether the leak is above or below-ground. These
characteristics overcome problems traditionally plaguing other
odorant-based, leak-detection techniques using odorants such as
10 mercaptans, Being more water-soluble, mercaptans tend to remain
in solution, migrating away from a leak site in the aqueous
phase of a test-fluid. This higher water-solubility of
mercaptans severely limits the precision with which
mercaptan-based leak-detection systems can locate leaks because
the aqueous phase in which the odorants are soluble can disperse
over a very wide area.
According to the present invention, leaks in pipelines
and associated facilities are detected by injecting the test
fluid into a pipeline or facility and then detecting the
odiferous component (preferably dimethylsulphide) of the
test-fluid in the immediate vicinity of the leak. In one
embodiment of the invention, the test-fluid may be passed
through a pipeline or facility as a batch-loaded slug or as a
slug loaded within a pig-train. During this procedure, the
pipeline or facility may remain in service or may be temporarily
taken out of service while the leak test is being conducted. In
another embodiment, the pipeline or facility is shut down and
filled entirely or in part with the test-fluid. In a third
embodiment that is preferred for use in pipelines transporting
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gas or LPG, the test fluid is injected directly into the gas
5 stream. DMS may also be injected directly into the gas stream
without the other test-fluid components. The method oE
injection can vary, although the preferred method is to inject
the test-fluid or DMS using conventional pumps such as those
used for mercaptan-odorization of natural gas. The advantage to
10 using this embodiment is that any "down-time" of the pipeline or
facility being tested is minimized and leak-location may be
conducted while the line remains in service.
Any suitable means of detecting the test-fluid or its
15 components near the leak site may be utilized, including gas
chromotography, and animal or human olfaction. Presently, the
preferred detection technique is to use dogs (Canis familiaris)
which have been trained to search for the odorant and to
indicate by using specific behavior patterns where they have
20 found the highest concentration of the odorant.
One embodiment of the the novel test-fluid contains
dimethylsulphide in the range of about 0.1 to about 15 volume
percent. Preferably, the composition contains dimethylsulphide
in the range of about O.l to about 7.0 volume percent, and most
preferably in the range of about 0.1 to about 0.3 volume
percent. The test-fluid also contains a solvent in the range of
about 0.7 to about 99.9 volume percent and preferably in the
range of about 0.7 to about 50 volume percent. The test-fluid
can also contain water in the range of about 50 to about 85
volume percent. When the test fluid i5 injected into a gas
stream, however, very low concentrations of mutual solvent and
water should be used. In specific applications of the
technology, additional test-fluid components may be introduced
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to counteract factors acting to inhibit the performance of the
test-fluid, or which might act to damage the pipeline or
associated facility. Such additives might include
bacteriocides, oxygen scavengers, and inhibitors. It is
important to note that the success of this test-fluid in
precisely locating leaks is critically dependent on the
combination of physical/chemical attributes contributed to the
overall test-fluid by its various components. Factors such as
precision, cost-effectiveness, and temperature-stability may be
compromised if test-fluid composition is changed.
Other odorants believed to be suitable in the test fluid
composition because of the similarity of their physical and
chemical properties to DMS include dimethyl disulphide, thio
phenols, xanthate esters, thiophenes, sulphides and thio
esters. A mixture of DMS and N-butyl mercaptan is also believed
.o be suitable. The mixture apparently produces a
synergistically stronger odor. One of ordinary skill can easily
determine concentration ranges for the above listed odorants in
the test-fluid composition.
In order to illustrate the benefits of the invention,
tests were conducted both in the laboratory and in pipelines and
associated ~acilities. After confirmation from laboratory tests
that the test-fluid odorant would percolate through a soil
column, a first set of field trials was conducted at a site
using five constructed leaks in buried pipelines. Four pipeline
leaks were used to test detectability by trained dogs and all
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four leaks were detected by the dogs. The fifth leak was
plugged and the dogs confirmed that no leaking occurred at that
location. A second set of field trials was conducted at a
different location with four constructed leaks in buried
pipelines. All four leaks were detected by dogs including one
located twelve feet (3.66m) below the surface. The invention
was then used to detect actual leaks at two different
facilities. At the first facility, a pin-hole leak was detected
and pinpointed by dogs in a ten-year-old, 3 km (2 mi), 2200 psi
(15,169 Kpa) produced-water line buried in clay to a depth of
seven feet (2.14m). At the second facility, dogs detected one
major leak, a minor leak and two leaking valves. The major leak
was approximately 0.5 cm (0.19 in.) in diameter in a 28-year-old
lS glycol line buried to 1.2 meters (3.94 ft.). Detection of this
leak prevented imminent rupture of an adjacent sour gas line
affected by the leak.
A field test was also conducted to demonstrate another
embodiment of this invention wherein a slug of test fluid is
injected in a pipeline in a pig-train. Dogs detected a
constructed leak 0.125 inches (0.3cm) in diameter in an 18 inch
(46 cm) diameter, 7 km (4.2 mi) long pipeline.
The preferred embodiments of the present invention have
been described above. It should be understood that the
foregoing description is intended only to illustrate certain
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embodiments of the invention and is not intended to define the
invention in any way. Other em~odiments o~ the invention can be
employed without departing from the full scope of the invention
as set forth in the appended claims.
