CA2598949C - Collector line for leakage monitoring and leakage location - Google Patents

Abstract

A collector line (1) for leakage monitoring and leakage location on a plant comprising a carrier tube (2) the wall of which has openings (4), which are sealed with silicone rubber. This makes it possible to use the collector line (1) during low ambient temperatures.

Description

SN/. P060113 1 Dr.
Alfred Mortel Specification Collector line for leakage monitoring and leakage location The invention relates to a collector line for leakage monitoring and leakage location on a plant such as is known from EP 0 175 219 B1. This invention moreover relates to a device and a method for leakage monitoring and leakage location on a plant in which such collector line is used.
A collector line is known from EP 0 175 219 B1, which consist of a carrier tube which is provided with a permeable layer on its exterior surface, through which a substance from a leakage in the plant, for example a pipeline, can diffuse, which escapes into the environment of the collector line and must be detected. The carrier tube is impermeable for this substance. Its wall is provided with openings so that any substance passing through this permeable layer can get to the inside of the collector line through these openings. Using a method known from DE 24 31 907 C3, the location at which the substance has penetrated into the collector line can then be determined. This location corresponds to the place at which the substance has escaped from the monitored plant section. For this purpose, the substance which has penetrated into the collector line is fed with a pump connected to the collector line together with a carrier gas contained in the collector line to a sensor which is also connected to the collector line.
If the flow rate is known, using the time interval between switch-on of the pump and when the substance arrives at the sensor,

2 the location at which the substance penetrates into the collector line and thus the location of the leakage in the plant section can be determined.
As a material for the permeable layer, ethylene vinyl acetate, EVA, was found to be particularly suitable in a multitude of applications. The use of EVA as a permeable layer is problematic under environmental conditions where very low temperatures can occur, however, such as during the monitoring of aboveground installed oil pipelines, such as is the case in arctic and subarctic areas. Because it has been shown that the diffusion rate of the substances to be detected though a wall of EVA
exponentially drops with the temperature, and in practice limits the range or applications with EVA
as a permeable layer in such collector lines to temperatures above 0 C
The object of some embodiments of the invention therefore is to specify a collector line for leakage monitoring and leakage location on a plant which is also suitable for used at low temperatures. In addition, the objectives of the invention are to present a device and a method for leakage monitoring and leakage location with said connection line that is suitable for use at low temperatures.
According to an embodiment of the invention, there is provided a pipeline, the pipeline comprising: an inner pipe conveying a material and having a longitudinal axis; a thermal insulation layer surrounding said inner pipe; a channel extended in said thermal insulation layer parallel to said longitudinal axis of said inner pipe; an auxiliary pipe embedded in said insulation layer, perforated with holes or slots and forming said channel; and a collector line disposed in said channel for leakage monitoring and leakage location at said inner pipe, said collector line including: a carrier tube being impermeable to a substance to be detected and having a wall with openings formed therein; and a at least one first layer closing said openings, being formed of silicone rubber and being permeable to the substance to be detected.
According to another embodiment of the invention, the collection line comprises a carrier tube in which the wall is provided with openings that are sealed with at least one first layer which is permeable for the substance to be detected, which consists of silicone rubber SN/?060113 3 Dr.
Alfred MOrtel and in particular completely covers the exterior surface of the carrier tube.
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Consisting of silicone rubber within the meaning of the present invention means that this is the base matrix or the base material of the first layer to which further fillers or additives may have been added.
The invention is thus based upon the knowledge that silicone rubber, even though it is normally used as an elastic sealant, particularly has high permeability for crude or mineral oils and gasoline and because of its high low temperature stability has high permeability even at low temperatures and is therefore suitable as a permeable layer of a collection line also for use under environmental conditions in which low temperatures can occur.
In an advantageous development of the invention, the carrier tube comprises a ,second electrically conductive layer which extends in its longitudinal direction into which the substance may penetrate and the ohmic resistance thereof is dependent on the level of penetrant material therein. With such a collection line, the presence of a substance escaping during a leakage from the plant in large quantities can be permanently monitored by measuring the resistance of the electrically conductive, substance sensitive layer between two measuring points which are spatially far apart from each other. In other words: permanent leakage monitoring is possible which is independent of the times at which a pump connected to the collection line is switched on.

SN/.P060113 4 Dr.
Alfred Martel This has the advantage that big leakages can be registered with very short time delay. In fact, in order to be able to register even small leakages with the known leakage monitoring and leakage location device, relatively long collection times are required which can be up to 24 hours. Only then, in view of the unavoidable longitudinal diffusion and the absorption that occurs inside of the collection line over an extended section, a sufficient quantity of the substance to be detected has penetrated into the collection line in order to be able to transfer it to the sensor at a concentration necessary for detection.
Particularly with long collection lines, such as laid along pipelines, the carrier gas is therefore conveyed through the collection line at larger time intervals or interrogation intervals, for example every 6 to 24 hours, so that in the least favorable case, a time interval between the occurrence of the leakage and its detection can pass that is composed of the time interval between two consecutive measurements and the time which the penetrant substance requires from the start of the pump sequence until it arrives at the sensor. A time interval in the order of several hours can however be accompanied by significant irreversible damage, particularly in the case of larger leakages, both to the plant as well as to the environment.
This damage can be prevented by using a collection line with an electrically conductive second layer, since with such a collection line both a high detection sensitivity in the event of small leakages, as well as a high speed of response in the event of large leakages, can be achieved.
=
In a further development of the invention, the electrically conductive layer consists of a carbon black filled polymer material, SNLP060113 5 Dr.
Alfred MOrtel which preferably likewise involves a silicone rubber. This facilitates the electrically conductive layer to be produced in a particularly cost effective manner, since, on the one hand, it can likewise be applied to the carrier tube just as easily as a layer made of pure silicone rubber, i.e. one that is not filled with carbon black, and by filling it with fine-grained carbon black, in which the grain size is preferably within the nm range, the electrical conductivity of the carbon black particles in contact with each other can be brought about through the development of contact bridges between them in a particularly simple manner, and since, on the other hand, the electrical conductivity of the carbon-black filled silicone rubber largely depends upon the swelling that occurs during the penetration of the substance and the accompanying destruction of the carbon black bridges.
Since the electrically conductive layer is also permeable in this case, it can completely cover the exterior surface of the carrier tube. In this development, the electrically conductive layer can also be used to monitor the collector line with respect to mechanical damage, for example for fracture.
If the permeable first layer is electrically insulating and covers the electrically conductive second layer, the electrically conductive layer is electrically insulated from the environment, so that the collector line can also be installed in the ground or in contact with electrically conductive plant components. Moreover, in the event that the electrically conductive second layer is permeable and surrounds the carrier tube completely and thus also seals the openings contained therein, a decrease in the permeation rate caused by the admixture of carbon black can be reduced, since this electrically conductive permeable layer only has to have a thickness to the extent that is necessary for monitoring of the electrical resistance and/or the electrical conductivity.
A particularly simple embodiment provides for only one first permeable layer, iehich is electrically conductive through the admixture of carbon black, so that its electrical resistance depends on the level of penetrant material therein. In one such development, both a high detection sensitivity as well as a high speed of response can be achieved with a one-layer collector line.
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Particularly advantageous developments of a device and a method for leakage detection and leakage location using a particularly advantageous development of the collector line according to some embodiments of the invention. _ By measuring the electrical resistance of the electrically conductive layer according to an embodiment of the invention, permanent leakage monitoring is possible with little effort in terms of apparatus and technical measurement complexity.
In the method according to an embodiment of the invention, the time interval between the occurrence of a leakage and leakage location is reduced by using an increase in resistance as tripping or triggering signal for performing a measurements to locate the leakage, in that a fluid carrier medium is pumped through the collector line and analyzed with a sensor for a substance that escapes during the leakage.

SN/ .P060113 7 Dr.
Alfred MOrtel A leakage location is therefore no longer exclusively performed at fixed specified time intervals but in addition or only when the occurrence of a leakage is detected by resistance measurement.
A collector line of the type mentioned at the outset, in particular a collector line as taught by the invention, is particularly suited for monitoring of a pipeline carrying the substance.
In one particularly suitable development for use of a collector line of the type mentioned at the outset, a pipeline comprises an inner pipe conveying the substance, which is surrounded by an insulation layer in which a channel for accepting a collector line is arranged parallel in relation to the longitudinal axis of the inner pipe.
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Such pipeline can be particularly easily provided with a collector line of the type mentioned at the outset. Through this measure, the collector line is moreover protected against environmental effects.
If the channel is formed by an auxiliary pipe embedded into the insulation layer, the subsequent introduction of the collector line is simplified and the risk of damaging the insulation layer during the installation of the collector line is decreased.
The channel is preferably arranged at a distance from the inner pipe. As a result, the entire exterior surface of the inner pipe contacts the insulation layer, and its adhesion to the inner pipe is not impaired by the channel.

SN/ PO60113 8 Dr.
Alfred MOrtel For further explanation of the invention, reference is made to the exemplary embodiments of the invention, as follows: =
Fig. 1 and 2 present a collector line as taught by the invention as a longitudinal section and/or cross-section, Fig. 3 presents an alternative embodiment of the openings made in the collector line, Fig. 4 ¨ 7 presents further advantageous developments of a collector line as taught by the invention in their respective schematic cross-section, Fig. 8 presents a collector line as taught by the invention which is provided with pressure resistant braiding, as an isometric view, Fig. 9 presents a device with a collector line according to Fig. 4 - 7, also as a schematic diagram, Fig. 10, 11 presents a particularly advantageous arrangement of a collector.line as taught by the invention in a pipeline carrying crude oil, as a schematic, partially longitudinal and/or cross-section.
According to Fig. 1 and 2, a collector line 1 comprises a carrier tube 2, for example from polyvinyl chloride PVC, in particular from polyvinylidene fluoride PVDF or polyether ketone PEEK, in which the wall is provided with a multitude of radial openings 4. On the carrier tube 2, a permeable contiguous first layer 6 consisting of silicone rubber for a substance L to be detected is arranged, which completely covers the carrier tube 2 and seals the openings 4 in this manner. Particularly suitable are cross-linked silicones, organopolysiloxanes, particularly wide-meshed cross-linked silicone rubbers (diorganopolysiloxanes) SN/ P060113 9 Dr.
Alfred Mortel with particularly high absorptivity of the substance L to be detected, i.e.
polysiloxanes, which exhibit high swelling in the presence of substance L, particularly the commercially available MVQ HTV silicone rubber (HCR silicone rubber) SX 70 W which consists of a mixture of polynnethylvinylsiloxanes and highly dispersed silicic acids or alternatively of a mixture of polydimethylsiloxanes, polyvinylmethylsiloxanes, polyphenylmethylsiloxanes, polyphenylvinylmethylsiloxanes and silicic acids.
Fig. 3 represents an embodiment in which the openings 4 have a conical shape and taper toward the inside of carrier tube 2 and are filled with a porous filler material, which practically does not impede the diffusion of the substance L into the inside of carrier tube 2. This facilitates the covering of the carrier tube 2 with a permeable first layer 6 which consists of silicone rubber, since this can in this case also be applied in a low viscosity liquid condition, without filling the openings 4 or flowing into the inside of carrier tube 2.
As an alternative to this, it is also possible to incorporate the openings 4 through suitable manufacturing methods, for example laser drilling, in large numbers into the carrier tube 2 and with a very small diameter, so that the silicone rubber, even when it is applied in electric condition, can practically not penetrate into these openings 4.
In the exemplary embodiment according to Fig. 4, an electrically conductive second layer 8 has been applied to the exterior surface of the carrier tube 2, which is surrounded by a permeable first layer 6, which, in this development, is electrically insulating. This electrically conductive second layer 8 is equally permeable SN/ P060113 10 Dr.
Alfred MOrtel for the substance L to be detected and moreover reacts sensitively to substance L in such a manner, that its (specific) electrical resistance is dependent upon the presence of substance L.
The electrically conductive second layer 8 in the exemplary embodiment consist of a polymer material filled with electrically conductive particles, which in this case involves an electrically isolating polymer base material in particular also a silicone rubber, to which, in order to bring about electrical conductivity, conductive particles have been admixed which are carbon black, in the example.
Because of the substance L entering and passing through it, the electrically conductive second layer 8 experiences a change in its structure, such as swelling. In this manner, the bridges between the electrically conductive particles break open and the electrical conductivity which is based upon these bridges in the silicone rubber to which these =
conductive particles have been added, deteriorates.
The proportion of carbon black needed in practice depends on the length of the collector line, in order to achieve electrical resistance values in the range of several mC2 that can be registered using little technical measurement complexity.
In the exemplary embodiment, the layer thicknesses of layers 6 and/or 8 are 1 mm in each case. The wall thickness of carrier tube 2, which preferably consist of PVDF or PEEK, is approximately 1 mm with an inside diameter of approximately 10 mm.

SN/ P060113 11 Dr.
Alfred MOrtel The exterior, electrically insulating permeable first layer 6 is moreover surrounded by permeable, elastic protective braiding, which is not shown in the figure, for protection against mechanical damage.
The carrier tube 2 can moreover be provided with a coating on its internal surface area, which consist of a material that has only a low absorption capacity for substance L, in order to extensively reduce the signal attenuation by absorption in carrier tube ? which develops if the distance between the leakage location and the detection sensor is large.
This coating, for example from Teflon PTFE, is applied to the internal surface area, before the radial openings 4 are made in the carrier tube.
According to Fig. 4, a single-layer structure is provided in which the first layer 6, which is permeable for substance L, is electrically conductive through admixture of carbon black.
In other words: only one single layer is provided which combines both the properties of the first layer 6, that is the good permeability for the substance L to be detected, as well as the properties of the electrically conductive second layer 8, that is the change in the electrical resistance, if substance L penetrates into it.
In principle, it is also not mandatory that the electrically conductive second layer 8 in the presence of an electrically insulating permeable first layer 6 which completely surrounds carrier tube 2 covers said tube completely. In the exemplary embodiment according to Fig. 6, the electrically conductive second layer 8 covers only a band-shaped subarea of the exterior surface of the carrier tube 2 which extends in a longitudinal direction.

SN/ P060113 12 Dr.
Alfred MOrtel In other words: the electrically conductive second layer 8 and the permeable first layer 6 are arranged side-by-side on carrier tube 2. In this exemplary embodiment, it is also not mandatory that the second layer 8 is permeable for the substance L.
In the embodiments illustrated in Fig. 5 and 6, the collector line 1 is suitable for installation in an electrically insulating environment.
In the exemplary embodiment illustrated in Fig. 7, the electrically conductive second layer 8 has the shape of a band that is embedded in the first layer 6, which in this exemplary embodiment is electrically insulating and insulates the band-shaped second layer 8 electrically insulated from the environment, in order to facilitate the use of the collector line 1 in an electrically conductive environment. In addition, a band-shaped return conductor 9 is embedded into the first layer 6, which only occupies one sector of the carrier tube 2 circumference, the electrical resistance of which is not affected by substance L. This return conductor 9 is electrically connected on one end of collector line 1 with the second layer 8, which enables its resistance to be measured.
Alternatively to this, return conductor 9 can also consist of the same material as the second layer 8, so that its resistance is likewise affected by substance L.
The collector line 1 can in all exemplary embodiments according to Fig. 1 to Fig. 7 in addition be enveloped on the outer periphery with a permeable braiding 11, as illustrated in Fig. 8. This braiding 11 which can consist of polyethylene PE for example, serves both as protection against mechanical SN/ P060113 13 Dr.
Alfred MOrtel damage as well as for mechanical stabilization, if excess pressure exists on the inside of carrier tube 2 for conveying the carrier gas, which would result in a destruction of the silicone rubber layer 6 which covers openings 4.
According to Fig. 9, the collector line 1 is laid along a pipeline 10 between a pomp 12 and a sensor 14 for the substance to be detected. An evaluation and control unit 16 measures the electrical resistance of the electrically conductive layer 6, 8 along a section s permanently, i.e. it is also measured even when pump 12 is not activated, i.e.
when a fluid carrier medium M inside carrier tube 2 is at rest. In an example for this, a separate return conductor 18 is installed along the collector line 1. If the resistance of the electrically conductive second layer 8 exceeds a specified threshold value because of a leakage of an escaping substance L in the environment of the collector line 2 (shown by a dotted line), a control signal 20 is generated in the control and evaluation unit 16 in order to start up the pump 12 and perform a leakage location in accordance with the known method discussed at the outset.
Depending upon the installation location of collector line 1 it can also be possible that a separate return conductor 18 or a return conductor 9 integrated into the collector line 1 (Fig. 4) is not necessary, in that, for example, a ground contact is established at the terminal point of the section, as is indicated in this figure by dotted lines.

SN/ P060113 14 Dr.
Alfred Martel According to Fig. 10, a pipeline 30 conveying substance L, for example crude oil, comprises an inner pipe 32 of steel, which is surrounded by an insulation layer 34 consisting of polyurethane. A channel 36 is introduced into the insulation layer 34 at a small distance to the exterior surface of the inner pipe 32, which runs parallel to the longitudinal axis 38 of the inner pipe 32 and in which a collector line 1 is installed as schematically illustrated.
In the exemplary embodiment according to Fig. 11, a channel 36 is formed by an auxiliary pipe 40 embedded in the insulation layer 34, into which the collector line 1 can be inserted. The auxiliary pipe 40 is perforated with holes or slots and is thus open for substance L to pass through, which is conveyed in pipeline 30 and which escapes from the inner pipe 32 in case of leakage.
With a pipeline 30 configured in this way and a collector line 1 installed therein, any leakages occurring in the inner tube 32 can be detected already before they escape into the environment of pipeline 30, since the escaping substance L initially reaches the insulation layer 34, where it accumulates and diffuses into the collector line 1.

14a SN/ P060113 Dr.
Alfred Miirtel List of references 1 Collector line 2 Carrier tube 4 Openings 6 First layer 8 Second layer 9 Return conductor 11 Braiding Pipeline 12 Pump 14 Sensor .
16 Evaluation and control unit 18 Separate return conductor Control signal Pipeline 32 Inner pipe 34 Insulation layer 38 Longitudinal axis Auxiliary pipe L Substance

Claims (10)

CLAIMS:

1. A pipeline, the pipeline comprising:
an inner pipe conveying a material and having a longitudinal axis;
a thermal insulation layer surrounding said inner pipe;
a channel extended in said thermal insulation layer parallel to said longitudinal axis of said inner pipe;
an auxiliary pipe embedded in said insulation layer, perforated with holes or slots and forming said channel; and a collector line disposed in said channel for leakage monitoring and leakage location at said inner pipe, said collector line including:
a carrier tube being impermeable to a substance to be detected and having a wall with openings formed therein; and a at least one first layer closing said openings, being formed of silicone rubber and being permeable to the substance to be detected.

2. The pipeline according to claim 1, which further comprises an electrically conductive second layer extended in longitudinal direction of said carrier tube, said electrically conductive second layer being at least penetrable by the substance and having an ohmic resistance dependent on a level of penetrant material therein.

3. The pipeline according to claim 2, wherein said electrically conductive second layer is formed of a carbon black filled polymer material.

4. The pipeline according to claim 3, wherein said carbon black filled polymer material is a carbon black filled silicone rubber.

5. The pipeline according to claim 4, wherein said electrically conductive second layer completely covers an exterior surface of said carrier tube.

6. The pipeline according to claim 2, wherein said first layer is electrically insulating and covers said electrically conductive second layer.

7. A device for leakage monitoring and leakage location at a plant, the device comprising:
a pipeline according to claim 2; and a device for recording an electrical resistance of said electrically conductive layer.

8. A method for leakage monitoring and location, the method comprising the following steps:
recording an electrical resistance of an electrically conductive layer along a segment of an installed pipeline according to claim 2;
triggering a measurement to determine a leakage location upon an increase in the electrical resistance; and pumping a fluid carrier medium through the collector line and analyzing the fluid carrier medium with a sensor for a material escaping during a leakage.

9. The pipeline according to claim 1, wherein said first permeable layer is electrically conductive due to an admixture of carbon black.

10. The pipeline according to claim 1, wherein said channel is disposed at a distance from said inner pipe.