pH sensor device for insertion into the soil, method for measuring the pH value, especially for cathodic protection

Description

Technical Field

[0001] The present invention relates to the field of soil characteristic determination. In particular, it relates to determining the pH of a soil region in which a pipeline can be installed and for which cathodic protection is implemented. Previous technique

[0002] Pipes buried in the ground that carry fluids (typically gas) are generally made of steel with a composition that makes corrosion possible. This corrosion is usually associated with the pH of the soil, or more precisely with the pH of a fluid contained in the soil (for example, water).

[0003] For various materials, diagrams known as Pourbaix diagrams exist. These diagrams allow a material to be placed in different zones that illustrate the risk of corrosion (typically corrosion, passivation, immunity) based on two parameters: the pH of the fluid in contact with the material and the electrical potential applied to the material. Consequently, an electrical potential is generally applied to pipelines to ensure they remain within the zone where the reduction in the corrosion rate is sufficiently low to comply with applicable standards. Methods in which an electrical potential is applied to a pipeline are called cathodic protection methods.

[0004] The NF EN ISO 15589-1 standard requires that the electrical potential of buried metallic structures be maintained below -0.85V / Cu-CuSO4. In practice, the electrical potential of the pipes is maintained at approximately -1V / Cu-CuSO4.

[0005] As one might expect, the pH of fluids contained in the soil can vary depending on many parameters, and this pH can even be influenced by the cathodic protection itself.

[0006] Therefore, knowing the pH value of the fluid surrounding a pipe is critical.

[0007] It is not feasible to carry out an excavation to reach an underground pipe and measure a pH value, given the cost involved.

[0008] It has been proposed to place pH test strips in the soil near pipes, but not at the same depth. This method does not provide a precise pH reading, only an approximate value. Furthermore, it is subjective, as it depends on the operator's interpretation of the paper's color, which can be affected by the soil's color itself. Finally, a measurement using pH paper is a single, isolated reading and does not provide continuous pH monitoring.

[0009] The leachate method involves taking a sample of soil, diluting it, and measuring the pH of the resulting solution. This method provides an approximation of the pH, but it is not sufficiently precise because the solution is diluted, which inevitably alters the actual pH value. This method also has the drawback of only being feasible in a laboratory setting and using a standard pH probe (which generally only works in liquids).

[0010] We also know of a pH sensor marketed by the American company MC Miller Co. Inc. that uses an antimony-based electrode. This pH sensor has drawbacks. First, antimony is toxic and carcinogenic, which poses safety problems for users. Second, this sensor provides an open-circuit potential value that is correlated to a pH value, but this correlation is only possible after prior calibration in an unknown environment. Therefore, uncertainty remains in this measurement because the pH varies from one environment to another depending on the species present.

[0011] Document WO2008031453 describes a method for determining the passivation properties of a mixture containing at least two components (cement and water). In this document, measuring passivation on the surface of a reference steel allows for the detection of the presence of water, aggressive substances, excessive chloride content, or a pH that is too low.

[0012] From the prior art, we know the documents EP 2 602 609, US 2007 / 298278, US 2019 / 368054, CN 1 936 562, and "Metal Oxides and lon-Echange Surfaces as pH sensors in Liquids: State-of-the-Art and Outlook" (Peter Kurzweil, SENSORS, Vol. 9, No. 6, June 23, 2009, pages 4955-4985).

[0013] The invention aims to resolve at least some of the aforementioned drawbacks. Description of the invention

[0014] To this end, the invention proposes a method according to claim 1.

[0015] This process will preferably be implemented near a truly buried pipeline, for example above this pipeline.

[0016] For example, this method can be implemented near a pipe potential measurement (or sampling) station, typically located above the pipes. These measurement stations are, of course, situated at ground level. In this case, the invention advantageously allows the same electrical potential to be applied to the metallic element as that applied to the pipe (it is taken directly from the pipe). This results in an even more realistic pH measurement at the level of the buried pipe.

[0017] The inventors of the present invention observed that it is possible to use polymer materials to make pH sensors, and that by combining these sensors with a metallic element receiving an electrical potential, it is possible to perform a shallow measurement in an environment similar to that of a buried pipeline which also receives a cathodic protection electrical potential. The pH measurement by the sensor thus clearly illustrates a pH measurement that could be made in the immediate vicinity of a pipeline (for example, a few tens of centimeters from a pipeline).

[0018] The use of polymers also allows for a robust sensor that can be used in the ground with a long lifespan. Furthermore, these polymers do not have the drawbacks of sensors containing antimony, which are dangerous for users. Preferably, polymers containing proton-attracting groups are chosen, thus affecting the electrical potential at the surface.

[0019] Typically, electrical potential is an electrical potential having a value that could be applied to a pipe (e.g., less than -0.85V / Cu-CuSO4).

[0020] To apply this electrical potential, one can use one of the means of electrical connection involving a cable.

[0021] Also, the surface comprising a polymer material capable of attracting protons can be arranged so as to at least partially cover another surface of the pH sensor, for example a surface of another metal element which will be conductive and able to transmit the signal resulting from the presence of protons on the surface comprising a polymer material.

[0022] According to a particular embodiment, the polymer contains one or more amino groups (in their molecular chain).

[0023] The inventors observed that amino groups work well for the formation of pH sensors.

[0024] As an example, the polymer can be a conductive polymer.

[0025] According to a particular embodiment, the polymer containing amino groups is chosen from the group comprising polypyrroll and poly(3,4-ethylenedioxythiophene).

[0026] Both of these polymer materials are conductive.

[0027] According to the invention, the device comprises a body having at least one first opening configured to allow, when the device is inserted into the ground, the fluid contained in said region to be in contact with said surface comprising a polymer material and with said surface of the metallic element, and at least one second opening configured to receive said electrical connection means.

[0028] This body may include a polymer-based material chosen for its mechanical properties and resistance to fluids with which the body may come into contact in the ground.

[0029] As a guideline, the first opening could be the lower opening of the body, facing downwards when the device is inserted into the ground. The second opening will face upwards to allow passage for the electrical connection means.

[0030] According to the invention, said surface comprising a polymer material and said surface of the metallic element are arranged recessed with respect to an external surface of the body where the openings are formed.

[0031] This removal helps to protect both surfaces.

[0032] For example, these two surfaces can be recessed by one millimeter.

[0033] According to a particular embodiment, the device includes first means for maintaining the seal arranged at the interface between on the one hand said surface comprising a polymer material and said surface of the metallic element and on the other hand the body, to prevent the fluid contained in said region from penetrating inside the body.

[0034] It has been observed that maintaining the system's watertightness is particularly important when it is in contact with fluids present in the soil. The means of creating a watertight seal may, for example, include one or more gaskets.

[0035] According to a particular embodiment, the device includes second means for maintaining the seal arranged at the interface between, on the one hand, the electrical connection means and, on the other hand, the body, to prevent the fluid contained in said region from penetrating inside the body.

[0036] Similarly, these second means of creating a seal may include one or more gaskets and / or a stuffing box.

[0037] According to a particular embodiment, the pH sensor and / or the metallic element are removable from the body.

[0038] It can be particularly useful to be able to change these elements independently of other elements of the device.

[0039] Removable means that the pH sensor and / or the metal element can be removed either without tools (for example if they are fixed by clips), or with a tool (for example if they are fixed by screws).

[0040] Electrical connection means can be connectable and disconnectable means, for example including plugs.

[0041] According to a particular embodiment, said surface comprising a polymer material and said surface of the metallic element are separated by a strip having a thickness between 0.5 and 1.5 millimeters, for example equal to 1 millimeter.

[0042] This strip prevents any electrical contact between the metal element and the polymer surface. Preferably, a 1-millimeter thick strip should be used so that the presence of the metal element clearly illustrates the environment in which an underground pipe is located.

[0043] According to a particular embodiment, said surface of the metallic element has an annular shape and said surface comprising a polymer material is arranged so as to be surrounded by said surface of the metallic element.

[0044] It has been observed by the inventors of the present invention that this arrangement, in which the surface comprising a polymer material is surrounded by the surface of the metallic element, clearly illustrates the proximity of a sensor to a pipe, and in particular allows for better sensitivity to changes in pH of the medium in contact with the surface of the polymer material.

[0045] According to a particular embodiment, said surface of the metallic element has an area of ​​at least greater than or equal to 1 cm² and said surface comprising a polymer material has an area of ​​at least greater than or equal to 0.07 cm².

[0046] According to a specific implementation method, the process includes: an implementation of the pH measurement process as defined above for a region of soil located above a pipeline, a determination of a new electrical potential value to be applied to said pipeline from the result of said pH measurement.

[0047] Thus, the invention makes it possible to improve the cathodic protection of buried pipelines, without it being necessary to implement measures directly at the level of the buried pipelines.

[0048] As an indication, the determination of the new electrical potential value can be carried out partly automatically, for example by a computer program run by a processor of the device or connected to the device, and on the basis of data stored in a memory of the device or another device such as a Pourbaix diagram.

[0049] For example, this computer program can deliver a range of possible new values, or a single possible value.

[0050] The invention also proposes a device according to claim 11. Brief description of the drawings

[0051] Other features and advantages of the present invention will become apparent from the description below, with reference to the accompanying drawings, which illustrate an example of an embodiment without being limiting in any way. In the figures: [ Fig. 1 ] There figure 1 is an example of a Pourbaix diagram. Fig. 2 ] There figure 2 is a cross-sectional view of a first example of the device. Fig. 3 ] There figure 3 is a bottom view of the first example device. Fig. 4 ] There figure 4 is an exploded view of the first example device. Fig. 5 ] There figure 5 is a cross-sectional view of a second example device. Fig. 6 ] There figure 6 is a bottom view of the second example device. Fig. 7 ] There figure 7 is an exploded view of the second example device. Fig. 8 ] There figure 8 illustrates electrical potential tapping stations used in an example above a pipeline. Description of the implementation methods

[0052] We will now describe devices that allow us to measure the pH of fluids contained in the soil, which can be inserted into the soil at a shallow depth, and which obtain a value that illustrates well that which could be measured near a deeper buried pipe.

[0053] There figure 1 is an example of a Pourbaix diagram, which shows in which zone a metal is in contact with a fluid, depending on the pH of that fluid and the electrical potential applied to the metal.

[0054] Three main zones are identified: the passivation zone Z1, the corrosion zone Z2, and the immunity zone Z3. Generally, an electrical potential is applied to place a metal in a zone where the risk of corrosion is low or where the corrosion rate is low.

[0055] In the event of a variation (decrease or increase) in pH, it may therefore be useful to determine a new value of electrical potential to apply, for example automatically by reading in a map based on a Pourbaix diagram.

[0056] It has also been observed that applying an electrical potential to a metal can have an effect on the pH value.

[0057] Therefore, using a simple shallow pH sensor is not sufficient to determine the pH value of the fluid in contact with an enclosed pipe.

[0058] It can be noted that generally, pipes are buried at minimum depths of 80 cm. With the invention which will be described below, it is possible to implement a measurement at a shallow depth, typically on the order of 20 to 50 cm, but still obtaining a pH value which clearly illustrates that which could be measured near the pipe, for example at a distance of less than ten centimeters.

[0059] On the figure 2 A cross-sectional image of a pH sensor device (100) is shown. This device is designed to be inserted into the ground, for example, at a depth of approximately 20 to 30 cm, and advantageously above a pipe for which corrosion is to be checked. More precisely, this device can be inserted into the ground near an electrical potential measurement station (or potential tap) for the pipe, which is generally located above the pipes.

[0060] This device 100 includes a pH sensor 101 comprising an electrode having a surface 102 made of polypyrrole, located at the bottom of the figure. The invention is not, however, limited to the use of polypyrrole and also relates to the use of other conductive polymers, such as poly(3,4-ethylenedioxythiophene), also known as PEDOT.

[0061] The invention is nevertheless not limited to the use of these two materials and can be implemented with any polymer capable of attracting protons, for example polymers comprising one or more amino groups.

[0062] Obtaining a polypyrrole layer can be achieved by following the method described in the thesis "Electrochemical synthesis of nanostructures of conductive polymers without the use of a support matrix" (Ahmed Fakhry, 2014, Pierre and Marie Curie University).

[0063] More specifically, a polypyrrole film can be formed electrochemically on a support which can be stainless steel, platinum, gold, etc. This support is designated 103 in the figure and, together with surface 102, forms an electrode of the pH sensor 101. Thus, the polypyrrole covers the surface of the support to form the external surface 102.

[0064] The formation or synthesis takes place in a three-electrode cell containing a solution with a pyrrole monomer, a dopant such as perchlorate (ClO4-) and a supporting electrolyte, for example K2HPO4.

[0065] This allows for the creation of polypyrrole nanostructures that are oriented towards the outside of the sensor, downwards in the figure.

[0066] It is worth noting that polypyrrole is a conductive polymer whose molecular structure contains amino groups that have an affinity for protons present in the medium in contact with the polypyrrole (for example, a fluid). The reaction of protons with these amino groups creates an excess of local charge density at the surface of the polypyrrole-containing electrode. The response, measured by a change in electrical potential, can thus be considered a behavior controlled by a surface reaction occurring on the polymer film.

[0067] It is also worth noting the use of polypyrrole as a material for the surface of a pH sensor. Polypyrrole is an environmentally friendly, easy-to-synthesize, and inexpensive material.

[0068] Furthermore, it should be noted that it is possible to perform a calibration step on the sensor. This calibration can be carried out in a liquid medium or even in soil in the presence of a liquid. In soil, the electrode is placed in a region with a known pH to measure the free potential or open-circuit potential. By repeating this measurement for different pH levels, the electrode and sensor are calibrated, and the sensor can then be used in all media.

[0069] The device 100 also includes a metallic element 104, typically formed from a material which is preferably the same as that of the pipe for which a measurement is to be carried out.

[0070] The metallic element may also be referred to as a metallic coupon or a gravimetric coupon by a person skilled in the art.

[0071] This element has an annular surface 105 which surrounds the surface 102 described above.

[0072] In fact, surfaces 105 and 102 are both arranged downwards in the figure, in the middle of a first opening 106 in a body 107 in which the pH sensor and the metal element are placed. The body can be made of a polymeric material, for example, polypropylene. The body 107 here has a substantially cylindrical shape with a circular base, but other shapes are possible.

[0073] The two surfaces 105 and 102 are therefore left free so that if the device is inserted into the soil, these surfaces will be in contact with the fluid contained in the soil, thus, surface 102 will be used for pH measurement purposes.

[0074] In order for this measurement to accurately illustrate the pH value that could be measured directly near an underground pipe to which an electrical potential has been applied, an electrical potential is also applied to the metallic element 104. As a result, the surface 105 will be able to affect the pH in the same way as in the vicinity of the pipe, which makes the measurement by the sensor 101 very close to that which could be made near the underground pipe.

[0075] It should be noted that surfaces 102 and 105 are recessed relative to surface S of the body, this recess having a depth denoted r on the order of one millimeter, to protect both surfaces.

[0076] To apply this electrical potential, electrical connection methods are used, including: a cable 108 to bring an electrical potential to the metal element 104, a plug 109 mounted on the end of the cable which is in the device, and a connector 110, for example of nickel-coated brass, pressed by screwing against the metal element 104.

[0077] It should be noted that to prevent fluid from entering the body, a seal 111 is arranged around the surface 105, between the metal element 104 and a portion of the body 107 against which the seal is held. The seal 111 forms one of the primary means of maintaining the seal.

[0078] To be able to read the pH value provided by sensor 101, electrical connection means are also used, including: a cable 112, and a plug 113 inserted into the sensor 101.

[0079] The two cables 108 and 112 are joined in a sheath 114 to form a cable bundle, and the two ends of these cables 108 and 112 which are not in the body 107 are connected respectively to plugs 114 and 115, for example plugs according to IEC 61010.

[0080] The two cables 108 and 112 joined in the sheath 114 exit the body 107 through a second opening 116 of the body, and the body is closed by a cap 117, for example made of polypropylene, and opened to allow the two cables 108 and 112 joined in the sheath 114 to pass through a cable gland 118 which will form second means of maintaining the seal.

[0081] There figure 3 is a bottom view of device 100 described with reference to the figure 2 In this figure, we see the polypyrrole surface 102, which has a circular shape and is placed at the center of the device. Surface 102 is surrounded by the annular surface 105.

[0082] This figure also shows the section plane II' corresponding to the figure 2 .

[0083] For reference, surface 102 has an area of ​​0.07 cm². Surface 105 has an area of ​​1 cm². Larger areas are possible for both of these surfaces.

[0084] Advantageously, an annular strip 119 separates surfaces 102 and 105. This strip has a thickness e .

[0085] There figure 4 is an exploded view of device 100 described with reference to figures 2 And 3 . In this figure, we can also see that the sensor 101 is inserted into a sleeve 120 at its end having the surface 102, and into an insulating mounting flange 121 at the connector 110.

[0086] There figure 5 is a cross-sectional view of a 100' device, which differs from that of the figures 2 à 4 in that the surface of the metallic element and the surface containing polypyrrole are adjacent without the metallic surface surrounding the polypyrrole surface. The elements are identical to those described with reference to figures 2 à 4 will not be described in relation to the 100' device for the sake of brevity.

[0087] More specifically, the device 100' includes a pH sensor 101' with a surface 102' comprising polypyrrole. The sensor 101' is identical to the sensor 101 except that it is placed against a wall of the body 107' of the device 100', and inserted directly into the body 107.

[0088] The device 100' also includes a metallic element 104' with a surface 105. The metallic element 104' is arranged to be diametrically opposite the pH sensor 101'. A nickel-plated brass connector 110' is also used to receive the electrical potential in the same way as using connector 110 of the device 100. The connector 110' is mounted in the body 107'. Connectors made of other materials could be used, for example, other conductive connectors.

[0089] Here, the body 107 has two first openings 106A' and 106B' which respectively receive the surfaces 102' and 105'.

[0090] Surfaces 102' and 105' are recessed relative to surface S' of the body, with a recess having a depth r on the order of one millimeter.

[0091] There figure 6 is a view from below of the device 100' described with reference to the figure 5 In this figure, we see the polypyrrole surface 102', which has a circular shape and is located on the right of the figure. Surface 102' is adjacent to the disc-shaped surface 105', which is located on the left of the figure.

[0092] This figure also shows the section plane II-II' corresponding to the figure 5 .

[0093] There figure 7 is an exploded view of the 100' device described with reference to figures 5 et 6 . In this figure, we can also see that the sensor 101' is inserted into a sheath 120 at its end having the surface 102. Here, the sheath is partly projecting from the body 107'.

[0094] A 122' sheath is also used for the 104' metal element.

[0095] Furthermore, in this embodiment, two seals 123' and 124' are used, respectively associated with the pH sensor 101' and the metal element 104'.

[0096] On the figure 8 We have represented an installation comprising a 200 mm pipe that is buried in the ground S . At a first location E1, a measuring station, or potential tap 300 is installed to be connected to the 200 conduit by a 400 cable. At a second location E2, a measuring station, or potential tap 300 is also installed to be connected to the 200 conduit by a 400 cable.

[0097] These potential taps are generally used to measure the electrical potential of the pipeline to which an electrical potential has been applied for cathodic protection purposes. For example, these taps are placed every 4 kilometers.

[0098] Devices equipped with pH sensors, such as those described above, can be used with reference to... figures 2 à 4to measure the soil pH at locations E1 and E2. In fact, it is difficult to reach pipe 200 to take a measurement. However, at shallow depths, devices 100 can be inserted into the soil so that they are in contact with the same environment as the pipe.

[0099] Here, potential taps 300 are used to apply electrical potentials directly to the conduit on the metallic elements of the devices 100, in particular using the sheathed cables 114.

[0100] These measurements allow us to monitor the evolution of pH in different regions, which then allows us to determine the value of the electrical potential to be applied to the 200 pipeline to prevent corrosion, for example by using a Pourbaix diagram.

Claims

1. A method for measuring the pH of a fluid contained in a region of soil containing a soil fluid the pH of which is to be known, comprising: - inserting a pH sensor device into the soil so as to be in contact with the region containing a soil fluid the pH of which needs to be known, the device comprising: - a pH sensor (101) comprising a surface (102), - a metallic element (104) equipped with a surface (105) configured to be in contact with said region containing the fluid when the device is inserted into the soil, - means of electrical connection (108, 109, 110) connected at least to the metallic element and configured to receive a cathodic protection electrical potential for the metallic element, the insertion being implemented so that said surface (105) of the metallic element and said surface (102) are in contact with fluid contained in a region of soil - applying a cathodic protection electrical potential to the metallic element by means of the electrical connection (108, 109, 110), and, - measuring the pH by means of the pH sensor (101), wherein the device comprises a body (107) equipped with at least one first opening (106) configured to allow, when the device is inserted into the soil, the fluid contained in said region to be in contact with said surface (102) and with said surface (105) of the metallic element, and at least one second opening (116) configured to receive said means of electrical connection, the measurement method being characterized in that the surface (102) comprises a polymer material able to attract protons and is arranged so that the polymer material is in contact with said region containing a fluid when the device is inserted into the soil, and in that said surface (102) comprising a polymer material and said surface (105) of the metallic element are arranged, recessed, relative to an external surface of the body wherein the openings are formed.

2. The method according to claim 1, wherein the polymer contains one or more amino groups.

3. The method according to claim 2, wherein the polymer is selected from the group comprising polypyrrole and poly(3,4-ethylenedioxythiophene).

4. The method according to claim 1, wherein the device comprises first means (111) for maintaining the seal, arranged at the interface between, on the one hand, said surface (102) comprising a polymer material and said surface (105) of the metallic element and, on the other hand, the body, to prevent the fluid contained in said region from penetrating into the interior of the body.

5. The method according to any one of claims 1 or 4, wherein the device comprises second means (118) for maintaining the seal arranged at the interface between, on the one hand, the means of electrical connection and, on the other hand, the body, to prevent the fluid contained in said region from penetrating into the interior of the body.

6. The method according to any one of claims 1, 4 or 5, wherein the pH sensor and / or the metallic element are removable relative to the body.

7. The method according to any one of claims 1 to 6, wherein said surface (102) comprising a polymer material and said surface (105) of the metallic element are spaced apart by a strip having a thickness between 0.5 and 1.5 millimeters.

8. The method according to any one of claims 1 to 7, wherein said surface (105) of the metallic element has an annular shape and said surface (102) comprising a polymer material is arranged so as to be surrounded by said surface (105) of the metallic element.

9. The method according to any one of claims 1 to 8, wherein said surface (105) of the metallic element has an area at least greater than or equal to 1 cm2 and said surface (102) comprising a polymer material has an area at least greater than or equal to 0.07 cm2.

10. A cathodic protection method for a pipeline comprising: - implementing the pH measurement method according to any one of claims 1 to 9 for a region of soil located above a pipeline, - determining a new value of electrical potential to be applied to said pipeline based on the result of said pH measurement.

11. A pH sensor device, intended to be inserted into the soil to be in contact with a region containing a soil fluid the pH of which needs to be known, comprising: - a pH sensor (101) comprising a surface (102), - a metallic element (104) equipped with a surface (105) configured to be in contact with said region containing the fluid when the device is inserted into the soil, - means of electrical connection (108, 109, 110) connected at least to the metallic element and configured to receive a cathodic protection electrical potential for the metallic element, wherein the device comprises a body (107) equipped with at least one first opening (106) configured to allow, when the device is inserted into the soil, the fluid contained in said region to be in contact with said surface (102) and with said surface (105) of the metallic element, and at least one second opening (116) configured to receive said means of electrical connection, the pH sensor device being characterized in that the surface (102) comprises a polymer material able to attract protons and is arranged so that the polymer material is in contact with said region containing a fluid when the device is inserted into the soil, and in that said surface (102) comprising a polymer material and said surface (105) of the metallic element are arranged, recessed, relative to an external surface of the body wherein the openings are formed.