Method for detecting corrosion and assessing infiltration by measuring the value of a magnetic characteristic.

Abstract

Method for detecting corrosion and assessing infiltration by measuring the value of a magnetic characteristic. One aspect of the invention relates to a method for detecting corrosion of a corrodible ferromagnetic layer (100) comprising: a step (E1) of acquiring data from different locations (Em10, Em11, Em12) of at least one magnet (10, 11, 12), of the magnetic characteristic value for each magnet (10, 11, 12); a step of determining (E2) a location (Ea210, Ea211, Ea212) of a measuring device (20); a step of measuring and recording (E3) a magnetic flux density (B) at the location (Ea210, Ea211, Ea212); a step of estimating (E4) by the processor (21) a magnetic characteristic value of at least one magnet (10, 11, 12). function of the magnetic flux density (B) measured a comparison step (E5) of the estimated magnetic characteristic value and that estimated previously or acquired,a deduction step (E6) of corrosion of the corrodable layer (100, 110, 120) based on the comparison performed in the comparison step (E5). Figure to be published with the abbreviation: Figure 2,

Description

Title of the invention: Method for detecting corrosion and evaluating infiltration by measuring the value of a magnetic characteristic. TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of detecting and / or preventing corrosion by measuring a value of a magnetic characteristic. This measured value is that of a magnetic field of a magnet at a given location.

[0002] In particular, the technical field of the invention is that of detecting and monitoring the corrosion of a metal portion attached to a magnet.

[0003] It relates in particular to the measurement of a magnetic characteristic value at a given location of the magnetic field of a magnet of a corrosion-sensitive indicator present in a wall of a civil engineering structure, for the prevention of corrosion of at least one metal reinforcement in a porous coating forming the wall. The coating may be made of concrete, for example. By "a coating" is meant a porous layer in the solid state coating the metal reinforcement. For example, in the case of a civil engineering structure made of reinforced concrete, the concrete is considered to be the coating. Thus, the invention can, using an indicator, prevent corrosion of a metal reinforcement of a wall of a civil engineering structure.

[0004] Generally speaking, the present invention can be used to detect and monitor corrosion in all types of metal reinforcement that is difficult to access.

[0005] The present invention therefore relates to the detection of corrosion location from magnetic data and in particular the detection of corrosion of a member from a reading or measurement of a magnetic characteristic value at a given location of a magnetic field of a permanent magnet. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0006] There are different means of deducing corrosion of a metallic portion, whether visual, chemical, electrical resistivity or by wave such as ultrasound.

[0007] However, some of these means require direct access to the metal portion, which is not always the case, for example for the metal reinforcement embedded in concrete in a reinforced concrete wall.

[0008] It is advantageous to know the condition of the coating to prevent aging of the reinforcement.

[0009] Indeed, if we exclude its natural aging, the lifespan of a civil engineering structure, for example in reinforced concrete, can be limited by the penetration of aggressive agents such as chloride ions or by freeze-thaw cycles which lead to a swelling and cracking as well as flaking of surfaces exposed to de-icing salts.

[0010] A common factor in these pathologies is corrosion. The quantification of this corrosion on average or in surface gradient is subsequently a primordial phase in the diagnosis of maritime structures.

[0011] Coring checks on reinforced concrete are regularly carried out by project owners to determine the chloride ion concentration and thus estimate the progress of any possible degradation using predictive models to optimize coating repairs. Unfortunately, these coring checks are destructive, which minimizes sampling via coring, and therefore limits the estimation of the progress of degradation at the level of the entire structure.

[0012] Also, in operational terms, the method commonly used for monitoring and prevention in the face of such pathologies involves regular visual inspections to identify cracks emerging on the surface of the structure's walls, followed by repairs in the form of coating to prevent chlorinated water from reaching the steel.

[0013] Furthermore, different non-destructive testing (NDT) techniques exist and make it possible to estimate significant parameters (performance indicators) of the lifespan of a structure, such as the saturation rate of concrete and porosity.

[0014] However, difficulties arise in identifying cost-effective and reproducible methods providing useful data over long periods of time, since the corrosion phenomenon of the reinforcement of structures tends to occur slowly.

[0015] In some applications, integrated monitoring techniques are implemented using sensors of different technologies placed in the coating concrete in order to measure the concentration of chlorides.

[0016] For example, a corrosion detection system is known comprising a witness comprising an electrical resistance which increases when the witness is corroded, a means for measuring the resistance and an RFID chip allowing, during a check, the means for measuring the resistance to be powered and the information transmitted to an external reader.

[0017] However, such a witness has a high cost and in the event of deterioration of the RFID chip or the measuring means, or even of a connection between the different elements of the witness, the external reader will receive erroneous information.

[0018] Further, the system may include an interrogator outside the wall of the structure and a witness in the wall, the interrogator includes a magnetic field generator including an induction or electromagnetic wave radar and a reader magnetic field and the indicator may comprise a non-magnetic, non-metallic holding member such as a polymer or ABS resin and a corrodible conductor. Corrosion may be measured by supplying a primary magnetic field to the concrete by the generator, the corrodible conductor generates an induced current forming a second magnetic field and the interrogator reads the second magnetic field generated by the corrodible conductor.

[0019] However, such a witness does not provide information when the corrodible conductor has undergone sufficiently high corrosion to no longer have conductivity between these ends. In addition, the electromagnetic radar is an active tool which propagates a wave to the witness which depends on several factors including environmental factors such as the humidity level and the chloride level between the radar and the witness, that is to say in the structure and outside. Thus, the reading result will not be identical depending on the weather and are not precise since they are sensitive to different environmental factors. Finally, such a witness must be mapped during the construction of the structure otherwise there is a risk that the radar transmits and the reader reads waves coming from other elements of the structure which can return the waves such as the reinforcement of the structure or metal debris in the concrete.Finally, such witnesses must be large enough to reflect the wave coming from the active device, for example electromagnetic radar; this volume can cause damage to the structure.

[0020] These different witnesses and systems therefore have extremely high costs in terms of deployment on the scale of a large structure, and still present major technical constraints (robustness, reliability, autonomy.)

[0021] Document US2004100278 further describes a device and its method, measuring ferromagnetic resonance properties by applying a magnetic field to the structure by arranging a magnet near the structure. The ferromagnetic resonance will be different depending on the corrosion state of the corroded reinforcement.

[0022] This device does not prevent corrosion but measures the state of corrosion of the reinforcement. It is therefore not possible to carry out preventive maintenance to prevent corrosion of the reinforcement since corrosion of the reinforcement has already begun when a state of corrosion is detected.

[0023] Furthermore, these different solutions lead to targeted evaluations, which makes the evaluation process tedious. For example, in the case of using a measuring sensor, it must be connected to the metal portion or have its antenna opposite the indicator to be measured and therefore do not allow corrosion information to be obtained from a wider area, for example, than the volume opposite the sensor antenna.

[0024] Finally, one of the problems is that the structure can vary, for example the thickness can increase or decrease due to humidity, heat can distort measurement values. Summary of the invention

[0025] The invention provides a solution to at least one of the problems mentioned above, by comparing a measurement of a magnetic characteristic value at a given location of a magnetic field of a magnet with acquired magnetic field data to deduce corrosion therefrom.

[0026] One aspect of the invention relates to a method for detecting corrosion of a ferromagnetic corrodible layer comprising: a. a step of acquiring and storing data in a memory including at least data: • of different locations of at least one permanent magnet in a global three-dimensional reference frame X, Y, Z, • magnetic characteristic value (B%, B, for each magnet in a three-dimensional frame specific to the magnet, b. a step of determining a location of a device for measuring a magnetic characteristic value (B), distant from the at least one magnet, in the global three-dimensional reference frame by a processor of a detection device, c. a step of measuring a value of a magnetic characteristic (B) by means of the measuring device at the location determined in the determining step, and recording, in a database, the value of the measurement, the location and the date of the measurement, d. a step of estimation by the processor of at least the value of a magnetic characteristic (B%, B, of at least one magnet according to its own three-dimensional reference frame, as a function of the value measured in the measurement step and the location of the magnet acquired in the acquisition step, e. a step of comparing the magnetic characteristic value (B%, B, estimated for at least one magnet and that previously estimated or acquired, f. a step of deducing corrosion of the ferromagnetic corrodible layer between the at least one location of the magnet and the location of the device based on the comparison of the magnetic characteristic value carried out in the comparison step.

[0027] Thanks to the invention, it is possible to deduce corrosion of a ferromagnetic corrodible layer by comparing a value of a magnetic characteristic of the magnet according to its reference. Indeed, if a ferromagnetic corrodible layer is in perfect condition, the magnetic characteristic value is very low due to the magnetic field magnetic field short-circuited by the ferromagnetic corrodible layer whereas if it is corroded, the magnetic characteristic value approaches that of the magnet without ferromagnetic corrodible layer since once corroded, it no longer short-circuits or only slightly short-circuits the magnetic field. In addition, estimating the value of a magnetic characteristic (B, of the magnet according to its own reference frame makes it possible to reduce corrosion estimation errors, for example an error linked to the distance between the measurement location and the magnet which has changed due for example to an expansion of the wall (for example due to freezing / thawing). Indeed, if the measured value is directly compared while the location is incorrect, the corrosion deduction can also be incorrect.Estimating the value of a magnetic characteristic (B, of the magnet according to its own reference frame also makes it possible to limit the risk that an agent disturbing the magnetic flux could cause a measurement error, by detecting this disturbing agent and estimating the value by taking into account the disturbance by this agent.

[0028] In addition to the characteristics which have just been mentioned in the preceding paragraph, the corrosion detection method according to one aspect of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations:

[0029] According to one embodiment, the value of a measured magnetic characteristic is an arbitrary unit of a magnetic flux density.

[0030] According to one embodiment, each magnet is attached to a ferromagnetic metal element forming the ferromagnetic corrodible layer and in that the data acquisition and storage step further comprises data of magnetic characteristic values ​​(B, as a function of the thickness of the non-corroded ferromagnetic metal element with the components of the three-dimensional reference frame specific to the magnet x, y and z.

[0031] According to an example of this embodiment, the acquired magnetic characteristic value of the magnet is based on the ferromagnetic metallic element forming the ferromagnetic corrodible layer, and if the estimated value is greater by at least one predetermined value than the acquired value, then the deduction step f) deduces that the ferromagnetic corrodible layer is corroded.

[0032] According to another example of this embodiment, the acquired magnetic characteristic value of the magnet is based without the ferromagnetic metallic element forming the ferromagnetic corrodible layer, and if the estimated value is less than a predetermined value added to the acquired value, then the deduction step f) deduces that the ferromagnetic corrodible layer is corroded.

[0033] According to another example of this embodiment the characteristic value ma acquired magnetic field of the magnet is based on a measurement at a first instant, if that estimated at an instant subsequent to the first instant is greater by at least one predetermined value than that acquired during a measurement at the first instant then the deduction step f) deduces that the ferromagnetic corrodible layer is corroded.

[0034] According to an example of this embodiment, the memory comprises a calibration curve of the magnetic characteristic value of the magnet with respect to the corrosion of the ferromagnetic corrodible layer attached to the magnet and in that step f) of deducing corrosion of the ferromagnetic corrodible layer comprises the use of this curve by an inverse method to deduce therefrom a corrosion state value of the ferromagnetic corrodible layer.

[0035] This example makes it possible to give a state of corrosion, for example a percentage of corrosion of the corrodible ferromagnetic layer or even a thickness of the remaining non-corroded ferromagnetic layer.

[0036] According to this example, the method uses an inverse method to determine from the calibration curve, a corrosion state and further a possibility of a pathogen infiltration state.Indeed, a calibration curve can be produced in the laboratory which can be modified by experiment, in which a plurality of characteristic magnetic values ​​of witnesses are measured in the laboratory, each comprising an identical magnet and a corrodible layer initially identical (same material and same thickness) at the same or different predetermined distances to calculate from the Biot Savart law a magnetic moment of each witness, in which the different measurements are carried out by having their corrodible layers according to different predetermined corrosion rates which can be determined as a function of a chloride content in a structure by experiment, by relating each measured magnetic moment value to the chloride content in a corresponding structure.Thus, by the inverse method, we measure or calculate the magnetic moment of the sensor from the device and by the inverse method deduce the corrosion rate and / or, as required, a chloride content from the measurement of the magnetic moment using the calibration curve produced in the laboratory.

[0037] According to one embodiment, the method comprises a plurality of steps of determining the location of the apparatus and steps of measurements at different locations in a limited area and in that the estimation of the characteristic value is refined at each measurement of magnetic flux density (B) of a location. This makes it possible to adapt to a change in the actual distance between the magnet and the measuring apparatus or another magnet producing a magnetic field in an area close to the magnet for which a value is estimated. For example, in the case of two magnets close to each other against a ferromagnetic corrodible layer, as long as the ferromagnetic corrodible layer is not corroded, there will be no impact on the measurement because the ferromagnetic corrodible layer of the magnets will short-circuit their magnetic field but when the ferromagnetic corrodible layer of the magnets is corroded, the measurement by the measuring device at the determined location may pick up the magnetic field of one or both magnets and estimate a wrong value of a magnetic characteristic (B, of the magnet and therefore a deduction of corrosion of the ferromagnetic corroded layer but not necessarily in the right place. Using several measurements in a predetermined area relative to the magnet makes it possible to estimate more precisely the value of a magnetic characteristic (B, of the real magnet since one of the measurements by the device at the first, second, third, etc. locations will necessarily be less influenced by the other magnet.

[0038] According to one embodiment, the model uses the Biot-Savart law to estimate the value of a magnetic characteristic (B, according to its own three-dimensional reference frame x, y and z. Knowing the location of the magnet and that of the device, this makes it possible to easily calculate and estimate the magnetic moment of the magnet in its reference frame.

[0039] According to one embodiment, the data acquisition and storage step further comprises orientation data of the poles of the magnets relative to the point of origin of the global reference frame. This makes it possible to estimate a magnet oriented randomly relative to the measurement location. For example, in the case of a wall comprising a porous coating in which a witness comprising the magnet and the corrodible layer, the witness may have been either randomly positioned or disoriented during the procedure of pouring the porous coating, the acquisition step comprises a measurement of the orientation of the magnet relative to the auscultation surface to acquire the orientation and thus to take into account the orientation of the magnet relative to the surface against which the measuring device performs the measurement at the determined location. The orientation of the magnet may be carried out using the measuring device or a compass.So only in the case where the magnet is positioned with its face having the north and south pole in parallel with the face of the wall, the magnet will be unusable or difficult to use.

[0040] For example, the apparatus comprises a magnetometer with a Hall probe to enable the directions and senses of the magnetic field to be measured and thus the orientation of the magnet to be determined. For example, a regular dome will represent a magnet positioned such that a face comprising north and south is perpendicular to the probe of the magnetometer, making it possible to indicate that this face of the magnet is parallel to the auscultation surface, and if the dome is irregular, the apparatus may comprise a corrective factor making it possible to indicate the orientation of the surface of the magnet by report to its probe.

[0041] According to one embodiment, the method may further comprise a step of estimating the orientation of the magnet using the measured values ​​of a magnetic characteristic and the step of estimating by the processor at least the value of an estimated magnetic characteristic is a function of the determined orientation. This makes it possible to take into account the case of a different orientation of the magnet relative to the origin. For example, in the case of a witness comprising a magnet and a corrodible layer in a wall, in the event of a crack crossing the area of ​​the magnet, the magnet may be slightly inclined relative to its initial orientation and therefore modify the value of the magnetic characteristic (B, m) to be measured on the face of the wall relative to a value measured if the magnet had kept its initial orientation.

[0042] According to one embodiment, in which a corrosion indicator is located in a porous coating of a wall, in particular reinforced concrete, the corrosion indicator comprising one of the magnets and at least one ferromagnetic corrodible layer integral with the magnet connecting the north pole to the south, and in which the step of deducing corrosion of the ferromagnetic corrodible layer and that of the ferromagnetic corrodible layer of the indicator.

[0043] Such a witness thus makes it possible, when it is placed between the armature and the surface of the wall against which the measurement is carried out by the measuring device, to estimate by the processor, in the event of deterioration of the ferromagnetic corrodible layer, at least the value of a magnetic characteristic (B, of the magnet by means of the measurement or measurements by the measuring device, higher than that estimated when the ferromagnetic corrodible layer was in perfect condition and thus indicate to a maintenance operator that the porous wall comprises agents pathogenic to corrosion at least up to the location of the witness comprising this ferromagnetic corrodible layer.

[0044] According to one embodiment, the step of acquiring location data of the magnets in the global reference frame X, Y, Z comprises: a. a sub-step of searching for a signal of a magnetic flux density (B) by means of the measuring apparatus for a magnetic characteristic value of the magnetic field in a limited area and measuring and recording the most significant signal value of each limited area, b. a sub-step of recording a location in the global three-dimensional frame by a processor in a memory when the measuring apparatus has measured a value of a most significant magnetic characteristic, c. a sub-step of deducing the distance between the magnet and the location and recording the location of each permanent magnet in a global three-dimensional reference point.

[0045] Such an embodiment makes it possible, on the one hand, to obtain a starting reference of one or more values ​​of a magnetic characteristic of a magnetic field provided by the magnet located at a measurement location, and on the other hand to acquire data to map the location of the magnet, for example of the witness.

[0046] Another aspect of the invention also relates to a method for estimating the content of a pathogenic agent in a wall comprising a porous packaging, comprising: - the corrosion detection method described previously, - a step of deducing infiltration of pathogenic agent in the wall as a function of a calibration curve, the locations of the witness(es) comprising the magnet and corrosion evaluations of the ferromagnetic corrodible layer.

[0047] This allows maintenance agents to estimate the timing and location of preventive maintenance by resolidifying the porous coating of the wall to prevent the reinforcement from being damaged.

[0048] According to this example, the method uses an inverse method to determine from a calibration curve produced by laboratory or by experiment, the infiltration state of a pathogenic agent. Indeed, a calibration curve can be produced in the laboratory which can be modified by experiment, in which a plurality of values ​​of a magnetic characteristic of controls comprising the magnet and a corrodible layer initially identical (same material and same thickness) at the same or different predetermined distances are measured in the laboratory, and having their corrodible layers according to different predetermined corrosion rates as a function of a chloride content in a structure and from Biot Savart's law to determine a magnetic moment value to produce this calibration curve by relating each magnetic moment value to the chloride content in a corresponding structure.Thus, by the inverse method, we can measure or calculate the magnetic moment of the sensor from the device and use the calibration curve produced in the laboratory to determine the chloride content of the portion of the structure comprising the witness as a function of the magnetic moment of the sensor, and therefore by the inverse approach deduce a chloride content from the measurement of the magnetic moment.

[0049] The invention is therefore likely to be used more particularly for the detection of infiltration of pathogenic agent which can cause corrosion of a reinforcement in the structures of civil engineering infrastructures (buildings, dams, bridges, tunnels, swimming pools, etc.), in particular the structures of maritime infrastructures and the foundations of coastal or offshore works (dykes, jetties, wind turbines, offshore platforms, tidal dams, hydro turbines, etc.). A structure of an infrastructure can be a part of the infrastructure, for example a wall, post or even a portion of these.

[0050] The invention can be used in a preventive maintenance context since by detecting an area infiltrated by a pathogenic agent, it is possible for the maintenance agent to limit the spread of a pathology, for example by sealing the detected area or by replacing (destruction of the porous wall (for example concrete) and masonry with a new porous wall) the detected area to extend the residual life of the infrastructure and therefore limit the costs related to the maintenance of the structure. Indeed, by carrying out preventive maintenance, the structure will not be or will be less quickly corroded and therefore the building will have a longer life without very significant work which is very expensive.

[0051] According to one embodiment, the step of deducing infiltration of pathogenic agent into the wall as a function of a calibration curve comprises a sub-step: - of estimating the location of the infiltrated zones in the overall pathogenic agent reference frame in the coating as a function of the locations of the magnet of each witness having a ferromagnetic corroded layer, the determined corrosion state value information of the different ferromagnetic layers and the time between the measurements deducing corrosion of the ferromagnetic corrodible layer of the witness, - deduction of pathogen infiltration rates in each estimated area in the wall based on a calibration curve, the locations of the magnet of each witness and corrosion assessments.

[0052] According to one example, the sub-step of estimating the location of the infiltrated zones also estimates an intermediate zone between two neighboring non-juxtaposed infiltrated zones and the sub-step of deducing the pathogen infiltration rate deduces an infiltration rate therefrom.

[0053] According to one embodiment, the step of deducing infiltration of pathogenic agent in the wall is a function of the different corrosion estimates of one or more witnesses over time.

[0054] According to one embodiment, the step of deducing pathogen infiltration in the wall is a function of the different corrosion estimates of the other neighboring zones over time. This makes it possible to identify the pathogen infiltration radiation.

[0055] According to one embodiment, the method comprises a step of modeling the wall comprising a porous coating and a reinforcement cast in the coating and the location of the different magnets of each witness comprising the magnets in the wall and a step of modeling and displaying the estimation of the content of an agent in the wall by displaying the estimated localized zones and their deduced infiltration rates. This makes it possible to produce a map of the infiltration of the agent pathogenic.

[0056] The invention also relates to an autonomous detection device for implementing the corrosion detection method described above with or without the different characteristics of the embodiments described above, comprising the processor, the memory and the magnetic flux density measuring device and in that it comprises a device for moving the measuring device along at least two axes of the global reference frame to move it facing the auscultation surface of a wall and in that the movements of the measuring device are controlled by a control unit comprising the processor as a function of the measured values ​​of a magnetic characteristic and / or location of different acquired magnets.

[0057] According to one embodiment, the apparatus is further adapted to produce the method for estimating the content of a pathogenic agent described above.

[0058] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0059] The figures are presented for information purposes only and in no way limit the invention.

[0060] [Fig. 1] shows a schematic representation of a block diagram of the corrosion detection method according to the invention.

[0061] [Fig.2] shows a schematic representation of a first example of implementation situation of the corrosion detection method according to the invention

[0062] [Fig.3] shows a schematic representation of a flux measurement curve ma genetics of witnesses according to a state of corrosion of their ferromagnetic corrodible layer.

[0063] [Fig.4] shows a schematic representation of a curve representing the variation of magnetic flux as a function of witness time according to different corrosion states and measurement distance.

[0064] [Fig.5] shows a schematic representation of the example of [Fig.2] in situation of pathogen infiltration.

[0065] [Fig.6] shows a schematic temporal representation of the relative variation of magnetic flux B% of the witnesses of the example in [Fig.5].

[0066] [Fig.7] shows a schematic representation of agent infiltration deduction pathogen of the example of [Fig.2] with the crack shown in [Fig.5] after a period.

[0067] [Fig.8] shows a schematic representation of a second example of the implementation of the corrosion detection method according to the invention.

[0068] [Fig.9] shows a representation of calibration curves between a rate of corrosion and a value of a magnetic characteristic of two corrodible layers of different thicknesses. DETAILED DESCRIPTION

[0069] [Fig.l] shows a schematic representation of a block diagram of the corrosion detection method according to the invention.

[0070] The method for detecting corrosion of a ferromagnetic corrodible layer comprises a first step E1 of acquiring and storing data in a memory including at least data from different locations Emx, of at least one permanent magnet 10 in a global three-dimensional frame of reference X, Y, Z and values ​​of a magnetic characteristic among the flux density (B) or one or more magnetic moments (^), for each magnet (10) in a three-dimensional frame of reference specific to the magnet.

[0071] [Fig.2] shows a schematic representation of a first example of the corrosion detection method according to the invention.

[0072] [Fig.2] includes the global reference X, Y, Z. [Fig.2] represents a portion of a reinforced concrete wall 4, hereinafter called wall 4, cut along the X axis in a reinforcement 41 of the wall 4 and witnesses 1 placed in a porous coating 42 of the wall 4.

[0073] The witnesses 1 are located at different depths of an auscultation surface 421. In this case, in this example, the witnesses 1 are all located between the auscultation surface 421 and the frame 4L

[0074] In an example of this embodiment, the witnesses 1 of the wall 4 are identical and each witness 1 comprises a magnet 10, 11, 12 having a magnetic flux density of 1 tesla. Of course, the magnetic flux density can be less than or greater than 1 tesla. In this example, each witness 1 also comprises a corrodible layer of ferromagnetic materials 100, 110, 120.

[0075] The wall 4 comprises an auscultation surface 421, in this case in the X,Y plane. The X,Y plane further allows a detection apparatus 2 explained below to represent the position of the indicators by projection onto the osculation surface 421 and the Z direction represents the depth of the indicators relative to the auscultation surface 421. The indicators 1 are, in this exemplary embodiment, located at different depths relative to the auscultation surface 421, in this case, they are spaced from each other by 10 mm and at different locations, in this case located on the same value of the X axis (for example 1 meter) and at different values ​​along the Y axis, in this case spaced from each other by 40 mm.The first witness is located at a location EmlO such that the magnet 10 has its boundary of the two poles located at +35 mm on the Y axis, its surface opposite its corrodible layer at +5 mm on the Z axis, and at +1 m for the X axis, the second witness is located at an em. placement Eml 1 such that magnet 11 has its boundary of the two poles located at -5 mm on the Y axis, its surface opposite its corrodible layer at +15 mm on the Z axis and at +1 m for the X axis, the third witness is located at a location Eml2 such that magnet 12 has its boundary of the two poles located at -45 mm on the Y axis, its surface opposite its corrodible layer at +25 mm on the Z axis and at +1 m for the X axis.

[0076] Each witness 1 is oriented in the porous coating 42 such that the layer of ferromagnetic materials 100, 110, 120 is closer to the auscultation surface 421 than the magnet 10, 11, 12.

[0077] The witnesses may have a different inclination from each other relative to the auscultation surface. The apparatus may comprise a means for determining the inclination of the magnet by measuring different values ​​of a magnetic characteristic. An example of inclination is that a face comprising the north and the south is inclined relative to the Y and / or X axis, i.e. not parallel to the auscultation surface. For example, the apparatus comprises a magnetometer with a Hall probe to enable the directions and senses of the magnetic field to be measured and thus the orientation of the magnet to be determined.For example, a regular dome will represent a magnet positioned such that the face comprising north and south is perpendicular to the probe of the magnetometer, making it possible to indicate that this face of the magnet is parallel to the auscultation surface and if the dome is irregular, the device can include a corrective factor making it possible to indicate the orientation of the surface of the magnet relative to its probe.

[0078] In this example, the first step E1 of acquiring and storing data in a memory of the data of different locations Eml0, Emll, Eml2, of the three permanent magnets 10, 11, 12 in the global three-dimensional reference frame X, Y, Z is carried out using a detection device 2 comprising a measuring apparatus 20 for measuring magnetic characteristic values ​​which is in this example the magnetic flux density B.

[0079] The first step E1 comprises a sub-step E10 of searching for a signal of a magnetic flux density B by moving the measuring device 20 against the auscultation surface 421 and when a signal of a magnetic flux density B is measured, moving the measuring device 20 in a limited area until the largest value of magnetic flux density is obtained in order to identify the location of the magnet 10, 11, 12.

[0080] The detection device 2 comprises a processor 21 and a memory 22, configured to record in the memory 22 the magnetic flux density and location values ​​when its measuring device 20 has measured the value of the largest magnetic flux density B.

[0081] The first step El therefore comprises a sub-step El 1 of recording the value B10, B11, B12 of the largest signal of the limited area as well as the location Emx when the measuring device 20 measured the value of the largest magnetic flux density B for each magnet 10, 11, 12.

[0082] The first step E1 further comprises a sub-step E12 of deducing the distance between the magnet and the location Ea210, Ea211, Ea212 of the detection device 2 and recording the location Eml0, Eml1, Eml2 of each permanent magnet 10, 11, 12 in the global three-dimensional reference frame X, Y, Z as a function of the location of its measuring device 20 and the deduced distance. Furthermore, this deduction sub-step E12 deduces and records at least one magnetic characteristic value of the magnet in a three-dimensional reference frame xl0, yl0, zl0, specific to the magnet as a function of the deduced distance and the value B10, B11, B12 of the most important signal as well as the magnetic flux density, in this case a value of 1 te sla.

[0083] [Math.l] B ( r ) = 4^(3 ( rjn )r~ | || )

[0084] For example, the magnetic characteristic value "magnetic flux density B" of the magnet 10 in its reference frame X10, Y10, Z10 is 76.5 milli-teslas at the location X= +1000 mm, Y= +35 mm, Z= 0 mm. The magnetic characteristic value can be the magnetic flux density B or magnetic moments) or even the intensity of the magnetic field H at a given point.

[0085] [Fig.3] shows a schematic representation of a measurement curve of the magnetic flux density B of the magnets 10, 11, 12 of each witness 1 according to a state of corrosion of their corrodible layer 100, 110, 120.

[0086] This measurement curve may, for example, be a calibration curve produced in the laboratory which may be modified by experiment, in which a plurality of values ​​of a magnetic characteristic of witnesses are measured in the laboratory, each comprising an identical magnet and a corrodible layer which are initially identical (same material and same thickness) at the same or different predetermined distances to calculate, from the Biot Savart law explained below, a magnetic moment of each witness, in which the different measurements are carried out by having their corrodible layers according to different predetermined corrosion rates which may be determined as a function of a chloride content in a structure by experiment, by relating each estimated magnetic moment value to the chloride content in a corresponding structure.

[0087] It can be seen in this figure that when the corrodible layer of the indicators 1 is not corroded, the detection device 2 measures by its measuring device 20 a density of the magnetic flux B10 of approximately 24.38mT at the location Ea210 in vis- opposite for the first witness, of approximately 5mT at location Ea211 opposite the second witness, of approximately 1.49mT at location Ea212 opposite the third witness.

[0088] [Fig.9] represents two calibration curves of two fictitious witnesses produced in laboratory, in a reference frame representing on the ordinate a value of a magnetic characteristic, here an arbitrary unit AU of which 1 AU equals 0.05mT and on the abscissa the relative mass loss of the corrodible layer of the witness corresponding here to the corrosion rate. In this example, the same cylindrical magnet of 8 mm diameter and 2 mm thickness was placed under two series of corrodible layers at different corrosion rates to carry out the magnetic measurements. Each corrodible layer of a series was identical to the initial state. In this case the corrodible layers in the initial state (not corroded) of a first series had a thickness of 0.5mm and those of the second series had a thickness of 1mm. In this example, each corrodible layer is a right square prism with square faces of dimension 15x15 mm.In particular, measurements with the magnet and the magnetometer device with the distance of 3 cm were carried out on each corrodible layer to ensure that each corrodible layer of a series gives a signal identical to the other corrodible layers of the same series within the measurement errors. The corrodible layers were then placed in a 30 gL-1 NaCl solution to accelerate their corrosion, for example by electrolysis in a solution of 30 g of NaCl per liter of water, weighed and measured their values ​​of a magnetic characteristic AU by a magnetometer sensor placed 3 cm from the corrodible surface of the ferromagnetic layer opposite the magnet.

[0089] It can be seen in this [Fig.9] that the thicker the corrodible layer, the smaller the value of a measured magnetic characteristic for the same corrosion rate but that they vary substantially identically with respect to their corrosion rate. Thus, according to an example having witnesses different in their corrodible layer thickness, the witnesses having a corrodible layer of greater thickness will be close to the monitoring surface and those having a smaller thickness closer to the reinforcement, thus making it easier to use the same measurement range of a measuring device.

[0090] In this example, the measurement of the mass loss relative to the corrodible layer in the initial state in percentage corresponds to the different corrosion rates in percentage. The corrosion rate can be measured differently, for example by geometric dimensioning.

[0091] The measuring distance between the measuring device 20 and the magnet therefore has a significant influence on the measured value. Indeed, it can be seen that for 1 cm of difference in depth between the first and second witness, the measurement is divided in this example by 5 for a non-corroded layer and that for 1cm of difference in depth between the second and third witness, the measurement is divided in this example by 3.33 for a non-corroded layer.

[0092] Furthermore, it can be seen that the greater the measurement distance between the measuring device 20, the less the corrosion of the corrodible layer 100, 110, 120 influences the measured magnetic flux density B. Indeed, for a witness having its layer corroded at 100% in this example, the third witness having a measurement distance of 25mm has a variation of 19% while the first witness also having its corrodible layer corroded at 100% has a variation of 214%, i.e. 2.14 times the measurement carried out at time T0.

[0093] The measuring apparatus 20 may be modified or may have different configurations or calibrations to adapt to the sensitivity of the magnetic fields to be measured.

[0094] Thus, according to an example, thanks to the knowledge of a magnetic flux density of 1 tesla, and of the Biot-Savart law (deduced from Maxwell's equations): B(r) = 3(rm)r- r 2 in

[0095] Where r = the predetermined distance and B(r) the measured flux density and po is the magnetic permeability of the vacuum and is equal to: luO^r-IO7 SI]

[0096] The detection device 2 with its processor 21 is configured, by having a program, for example, to calculate and estimate or deduce therefrom the value of the moment muz ,mi2z, mnz according to its own three-dimensional reference frame x, y and z at a location Ea210, Ea211, Ea212, which is recorded in a memory. The recorded location may be that acquired in step El by determining the location where the value of a measured magnetic characteristic best corresponds to the location opposite a witness. This estimation of the value of the magnetic moment mnz ,mi2 z, mnz is therefore carried out from the Biot Savard law and the measured magnetic flux density value B and the distance r deduced during the distance deduction sub-step r E12 of step EL

[0097] The detection device 2 therefore stores in memory a value of a magnetic characteristic acquired in step E1 of each magnet 10, 11, 12 according to their reference at a predetermined location which may be the origin.

[0098] The method further comprises a step of determining a location of the measuring device 20 in the global three-dimensional reference frame by the processor 21.

[0099] For example, the determined location may be the predetermined location or a another location Ea210, Ea211, Ea212 recorded if the auscultation surface has not changed otherwise it can determine another one. In particular, the detection device 2 can comprise a human-machine interface to guide the user to move the device to the recorded location and furthermore for example a button, so that the user can give the information that the location Ea210 or Ea211 or Ea212 is no longer accessible (for example swelling of the wall 4 due to freezing / thawing), in this case the device determines another location which can for example be the one closest to the location Ea210 or Ea211 or Ea212.

[0100] The method further comprises a step E3 of measuring a value of a magnetic characteristic, here a magnetic flux density B, by means of the measuring device 20 at the determined location, in this case at each of the locations Ea210, Ea211, Ea212, and recording in a database the data concerning the measurement, the location and the date of the measurement.

[0101] The method may comprise a plurality of location determination steps E2 and measurement steps E3 at different locations in a limited area and in that the estimation of the characteristic value is refined at each measurement of magnetic flux density (B) of a location. This may be the case, for example, if the auscultation surface is modified or if a magnetic field disturbance agent requires different measures to reduce the risk of estimation error E4 described below. Furthermore, these repeated steps may also be carried out at the beginning during the data acquisition step E1 explained above.

[0102] For example, the corrodible layer 100, 110, 120 of each witness 1 has undergone corrosion due to infiltration of a pathogenic agent, for example ions from salt water.

[0103] The corrodible layer 100, 110, 120 of each witness 1 has a thickness of 1 mm and is made of iron, at time T0 when step E1 has been carried out. The corrodible layer of the witness may be made of materials other than iron, such as nickel and cobalt or other alloys.

[0104] Figure 4 represents a curve representing the relative variation of magnetic flux B% as a function of time of the three witnesses according to different states of corrosion and distance, for example T1 is 2 years after T0, T2 is 4 years after T0 and T3 6 years after T0. In this example, the value of a magnetic characteristic is a percentage variation of a flux density (B) or of one or more magnetic moments (y^) at a point in the x,y,z reference frame specific to the magnet 10, 11, 12. The reference frame specific to the magnet can also be the global reference frame.

[0105] In [Fig.3], it can be seen that the more the corrodible layer 100, 110, 120 is corroded, the greater the magnetic field density B measured at the location Ea210, Ea211, Ea212, by the measuring device 20.

[0106] For example, at T2, each corrodible layer is corroded by 2 / 3, that is to say that the corrodible layer 100, 110, 120 in the form of an iron plate with a thickness of 1 mm now comprises only 33% of its initial thickness, i.e. in this example 0.3 mm of non-corroded iron.

[0107] The curves of figures 3 and 4 can for example be calibration curves allowing the detection device 2, using a program in the memory 22 using the processor 21, to correlate the variation in corrosion of a type of indicator with its magnetic field as a function of the measurement distance by the inverse method.

[0108] The method comprises an estimation step E4, carried out by the detection device 2 using a program in the memory 22 and the processor 21, of at least the value of a magnetic characteristic, of at least one magnet 10, 11, 12 according to its own three-dimensional reference frame, as a function of the magnetic flux density B measured in step E3 and the location Eml0, Eml1, Em12 of the magnet acquired in step El at the location Ea210, Ea211, Ea212 of the measuring device 20. Thus, by modifying the location of the measuring device 20 with respect to that memorized Ea210, Ea211, Ea212 there will be a significant influence, even for 1mm. The method makes it possible, from this new location, to identify the value of a magnetic characteristic (B, of at least one magnet according to its own three-dimensional reference frame.The first location Ea210, Ea211, Ea212 of the measuring device 20 for the measurement in step 10 may be inaccessible for various reasons, for example expansion of the wall linked to the infiltration of agent, or heat, a layer added to the wall, for example linked to a repair, etc.

[0109] The method therefore comprises a step E5 of comparing the value of a magnetic characteristic (B, of at least one magnet, estimated at this instant in step E4 and that previously estimated at an instant prior to step E4 or acquired in step E10 of this same magnet. By "previously estimated magnetic characteristic", here is meant a comparison of the value of a magnetic characteristic (B, of at least one magnet deduced with the measurement carried out at an instant T, for example at the instant T2 and value of a magnetic characteristic (B, of at least one magnet at an instant deduced with the measurement carried out at a previous instant for example T1, in this example at the instant TL

[0110] Finally, the method comprises a step E6 of deducing corrosion of the corrodible layer 100, 110, 120 between the at least one location of the magnet and the location of the measuring device 20 as a function of the comparison of the value of a magnetic characteristic in step e) and that acquired in step a).

[0111] Indeed, if the value of a magnetic characteristic increases, we can deduce corrosion.

[0112] The method may further comprise in the memory a calibration curve of the value of a characteristic of the magnet 10, 11, 12 with respect to the corrosion of the corrodible layer 100, 110, 120 of the witness 1 and in that the step E6 of deducing a corrosion of the corrodible layer 100, 110, 120 is produced by the processor which uses this curve to deduce therefrom a corrosion state value of the corrodible layer 100, 110, 120. For example, the corrosion calibration curve is such as that of [Fig. 3], to estimate the percentage of corrosion of the corrodible layer 100, 110, 120. The method may therefore use an inverse method to determine from a calibration curve, produced by laboratory or by experiment, a corrosion rate of the corrodible layer linked to a magnetic moment value deduced from from the measurement of the value of a magnetic characteristic.

[0113] [Fig.5] schematically represents an example of a situation of the wall in which a crack 43 has formed allowing infiltration of a pathogenic agent represented by arrows, such as sodium chloride has become embedded in the wall with a deformation 4210 of the auscultation surface 421.

[0114] Measurements are carried out at T1 2 years, T2, and T3 after the time T0 in which the data acquisition step 10 was carried out.

[0115] Due to the deformation of the auscultation surface 421 during the crack 43, the method comprises in the determination step E2, the determination of the location Ea210', Ea211', (the location Ea212 being able to be exploitable) of the measuring device of a value of a magnetic characteristic can comprise a sub-step of indicating the location, for example by indicating by visible signals, the direction to take to position the measuring device 20 at the determined location Ea210', Ea211'. The origin of the global reference point, to locate the measuring device and the magnets in space, can be a physical point, for example visible on an outlet of the wall of one end of a stake of the armature 4L. The determination of the reference point can be manual at each instant and recorded in the memory by the processor.The determination of the location Ea210' can also be carried out manually by being imposed by the operator, and the processor determines the location Ea210', Ea211' according to the origin of the global reference frame. The determination of the location Ea210' can be carried out by the processor using information from a sensor of the detection device 2, of the radar type which can be infrared, or any other type of sensor to enable the identification of a precise location relative to an origin of a reference frame.

[0116] In addition, the apparatus may include software to indicate the angular orientation relative to the witness or correct the measurement relative to this angular orientation. Indeed, the auscultation surface may, by its deformation, prevent having the same orientation as during the first acquisition or the old acquisition and thus give a wrong measurement by having the device oriented differently in relation to the magnet than in its previous measurements.

[0117] Figure 6 shows a schematic temporal representation of the relative variation of the flux density (B%) or one or more magnetic moments (^), of the witnesses of the example of [Fig.5] at different periods T1, T2, T3 relative to T0.

[0118] As can be seen, at time T1, the infiltration of pathogenic agent has caused corrosion of the corrodible layer 110 of the second witness since there has been a determination of a variation in magnetic flux of approximately 5% compared to time T0 which for example according to the calibration curve of the second witness can correspond to a corrosion state of 40%. The two other deductions of values ​​of a magnetic characteristic of the other two witnesses remained stable at time TL At this time T1, the device can deduce that an infiltration of pathogenic agent in the coating has passed in front of or behind the first witness but that there is little risk that it has reached the depth of the reinforcement 4L

[0119] At time T2, the infiltration of pathogenic agent has caused corrosion of the corrodible layer 100 of the first witness since a variation in magnetic flux of approximately 20% is determined, i.e. corrosion having a corrosion state of approximately 33% according to the reference curve of [Fig. 3] and the corrodible layer 110 of the second witness since a variation in magnetic flux of approximately 12% is determined, i.e. corrosion for example having a corrosion state of approximately 70%.

[0120] From the instant T1, the detection device 2 can be configured to carry out a method of estimating the content of a pathogenic agent in the wall 4 in the porous packaging further comprising, from the corrosion detection method, a step of deducing infiltration of pathogenic agent E7 in the wall as a function of a calibration curve, locations of the witness(es) and corrosion evaluations, the time between the measurements between the measurements deducing corrosion of the corrodible layer of the witness. The step of deducing infiltration of pathogenic agent E7 in the wall 4 is a function of the different corrosion estimations of one or more witnesses 1 over time.

[0121] The method uses an inverse method to determine from a calibration curve not shown, produced by laboratory or by experiment, the state of infiltration of a pathogenic agent. Indeed, a calibration curve can be produced in the laboratory which can be modified by experiment, in which a plurality of values ​​of a magnetic characteristic of controls comprising the magnet and a corrodible layer initially identical (same material and same thickness) at the same or different predetermined distances are measured in the laboratory, and having their corrodible layers according to different predetermined corrosion rates as a function of a chloride content in a structure and from Biot Savart's law to determine a magnetic moment value to produce this calibration curve by relating each magnetic moment value to the chloride content in a corresponding structure or use the calibration curve of [Fig.3] (magnetic moment, distance and corrosion rate) or that of [Fig.9] (different corrosion rates, value of a magnetic characteristic at a predetermined distance and different initial thicknesses), with another calibration curve including the corrosion rate and a chloride content not shown. Thus, by the inverse method, the magnetic moment of the sensor can be measured or calculated from the device and the calibration curve produced in the laboratory can be used to determine the chloride content of the portion of the structure comprising the witness as a function of the magnetic moment of the sensor, and therefore by the inverse approach, deduce a chloride content from the measurement of the magnetic moment.

[0122] The step of deducing pathogen infiltration E7 comprises a first sub-step of estimating the location of the infiltrated zones E70 in the global reference frame by pathogenic agents in the coating as a function of the determined corrosion state values ​​of the different layers and the time between the measurements.

[0123] The step of estimating the content of a pathogenic agent E7 comprises a second sub-step of deducing the infiltration rate of pathogenic agent E71 in each zone estimated in particular by the inverse method with a calibration curve as described previously.

[0124] For example, at time T1, the detection device is configured to estimate the location of an area infiltrated by a pathogenic agent around the magnet 11 of the second witness due to its corrodible layer 110 having a corrosion state of 40% deduced in step E6 and a deduction of pathogenic agent infiltration rate linked to this state.

[0125] [Fig.7] represents a graphical representation of estimation of the content of a pathogenic agent in the wall 4 at time T2, in which the detection device 2 is configured to estimate a first zone 44 around the magnet 10 comprising a certain size and a second zone 46 around the magnet 11 comprising a size greater than that of the first zone 44 since at time T1 a first zone had already been located and the deduction of the corrosion state value of the corrodible layer 110 continued to increase.

[0126] Furthermore, the detection device 2 is configured to further estimate an intermediate zone 45 between the two neighboring infiltrated zones 44, 46 which is not juxtaposed and deduces therefrom a pathogen infiltration rate having a value between the two rates of the two other zones 44, 46.

[0127] The detection device 2 can further be configured to model the wall 4 with the porous coating 42, the reinforcement 41, the location of the different indicators or magnet 10, 11, 12 in the wall 4 and a step of modeling and displaying the estimation of the content of an agent in the wall by displaying the estimated localized areas and their deduced infiltration rate, as shown in [Fig.4].

[0128] [Fig. 8] represents a schematic representation of a second example of implementation of the corrosion detection method according to the invention in which the magnet 10 can be moved over a surface of a corrodible layer 90 as well as the measuring device 20 can be moved over an opposite surface of the corrodible layer 90.

[0129] In this example, the corrodible layer 90 is a part of a bodywork 9 in which the magnet 10 is inserted through an opening 91. Thus the corrosion detection method makes it possible to detect the corrosion of a corrodible layer 90 whose surface is difficult to access.

[0130] According to another example not shown, it is the measuring device 20 which is inside the bodywork and the magnet 10 which is outside on the corrodible layer 9.

[0131] In this example, the thickness 92 or the different thicknesses of the corrodible layer 90 is / are known and the step E1 of acquiring and storing data in a memory of which at least data from different locations can correspond to a plurality of locations Em20 of the magnet 10 on the corrodible layer of which the measurement distance can change for example as a function of different thicknesses 92 of the corrodible layer 90. The value of a measured magnetic characteristic of the magnet 10 can correspond to the flux (B) or one or more magnetic moments (^) of the magnet 10 in its reference frame. This step can be carried out on the bodywork not comprising a corroded layer.

[0132] In this example, the corrodible layer 9 comprises a corroded zone 900 and a dented portion 901 also comprising a corroded zone 902.

[0133] The detection device 2 is also configured to carry out the step E2 of determining a location Ea20, Ea21 of the measuring device 20 of a magnetic characteristic value in its overall three-dimensional reference frame X, Y, Z relative to the location of the magnet Em20, Em21 or may also be as a function of previous measurements having deduced corrosion or a suspicion of corrosion by the user, for example at the dented portion 901.

[0134] The detection device 2 is configured to carry out, as in the first example, the step E3 of measuring a magnetic flux density B and recording in a database the measurement, the location Ea20, Em20 of the measuring device 20 and of the magnet 10' and the date of the measurement and the step E4 of estimating by the processor at least the value of a magnetic characteristic (B%, ^), of the magnet 10' according to its own three-dimensional reference frame x, y and z and comparison E5 of its value of a magnetic characteristic (B, estimated and that previously estimated or acquired in step El.

[0135] Finally, the detection device 2 is configured to carry out the step E6 of deducing the corrosion of the corrodible layer 9 between the at least one location of the magnet Em20, Em21 and the location Ea20, Ea21 of the measuring device 20 as a function of the comparison of the value of a magnetic characteristic acquired in step El.

[0136] For example, the detection device 2 is configured to deduce corrosion between the location of the magnet Em20, and the location of the device Ea20.

[0137] The method may also comprise a step of estimating the orientation of the magnet 10'. For example, in the dented portion 901, the magnet 10' or the measuring device 20 can hardly be placed opposite each other. For example, as in [Fig.8], at the location of the magnet Em21, the magnet 10' may be inclined relative to the measuring device 20 at the location Ea21.

[0138] Then the detection device 2 can be configured to take this orientation into account in the location determination step E2 and thus further determine the inclination of its measuring device 20 to be opposite the two poles of the magnet 10' in a balanced manner. The detection device 2 can be configured to also be a function of the orientation of the magnet 10' relative to the measuring device 20 in the estimation step E4 by the processor of at least the value of a magnetic characteristic (B%).

[0139] Unless otherwise specified, the same element appearing in different figures has a single reference.

Claims

Claims

1. A method of detecting corrosion of a ferromagnetic corrodible layer (100, 110, 120, 90) comprising: a) a step (El) of acquiring and storing data in a memory including at least data: • of different locations (Eml0, Eml 1, Eml2, Em20, Em21) of at least one permanent magnet (10, 11, 12, 10') in a global three-dimensional reference frame X, Y, Z, • value of a magnetic characteristic for each magnet (10, 11, 12, 10') in a three-dimensional reference frame specific to the magnet x, y and z, b) a step of determining (E2) a location (Ea210, Ea211, Ea212, Ea20, Ea21) of a measuring device (20) of a value of a magnetic characteristic, distant from the at least one magnet, in the global three-dimensional reference frame X, Y, Z, by a processor (21) of a detection device (2), c) a step of measuring (E3) a value of a magnetic characteristic (B) by means of the measuring device (20) at the location (Ea210, Ea211, Ea212, Ea20, Ea21) determined in the determining step (E2), and recording, in a base, the value of the measurement, the location of the device (Ea210, Ea211, Ea212, Ea20, Ea21) and the date of the measurement, d) a step (E4) of estimation by the processor (21) of a value of a magnetic characteristic (B%, B, ^), of at least one magnet (10, 11, 12; 10') according to its own three-dimensional reference frame x, y and z, as a function of the value measured in the measurement step (E3) and of the location (Eml0, Emll, Eml2, Em20, Em21) of the magnet (10, 11, 12, 10') acquired in the acquisition step (El), e) a step of comparing (E5) the magnetic characteristic value (B%, B, ^) estimated from at least one magnet (10, 11, 12, 10') and that previously estimated or acquired from this magnet, f) a step of deducing (E6) a corrosion of the ferromagnetic corrodible layer (100, 110, 120, 90) between the at least one location (Eml0, Emll, Eml2, Em20, Em21) of the magnet (10, 11, 12, 10') and the location of the device (Ea210, Ea211, Ea212, Ea20, Ea21) in function of the magnetic characteristic value comparison carried out in the comparison step (E5).

2. Method for detecting corrosion of a ferromagnetic corrodible layer (100, 110, 120, 90) according to the preceding claim, in which each magnet (10, 11, 12, 10') is attached to a ferromagnetic metal element forming the corrodible layer (100, 110, 120, 90) and in that the data acquisition and storage step further comprises data of values ​​of a magnetic characteristic (B, ^) as a function of the thickness of the non-corroded metal element, with the components of the three-dimensional reference frame specific to the magnet x, y and z.

3. Method for detecting corrosion of a ferromagnetic corrodible layer (100, 110, 120, 90) according to the preceding claim, in which the memory comprises a calibration curve of the value of a magnetic characteristic of the magnet (10, 11, 12, 10') relative to the corrosion of the metallic element attached to the magnet (10, 11, 12, 10') and in that the step of deducing (E6) a corrosion of the ferromagnetic corrodible layer (100, 110, 120, 90) uses this curve by an inverse method to deduce therefrom a corrosion state value of the ferromagnetic corrodible layer (100, 110, 120, 90).

4. A method for detecting corrosion of a ferromagnetic corrodible layer (100, 110, 120, 90) according to any one of the preceding claims, further comprising a plurality of location determination steps (E2) and measurement steps (E3) at different locations (Eal, Ea2) in a limited area (Z) and in that the estimation of the characteristic value is refined at each measurement of magnetic flux density (B) of a location (Eal, Ea2).

5. Method for detecting corrosion of a ferromagnetic corrodible layer (100, 110, 120, 90) according to one of the preceding claims, in which the step (El) of acquiring and storing data further comprises data on the orientation of the poles of the magnets relative to the point of origin of the global reference frame.

6. Method for detecting corrosion of a ferromagnetic corrodible layer (100, 110, 120) according to one of the preceding claims, in which a corrosion indicator (1) is located in a porous coating (42) of a wall (4), in particular of reinforced concrete, the corrosion indicator (1) comprising one of the magnets (10, 11, 12) and a ferromagnetic corrodible layer (100, 110, 120) integral with the magnet (10, 11, 12), and in which the step of deduction (E6) of corrosion of a ferromagnetic corrodible layer is that of the witness (1).

7. Method for detecting corrosion of a ferromagnetic corrodible layer (100, 110, 120, 90) according to any one of the preceding claims wherein the step of acquiring location data (Eml0, Emll, Eml2, Em20, Em21) and magnets (10, 11, 12) in the global reference frame X, Y, Z comprises: a. a sub-step of searching (E10) for a signal of a magnetic flux density (B) by means of the measuring apparatus (2) and measuring the signal value (B 10, B11, B12) which is the most important in a limited area, b. a sub-step of recording (El 1) a location (Ea2) of the measuring device (20) in the global three-dimensional reference frame X, Y, Z by a processor (21) in a memory (22) when the measuring device (20) has measured the most important signal value (B 10, B11, B12), i.e.a sub-step of deducing (El2) the distance between the magnet (10, 11, 12) and the location (Ea) and recording the location (EmlO, Emll, Eml2) of each permanent magnet (10, 11, 12) in the global three-dimensional reference frame X, Y, Z.

8. Method for estimating the content of a pathogen in a wall (4) comprising a porous package (42), comprising the corrosion detection method according to one of claims 1 to 7, and a step of deducing infiltration (E7) of pathogen in the wall as a function of a calibration curve, the locations (Eml0, Emll, Eml2, Em20, Em21) of the magnet (10, 11, 12) of each witness (1) comprising the magnet (10, 11, 12) and the corrosion evaluations of the ferromagnetic corrodible layer (100, 110, 120).

9. Method for evaluating pathogen infiltration in a wall comprising the method for estimating the content of a pathogen in a wall (4) according to the preceding claim in which the step of deducing pathogen infiltration (E7) in the wall (4) is a function of the different corrosion estimates of one or more witnesses over time.

10. Method for evaluating pathogen infiltration in a wall according to claim 9 wherein the step of deducing pathogen infiltration (E7) comprises a • Sub-step of estimating the location of the infiltrated zones (E70) in the overall pathogen agent reference frame in the coating as a function of the locations (Eml0, Emll, Eml2, Em20, Em21) of the magnet (10, 11, 12) of each witness (1) having a corroded ferromagnetic layer, determined corrosion state value information of the different ferromagnetic corrodible layers and the time between the measurements deducing corrosion of the ferromagnetic corrodible layer of the witness (1), • deduction of pathogen infiltration rate (E71) in each estimated zone in the wall based on a calibration curve, locations (Eml0, Emll, Eml2, Em20, Em21) of the magnet (10, 11, 12) of each witness (1) and corrosion assessments.

11. Method for evaluating pathogen infiltration in a wall according to the preceding claim, comprising a step of modeling the wall (4) comprising a porous coating (42) and a reinforcement (41) cast in the coating (42) and the location of the different indicators (1) comprising the magnets (10, 11, 12) in the wall (4) and a step of modeling an evaluation of pathogen infiltration in the wall (4) as a function of the step of deducing pathogen infiltration.

12. Detection apparatus (2) for implementing the method of the corrosion detection method according to one of claims 1 to 7, comprising the processor (21), the memory (22) and the flux density measuring apparatus (20) and in that it comprises a device for moving the measuring apparatus along at least two axes of the global reference frame (X, Y, Z) to move it facing an auscultation surface (421) of a wall (4) and in that the movements of the measuring apparatus (20) are controlled by a control unit comprising the processor (21) as a function of the values ​​of magnetic flux density measurements (B) and / or location (Em) of different magnets acquired.

Images