Sensor and method for determining environmental corrosivity and / or corrosion loss of a metal structure

Abstract

The present invention provides a resistometric sensor for measuring environmental corrosivity and / or corrosion loss of a metal structure, the said sensor comprising a substrate (1), at least one metal sensing track (5; 5a, 5b) provided on the substrate (1), at least one metal reference track (4) provided on the substrate (1), and a masking layer (3) covering the at least one reference track (4), wherein the substrate (1) is made of a thermally conductive material, and wherein an electrically non-conductive insulating layer (2) is provided between the substrate (1) and the at least one metal sensing track (5; 5a, 5b) and between the substrate (1) and the at least one reference track (4) to electrically insulate the tracks (4, 5; 4, 5a, 5b) from the substrate (1). A method of measuring the environmental corrosivity and / or corrosion loss is also claimed.

Description

[0001] Sensor and method for determining environmental corrosivity and / or corrosion loss of a metal structure

[0002] Field of Art

[0003] The present invention relates to the field of protection of metal constructions using corrosion monitoring, allowing for early warning in case of risk of structural damage of the metal constructions. More specifically, the invention relates to resistometric sensors used to measure environmental corrosivity towards the metal constructions and / or corrosion loss of metal structures.

[0004] Background Art

[0005] Corrosion of metals in the atmosphere accounts for the largest share of financial losses due to corrosion in general. In terms of planning the service life of metal structures and controlling the effect of the environment on their service life, it is necessary to know the corrosion rate of the structural metal under given conditions. One method of measuring the corrosion rate is the resistometric method working with resistometric sensors.

[0006] The resistometric method is one of the most widespread techniques that are used for monitoring metal corrosion under real conditions. The sensitivity, i.e. the smallest corrosion loss of metal that can be reliably and repeatably detected, is mainly determined by the thickness of the metal layer which decreases due to corrosion. The loss of thickness is measured through the increase in the electrical resistance of the corroding layer, while several calculation relationships can be used (M Kouril, T Prosek, B Scheffel & F Dubois (2013) High sensitivity electrical resistance sensors for indoor corrosion monitoring, Corrosion Engineering, Science and Technology, 48 :4, 282-287, DOI: 10.1179 / 1743278212Y.0000000074). The accuracy of measuring very small resistances is relatively small compared to measuring large resistances. Therefore, a higher sensitivity of thickness loss measurement is provided by thin sensing layers compared to thick ones. The disadvantage of thin sensing layers is a reduced service life. At the same corrosion rate, a thin layer will be consumed faster. Sensors with a thin sensing layer are therefore intended for conditions with low corrosion rates and for situations where it is necessary to capture small corrosion losses in a short time. Sensors with a thick sensing layer, on the other hand, are intended for situations where a long-term lifetime of the sensor is required or when high corrosion rates are expected.

[0007] The aim of developing new resistometric sensors is to increase their sensitivity, reliability, reproducibility, and at the same time maintain a sufficiently long service life.

[0008] A key factor for achieving maximum measurement reliability is an excellent compensation of the effect of temperature changes on the measurement of the thickness loss due to corrosion. This results from the fact that the electrical resistance of a conductor depends on temperature through the temperature dependence of the resistivity of the material. The change in the electrical resistance of the sensor is thus influenced not only by the change in the cross-sectional area due to corrosion, but also by the change in temperature in the surrounding environment. The standard solution is the use of the so-called reference track, which consists of a metal track identical to the sensing track. While the sensing track is exposed to the corrosive surrounding environment, the reference track is isolated from the corrosive surrounding environment and its electrical resistance is only affected by temperature changes. By combining the electrical resistance of the sensing and reference tracks, the effect of temperature on the measurement of the electrical resistance, and thus also the effect of temperature on the measurement of the corrosion loss of the sensing part, can be partially eliminated. However, isolation of the reference track from the corrosive surrounding environment inevitably leads to at least partial isolation of the reference track from temperature changes. This is especially evident in situations of rapid temperature fluctuations (e.g. sun exposure), or in sensors with strong protection of the reference track, i.e. in the case of sensors intended for very aggressive conditions. Other ways of compensating the effect of temperature, e.g. calculation of resistance change based on direct independent measurement of temperature change (US5243297A), use of adjustable current source depending on current temperature (US3609549A), by collecting and subsequent extraction of temperature variation effect from a signal (US4217544A), have not yet resulted in increased measurement sensitivity.

[0009] Disclosure of the Invention

[0010] The shortcoming of prior art resistometric sensors is a different response of the sensing track and of the reference track of the sensor to temperature changes in the surrounding environment. While the sensing track is in direct contact with the surrounding environment and thus immediately changes its temperature depending on changes in the temperature of the surrounding environment, the reference track is isolated by the substrate from one side and by its masking (insulating) layer from the other side.

[0011] The present invention overcomes the above-described disadvantages by providing a resistometric sensor for measuring environmental corrosivity and / or corrosion loss in a metal structure, said sensor having a substrate made of a thermally conductive material. The advantage of this solution is that the whole resistometric sensor, i.e. both the sensing track and the reference track, immediately adapt to changes in the temperature of the surrounding environment. In prior art sensors having an electrically and thermally non-conductive substrate, the sensing and reference tracks change their temperature differently, which causes fluctuations in the measured values. Furthermore, in such prior art sensors the temperature of the sensing track does not correspond to the temperature of the monitored structure due to slow heat / cold transfer, and the measured corrosion loss values do not correspond to reality.

[0012] The present invention provides a resistometric sensor for measuring environmental corrosivity and / or corrosion loss in a metal structure, the said sensor comprising a substrate, at least one metal sensing track provided on the substrate, at least one metal reference track provided on the substrate, and a masking layer covering the reference track, wherein the substrate is made of a thermally conductive material, and an electrically non-conductive insulating layer is provided between the substrate and the metal sensing track and the reference track to electrically insulate the tracks from the substrate. Both the sensing and the reference tracks are equipped with contact pads providing electrical connection with the electronic part of the system.

[0013] In an aspect, the present invention provides a method for measuring environmental corrosivity and / or corrosion loss in a metal structure, wherein a resistometric sensor of the invention is attached to the metal structure or mounted in the vicinity of the metal structure, a measuring current is applied to the tracks of the sensor, and voltages are read from the tracks of the sensor, the ratio of the read voltage to the electric current passing through the tracks equals the electric resistance of the sensing track(s) and the reference track(s), respectively, wherein increase of the electrical resistance corresponds to loss of thickness of the sensing track due to corrosion. The term “vicinity” relates to a position wherein the sensor is not directly attached to the metal structure but it is positioned so that it is exposed to the same environmental conditions, including e.g. temperature, humidity or other corrosive environment.

[0014] The thermally conductive material is a material with thermal conductivity at least 10 W.m'fK" as measured at room temperature (20 °C).

[0015] The substrate is preferably made of a metal or metal alloy, such as aluminium, steel, stainless steel, zinc, copper, lead, brass. Metals have the additional advantage of being malleable and can be adapted to the surface of the structure whose corrosion is being monitored.

[0016] The substrate preferably has a thickness of 0.5 to 2.0 mm.

[0017] The sensing track and the reference track are typically made of a material the corrosion resistance of which is to be measured. Therefore, the material of the sensing track and the reference track that best represents the corrosion behaviour of the monitored structure should be selected. In some embodiments, the sensing track and the reference track may be made of, for example, steel, iron, zinc, copper, silver, aluminum, nickel, chromium, titanium, tantalum, zirconium, tin or lead, or alloys containing these metals such as weathering steel, stainless steel, brass, bronze, aluminum alloys, nickel alloys, titanium alloys, zirconium alloys, etc. The reference track and the sensing track are made of the same material and have the same initial thickness.

[0018] A typical initial thickness of the sensing track and the reference track is within the range from 50 nm to 2500 pm, preferably from 200 nm to 50 pm in the case of highly sensitive sensors, and from 150 pm to 2000 pm or more preferably 150 pm to 1000 pm in the case durable sensors.

[0019] The term „initial thickness“ refers to the thickness of the sensing track and the reference track before the sensor is exposed to the corrosive surrounding environment. The thickness of the reference track must remain the same during the service life of the sensor, while the sensing track gradually loses its thickness as a result of corrosion loss during the service life of the sensor.

[0020] A sensor may contain one sensing track and one reference track, or more than one sensing track and one or more reference tracks, or the same number of sensing tracks and reference tracks. In case of a higher number of sensing tracks than reference track(s), all the tracks are positioned side by side at the single substrate and exposed to the same corrosion conditions, thus providing multiple independent results of corrosion depth.

[0021] In case of a higher number of sensing tracks of the same initial thickness, a single reference track of the same initial thickness is used for calculation of corrosion depth of all the sensing tracks.

[0022] In case of a higher number of sensing tracks with differing initial thicknesses of the sensing tracks, the initial thickness of the reference track(s) will correspond to the initial thickness of at least some sensing track(s), preferably at least one reference track has the same thickness as the initial thickness of the thinnest sensing track. In other words, the initial thickness of at least one reference track will correspond to the initial thickness of at least one sensing track(s).

[0023] The electrically non-conductive insulating layer has a thickness within the range 10 pm to 500 pm. The insulating layer should preferably be adhesive and adhere to the substrate on one side, and to the sensing track and reference track on the opposite side.

[0024] Examples of suitable materials for the insulating layer include selfstanding epoxy and polyester resins, chloroprene rubber, chlorinated and fluorinated polymers and copolymers, e.g. ethyleneacrylic acid thermoplastic copolymer, chloro-trifluoroethylene thermoplastic copolymer, acrylate or cyanoacrylate polymers and adhesives, or these materials used as an adhesive applied on polyethylene, polypropylene, polyethylene terephthalate, polyamide, polyimide, acrylonitrile-butadiene-styrene, polyvinyl-chloride, polytetrafluorethylene, or glassfibre or polymerfibre carrier.

[0025] The masking layer covering the reference track is a layer protecting the reference track from the corrosion conditions, so that the reference track remains uncorroded.

[0026] The masking layer preferably has a thickness within the range from the equivalent to triple the thickness of the reference track (i.e., lx to 3x the thickness of the reference track).

[0027] Typical materials used in masking layers include epoxy and polyester resins, silicon, polyurethane, polyacrylate, polyamide sealants and paints, or adhesive polyethylene, polypropylene, polyvinyl-chloride, polyamide, or polyimide tapes. The skilled person will understand that the sensing track(s) and the reference track(s) are provided with contact pads configured for attaching resistance measuring devices and optionally other parts of measuring equipment.

[0028] Sensors for measuring environmental corrosivity on metals and / or corrosion loss of metals contain one or more sensing tracks and reference tracks, wherein both types of tracks are made of the material (i.e., metal) whose corrosion loss is measured. The tracks are applied on top of a substrate made of a thermally conductive material, and an adhesive insulating layer is provided between the substrate and the tracks, said insulating layer ensuring the adhesion of the sensing track(s) and the reference track(s) to the substrate.

[0029] For measuring environmental corrosivity and / or corrosion loss of a metal, the sensor of the invention is connected in an electrical circuit which contains at least one source of measuring current and at least one device for measuring the voltage on the sensing track(s) and on the reference track(s).

[0030] Corrosion loss is determined based on the change in the ratio of the electrical resistances of the sensing track and the reference track, while these electrical resistances are obtained by measuring the voltage caused by the passage of an electric current through the sensing track(s) and the reference track(s), respectively. Proportion of the measured voltage to the electric current passing through the tracks equals the electric resistance of the sensing track(s) and the reference track(s), respectively.

[0031] The advantages of the sensors of the invention are based on the fact that the substrate with thermal conductivity higher than 10 W.m'fK'1, e.g. aluminum, copper, stainless steel, zinc, etc., equalizes the temperature of the sensing track and the reference track when the temperature of the surrounding environment changes, and this equalization is much faster than when an electrically insulating substrate with low thermal conductivity is used. Prior art sensors typically use substrates with thermal conductivity lower than 1 W.m'fK'1, e.g. glass thermal conductivity is app. 0.8 W.m'fK'1, glass fibre 0.04 W.m'l.K'land PVC 0.2 W.m'fK'1.

[0032] The supporting substrate of the sensor made of a metal sheet or other material with high thermal conductivity (higher than 10 W.m'fK'1) ensures the distribution of heat through the substrate so that any change in the temperature of the measured article causes a corresponding change in the temperature of the sensing track as well as of the reference track within a short time and both tracks change temperature at the same time, even though the reference track is separated from the surrounding environment by the masking layer, which is not the case for the sensing track.

[0033] The sensing track and the reference track are galvanically separated from the thermally conductive substrate (e.g. metal) by an electrically non-conductive layer which is thin enough not to block the temperature equalization. This layer performs only an insulating function. It does not perform a load-bearing function, so its thickness can be very small so that it does not prevent the transfer of heat between the thermally conductive substrate and the metal tracks.

[0034] The advantages of the resistometric sensor of the invention are as follows:

[0035] • elimination of the temperature difference between the sensing track(s) and reference track(s) during changes in the temperature of the surrounding environment;

[0036] • elimination of fluctuations in the values of the resulting thickness loss calculations, thereby increasing measurement accuracy;

[0037] • allowing to use higher initial thicknesses of the measuring part while maintaining high measurement sensitivity and the resulting longer service life of the sensor;

[0038] • quick adaptation of the temperature of the sensing and reference tracks to the temperature of the monitored structure to which the sensor is attached, thereby establishing the same corrosion conditions on the surface of the sensor as on the surface of the monitored structure,

[0039] • adaptability of the shape of the sensor, due to the metal substrate, to the curvature of the surface of the monitored structure (important for the application, for example, for monitoring pipe corrosion under insulation).

[0040] Brief Description of Drawings

[0041] Fig. 1 shows a schematic top view and a schematic cross-section view of a resistometric sensor of Example 1. (Reference signs: 1 - substrate, 2 - electrically non-conductive adhesion layer, 3 -masking layer, 4 - reference track, 5 - sensing track, 6 - contact pads a-h) Fig. 2 shows a record of calculated corrosion loss of a zinc sensor with initial thickness of both the sensing and reference tracks 50 m attached to a glassfibre substrate in non-corrosive conditions with varying ambient temperature.

[0042] Fig. 3 shows a record of calculated corrosion loss of a zinc sensor with initial thickness of both the sensing and reference tracks 50 pm attached to an aluminum substrate in non-corrosive conditions with varying ambient temperature.

[0043] Fig. 4 shows a record of calculated corrosion loss of a zinc sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a stainless steel substrate in non-corrosive conditions with varying ambient temperature.

[0044] Fig. 5 shows a record of calculated corrosion loss of a zinc sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a copper substrate in non-corrosive conditions with varying ambient temperature.

[0045] Fig. 6 shows a record of calculated corrosion loss of a zinc sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a zinc substrate in non-corrosive conditions with varying ambient temperature.

[0046] Fig. 7 shows a record of calculated corrosion loss of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a glassfibre substrate in corrosive conditions of the N-VDA test.

[0047] Fig. 8 shows a record of calculated corrosion loss of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to an aluminum substrate in corrosive conditions of the N-VDA test.

[0048] Fig. 9 shows a record of calculated corrosion loss of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a stainless steel substrate in corrosive conditions of the N-VDA test.

[0049] Fig. 10 shows a record of calculated corrosion loss of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a copper substrate in corrosive conditions of the N-VDA test.

[0050] Fig. 11 shows a record of calculated corrosion loss of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a zinc substrate in corrosive conditions of the N-VDA test. Fig. 12 shows a record of calculated corrosion rate of a steel sensor with initial thickness of both the sensing and reference tracks 50 m attached to a glassfibre substrate in corrosive conditions of the N-VDA test.

[0051] Fig. 13 shows a record of calculated corrosion rate of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to an aluminum substrate in corrosive conditions of the N-VDA test.

[0052] Fig. 14 shows a record of calculated corrosion rate of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a stainless steel substrate in corrosive conditions of the N-VDA test.

[0053] Fig. 15 shows a record of calculated corrosion rate of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a copper substrate in corrosive conditions of the N-VDA test.

[0054] Fig. 16 shows a record of calculated corrosion rate of a steel sensor with initial thickness of both the sensing and reference tracks 50 pm attached to a zinc substrate in corrosive conditions of the N-VDA test.

[0055] Fig. 17 shows a schematic top view of a resistometric sensor of Example 4 (Reference signs: 5a - sensing track, thickness: 1 mm, 5b - sensing track, thickness: 0.25 mm, 3 -masking layer, 4 - reference track, thickness: 0.25 mm, 1 - aluminum substrate, 2 - electrically non-conductive adhesion layer, 6 - contact pads, 7 - mounting cut-outs)

[0056] Fig. 18 shows a record of calculated corrosion loss of the sensitive steel sensing track (thickness 0.25 mm) and the durable sensing track (thickness: 1 mm) under identical corrosive conditions of Example 4.

[0057] Examples

[0058] The following examples further illustrate and facilitate the understanding of the invention, without intending to limit the scope of protection. The scope of protection is determined solely by the claims.

[0059] Example 1

[0060] The resistometric sensor in this example contains one sensing track and one reference track of the same thickness and made of the same metal. The choice of metal and its thickness depends on the application, i.e. which metal is monitored, with what sensitivity, and what is the required sensor lifetime. Fig. 1 shows an example of a sensor wherein the reference track 4 and the sensing track 5 are made of carbon steel with a thickness of 250 pm and mounted on an aluminum substrate 1 with a thickness of 1 mm. Electrically conductive connection between the substrate 1 and the reference track 4 and sensing track 5, respectively, is prevented by an adhesive electrically non-conductive layer 2 of ethylene-acrylic acid thermoplastic copolymer with a thickness of 102 pm. The reference track 4 is covered with a masking layer 3 of epoxy resin with a thickness of 0.5 to 0.7 mm.

[0061] The electrical resistance of the reference track 4 and the sensing track 5 is obtained by passing a measuring current through the metal track between contact pads b and c, and f and g, respectively, with contact pads c and f connected by an external conductor. While the measuring current, typically 0.1 to 100 mA, passes through both tracks 4 and 5, a voltage is measured at contact pads a and d, and e and h, respectively. The ratio of this voltage to the current passing through is equal to the electrical resistance of the sensing track 5 and the reference track 4, respectively.

[0062] Example 2

[0063] In this example, the resistometric sensors were used similar to the sensor described in example 1, but the material of the tracks was zinc. Each sensor contains one sensing track made of zinc and one reference track made of zinc, both tracks having the same initial thickness of 50 pm. The reference track is covered by a masking layer made of PVC, having a thickness of 150 pm. The sensor according to the invention had an aluminum substrate having the thickness 1.5 mm, and provided with an insulating adhesive layer made of ethylene-acrylic acid thermoplastic copolymer and having the thickness 102 pm. Further sensors containing substrates of copper, stainless steel, zinc were tested, too.

[0064] A comparative sensor had a fiberglass substrate having the thickness 1.5 mm.

[0065] In the first phase, the sensors were exposed to 22 °C (0 to 5 min), then placed in a chamber where tempering to 35 °C was initiated immediately after the sensors were inserted. At the 64thmin, the tempering was terminated and the chamber was left open to equilibrate the internal temperature with the ambient temperature of 22 °C. The resistances of all the sensing and reference tracks were recorded at minute intervals. Thickness loss values were then calculated from the measured data and plotted on a graph as a function of time for each measurement instant. If temperature changes did not affect the determination of thickness loss, no loss should be detected during the test, as no real metal loss occurs under non-corrosive conditions. The sensor on the laminate substrate showed the largest deviation from zero calculated loss with temperature changes (Fig. 2). Immediately after the start of heating, a spurious loss of sensor thickness on the laminate substrate (0.57 pm) was observed, which is due to uneven warming of the sensing and reference parts, with the reference part adapting thermally due to the thermally non-conductive substrate more slowly than the sensing part. The temperature influence lasted for 6 minutes.

[0066] On the contrary, after the warming was stopped and cooling to ambient temperature started, the sensor detected a false negative thickness loss (0.57 pm) on the laminate by the fact that the laminate with its relatively high heat capacity slowed down the cooling of the reference part. The settling of the calculated thickness loss to zero occurs after 45 minutes, when the temperature in the chamber also equilibrates with the ambient temperature. The sensor on the aluminium substrate shows no false thickness loss with temperature changes (Fig. 3). The maximum negative thickness loss detected was 0.08 pm, only 13 % of the highest false loss of the sensor on the laminate substrate. In the case of the sensor with stainless steel substrate (Fig. 4), the maximum false thickness loss was even only 3 % compared to the laminate substrate. The same results are provided by copper (Fig. 5) and zinc (Fig. 6) as a thermally conductive substrate (3 %).

[0067] Example 3

[0068] In this example, the resistometric sensors were used similar to the sensor described in example 1 and 2, the material of the tracks was carbon steel. Each sensor contains one sensing track made of carbon steel and one reference track made of carbon steel, both tracks having the same initial thickness of 50 pm. The reference track is covered by a masking layer made of epoxide, having a thickness of 150 pm.

[0069] The sensor had an aluminum substrate having the thickness 1.5 mm, and provided with an insulating adhesive layer made of ethylene-acrylic acid thermoplastic copolymer and having the thickness 102 pm. Further sensors containing substrates of copper, stainless steel, zinc were tested, too.

[0070] A comparative sensor had a fiberglass substrate having the thickness 1.5 mm.

[0071] Each sensor contains a substrate of the same thickness 1.5 mm but of different material - carbon steel, aluminium, copper, stainless steel, zinc, glass fibre. All sensors were exposed together in a climatic chamber with cyclically changing corrosive conditions according to the SEP 1850 (N-VDA) regulation. The cycle includes exposure to salt spray (1 wt. % NaCl solution at neutral pH), humidification and drying at temperatures up to 50 ° C and the freezing phase at -15 °C. Fig. 7 to 11 show the records of corrosion loss of a steel corrosion sensor with non-metallic and with various metallic substrates depending on the changing temperature within the selected time period of the cyclic corrosion test. Record of corrosion loss of steel with glassfibre substrate (Fig, 7) is visibly more fluctuating than the record for sensors with a metal substrate (Fig. 8 to Fig. 11). The large dispersion of measurements on a sensor with a non-metallic substrate is even more pronounced if the corrosion rate is calculated from the corrosion loss in at each moment of measurement. The calculated corrosion rate drops unrealistically at many points and even reaches meaningless negative values at many points (Fig. 12). The sensor corrosion rate recording on aluminum, zinc and copper is practically identical (Fig. 13, Fig. 15 and Fig. 16). Larger deviations are found in the recording of the corrosion rate of the sensor on stainless steel (Fig. 14), which is a manifestation of the lower thermal conductivity of stainless steel compared to the other metals used. The error in determining the corrosion rate when using a thermally non-conductive substrate reaches, for example, at time 18: 14, errors up to 73 %.

[0072] Example 4

[0073] The resistometric sensor on a metallic thermally conductive substrate according to the invention is particularly suitable for corrosion monitoring of the outer surface of a pipeline under thermal insulation. The metal substrate is able to adapt the temperature of the measuring parts to the surface temperature of the pipeline, and at the same time, the ductility of the metal substrate allows the shape of the resistometric sensor to be easily adapted to the curvature of the pipeline surface. Fig. 17 represents an example of a resistometric sensor with an aluminum substrate for corrosion monitoring under insulation, which allows early warning and has the ability to measure corrosion loss over a long period of time. The sensor consists of a sensing track 5a with a large thickness providing a long service life, a sensing track 5b with a small thickness, which determines the high sensitivity necessary for early warning, a reference track 4 of the same thickness as the sensing track 5b, and a masking layer 3 and a thermally conductive aluminium substrate 1. Mounting cut-outs 7 in the substrate allow for stable attachment of the sensor to the pipeline surface.

[0074] In this embodiment, the sensor was subjected to a corrosion test. It is clear from Fig, 18 that the thinner sensing track 5b provides information on corrosion loss with significantly higher accuracy and sensitivity, but already when a third of the initial thickness of the thinner sensing part 5b is consumed, the corrosion loss is overestimated. At that stage, the thicker sensing part 5a takes over the important function, which is able to further objectively inform about corrosion loss.

Claims

CLAIMS1. Resistometric sensor for measuring environmental corrosivity and / or corrosion loss, the said sensor comprising a substrate (1), at least one metal sensing track (5, 5a, 5b) provided on the substrate, at least one metal reference track (4) provided on the substrate (1), and a masking layer (3) covering the reference track (4), characterized in that the substrate (1) is made of a thermally conductive material, and an electrically non-conductive insulating layer (2) is provided between the substrate (1) and the metal sensing track (5, 5a, 5b) and the reference track (4) to electrically insulate the tracks from the substrate.

2. The resistometric sensor according to claim 1, wherein the thermally conductive material is a material with thermal conductivity at least 10 W.m'fK'1, as measured at room temperature (20 °C).

3. The resistometric sensor according to claim 1 or 2, wherein the thermally conductive material is a metal or metal alloy, preferably selected from the group consisting of aluminium, steel, stainless steel, zinc, copper, lead, and brass.

4. The resistometric sensor according to any one of the preceding claims, which contains one sensing track and one reference track, or more than one sensing track and one or more reference tracks, or the same number of sensing tracks and reference tracks.

5. The resistometric sensor according to any one of the preceding claims, which contains two or more sensing tracks of the same initial thickness, and a single reference track of the same initial thickness.

6. The resistometric sensor according to any one of claims 1 to 4, which contains two or more sensing tracks with differing initial thicknesses of the sensing tracks, and one or more reference track(s) the initial thickness of which corresponds to the initial thickness of at least some sensing tracks, preferably at least one reference track has the same thickness as the initial thickness of the thinnest sensing track.

7. The resistometric sensor according to any one of the preceding claims, wherein the electrically non-conductive insulating layer has a thickness within the range 10 pm to 500 pm.

8. The resistometric sensor according to any one of the preceding claims, wherein the electrically non-conductive insulating layer is adhesive and adheres to the substrate on one side, and to the sensing track and reference track on the opposite side.

9. Use of the resistometric sensor according to any one of the preceding claims for determining environmental corrosivity and / or corrosion loss of a metal for metal construction.

10. Method for measuring environmental corrosivity towards a metal structure and / or a corrosion loss of a metal structure, wherein a resistometric sensor is attached to the metal structure or mounted in the vicinity of the metal structure, a measuring current is applied to the tracks of the sensor, and voltages are read from the tracks of the sensor, the ratio of the read voltage to the electric current passing through the tracks equals the electric resistance of the sensing track(s) and the reference track(s), respectively, wherein increase of the electrical resistance corresponds to loss of thickness of the sensing track due to corrosion, characterized in that the resistometric sensor in the sensor according to any one of claims 1 to 8.

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