Patent Application
20190257770
The present invention relates to a microwave sensor adapted to determine the presence of anomalies, typically corrosion in an asset having at least one layer of a coating material on a surface thereof.
Corrosion monitoring is required in a wide range of industries, from microelectronics to oil and gas pipelines. Typically the material that is susceptible to corrosion has a layer of an insulating material on the exposed surface, making it difficult to assess the level of corrosion by eye. Traditional methods of monitoring have involved a level of destructive testing, for example, sand-blasting to remove the layers of insulating material to enable visual inspection of the corroded material. To carry out such destructive testing requires a certain amount of downtime for the asset in which the area of inspection lies, and therefore the testing is a commercially unattractive monitoring option. An improvement on destructive testing is to use so-called non-destructive testing, where light, radiation or sound are used to inspect the corrosion underneath the layers of insulating material in situ. Examples of this include using ultrasound, white light interferometry, X-Ray analysis and microwave analysis.
One particular use for non-destructive testing using microwave analysis is in the oil and gas industry as a corrosion sensor, to determine whether there is any anomaly present in pipelines. Pipelines are used to transport oil, gas or a mixture thereof (such as transmix) around and from oil and gas fields. Typically such pipelines have a multilayer structure, with a core formed from a tube having a diameter in the range 0.1 m-1.2 m and an outer cladding or insulating layer. For example, a common construction is to use a steel tube and a polymer based cladding. However, the steel tube is prone to corrosion and therefore other anomalies such as pitting, delamination, metal loss and water ingress, yet this is hidden from view by the polymer insulating layer. Microwave wavelengths are particularly suited to inspect such pipelines, as they give a clear indication of a defect even when hidden within the pipeline structure or between the core and cladding layer. When anomaly detection is carried out using microwave analysis, often a vector network analyser (VNA) is used to both generate and analyse the microwave signal. The VNA is a relatively costly and bulky piece of equipment, and so not suitable where a portable testing method is required. In addition to the cost and relative inconvenience of using a VNA, significant user training is required to be able to utilise the VNA and therefore the microwave analysis method to its full potential.
One option to improve on this situation and provide an anomaly sensor that is at least moveable with respect to the sample of interest is disclosed in U.S. Pat. No. 6,940,295. Rather than using a large, fixed sensor based on a VNA, a fixed translation device on which a microwave sensor is mounted by means of a support assembly is provided. The translation device is then able to move the microwave sensor along an object of interest, and if a second translation device positioned perpendicular to the first is used, the microwave sensor can scan across an entire surface. Any defects present in the material of interest are found by measuring the energy difference between incident and reflected microwave signals. WO2008/051953 also discloses a sensor mounted on a translation device, such that the sensor can be moved across the surface of a material of interest at a fixed scanning distance. Two incident microwave signals are provided, having orthogonal polarisations. Defects in the material of interest are detected by comparing the incident and reflected polarised microwave signals to determine a phase difference. Although such sensors are non-contact devices, and therefore non-destructive, both require the material of interest to be positioned relative to the translation devices, and are therefore not truly portable.
Devices offering greater flexibility by not being mounted on a fixed translation device are disclosed in U.S. Pat. Nos. 6,674,292. 6,674,292 discloses a hand-held microwave non-destructive testing device provided with rollers to contact the surface of the material of interest and provide a fixed scanning distance for the microwave sensor. Defects in a material of interest are detected by analysing the energy difference between incident and reflected microwave signals. Again the scanning distance is fixed, in this case by providing rollers on the housing carrying the microwave sensor, such that whilst the microwave sensor is non-destructive, it is not non-contact.
It is therefore desirable to find a way to provide simple, portable, non-contact and non-destructive testing of the presence of anomalies such as delamination, water ingress and corrosion within a structure formed from a material having a least one layer of a coating material on a surface thereof.
The present invention aims to address these issues by providing, in a first aspect, a microwave sensor, adapted to determine the presence of anomalies in an asset formed from a material having at least one layer of a coating material on a surface thereof comprising a microwave transceiver; and a waveguide; the waveguide being operably coupled to the microwave transceiver, wherein the microwave transceiver transmits a first continuous wave microwave signal incident on the at least one layer and receives a second continuous wave microwave signal reflected from the at least one layer, wherein the first and second continuous wave signals are combined into an intermediate continuous wave microwave signal having a phase difference indicative of an anomaly in the material, and wherein the first and second continuous wave microwave signals are frequency modulated continuous wave signals.
By using a frequency modulated continuous wave microwave signal to create a phase difference indicative of the anomaly in a material, a simple, portable, non-contact and non-destructive testing of the presence of corrosion within a structure formed from a material having a least one layer of a coating material on a surface thereof can be provided.
Preferably, the waveguide is sized and configured to provide a measurable area and resolution of the first and second continuous wave microwave signals.
The waveguide may be cone shaped. Preferably, the cone is a square-based cone.
The sensor may further comprise an alignment module. Preferably, the alignment module is a laser alignment module.
The sensor may be adapted to fit within a hand-held unit.
The sensor may be operable in a near-field mode. Alternatively, the sensor may be operable in a far-field mode.
Preferably, the microwave transceiver generates a broadband microwave spectrum.
The at least one layer of a coating material may be an insulating material.
The coating layer may have a first surface and a second surface, opposite one another, the substrate has a first surface and a second surface, opposite one another, and the material system has an interface between the coating layer and the substrate, such that the anomalies are at a surface of the coating layer, a surface of the substrate and the interface between the coating layer and the substrate, or within the coating layer or the substrate.
The anomalies may comprise delamination, water ingress, corrosion, a material defect, a local variation in chemical composition, a liquid or a gas.
In a second aspect, the present invention provides a use of a frequency modulated continuous wave microwave transceiver operably coupled to a waveguide to determine the presence of an anomaly in an asset formed from a material having at least one layer of a coating material on a surface thereof.
In a third aspect, the present invention provides a method of determining the presence of anomalies in an asset formed from a material having at least one layer of a coating material on a surface thereof, comprising transmitting a first continuous wave microwave signal to be incident on the at least one layer of a coating material; receiving a second continuous wave microwave signal reflected from the at least one layer of a coating material; combining the first continuous wave microwave signal and the second continuous wave microwave signal into an intermediate continuous wave microwave signal having a phase difference indicative of an anomaly in the material; wherein the first continuous wave microwave signal and the second continuous wave microwave signal are frequency modulated continuous wave signals.
The material may have two or more layers of a coating material on a surface thereof.
Preferably, the material is a metal. In this case, the at least one layer of a coating material may be an insulating material.
Preferably, the material forms part of a pipeline.
The method may further comprise transmitting the first continuous wave microwave signal in a near-field mode. Alternatively, the method may further comprise transmitting the first continuous wave microwave signal in a far-field mode.
Preferably, the first continuous wave microwave signal forms part of a broadband microwave spectrum.
In a fourth aspect, the present invention provides a system for determining the presence of anomalies in a material system of an asset comprising a substrate having at least one coating on a surface thereof; comprising a microwave transceiver and a waveguide, the waveguide being operably coupled to the transceiver, the transceiver adapted to transmit a first continuous wave microwave signal and receive a second continuous wave microwave signal; a controller adapted to control the transmission and reception of the first and second continuous wave microwave signals; a processor adapted to combine the first and second continuous wave microwave signals to produce an intermediate continuous wave microwave signal having a phase difference indicative of the presence of anomalies; and a display adapted to display the intermediate continuous wave microwave signal; wherein the first and second continuous wave microwave signals are frequency modulated continuous wave signals.
Preferably, the waveguide is sized and configured to provide a measurable area and resolution of the first and second continuous wave microwave signals.
The waveguide may be cone shaped. In this situation, preferably the cone is a square-based cone.
The system may further comprise an alignment module. Preferably, the alignment module is a laser alignment module.
The microwave transceiver, the waveguide and the control board may be adapted to fit within a hand-held unit.
The sensor may be operable in a near-field mode, such that a sample of material having at least one coating on a surface thereof is placed within the waveguide. Alternatively the sensor may be operable in a far-field mode, such that a sample of material having at least one coating on a surface thereof is placed outside the waveguide.
Preferably the microwave transceiver generates a broadband microwave spectrum.
The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which:
The present invention adopts the approach of creating a microwave sensor, adapted to determine the presence of anomalies an asset comprising a material having at least one layer of a coating material on a surface thereof based on a frequency modulated continuous wave microwave signal. Such a sensor comprises a microwave transceiver and waveguide. The waveguide is operably coupled to the microwave transceiver, and the microwave transceiver transmits a first frequency modulated continuous wave microwave signal. This signal is incident on the at least one layer, and the transceiver receives a second frequency modulated continuous wave microwave signal reflected from the at least one layer. The first and second frequency modulated continuous wave signals are combined into an intermediate modulated continuous wave signal, having a phase difference from which the presence of corrosion is determined. The anomalies may comprise delamination, water ingress, corrosion, a material defect, a local variation in chemical composition, a liquid or a gas This approach differs from those of the prior art in the use of a frequency modulated signal to determine the presence of anomalies rather than the energy of the reflected microwaves or a phase difference between orthogonally polarised microwave signals. As is discussed in more detail below the integration of frequency modulated continuous wave microwave capability into a simple, portable device enables defect testing to be carried out in environments and within timescales not currently achievable.
The waveguide 3 is sized and configured to provide a measurable area and resolution of the first and second frequency modulated continuous wave microwave signals. A cone-shaped waveguide is particularly suitable for use in the present invention, with a square-based cone being particularly preferred. However, any shape of waveguide that enables the generation and amplification of the standing wave required for the invention to function may be used. The term continuous wave microwave signal is used to distinguish a wave that is transmitted continuously from a microwave source from a traditional pulsed microwave signal, as used, for example, in radar.
The function of the transceiver 2 is shown in more detail in
A simple and frequently used function to represent the time evolution of the frequency of the first frequency modulated continuous wave microwave signal is a sawtooth function. The second frequency modulated continuous wave microwave signal will be subject to a time delay when compared with the first frequency modulated continuous wave microwave signal due to the time of flight between the microwave sensor and the material of interest. This causes a frequency difference that can be detected as a signal in a low frequency range.
In the present invention, the material of interest is immobile, with the first frequency modulated continuous wave slowed down as it penetrates into the layer of coating material on the surface of the material of interest. Once the first frequency modulated continuous wave microwave signal is generated and fed to the waveguide 3, the waveguide 3 acts as a resonator and a standing wave is set up within the cavity formed by the waveguide 3. The second frequency modulated continuous wave microwave signal is formed from the signal reflected from the materials forming the material of interest and the coating layer on a surface thereof. The first frequency modulated continuous microwave signal is incident on the layer of coating material, slowed down by this layer and then reflected by the material underneath. In typical applications the coating layer is a layer of an insulating material, such as dielectric material, and the material of interest is metallic, either an alloy or a pure metal.
In many applications there are relatively high demands on the accuracy of the resonant frequency shift, Q factor shift and change of values of the dielectric permittivity. The frequency of the first frequency modulated continuous microwave signal is swept over a frequency range (sometimes referred to as a sweep range) in discrete frequency steps, while being transmitted continuously. At each frequency the phase difference between the first frequency modulated continuous wave microwave signal and the second frequency modulated continuous wave microwave signal is determined, with the frequency at each step being maintained long enough to allow the second frequency modulated continuous wave microwave signal to return after reflection.
By sweeping the frequency range in a stepwise manner, and detecting, for each frequency, the phase difference between the first frequency modulated continuous wave microwave signal and the second frequency modulated continuous wave microwave signal, it is possible to determine the distance between the waveguide 3 and the surface of the coating material. The distance typically corresponds to several full periods of the first frequency modulated continuous wave microwave signal plus a portion of a period, with the phase difference only providing information about the portion of a period. Therefore a single frequency measurement is not enough to determine the distance between the waveguide 3 and the material of interest. By making several phase difference measurements at different frequencies it is possible to determine the correct number of full periods, and therefore the distance to the material of interest. However, the first frequency modulated continuous wave microwave signal has a certain physical width, resulting in many reflections being received from the material of interest and any other microwave reflectors present. For stepped frequency continuous wave distance measurements, as described above, the phase difference between the transmitted first frequency modulated continuous wave microwave signal and the received second frequency modulated continuous wave microwave signal is determined. The phase detector outputs a value that is related to the cosines of the phase difference. Microwave sensor 1 is placed at a distance D from a sample of a material having a layer of coating material on a surface thereof, such as an insulated pipe (concrete cladding on a steel core). The first frequency modulated continuous wave microwave signal has a frequency in the GHz range, and, swept over a frequency range of 1500 MHz in a stepwise manner from a start frequency of 24 GHz. Each step is 1 MHz. The first frequency modulated continuous wave microwave signal is transmitted into the waveguide 3, and it is reflected by means of the material of interest forming the second frequency modulated continuous wave microwave signal. The frequency of the first frequency modulated continuous wave microwave signal is then incremented one step and the measurement is repeated. This is continued throughout the frequency range of the first frequency modulated continuous wave microwave signal, creating several phase difference values, one for each frequency of the first frequency modulated continuous wave microwave signal. Finally, the distance between the waveguide 3 and the sample is determined by means of the phase difference values. The permittivity or factor value determination is based on the bandwidth of the frequency range and the distance between the waveguide 3 and the sample.
The output of the microwave sensor 1 corresponds to the cosine of the phase difference dØ between the first frequency modulated continuous wave microwave signal and the second frequency modulated continuous wave microwave signal, which is given by the reflected phase difference cos(dØ). The phase difference will vary between +1 and −1, corresponding to phase value between 0 and 180°. Typically this difference corresponds to a few full periods of the first frequency modulated continuous wave microwave signal plus a portion of a period.
The transceiver 2 outputs an intermediate modulated continuous wave signal S described by:
S/D=2*BW/(c*T)
where D is the distance between the waveguide 3 and the sample, BW is the bandwith of the first frequency modulated continuous wave microwave signal, c is the speed of light, and T is the time taken for the first frequency modulated continuous wave microwave signal to sweep across the frequency range.
If a sample is placed distance D away from the waveguide 3, then the time difference t between the first and second frequency modulated continuous wave microwave signals is:
t=2D/c
In any practical system, the frequency cannot be continuously changed in one direction; hence only periodicity in the modulation is necessary. Frequency modulation includes triangular waveforms, saw tooth waveforms, sinusoidal waveforms, square waveforms and other suitable waveforms. When a triangular frequency modulated waveform is used, the resulting beat frequency is constant, except for at the turn-around region in the frequency sweep. The first frequency modulated continuous wave microwave signal and the second frequency modulated continuous wave microwave signal are multiplied in a mixer. The high frequency term is filtered out using a low-pass filter a beat frequency fb is obtained. If there is no Doppler shift in the signal, then
f
b
=tm
f=2R/(cmf)
where t is the time taken to complete the sweep through the frequency range, R is the distance from the waveguide 3 to the sample, c is the speed of light and mf is the slope of the frequency change of the first frequency modulated continuous wave microwave signal.
But:
m
f
=Δf/(1/(2fm))=2fmΔf
where fm is the modulation rate of frequency and Δf is the maximum deviation of frequency. Therefore:
f
b=(4RfmΔf)c
Usually two beat frequencies exist in frequency modulated continuous wave systems, due to the Doppler effect associated with the penetration of microwave signals into the sample, and scattering effects given by:
f
1=(4RfmΔf)/c+fd
f
2=(4RfmΔf)/c−fd
where fd is the frequency associated with the Doppler shift. The first cosine term of the intermediate signal S describes a linearly increasing frequency modulated signal (chirp) at about twice the carrier frequency, with a phase shift that is proportional to the delay time Td. This term is generally filtered out actively by a low pass filter (LPF). The second cosine term describes the beat signal at a fixed frequency, which can be obtained by differentiating the instantaneous phase term with respect to time. The beat frequency is directly proportional to the distance D of the target from the waveguide 3. Therefore, by determining the beat frequency, this distance D can be determined directly. The beat frequency may also be used to determine the dielectric properties of the sample.
In the situation where an anomaly, such as corrosion, occurs on a pipeline, for example, the variation in the beat frequency can be used to determine the regions where corrosion exists, either by determining that there is a localised variation in distance between the metal core of the pipeline and the waveguide 3, of there is a localised change in the dielectric properties of the metal core. As the system is sensitive to changes in distance and material composition this may be achieved through a dielectric material such as the concrete cladding on the metal core of a pipeline. Furthermore a time delay may be seen in the intermediate signal due to the difference in dielectric properties between regions with and without corrosion. The coating layer may have a first surface and a second surface, opposite one another, the substrate has a first surface and a second surface, opposite one another, and the material system has an interface between the coating layer and the substrate. This means that the anomalies are at a surface of the coating layer, a surface of the substrate and the interface between the coating layer and the substrate, or within the coating layer or the substrate.
In order to determine the repeatability of making such measurements, initially a microwave sensor in accordance with an embodiment of the present invention was used to identify defects in the surface of a copper sheet. Initially defects were made in the surface of a copper sheet resulting in a series of circular depressions having equal surface area in the surface of the copper sheet, one of a shallow depth, one of an intermediate depth and one of a deep depth. In order to determine the resolution of the microwave sensor the depth of the depressions was varied, so that the resolution between the shallowest and the deepest depression could be examined.
Following this initial investigation, further testing was carried out to determine the efficacy of the sensor in determining the present of corrosion. Initial corrosion samples were simulated by etching copper sheets in a bath of ferric chloride solution.
Further testing was then done to review the efficacy of the microwave sensor in relation to advanced corrosion. Increasing both the concentration of the ferric chloride etching solution and/or the time the copper sheet remains in the etchant and/or the current applied to the copper sheet during the etching process creates extensive pitting of the surface of the copper sheet. Rust may also form, and there may be some loss of copper underneath the rust. The surface roughness is also increased. Each of these features/artefacts may be detected using a microwave sensor in accordance with an embodiment of the present invention.
The microwave sensor may be operated in a far-field mode. Alternatively, the microwave sensor may be operated in a near-field mode. The near field mode is created when the microwave sensor is excited below a defined cut-off frequency, and the far field mode when excited above the cut-off frequency. The cut-off frequency is defined as the resonant frequency of the waveguide 3.
In the near field mode, a very high Q factor standing wave pattern is required. For example, for near field operation a Q factor more than ten and ideally more than twenty is preferred. When this occurs there is no intrinsic wave impedance match with the surroundings (air). Instead the corrosion sensor is operated below a cut-off frequency when compared to the resonant frequency of the waveguide, for example in TM mode, thereby producing an evanescent wave constituting a near field within the waveguide 3. In this situation a sample is introduced into the waveguide 3
In the far field mode, the field of the excitation wavelength radiates beyond the dielectric reflector surface, as the corrosion sensor is operated above a cut-off frequency. In this case the sample is at a distance that can range between 0.1 mm to 100 cm from the microwave sensor. When the sensor is operated in the far field mode reflected signal parameters, such as the backscattering (diffuse reflection), specular reflection of the first continuous wave microwave signal, the time difference between the first continuous wave microwave signal and the second continuous wave microwave signal and the magnitude of the backscattered or specular reflection of the first continuous wave microwave signal can be measured. Alignment of the microwave sensor may be provided, such as the provision of an alignment module to align the waveguide 3 accurately with a sample. If the microwave sensor further comprises an alignment module, this is preferably a laser alignment module.
It can be seen from the above examples that a frequency modulated continuous wave microwave transceiver operably coupled to a waveguide can be used to determine the presence of anomalies of a material having at least one layer of a coating material on a surface thereof.
From the above examples it can be seen that a microwave sensor in accordance with the various embodiments of the present invention can be used in a method of anomaly detection. This is outlined in
The microwave sensor described above is suitable for use in a number of applications where anomalies in an asset need to be monitored. Anomalies may comprise at least one of a material defect, a local variation in chemical composition, a liquid or a gas. For example, the microwave sensor may be used to detect pitting, delamination, metal loss and water ingress in relation to pipelines in the oil and gas industries, or in other industries such as manufacturing industries where fluids are used or manufactured and where the purity or quality of a material flowing through a pipeline is critical, in the nuclear waste industry, where monitoring of corrosion of storage vessels is a major challenge, in industries where metallic components are manufactured and where surface contamination can affect surface quality and/or component quality. These and other advantages and embodiments will be apparent from the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1618378.2 | Oct 2016 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2017/053277 | 10/31/2017 | WO | 00 |
