Non-destructive testing method for the mechanical properties of a tubular ferromagnetic structure.

Abstract

Method for non-destructive testing of the mechanical properties of a tubular ferromagnetic structure The invention relates to a non-destructive testing method for determining the mechanical properties of a ferromagnetic structure. The method includes acquiring data representative of an electromagnetic signal from the emission of eddy currents by an eddy current transmitter and correlating the representative data with mechanical properties of the ferromagnetic structure. Abstract figure: [Fig. 1]

Description

Title of the invention: Method for non-destructive testing of the mechanical properties of a tubular ferromagnetic structure. Technical field

[0001] The invention relates to the field of non-destructive testing of the conformity of a ferromagnetic structure. In particular, the invention relates to the determination of the mechanical properties of a ferromagnetic structure and more particularly of a ferromagnetic tubular component. Technological background

[0002] Ferromagnetic tubular components are widely used in various fields of the energy industry such as power generation, oil and gas, as well as in mechanical engineering. Like most metallurgical products, tubes are susceptible to defects related to their manufacture, such as material inclusions in the steel, cracks on their internal or external surface, or porosities. Generally, any heterogeneity in the ferromagnetic matrix is ​​seen as an imperfection that is likely to adversely affect the mechanical strength of the tube in service.

[0003] The tubes are therefore checked after their manufacture, not only to detect any defects, but also, where appropriate, to determine information useful for assessing the danger of these defects. For example, a tubular component may undergo heat treatment, rolling, spinning, machining, straightening, etc. Thus, measuring the mechanical properties of a ferromagnetic structure is important to provide information on the integrity and quality of the ferromagnetic structure.

[0004] Thus, in particular, a non-destructive testing method using eddy currents is used. In this method, electromagnetic waves propagate in the ferromagnetic structure and, among the waves reflected by said ferromagnetic structure, the mechanical properties attributed to the geometry of said structure are sought.

[0005] Furthermore, the main mechanical properties of a ferromagnetic structure include, among others, the elastic limit, the breaking strength and the residual stress.

[0006] Non-destructive testing methods using Barkhausen noise or harmonic or multi-frequency eddy currents are known from the prior art.

[0007] However, a process using Barkhausen noise is difficult to implement in production because it is very sensitive to the surface condition, and has limitations on the penetration depth.

[0008] Furthermore, a process using harmonic or multi-frequency eddy currents is influenced by the surface roughness and the geometry of the ferromagnetic structure.

[0009] There is therefore a need to develop a simple and reliable control method with good spatio-temporal resolution of the ferromagnetic structure. Summary

[0010] An idea underlying the invention is to control the conformity and performance of a ferromagnetic structure such as a ferromagnetic tubular component. In particular, an idea underlying the invention is to enable such conformity and performance control by means of a reliable method. An idea underlying the invention is to enable the mechanical properties of a ferromagnetic structure to be determined accurately.

[0011] For this, the invention provides a method for non-destructive testing of a ferromagnetic structure, the non-destructive testing method comprising the following steps: • providing data representative of an electromagnetic signal, said electromagnetic signal resulting from an electromagnetic response to the emission of an eddy current in the ferromagnetic structure, said electromagnetic signal having a peak, said data comprising at least one of: • a square root of the average of the squares of the electromagnetic signal (also called “Root Mean Square” or “RMS” in English), • a width at half height of the maximum of said peak (also called “Full Width at Half Maximum” or “FWHM” in English), • a specific point of the electromagnetic signal, • correlate said data with at least one of the mechanical properties of the ferromagnetic structure

[0012] Thanks to these characteristics, it is possible to non-destructively control a ferromagnetic structure by determining one of the following parameters: the width at half-height of the maximum of the peak, the mean of the squares of the electromagnetic signal in reception and a specific point of the electromagnetic signal. In particular, the method makes it possible to determine the distribution of at least one of the mechanical properties of the ferromagnetic structure and therefore to check that the mechanical properties thus determined are satisfactory. Furthermore, another advantage is that this method allows non-destructive analysis over the entire surface of the structure to be analyzed with a resolution of at least 5 mm along said ferromagnetic structure.

[0013] Being a non-destructive process, the use of eddy currents ensures that the properties of the ferromagnetic structure are not altered.

[0014] According to embodiments, such a method may comprise one or more of the following features.

[0015] According to one embodiment, the eddy currents used are low-frequency eddy currents in pulsed mode.

[0016] Low-frequency pulsed eddy currents make it possible to dispense with the preparation of the surface of the ferromagnetic structure and its geometry. In other words, by using low-frequency pulsed eddy currents, no surface preparation is necessary.

[0017] Furthermore, the use of low frequency pulsed eddy currents combined with high frequency eddy currents significantly improves repeatability by allowing the acquisition of relative data at one, several, or each point of the ferromagnetic structure and by providing better spatio-temporal resolution.

[0018] The use of low and / or high frequency pulsed eddy currents allows deeper probing of the structure due to a reduced skin effect compared to harmonic and multi-frequency eddy currents.

[0019] According to one embodiment, the eddy currents used are combined with a high frequency alternating current. The advantage is that high frequencies allow the use of smaller and more compact conductors with less losses by electromagnetic radiation.

[0020] According to one embodiment, the method comprises a step of providing data representative of a signal comprising the following steps: • generate eddy currents in the ferromagnetic structure, • receiving an electromagnetic response to said generation of the eddy current, said electromagnetic response being received using a sensor oriented at a point on a surface of said ferromagnetic structure, • generate representative data from said electromagnetic response.

[0021] According to one embodiment, the sensor(s) may be oriented at one or more points of the ferromagnetic structure. For example, measurements may be made in the different orientations to verify the isotropy of the mechanical properties, and the measurement may actually be made from the inside of the ferromagnetic structure to be analyzed, for example a tube.

[0022] According to one embodiment, the sensor(s) may be mounted on the ferromagnetic structure using a base. This base ensures the guidance and mobility in rotation and translation of the sensor(s) along the ferromagnetic structure.

[0023] Alternatively, the sole can be a mechanical arm which makes it possible to guarantee the stability and reproducibility of the measurement conditions.

[0024] According to one embodiment, the sensor is in contact with the surface of the ferromagnetic structure. This makes it possible to have a more intense signal and therefore to improve the accuracy of the measurement.

[0025] According to an alternative embodiment, the sensor is spaced from the surface of the ferromagnetic structure. Said space is the distance between the sensor and the surface of the ferromagnetic structure (also called "air-gap" in English) can vary depending on the geometry of the ferromagnetic structure. This makes it possible to reduce the wear of the sensor used.

[0026] According to one embodiment, the processing of the data representative of an electromagnetic signal is carried out by a data processing program. The program makes it possible in particular to calculate a mechanical property such as the elastic limit, the breaking strength and the residual stress of the ferromagnetic structure. This calculation is fast and reliable. This calculation is made from a previously established correlation curve.

[0027] According to one embodiment, the mechanical properties comprise at least one of: • an elastic limit of the ferromagnetic structure (also called in English “Yield Strength” or “Ys”), • a resistance to rupture of the ferromagnetic structure (also called in English “Ultimate Tensile Strength” or “UTS and • a residual stress of the ferromagnetic structure.

[0028] According to one embodiment, the width at half-height of the maximum of the peak of the electromagnetic signal allows the correlation to the elastic limit of the ferromagnetic structure. The inventors noted that it was possible to use one or more other parameters such as the specific point of the electromagnetic signal for example. These can be taken in isolation or in combination in order to obtain the elastic limit of the ferromagnetic structure.

[0029] According to one embodiment, the width at half-height of the maximum of the peak of the electromagnetic signal is correlated with a breaking strength of the ferromagnetic structure.

[0030] In an alternative mode, the full width at half maximum of the peak of the electromagnetic signal measured in the forward direction of the magnetic field (FWHM +) is correlated to an elastic limit of the ferromagnetic structure.

[0031] In an alternative mode, the width at half-maximum of the maximum of the negative peak of the electromagnetic signal is correlated to an elastic limit of the ferromagnetic structure.

[0032] According to one embodiment, the square root of the mean of the squares of the electromagnetic signal and the specific point of the electromagnetic signal are correlated to a residual stress of the ferromagnetic structure.

[0033] According to one embodiment, the method further comprises a step of comparing a mechanical property of a ferromagnetic structure with a mechanical property of a reference ferromagnetic structure.

[0034] According to one embodiment, the term “ferromagnetic structure” means a ferromagnetic structure having been transformed with respect to a reference ferromagnetic structure, for example a ferromagnetic tube having undergone heat treatment, spinning, etc.

[0035] Thanks to these characteristics, it is possible to obtain a result in relative mode making it possible to ensure the reliability and quality of the ferromagnetic structure compared to the reference ferromagnetic structure, and therefore to ensure its conformity, in particular for its placing on the market.

[0036] According to one embodiment, the method comprises a step of comparing a mechanical property of a ferromagnetic structure, said ferromagnetic structure being previously detensioned.

[0037] According to one embodiment, the method comprises a step of comparing a mechanical property of a ferromagnetic structure, said ferromagnetic structure being previously deformed then relieved of tension. In the context of an analyzed tube, deformation is understood to mean any modification, for example an expansion or a conification.

[0038] According to one embodiment, the comparison between the ferromagnetic structure and the reference ferromagnetic structure is made on a similar part of said ferromagnetic structures. Said part may be, for example, one end of a tube.

[0039] Thus, according to another embodiment, the comparison step relates to a part of the ferromagnetic structure, said ferromagnetic structure being deformed then detensioned or only detensioned relative to a part of the reference ferromagnetic structure. Said part of the reference ferromagnetic structure being the same as that of the ferromagnetic structure.

[0040] Thanks to these characteristics, it is possible to quickly check the reliability of the ferromagnetic structure and to ensure the conformity of said ferromagnetic structure.

[0041] Thanks to these characteristics, it is also possible to evaluate the state of a ferromagnetic structure, particularly the level of deformation of a tube and more particularly the level of stress relief of a tube. The level of deformation is given by a percentage. For example, in the case of a tube this will be the percentage of deformation compared to the initial diameter of the tube.

[0042] According to one embodiment, the method comprises a step of establishing a calibration curve, said calibration curve providing an absolute value of the desired mechanical property.

[0043] According to one embodiment, one or more calibration curves are previously established on one or more samples of ferromagnetic structures having the same shade and grain size. By same shade is meant an equivalent chemical composition and the grain size corresponds to that which is measured by metallography for example for a ferritic structure.

[0044] Thanks to these characteristics, the calibration curves allow the precise calculation of an absolute value of the desired mechanical property.

[0045] According to one embodiment, the system is configured to implement a method for non-destructive testing of a ferromagnetic structure comprising: • an eddy current transmitter configured to generate an eddy current in said ferromagnetic structure • a sensor configured to receive an electromagnetic signal in response to said generation of eddy currents • a processing unit configured to generate a representative data response from said electromagnetic response signal Brief description of the figures

[0046] The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes, with reference to the appended drawings. • [Fig.l] is a schematic diagram of a system configured to implement the method of the present invention. • [Fig.2] is a flowchart illustrating a non-destructive testing process for a ferromagnetic structure. • [Fig.3] is a graph showing an electromagnetic response of a ferromagnetic structure measured in the forward and reverse direction of the electromagnetic field. Definitions

[0047] The term “ferromagnetic structure” means any type of ferromagnetic tubular component,

[0048] The term “specific point of the electromagnetic signal” means a point depending on the nuance of the ferromagnetic structure and corresponding to a point of the signal acquisition before and / or after reaching magnetic saturation. The nuance of a ferromagnetic structure provides information on the potential use of such a tube depending on its mechanical, physical and chemical characteristics.

[0049] The term “reference ferromagnetic structure” means that it is a raw component, for example a tube that has not undergone any shaping constraints other than the heat treatment allowing it to achieve the desired mechanical properties.

[0050] The terms "stress relieved" and "stress relieving" mean that a ferromagnetic structure and more particularly a tubular component is subjected to a process making it possible to reduce the residual stresses in the microstructure following machining or treatment operations, for example heat treatment.

[0051] "Deformation" means any changes in shape, dimensions or configuration of a tube under the influence of external forces, stresses or temperatures. This deformation can occur in different forms, such as compression, traction, stretching or bending.

[0052] The term "skin effect" refers to an electromagnetic phenomenon that occurs when alternating electric currents flow through a conductor. This effect results in an uneven distribution of the electric currents across the cross-section of the conductive material. More specifically, as the frequency of the alternating current increases, the currents tend to concentrate at the surface of the material, with a significant decrease in the current intensity in the core of the material. As a result, the effective penetration depth of the electric currents into the material decreases with increasing frequency.

[0053] FWHM + is understood to mean the component measured in the direct direction of the magnetic field.

[0054] FWHM - is understood to mean the component measured in the reverse direction of the magnetic field.

[0055] Peak + is understood to mean the peak measured in the direct direction of the magnetic field.

[0056] By peak - is meant the peak measured in the opposite direction of the magnetic field. Description of the embodiments

[0057] Oil, gas or other exploitation requires a significant number of ferromagnetic structures including tubular components. Due to the numerous constraints that these tubular components undergo both during their installation and during their operation, these tubular components meet standards in order to avoid any degradation and any leakage into the environment.

[0058] In particular, it is necessary to ensure that a ferromagnetic structure meets reliability and quality requirements. Thus, a ferromagnetic structure subjected to constraints must meet requirements to remain reliable.

[0059] [Fig.l] is a schematic diagram illustrating a system configured to implement a non-destructive testing method using eddy currents.

[0060] In this system, an eddy current transmitter 6 generates eddy currents which propagate within the ferromagnetic structure 5.

[0061] A sensor 7 receives one or more electromagnetic responses resulting from said generation of eddy currents.

[0062] The sensor 7 is oriented at several points on the surface of the ferromagnetic structure 5. At several points, we mean an orientation of the sensor 7 in the longitudinal or transverse direction of the tube.

[0063] The sensor 7 is movable in translation along the ferromagnetic structure 5.

[0064] The sensor 7 is movable in rotation along the ferromagnetic structure 5.

[0065] The sensor 7 is mounted on the ferromagnetic structure 5 for example using a sole. This sole ensures the guidance and mobility in rotation and translation of the sensor 7 along the ferromagnetic structure 5.

[0066] A processing unit 8 is connected to the eddy current transmitter 6 and to the sensor 7.

[0067] The processing unit 8 comprises, according to [Fig.l], a position encoder 81, a processor 82, a memory 83 and a display 84.

[0068] The position encoder 81 makes it possible to detect a precise position of an element, by converting its displacement into electrical, optical or magnetic signals.

[0069] The processor 82 is configured to generate representative data resulting from one or more electromagnetic responses.

[0070] The memory 83 stores said representative data.

[0071] The memory 83 further stores a reference database.

[0072] The memory 83 further stores one or more sequences of instructions.

[0073] Said sequences of instructions used to implement the method of the present invention as illustrated with reference to [Fig.2]

[0074] The memory 83 comprises, for example, one or more data processing programs.

[0075] The processor 82 executes the instruction sequence(s).

[0076] The processing unit 8 also comprises a display 84, for example a computer screen.

[0077] The display 84 serving to visualize the results of the method of the present invention.

[0078] [Fig.2] is a flowchart illustrating a method of non-destructive testing of a ferromagnetic structure.

[0079] Referring to [Fig.2], the method begins with a step 1 of providing data.

[0080] This first step 1 comprises a step 100 in which the eddy current transmitter 6 generates a low-frequency pulsed eddy current and a high-frequency eddy current generated by the sensor 7 within the ferromagnetic structure 5.

[0081] The current generated by the eddy emitter 6 is in pulsed mode.

[0082] Then, a step 101 occurs, in which the sensor 7 receives a response electromagnetic to said generation of eddy currents.

[0083] The method continues with a step 102 which generates the data representative of an electromagnetic signal, said electromagnetic signal resulting from the response of step 101.

[0084] Said generated representative data comprises at least one of: • A width at half-height of the maximum of the peak of an electromagnetic signal (also called “Full Width at Half Maximum” or “FWHM” in English), • a square root of the average of the squares of the electromagnetic signal (also called “Root Mean Square” or “RMS” in English), • a specific point of the electromagnetic signal.

[0085] Then, a step 2 is carried out in order to correlate the representative data with mechanical properties of the ferromagnetic structure 5.

[0086] At least one of these representative data is correlated with the reference database. The data of said reference database are associated with a mechanical property.

[0087] Thus, step 2 comprises a step 200 correlating the width at half-height of the maximum of the peak of the electromagnetic signal with an elastic limit of the ferromagnetic structure 5.

[0088] Step 2 includes a step 201 correlating the width at half-height of the maximum of the peak of the electromagnetic signal with a breaking strength of the ferromagnetic structure 5.

[0089] Step 2 includes a step 202 correlating the square root of the mean of the squares of the electromagnetic signal and the specific point of the electromagnetic signal with a residual stress of the ferromagnetic structure 5.

[0090] Depending on the desired need, the results obtained for each of the steps 200, 201 and 202 can be used in a first mode called relative mode 3 or in a second mode called absolute mode 4.

[0091] The relative mode 3 comprises a step 300 which compares the mechanical properties of the ferromagnetic structure 5 with a reference ferromagnetic structure.

[0092] According to one embodiment, said ferromagnetic structure 5 is, beforehand, subjected to stress relief alone.

[0093] In an alternative embodiment, said ferromagnetic structure 5 is, beforehand, subjected to deformation then stress relief. Said deformation can reach the maximum possible deformation before the rupture of said structure. In the case of steel, this will be the maximum tensile strength for example.

[0094] Said ferromagnetic structure 5 may be subjected to stress relief or deformation then stress relief on a part of its structure only, for example on the threaded end of a tubular component only.

[0095] Next, a step 301 occurs, determining one or more similarities between the mechanical properties of the ferromagnetic structure and the mechanical properties of the reference ferromagnetic structure. If the mechanical properties of the ferromagnetic structure are within the required tolerance range compared to those of the reference ferromagnetic structure, the ferromagnetic structure is considered to be compliant.

[0096] Absolute mode 4 includes a step 400 which establishes calibration curves on samples of ferromagnetic structures.

[0097] The samples of ferromagnetic structures have the same shade as ferromagnetic structure 5.

[0098] The ferromagnetic structure samples have the same grain size as the ferromagnetic structure 5.

[0099] Step 400 presents the same parameterization of the excitation signal during the production of the calibration curves and during the analysis of the ferromagnetic structure 5.

[0100] Step 400 further presents the same parameterization of the acquisition signal during the production of the calibration curves and during the analysis of the ferromagnetic structure 5.

[0101] In other words, the samples of ferromagnetic structures have similar structures and test conditions.

[0102] Then, in a step 401, the calibration curves are used to determine an absolute value of the desired mechanical property. It makes it possible to conclude whether or not the product is compliant or to readjust accordingly the parameterization of the process which made it possible to obtain the desired mechanical property.

[0103] A step of adjusting the mechanical assembly (not shown in Figures 1 and 2) allowing the movement of the eddy current transmitter 6 and the sensor 7 is implemented during the method of the present invention.

[0104] This adjustment step makes it possible, among other things, to overcome the effects of the variation in the distance between the sensor and the surface of the ferromagnetic structure 5, caused by the geometry of said ferromagnetic structure 5. In the context of a tube, the franking is done thanks to a sole machined to the tube diameter and the means of movement holding the assembly which applies sufficient pressure on the sole allowing it to follow and match the curvature of the tube even in the event of poor straightness of the latter.

[0105] This step preferably occurs before step 100.

[0106] A step of adjusting the field induced in the ferromagnetic structure 5, not shown in Figures 1 and 2, is implemented during the method of the present invention.

[0107] This adjustment step includes an adaptation of the frequency, the voltage of the high-frequency signal, the duration of the magnetization pulse and the desired time interval, between two points, acquired along this magnetic pulse. This choice depends on each nuance, the mounting conditions and the temperature of the part.

[0108] This step preferably occurs before step 100.

[0109] A first data acquisition step, not shown in Figures 1 and 2, is also implemented during the method of the present invention.

[0110] This step allows the adjustment to be refined for better resolution of the electromagnetic response.

[0111] This step preferably occurs before step 102.

[0112] A data analysis step, not shown in Figures 1 and 2, is implemented during the method of the present invention. During this analysis, the best point of the magnetization cycle for representation is chosen.

[0113] This step allows the data to be traced at each position.

[0114] This step preferably occurs between step 1 and step 2, more particularly between step 102 and step 200.

[0115] Furthermore, a step of rereading and representing the data in unrolled tube mode, not shown in Figures 1 and 2, is implemented during the method of the present invention. By unrolled tube is meant a representation of the data in two dimensions of a tube. The representation of the data is done by means of a rereading program making it possible to choose the relevant point.

[0116] This step makes it possible to identify anomalies linked to the geometry of the ferromagnetic structure. The straightness problem generates a very large space between the sensor and the surface of the ferromagnetic structure (also called "air-gap" in English) and said problem also generates a significant weakening of the signal.

[0117] This step occurs between step 1 and step 2, preferably between step 102 and step 200.

[0118] [Fig.3] is a graph showing the electromagnetic response of a tubular ferromagnetic structure by implementing the method according to the invention.

[0119] In [Fig.3], an electromagnetic response in the forward and reverse direction of the field is illustrated.

[0120] We thus observe the FWHM parameter - which corresponds to the width at half-height of the maximum of the peak measured in the opposite direction of the electromagnetic field (peak max -).

[0121] Also, this figure illustrates the FWHM + parameter which corresponds to the width at half-height of the maximum of the peak measured in the direct direction of the electromagnetic field (peak max +).

Claims

Claims

1. Electromagnetic method for non-destructive testing of a ferromagnetic structure (5) comprising the following steps: • providing data (1) representative of an electromagnetic signal, said electromagnetic signal resulting from an electromagnetic response (101) to the emission of eddy currents in the ferromagnetic structure (5), said electromagnetic signal having a peak, said data comprising at least one of: • a square root of the mean of the squares of the electromagnetic signal, • a width at half-height of the maximum of said peak, • a specific point of the electromagnetic signal, • correlating said data (2) with at least one of the mechanical properties (200, 201, 202) of the ferromagnetic structure (5).

2. The method of claim 1, wherein the eddy currents used are pulsed mode eddy currents.

3. Method according to one of the preceding claims, in which the step of providing data (1) representative of a signal comprises the following steps: • Generating in the ferromagnetic structure an eddy current (100), • receiving an electromagnetic response (101) to said generation of the eddy current (100), said electromagnetic response being received using a sensor (7) oriented at a point on a surface of said ferromagnetic structure (5), • generating the representative data (102) from said electromagnetic response.

4. Method according to one of the preceding claims, in which said mechanical properties comprise at least one of: • an elastic limit of the ferromagnetic structure, • a breaking strength of the ferromagnetic structure, and • a residual stress of the ferromagnetic structure.

5. Method according to one of the preceding claims, in which the width at half-maximum of the maximum of the peak of the electromagnetic signal is correlated to an elastic limit of the ferromagnetic structure (200).

6. Method according to one of the preceding claims, in which the width at half-maximum of the maximum of the peak of the electromagnetic signal is correlated with a breaking strength of the ferromagnetic structure (201).

7. A method according to any preceding claim, wherein the square root of the mean of the squares of the electromagnetic signal and the specific point of the electromagnetic signal are correlated to a residual stress of the ferromagnetic structure (202).

8. Method according to one of the preceding claims, comprising a step of comparing a mechanical property of a ferromagnetic structure with respect to a mechanical property of a reference ferromagnetic structure (300).

9. The method of claim 8, wherein said comparing step relates to the ferromagnetic structure, said ferromagnetic structure being previously de-stressed.

10. The method of claim 9, wherein said comparing step relates to the ferromagnetic structure, said ferromagnetic structure being first deformed and then detensioned.

11. Method according to one of the preceding claims, comprising a step of establishing a calibration curve (400), said calibration curve providing an absolute value of the desired mechanical property (401).

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