WO2007141428A1

WO2007141428A1 - Non-destructive control device and method for determining the presence of magnetic material in materials which are non-magnetic or exhibit magnetic anisotropy, either crystalline, or of the metallurgical structure, form or stress

Info

Publication number: WO2007141428A1
Application number: PCT/FR2007/000942
Authority: WO
Inventors: Daniel Roger Chauveau; Eric Crescenzo
Original assignee: Institut De Soudure
Priority date: 2006-06-07
Filing date: 2007-06-07
Publication date: 2007-12-13
Also published as: FR2902191B1; FR2902191A1

Abstract

The invention relates to a non-destructive control device for determining the presence of magnetic material in non-magnetic or ferromagnetic materials with or without magnetic anisotropy, and especially the existence of first steel or carbon weld passes in a stainless steel welding, said device comprising magnetic field generating means for magnetising the magnetic body to be detected, and magnetic field measuring means for measuring the variation of the magnetic current related to the presence of a magnetic anomaly localised in the material to be controlled. Said device comprises at least one measuring probe (S) arranged in such a way as to be positioned on or close to the material to be controlled, each measuring probe consisting of a box (1) containing magnetic field generating means, and at least one magnetic field measuring sensor (3) connected to a field-strength meter. The weldings are inspected in situ.

Description

Non-invasive control device and method for determining the presence of magnetic material in non-magnetic materials or having magnetic anisotropy: crystalline, of metallurgical structure, of shape or of tension

The present invention relates to a device and a method of non-destructive testing for determining the presence of magnetic material in non-magnetic materials or having a magnetic anisotropy: crystalline, metallurgical structure, shape or voltage.

Indeed, it happens in particular that during welding of stainless steel materials, errors occur in the type of filler metal used. This problem arises particularly on certain sites when welding piping, storage tanks, pressure vessels, cryogenic pipe .... Indeed, the first welding pass is sometimes made of carbon steel instead of being stainless steel, which can lead to severe degradation when using the facilities. It is therefore vital for the operator to have a reliable and fast tool allowing in case of suspicion of wrong way, to perform a quick and reliable sorting of welds made. This problem can occur as well in manufacturing as in maintenance or during a repair.

Numerous methods are known for determining the presence of defects and pollution in materials, in particular using a magnetic field variation within the material. These methods are intended to identify structural defects, in particular at the level of homogeneity, the compactness of the material.

In patent FR 2 736 719, there is provided a method of controlling the compactness of a layer of magnetizable material inserted in a set of layers forming a flexible. Thus, the magnetic material layer of the product is first magnetized and then the magnetic field resulting from this remanent magnetization is measured, the variations in this measurement making it possible to detect any defects in said layer by the inside of the hose. We therefore propose two successive stages, one of magnetization and the other of measurement. Furthermore, it is necessary to provide the field generation means spaced from the field measuring means during the measurement, which generates a bulk. In addition, such a device is made so that it can be used by the inside of the hose, which is not always possible in case of inspection.

US 4,727,321 describes a method and a device for magnetic and ultrasonic testing of ferromagnetic objects. To do this, the device comprises means for generating a magnetic field to cause dispersion flows in case of anomalies, these fluxes being measured by at least one magnetic field sensor and secondly means for generating ultrasonic waves, using the magnetic field by means of an electrodynamic transducer, these ultrasonic waves being reflected by the anomalies structural and measured by said transducer. To create the magnetic field, at least two magnets are used with their polar mass at a distance from each other pointed towards the body to be tested, and positioned diametrically opposite each other on the conduit to be tested. magnetic field sensor being arranged in the space between the polar masses, at a location near the body surface where the field components are both perpendicular to the surface and extending in the direction of the surface and parallel to the surface. this one. The transducer having a transmitting coil is set up, the transducer comprises a receiving coil which is connected to a first input of logic means for processing the information. Such a device is heavy to implement because of its structure and does not allow on-site inspection inspections.

US 5,145,637, US 2002/0033049 also discloses the use of both ultrasonic and / or eddy current coils for non-destructive inspection of a material for defects.

Devices are also known in which the magnetic field for the detection of structural defects is generated by coils as described in GB 160 855 and FR 2 582 813 in which a magnetic field is generated by a coil which propagates in a coil. the piece to be tested and a resulting magnetic field generates a current in the receiver coil, this field varying as a function of the ferromagnetic ferrite content contained in the metal. The use of coils implies a relatively heavy structure to implement (power generation, power supply, etc.)

In documents US Pat. No. 3,753,085, WO 2005/031336, it is proposed to create bidirectional magnetization at the level of the inspection zone. It has also been proposed in EP 0 831 323, a method for testing without destruction a sample consisting of two welded magnetizable materials. A magnetic field is applied in a direction perpendicular to the weld. Defects are detected using a coordinate axis system. X, being the axis of the length of the weld, y being the axis parallel to the magnetization and Z, perpendicular to the surface of the sample. The defects are detected by gradient measurements in the magnetic field components.

Again, for these three proposed solutions, the structure is relatively bulky and complex to implement. Indeed, these methods are generally bulky and difficult to implement during inspection on site or site. Moreover, these devices only concern the search for defects in compactness (cracks, etc.) and are not intended to verify the metallurgical homogeneity of the materials used.

In US-A-6 320 375 there is provided a method for detecting rare earth metal oxide inclusions in titanium and other non-magnetic or metallic alloy molded products. It is thus proposed to use a magnetic field emanating from a DC magnetic field source in which the molded product is transparent while the defect linked to an inclusion of rare earth metal oxide amplifies the field at the location of the defect. due to the paramagnetic response of the rare earth metal oxide. According to a proposed embodiment, a Hall magnetic field sensor is attached to a permanent magnet such as neodymium-iron-boron type with high energy density. The required sensitivity and resolution as well as the depth of evaluation can be adjusted to data for inclusions at various depths on known material thicknesses. This can be optimized by changing the orientation of the magnetic dipole, the length of the dipole, the "polar" force of the dipole, the orientation of the sensor with respect to the orientation of the dipole. Such a control device is however only envisaged on non-ferrous materials, on the basis of the detection of the paramagnetic response of the rare earth metal oxide and can not be implemented such as, to search for ferromagnetism pollution especially when it must detect this pollution in a medium that can itself be ferromagnetic as is the case in the melted zone of certain grades of stainless steel.

Various other solutions have been investigated for the presence of first pass carbons in stainless steel welds such as the use of simple permanent magnets, eddy currents. These, however, do not allow to obtain a numerical value directly representative of the presence of the anomaly and its position in the thickness of the weld bead and are limited to the control of the near surface. They can be influenced by the random rate of ferrite present in the weld and do not deliver an instantaneous result.

The present invention overcomes these disadvantages by providing a complete and portable device for inspecting a material having a large thickness. It also relates to a control method for instantly making a conformity diagnosis with respect to reference values determined on calibration wedges and / or representative samples of the welds to be inspected. It exploits the measurement of magnetic flux variation related to the presence of a magnetic anomaly located in the material to be inspected. For this purpose, the invention relates to a device for non-destructive testing for determining the presence of magnetic material in non-magnetic or ferromagnetic materials with or without magnetic anisotropy, and in particular the existence of first passes of steel welds. to carbon in a stainless steel weld, said device comprising means for generating a magnetic field capable of magnetizing the magnetic body to be detected and means for measuring the magnetic field for measuring the variation of the magnetic flux related to the presence of a magnetic anomaly localized in the material to be tested, characterized in that it comprises at least one measurement probe arranged to be positioned on or near the material to be inspected, each measuring probe consisting of a housing in which are arranged the means for generating a magnetic field and at least one measurement sensor for each magnetic mp connected to a field meter.

Advantageously, a device according to the invention comprising at least one such probe makes it possible to obtain, in a small space requirement, the magnetization force necessary to generate the magnetic field as well as the measurement of the variation of the magnetic flux associated with the presence a magnetic anomaly localized in the material to be controlled even when the thickness of the material to control is important. We can therefore have a device with several probes.

In addition, the device according to the invention makes it possible to carry out a control of parts even in the case of limited access, it is indeed not necessary to have access on both sides (inside / outside) of the part since one or more probes may be placed on or in the vicinity of the weld bead, even if the part is coated with a non-magnetic insulator such as a coating, a paint, and the like.

The device according to the invention further comprises means for processing and analyzing the collected measurements. The treatments and analyzes of the collected measurements are comparisons of the values measured between the positions, directions or directions of the probes and between the calibration wedges or reference welds and the weld to be inspected, which are carried out either manually or automatically by algebraic operations. and / or logic using an electronic circuit such as a microprocessor that can be directly integrated with the field meter.

The means for generating the magnetic field may consist of one or more magnets of high power, preferably of the rare-earth iron (neodymium-iron-boron) type, superimposed or not, with or without a device for channeling the field lines. These means are adapted to the thickness of the Siaterial to be controlled in order to optimize their magnetic force.

The magnetic field measuring means may comprise at least one magnetic field measurement sensor such as those having a hall effect, magnetoresistance.

Preferably, each probe comprises a plurality of magnetic field measuring sensors arranged above, between, or below the magnets as magnetic field generation means and also arranged in directions, orientations and different positions in the space relative to each other. said magnetic field generating means.

In addition, in each probe, the magnetic field measurement sensors are advantageously positioned offset from the magnetic flux created by the magnets.

Such an arrangement of permanent magnets and sensors for measuring magnetic fields in each probe therefore makes it possible to obtain a probe of limited size and having all the properties necessary for the detection of a variation of the magnetic flux related to the presence of magnetic fields. a magnetic anomaly localized in the material to be controlled even when the thickness of the material to be controlled is important and has a certain ferromagnetism.

Thus, for example, a probe may comprise two magnetic field measuring sensors measuring the normal component of the field, said sensors being positioned in the same plane under the first magnet, on the part to be controlled, and arranged in two orthogonal directions. It may also be provided that each probe comprises two magnetic field measuring sensors, one of which is placed under the first magnet on the part to be controlled and the other on the magnet furthest from said piece.

Preferably, the magnetic field measuring sensor or sensors are arranged so as to provide an air gap with the face of one of the magnets.

Each magnetic field measuring sensor is preferably connected to a field meter by a shielded connecting cable and via a connector.

The device further comprises means for storing the measurements made and arithmetic comparison and / or logic thereof. Each probe may comprise ⁶ further in the same housing an ultrasonic transducer in which the measurement result is used to optimize the threshold value to decide on the conformity of the part to be inspected. The ultrasonic transducer is magneto acoustic (EMAT) and uses the same permanent magnets used to generate the magnetic field.

The device may further comprise a fugitive current sensor for separating the influence of the disturbing parameters.

Preferably, each probe is associated with a displacement encoder. Thus, it is possible to perform the positioning a posteriori field measurements performed in a reference linked to the inspected part.

The invention also relates to a non-destructive testing method for determining the presence of magnetic material in non-magnetic or ferromagnetic materials with or without magnetic anisotropy, such as welds and in particular the existence of first passes of steel welds. carbon in a stainless steel weld using the device according to the invention, characterized in that it comprises the following steps consisting of:

-check the effectiveness of the equipment on calibration blocks,

-call the zero in the air far from any source of magnetic field other than the terrestrial field, -deturn longitudinally and / or transversely, continuously or step by step the (the) probe (s) on or near the weld to be inspected on the workpiece and measure the different field values such as H ₁ and H _j ,

comparing the direct field measurements made simultaneously or successively in different directions, such as in particular two orthogonal directions, in particular along the axis of the weld bead Hi and a perpendicular direction Hj, the probe being able to be applied directly on the part to be checked or by means of an integral end piece of thickness adapted to the part to be checked,

-repair or memorize the zones exceeding the reference values determined or calculated during a preliminary calibration phase and

-determining the defective lengths either manually or from a record when the probe was used in association with a displacement encoder.

Preferably, the remanent field is used instead of the direct field, whether the measurements are made before or after local demagnetization of the area to be inspected. Advantageously, the pre-calibration phase consists of the following steps: a) calibrating the field measuring device to obtain 100, or any other power value or multiple of 10, when the probe is applied to a ferromagnetic sample and 0 in the air (B) or on a non-magnetic material with or without insert, b) draw a calibration curve by superimposing one or more shims of different thickness of non-magnetic material or representative of the material to be inspected on a ferromagnetic steel shim and taking measurements successively by placing the probe in position C so as to obtain a correlation between the measured field values and the depth at which the ferromagnetic steel is located; c) to carry out reference measurements carried out at using the probe according to different control directions and / or position on a sample deemed to be in conformity and on a sample the threshold value by combination of algebraic and / or logical operation between these values, the calibration curve determined according to b) being able to be associated with this combination, said reference measurements being able to be carried out using the field direct or the residual field, before or after demagnetization.

One embodiment of the present invention will be described hereinafter by way of nonlimiting example, with reference to the appended drawing in which:

FIG. 1 is a diagrammatic view of a block diagram showing the combination of one or more probes, a displacement encoder integral with the probe or probes and the electronic elements that can be implemented in a form of FIG. complete execution according to the invention,

FIG. 2 represents a view in longitudinal section of a first example of a probe of a device according to the invention; FIG. 3 represents a view from below of a second example of a probe of a device according to the invention;

FIG. 4 represents a view from below of a third example of a probe of a device according to the invention; Figures 5 and 6 show the main phases of the calibration phase and the control method according to the invention.

A probe S according to the invention which is shown in Figure 2 is preferably constituted by a housing 1 made of non-magnetic material in which is placed one or more permanent magnets 2 of high power. In the example shown, two permanent magnets 2, 2 'have been superimposed. In the case of a large thickness to be controlled, devices for channeling c8ιamp lines of ferromagnetic material can be added.

Above, between or below the magnets 2 are positioned one or more sensors 3, 3 'in directions that may be different. As can be seen in FIG. 2, a magnetic field measuring sensor 3 is positioned below the permanent magnet 2 so as to be located between the latter and the part to be inspected. One could also provide a second sensor positioned on the other side of the probe above the permanent magnet 2 ', or another sensor between the two magnets 2 and 2'.

As can be seen in FIG. 3, two sensors 3, 3 'are placed below the magnet 2 in two different directions, which makes it possible to measure the values or the variations of magnetic fields.

The sensor or sensors 3, 3 'are connected by a shielded connection cable 4 via a connector 5 to the field meter 7 of the device.

It is advantageous to shift the sensors 3, 3 'relative to the maximum magnetic flux created by the magnets 2, 2' and / or to arrange them so as to provide an air gap with respect to the face of the magnet 2 in order to avoid saturation of the sensors and increase their sensitivity.

Depending on the depth at which the carbon steel to be detected is found, the performance of the probe can be optimized by acting on: the power of the magnets,

the use or not of a device for channeling the field lines, the type and sensitivity of the sensors,

the number, position, direction and orientation of said sensors,

the measurement mode: absolute or differential, for example using two probes,

- the air gap between the probe and the material to be checked (for example welding).

The device according to the invention is designed to be able to perform and process the measurements according to the principle of the block diagram of FIG. 1, either using a set of memories and a microprocessor integrated in the field strength meter, or using a microcomputer connected to the field meter. The measurements made at the sensor or sensors 3, 3 'placed in one or more probes S are carried out using a field meter 7 which may be provided with several measuring channels. The measurements are either directly processed manually from a visual reading on the screen of the field strength meter, or processed automatically: by comparing measured values between different sensors 3, 3 'placed in the same probe,

by comparison made by algebraic and / or logical operations carried out between probe and / or sensors,

- By comparison with reference values stored in the device that can take into account the actual thickness of the weld measured by ultrasound using an ultrasonic transducer (Trad.US).

According to one version of the invention, it is possible to automatically trigger an audible or visual alarm or to present the results as shown in the diagram of FIG. 6. In the latter case, the measurement probe or probes S (FIGS. 2, 3 and 4) are made integral with a displacement encoder 8, which after reading and storage in a buffer memory allows the posterior positioning of the field measurements made in a reference linked to the inspected part.

The calibration phase according to the invention makes it possible to overcome significantly the variation of the ferrite content in the weld. This phase is shown schematically in FIG. 5, and consists in adjusting the settings of the field meter so that it displays the value of a multiple of 10 when the probe (position A) is placed on a sheet of carbon steel 10 and 0 when the probe is placed in the air (position B) or on a non-magnetic material far from any magnetic ferromagnetic part with or without insert. In one embodiment of the invention, it is thus possible to obtain different sign values (+/-) between the defective zones and the others.

An estimate of the threshold value for determining the presence of a carbon steel pass is determined by placing one or more stainless steel shims of the same grade as that of the base metal constituting the welded component to be inspected. The cumulative thickness of the stainless steel shims 20 is equivalent to the thickness of molten metal located above the carbon steel pass.

This reference value is particularly useful in the case of welds made on stainless steel with a low ferrite content. When the solder has a high ferrite content, the procedure according to the invention requires the determination of reference values in two different orthogonal directions, for example in the direction of the bead (Hi) and perpendicular thereto (H _j ). . The probe S is then placed on a part or a sample deemed to be sound and representative of the weld to be inspected and the measured values (H ₁ and H _j ) are memorized for this position. The previous operation is repeated on a part or a sample having a carbon steel pass 40 and is memorized also the measured values. The absolute values of these measurements and / or the results of the algebraic and / or logical operations between these values are generally much lower compared to what is measured in the presence of a carbon steel pass. This way of proceeding makes it possible to limit the influence of the phenomena of preferential magnetic anisotropy of the welded structure.

When reference values have been determined as previously described, inspection of suspicious welds may be undertaken. The main operations of the control method according to the invention illustrated in FIG. 6 are the following: a) checking the efficiency of the equipment on the calibration shims, b) setting the zero in the air far from any source of magnetic field other than the earth field, c) longitudinally and / or transversely, continuously or stepwise displacement of the (the) probes S on or near the weld 50 to be inspected existing on the piece P and measurements of the different field values such as for example Hi and H _j , d) comparing field measurements made simultaneously or successively in different directions, in particular two orthogonal directions (in particular along the axis of the weld bead H ₁ and a perpendicular direction Hj ), e) identification or storage of zones exceeding the reference values determined or calculated during the calibration phase and determination of defective lengths, ie or from a record E when the probe has been used in association with a displacement encoder 8.

The control method can be applied by exploiting the direct and / or remanent field before and / or after degaussing the pieces. In the case of inconsistent measurements, the use of residual field values can be performed and in the most difficult cases the measurements are redone after local demagnetization with an appropriate means of the areas to be inspected.

If the probe used has an ultrasonic transducer, the measured values can be automatically compared to the reference threshold values as a function of the thickness measurement made on the weld.

According to a variant of the invention, the ultrasonic transducer used is magneto acoustic effect EMAT (Electromagnetic Acoustic Transducer). Indeed it is possible to take advantage of the existing magnetization to generate the ultrasonic wave. According to another embodiment of the invention, a current eddy sensor is integrated in the probe in order to separate influencing parameters.

The invention is of course not limited to the examples given but also encompasses all the variants defined in the dependent claims.

Claims

claims

1. Device for non-destructive testing to determine the presence of magnetic material in non-magnetic or ferromagnetic materials with or without magnetic anisotropy, and in particular the existence of first passes of carbon steel welds in a steel weld stainless steel, said device comprising means for generating a magnetic field capable of magnetizing the magnetic body to be detected and means for measuring the magnetic field for measuring the variation of the magnetic flux related to the presence of a magnetic anomaly located in the material to be tested, characterized in that it comprises at least one measuring probe (S) arranged to be positioned on or near the material to be inspected, each measuring probe (S) consisting of a housing (1) in which the means for generating a magnetic field (2, 2 ') and at least one magnetic field measuring sensor are arranged (3, 3 ') connected to a field meter.

2. Device according to claim 1, characterized in that it further comprises means for processing and analysis of the collected measurements from said one or more probes.

3. Device according to one of claims 1 and 2, characterized in that the means for generating a magnetic field are constituted by at least one permanent magnet (2, 2 ') of high power,

4. Device according to one of claims 1 to 3, characterized in that each probe (S) comprises a plurality of magnetic field measuring sensors (3, 3 ') arranged in directions, orientations and different positions in space by relative to the magnetic field generating means.

5. Device according to one of claims 1 to 4, characterized in that, in each probe (S), or the magnetic field measuring sensors are positioned offset from the magnetic flux created by the magnets.

6. Device according to one of the preceding claims, characterized in that a probe (S) comprises two magnetic field measuring sensors (3, 3 ') measuring the normal component of the field, said sensors being positioned in the same plane under the first magnet, control room side, and arranged in two orthogonal directions.

7. Device according to one of the preceding claims, characterized in that each probe (S) comprises two magnetic field measuring sensors, one of which is placed under the first magnet side of the part to be controlled and the other above the magnet farthest from said room.

8. Device according to any one of claims 3 to 7, characterized in that the or the magnetic sensors (3, 3 ') are arranged to provide an air gap with the face of one of the magnets (2, 2' ).

9. Device according to one of claims 1 to 8, characterized in that it further comprises means for storing the measurements made and arithmetic comparison means and / or logic thereof.

10. Device according to claim 9, characterized in that it comprises a microprocessor which can be directly integrated with the field meter (7).

11. Device according to one of claims 1 to 10, characterized in that each probe (S) further comprises in the same housing (1) an ultrasonic transducer whose measurement result is used to optimize the threshold value for ruling on the conformity of the part to be inspected.

12. Device according to claim 11, characterized in that the ultrasonic transducer is magneto acoustic effect (EMAT) and in that it exploits the same permanent magnets that used to generate the magnetic field.

13. Device according to one of claims 1 to 12, characterized in that it further comprises a fugitive current sensor for separating the influence of disturbing parameters.

14. Device according to one of claims 1 to 13, characterized in that each sensor is associated with a displacement encoder.

15. Non-destructive testing method for determining the presence of magnetic material in non-magnetic or ferromagnetic materials with or without magnetic anisotropy, such as welds and in particular the existence of first passes of carbon steel welds in a stainless steel weld using the device according to any one of claims 1 to 14, characterized in that it comprises the following steps:

-check the effectiveness of the equipment on calibration blocks,

-call the zero in the air far from any source of magnetic field other than the terrestrial field,

displacing longitudinally and / or transversely, continuously or stepwise, the probe (s)

(S) on or near the weld to be inspected on the workpiece (P) and measure the different field values such as Hj and H _j ,

comparing the direct field measurements performed simultaneously or successively in different directions, such as in particular two orthogonal directions, in particular along the axis of the weld bead Hj and a perpendicular direction Hj, the probe

(S) can be applied directly on the part (P) to be controlled or by means of a fixed end piece of thickness adapted to the part to be checked,

-determining the defective lengths either manually or from a recording (E) when the probe (S) has been used in association with a displacement encoder.

16. Control method according to claim 15, characterized in that exploits the remnant field instead of the direct field, the measurements are performed before or after local demagnetization of the area to be inspected.

17. Control method according to one of claims 15 and 16, characterized in that the preliminary calibration phase consists of the following steps consisting of: a) calibrating the field measuring device to obtain 100, or any other power value; or multiple of 10, when the probe is applied (A) to a ferromagnetic sample (10) and 0 to air (B) or to a non-magnetic material with or without a spacer, b) draw a calibration curve in superimposing one or more shims (20) of different thickness of non-magnetic or representative material of the material to be inspected on a ferromagnetic steel shim (20) and successively taking measurements by placing the probe in position (C) so as to obtain a correlation between the measured field values and the depth at which the ferromagnetic steel is located, c) to carry out reference measurements carried out using the probe (S) according to different d control irreversions and / or position on a sample deemed to be compliant and on a sample deemed to be non-compliant and determine the threshold values by combination of algebraic and / or logical operation between these values, the calibration curve determined according to (b) being associated with this combination, said reference moorings can be performed using the direct field or the residual field, before or after demagnetization.

18. The method of claim 17, characterized in that one obtains values of different sign (+/-) between the defective zones and the others.