Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
  • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
  • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
  • G01N27/9013—Arrangements for scanning

Definitions

• the invention relates to an eddy current sensor using separate transmitter and receiver windings to carry out non-destructive testing of electrically conductive parts.
• the invention also relates to a tool for non-destructive testing of tubes, this tool comprising at least one eddy current sensor.
• the sensor according to the invention can be used to carry out non-destructive testing of a part of any shape and size, as soon as the nature of the material or materials constituting this part makes it possible to induce eddy currents therein.
• a preferred application in no way limitative, relates to the control of the tubes of the steam generators which equip nuclear power plants.
• the simplest sensors are sensors comprising a single winding used both as a transmitter and as a receiver.
• the most common sensors are used in differential measurement. These sensors generally use two windings connected in series, both used also as transmitters and as receivers. Because the windings are placed opposite two neighboring regions of the part, any difference in impedance between the two windings reveals the presence of a defect in the material and its extent.
• the eddy current sensors each winding of which acts both as a transmitter and as a receiver, carry out local measurements which make it possible to establish the mapping of the faults present inside a part to be checked.
• this type of sensor only detects faults which are present over a limited depth from the surface of the part close to the measurement windings. Thus, in the case of checking the steam generator tubes, certain point sensors only detect faults on the external wall when these have a depth greater than 40% of the thickness of this wall.
• the main object of the invention is an eddy current sensor of original design, usable for the control of pieces of any shape, in which the transmission and reception functions are provided by separate windings, arranged in such a way that the performance of detection of faults is significantly increased compared to that of existing sensors (for example so as to detect faults on the external wall having a depth limited to about 20% of the thickness of this wall, in the case of the control of the tubes of a steam generator) without the need to have recourse to a subsequent compensation treatment.
• an eddy current sensor comprising two transmitting windings and at least one receiving winding arranged symmetrically with respect to a reference plane intended to be oriented in a direction substantially normal to a surface of a part to be checked, the emitting windings being arranged on either side of the reference plane and each comprising a median plane substantially parallel to the reference plane and at least one active part which has a shape substantially complementary to that of the surface, and the receiver winding being oriented perpendicular to the reference plane placed between the active parts of the transmitter windings, and comprising a median plane which forms an angle of about 90 ° with the reference plane; characterized in that the two transmitter windings are connected and coils in such a way that they induce opposite magnetic fields in a spatial area containing the receiver winding, so that the latter is not traversed by any electric current when the region of the part to be inspected located opposite the sensor is free from faults.
• the carrying out of the transmission and reception functions by separate windings and the particular arrangement of these windings makes it possible to significantly increase the resolution or the detection depth of the sensor, while retaining performances comparable to those of existing local detection sensors.
• each transmitting winding comprises a single active part corresponding to a fraction of the circumference of this winding, the sensor comprising a single receiving winding placed between these active parts. This characteristic makes it possible to control parts of any shape, that is to say both tubes and plates.
• the subject of the invention is also a tool for non-destructive testing of a tube, capable of being moved inside the latter.
• This tool comprises a rotary central body which has a longitudinal axis, and two centering rings which support the body in the tube so that the axis of the body is substantially coincident with that of the tube.
• the rotary central body then supports at least one eddy current sensor as defined previously.
• the rotary central body supports a first sensor whose reference plane is perpendicular to the longitudinal axis of the body and a second sensor whose reference plane contains the longitudinal axis of the body.
• the first and second sensors are then mounted on the rotary central body at locations diametrically opposite with respect to the longitudinal axis of the body.
• FIG. 1 is a perspective view schematically showing a tool equipped with two eddy current sensors according to the invention, capable of being introduced into a steam generator tube, to ensure non-destructive control;
• FIG. 2 is a sectional view diagrammatically illustrating one of the sensors mounted on the tool of Figure 1, as well as the portion of
• FIG. 3 is a sectional view along line III-III of Figure 2;
• FIG. 4 is a sectional view in diagram ⁇ tick comparable to Figure 2 illustrating the second sensor of the tool of Figure 1; and - Figure 5 is a sectional view along line VV of Figure 4.
• FIG. 1 there is shown in phantom a section of tube T which we want to perform non-destructive testing.
• This section of tube can in particular be part of a steam generator fitted to a nuclear power plant.
• the corrosive environment in which the tubes of the steam generators are found imposes regular checks aimed at detecting possible degradations necessitating plugging or repairing the tubes concerned.
• FIG. 1 there is shown by way of non-limiting example, a tool 10 designed to perform non-destructive testing of the tube T, by means of two eddy current sensors according to the invention.
• the eddy current sensors in accordance with the invention can be used for any other type of non-destructive testing.
• these sensors can be used both to carry out the control of a tubular part from the inside thereof, and to carry out the control of parts of any other shape such as flat parts or any profiles, by one or other of the faces of these parts.
• the non-destructive testing tool 10 illustrated in FIG. 1 has a known overall configuration which is not part of the invention. To facilitate understanding, we simply indicate here the general characteristics of this tool.
• the non-destructive testing tool 10 has substantially the shape of a cylinder whose longitudinal axis is intended to be substantially coincident with that of the tube T. It comprises a front body 12, in the form of a warhead, facilitating its penetration into the tube T, as well as a rear body 14 by which the tool is connected to an external installation (not shown) through a flexible cable 15.
• This flexible cable 15 makes it possible to control the movements of the tool 10 in the tube T and transmit between the tools and the external installation the electrical signals necessary for the control.
• the front body 12 and the rear body 14 are non-rotating elements which both support a flexible centering ring 16, 18 by means of which the tool 10 is centered in the tube T.
• the non-destructive testing tool 10 comprises a rota ⁇ tif central body 20 centered on the longitudinal axis of the tool and capable of being rotated at speed constant around this axis when the latter moves inside the tube T.
• the rotation of the central body 20 is controlled by a motor (not shown) housed in the rear body 14.
• the rotary central body 20 of the tool 10 for non-destructive testing carries two eddy current sensors, designated respectively by the references 22a and 22b. These two sensors 22a and 22b are located on the central body 20 at locations diametrically opposite with respect to the longitudinal axis of the tool. For this reason, the sensor 22b is not visible in FIG. 1.
• the combined translational and rotational movements of the central part 20 of the tool 10 have the effect of displacing the sensors 22a and 22b according to a helical movement inside the tube T. A scanning of the wall of this- this is thus ensured.
• the parts 24a and 24b of the central body 20 which surround the sensors 22a and 22b are made of electrically insulating material.
• the eddy current sensor 22a which equips the tool 10 in Figure 1.
• this sensor 22a comprises two transmitter windings 26 and a receiver winding 28.
• the transmitter windings 26 are arranged symmetrically, on either side of a reference plane PI, provided to be oriented perpendicular to the inner surface of the tube T, that is to say in the case of the sensor 22a perpendicular to the axis of the tube T.
• the reference plane PI constitutes a plane of symmetry for the receiver winding 28.
• the median planes of the emitting windings 26 are arranged substantially parallel to the reference plane PI on either side of the latter.
• the median plane of the receiving winding 28 is oriented perpendicular to the reference plane PI.
• the dimensions of the receiver winding 28 are substantially smaller than those of the transmitter windings 26.
• each of the emitting windings 26 comprises an active part 26a, which corresponds to a fraction of the circumference of this winding and has a shape complementary to that of the interior surface of the tube T. Because the median planes of the emitting windings 26 are parallel to the reference plane PI which is oriented perpendicular to the axis of the tube T, these active parts 26a of the emitting windings 26 therefore have in this case an arc shape. Over the rest of the circumference of the emitting windings, these can take any shape.
• the receiver bearing 28 is placed between the active parts 26a of the transmitter windings 26.
• the transmitter windings 26 are electrically connected in series so as to be supplied simultaneously by the same alternating electric current of any shape (sinusoidal, pulse or other).
• the primary magnetic fields thus generated by the two emitting windings 26 create field lines L1, L2, part of which travels in the wall of the tube T, opposite the active parts 26a of the emitting windings 26.
• the geometrical configuration which comes from The description of the eddy current sensor 22a according to the invention is such that the receiver winding 28 is at the center of these field lines L1, L2.
• the electrical connection of the transmitter windings 26 and the direction of their windings are made in such a way that the primary magnetic fields which they generate are oriented in the direction opposite in the spatial zone in which the receiver winding 28 is located. Due to the perfect symmetry of the sensor and the arrangement described above, the receiver winding 28 is therefore not traversed by any electric current as long as the region of the tube T located opposite the sensor is free of faults. The electric current flowing in the receiver winding 28 is therefore directly representative of a fault present in the region of the tube situated opposite the sensor, without it being necessary to carry out any subsequent electrical treatment.
• the receiver winding 28 is insensitive to the permanent state of the secondary magnetic field created by the eddy currents induced in the primary tube T.
• the receiver winding 28 therefore only detects variations in the secondary magnetic field which result from the presence of defects in the thickness of the wall of the tube T. More specifically, the orientation of the eddy current sensor 22a illustrated on Figures 2 and 3 can detect cracks which extend mainly along the longitudinal axis of the tube T.
• the eddy current sensor according to the invention and in particular its insensitivity to the permanent secondary magnetic field allow it to detect faults at a depth substantially greater than the existing eddy current sensors.
• the sensor according to the invention detects faults up to about 80% of the thickness of the wall of the tube T, while the existing sensors detect such defects only on a depth less than 60% of this thickness.
• the Fou ⁇ cault 22a current sensor is practically insensitive to cracks oriented along the circumference of the tube T
• the tool 10 illustrated in FIG. 1 advantageously comprises a second eddy current sensor 22b produced according to the same principle as the sensor 22a but whose orientation is offset by 90 ° relative to the latter.
• the sensor 22b also comprises two transmitter windings 26 and a receiver winding 28 whose relative arrangement is the same as that of comparable windings of the sensor 22a. More specifically, these three windings 26 and 28 are also arranged symmetrically with respect to a reference plane P2.
• this reference plane P2 is perpendicular to the reference plane PI of the sensor 22a. More precisely, this reference plane P2 in this case contains the longitudinal axis of the tool.
• the active parts 26 ′ of these emitting windings are oriented in this case parallel to generators of the tube T. These active parts are therefore rectilinear, as illustrated in particular in Figure 4.
• the emitting windings 26 of the sensor 22b are electrically connected and coils in a direction such that the primary magnetic fields which they generate when they are excited are oriented in opposite directions in the region of the receiver winding 28.
• This characteristic illustrated by the field lines L1 and L2 in FIG. 5, makes it possible to obtain an output signal from the receiver winding 28 directly representative of the presence of a defect, without requiring further processing.
• the senor 22b is sensitive to faults oriented circumferentially in the tube T.
• the assembly formed by the sensors 22a and 22b therefore makes it possible to detect all the types of faults present in the tube T, on a significantly greater depth than existing sensors and without it being necessary to carry out any processing intended to eliminate a continuous component of the signals delivered by the sensors, since this component does not exist.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Analytical Chemistry (AREA)
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• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
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• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

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• 1996
  • 1996-01-24 FR FR9600790A patent/FR2743890B1/fr not_active Expired - Fee Related
• 1997
  • 1997-01-23 CA CA002214773A patent/CA2214773A1/en not_active Abandoned
  • 1997-01-23 JP JP9526608A patent/JPH11502938A/ja active Pending
  • 1997-01-23 WO PCT/FR1997/000133 patent/WO1997027476A1/fr not_active Application Discontinuation
  • 1997-01-23 EP EP97901658A patent/EP0815441A1/de not_active Withdrawn
  • 1997-01-23 US US08/913,894 patent/US5914595A/en not_active Expired - Fee Related

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