Positioning system for gamma-ray shooting

Abstract

Positioning system (1) for gamma radiography inspection of a weld bead, comprising: - a first flexible device (7) on which at least one first positioning mark is represented and which includes at least one radiographic marker; - at least a second flexible device (25) on which a second positioning mark is represented, and which includes a film holder and a tip holder (3) for an irradiation tip (5), the second flexible device being arranged to be installed on the workpiece by surrounding it, after the installation of the first flexible device, so that the second positioning mark is positioned in a predetermined position defined by a position of the first positioning mark. ABBREVIATED FIGURE: Fig. 1

Description

Title of the invention: Positioning system for gamma-graphic shooting

[0001] The invention relates to the field of weld control by gammagraphy.

[0002] BACKGROUND OF THE INVENTION

[0003] Radiographic testing by ionizing radiation is a non-destructive testing technique, which is used in a large number of applications in different industrial sectors: nuclear, petrochemical, boilermaking, aeronautics, etc.

[0004] This is a very effective technique for controlling metal parts and therefore for detecting defects in the parts, and for determining the risk of propagation of these defects.

[0005] Radiographic inspection is also used to detect defects in welds (blowholes, cracks, porosities, etc.).

[0006] Radiographic control uses a source which emits ionizing radiation, and a receiver which is generally an X-ray film but which can be a more complex device (electronic, camera, etc.).

[0007] The source of ionizing radiation is an X-ray generator (this is called X-ray radiography), or a radioactive source of gamma rays (this is called gammagraphy). In the latter case, the source is, for example, an iridium 192 source.

[0008] We are particularly interested here in the technique of gammagraphy control of weld beads allowing the assembly of the different portions of parts, which are for example tubular parts.

[0009] To implement this technique, a tip holder is positioned on the external wall of the part to be inspected, at the level of the weld bead. The tip holder is intended to accommodate an irradiation tip connected to the source via a sheath. The film is positioned on the external wall opposite the tip holder. A gamma-graphic shot is then carried out, then the positions of the film and the tip holder are modified to prepare for another shot.

[0010] This technique allows for very effective control of the weld bead, but presents a certain number of difficulties.

[0011] One of these difficulties concerns the safety of the operator when the inspection takes place in a hostile environment. This is the case, for example, when it comes to inspecting the welds of the piping of a primary or secondary circuit of a reactor in a nuclear power plant. It is essential in such a situation to ensure that the inspection is carried out as quickly as possible to reduce the duration of exposure to the radioactivity of the operator. It is therefore important not only to avoid unnecessary firing, but also to ensure the shortest possible firing preparation time.

[0012] It is also essential to ensure that the tip holder and the film are positioned very precisely and perfectly repeatably according to the different shots. It is also necessary that the radiographic location carried out is very precise so that the analysis of the radiographic films, after their development, allows the precise location of the defects potentially present in the weld bead.

[0013] SUBJECT OF THE INVENTION

[0014] The object of the invention is, during a gammagraphy inspection, to ensure positioning of the tip support and the radiographic film, and radiographic location, which are precise, repeatable and quick to carry out. Summary of the invention

[0015] With a view to achieving this aim, a positioning system is proposed, intended to be used during a gammagraphy inspection of a weld bead on a part, and comprising:

[0016] - a first flexible device on which is represented at least one first positioning mark, and comprising a positioning indicator and at least one radiographic mark, the first flexible device being arranged to be installed on the part by surrounding it, so that the positioning indicator is positioned in a reference position defined by a position of a reference mark formed on the part, on or near the weld bead;

[0017] - at least one second flexible device on which is represented a second positioning mark, and comprising a film holder containing an X-ray film, and a tip holder arranged to accommodate an irradiation tip,

[0018] the second flexible device being arranged to be installed on the part by surrounding it, after the installation of the first flexible device, so that the second positioning mark is positioned in a predetermined position defined by a position of the first positioning mark, the tip holder and the radiographic film then being positioned on the weld bead and opposite each other with respect to the part.

[0019] To carry out a gammagraphic shot, the first flexible device is therefore installed around the part, positioning the positioning indicator in the reference position which is defined by the position of the reference mark formed on the part.

[0020] Then, the second flexible device is installed around the part, positioning the second positioning mark in the predetermined position which is defined by the position of the first positioning mark.

[0021] The irradiation tip is then introduced and fixed in the tip holder, and takes the shot.

[0022] In the case where the first flexible device comprises several first positioning marks, it is possible to use a plurality of second flexible devices and carry out several successive shots by successively positioning each second flexible device relative to a distinct first positioning mark.

[0023] The positions relative to each other and relative to the part of the film support (and therefore of the film), of the tip support (and therefore of the irradiation tip), and of the radiographic marker, are thus perfectly known and repeatable according to the different shots.

[0024] The installation of the first flexible device and each second flexible device is very quick to carry out. The positioning system allows the operator, for each shot, to position the tip holder, the film and the radiographic marker very precisely and very quickly.

[0025] A positioning system as previously described is further proposed, comprising a plurality of second flexible devices, the first flexible device comprising a plurality of first positioning marks regularly distributed along a length of the first flexible device, each second flexible device being intended to be positioned relative to a first positioning mark distinct from the first flexible device to carry out a grammatical shot and then to be removed to be replaced by another second flexible device, the positioning system thus making it possible to carry out a plurality of successive gammagraphic shots regularly distributed over a circumference of the weld bead.

[0026] A positioning system as previously described is further provided, wherein the first flexible device comprises a flexible body arranged to surround the part, such that a length of the flexible body extends along a contour of the part when the first flexible device is installed, the at least one first positioning mark, the positioning indicator and the at least one radiographic marker being positioned on the flexible body.

[0027] A positioning system is further proposed as previously described, in which the at least one radiographic marker of the first flexible device comprises a graduation in units of length, comprising graduation elements made of lead, and defined according to the length of the flexible body.

[0028] A positioning system is further proposed as previously described, in which the at least one radiographic marker of the first flexible device comprises at least two reference elements, made of lead, and intended to define a central analysis zone on the radiographic film.

[0029] A positioning system as previously described is further proposed, in wherein the flexible body of the first flexible device comprises a first portion and a second portion defined within a width of the flexible body, the first portion comprising the at least one first positioning mark, and the second portion comprising the positioning indicator and the at least one radiographic marker.

[0030] A positioning system is further proposed as previously described, in which the first flexible device comprises an axial stop making it possible to ensure that the second flexible device is positioned axially correctly on the part.

[0031] A positioning system is further proposed as previously described, the second portion of the flexible body being less thick and being intended to be positioned closer to the weld bead than the first portion so that, when the first flexible device and the second flexible device are installed around the part and the second positioning mark is positioned in the predetermined position, the film support rests on the second portion, the difference in thickness between the first portion and the second portion creating a shoulder forming the axial stop.

[0032] A positioning system is further proposed as previously described, the positioning indicator being a notch made in an edge of the flexible body, in which the reference mark must be positioned when the first flexible device is installed on the part.

[0033] A positioning system as previously described is further proposed, in which the first flexible device further comprises a first strap, to which the flexible body is fixed, and arranged to surround the part and to fix the first flexible device to the part.

[0034] A positioning system as previously described is further provided, in which the second flexible device further comprises a second strap, to which the tip holder and the film holder are attached, and arranged to surround the part and to attach the second flexible device to the part.

[0035] A positioning system as previously described is further provided, in which the second positioning mark is positioned on the film support.

[0036] We further propose a gammagraphic control method using the positioning system as previously described, and comprising a control phase comprising the steps of:

[0037] - installing and fixing the first flexible device on the part, so that it surrounds the part and so that the positioning indicator is positioned in the reference position;

[0038] - then, install and fix the second flexible device on the part, so that it- this surrounds the part and that the second positioning mark is positioned in the predetermined position;

[0039] - insert and fix the irradiation tip in the tip holder, and carry out a grammatical shooting.

[0040] A gammagraphic control method as previously described is further proposed, using a positioning system as previously described, the gammagraphic control method comprising several control phases carried out successively, each control phase being carried out using a second separate flexible device positioned relative to a first positioning mark separate from the first flexible device.

[0041] The invention will be better understood in light of the following description of a particular non-limiting embodiment of the invention. Brief description of the drawings

[0042] Reference will be made to the attached drawings, among which:

[0043] [Fig-1] [Fig.l] represents a part to be controlled, the positioning system installed on the part and viewed from one side and from another side of the part, as well as the irradiation tip and the sheath which connects the irradiation tip to the source;

[0044] [Fig.2] [Fig.2] represents the external face and the internal face of the first device flexible, as well as the first flexible device installed on the part and seen from one side and from another side of the part;

[0045] [Fig.3] [Fig.3] represents the inner face and the outer face of the second flexible device, as well as the second flexible device installed on the part and seen from one side and from another side of the part;

[0046] [Fig.4] [Fig.4] represents steps of a gammagraphic control method made using the positioning system;

[0047] [Fig.5] [Fig.5] represents an X-ray film, after development, obtained following a check carried out using the positioning system. DETAILED DESCRIPTION OF THE INVENTION

[0048] With reference to [Fig.l], the positioning system 1 is intended to be used during a gammagraphy inspection of a weld bead on a part 2. The part 2 is here a tubular part, and for example a pipe elbow of the safety injection circuit (RIS) connected to the primary circuit of a reactor of a nuclear power plant.

[0049] The positioning system 1 makes it possible to ensure rapid, precise and repeatable positioning, relative to the weld bead, of a tip support 3, an X-ray film 4 and at least one X-ray marker. The tip support 3 is intended to accommodate a tip 5 which is itself connected to a radioactive source by an ejection sheath 6.

[0050] The positioning system 1 firstly comprises a first flexible device 7.

[0051] With reference to [Fig.2], the first flexible device 7 comprises a flexible body 8 and a first strap 9.

[0052] The flexible body 8 is here made with (at least) a flexible material (silicone for example). The first strap 9 is here a fabric strap.

[0053] The first strap 9 is fixed to an external face 10 of the flexible body 8 (for example by gluing, sewing).

[0054] Here, by “internal face” we mean a face intended to be applied to the part 2, and by “external face” we mean a face opposite the internal face.

[0055] The first strap 9 extends parallel to the length of the flexible body 8 (in any case when the flexible body 8 and the first strap 9 are arranged flat).

[0056] Here, by "length" is meant the dimension of an object which extends along the contour of the part 2 when said object is installed on the part 2 by surrounding it, and by "width" is meant the dimension of the object perpendicular to the length.

[0057] The first flexible device 7 also comprises a first clip buckle comprising a male part 11 located at a first end of the first strap 9 and a female part 12 located at a second end of the first strap 9.

[0058] The length of the flexible body 8 is approximately equal to the circumference of the part 2 so that when the first flexible device 7 is installed on the part 2 and the flexible body 8 surrounds the part, the ends of the flexible body 8 meet without overlapping.

[0059] The flexible body 8 comprises a first portion 14 and a second portion 15 defined in the width of the flexible body 8. When the first flexible device 7 is installed on the part 2, the second portion 15 of the flexible body 8 is closer to the weld bead 16 than the first portion 14.

[0060] The second portion 15 of the flexible body 8 is less thick than the first portion 14.

[0061] At least one first positioning mark 17, in this case a plurality of first positioning marks 17, are represented on the first flexible device 7.

[0062] The first positioning marks 17 are here five in number and are positioned on the external face of the first portion 14 of the flexible body 8. The first positioning marks 17 extend successively, and are regularly distributed, along the length of the flexible body 8.

[0063] The first positioning marks 17 are first triangles each associated with one of the letters A, B, C, D, E. Each first triangle comprises a vertex positioned on the edge 18 of the first portion 14, which separates the first portion 14 from the second portion 15, and a side opposite said vertex, which is parallel to the edge 18.

[0064] Each first triangle thus forms an arrow oriented towards the welding bead 16 when the first flexible device 7 is installed around the part.

[0065] The first flexible device 7 also comprises at least one radiographic marker.

[0066] The first flexible device 7 comprises in this case a graduation 20 in units length (in cm), which includes graduation elements (numbers) made of lead, and which is defined according to the length L1 of the flexible body 8.

[0067] The first flexible device 7 further comprises at least two reference elements 21 (here five), made of lead, and intended to define a central analysis zone on each radiographic film 4 obtained. The reference elements 21 have the form of lines which extend from the edge 19 of the second portion 15 and perpendicular to the edge 19 (which is also an edge of the flexible body 8 along its length).

[0068] The first flexible device 7 further comprises a positioning indicator 23, which allows it to be positioned axially and oriented relative to the weld bead 16.

[0069] The positioning indicator 23 is here a notch made in the edge 19 of the flexible body 8 at the level of the number 0 of the graduation 20

[0070] This axial and angular positioning uses a reference mark 24 formed on the part 2 near the weld bead 16, which is a “stamped L”. The reference mark 24 defines a reference position for the positioning indicator 23 (and therefore for the origin of the graduation 20).

[0071] When the operator installs the first flexible device 7, he ensures that the positioning indicator 23 is positioned in the reference position defined by the reference mark 24, that is to say that the reference mark 24 is positioned in the notch 23.

[0072] It is noted that the first strap 9 extends over the first portion 14, between the first positioning marks 17 and the edge of the first portion 14 opposite the edge 18.

[0073] With reference to [Fig. 3], the positioning system 1 also comprises at least one second flexible device 25, here five second flexible devices 25, all identical.

[0074] Each second flexible device 25 is intended to be positioned relative to a first positioning mark 17 distinct from the first flexible device 7 to carry out a grammatic shot, then to be removed to be replaced by another second flexible device 25. The positioning system 1 thus makes it possible to carry out a plurality of successive gammagraphic shots distributed over the circumference of the weld bead 16.

[0075] Each second flexible device 25 comprises a film holder 26 in which the X-ray film 4 is positioned, the tip support 3 arranged to accommodate the irradiation tip 5, and a second strap 28. The second strap 28 is here a fabric strap.

[0076] The film holder 26 is a pouch which contains the film 4 (and possibly several films, for example two films for a double-film shot), one or more filters and one or more blocking screens. All these elements are stacked in the pouch 26 forming different “sandwich” layers.

[0077] An image quality indicator 29 (IQI) is stuck on the internal face of the pocket 26: it is therefore located between the part 2 and the film 4 when the second flexible device 25 is installed on the part 2.

[0078] The tip support 3 and the pocket 26 are fixed to the second strap 28 (for example by gluing, sewing).

[0079] The second strap 28 extends parallel to the length of the pocket 26 (in any case when the second strap 28 and the pocket 26 are arranged flat), and passes through a central part of the external face of the pocket 26.

[0080] The pouch 26 and the tip holder 3 are positioned so that, when the second flexible device 25 is installed on the part 2 by surrounding it, the irradiation tip 3 is located opposite the X-ray film 4 relative to the part 2.

[0081] The second flexible device 25 also comprises a second clip buckle comprising a male part 30 located at a first end of the second strap 28 and a female part 31 located at a second end of the second strap 28.

[0082] A second positioning mark 32 is shown on the second flexible device 25.

[0083] The second positioning mark 32 is here positioned on the external face of the pouch 26 containing the X-ray film 4. It could also extend from the second strap 28 by being for example sewn or glued to it.

[0084] The second positioning mark 32 is here a second triangle which comprises a vertex positioned on the edge 34 of the pocket 28, and a side parallel to the edge 34.

[0085] The second triangle thus forms an arrow oriented towards the first portion 14 of the flexible body 8 of the first flexible device 7 when the first flexible device 7 and the second flexible device 25 are installed on the part 2.

[0086] The second flexible device 25 is therefore intended to be installed around the part 2 after the installation of the first flexible device 7 and so that the second positioning mark 32 is positioned in a predetermined position defined by a position of one of the first positioning marks 17.

[0087] In Figures 1 and 3, the predetermined position of the second positioning mark 32 is defined by the position of the first positioning mark 17 associated with the letter D.

[0088] The predetermined position of the second positioning mark 32 is here a position in which the apex of the second triangle forming the second positioning mark 32 is at the same axial position (considering the axis of the part 2) and radial position as the apex of the triangle forming the first positioning mark 17 associated with the letter D.

[0089] As seen in [Fig.l], when the first flexible device 7 is installed correctly, that is to say when the reference mark 24 is located in the notch forming the positioning indicator 23, and the second flexible device 25 is positioned correctly, that is to say the second positioning mark 32 is correctly positioned relative to the first positioning mark 17 (associated with the letter D in this case), the pouch 26 rests on the second portion 15 of the flexible body 8 of the first flexible device 7.

[0090] The first flexible device 7 comprises an axial stop making it possible to ensure that the second flexible device 25 is positioned axially correctly on the part 2.

[0091] The difference in thickness between the first portion 14 and the second portion 15 of the flexible body 8 of the first flexible device 7 creates a shoulder 35 which forms this axial stop.

[0092] The axial stop and the positioning marks 17, 32 make it possible to ensure to the operator that the second flexible device 25, and therefore the tip support 3 and the radiographic film 4, are perfectly positioned relative to the first flexible device 7, and therefore relative to the radiographic markers 20, 21 and the reference mark 24.

[0093] We will now describe, with reference to [Fig.4], the implementation of a gammagraphic control method using the positioning system 1.

[0094] The positioning system 1 here comprises, as we have seen, the first flexible device 7 and a plurality of second flexible devices 25, in this case five second flexible devices 25 (as many second flexible devices 25 as first positioning marks 17).

[0095] The operator installs and fixes the first flexible device 7 on the part 2, so that it surrounds the part 2 and is positioned close to the welding bead 16, and so that the positioning indicator 23 is positioned in the reference position defined by the reference mark 24 (step E1).

[0096] The operator tightens the first strap 9 and fixes the first flexible device to the part using the first clip loop 11,12 (step E2).

[0097] Previously, the operator prepared the five second flexible devices 25 (step E3). In particular, he prepared the pouches 26 containing the films 4: loading movies, filters, blocking screens, etc.

[0098] Following step E2, the operator selects one of the first positioning marks 17 (for example the one associated with the letter A), and carries out the following control phase Pc.

[0099] It installs one of the second flexible devices 25 on the part 2, so that it surrounds the part 2 and the second positioning mark 32 is positioned in the predetermined position defined by the position of the first positioning mark 17 chosen. The pocket 26 comes into axial abutment against the shoulder 35 (step E4).

[0100] The operator tightens the second strap 28 and fixes the second flexible device 25 to the part 2 using the second clip loop 30, 31 (step E5).

[0101] Then, the operator introduces and fixes the irradiation tip 5 in the tip holder 3 (step E6).

[0102] The operator then performs the grammatical shot. The radiographic film 4 is impressed by the radiation beam produced by the source (step E7).

[0103] The operator carries out five control phases Pc such as the one just described, that is to say a control phase for each first positioning mark 17 (for example, he selects the letter B after the letter A, then the letter C, etc.). As soon as a control phase PC is carried out, the operator removes the second flexible device 25 and installs another one.

[0104] Each control phase Pc is therefore carried out using a second separate flexible device 25 positioned relative to a first positioning mark 17 separate from the first flexible device 7.

[0105] When he has carried out these five control phases Pc, the operator develops the radiographic films 4 in the dark room (step E8).

[0106] With reference to [Fig. 5], the operator obtains for each shot, after development, a radiographic film 4 similar to that visible in [Fig. 5]. On this film 4, we can distinguish the image of the graduation 20, the image of the two reference elements 21 which make it possible to define the relevant central analysis zone 36 on the film 4, and the image of the IQI 29. The central analysis zone 36 corresponds to the portion of the film 4 located precisely opposite the tip support 3 during the gammagraphic shot.

[0107] The five shots that he took, with the tip support 3 and the film 4 positioned in five separate positions regularly distributed around the weld bead 16, allow the operator to carry out an exhaustive analysis of the weld bead 16.

[0108] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0109] The number of second flexible devices used can of course be other than five. A single second flexible device could be used, either to carry out a single shot, or by replacing the film holder each time and repositioning the second flexible device for the next shot.

[0110] The number of first positioning marks and the manner in which they are represented on the first flexible device (shape, positioning, etc.), could of course be different from what has been described herein. Similarly, the radiographic markers could be different and positioned differently.

[0111] The part on which the controlled weld is located is not necessarily a tubular part.

[0112] The straps could be arranged differently. For example, the first strap could be attached to the inner face of the flexible body of the first flexible device.

[0113] The flexible devices do not necessarily include a strap to fix them to the part. For the first flexible device, for example, the fixing means used (by elastic fitting, hook system, Velcro, etc.) could be directly positioned on the ends of the flexible body.

Claims

1.

2.

3. Claims Positioning system (1), intended to be used during a gammagraphy inspection of a weld bead (16) on a part (2), and comprising: - a first flexible device (7) on which at least one first positioning mark (17) is represented, and comprising a positioning indicator (23) and at least one radiographic marker (20, 21), the first flexible device being arranged to be installed on the part by surrounding it, so that the positioning indicator is positioned in a reference position defined by a position of a reference mark (24) formed on the part, on or near the weld bead; - at least one second flexible device (25) on which a second positioning mark (32) is shown, and comprising a film holder (26) containing an X-ray film (4), and a tip holder (3) arranged to accommodate an irradiation tip (5), the second flexible device being arranged to be installed on the part by surrounding it, after the installation of the first flexible device, so that the second positioning mark (32) is positioned in a predetermined position defined by a position of the first positioning mark (17), the tip holder and the X-ray film then being positioned on the weld bead and opposite each other with respect to the part. Positioning system according to claim 1, comprising a plurality of second flexible devices (25), the first flexible device (7) comprising a plurality of first positioning marks (17) regularly distributed along a length of the first flexible device (7), each second flexible device (25) being intended to be positioned relative to a first positioning mark (17) distinct from the first flexible device (7) to carry out a gammagraphic shot and then to be removed to be replaced by another second flexible device, the positioning system thus making it possible to carry out a plurality of successive gammagraphic shots regularly distributed over a circumference of the weld bead (16). Positioning system according to one of the preceding claims, wherein the first flexible device (7) comprises a flexible body (8) arranged to surround the workpiece, such that a length of the flexible body extends along a contour of the workpiece (2) when the first flexible device is installed, the at least one first positioning mark (17), the positioning indicator (23) and the at least one radiographic marker (20, 21) being positioned on the flexible body.

4. Positioning system according to claim 3, wherein the at least one radiographic marker of the first flexible device comprises a graduation (20) in units of length, comprising graduation elements made of lead, and defined according to the length of the flexible body (8).

5. Positioning system according to one of claims 3 or 4, in which the at least one radiographic marker of the first flexible device (7) comprises at least two reference elements (21), made of lead, and intended to define a central analysis zone (36) on the radiographic film (4).

6. Positioning system according to one of claims 3 to 5, wherein the flexible body (8) of the first flexible device (7) comprises a first portion (14) and a second portion (15) defined in a width of the flexible body, the first portion comprising the at least one first positioning mark, and the second portion comprising the positioning indicator and the at least one radiographic marker.

7. Positioning system according to one of the preceding claims, in which the first flexible device (7) comprises an axial stop making it possible to ensure that the second flexible device (25) is axially positioned correctly on the part.

8. Positioning system according to claims 6 and 7, the second portion (15) of the flexible body (8) being less thick and being intended to be positioned closer to the weld bead (16) than the first portion (14) so that, when the first flexible device (7) and the second flexible device (25) are installed around the part and the second positioning mark (32) is positioned in the predetermined position, the film support (26) rests on the second portion (15), the difference in thickness between the first portion and the second portion creating a shoulder (35) forming the axial stop.

9. Positioning system according to one of claims 3 to 8, the positioning indicator (23) being a notch made in an edge (19) of the flexible body (8), in which the reference mark (24) when the first flexible device (7) is installed on the part.

10. Positioning system according to one of claims 3 to 9, wherein the first flexible device (7) further comprises a first strap (9), to which the flexible body (8) is fixed, and arranged to surround the part and to fix the first flexible device (7) to the part (2).

11. Positioning system according to one of the preceding claims, wherein the second flexible device (25) further comprises a second strap (28), to which the tip holder (3) and the film holder (26) are fixed, and arranged to surround the part and to fix the second flexible device to the part.

12. The positioning system of claim 11, wherein the second positioning mark (32) is positioned on the film holder (26).

13. Gammagraphic inspection method using the positioning system (1) according to one of the preceding claims, and comprising a inspection phase (Pc) comprising the steps of: - installing and fixing the first flexible device (7) on the part (2), so that it surrounds the part and so that the positioning indicator (23) is positioned in the reference position; - then, installing and fixing the second flexible device (25) on the part, so that it surrounds the part and the second positioning mark (32) is positioned in the predetermined position; - introducing and fixing the irradiation tip (5) in the tip holder (3), and carrying out a grammagraphic shot.

14. Gammagraphic control method according to claim 13, using a positioning system (1) according to claim 2, the gammagraphic control method comprising several control phases (Pc) carried out successively, each control phase being carried out using a second separate flexible device (25) positioned relative to a first positioning mark (17) separate from the first flexible device (7).

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