Method for detecting cracks in a tubular pipe

Abstract

The invention relates to a method for detecting and characterising a stress corrosion crack in a tubular pipe (2) at a welded joint (3), the method comprising: a) for measurement positions, positioning the measurement probe (1) and consecutively transmitting and receiving a first, direct-mode, plane-wave burst configured to scan a first region of interest (50) defining an angular range of interest, and at least one second, indirect-mode, burst scanning the angular range of interest; b) constructing a first representation on the basis of the first bursts and a second representation on the basis of the second bursts; c) identifying a trace (220, 240) that appears as a localised variation in amplitude in the first representation and the second representation, with two amplitude peaks (254, 252) in the first representation; d) determining a height of the corrosion crack on the basis of a distance between the two amplitude peaks (254, 252) of the trace (220, 240).

Description

[0001] METHOD FOR DETECTING CRACKS IN A PIPELINE

[0002] TUBULAR

[0003] Technical field

[0004] The present invention relates generally to non-destructive testing, and more specifically to a method for detecting and characterizing defects in a tubular pipe. Such a method is applicable in many industrial sectors including, but not limited to: electricity production, petrochemicals, chemistry, the food industry, and more generally, industries operating with fluids circulating in welded steel tubular pipes.

[0005] Technological background

[0006] Tubular pipes are generally made up of several sections linked together by joints. These joints can notably be welds.

[0007] A steel tubular pipe carrying fluid is subject to high stresses, especially when these tubular pipes undergo significant temperature and pressure variations, and also chemical attacks carried by the fluids (gas, water, hydrocarbons, etc.). Defects, called fatigue defects, may appear, resulting in cracks in the pipe material. It should be noted that only the outside of the pipe is generally accessible, and that inspections must be carried out from this exterior only. Many non-destructive testing processes have been developed to detect these fatigue defects, and in particular processes using ultrasonic waves.

[0008] However, current methods are not suitable for certain materials or for significant thicknesses of the pipe wall under stress. In addition, other types of defects may appear, which current non-destructive testing methods cannot reliably detect or characterize. This is particularly the case for stress corrosion cracks. Stress corrosion of a metal or alloy results from the combined action of a tensile mechanical stress (residual or applied stress) and an aggressive surrounding environment for a material sensitive to the phenomenon. It is generally considered that these three conditions (stress, environment and sensitivity of the material to the phenomenon) must be met simultaneously to observe stress corrosion.Unlike fatigue cracks, stress corrosion cracks, or SCCs, are branched and very slightly open cracks, and above all extend from the inside of the pipe, near a welded junction between two sections of the tubular pipe. Due to the large number of welds on tubular pipes that an industrial installation may have, it is necessary to have a method that not only detects these SCCs, but also characterizes them. Characterization means the location of an SCC and the determination of the height of an SCC, i.e. its radial extension from the inside of the pipe. It is desirable to be able to reliably characterize SCCs even when they are low in height, for example a few millimeters, in order to anticipate pipe degradation.Such sensitivity is all the more difficult since monitoring using ultrasonic waves from the outside requires the said ultrasonic waves to pass through the entire thickness of the wall of the tubular conduit.

[0009] Crack detection and characterization is even more difficult when the tubular pipe is made of austenitic stainless steel. Austenitic stainless steels are steels with a coarse microstructure (large grain size). These different elements generate significant structure-borne noise and attenuate the propagation of the ultrasonic beam, which makes the use of ultrasound complex.

[0010] Presentation of the invention

[0011] A method for detecting and characterizing a stress corrosion crack in a steel tubular pipe at an inspection zone extending from a welded junction between two portions of the tubular pipe by means of an ultrasonic probe is proposed, comprising: a) for a plurality of measurement positions distributed circumferentially around the tubular pipe on an outer surface of the tubular pipe at the welded junction: a1) placing the measurement probe against the outer surface at the measurement position, the measurement probe having an emission surface forming an angle of between 10° and 30° relative to a plane tangent to the outer surface of the tubular pipe supporting the measurement probe, a2) successively transmitting and receiving at least two bursts of ultrasound of the same frequency to obtain a plurality of measurement signals,a first plane wave burst in direct mode being configured to scan a first area of ​​interest encompassing the inspection area and the welded joint with a beam axis scanning an angular scanning range at least 10° greater than an angular range of interest occupied by the area of ​​interest relative to a plane tangent to the outer surface of the tubular pipe supporting the measuring probe, and at least one second burst in indirect mode scanning the angular range of interest, b) constructing a first representation from the first bursts at a plurality of measurement positions distributed circumferentially around the tubular pipe in which a characteristic area of ​​the welded joint appears, and constructing a second representation from the second bursts at a plurality of measurement positions distributed circumferentially around the tubular pipe,the first representation and the second representation being two-dimensional data sets associating an amplitude with a location in a two-dimensional space, c) identifying a trace of a stress corrosion crack appearing as a localized variation in amplitude in the first representation and the second representation, the trace having two amplitude peaks in the first representation constructed from the first direct-mode plane wave bursts, d) determining a height of the corrosion crack from a distance between the two amplitude peaks of the trace in the first representation constructed from the first direct-mode plane wave bursts, the height of the crack extending from an internal surface of the tubular pipe.,

[0012] With the proposed method, it is possible to accurately determine the height of a stress corrosion crack from the outside of the tubular pipe, allowing increased accuracy in assessing the condition of the tubular pipe, especially when the tubular pipe is made of austenitic stainless steel.

[0013] This process is advantageously supplemented by the following characteristics, taken alone or in any technically possible combination thereof:

[0014] - the plurality of bursts comprises at least one plane wave indirect mode burst and at least one spherical wave indirect mode burst, the second construction being obtained from at least one of the plane wave indirect mode burst and the spherical wave indirect mode burst;

[0015] - the plurality of bursts comprises a direct mode and plane wave burst whose region of interest extends over the entire thickness of the pipe, including the interior surface of the pipe;

[0016] - the trace of a stress corrosion crack has a first amplitude peak with a maximum amplitude greater than at least 1.5 times a maximum amplitude of the second amplitude peak;

[0017] - the trace of a stress corrosion crack has an amplitude trough separating the first amplitude peak and the second amplitude peak, with a minimum amplitude less than 1.5 times the maximum amplitude of the second peak;

[0018] - the first amplitude peak corresponds to a foot of the stress corrosion crack opening onto the internal face of the tubular wall, and the second amplitude peak corresponds to a head of the stress corrosion crack opposite the foot of the crack;

[0019] - the characteristic zone of the welded joint is a trace of an echo of penetration of the ultrasound appearing as a localized variation of amplitude in the first representation or is a trace of a transition zone between a wall of the tubular conduit and a melted zone of the welded joint, said trace of the transition zone appearing as a line of variation of amplitude;

[0020] - in step c), the trace of a stress corrosion crack is searched for in a search area likely to contain traces of stress corrosion crack, this search area being located by means of the trace of the penetration echo, or by means of the trace of the transition zone;

[0021] - the measuring probe is carried by a movable assembly on a collar extending over and around the welded joint, and placing the measuring probe at a measuring position among the plurality of measuring positions distributed circumferentially around the tubular conduit comprises moving the movable assembly along the collar to said measuring position;

[0022] - the mobile assembly comprises a carriage configured to be moved along the collar and an instrument holder configured to couple the carriage and the measuring probe;

[0023] - the instrument holder comprises at least one index wheel configured to rotate as the carriage moves along the collar around the tubular conduit, associated with an indexing sensor capable of quantifying the rotation of the index wheel, and the emission of bursts of ultrasonic waves is conditioned by index information recorded by the indexing sensor.

[0024] The invention also relates to a computer program product comprising program code instructions for executing the steps of the method according to the invention, in particular steps b), c) and d), when said program is executed on a computer. The computer program product may take the form of a non-volatile medium on which the instructions are stored.

[0025] Presentation of figures

[0026] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0027] - Figure 1 is a diagram showing steps of the method according to a possible embodiment of the invention;

[0028] - figure 2 schematically shows a measuring probe near a welded junction between two portions of the tubular conduit, according to a possible embodiment of the invention;

[0029] - Figure 3 schematically shows the relative orientations of two sets of transducer elements of the ultrasonic measuring probe, according to a possible embodiment of the invention;

[0030] - figure 4a shows an overall view of a collar of a wearer of the measuring probe, according to a possible embodiment of the invention;

[0031] - figure 4b shows an example of a clasp of the necklace of figure 4a, according to a possible embodiment of the invention;

[0032] - figure 5 shows an example of a carriage of a measuring probe carrier, according to a possible embodiment of the invention;

[0033] - figure 6 shows an overall view of an example of a carrier, according to a possible embodiment of the invention;

[0034] - figure 7 shows an overall view of an instrument holder of a measuring probe carrier, according to a possible embodiment of the invention;

[0035] - figure 8 schematically shows the emission of a first burst of ultrasound, according to a possible embodiment of the invention;

[0036] - figure 9 schematically shows the emission of a second burst of ultrasound or a third burst of ultrasound, according to a possible embodiment of the invention;

[0037] - figure 10 schematically shows the emission of a fourth burst of ultrasound, according to a possible embodiment of the invention; - figure 11 shows examples of representations resulting from a construction from the measurement signals;

[0038] - Figure 12 shows examples of representations resulting from a construction from the measurement signals;

[0039] - Figure 13 shows two amplitude peaks of a stress corrosion crack trace appearing as a localized amplitude variation in a representation.

[0040] Detailed description

[0041] With reference to Figure 1 and Figure 2, a method for detecting and characterizing a stress corrosion crack in a steel tubular pipe 2 will be described, at a welded junction 3 between portions 2a, 2b of the tubular pipe 2. A molten zone 3a, or weld bead, is present between the respective ends of the portions 2a, 2b of the tubular pipe 2. A first SOI step consists of carrying out measurements for a plurality of measurement positions distributed circumferentially on an outer surface of the tubular pipe at a welded junction 3 between two portions 2a, 2b of the tubular pipe by means of an ultrasonic measuring probe 1.For each measurement position, the ultrasonic measurement probe 1 (step SOI 1) is first placed against the surface outside the measurement position, and then at least two bursts of ultrasound of the same frequency are successively transmitted and received to obtain a plurality of measurement signals (step S012) at this measurement position.

[0042] As illustrated in FIG. 2, the ultrasonic measuring probe 1 is arranged against the outer surface 2a of the tubular conduit 2 at a measuring position. The ultrasonic measuring probe 1 has an active emission surface 4 forming an angle of between 10° and 30° relative to a plane tangent to the outer surface 2a of the tubular conduit 2 supporting the ultrasonic measuring probe 1. To do this, the ultrasonic measuring probe 1 comprises a shoe 6 comprising an interface surface 6a in contact with the outer surface of the tubular conduit, and an inclined plane (typically with an angle of between 10° and 30° relative to the interface surface) on which the active emission surface 4 of the ultrasonic measuring probe 1 is arranged, comprising sets of ultrasonic transducers 8. A coupling medium such as water may be arranged between the interface surface 6a of the shoe 6 and the outer surface of the tubular conduit.The shoe 6 can be made of any material allowing both the ultrasonic transducers 8 to be held in position and the ultrasonic waves to be transmitted through the shoe 6. For example, the shoe can be made of crosslinked polystyrene.

[0043] The ultrasonic measuring probe 1 is configured to highlight the trace of a stress corrosion crack appearing as a localized variation in amplitude in a representation from the measurement signals, the trace having two distinct amplitude peaks. To do this, it is possible to vary several parameters of the measuring probe 1, depending on the equipment used. Below are presented some parameters allowing good results to be obtained, although these do not necessarily have to be required for the implementation of the method.

[0044] The ultrasonic measuring probe 1 is configured to emit bursts of ultrasonic waves at a frequency between 2 and 10 MHz, and preferably between 2 and 7.5 MHz. The ultrasonic measuring probe 1 is multi-element and comprises two sets 8a, 8b of transducer elements aligned in the form of strips, as illustrated in FIG. 3. In use, one strip 8a is used for transmission while the other strip 8b is used for reception.

[0045] The two bars 8a, 8b may be separated by 2 to 10 mm, and preferably by 0.5 mm to 3.5 mm. The bars are arranged to obtain a refracted angle of between -10° and 70°, in an austenitic steel with an approximate speed of the ultrasonic waves of 5700 m / s, after a path in the shoe 6 of between 10 mm and 30 mm. The bars 8a, 8b may for example each comprise between 32 and 34 transducer elements. The pitch between the transducer elements may be for example between 0.6 mm and 1 mm.

[0046] Preferably, the bars 8a, 8b are not arranged on the same plane, nor parallel. In particular, the bars 8a, 8b may be arranged with a squint angle P, or "squint angle" in English, which may be approximated by half the angle formed by the alignments of transducer elements of each bar. The squint angle P may be between 0.1° and 3°. The bars 8a, 8b may have a roof angle a, that is to say a half-angle formed by the axes of the two acoustic beams, between 1.25° and 3.25°.

[0047] The two phases of the measuring step are repeated several hundred times, the number of measuring positions being preferably greater than 100 around the welded junction 3. In order to allow easy placement of the ultrasonic measuring probe 1 at each measuring position, it is possible to use a probe carrier 10 as illustrated in Figure 6 and detailed in Figures 4a, 4b, 5, and 7. The purpose of the probe carrier 10 is to carry the measuring probes 1 so that said measuring probes 1 can be movable on and along the probe carrier 10. The probe carrier 10 is placed around the control zone near or on the welded junction 3, thus surrounding the tubular elements.Preferably, the carrier 10 comprises several elements: a circular collar 12 enclosing the tubular conduit 2, and an assembly movable along the collar, which may in particular comprise a carriage 14 configured to be moved along the collar 12 and an instrument holder 16 configured to couple the carriage 14 and the measuring probe 1.

[0048] Figure 4a shows an example of a circular collar 12 intended to be mounted on the periphery of the tubular conduit 2 and to grip it. The collar 12 is articulated, comprising several sections 12a, 12b, 12c in the form of circular arcs connected two by two by pivot connections, as well as a clasp 18 comprising several closing positions. Figure 4b shows an example of a clasp 18. A section 12b of the collar is extended by an arm 20 carrying at its end a crosspiece 22 transverse to the arm 20. Another section 12a of the collar comprises housings 24 configured to receive the crosspiece 22 after radial insertion thereof and to hold it against circumferential traction. The housings 24 are distributed at several circumferential positions, allowing tightening adapted to the external diameter of the tubular conduit 2 by offering closing positions for several diameters.

[0049] Figure 5 shows an example of a trolley, comprising at least two curved portions 14a, 14b connected by a joint 26, typically establishing a pivoting connection. In this example, a locking member 28 straddling the two curved portions 14a, 14b is actuable by a control member 30 which can also act as a handle for movement. Other dedicated handles 32 may be provided. The locking member 28, preferably a pneumatic cylinder, can move from an unlocking position in which the two curved portions 14a, 14b are movable thanks to the joint 26 to a locking position in which the joint 26 is locked, preventing relative movement between the two curved portions 14a, 14b.When the carriage 14 is placed on the collar 12, the articulation 26 is left movable by the locking member 28, and the internal faces of the curved portions 14a, 14b are arranged against the external face of the collar 12. By an action on the control member 30, for example a pressure if it is a pusher, the articulation 26 is then locked by the locking member 30. The carriage 14 also comprises wheels 34 sized to be in contact with the external face of the tubular conduit 2 when the carriage 14 is in place on the collar 12 enclosing this external face of the tubular conduit 2.

[0050] As illustrated in Figure 6, the carriage 14 and the instrument holder 16 are configured so that the instrument holder 16 is mounted integral with the carriage 14. The movement of the carriage 14 therefore causes the movement of the instrument holder 16. As visible in Figure 7, the instrument holder 16 comprises at least one support arm 36 configured to receive an ultrasonic measuring probe 1 on brackets 38 for fixing said support arms 38, offset from the welded joint 3. Preferably, the instrument holder 16 comprises a support arm 36 on each side of its circumferential direction of movement. The instrument holder 16 also comprises at least one index wheel 40, 42, configured to rotate as the carriage 14 moves along the collar 12 around the tubular conduit 2, associated with an indexing sensor capable of quantifying the rotation of the index wheel 40, 42.Preferably, the instrument holder 16 comprises two index wheels 40, 42: a first wheel 40 configured to roll on the tubular conduit 2 and intended for marking on the curvilinear abscissa during the circular movement of the instrument holder 16, and a second wheel 42 configured to roll on a guide 43 between a central portion of the instrument holder 16 and the arm 36 in order to determine an axial offset (along the main axis of the tubular conduit at the welded junction 3) of this arm 36 and therefore of the measuring probe 1 carried by this arm 36 relative to the welded junction 3.

[0051] As can be seen in Figure 2, at a measurement position, the measurement probe 1 is not located radially facing the welded junction 3 or the inspection zone extending from the latter in which the FC S are likely to be located. The measurement probe is arranged so as to encompass in an oblique scan an area of ​​interest 44 encompassing the inspection zone and the welded junction 3, and is therefore offset relative to them. By positioning the collar 12 on the welded joint 3, at the weld bead (melted zone 3a), and by holding the measuring probe 1 by an arm 36 extending from the movable assembly mounted on the collar 12, correct positioning of the measuring probe 1 is obtained for all the measuring positions, which makes it possible to inspect an inspection zone extending all around the welded joint 3 and extending laterally relative to the welded joint 3.

[0052] When the collar 12 is mounted on the tubular conduit 2, and the carriage 14 is provided with the instrument holder 10 mounted on the collar 12, the measuring probe 1 can be moved successively between the measuring positions around the circumference of the tubular conduit 2. The rotational movement can be caused manually by pushing on a handle 32, or a motorization can be provided to move the carriage 14 along the collar 12, for example by motorizing the wheels of the carriage 14. During the movement of the carriage 14, the index wheel 40, 42 makes it possible to determine that a new measuring position has been reached, typically after a predetermined distance has been traveled (typically 1 to 3 mm), and the sensor sends index information to the measuring probe 1 or to a control unit to which the measuring probe 1 is connected, in order to cause the emission of bursts of ultrasound at this measuring position.The emission of bursts of ultrasonic waves is thus conditioned by the index information recorded by the indexing sensor. As a result, it is sufficient to make the mobile assembly travel the circumference of the tubular conduit 2 along the collar 14 to travel the plurality of measurement positions distributed circumferentially on an outer surface of the tubular conduit 2, and acquire the corresponding measurement signals there.

[0053] At each measurement position, the measurement probe 1 successively transmits and receives at least two bursts of ultrasound of the same frequency to obtain a plurality of measurement signals. Preferably, at least three bursts of ultrasound are successively transmitted and received, and more preferably at least four bursts of ultrasound are successively transmitted and received. In the following example, four bursts of ultrasound are successively transmitted and received. The order of the bursts is given for information purposes only and may be modified.

[0054] A first burst emits in longitudinal plane wave in direct mode (i.e. considering only a direct round trip of the ultrasonic waves between the transducer elements in the region of interest, without taking into account possible additional paths linked to rebounds and associated with 1 or more changes in the propagation mode of the ultrasound) and is configured to scan a first zone of interest 50 with a beam axis scanning an angular scanning range greater by at least 10° than an angular range of interest occupied by the first zone of interest 50 with respect to a plane tangent to the external surface of the tubular pipe 2 supporting the measuring probe 1.The first area of ​​interest 50 is centered on an area 54, located between the welded junction 3 and the measuring probe 1, where the FCS are likely to be located, and on the one hand follows the contours of a portion of the tubular conduit at the welded junction 3, and extends a few millimeters from the latter in said portion of tubular conduit 2, typically over a distance ranging from 5 mm to 20 mm from the melted area 3a. The first area of ​​interest 50 also extends from the inside of the tubular conduit 2, a few millimeters (typically between 5 and 10 mm) from the internal surface 52 of the tubular conduit 2, up to a height of at least 15 mm, and preferably at least 20 mm in the thickness of the wall of the tubular conduit 2. Preferably, the first area of ​​interest 50 passes through the welded junction 3.

[0055] For example, the first area of ​​interest 50 may be located at a location between angles 45° and 60° relative to a plane tangent to the outer surface 5 of the tubular conduit 2, from the penetration of the ultrasonic waves into the wall of the tubular conduit 2, which is referred to as the angular range of interest. The transducer elements are then controlled to emit ultrasound by scanning an angular scanning range, for example by means of emission delays between them. Scanning is understood to be the displacement of a beam axis corresponding to an axis of higher intensity of the ultrasound or to a median axis of the emitted ultrasound beam. This angular scanning range extends on either side of the first angular range of interest 50, preferably by at least 5° on each side of the angular range of interest, and more preferably by at least 10°.For example, for an angular range of interest extending between angles 45° and 60°, a scanning angular range might be between 28° and 70° with an angular step between 1° and 3°.

[0056] A second burst of ultrasound is emitted, with plane waves in indirect mode sweeping the angular scanning range. The waves can then be transverse, or longitudinal or a combination of the two. The flight time of the waves is longer, which results, as illustrated in Figure 9, in taking into account waves having undergone multiple reflections, and in particular in taking into account waves having undergone reflection on the internal surface of the tubular conduit. The second area of ​​interest 56 then encompasses and extends the first area of ​​interest in a distal direction opposite to the measuring probe 1. A third burst of ultrasound is emitted according to the same modalities as the second burst of ultrasound, however with spherical waves rather than plane waves. The second ultrasound burst and the third ultrasound burst serve to distinguish FCS from other artifacts in the measurement 1 signals, and are complementary.

[0057] A fourth burst of ultrasound, illustrated by Figure 10, in direct mode, is this time centered on a fourth area of ​​interest 58 extending below the measuring probe 1, over the entire thickness of the wall of the tubular conduit 2, and more precisely from the shoe 6 of the measuring probe 1 to more than one thickness of the wall beyond the internal surface 52 of the wall of the tubular conduit. Preferably, this fourth area of ​​interest 58 does not reach the welded junction 3. This fourth burst is used to take into account the echoes of the shoe-conduit interface (in order to determine the coupling), the background echoes on the internal surface 52 of the wall of the tubular conduit 2, and their repetitions, in order to be able to determine the attenuation of the ultrasound.

[0058] Once the measurement signals have been obtained for the plurality of measurement positions, a reconstruction of a first representation is carried out from the first bursts in which a characteristic area of ​​the welded joint 3 appears. A construction of at least one other representation is also carried out from the measurement signals of the second bursts, and where the third bursts. Preferably, a reconstruction is carried out for each of the other bursts: there is thus a construction of a representation from the second bursts, a construction of a representation from the third bursts and a reconstruction of a representation from the fourth bursts.The reconstructions of the different representations from the different bursts of ultrasound, in general, can be made with or without mode conversion, that is to say by exploiting the passage from a longitudinal mode to a transverse mode or vice versa, as is practiced and well known in the state of the art. By mode, we mean the mode of propagation of the ultrasound: a longitudinal mode which corresponds to the main direction of propagation of the ultrasonic wave, and a transverse mode which is normal to the longitudinal mode.

[0059] Preferably, the reconstruction is performed using the total focusing method, or TFM, which systematically applies the basic focusing principle of phased array ultrasound within a defined region of interest. The region of interest is segmented into a grid of positions, or "pixels," and multi-element beamforming focusing is applied to each pixel within this grid. TFM generates a representation of the region of interest that is focused everywhere and at all depths.

[0060] Figures 11 and 12 show examples of representations thus obtained. The representations are two-dimensional data sets associating an amplitude with a location in a two-dimensional space. The representations can therefore take the form of images, as in these figures. Figure 11 shows for example a first representation 100 obtained from the first bursts, according to a plane transverse to the welded junction (T-scan), and therefore perpendicular to the circumference of the pipe. The contour of the ends of the two portions 102, 104 coupled by the welded junction is represented there, which makes it possible to highlight a trace of penetration echo 106 of the ultrasound at the weld bead (melted zone 3 a) appearing as a localized variation of amplitude in the first representation 100. The trace of the penetration echo is therefore a characteristic zone of the welded junction 3.There is also found the trace of a transition zone 108 between a wall of the tubular conduit 2 and a melted zone 3a of the welded junction 3, said trace of the transition zone 108 appearing as a line of amplitude variation which follows the geometry of the end of the portion 2a of the tubular conduit 2. The trace of the transition zone 108 is also a characteristic zone of the welded junction 3. Other characteristic zones of the welded junction 3 can be highlighted, since they appear in a representation even in the absence of a defect.

[0061] A search area 110 likely to contain traces of stress corrosion cracking has been circled in dotted lines. It is in this search area 110 that a possible trace of a stress corrosion crack appearing as a localized variation in amplitude in the first representation is searched for. For example, the search area 110 extends in a portion 102 from its end to a distance extending between 5 and 20 mm in the portion 102. The penetration echo trace 106 makes it possible to know the position of the welded junction between two portions of the tubular pipe, and therefore to locate, in the first representation, the area 110 likely to contain FCS.Figure 10 also shows another representation 112 constructed from the first bursts, but according to a different plane since it is here a C-scan, corresponding to an unrolling of the internal surface of the tubular conduit, where the weld bead 114 appears as an alignment of traces. The search zone 116 likely to contain FCS has been surrounded by dashes.

[0062] In the example of Figure 11, there is no trace of a stress corrosion crack in the search area 110 of the first representation in the plane transverse to the welded junction. Figure 12 shows another example, with a first representation 200 obtained from the first bursts, according to a plane transverse to the welded junction (T-scan). There we find the outline of the ends of the two portions 202, 204 coupled by the welded junction 3, and the penetration echo trace 206 making it possible to locate the search area 210 likely to contain traces of stress corrosion cracks. There is also found the trace of a transition zone 208 between a wall of the tubular conduit 2 and a melted zone 3a of the welded junction 3, said trace of the transition zone 208 appearing as a line of amplitude variation which follows the geometry of the end of the portion 2a of the tubular conduit 2.The search zone 116 likely to contain FCS may in particular extend into portion 2a from this trace of the transition zone 208.

[0063] In this example, there is a trace 220 of a stress corrosion crack appearing as a localized variation in amplitude in the first representation.

[0064] Other representations are illustrated, in which the location of the trace 220 has been located by a frame 222. There we find the C-scan 212, with the weld bead 214. The first representation 200 and the C-scan 212 come from the first bursts, and therefore come from waves in direct mode. At least one other representation (designated as a second representation) is constructed from bursts other than the first bursts, said other bursts being in indirect mode. These are typically the second bursts and / or the third bursts. This other representation is used to distinguish the trace of the corrosion crack among the artifacts.In this example we have a second representation 230 in T-Scan, and a second representation in C-scan 240, which can be constructed from the second bursts or the third bursts, or by combining the measurement signals of the second bursts and the third bursts, and for example by subtracting them.

[0065] A trace of a stress corrosion crack appears as a localized variation in amplitude in the first representation and the second representation, the trace having two amplitude peaks in the first representation. If a localized variation in amplitude does not appear in the second representation 230, 240, then a localized variation in amplitude in the first representation is not identified as a trace of a stress corrosion crack. Since the measurement signals result from the bursts in indirect mode, they are less sensitive to possible artifacts, and therefore make it possible to distinguish the traces of stress corrosion cracks from other artifacts. These artifacts are for example caused by a deflection of the ultrasonic wave beam, a variation in geometry of the portions of the tubular pipe 2, the structure of the material constituting the tubular pipe 2, or the internal surface condition of the tubular pipe 2.It is thus possible to identify traces of stress corrosion cracks (step S03).

[0066] When a trace of a stress corrosion crack has been identified, a height of the corrosion crack can be determined from a distance between the two amplitude peaks of the trace (step S04). Figure 13 shows, at the bottom, an example of a trace 240 of a stress corrosion crack identified in a first representation in transverse plane. It can be seen that the local variation in amplitude of the trace 240 comprises two distinct parts: a first part 242, larger both in amplitude and in area, and a second part 244, smaller both in amplitude and in area.The first part 242 of the trace 240 corresponds to the root of the stress corrosion crack, that is to say to the part of the crack which opens onto the internal face of the tubular pipe, while the second part 244 of the trace 240 corresponds to the head of the stress corrosion crack, that is to say to the part of the crack which is deepest in the wall, and therefore furthest from the internal face 52 of the tubular pipe.

[0067] Above this example is represented a graph 250 showing the amplitudes corresponding to the trace 240. A first amplitude peak 252 can be clearly seen which corresponds to the root of the crack and a second amplitude peak 254 which corresponds to the head of the crack. The first amplitude peak 252 has an amplitude greater than the second amplitude peak 254, typically with a maximum amplitude of the first amplitude peak 252 greater than the maximum amplitude of the second amplitude peak 254, and preferably at least 1.5 times greater than the maximum amplitude of the second amplitude peak 254, and more preferably at least twice greater. The amplitudes are not necessarily directly amplitudes of the measurement signals, but can be any indicator linked to the energy of the measurement signals.

[0068] It should be noted that the various parameters of the measuring probe can be modified in order to reveal preferential characteristics on the trace 240. In particular, it is sought to reveal a maximum of energy on the head of the crack, that is to say that one seeks to obtain a very pronounced first amplitude peak 252. One also seeks to maximize the distance between the two amplitude peaks 252, 254. Finally, one seeks to obtain an amplitude trough 256 between the two amplitude peaks 252, 254, preferably with an amplitude trough 256 whose minimum is less than 1.5 times the maximum amplitude of the second peak 254.

[0069] In order to calculate the distance between the two amplitude peaks 252, 254 of the trace 240, it is possible to determine the distance between the respective maximums of these amplitude peaks 252, 254. The distance between the two amplitude peaks 252, 254 of the trace 240 is directly related to the height of the crack, that is to say to the depth of the crack between its root and its head. Knowledge of the height of the stress corrosion crack makes it possible to characterize the stress corrosion crack, and therefore to evaluate the significance of this stress corrosion crack in terms of mechanical strength of the tubular pipe.

[0070] It is then possible to determine whether a maintenance operation, such as reinforcing the tubular conduit with a hoop or replacing a portion of the tubular conduit, must be carried out, and when. It is also possible to monitor the height of the cracks over time by re-checking the tubular conduit 2. It is therefore possible to plan such maintenance operations and then carry them out.

[0071] The invention is not limited to the embodiment described and shown in the attached figures. Modifications remain possible, in particular from the point of view of the constitution of the various technical characteristics or by substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims

Claims 1. A method for detecting and characterizing a stress corrosion crack in a steel tubular pipe (2) at an inspection zone (54) extending from a welded junction (3) between two portions (2a, 2b) of the tubular pipe (2) by means of an ultrasonic probe (1), comprising: a) for a plurality of measurement positions distributed circumferentially around the tubular pipe (2) on an outer surface (5) of the tubular pipe (2) at the welded junction (3): a1) placing the measuring probe (1) against the outer surface (5) at the measurement position, the measuring probe (1) having an emission surface forming an angle of between 10° and 30° relative to a plane tangent to the outer surface (5) of the tubular pipe (2) supporting the measuring probe (1), a2) successively transmitting and receiving at least two bursts ultrasound of the same frequency to obtain a plurality of measurement signals,a first plane wave burst in direct mode being configured to scan a first area of ​​interest (50) encompassing the inspection area (54) and the welded joint (3) with a beam axis scanning an angular scanning range at least 10° greater than an angular range of interest occupied by the area of ​​interest with respect to a plane tangent to the outer surface (5) of the tubular pipe (2) supporting the measuring probe, and at least one second burst in indirect mode scanning the angular range of interest, b) constructing a first representation from the first bursts at a plurality of measurement positions distributed circumferentially around the tubular pipe in which a characteristic area of ​​the welded joint (3) appears, and constructing a second representation from the second bursts at a plurality of measurement positions distributed circumferentially around the tubular pipe,the first representation and the second representation being two-dimensional data sets associating an amplitude with a location in a two-dimensional space, c) identifying a trace (220, 240) of a stress corrosion crack appearing as a localized variation in amplitude in the first representation and the second representation, the trace (220, 240) having two amplitude peaks (254, 252) in the first representation constructed from the first direct mode plane wave bursts, d) determining a height of the corrosion crack from a distance between the two amplitude peaks (254, 252) of the trace (220, 240) in the first representation constructed from the first plane wave bursts in direct mode, the height of the crack extending from an internal surface (52) of the tubular conduit (2).

2. The method of claim 1, wherein the plurality of bursts comprises at least one plane wave indirect mode burst and at least one spherical wave indirect mode burst, the second construction being obtained from at least one of the plane wave indirect mode burst and the spherical wave indirect mode burst.

3. A method according to any preceding claim, wherein the plurality of bursts comprises a direct mode and plane wave burst whose region of interest extends over the entire thickness of the pipe, including the inner surface of the pipe.

4. A method according to any preceding claim, wherein the trace (220, 240) of a stress corrosion crack has a first amplitude peak (252) with a maximum amplitude greater than at least 1.5 times a maximum amplitude of the second amplitude peak (254).

5. The method of claim 4, wherein the trace (220, 240) of a stress corrosion crack has an amplitude trough separating the first amplitude peak (252) and the second amplitude peak (254), with a minimum amplitude less than 1.5 times the maximum amplitude of the second peak (254).

6. Method according to any one of claims 4 or 5, in which the first amplitude peak (252) corresponds to a foot of the stress corrosion crack opening onto the internal face (52) of the tubular wall (2), and the second amplitude peak (254) corresponds to a head of the stress corrosion crack opposite the foot of the crack.

7. Method according to any one of the preceding claims, in which the characteristic zone of the welded junction (3) is a trace of a penetration echo (106, 206) ultrasound appearing as a localized variation in amplitude in the first representation or is a trace of a transition zone (208) between a wall of the tubular conduit (208) and a melted zone (3a) of the welded junction (3), said trace of the transition zone (208) appearing as a line of variation in amplitude.

8. Method according to the preceding claim, in which in step c), the trace (220, 240) of a stress corrosion crack is searched for in a search zone (110) likely to contain traces of stress corrosion crack, this search zone (110) being located by means of the trace of the penetration echo (106, 206), or by means of the trace of the transition zone (108, 208).

9. A method according to any preceding claim, wherein the measuring probe (1) is carried by a movable assembly on a collar (12) extending over and around the welded joint (3), and positioning the measuring probe (1) at one of the plurality of measuring positions distributed circumferentially around the tubular conduit (2) comprises moving the movable assembly along the collar (12) to said measuring position.

10. Method according to the preceding claim, in which the mobile assembly comprises a carriage (14) configured to be moved along the collar (12) and an instrument holder (16) configured to couple the carriage (14) and the measuring probe (1).

11. Method according to the preceding claim, in which the instrument holder (16) comprises at least one index wheel (40, 42) configured to rotate as the carriage (14) moves along the collar (12) around the tubular conduit (2), associated with an indexing sensor capable of quantifying the rotation of the index wheel, and the emission of bursts of ultrasonic waves is conditioned by index information recorded by the indexing sensor.

12. Computer program product comprising program code instructions for executing steps b), c) and d) of the method according to any one of the preceding claims, when said program is executed on a computer.

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