METHOD FOR MANUFACTURING AND TESTING A HIGH-STRENGTH STEEL PIPE PRODUCT AND TEST PROBE

Description

[0001] The invention relates to a method for manufacturing and testing a high-strength tubular product and a test probe, in particular for use in the method.

[0002] High-strength and ultra-high-strength steel tubular products are used in many technical and industrial applications. The production of such high-strength and ultra-high-strength steel tubular products is described, for example, in EP 3 233 577 B1, DE 10 2018 106 546 A1, DE 10 2018 123 316 A1, and DE 10 2019 103 502 A1 for various applications. Airbag tubes are specifically described there as such tubular products.

[0003] Such high-strength or ultra-high-strength steel tube products must be inspected for defects due to the stresses they endure in their intended technical and / or industrial applications, particularly in the areas formed during the manufacturing process from an original steel tube. The forming of the tubes can be carried out using a variety of common forming processes, such as hot forming and cold forming.

[0004] This invention specifically addresses the testing of formed end sections of a high-strength tubular product. Various testing methods are available. One option is to perform an ultrasonic test of the tubular product in a liquid (coupling medium). However, it must be considered that the tested tubular product must be cleaned and dried after testing for further processing, which results in higher energy and time expenditure during both the manufacturing and testing phases. Furthermore, the liquid used may cause corrosion of the high-strength tubular product. Additionally, this testing technology cannot reliably detect all relevant types of defects.

[0005] Another way to test the surfaces in the formed end regions of a pipe product is to use eddy current testing with appropriate

[0006] The testing of pipe products involves the use of eddy current testing with appropriate eddy current sensors. Eddy current testing is both non-contact and non-destructive, but can only be used to test electrically conductive materials, which is the case for steel pipe products. Eddy current testing utilizes the effect that impurities and damage in an electrically conductive material also have a different conductivity or permeability than the material itself. The measurement signal depends on the three parameters of conductivity, permeability, and the distance between the detector and the material surface, allowing for the detection of surface damage to the object being tested. Furthermore, eddy current testing can also be used to measure coating thickness and to examine material properties, particularly microstructure.Within the scope of the invention, the focus here is essentially on the defect inspection of the surfaces or wall surfaces of the manufactured pipe product in its formed end areas.

[0007] When testing for surface or wall damage, a suitable eddy current sensor is moved across the object being tested. As long as the electrical resistance is homogeneous and the eddy currents flow freely through the material, the material or surface is undamaged. Both damage to the material or surface and the inclusion of foreign material in the sample wall change the resistance and the eddy current intensity. This change can be detected using eddy current testing and visualized or identified using appropriate imaging techniques via an evaluation algorithm. The coils of the eddy current sensors used are configured to largely compensate for small changes in material properties or the distance of the sensor from the material surface.

[0008] For example, DE 196 41 888 A1 discloses a weld inspection of reactor control rod sleeves inside their casings using a corresponding eddy current probe. Furthermore, WO 99 / 04253 A1 discloses an internal inspection of a pipe's inner wall using an eddy current test. US 10,788,456 B2 also discloses an internal pipe inspection using an eddy current test.

[0009] DE 10 2013 002775 A1 discloses a forming tool for components, wherein an eddy current probe is arranged within the forming tool, by means of which a crack test can be carried out on a component arranged in the forming tool.

[0010] While all known methods inspect the surface of the pipe's interior for defects, damage can occur not only on the inner walls but also on the outer walls when forming a steel pipe into a tubular product. Even if the inner walls are flawless, surface damage to the outer wall, particularly in its formed end sections, can lead to malfunctions during normal use or even to the pipe's destruction. Although such an inspection of the outer wall in the formed end sections is possible, it involves increased time, material, and cost expenditure.

[0011] It is therefore an object of the invention to provide a method for the production and testing of a high-strength or ultra-high-strength steel tube product, which enables cost-effective, time-saving, and material-saving testing of the formed end regions of such a tube product. Furthermore, it is an object of the invention to provide a suitable test probe for use in the method according to the invention and, finally, a suitable tube product.

[0012] With regard to the method, this problem is solved by a method having all the features of claim 1. With regard to the probe, the problem is solved by a probe having all the features of claim 12.

[0013] The inventive method for manufacturing and testing a high-strength steel tube product comprises the following process steps: a. Providing a steel tube, which can be seamless or welded; b. Forming the steel tube into a tubular product, wherein the steel tube is formed at least in one of its end regions; c. Checking the inner wall and the outer wall in at least one formed end region of the tubular product for defects using a test probe adapted to the at least one formed end region, which has at least one eddy current sensor for checking the inner wall and at least one eddy current sensor for checking the outer wall of the at least one formed end region of the tubular product, wherein several eddy current sensors are provided on at least one arm and / or several sensors are provided on an inner part.

[0014] The method according to the invention makes it possible in a simple manner to inspect both the outer and inner walls of a formed end section of a steel tube product for defects and damage using eddy current testing, without requiring additional time or a separate test bench for the additional surface inspection of the outer surface of the tube product. The test probe is designed to have eddy current sensors that simultaneously inspect the surface of both the inner and outer walls of at least one formed end section of the tube product.However, the inventive method not only optimizes the time required to inspect the surface of the outer and inner walls, but also allows the same evaluation electronics to be used for the additional inspection of the surface of the outer wall of the at least one formed end section of the tubular product as for the inspection of the inner wall of the at least one formed end section of the tubular product. This results in an overall improvement, or even the reliable achievement, of the measurement resolution and detection rate for certain types of defects, compared to individual tests using ultrasound or one-sided eddy current testing. Finally, this also minimizes the equipment required for inspecting the inner and outer walls of the at least one formed end section of the tubular product.This involves the use of multiple sensors on at least one arm and / or multiple sensors on the inner part, so that, for example, testing can be carried out with different measurement frequencies and / or sensitivities of the eddy current sensors in order to detect different types of defects and / or defects at different depths of the pipe wall, or to be able to examine larger pipe sections simultaneously.

[0015] Within the scope of the invention, the term "inner wall" refers to the inner wall surface or the portion of the pipe wall extending from the inner wall surface. Similarly, within the scope of the invention, the term "outer wall" refers to the outer wall surface or the portion of the pipe wall extending from the outer wall surface.

[0016] According to a first advantageous embodiment of the method according to the invention, the testing of the inner and outer walls takes place simultaneously. This parallel testing reduces the testing time by at least half compared to serial testing.

[0017] It has proven particularly advantageous that the inspection of the inner and outer walls of the at least one formed end section of the tubular product is carried out by fixing the tubular product in place and rotating the test probe axially over the at least one formed end section. The eddy current sensors then inspect both the inner and outer walls of the at least one formed end section for defects. The axial and rotational movement of the test probe ensures that the eddy current probes cover the entire surface of both the inner and outer walls of the at least one formed end section, thus guaranteeing a complete inspection of both the inner and outer walls.

[0018] The embodiment of the inventive method has proven particularly advantageous in which the simultaneous testing of the inner and outer walls in the at least one formed end region of the tube product is carried out directly following the final manufacturing steps, in particular the forming according to step b), and especially in a sequentially linked manner. This measure allows the testing of the surfaces of the inner and outer walls of the formed end region to be performed during the manufacturing step or immediately thereafter, without the need for a separate test bench. Consequently, the logistical effort required to transport the manufactured tube products together to a separate test bench is also eliminated.

[0019] In a further embodiment of the method according to the invention, the testing is carried out after demagnetization of the at least one formed end region. This avoids false detections due to any magnetic properties that may be present in the formed end region.

[0020] In a further advantageous embodiment of the method according to the invention, the steel tube provided consists of a steel alloy which, in addition to iron and unavoidable melting-related impurities, comprises the following alloying elements in mass percent, wherein the following percentages in this document always refer to mass percent: C (0.07 to 0.50%; preferably 0.08 to 0.15%), Si (0.01 to 0.60%; preferably 0.01 to 0.50%), Mn (0.3 to 1.7%; preferably 1.0 to 1.7%), Cr (max. 1.2%; preferably 0.2 to 0.9%), Mo (max. 1.2%; preferably max. 0.2%), Ni (max. 0.4%; preferably 0.15 to 0.4%), Al (0.01 to 0.10%), V (max. 0.15%), Nb (max. 0.06%) and Ti (max. 0.06%).

[0021] Melt-related impurities are, in particular, impurities that enter the steel alloy during steel production, especially during the generation of the melts and the treatment of the materials added to the melt. According to the invention, carbon (C) is present in the steel in an amount ranging from 0.07% to 0.50%. At a carbon content of 0.07%, sufficient strength can still be ensured and the formation of cementite (Fe3C) in the steel can be kept to a minimum. Furthermore, sufficient toughness can be guaranteed. However, if the carbon content is too high, carbide formation in the steel is promoted, which reduces the impact toughness. Therefore, according to the invention, the carbon content is preferably limited to a maximum of 0.15%. According to one embodiment, the carbon content can be in the range of 0.08% to 0.15%.

[0022] Silicon (Si) is preferably present in an amount in the range of 0.01 to 0.60%, more preferably in the range of 0.01 to 0.50%. Silicon increases the tensile strength and yield strength of the provided steel tube.

[0023] Manganese (Mn) is preferably present in an amount ranging from 0.3 to 1.7%. Manganese increases the yield strength and tensile strength of the steel alloy. Furthermore, manganese, as a substitute for carbon, improves weldability. According to a preferred embodiment, manganese is present in an amount ranging from 0.5 to 1.7%, and particularly preferably in the range of 0.6 to 1.7%.

[0024] Chromium (Cr) is preferably present in an amount of no more than 1.2%. Chromium increases the toughness and tensile strength of the steel alloy. According to a preferred embodiment, chromium is present in an amount in the range of 1.0% and particularly preferably in the range of 0.2 to 0.9%.

[0025] Molybdenum (Mo) is preferably present in an amount of no more than 1.2%, and in particular no more than 0.2%. Molybdenum particularly improves the tensile strength and weldability of the steel alloy.

[0026] Nickel (Ni) is preferably present in an amount of no more than 0.4%, preferably between 0.15% and 0.4%. Nickel increases the tensile strength and the yield strength.

[0027] Aluminium (Al) is preferably present in an amount in the range of 0.01 to 0.10%.

[0028] Vanadium (V) is preferably present in an amount of no more than 0.15%. Vanadium increases the tensile strength of the alloy.

[0029] Niobium (Nb) is preferably present in an amount of no more than 0.06%.

[0030] Titanium (Ti) is preferably present in an amount of no more than 0.06%.

[0031] In another embodiment of the inventive method, the tubular product has a microstructure of elongated, tempered martensite, in particular with an average martensitic packet size of d avg < 3 µm. Such properties of the tubular product can be achieved, for example, by tempering (i.e., by hardening and subsequent tempering) and cold drawing after tempering, in particular before the testing described in step b).

[0032] According to a further embodiment of the method according to the invention, the tubular product, in particular the airbag tube, has a microstructure of elongated, tempered martensite. This microstructure is preferably achieved, in particular, by heat treatment followed by cold drawing.

[0033] According to an alternative embodiment, a tubular product, in particular an airbag tube, can also consist of an air-hardenable steel alloy, such as that disclosed, for example, in EP 1 474 538 A1. This steel alloy and the tube manufacturing steps disclosed therein form part of the present disclosure with respect to step a) of claim 1, namely the provision of the steel tube.

[0034] Preferably, the pipe product has a transition temperature of less than 233.15 K. The transition temperature is preferably determined by the ring-Charpy test. For example, the transition temperature is determined by taking a sample from the respective length segment as an annular impact test specimen, i.e., as a narrow pipe section with a notch introduced for testing purposes. After cooling to the low-temperature test conditions, an axial impact is applied to the specimen. The low temperature at which the specimen transitions from plastic to brittle fracture behavior is referred to as the transition temperature. It is understood that several specimens must be tested to characterize a length segment in order to determine this temperature.

[0035] In addition to airbag tubes, the following further tube applications can be manufactured or used in the method according to the invention: drive shafts, stabilizers, and axle components, in particular made of an air-hardening steel alloy as disclosed in DE 10 2017 297 369 A1, DE 10 2016 107 143 A1, and DE 10 2015 111 150 A1. The steel alloys and tube manufacturing steps disclosed therein form part of the present disclosure with respect to step a) of claim 1, namely the provision of the steel tube, and step b), the forming of the steel tube into a tube product.

[0036] Preferably, the tubular product and / or the supplied steel tube has a wall thickness of less than 4 mm. Such a wall thickness can also be used, in particular, for airbag tubes.

[0037] It is particularly advantageous to perform fault detection in the transition zone by using an eddy current sensor in the undercut of the transition zone between the inner or outer wall. This ensures that the eddy current sensors can be positioned within the transition zone, allowing them to be located at a distance from the wall sufficient for detection and thus testing. This positioning can be achieved through appropriate mechanisms in the arms and / or the inner part. Examples include a sensor holder that spreads, a laterally moving sensor holder, or a segmented test probe, although this list is not exhaustive.

[0038] In principle, distance compensation can also be integrated into the method according to the invention. This compensates for rotation- and / or clamping-related distance variations between the eddy current sensors and the wall surfaces, for example in the error evaluation, the electronics and / or the software used.

[0039] The test probe according to the invention is characterized in that it has a bridge connecting at least one arm, on the inner wall of which at least one eddy current sensor is arranged, and a holding element for receiving at least one eddy current sensor. The test probe is designed as a body of revolution about a central longitudinal axis, with the bridge section being a circular disk, the two arms together being a hollow cylinder arranged on the edge of the circular disk, and the holding element being a solid cylinder arranged around the center of the circular disk. A test probe constructed in this way enables the simultaneous testing of the outer and inner walls of a tubular element, in particular a tubular product, manufactured according to the method described above, in a simple manner.The eddy current sensors arranged on the inner walls of the first and second arms, which are mounted on the bridge, allow for the simple inspection of the outer surface of an end section of a tubular product. At least one eddy current sensor, mounted on the holding element, is designed to inspect the inner wall of the end section. By rotating and axially moving the probe across the end section of the tubular product, the entire surface of both the inner and outer walls can be inspected for defects and damage. Such a probe can be easily formed from a solid metal body, particularly by milling. It is especially advantageous that such a solid body has a high weight and is therefore relatively insensitive to slight imbalances occurring during rotation.This is particularly important because the individual eddy current sensors of the test probe are located at different points on the rotating body and could therefore cause slight imbalances during rotation. With a solid test probe, especially one made of metal, the weights of the eddy current sensors are thus reduced, so that the slight imbalances they generate are not disruptive during the rotation of the probe. A test probe designed as a rotating body in this way may subsequently also be referred to as a pot probe.

[0040] It is particularly advantageous if the holding element is mounted equidistant from the first and second arms on the bridge. This design of the invention ensures that, when the arms rotate over the end region of the tubular product, both arms maintain the same distance from the outer wall of the tubular product. In this respect, eddy current sensors directly opposite each other on the two arms would deliver exactly the same signals, making them comparable and enabling redundant testing. However, an opposing arrangement of eddy current sensors on the two arms is not provided, as a defect in one eddy current sensor would be detectable by other means or would be immediately apparent.The geometry of the inner walls of the two arms can be adapted to the geometry of the end region of a tubular product to be inspected, so that, by means of appropriately arranged eddy current sensors, they always have the same distance to the surface being inspected of the formed end region of the tubular product.

[0041] Alternatively, the test probe may not have the geometry of a solid of revolution. This is particularly true if it only has one arm for testing an outer wall. The holding element for testing inner walls can also be designed as an arm that extends from the probe's shank and can be inserted into the interior of the pipe being tested.

[0042] The test probe can be moved perpendicular to the axis of rotation of the pipe being tested, allowing the arm for testing outer walls and the holding element for testing inner walls to be positioned against undercuts at the ends of the pipe. The geometry of the arm and the holding element is adapted to the geometry of the pipe end being tested. When the pipe end is being tested, the axis of rotation of the test probe corresponds to the longitudinal axis of the pipe being tested.

[0043] Further objectives, advantages, features, and applications of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawings. All features described and / or illustrated, individually or in any meaningful combination, constitute the subject matter of the present invention, even independently of their compilation in the claims or their cross-references.

[0044] They show: Figure 1: Illustration at the beginning of the test step of the inventive method for testing two formed end regions of a pipe product according to the invention with test probes according to the invention, Figure 2: Illustration of the testing of the end sections of the pipe product Figure 1 Figure 3: Representation of the testing of an end section of another pipe product at the end of the test with another test probe according to the invention; Figure 4: Representation of the testing of an end section of another pipe product at the end of the test with another test probe according to the invention; Figure 5: Representation of the testing of an end section of another pipe product at the end of the test with another test probe according to the invention; and Figure 6: Representation of various types of defects that can occur in a pipe product according to the invention.

[0045] In Figure 1A tubular product 1 according to the invention, in particular an airbag tube, with formed end regions 10-1, 10-2, is shown. These end regions are to be tested for defects in the inner wall 7 and the outer wall 8 by means of a test probe 9. The end regions have a transition region 11-1, 11-2 between the formed or reduced cross-section of the tubular product 1 and the cross-section of the provided steel tube. The illustration of the Figure 1 Figure 1 shows the beginning of the test. The tube product 1 is designed such that its end regions 10-1, 10-2 were tapered during its manufacture. In further embodiments not shown here, it is also conceivable that the end regions of the tube product were widened. The forming process during the manufacture of the tube product from a steel tube can be carried out according to known methods not described in detail here.

[0046] The end regions 10-1 and 10-2 of the pipe product 1 are rotationally symmetrical, with an inner wall 7 and an outer wall 8. Two test probes 9 are used to check for defects in the inner walls 7 and outer walls 8 of the end regions 10-1 and 10-2 of the pipe product 1. The test probes 9 consist of a web 16 connecting a first arm 2 and a second arm 3, with a retaining element 4 arranged on the web 16 at an equidistant distance from the two arms 2 and 3. Eddy current sensors 13, 14 and 15 are arranged on the two arms 2 and 3, which are positioned such that they can check areas of different diameters of the end regions 10-1, 10-2 of the tube product 1, wherein the distances between eddy current sensor 13, 14 and 15 and the respective area of ​​the outer walls 8 are essentially the same.An eddy current sensor 12 is also arranged on the holding element 4, with which the inner walls 7 of the end regions 10-1 and 10-2 of the tube product are checked for defects.

[0047] Since the representation of Figure 1 As shown in the sectional view, it should be noted with regard to the test probes 9 that these are solid metal elements in the form of a body of revolution, such that the bridge 16 is designed as a circular disk, while the two arms 2 and 3 together form a hollow cylinder and are arranged on the edge of the circular disk bridge 16. Similarly, the retaining element 4 is designed as a solid cylinder on the circular disk bridge 16 and is arranged at its center. The end regions 10-1, 10-2 are shown according to... Figure 1After forming, the test probes are identical and have the same cross-section and the same transition regions 11-1, 11-2. However, the cross-sectional geometry, length, and width of the transition regions 11-1 and 11-2 may differ. Accordingly, the test probes 9 may also differ in detail, particularly in their geometry adapted to the end regions 10-1, 10-2, despite having the same reference numerals. Furthermore, the test probes 9 according to the invention do not necessarily have to be designed as bodies of revolution. If they are designed as bodies of revolution, they do not necessarily have to be made of solid metal elements. For example, hollow elements with metal sheet walls would also be conceivable. Moreover, the material from which the test probe is made is not limited to metals.

[0048] As already mentioned, the representation of the Figure 1The situation at the start of the inspection of the end sections 10-1 and 10-2 of the pipe product 1 for defects. The test probes 9 are already in rotation, with arrows 5 indicating the direction of rotation and the rotation occurring around the central longitudinal axis 19. In addition to the rotational movement 5, the test probes 9 also undergo an axial movement, indicated by arrows 6.

[0049] During the axial movement of the test probes 9, they continue to rotate around the central longitudinal axis 19, so that the surfaces of the outer walls 8 and inner walls 7 in the end regions 10-1 and 10-2 of the pipe product 1 can be checked for defects and damage over their entire surface by means of the eddy current sensors 12 to 15.

[0050] The procedure of the test probes 9 in the axial direction continues until the test probes 9 reach the in Figure 2The pipe product 1 has reached the position shown. In this position, the pipe product 1, with its end sections 10-1 and 10-2, is completely immersed in the test probes 9, so that the outer and inner walls 8 and 7 of the pipe product 1 have already been completely inspected once. The inspection is now complete, and the test probes 9 can be returned to their starting position as shown. Figure 1 The procedure can be carried out as follows. In this process, rotation of the test probes 9 can now be omitted, since a complete inspection of the surfaces of the inner walls 7 and the outer walls 8 in the end regions 10-1 and 10-2 of the pipe product has already been carried out. Alternatively, it is possible to perform another inspection of the surfaces of the inner walls 7 and the outer walls 8 of the pipe product 1 while the test probes 9 are being withdrawn from the end regions 10-1 and 10-2 of the pipe product 1.

[0051] If no defects are found during the inspection of end sections 10-1 and 10-2 of the pipe product 1, the pipe product 1 will be used for further processing. However, if defects or damage are detected during the inspection, the corresponding pipe product 1 will be rejected.

[0052] In the Figure 3 Figure 1 shows the testing of an end section of another pipe product 1 at the end of the test using a further test probe 9 according to the invention. The test probe 9 essentially corresponds in its construction to that of the Figure 1 and 2 and is therefore provided with identical reference numerals. The pipe product 1 of the Figure 3 However, its end region 10-1 differs from the end region of the pipe product. Figure 1 and 2 and, although it is also tapered in a transitional area 11-1, it additionally exhibits an outwardly projecting bulge. The examination is carried out analogously to that in the Figure 1 and 2 The described test has been performed, so a further execution is omitted here.

[0053] The Figure 4Figure 1 shows an inspection of an end section of another tubular product 1 at the end of the inspection using another test probe 9 according to the invention. In this case, the tubular product is not tapered in its end region 10-2, but instead has a bead directed towards the inside of the tube in a transition region 11-2. The test probe 9 used here is not rotationally symmetrical about its axis of rotation, which corresponds to the longitudinal axis 19 of the tubular product. Rather, the test probe 9 has a web 16, at one end of which an arm 3 is arranged. This arm 3 is provided on its inner wall 17 with three eddy current sensors 13, 14, and 15 for inspecting the outer wall 8 of the tubular product in the region of the bead. Furthermore, the test probe has a retaining element 4, which is also designed as an arm and is arranged on the web 16 opposite the arm 3.This holding element 4 is equipped with an eddy current sensor 12 for testing the inner wall 7 of the pipe product 1 in the region of the bead of the end section 10-2. The arm 3 and the holding element 4 are spaced at different distances from the axis of rotation of the test probe 9, so that when the test probe 9 rotates, the holding element 4 is guided along the outer wall 8 of the pipe product 1 in its end section 10-2, while the holding element 4 is guided along the inner wall 7 of the pipe product 1 in its end section 10-2.

[0054] The Figure 5Figure 1 shows an inspection of an end section of another tubular product 1 at the end of the inspection using another test probe 9 according to the invention. In this case, the tubular product is not tapered in its end region 10-1, but instead has a bead directed towards the outside of the tube in a transition region 11-1. The test probe 9 used here is not rotationally symmetrical about its axis of rotation, which corresponds to the longitudinal axis 19 of the tubular product. Rather, the test probe 9 has a web 16, at one end of which an arm 3 is arranged. This arm 3 is provided with an eddy current sensor 13 on its inner wall 17 to inspect the outer wall 8 of the tubular product in the region of the bead. Furthermore, the test probe has a retaining element 4, which is also designed as an arm and is arranged on the web 16 opposite the arm 3.This holding element 4 is equipped with three eddy current sensors 12, 12 and 12 for testing the inner wall 7 of the pipe product 1 in the region of the bead of the end region 10-1. The arm 3 and the holding element 4 are spaced at different distances from the axis of rotation of the test probe 9, so that when the test probe 9 rotates, the holding element 4 is guided along the outer wall 8 of the pipe product 1 in its end region 10-1, while the holding element 4 is guided along the inner wall 7 of the pipe product 1 in its end region 10-1.

[0055] The in Figure 4 and 5The described embodiments of the invention are tested as follows. Before and / or during the testing of the tubular product 1, the test probe 9 is moved into and over the end region 10-1 or 10-2 to be tested in such a way that it is guided simultaneously or sequentially along a central longitudinal axis 19 of the tubular product 1 and radially to the tube axis 19 in order to reach the undercut formed by the transition region 11-1 or 11-2 with the arm 3 and holding element 4 without collision. After the measurement is completed, the test probe 9 is moved away from the end region 10-2 parallel and transversely to the central longitudinal axis 19 without collision.

[0056] In the Figure 6Examples of defects in the wall of a pipe product 1 according to the invention are shown by way of example and are not exhaustive. These defects can be detected by means of an inspection using the method according to the invention. It is possible to reliably detect various surface defects A, B, C, D as well as inclusion defects E during an inspection and to visualize them using known methods on known imaging devices such as screens.

[0057] Regarding the inclusion error E, the detection rate also depends on the performance of the eddy current sensors used to test the pipe product 1. Generally, the higher the performance, the greater the detection depth.

[0058] Surface defect A is a more or less perpendicular crack in the surface of pipe product 1, while surface defect B is a crack that changes direction multiple times depending on its penetration depth. Surface defect C is a more or less straight crack, but unlike surface defect A, it is not perpendicular to the surface of the pipe product. Surface defect D is less of a crack in the surface of the pipe product, as its penetration depth is relatively shallow compared to surface defects A, B, and C. Rather, surface defect D is in the form of a crater-like surface defect.

[0059] Alone Figure 6The surface defects shown can be detected reliably and precisely using the method according to the invention. Compared to ultrasonic testing, eddy current testing has the advantage that it can be performed dry. Therefore, compared to ultrasonic testing, not only is there a time saving due to the rapid surface inspection inherent in eddy current testing, which takes only a few seconds, but the time required to dry the pipe product is also eliminated. Furthermore, the wet testing method used in ultrasonic testing can lead to corrosion problems in the pipe products, which cannot occur with eddy current testing. Reference symbol list

[0060] 1 Tube product 2 First arm 3 Second arm 4 Holding element 5 Rotational movement 6 Axial movement 7 Inner wall 8 Outer wall 9 Test probe 10-1 End area 10-2 End area 11-1 Transition area 11-2 Transition area 12 Eddy current sensor 13 Eddy current sensor 14 Eddy current sensor 15 Eddy current sensor 16 Web 17 Inner wall 18 Inner wall 19 Central longitudinal axis A Surface defect B Surface defect C Surface defect D Surface defect E Inclusion defect

Claims

1. A method for manufacturing and testing of a pipe product (1) of steel comprising the following steps: a) providing a steel pipe, b) forming the steel pipe into the pipe product (1), wherein the steel pipe is formed at least in one of its end regions (10-1, 10-2), c) testing the inner wall (7) and the outer wall (8) in at least one formed end region (10-1, 10-2) of the pipe product (1) for defects using at least one test probe (9) adapted to at least one formed end region (10-1, 10-2), which has at least one eddy current sensor (12) for testing the inner wall (7) and at least one eddy current sensor (13, 14, 15) for testing the outer wall (8) of the at least one formed end region (10-1, 10-2) of the pipe product, wherein several eddy current sensors (13, 14, 15) are provided on at least one arm (2, 3) and / or several sensors (12) are provided on an inner part (4).

2. The method according to claim 1, characterized in that, in step c), the inner wall and the outer wall are tested simultaneously.

3. The method according to claim 1 or 2, characterized in that the testing of the inner wall (7) and the outer wall (8) of the at least one formed end region (10-1, 10-2) of the pipe product (1) is carried out such that the pipe product (1) is fixed and the test probe (9) is moved axially in a rotating manner over the at least one formed end region (10-1, 10-2) of the pipe product, wherein the inner wall (7) and the outer wall (8) of the at least one formed end region (10-1, 10-2) of the pipe product are checked for defects by means of the eddy current sensors (12, 13, 14, 15).

4. The method according to any one of the preceding claims, characterized in that the testing of the inner wall (7) and the outer wall (8) in the at least one formed end region (10-1, 10-2) of the pipe product (1) is carried out following the final manufacturing steps, in particular the forming according to step b) and in particular in a sequential manner therewith.

5. The method according to any one of the preceding claims, characterized in that the testing is carried out following demagnetization of the at least one formed end region.

6. The method according to any one of the preceding claims, characterized in that the steel pipe provided consists of a steel alloy which, in addition to iron and melt-related impurities, contains the following alloying elements in mass percent: C (0.07 to 0.50%; preferably 0.08 to 0.15%), Si (0.01 to 0.60%; preferably 0.01 to 0.50%), Mn (0.3 to 1.7%; preferably 1.0 to 1.7%), Cr (max. 1.2%; preferably 0.2 to 0.9%), Mo (max. 1.2%; preferably max. 0.2%), Ni (max. 0.4%; preferably 0.15 to 0.4%), Al (0.01 to 0.10%), V (max. 0.15%), Nb (max. 0.06%) and Ti (max. 0.06%).

7. The method according to any one of the preceding claims, characterized in that the pipe product (1) has a microstructure of elongated, tempered martensite, in particular with an average martensitic packet size of davg < 3 µm.

8. The method according to any one of the preceding claims, characterized in that the pipe product (1) has a tensile strength of at least 900 MPa and a transition temperature of less than 233.15 Kelvin.

9. The method according to any one of the preceding claims, characterized in that an eddy current sensor (15) of the test probe (9) is positioned such that, after the test probe has been inserted into the end region, it corresponds to the position of the transition region (11-1, 11-2).

10. The method according to any one of the preceding claims, characterized in that the testing is carried out with different measuring frequencies or sensitivities of the eddy current sensors (13, 14, 15) in order to determine different types of defects and / or defect depths.

11. The method according to any one of the preceding claims, characterized in that testing for defects in the transition area (11-1, 11-2) is carried out by passing an eddy current sensor (12, 13, 14, 15) in an undercut of the transition area (11-1, 11-2) of the inner or outer wall (7, 8).

12. A test probe (9), in particular for use in a method according to any one of the preceding claims, characterized in that it has a web (16) which interconnects a) at least one arm (2, 3) on the inner wall (17) of which at least one eddy current sensor (13; 14, 15) is arranged, and b) a holding element (4) for receiving at least one eddy current sensor (12), wherein the test probe (9) is configured as a rotary body about a central longitudinal axis (19), wherein the web (16) is configured as a circular disk, the two arms (2, 3) together being in the form of a hollow body with a circular inner face, and the holding element (4) is configured as a body with a circular outer face.

13. The test probe (9) according to claim 12, characterized in that the holding element (4) is mounted equidistantly to a first and a second arm (2, 3) on the web (16).