Apparatus for the eddy current testing of the pipes in a heat exchanger.

p0001The invention relates to a device for eddy current testing and is applicable to the examination of the pipes of a heat exchanger with a U-tube bundle.

p0002From DE-C-28 37 486 a device for eddy current testing is known in which a test probe having parallel in two planes arranged transversely to the tube axis and embedded in a coil body annular coils is provided. The probe is on the one hand carrying a guide body flexible hose connected to a pusher hose and connect the other hand, a guide body supporting flexible hose to an insertion tip. The flexible hoses have greater flexibility than the thrust tube, through the means of a push device, the probe can be inserted into a tube of the U-tube bundle. In this known embodiment, the two coil axes are coaxial to the longitudinal axis of the test probe on the bobbin. So that one can still detect errors in the straight and curved portion of the test tube, but it is not possible to locate the exact position on the circumference of the tube.

p0003It is also an eddy current probe having a coil are known, the press-on surface extends only over a part of the inner periphery of the test tube. In this embodiment, it is necessary to enable the probe to scan the tube in rotation.

p0004By US-A-4303884 an eddy current probe is known which comprises a plurality of axially extending resilient plastic strips which form the periphery of the probe. On each strip, a coil for eddy current testing is fixed. In this configuration it is not necessary to rotate the probe because during the insertion movement through the coils, the entire inner surface of the test tube is coated. However, the known version is suitable only for testing of straight tubes. The location of a fault is also indicated only by a length dimension, so that can only be concluded, at what level of the pipe is the problem.

p0005The invention is based on the object of specifying a device for eddy current testing, with the location of an error in the curved portion of the tube of a heat exchanger can be located not only in a linear dimension, but also an angular, so the flaw also along the circumference to be tested the tube can be detected. For the analysis of eddy current testing and the measures to be taken, it is desirable to be able to determine the precise location of a fault in the pipe, in order to draw possible conclusions, is due to what caused the error. For example, interested in whether the error is due to a support point of the tube of a tube bundle. Such supports are also provided in the curved portion of the tube bundle of a heat exchanger.

p0006According to the invention, the object is achieved by a device for eddy current testing of tubes of a heat exchanger with a U-tube bundle, in which an insertion tip of a probe is connected via elastic hoses with the interposition of at least three coils with a push tube, by means of a pusher in a tube of the bundle can be inserted, wherein the pressing surfaces of the coil each extend only over a part of the inner circumference of the pipe, the coils are offset on the periphery of the test probe and the probe longitudinal axis against each other and the test probe in a position detection unit is disposed.

p0007In this way you can detect by a length and angle measurement in a simple manner errors in tight radii of curvature of the U-tube.

p0008Further developments of the invention are explained with reference to the drawing in which an embodiment is illustrated. In which:<ul><li>1 shows a longitudinal section of an eddy current probe on an enlarged scale,</li><li>FIG 2 to 5 cross sections to from FIG 1 obvious places,</li><li>6 shows a device for eddy current testing in a side view,</li><li>FIG 7 is an electrical circuit diagram of the position detection unit of the probe,</li><li>FIG 8 is a cross section of the contact arrangement of the position detection unit and</li><li>9 shows the arrangement of the resistors.</li></ul>

p0009As can be seen from FIG 1 and 6, the means for eddy current testing of the tubes of a heat exchanger with a U-tube bundle of a probe 1, in which an introducer tip 2 via elastic hoses 3a to 3m interposition of Abstütungen 8a to 8g and coils 4a to 4h is connected with a body designed as a connector connecting body 5 to which a thrust tube 6 is connected, which is pushed by a thrust device into a tube 7 of the U-tube bundle. The elastic tube pieces 3a to 3m, the flexibility is greater than the thrust of the tube 6 are guided in the pipe to be tested by the struts 8a to 8g, which are ring-shaped.

p0010Of Figure 1 in connection with the Figures 3-7 it can be seen that the pressing surfaces 9 (Fig 2) of the bobbin 4a to 4h respectively only over a part of the outer periphery (sector) of the probe 1 and the inner periphery of the test tube extend. The coils 4a to 4h are at the periphery of the probe 1 by predetermined Win kelα (2, 3) and also in the probe longitudinal axis to the length A (Fig 6) offset from one another so that, when pushed through the probe 1 through the tube to be tested each coil 4a to 4h scans a predetermined part of the inner surface of the tube. The coils 4a to 4h are (2 in FIG perpendicular to the plane) arranged with its winding axis W parallel to the probe axis and in coil support 10a, 10b at least partially encapsulated. These coil support 10a, 10b are in perpendicular to the probe axis recesses 11 to 14 of bobbin holders 15a to 15d (FIG 2-5) arranged to be movable. In this case, have the coil support 10a, 10b arranged parallel to the probe axis journal 10c, 10d (FIG 1) which permit a rocking movement and vertical movement and this, in radial slots 15e, 15f of the bobbin holders 15a to 15d are mounted. Thereby, a good adaptation of the pressure surfaces of the coils 9 to the inner surface of the pipe in pipe bends can be achieved. The coil support 10a, 10b are pressed by springs 10e in the recesses 11 to 14 to the outside.

p0011In the illustrated embodiment, two coil support 10a, 10b resiliently mounted in a recess, each having a coil. The probe 1 has so four in the probe longitudinal axis staggered recesses 11 to 14 each with two coil carriers, for example, 10a, 10b, the recesses being disposed 11 to 14 offset by an angle of α = 45 ° to each other, so that the pressing surfaces 9 of the coil 4A to 4H overlap with each other.

p0012The cable ends 17a, 18a of the coils are led to terminals 17b, 18b on the coil carrier (FIG 2). From there lead movable wires 17c, 18c to electrical circuit boards 19 which are held inside the bobbin holders 15a to 15d by pins 16 with slots 16a. Of each circuit board 19, two electrical cables 20, 21 result in channels in the bobbin holders and from there via the interior of the elastic tube parts 3e to 3m (FIG 1) and the push hose to a connection box 23 and in FIG 6 to the terminal body 5 and of there by the thrust hose 6 to a connection box 23 which is connected to an evaluation and display device 22nd

p0013For locating an error, a position detection unit 25 is provided in the probe first This position detection unit 25 is - as FIG 7.8 and 9 - of an electrically resistive network 26 having a plurality of contacts 27 to 34 to run taps Gebild et. The contacts 27 to 34 are arranged on the inner periphery of a two-part hollow support 8a with the interposition of insulating bodies at regular intervals (FIG 8). The contacts 27 to 34 is a contact body 35 (FIG 1) associated in the form of a spherical body, which is held on a tensioned in the probe cable 36 suspended in one of the probe axis. This cable 36 is on one hand mounted on a bracket 37 by a screw 38 inside the introducer tip 2 by the supports 8a to 8e passed placed to the coil holders in channels (FIGS 2-5) and on the other hand anchored at the terminal body 5 for the pushing hose 6 and from there, if used by the thrust hose for connecting box 23 (FIG 1). To hold the rope 36 is always stretched, a tension spring is in one of the guide body 8c arranged. 39 The resistors 40 to 47 of the resistor network 26 are also housed in the cavity of a support 8b. The resistor network 26 is connected via electrical lines 48, 49 and the contact body 35 via an electric line 50 to the evaluation and display device 22, which is equipped with display and / or recording devices 51, 52, 53 (FIG 6).

p0014In recording device 51 having an oscillograph that Wirbelstromprüfergebnisse be graphed.

p0015The pushing device 7 is provided with a counter 7a, lead from the electrical lines to the display device 51 indicating the insertion length of the probe in the test tube. The leads 48 to 50 are through the interior of the elastic tube pieces 3a - 3n performed with the bobbin holders 15a to 15d, the lines 48 to 50 housed together with the cables 20, 21 in channels 54 (Fig 5). As shown in FIG 7 also shows the electric lines 48, 49 are connected to a DC voltage source 55th The resistor network 26 forms a voltage divider, defined at the taps pending tensions that have, for example, the values ​​2, 4, 6, 8, 10, 12, 14, 16 volts. Where the probe in the bow section of the test tube, the contact body touches 35 one of the contacts 27 to 34. Since the coils 4a to 4h the contacts 27 to 34 permanently assigned, thus the position of the individual coils in the tube sheet is fixed. The voltage applied between the lines 49 and 50 tension is a measure of the angular position of the individual coils in the sheet of the test tube. The respective voltage value detected by the voltage formed as a clerk recorder 53rd

p0016The arranged between the supports 8a to 8e and coils 15a to 15d elastic tube pieces 3a to 3n are formed by hollow shaft sections which consist essentially of a flexible wire coil 24 with mutual radial toothing of the helices (FIG 1). The hollow shaft portions have helical ribs 55 that form an external thread. The supports 8a to 8e and bobbin holders 15a to 15d have a central through-opening and at both ends. Approaches 43 with internal threads 44 for screwing the hollow shaft sections

p0017The accuracy of the detection of the angular position of a fault can be increased with the number of coils, if it is not - as shown in the embodiment - is sufficient to spread with four coil pairs circumferential angle of 45 °. But if only low demands are placed on the location of a fault, so you can also take less than four pairs of windings, possibly manage with three vesetzte to 120 ° windings.