Abstract:
A device for ultrasonic weld seam testing of longitudinally includes two testing carriages swingably suspended and moveable on the pipe surface to the right and left of the weld seam for longitudinal flaw inspection, and one testing carriage swingably suspended in central relationship to the weld seam and moveable on the pipe surface for transverse flaw inspection. Each testing carriage has a mount for accommodating at least one testing head which includes an oscillator, and at least one coupling medium connection having a channel ending in the region of the oscillator and configured as nozzle in the outlet area. The test head for longitudinal flaw inspection can be arranged at various fixed and predefined angle positions at variable distance to the nozzle in the mount, and the test head for transverse flaw inspection can be arranged, together with the mount, at a variable distance to the pipe surface in a support element accommodating the mount.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a device for ultrasonic inspection of the weld seam of longitudinally welded pipes—in particular large pipes, for longitudinal and transverse flaws according to the preamble of claim  1 . 
   A device for ultrasonic testing of longitudinal weld seams for longitudinal and transverse flaws has been published by Scott Lebsack and Helmut Heckhauser in the magazine “Materials Evaluation” (August 1995, pages 886-891), entitled “Immersion Probe Arrays for Rapid Pipeline Weld Inspection”. Included here is a holding system in which two test head systems are mounted. Each test head system includes four test heads to inspect for longitudinal flaws and a test head to inspect for transverse flaws. The two test head systems for longitudinal flaw inspection are positioned to the right and left next to the weld seam. The test head for transverse flaw inspection extends slantingly at an angle of about 45° in relation to the weld seam. The oscillators in the test heads are round with a diameter of 5 mm. The test head systems operating in immersion technique is provided with connections for the coupling medium. 
   DE 198 26 759 C1 discloses a device for ultrasonic testing of longitudinal weld seams for transverse flaws. This known device includes at least one test head which is arranged in a holder element and extends in line with the weld seam and which is provided with an oscillator. The test head is provided with at least one coupling medium connection having a channel ending in the area of the oscillator. Disposed in the test head is a broad rectangular oscillator having a width extending transversely to the weld seam. The channel carrying the coupling medium is shaped in the form of a nozzle in the outlet area and has an opening transverse to the weld seam in correspondence to the width of the rectangular oscillator. The outlet zone of the nozzle is adjusted to the weld seam elevation. The respective nozzle element is connected with the housing by means of long screws which traverse the housing accommodating the test head. 
   The inspection for transverse flaws includes, preferably, two test heads in tandem disposition. The tandem disposition is suited to different thicknesses of the pipe being tested by fixedly securing one test head on a test carriage and arranging the second test head in a manner to be able to move axially in relation thereto. 
   The conventional devices have the drawback that the adaptation to greatly varying pipe sizes is difficult and complicated to implement and that there are also problems in connection with adjusting the angle of sound incidence in a reproducible manner. Maintenance works involving replacement of damaged parts are also time-consuming. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to provide a device for ultrasonic weld seam testing of longitudinally welded pipes, in particular large pipes, for longitudinal and transverse flaws, which allows a simple adaptation to varying pipe sizes and which ensures a reproducible adjustment of the angle of sound incidence. Maintenance works should be simplified by the novel device. 
   This object is attained by a device for ultrasonic weld seam testing of longitudinally welded pipes, in particular large pipes, for longitudinal and transverse flaws, which device includes two swingably suspended test carriages which are movable on the surface of the pipe to the right and left next to the weld seam and provided to inspect for longitudinal flaws, and a swingably suspended test carriage which is aligned in the center relative to the weld seam for movement on the surface of the pipe and provided for transverse flaw inspection, wherein each test carriage includes a transducer for accommodating at least one test head which has an oscillator, and at least one coupling medium connection having a channel which ends in the area of the oscillator and is configured in the outlet zone in the form of a nozzle, wherein the respective nozzle element is connected by screws with the transducer, characterized in that the test head for longitudinal flaw inspection can be arranged in different, fixed and predefined angle positions but at variable distance to the nozzle element in the transducer ( 8 ) and that the test head(s) for transverse flaw inspection including all the respective transducers are commonly arranged at a variable distance to the pipe surface in a frame accommodating the transducers. 
   According to the teaching of the invention, the test head for longitudinal flaw inspection can be arranged in different, fixed predefined angle positions but at variable distance to the nozzle element in the mount. Furthermore, the test head(s) for transverse flaw inspection including all the respective mounts are commonly arranged at a variable distance to the pipe surface in a frame which accommodates the transducers. 
   The proposed arrangement has the advantage that there is a flexibility to provide different angle positions in order to suit different testing tasks while the angle position, once selected, can be securely fixed in a reproducible manner. This can, for example, be realized by forming an exchangeable insert, comprised of two side panels and a connection piece, and providing on the inside of each of the side panels a recess at a certain angular disposition for insertion and securement of the mount for the test head. This ensures that the test head emits acoustic beams in the angular disposition predefined in the recess. The securement of the mount between both side panels is, preferably, realized by means of screws insertable through the sidewall and rotatable into the mount. 
   In view of the proposed variable distance of the test head from the nozzle element, the gap for the coupling medium, established between the nozzle element and the end surface of the test head, can be modified. This adaptation can be utilized to control the required coupling for a reliable inspection, on the one hand, and to influence the drainage of the coupling medium, on the other hand. 
   It is proposed in connection with the test carriage for transverse flaw inspection to dispose the respective mount for each test head in a support element, which can be adjusted in height in relation to the surrounding frame. Thus, all test heads arranged in the test carriage for transverse flaw inspection can be commonly placed in a very simple manner at the desired distance to the pipe surface. The need for a complicated adjustment of each individual test head is thus eliminated. 
   Preferably, the test carriage for transverse flaw inspection includes three test heads. One test head is fixed, a second test head moves axially thereto for transverse flaw inspection, and a third test head is fixed for doubling inspection. 
   In order to realize the known axial displacement of the second test head, the arrangement of two spindles in the support element is proposed which are each provided at their end surface with a toothed belt disk. When wrapping an endless toothed belt about both toothed belt disks, rotation of one spindle by means of a knurled nut results in a rotation of both spindles to thereby change the axial distance of the second test head in relation to the first test head. 
   The nozzle elements are exposed to wear as a consequence of their possible contact of the underside with the pipe surface. In order to enable easy replacement, it is proposed to secure them from below to the transducer with screws. By simply lifting off the test carriage, access to the fastening screws is established so that the worn-out nozzle element can simply be replaced. 
   Generation of disturbance signals can be avoided by making the nozzle elements of wear-resistant plastic, preferably Teflon. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features, advantages and details of the invention are set forth in the following description of an exemplified embodiment illustrated in a drawing: 
     It is shown in: 
       FIGS. 1  to  3  front, side and top views of a test carriage according to the invention for longitudinal flaw inspection, 
       FIGS. 4   a, b  front and top views of a mount for the test head for longitudinal flaw inspection, 
       FIGS. 5   a, b  side and top views of a side panel, 
       FIGS. 6   a, b  side and top views of a nozzle element for longitudinal flaw inspection, 
       FIGS. 7  to  9  front, side and top views of a test carriage according to the invention for transverse flaw inspection, 
       FIGS. 10   a, b  side and front views of a side part of the frame, 
       FIGS. 11   a ,  11   b  front and top views of a side part of the support element, 
       FIGS. 12   a, b , two views and a section of a guide part, 
       FIGS. 13   a, b  top and front views of a tandem disposition of two mounts for receiving test heads for transverse flaw inspection, 
       FIG. 14   a  a front view of a mount for receiving a test head for doubling inspection, 
       FIG. 14   b  a section of  FIG. 14   a.   
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1  to  3  shows front, side and top views of a test carriage according to the invention for longitudinal flaw inspection, whereby the mount  8  ( FIG. 4 ) for receiving a test head has been omitted in the top view (FIG.  3 ). The test carriage  1  is swingably suspended by means of two side columns  3 ,  3 ′ and a crossbar  4  interconnecting the side columns  3 ,  3 ′. 
   The position of the longitudinal weld seam  5  to be tested in relation to the test carriage is shown in FIG.  3 . For sake of completeness, it should be noted that an analogous test carriage is arranged on the left side of the longitudinal weld seam for longitudinal flaw inspection. 
   The test carriage  1  is movably arranged on the pipe surface by means of four ball castors  7 - 7 ′″ clamped in the base plate  6  of the test carriage  1 . As will be described in more detail hereinafter, the test carriage  1  includes for the test head  9  a mount  8  ( FIG. 4 ) which can be mounted on the test carriage  1  at a certain predetermined angular disposition. Arranged in the mount  8  is also a nozzle  10  for supply of coupling medium. 
   In order to prevent an excess flow of coupling medium in the direction of the longitudinal weld seam  5  that may result in signal interferences, a flat jet nozzle  12  and a baffle plate  13  ( FIGS. 1 ,  2 ) are secured to a plate  11 . 
     FIG. 3  illustrates in conjunction with  FIGS. 4 and 5  the manner by which the mount  8  is secured in the test carriage  1 . Hereby two side panels  14 ,  14 ′ are arranged in opposite disposition in a rectangular opening of the base plate  6  and interconnected by a connection piece  15  to thereby form an exchangeable unitary structure. 
   According to the illustration in  FIG. 5 , the side panel  14 ′ is characterized by a slanted recess  16 ′ which is extends on the inside at a certain fixedly predefined angle α. This angle α is calculated depending on the desired angle of sound incidence and accordingly milled into the side panel  14 ′ as slanted recess  16 ′. The different milled side panels  14 ,  14 ′ define each together with the rigid connection piece  15  an assembly kit for a particular angle of sound incidence. 
   The mount  8  includes complementary to the recess  16 ,  16 ′ two nose-like protrusions  17 ,  17 ′ in opposite relationship so that the mount  8  can be inserted in a simple manner between the side panels  14 ,  14 ′. The securement of the mount  8  between both side panels  14 ,  14 ′ is implemented by means of screws, not shown here, which traverse the side panels  14 ,  14 ′ and are rotatable into the mount  8 . The respective side panel  14 ′ includes hereby two throughbores  18 ,  18 ′, and the mount  8  includes hereby in the area of each of the nose-like protrusions  17 ,  17 ′ two threaded bores  19 - 19 ′″. 
   The proposed arrangement has the advantage that a defined angle of sound incidence is established for the test head  8 , when an angle α is established for the recess  16 ,  16 ′ so that the inspection can be constantly carried out with the same predefined angle of sound incidence in a reproducible manner upon use of the assembly kits. The previously typical adjustment of the test head  8  is thus eliminated. 
   Securement of the test head  9  in the mount  8  is realized by providing a bore  21  in the center of the mount. The actual securement is realized by two, not shown, clamping screws which can be laterally rotated in. The mount  8  includes hereby two lateral threaded bores  20 ,  20 ′. The test head  9  can therefore be clamped in the bore  21 ; is, however, adjustable in height, without altering the angle of sound incidence. In addition to the bore  21  for the test head  9 , the mount  8  includes a second smaller bore  22  for arrangement of the nozzle  10 . Provided in opposition thereto is a vent bore  23 . 
   The facts relating to the angle of sound incidence will now be described again with reference to the illustration of FIG.  2 . As a consequence of the recesses  16 ,  16 ′, milled in the side panels  15 ,  15 ′ at a predefined angle α, the mount  8  and thus the test head  9  are secured in the test carriage  1  at this angle α. By extending the axis  24  of the test head  9 , an intersection  26  is established with the horizontal  25 . The horizontal  25  is defined by the contact points of the castors  7 - 7 ′″. The vertical  27 , extending through the pivot axis  2 , also extends through said intersection  26 . Regardless of the selection of an angle α for the recess  16 ,  16 ′, it is always assured that the previously explained geometric conditions with respect to the intersection  26  do not change. Only in this case is it possible to maintain a reproducible angle of sound incidence. 
     FIG. 6  shows the nozzle element  28  which pertains to the mount  8  and is provided for longitudinal flaw inspection. The angular configuration of this nozzle element  28  is suited to the angular configuration of the arrangement of the test head  9 . There is, however, no need to provide a same fine-tuned gradation in order to make a specially suited nozzle element  28  for each angle of sound incidence. Rather, it is possible to use a nozzle element  28  for a few angles of sound incidence that are not too far apart. Provided in the nozzle element  28  is a ring channel  29  for overflow of the coupling medium. The drainage hole  30  for the coupling medium is located in the center. The nozzle element  28  is secured by means of four screws  31 - 31 ′″ ( FIG. 2 ) which extend through bores in the mount  8  and are rotated into the threaded bore  32 - 32 ′″ of the nozzle element  28 . The description of the nozzle element for transverse flaw inspection will further explain the manner in which the type of securement may be modified to achieve a simple exchange capability. 
   Preferably, the nozzle element  28  is made of Teflon in order to suppress disturbance signals. 
     FIGS. 7-9  show front, side and top views of a test carriage  35  according to the invention for transverse flaw inspection. It is also swingably suspended by means of two side columns  36 ,  36 ′ and a top bar  37 . Comparable to the test carriage  1  for longitudinal flaw inspection, also the test carriage  35  for transverse flaw inspection is movably arranged on the pipe surface by means of firmly clamped ball castors  38 - 38 ′″. 
     FIG. 7  depicts the problem relating to the adaptation to different diameters of pipes  39 ,  40 . As can be clearly seen from this example, a height difference of 3.88 mm is to be bridged in the area of the longitudinal weld seam  5 , when changing from testing a pipe with an outer diameter of 508 mm to testing a pipe with an outer diameter of 1422 mm. The following description relates to the manner of this adaptation in accordance with the invention. 
   The test carriage  35  has hereby two side panels  41 ,  41 ′ ( FIGS. 9 ,  10 ). The respective side panel  41  is characterized by a horizontal web plate  42  with a bore  43 - 43 ′″ for receiving the clamping elements  44 - 44 ′″ for the ball castors  38 - 38 ′″. Furthermore, each side panel has welded thereon two vertical web plates  45 - 45 ′″ which form together with a crossbeam  46 ,  46 ′ the outer frame of the test carriage  35 . Disposed in each of both edge zones of each side panel  41 ,  41 ′ is a slanted recess  47 ,  47 ′. 
     FIG. 11  shows a side panel  48 ,  48 ′ of the inner support element. It is provided on the top side with two loop-like webs  49 - 49 ′″. These webs  49 - 49 ′″ have bores  50 - 50 ′″ for insertion of a stud bolt  51 - 51 ′″. In a same manner, also the previously described side panels  41 ,  41 ′ of the outer frame are provided with bores  52 - 52 ′″ for insertion of stud bolt  53 - 53 ′″. The two side panels  48 ,  48 ′ of the inner support element are interconnected by two supports  54 ,  55 . The inner support element is vertically adjustably arranged in the outer frame in order to be able to compensate for the different curvature of the pipes to be tested, as described in FIG.  7 . The vertical adjustment of the support element in accordance with the invention in relation to the outer frame is realized by means of a guide part  56 - 56 ′″ ( FIG. 12 ) which includes a collar-like disk  57  and an attached rectangular guide block  58 . The guide part  56  is traversed by two bores  59 ,  59 ′. The respective guide part  56 - 56 ′″ is inserted through the recess  47 - 47 ′″, shown in  FIG. 10 , and connected with the side panels  48 ,  48 ′ of the support element by means of screws, not shown here. 
   By turning a knurled nut  60 , an adjustment nut  61  is moved axially (FIG.  9 ). By means of the support  54 , this axial movement of the adjustment nut  61  is transmitted into the entire support element. The guide blocks  58  of the guide parts  56 - 56 ′″, arranged slantingly in the recesses  47 - 47 ′″, convert the axial movement of the adjustment nut  61  in a resultant vertical displacement of the support element in relation to the outer frame in accordance with a slant of the recess  47 - 47 ′″. 
   In order to prevent an inadvertent shift during testing, the adjustment nut  61  may be secured in place by means of a clamping screw  62 . The inner support element and the outer frame are braced together by springs  63 - 63 ′″ so that both parts are kept under tension relative to one another. 
   It is already known in the prior art to move two test heads in tandem configuration for transverse flaw inspection toward one another in axial direction. A mount  64 ,  64 ′. connected with the support element, has a rectangular opening  65 ,  65 ′ for placement of—not shown here—test heads with a rectangular oscillator. 
   The mount  64 , located on the left-hand side in  FIG. 9 , is fixedly secured on the support  55 , while the second mount  64 ′ is axially movable. The axial displacement is implemented by means of two spindles  66 ,  66 ′. Arranged on the right-hand end of each spindle  66 ,  66 ′ is a toothed disk  67 ,  67 ′. Wrapped about both toothed disks  67 ,  67 ′ is an endless toothed belt  68  which can be kept taut by a cam  69  (FIG.  7 ). 
   Secured to the toothed disk  67  on the left-hand side of  FIG. 7  is a knurled nut  70  to allow movement of the toothed belt  68 . A movement of the toothed belt  68  causes both spindles  66 ,  66 ′ to rotate so that the mount  64 ′ and thus also the test head are moved in axial direction. 
   In this exemplified embodiment, the test carriage for transverse flaw inspection has arranged therein also a third mount  71  which receives a test head for the doubling inspection and is securely fixed with the support  54 . The afore-described height adjustment of the support element results in a common movement of all attached mounts  64 ,  64 ′  71  so as to ensure that all three test heads have the same distance to the pipe surface. 
     FIG. 13  shows a top view and a front view of two mounts  64 ,  64 ′ in tandem configuration for receiving test heads for transverse flaw inspection. As this has already been described in detail in the prior art, a more detailed discussion thereof is omitted. However, it should be noted that in accordance with the invention the nozzle elements  72 ,  72 ′ for the transverse flaw inspection are connected from below by means of screws  73 ,  73 ′ with the respective mount  64 ,  64 ′. The nozzle elements  62 ,  62 ′ are also made in this exemplified embodiment of Teflon. It may be required to arrange a seal  71 ,  74 ′ to effect a sealing between nozzle element  72 ,  72 ′ and mount  64 ,  64 ′. 
     FIG. 14  shows a mount for receiving a test head for doubling inspection. The nozzle element  75  is also connected from below by means of screws  76 ,  76 ′ with the mount  71 . Optionally arranged therebetween is a sealing ring  77 . As the mount  71  is placed transversely over the weld seam  5 , the nozzle element  75  includes a respectively configured recess  78 .