Abstract:
An internal inspection unit for pipe has ultrasonic transducers that inspect weld volume, weld root, and wall thickness. The ultrasonic transducers are mounted to a portion of the inspection unit that is rotatable, but no more than one full revolution. One of the units has independently movable shoes for each separate transducer. The shoes are moved between retracted and extended positions by pneumatic cylinders. The other unit has shoes that support more than one transducer, the shoes being biased outwardly by springs.

Description:
[0001]    This application claims the provisional application filing date of Apr. 5, 2002, Serial No. 60/370,444 entitled “Internal Riser Inspection Device.” 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates in general to non-destructive testing of pipe, and in particular to a test unit that is conveyed internally through pipe for ultrasonically inspecting the pipe wall thickness and welds.  
         BACKGROUND OF THE INVENTION  
         [0003]    Non-destructive testing of pipe has been done for many years utilizing ultrasonic transducers, eddy current measurements, x-ray and other techniques. Operators using pulse echo techniques with ultrasonic transducers can determine wall thickness, which is a measure of any corrosion that has occurred. For welds, operators have used flight diffraction (“TOFD”) techniques with ultrasonic transducers. Also, a method known as pulse echo shear wave has been combined with TOFD transducer measurements to inspect portions of the weld that are missed by the TOFD transducer.  
           [0004]    One type of pipe that requires periodic inspection is a drilling riser. Drilling risers, which are utilized for offshore drilling, extend from the drilling rig to a blowout preventer and lower marine riser package, which connect to a subsea wellhead. Drilling risers are made up of sections bolted together with flanges, each section being typically from 60-90 feet in length. Each drilling riser section has a central riser pipe that is normally about 18-24 inches in diameter. Several auxiliary lines are mounted to the exterior of the central riser pipe, the auxiliary lines being used for a choke, kill and hydraulic boost purposes. The auxiliary lines are smaller in diameter and mounted parallel and offset to the axis of the central riser pipe. Normally there will be at least one weld within each riser section, this being a center weld that connects two tubular pipes together to form the riser section. Also, normally the flange connectors are mounted to the ends of the riser sections by welding. Many risers also have buoyant jackets mounted to the exterior.  
           [0005]    A drilling vessel may have several thousand feet of riser pipe, depending on the depth to which it is rated. During use, drill pipe with drill bits on the end, casing, and other well tools are lowered through the riser. Drilling mud returns up the riser. The auxiliary lines are pressurized for various purposes from time to time. The drilling riser is re-used after each well. Consequently it is necessary to periodically inspect the riser to make sure that it has no weaknesses that could result in leakage.  
           [0006]    Inspection in the past has been done primarily by transporting the riser sections to a facility on land that performs the inspection services. The facility removes the buoyancy jackets and auxiliary lines from each section. The riser sections are cleaned and inspected from the exterior with various ultrasonic transducers. If the riser is coated with an epoxy, it must be removed at each inspection site. After inspection, the riser sections are reassembled and shipped back to the drilling vessel.  
           [0007]    The transport of the riser sections to a testing facility on land is expensive. Also, it is time consuming to transport, clean, disassemble, inspect and reassemble the riser sections. During this time, unless a spare drilling riser can be obtained, the drilling rig would not be able to operate. Drilling rigs are very costly on a daily basis.  
           [0008]    It has been proposed to inspect the drilling risers at the drilling vessel. Many drilling vessels have the ability to stack the riser sections horizontally on the vessel while not in use. However, there are a number of problems in doing so. The interior of the drilling riser is often not very clean, and may be coated with dried drilling mud. The central riser pipe is often out of round in portions. The welded areas of the central pipe may be misaligned slightly. Also, there is normally not much access room on the drilling rig at the ends of each riser section for staging the equipment necessary to do the inspection.  
         SUMMARY OF THE INVENTION  
         [0009]    In this invention, tools are provided for inspecting riser pipe sections from the interior. A first ultrasonic transducer is mounted to an inspection unit for determining wall thickness of a pipe, and second and third ultrasonic transducers are mounted to the inspection unit for inspecting weld volume defects. The inspection unit is inserted into the pipe and conveyed along the pipe. Periodically, the first ultrasonic emits an acoustical signal into the pipe perpendicular to the pipe axis and detects a return acoustical signal from the pipe to determine wall thickness, which is an indication of corrosion.  
           [0010]    For inspecting welds, the unit is placed in a position that positions the second and third ultrasonic transducers on opposite sides of the weld. The second transducer is caused to emit an acoustical signal into the weld, the reflection of which is detected by the third transducer to determine if a volume of the weld has any defects.  
           [0011]    Preferably, the inspection unit has fourth and fifth ultrasonic transducers for inspecting a root of a weld, which is an area that the second and third ultrasonic transducers miss. The fourth and fifth transducers are placed on opposite sides of the weld simultaneously with the second and third ultrasonic transducers. Each of these is a pulse echo shear wave transducer oriented at an acute angle relative to the pipe axis. Each transducer emits a signal that reflects from the exterior surface of the pipe back inward through a root of the weld. After passing through the root, the reflected signal reflects back outwardly. If there are no defects, the pulse echo shear wave transducers do not receive any reflected signals. If a defect is present, the reflected signal is diffracted and received by the pulse echo shear wave transducer.  
           [0012]    The inspection unit rotates while inspecting the welds. Preferably, a coupling liquid, such as water, is fed through a line to a cavity between each transducer and the wall of the pipe. In the embodiments shown, the inspection unit also rotates less than one turn while performing the wall thickness inspections. The inspection unit is programmed to collect data of the wall thickness at selected azimuth increments during the rotation.  
           [0013]    Each of the transducers for the central pipe inspection device is mounted to a separate independently movable shoe. The inspection device preferably utilizes pneumatic cylinders to urge the shoes into contact with the inner diameter of the large diameter pipe. The operator can selectively move the transducers from retracted to extended positions. To save on shoe wear, the pulse echo transducers can be retracted while performing the weld inspections with the TOFD transducers and pulse echo shear wave transducers. Similarly, the TOFD transducers and pulse echo shear wave transducers can be retracted while performing the wall thickness inspection.  
           [0014]    For the auxiliary lines, a smaller diameter unit is utilized. In this unit, multiple shoes are employed, but more than one transducer may be mounted to each shoe. The shoe is spring biased rather that urged by a pneumatic cylinder. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a cross-sectional view of an internal inspection device located inside a central pipe of a riser, the inspection device being constructed in accordance with this invention.  
         [0016]    [0016]FIG. 2 is a cross-sectional view of the inspection device of FIG. 1, taken along the line  2 - 2  of FIG. 1.  
         [0017]    [0017]FIG. 3 is a perspective view of one of the transducer assemblies of the inspection device of FIG. 1.  
         [0018]    [0018]FIG. 4 is an enlarged cross-sectional view of part of one of the transducer assemblies of the inspection devise of FIG. 1.  
         [0019]    [0019]FIG. 5 is a schematic illustration of two of the wheels of the inspection device of FIG. 1, and showing an encoder.  
         [0020]    [0020]FIG. 6 is a schematic illustration of the various components of the inspection device of FIG. 1.  
         [0021]    [0021]FIG. 7 is a cross-sectional view of a portion of the riser in FIG. 1, showing an ultrasonic transducer measuring wall thickness utilizing a pulse echo method.  
         [0022]    [0022]FIG. 8 is a cross-sectional view of a weld of the riser of FIG. 1, showing TOFD transducers inspecting for defects in the volume of the weld.  
         [0023]    [0023]FIG. 9 is a schematic cross-sectional view of the weld of FIG. 8, showing pulse echo shear wave transducers inspecting for defects in the root of the weld.  
         [0024]    FIGS.  10 - 18  are schematic sequential illustrations of the rotational movement that the pulse echo transducers undergo at each inspection area along the riser pipe.  
         [0025]    [0025]FIG. 19 is a perspective view of an inspection device in accordance with the invention for inspecting auxiliary lines of a drilling riser.  
         [0026]    [0026]FIGS. 20 a  and  20   b  comprise a partially sectioned and exploded view of the inspection device of FIG. 19.  
         [0027]    [0027]FIG. 21 is an enlarged sectional view of the inspection unit of the inspection device of FIG. 19.  
         [0028]    [0028]FIG. 22 is a sectional view of the inspection unit of FIG. 21, taken along the line  22 - 22  of FIG. 21. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    The inspection device of FIG. 1 has a self-propelled drive unit  11 , which is shown within a central pipe  13  of a riser section. Drive unit  11  has two drive wheels  15  and two support wheels  16 , which are spaced axially from drive wheels  15 . Drive unit  11  is controlled and supplied with water by a plurality of lines  17  that extend out the end of pipe  13 . The operator has controls for causing drive unit  11  to move forward and backward by providing signals through some of the lines  17 .  
         [0030]    The operator also has an odometer display that displays an indication of the linear distance that drive unit  11  is located from a zero point at the end of riser section  13 . Encoder  18  (FIG. 5), which is mounted to the axle of support wheels  16 , provides this information. Encoder  18  is preferably a conventional unit that uses a light beam that passes through a large number of apertures formed in a disc, the disc rotating with support wheels  16 . Support wheels  16  are not driven, rather they freewheel. Consequently, any slippage that might occur in drive wheels  15  does not erroneously affect the odometer information provided to the operator.  
         [0031]    Drive unit  11  has a linear motor  20  (FIG. 6) and a rotational motor  21 . Linear motor  20  causes rotation of drive wheels  15 . Rotational motor  21  rotates a drive shaft  23  that extends parallel to the longitudinal axis of drive unit  11 . Rotational motor  21  has a linkage that causes it to rotate drive shaft  23  an increment that is less than one revolution, then rotate it back the other direction. A rotational encoder  25  (FIG. 6) provides an azimuth indication to the operator of the precise angle of rotation of drive shaft  23  at all times.  
         [0032]    An inspection unit  19  is mounted to the forward end of drive unit  11  on drive shaft  23  for rotation therewith. In this embodiment, inspection unit  19  is located forward of both sets of wheels  15 ,  16 , thus is supported in cantilever fashion by drive unit  11 . Inspection unit  19  includes a rearward disc  27  that is mounted to drive shaft  23 . Support rods  29  extend from rearward disc  27  forwardly. Support rods  29  are parallel to each other and parallel to the axis of drive shaft  23 . A forward disc  31  is located at the forward ends of support rods  29  parallel to disc  27 . Although, not shown, a pair of video cameras is preferably mounted on the forward face of forward disc  31 .  
         [0033]    A plurality of transducer mounting blocks  33  (FIG. 3) are mounted to the support rods  29 . Transducer mounting blocks  33  are mounted at selective points along the lengths of support rods  29 , which extend through holes within them. Each transducer mounting block  33  comprises a pneumatic cylinder and piston for moving rods  35  radially inward and outward between retracted and extended positions. A transducer plate  37  is mounted to the outer ends of pneumatic cylinder rods  35  for carrying a transducer shoe  39 . Each transducer shoe  39  has an outer face that curves in a convex form for mating with the inner diameter of the riser section  13  (FIG. 1). Transducer shoe  39  is a hard plastic material and can be readily replaced for different diameters of riser pipe  13 .  
         [0034]    A spacer block  41  supports each transducer shoe  39 , each spacer block  41  being mounted to transducer plate  37  and a pair of braces  43 . Braces  43  extend outward from drive shaft  23 , but are angled relative to an axis passing through either of the pneumatic cylinder rods  35 . Braces  43  are secured to spacer block  41  by fasteners  45 .  
         [0035]    Referring to FIG. 4, a recess or cavity  49  extends from the outer face of each transducer shoe  39  inward through transducer shoe  39  and upper spacer block  47 . A small water passage  50  extends through upper spacer block  47  and into transducer shoe  39 , where it joins cavity  49 . A small flexible tube  52  joins water passage  50  for delivering water to cavity  49 . A transducer  53  is mounted to the inward side of upper spacer block  47  at the base of cavity  49 . Transducer  53  is a conventional piezoelectric device that will emit and/or receive acoustical signals. In this embodiment, each transducer shoe  39  has only one transducer  53 . Wires  51  lead to transducer  53  to supply electrical energy to cause a sound pulse to be emitted. The transducers  53  used for pulse echo measurements convert acoustical reflected signals received into electrical energy, which is transmitted through one of the wires  51 .  
         [0036]    Referring to FIGS. 1 and 2, inspection unit  19  preferably has two transducer pairs  55  for measuring weld volume by the TOFD method. The TOFD transducers  55  within each pair are spaced axially apart a selected distance, with one being more forward of the other. Each pair of TOFD transducers  55  is 180 degrees from the other pair of transducers  55 . The forward transducer  55  in each pair is located in the same radial plane as the forward transducer  55  in the other pair. Similarly, the rearward transducer  55  in each pair is located the same axial position along inspection unit  19  as the rearward transducer of the pair located 180 degrees away.  
         [0037]    Inspection unit  19  also has two transducer pairs  57  (FIG. 2) for measuring a root of a weld by pulse echo shear wave techniques, also referred to herein as shear wave. Each pair of transducers  57  is positioned the same axial distance as the forward and rearward TOFD transducers  55 . Each transducer  57  is spaced a selected axial distance from the other transducer  57  of the pair. The pairs of shear wave transducers  57  are located 180 degrees apart from each other. FIG. 2 shows a pair of TOFD transducers  55  located at the zero degree position and another pair at the 180 degree positions, while shear wave transducers  57  are located at the 90 degree and 270 degree positions.  
         [0038]    In this embodiment, inspection device  19  also has four transducers  59  that measure wall thickness, particularly utilizing pulse echo techniques. Pulse echo transducers  59  are located at the zero degree, 90 degree, 180 degree, and 270 degree positions. Pulse echo transducers  59  are located in the same radial plane, which is spaced forward of transducers  55  and  57  in this exemplary embodiment. Note that a different number of transducers than four could be utilized for pulse echo transducers  59  as well as for the other transducers  55 ,  57 .  
         [0039]    Referring to FIG. 6, a controller  65  is located exterior of riser section  13  for remotely controlling the inspection device through lines  17 . Controller  65  includes a power supply, a computer, a monitor, a keyboard, and a joystick. Controller  65  also controls two pneumatic valves  67 ,  69 . Valve  67  is connected to a supply of air pressure and will selectively cause the piston within mounting block  33  of each pulse echo transducer  59  to move between a retracted position and a radially outward extended position. Valve  67  causes the four pulse echo transducers  59  to move radially outward in unison or to retract in unison. Valve  69  independently controls the remaining transducers, these being TOFD transducers  55  and shear wave transducers  57 . Valve  69  causes the four TOFD transducers  55  and the four shear wave transducers  57  to move between the retracted and extended positions in unison independent of pulse echo transducers  59 .  
         [0040]    Referring to FIG. 7, each pulse echo transducer  59  is of a type that transmits and receives. The shoe  39  (FIG. 3) that holds each transducer  59  is placed in contact with the inner diameter of riser section  13  with each pulse echo transducer  59  pointing radially outward, normal to the inner diameter of riser section  13 . Water is delivered to cavity  49  (FIG. 4) to provide a liquid coupling. Each transducer  59  transmits an acoustic signal through the water, which communicates to riser section  13 . The signal travels to the outer diameter of riser section  13 , and is reflected back to the inner diameter of riser  13 , where it is received by transducer  59 . The reflected signal reverberates back and forth between the inner and outer diameters of riser section  13 . The sound received by transducers  59  is converted into electrical signals, which are transmitted to controller  65  (FIG. 6). Controller  65  analyses them in a conventional manner. The thickness of riser section  13  is determined by measuring the time that it takes for the signal to return to the inner diameter of riser section  13 .  
         [0041]    [0041]FIG. 8 illustrates the TOFD method, which is also known in the art. Within each pair, one of the TOFD transducers  55  is a transmitter and the other is a receiver. The receiver is spaced axially from the transmitter, either on the forward side or the rearward side of the transmitter. TOFD transducers  55  are positioned on both sides of and in close proximity to a weld  71 . Weld  71  is a typical weld formed between two beveled ends of tubular members that make up riser section  13 . Weld  71  has a triangular cross-section, with the apex or root of weld  71  being at the inner diameter and the cap at the outer diameter. The axial distance between the TOFD transducers  55  in each pair is greater than the width of the cap of weld  71 . The TOFD transducers  55  are angled toward each other, so that the signal from the transmitter TOFD transducer  55  passes through the wall of riser section  13  at a selected angle, such as about 60 degrees and reflects to the receiver TOFD transducer  55 .  
         [0042]    Inspection unit  19  is rotated about drive shaft  23  (FIG. 1) while the transmitter TOFD transducer  55  emits sound pulses through the water coupling in cavities  49 . The signals pass through the volume of weld  71  and reflect from the outer diameter of weld  71  to the receiver TOFD transducer  55 . If weld  71  has a flaw  73 , some of the signals will be diffracted at the tips of flaw  73 . The diffracted signals are also received by the receiver TOFD transducer  55 , as illustrated. The time that it takes for the sound waves to reach receiver TOFD transducer  55  is different for the diffracted pattern versus the non-diffracted pattern, and this difference is analyzed in a known manner to provide an indication of flaw  73 .  
         [0043]    The TOFD method measures the volume of the weld, which is all of the weld except for the root portion in the vicinity of the inner diameter. The pulse echo shear wave technique is employed, as illustrated in FIG. 9, to inspect for any flaws in the root portion of weld  71 . Each shear wave transducer  57  is of a pulse echo type, having both a receiver and a transmitter. Each transducer  57  is angled toward the other in a manner similar to TOFD transducers  55  (FIG. 8). Shear wave transducers  57  are also axially spaced apart for positioning on opposite sides of weld  71  at approximately the same spacing as TOFD transducers  55 . Each shear wave transducer  57  within each pair emits a sound pulse, but at a slightly different time from the other transducer  57  in the same pair so as to avoid interference with each other. Shear wave transducers  57  are oriented so that the sound waves are directed toward the outer side of riser section  13  near but not through the volume of weld  71 . The angles are selected so that the sound pulse will contact the outer diameter of riser  13  and reflect back through the root of weld  71 . If the root is free of any defects, the reflected signal contacts the inner diameter of riser section  13  between shear wave transducers  57  and reflects back outward. Because of the positioning of shear wave transducers  57 , none of the shear wave transducers  57  will receive any reflected signals if the root is free of defects. However, if a flaw is encountered, diffraction will occur and one or both of the transducers  57  in each pair will receive a return signal that emanated from the other transducer  57 . Controller  65  analyzes the return signal in a known manner to provide an indication to the operator.  
         [0044]    In operation, the operator can inspect the wall thickness and welds  71  (FIG. 8) of riser  13  during one round trip pass through riser section  13 . The inspection devise does not need to be pulled from riser section  13  between inspecting for corrosion with pulse echo transducers  59  and inspecting for weld defects with TOFD transducers  55  and shear wave transducers  57 . In a preferred technique, the operator inspects all the welds  71  first, then inspects for corrosion. However, this could be reversed. Also, if desired, the operator could inspect a portion of riser section  13  for corrosion and inspect the welds  71  as they are encountered.  
         [0045]    In the preferred technique, however, the operator first retracts all of the transducers  55 ,  57 ,  59  by controlling valves  67 ,  69  (FIG. 6). The operator inserts the device into one end of the riser section  13 , which may be either the box end or the pin end. Once inserted, the operator advances drive unit  11  to a point that positions TOFD transducers  55  and shear wave transducers  57  on opposite sides of the first weld  71  (FIGS. 8 and 9). The operator stops the linear movement of unit  11  and moves shoes  39  containing transducers  55  and  57  outward by controlling valve  69  (FIG. 6). The operator causes water to flow to cavities  49  (FIG. 4) and actuates rotational motor  21  to rotate inspection unit  19 . The entire inspection unit  19  will rotate while pulses are continually emitted by the various transducers  55 ,  57  and received by the respective transducers  55 ,  57 . The operator receives signals from lines  17  and in the manner described above, analyzes weld  71  to determine for any defects.  
         [0046]    Preferably, inspection unit  19  rotates only 180 degrees at each weld  71 . Each pair of TOFD transducers  55  will sweep and measure 180 degrees, thus covering all 360 degrees of weld  71  during the 180 degree rotation. Similarly, each pair of shear wave transducers  57  will sweep 180 degrees. There is no need to rotate more than 180 degrees if the device has two pairs of TOFD transducers  55  and two pair of shear wave transducers  57 . If the inspection device had only a single pair of TOFD transducers  55  and shear wave transducers  57 , then it would be necessary to rotate inspection unit  19  one full revolution. Rotation more than one revolution is not needed and would twist lines leading to inspection unit  19  more than desired.  
         [0047]    Once the inspection of the first weld  71  is completed, the operator optionally retracts transducers  55 ,  57  to save wear on shoes  39  and actuates linear motor  20  to advance inspection unit  19  to the next weld  71 . The operator will have a general indication of the position of the next weld  71  based on information provided and the odometer reading provided by encoder  18  (FIG. 5). Also, the video cameras provide a visual aid for the operator to properly position transducers  55  and  57  on opposite sides of the next weld  71 . The operator optionally may leave inspection unit  19  in the 180 degree rotated position that existed at the conclusion of inspecting the first weld  71 . At the next weld  71 , the operator can inspect by rotating inspection unit  19  the opposite direction for 180 degrees. Once the operator reaches the opposite end, all of the welds  71 , normally three, will have been inspected, with the data recorded in a memory storage unit of the controller  65  (FIG. 6).  
         [0048]    The operator then may make wall thickness tests with the pulse echo transducers  59 . Rather than bringing drive unit  11  back to the beginning end of riser section  13 , it is more efficient to operate drive unit  11  in reverse and start making pulse echo measurements from the far end. The operator will be given instructions as to what lineal increments, or inspection areas, the wall thickness inspections are to be made. Also, the operator will be informed as to how many inspection sites are to be made around the circumference of riser section  13  at each inspection area or zone.  
         [0049]    Referring to FIGS.  10 - 18 , assume for example that the operator is to make pulse echo inspections at inspection areas one foot apart along the length of riser  13 . Also, the operator may be instructed to have an inspection site every 45 degrees around the circumference at each inspection zone. In this embodiment, there are only four pulse echo transducers  59 , each 90 degrees apart from the other. Consequently, the operator will provide instructions to controller  65  (FIG. 6) to collect data when rotational encoder  25  indicates that inspection unit  19  is in the zero degree rotational position, the 45 degree rotational position, and the 90 degree rotational position. Data is thus collected for inspection sites that are 45 degrees apart.  
         [0050]    In the example of FIGS.  10 - 18 , symbol  75  indicates the zero point for rotation of inspection unit  19  (FIG. 1). At the first inspection area, the operator actuates valve  67  to extend transducers  59  and valve  69  to retract transducers  55 ,  57 , unless they have already been retracted. The operator takes the first measurement while symbol  75  is in the zero degree position, providing data for inspection sites at the zero degree, 90 degree, 180 degree, and 270 degree positions. The operator actuates rotational motor  21  (FIG. 1), which causes inspection unit  19  to rotate. Controller  65  causes signals to be recorded and computed when inspection unit  19  reaches the next inspection site at the first inspection area, which is the 45 degree rotational position illustrated in FIG. 11. Rotational encoder  25  provides the azimuth information to controller  65 , which automatically causes the reading to occur at the 45 degree inspection site. At this point, all desired inspection sites at the first inspection area will have been made. In this embodiment, inspection unit  19  does not cease to rotate at the 45 degree inspection site, and will normally rotate a preprogrammed amount, such as 90 degrees. No additional reading, however, is taken in the position of FIG. 12. Also, sound pulses are continually emitted and received by transducers  59  during the full 90 degree rotation, but they are not recorded and computed by controller  65 . Readings could be made at much shorter rotational increments, such as 5 degrees, with the amount of data storage of controller  65  being the limitation. Furthermore, inspection unit  19  could be rotated 180 degrees, if desired, but with four transducers  59 , readings would be taken only during the first 90 degrees of rotation, regardless of the number of circumferentially-spaced inspection sites selected at each inspection zone.  
         [0051]    Once the rotation of inspection unit  19  is completed at the first inspection site of FIGS.  10 - 12 , the operator moves to the next inspection site, which is shown in FIGS.  13 - 15 , with the shoes for transducers  59  optionally retracted. The operator does not need to rotate inspection unit  19  back to the zero degree position of FIG. 10 prior to reaching the second inspection area. Rather, the operator can take readings simultaneously while causing inspection unit  19  to rotate in the reverse direction. Controller  65  is programmed to take readings at the desired azimuth increments during the 90 degree reverse rotation. At the conclusion of the 90 degree rotation at the one foot interval, shown in FIG. 15, the operator actuates linear motor  20  to move to the third inspection site, shown in FIG. 16- 18 . The process is then repeated until the full length of riser section  13  has been inspected. At any time, the operator is free to reverse linear motor  20  and retake readings at any particular inspection area. If more pulse echo transducers  59  are utilized than four, it may not be necessary to rotate inspection unit  19  because adequate coverage could be obtained without rotation.  
         [0052]    FIGS.  19 - 21  disclose a small diameter unit  77  for inspecting the auxiliary lines (not shown) of riser section  13  (FIG. 1). The auxiliary lines of riser section  13  may remain in place mounted to the exterior of the riser section  13  during this inspection. As in the inspection of the central pipe section  13  (FIG. 1), this is preferably done while riser section  13  is horizontal and located at the offshore drilling rig. Unit  77  has an elongated tubular housing  79  supported on a plurality of wheels  81 . In this exemplary embodiment, wheels  81  are not self-propelled, rather unit  77  is pulled through the auxiliary pipe by a cable. An inspection unit  83  is mounted to housing  79  between its ends. Inspection unit  83  is preferably mounted between two of the sets of wheels  81 . Video camera ports  85  are located in housing  79  for providing visual access for a video camera  86  (FIG. 20A).  
         [0053]    Small diameter unit  77  also has an odometer or encoder  87  mounted to the frame of housing  79 . Encoder  87  is driven by a gear train  89 , which in turn is driven by rotational movements of one of the sets of wheels  81 . A rotational motor  91  is located in housing  79  for rotating a shaft  93  (FIG. 20 b ), which is parallel to the longitudal axis of small diameter unit  77 . Shaft  93  extends into engagement with an axle  95  of inspection unit  83 . As in the first embodiment, motor  91  preferably rotates inspection unit  83  180 degrees for measurements of welds, and 90 degrees for inspection of wall thickness. An azimuth encoder (no shown) provides an indication of the particular angular orientation of inspection unit  83  at all times.  
         [0054]    As shown in FIG. 21, axle  95  is mounted on bearings  97  that allow the entire inspection unit  83  to rotate relative to housing  77  (FIG. 20A and 20B). A plurality of outer sleeves  99  are mounted to axle  95  for rotation therewith. Outer sleeves  99  have plurality of slots  101 , which in this embodiment comprises four. A transducer shoe  103  extends from each slot  101 . Each slot  101  is located 90 degrees from the other and is an elongated aperture parallel to the axis of axle  95 . Transducer shoe  103  is a hard plastic member that is mounted on a plate  105 . Plate  105  is urged outward by springs  107  located at each end. Springs  107  independently urge each transducer shoe  103  to a radial outward position.  
         [0055]    A plurality of mounting blocks  109  are located within each transducer shoe  103 . A plurality of cavities  111  extend through each transducer shoe  103  and mounting block  109 . A water passage  113  leads to each cavity  111 , water passage  113  being connected to a water conduit  115 . TOFD transducers  119  are located in two of the shoes  103 , with one pair of TOFD transducers  119  at the zero degree shoe  103  and the other at a 180 degree shoe  103  in FIG. 22. Similarly shear wave transducers  121  are mounted to shoes  103  at 90 degree and 270 degree positions. There are preferably four pulse echo transducers  123  spaced 90 degrees apart from each other.  
         [0056]    Small diameter unit  77  operates in the same manner as the large diameter unit, except that it is pulled manually from inspection zone to inspection zone or weld to weld, and transducer shoes  103  do not retract. While inspecting a weld, motor  91  rotates inspection unit  83  180 degrees. Rotational motor  91  rotates inspection unit  83  90 degrees at each inspection area while inspecting wall thickness. During that interval, the controller will cause data points to be taken at the selected rotational increments.  
         [0057]    The invention has significant advantages. It allows efficient inspection of riser pipe sections on a rig. This avoids transporting the riser pipe sections to land, stripping the buoyant members and auxiliary lines then inspecting the pipes from the exterior. Inspecting internally avoids problems encountered due to external coatings. Because of the coupling liquid, the interiors of the riser sections do not have to be spotlessly clean for inspection to be valid. The independently movable shoes accommodate for out-of-round pipe and misaligned welds. Performing the weld tests and the corrosion tests with the same unit reduces the amount of equipment required and also saves time in that it can be done during one trip through the riser section. Rotating the inspection unit less than one full turn allows the wires and tubes to be connected directly between the unit and the exterior without over twisting them. There is no need for electrical slip rings and rotational type manifolds.  
         [0058]    While the invention has been shown in only two of its forms, it should be apparent to those skilled in the art that is it not so limited but is susceptible to various changes without departing from the scope of the invention. For example, although shown inspecting riser pipe while stored horizontally, with modifications, the inspection device could be utilized while the riser pipe is suspended vertically as well.