BACKGROUND OF THE INVENTION This invention generally relates to apparatus and methods for rotating a probe carrying cable and more particularly relates to an apparatus and a method for rotating a process probe carried by a rotatable cable in a small-diametered nuclear steam generator heat transfer tube, such that the process probe rotates with sufficient torque and at a predetermined speed.

Occasionally, a nuclear steam generator heat transfer tube associated with a pressurized water nuclear reactor may degrade and experience through-wall cracking allowing the tube to leak. A leaking tube is undesirable because the pressurized fluid flowing through the tube is radioactive and leakage of the fluid through the crack will radioactively contaminate the steam generated by the steam generator. Thus, any tube exhibiting severe degradation may be internally sleeved at the site of the degradation so that the radioactive fluid will not radioactively contaminate the steam generated by the steam generator.

In order to identify a degraded tube, a nondestructive examination process probe (e.g., an eddy current or ultrasonic probe) is inserted into one of the tubes and moved axially therein by means of an attached cable to detect any degraded portions of the tube. As the examination probe is moved axially in the tube, it is also rotated about its longitudinal axis in order to suitably examine the interior surface of the tube both radially and axially. After the degraded portion of the tube is identified, the examination probe is removed and a sleeve is then disposed in the tube and radially expanded into intimate engagement with the tube wall in order to cover the degraded portion of the tube. The sleeve may then be welded to the inner surface of the tube, such as by means of a rotating laser welding process probe that is axially moved in the tube, positioned adjacent the sleeve and then activated as it is rotated in order to laser weld the sleeve to the tube.

In order to rotate the examination or laser welding process probe, one end of the previously mentioned cable is

connected to the process probe and the other end is connected to a motor that rotates the cable. The process probe rotates as the motor rotates the cable. In one prior art device, the motor is located adjacent the process probe, such that both the motor and 5 the process probe are simultaneously disposed in the heat transfer tube. Locating the motor adjacent the process probe assists in providing sufficient torque to the process probe. It is possible to locate the motor adjacent the process probe in the tube because many such tubes are large enough to accept larger

10 motors that are commercially and readily available in the industry. However, such a probe/motor/cable combination is most advantageously used to examine or repair heat transfer tubes having a relatively large inside diameter (e.g., approximately 0.420 to 0.775 inch in diameter) . This is so because only lb relatively large sized motors, that are disposed in such relatively large size tubes, possess sufficient torque (e.g., approximately 1.5 ounce-inch) to suitably rotate the typical process probe. It is important that sufficient torque be available to rotate the process probe. This is important because

20 lack of sufficient torque may cause the motor to stall. To avoid stalling, the electronics associated with such a motor have a current limit switch that senses the current drawn by the motor. When the limiting current is reached, the motor shuts-off. This avoids damage to the motor.

25 Applicant has observed, however, that some nuclear heat exchanger heat transfer tubes have relatively small inside diameters (e.g., approximately 0.410 inch in diameter) . Commercially available motors having sufficient torque to rotate the process probe are too large to fit within such small-

30 diametered heat transfer tubes. Conversely, commercially available motors small enough to fit within small-diametered heat transfer tubes lack sufficient torque to suitably rotate the process probe. Also, some existing ultrasonic sensor designs are too heavy to be satisfactorily rotated by commercially available

35 motors. Therefore, a problem in the art is to suitably rotate the process probe with sufficient torque so that the process

probe is capable of examining or repairing a small-diametered tube.

Moreover, applicant has observed that another defi¬ ciency of commercially available motors is that they are individually equipped with gears having a specified gear ratio therein for rotating the probe at a specified speed. Therefore, such motors are typically changed-out or substituted with a different motor when it is desired to use a different gear ratio for rotating the probe at a different speed. This may require the purchase and stocking in inventory of a plurality of motors in order to have the option to inspect or repair tubes at any desired speed. Therefore, another problem in the art is to avoid the costly purchase and stocking in inventory of a plurality of motors. A rotatable probe carrier is disclosed in U.S. Patent

5,174,165 titled "Flexible Delivery System For A Rotatable Probe" issued December 29, 1992 in the name of William E. Pirl. This patent discloses a flexible, hose-like delivery system for positioning and rotatably supporting an eddy current probe at a desired position along the longitudinal axis of a small-diame¬ tered nuclear steam generator heat transfer tube. The probe of the Pirl patent is rotated by a motor located externally to the steam generator tubes. However, this patent does not appear to disclose a solution to the problem of having to purchase and stock in inventory several motors in order to have the option to inspect tubes at any desired torque and speed.

Thus, although the above recited art may disclose apparatus for rotating a probe carrying cable, this art does not appear to disclose an apparatus and a method for rotating a process probe carried by a rotatable cable in a small-diametered nuclear steam generator heat transfer tube, such that the process probe rotates with sufficient torque and at a predetermined speed. Therefore, what is needed are an apparatus and method for suitably rotating a process probe carried by a cable in a small- diametered nuclear steam generator heat transfer tube, such that the process probe rotates with sufficient torque and at a predetermined speed.

SUMMARY Disclosed herein is an apparatus and method for rotating a process probe carried by a rotatable cable in a small- diameter nuclear steam generator heat transfer tube, such that the process probe rotates with sufficient torque and at a predetermined speed. The apparatus includes a motor disposed externally to the steam generator for rotating the process probe. The motor generates an input torque that is received by a cable engaged by the motor. A plurality of torque converter units interconnects the cable and the process probe. The torque converter units are disposed in the tube and converts the input torque into an output torque acting on the process probe, so that the process probe rotates with sufficient torque and at a predetermined speed as the motor rotates the cable. In its broad form the invention is an apparatus for rotating a process probe in a heat exchanger heat transfer tube, comprising rotation means disposed externally to the heat exchanger for rotating the process probe, said rotation means generating an input torque; and torque converter means inter- connecting the rotation means and the process probe and disposed in the tube for converting the input torque to an output torque, so that the process probe rotates at a predetermined speed.

In its broad form, the invention is also a method of rotating a process probe in a heat exchanger heat transfer tube, comprising the steps of generating an input torque by operating a motor disposed externally to the heat exchanger; and rotating the process probe at a predetermined speed by converting the input torque to an output torque by operating a torque converter unit interconnecting the motor and the process probe. An object of the present invention is to provide an apparatus and method for rotating a process probe carried by a rotatable cable in a small-diameter nuclear steam generator heat transfer tube, such that the process probe rotates with suffi¬ cient torque and at a predetermined speed. A feature of the present invention is the provision of a plurality of torque converter units stacked end-to-end for converting an input torque of the motor into an output torque

acting on the process probe in order to rotate the process probe with sufficient torque and at the predetermined speed.

An advantage of the present invention is that the process probe is rotated with sufficient torque to examine or repair small-diametered tubes without the need to dispose a motor in the tube.

Another advantage of the present invention is that use thereof avoids the costly purchase and stocking in inventory of a plurality of motors to suitably rotate the process probe. These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particu¬ larly pointing out and distinctly claiming the subject matter of the invention, it is believed the invention will be better understood from the following description taken in conjunction with the accompanying drawings wherein:

Figure 1 is a perspective view in partial vertical section of a typical nuclear steam generator with parts removed for clarity, the steam generator having a plurality of U-shaped heat transfer tubes disposed therein, this view also showing the apparatus of the invention connected to the steam generator for rotating a process probe disposed in a predetermined one of the steam generator tubes;

Figure 2 is a view in partial vertical section of the process probe disposed in the predetermined tube; this view also showing a plurality of torque converter units stacked end-to-end and connected to the process probe for imparting a predetermined torque to the process probe in order to rotate the probe at a predetermined speed;

Figure 3 is a view taken along section line 3-3 of Figure 2;

Figure 4 is a view in vertical section of a pair of adjacent torque converter units;

Figure 5 is an exploded view in vertical section of the pair of torque converter units illustrated in Figure 4;

Figure 6 is a view taken along section line 6-6 of Figure 3; and Figure 7 is a view taken along section line 7-7 of

Figure 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1, there is shown a typical nuclear heat exchanger or steam generator, generally referred to as 10, for generating steam. Steam generator 10 comprises a cylindrical body portion 20 enclosed at its lower end by a hemispherical shell 30. A transverse plate or tubesheet 40 divides steam generator 10 into a primary side 50 below tubesheet 40 and a secondary side 60 above tubesheet 40. The primary side 50 is divided by a divider plate 65 into an inlet section 67 and an outlet section 70.

Still referring to Fig. 1, tubesheet 40 has a plurality of holes 80 therethrough. A plurality of U-shaped heat transfer tubes 90 (only two of which are shown) have ends received in respective ones of the holes 80 so that one end of each tube 90 communicates with inlet section 67 and the other end of each tube 90 communicates with outlet section 70. Each U-shaped tube 90 may be of relatively small inside diameter (e.g. , approximately 0.410 inch) , such as found in Canadian nuclear steam generators. Moreover, each U-shaped tube 90, which may have a total length of approximately 60 feet, is laterally supported on secondary side 60 by a plurality of spaced-apart support plates 100. A plurality of manways 110 (only one of which is shown) provide access to inlet section 67 and outlet section 70 to allow servicing of steam generator tubes 90. Steam generated by steam generator 10 is transported to a turbine-generator (not shown) by means of a pipe (not shown) for generating electricity in a manner well known in the art.

Referring to Figs. 1 and 2, there is shown an appara- tus, generally referred to as 120, for rotating a process probe 130 in one of the tubes 90. It will be appreciated that the terminology "process probe" is defined herein to mean any type

of tool commonly used in the art to effect a process (e.g., inspection or repair) on a structure (e.g., a tube) while the tool is disposed near the structure. In this regard, such a process probe 130 may be a nondestructive examination device for nondestructively examining tube 90 for degradation, which examination device may be an eddy current or ultrasonic sensor. Alternatively, process probe 130 may be a repair tool for repairing a degraded portion of tube 90, which repair tool may be a laser welding device suitable for welding a sleeve (not shown) to the inner surface of tube 90 so as to cover or seal a degraded portion of tube 90.

Still referring to Figs. 1 and 2, apparatus 120 comprises rotation means, such as a motor 140, disposed exter¬ nally to steam generator 10 for rotating process probe 130. Motor 140 generates an input torque, which may be equal to or greater than approximately 1.5 ounce-inch. A motor 140 suitable for this purpose is available from Micro Mo, Incorporated located in Saint Petersburg, Florida.

Referring now to Figs. 1, 2, 3, 4 and 5, a flexible first shaft 150 has a first end portion 160 thereof engaged by motor 140, so that motor 140 is capable of rotating first shaft 150. As motor 140 rotates first shaft 150, first shaft 150 receives the input torque generated by motor 140. First shaft 150 also has a second end portion 170 extending through manway 110 and which is ultimately connected to process probe 130 in the manner disclosed hereinbelow. It will be appreciated that the terminology "input torque" is defined herein to mean that torque produced by motor 140 and received (i.e., input) to first shaft 150. Still referring to Figs. 1, 2, 3, 4 and 5, torque converter means, generally referred to as 180, interconnect motor 140 and process probe 130. More specifically, torque converter means 180 comprises a plurality of adjacent interconnected torque converter units 180a, 180b, 180c, 180d and 180e stacked end-to- end for converting the input torque of motor 140 to an output torque that acts on process probe 130, so that process probe 130 rotates with sufficient torque and at a desired predetermined

speed. More specifically, the previously mentioned second end portion 170 of first shaft 150 has a planet gear 185 there- surrounding. Planet gear 185 includes a plurality of first gear teeth 187, so that first gear teeth 187 rotate as first shaft 150 is rotated by motor 140. Moreover, each of the torque converter units 180a/b/c/d/e also includes a generally bowl-shaped housing 190 having a bore 200 through a base portion 210 thereof for reasons provided hereinbelow. For reasons disclosed hereinbelow, housing 190 may be formed of a lubricated polymer material, such as oil-impregnated "NYLON", available from Curbell, Incorporated located in Glenshaw, Pennsylvania. In addition, each base portion 210 has a hole 220 therein for receiving an end portion of a rotatable spindle 230 centered in and attached to a sun gear 240. Sun gear 240 comprises a plurality of second gear teeth 250 therearound, so that second gear teeth 250 rotate as spindle 230 rotates. Thus, sun gear 240 rotates about the axis of spindle 230 as planet gear 185 rotates because second gear teeth 250 engage first gear teeth 187. It will also be appreciated that each sun gear 240 resides in a cavity 255 defined by each bowl- shaped housing 190. Mounted on each sun gear 240 and attached to spindle 230 is a sun gear carrier 252 for purposes of stability and to provide a surface for a ring gear 260 to ride against. Sun gear carrier 252 defines a bore 253 centrally therethrough for reasons disclosed hereinbelow. In the preferred embodiment of the invention, there are a plurality of two sun gears 240 spaced-apart circumferentially around planet gear 185. Referring yet again to Figs. 1, 2, 3, 4 and 5, each torque converter unit 180a/b/c/d/e further includes the previ¬ ously mentioned ring gear 260. Each ring gear 260 defines an inverted chalice shape having a base portion 270 integrally attached to a stem portion 280. Each of the stem portions 280 includes planet gear 185 having first gear teeth 187 for engaging second gear teeth 250 of its respective sun gear 240. In addition, each stem portion 280 defines a bore 285 therethrough in communication with a cavity 290 defined by each base portion 280 of each ring gear 260. A plurality of third gear teeth 300 circumscribe cavity 290 for engaging second gear teeth 250 of sun

gear 240. In this manner, ring gear 260 rotates as sun gear 240 rotates because third gear teeth 300 engage second gear teeth 250.

Again referring to Figs. 1, 2, 3, 4 and 5, each bowl- shaped housing 190 and its associated ring gear 260 are sized such that base portion 270 of ring gear 260 matingly fits within cavity 255. Fitting base portion 270 within cavity 255 enables second gear teeth 250 to engage third gear teeth 300, so that ring gear 260 rotates as sun gear 240 rotates. In the preferred embodiment of the invention, the engagement of each sun gear 240 with its associated ring gear 260 obtains a 2-to-l gear ratio. Moreover, as previously mentioned, housing 190 is preferably an oil-impregnated polymer. This is important because forming housing 190 from an oil-impregnated polymer causes any interfacing surface 305 between housing 190 and ring gear 260 to obtain a low coefficient of friction as ring gear rotates in cavity 255. A low coefficient of friction between the interfac¬ ing surface 305 of housing 190 and base portion 270 obviates the need to interpose a plurality of bearings between housing 190 and ring gear 260. Use of bearings would otherwise result in an undesirable increase in the radial size of each torque converter unit 180a/b/c/d/e. Moreover, bearings are most appropriate for attaining relatively high revolutions per unit time, which is not required for the present application. In addition, not requiring the use of bearings results in lowered cost and greater ease of assembly.

Referring yet again to Figs. 1, 2, 3, 4 and 5, in the preferred embodiment of the invention, there are five adjacent interconnected torque converter units 180a/180b/180c/180d/180e stacked end-to-end for converting an input torque equal to or greater than approximately 1.5 ounce-inch provided by motor 140 into the desired final output torque acting upon process probe 130. Of course, it is understood from the description herein¬ above that there may be only one torque converter unit comprising torque converter means 180, such as only torque converter unit 180a, rather than the five torque converter units 180a/b/c/d/e of the preferred embodiment, if desired. Alternatively, any

number of coaxially stacked torque converter units may comprise torque converter means 180 depending on the amount of torque that is to act upon process probe 130 to rotate process probe 130 with sufficient torque and at a predetermined speed (e.g., 300 S revolutions per minute) .

Turning now to Figs. 6 and 7, torque converter means 180 further includes means for directing a flexible control conduit 320 therethrough. Conduit 320 terminates at process probe 130 for controllably operating process probe 130. When 0 process probe 130 is an eddy current or ultrasonic sensor, control conduit 320 may be a wire capable for conducting electrical pulses to and from process probe 130. Alternatively, when process probe 130 is a laser weld head, control conduit 320 may be a fiber optic cable for conducting laser light to process 5 probe 130. More specifically, torque converter unit 180a includes a channel 310 therein for passage therethrough of control conduit 320. Control conduit 320 extends from channel 310 and through bore 253 that is formed through sun gear carrier 252. A guide plate 340 having a hole 350 is interposed between 'J sun gear carrier and ring gear 260. The purpose of guide plate 340 is to guide control conduit 320 from one torque converter unit to its adjacent torque converter unit. More specifically, control conduit 320 passes from bore 253 and through hole 350 of each guide plate 340. With respect to torque converter unit 5 180e, an end cap 360 is mounted atop guide plate 340 and planet gear 185. End cap 360 has a hole 370 for passage therethrough of control conduit 320. Control conduit 320 may be connected to process probe 130 by means of a slip ring 380. Thus, control conduit 320 extends internally through torque converter units 0 180a/l80b/180c/180d/180e rather than externally with respect to torque converter units 180a/180b/180c/180d/180e. It is important that control conduit 320 extend internally through torque converter units 180a/180b/180c/180d/180e rather than externally with respect to torque converter units 180a/180b/l80c/180d/l80e . 5 This is important in order to conserve space in small-diametered tube 90. Conservation of space within tube 90 results in a relatively larger-size of torque converter means 180 than would

otherwise be the case if control conduit 320 were to extend externally with respect to torque converters I80a/I80b/I80c/I80d/I80e.

Still referring to Figs. 6 and 7, a flexible second shaft 390 has one end thereof attached to planet gear 185 of torque converter unit 180e, which planet gear 185 rotates second shaft 390 as sun gear 240 rotates planet gear 185.

Returning to Figs. 1 and 2, first shaft 150 may be surrounded by a flexible hose 400 for protecting first shaft 150 and control conduit 150 from damage. Moreover, hose 400 preferably has one end attached to torque converter means 180, as at location 405, for supporting torque converter means 180 and process probe 130 as torque converter means 180 and process probe 130 are translated in tube 90. A probe driver 410 engages hose 400 for translating hose 400 and process probe 130 attached thereto in tube 90, so that process probe 130 is capable of selectively advancing and retreating in tube 90. Moreover, apparatus 120 may further include a take-up reel or coiler 420 associated with first shaft 150 for coiling first shaft 150 thereabout and for uncoiling first shaft 150 therefrom as process probe 130 respectively advances and retreats in tube 90.

It is appreciated from the description hereinabove that an advantage of the present invention is that the process probe 130 is rotated with sufficient torque to examine or repair the small-diametered tube 90. This is so because the input torque of motor 140 is converted by torque converter means 180 into a predetermined output torque sufficient to rotate process probe 130 with sufficient torque and at a predetermined speed without disposing motor 140 in tube 90. it is further appreciated from the description herein¬ above that another advantage of the present invention is that use thereof avoids the costly purchase and stocking in inventory of a plurality of motors to rotate process probe 130. This is so because any number of torque converter units may be stacked end- to-end to obtain the desired torque and to rotate process probe 130 at the desired speed.

Although the invention is illustrated and described herein in its preferred embodiments, it is not intended that the invention as illustrated and described be limited to the details shown, because various modifications may be obtained with respect to the invention without departing from the spirit of the invention or the scope of equivalents thereof. For example, although the invention is described with reference to rotating a process probe in a small-diametered nuclear steam generator heat transfer tube, the invention is also suitable for use in rotating any similar tooling whether or not such tooling is disposed in a small-diametered nuclear steam generator heat transfer tube.

Therefore, what is provided is an apparatus and method for rotating a process probe carried by a rotatable cable in a small-diameter nuclear steam generator heat transfer tube, such that the process probe rotates with sufficient torque and at a predetermined speed.