Patent Document

BACKGROUND 
       [0001]    1. Field 
         [0002]    This invention relates generally to tube and shell steam generators and more particularly to cleaning apparatus for cleaning sludge from the secondary side from such a steam generator. 
         [0003]    2. Description of Related Art 
         [0004]    A pressurized water nuclear reactor steam generator typically comprises a vertically oriented shell, a plurality of U-shaped tubes disposed in the shell so as to form a tube bundle, a tube sheet for supporting the tubes at the ends opposite the U-like curvature, a divider plate that cooperates with the underside of the tube sheet and a channel head forming a primary fluid inlet header at one end of the tube bundle and the primary fluid outlet header at the other end of the tube bundle. A primary fluid inlet nozzle is in fluid communication with the primary fluid inlet header and a primary fluid outlet nozzle is in fluid communication with the primary fluid outlet header. The steam generator secondary side comprises a wrapper disposed between the tube bundle and the shell to form an annular chamber made up of the shell on the outside and the wrapper on the inside and a feedwater ring is disposed above the U-like curvature end of the tube bundle. 
         [0005]    The primary fluid having been heated by circulation through the reactor enters the steam generator through the primary fluid inlet nozzle. From the primary fluid inlet nozzle, the primary fluid is conducted through the primary fluid inlet header, through the U-tube bundle, out the primary fluid outlet header and through the primary fluid outlet nozzle to the remainder of the reactor coolant system. At the same time, feedwater is introduced into the steam generator secondary side, i.e., the side of the steam generator interfacing with the outside of the tube bundle above the tube sheet, through a feedwater nozzle which is connected to the feedwater ring inside the steam generator. In one embodiment, upon entering the steam generator, the feedwater mixes with water returning from moisture separators supported above the tube bundle. This mixture, called the downcomer flow, is conducted down the annular chamber adjacent the shell until the tube sheet located below the bottom of the annular chamber causes the water to change direction passing in heat transfer relationship with the outside of the U-tubes and up through the inside of the wrapper. While the water is circulating in heat transfer relationship with the tube bundle, heat is transferred from the primary fluid in the tubes to water surrounding the tubes causing a portion of the water surrounding the tubes to be converted to steam. The steam then rises and is conducted through a number of moisture separators that separate entrained water from the steam and the steam vapor then exits the steam generator and is typically circulated through a turbine to generate electricity in a manner well known in the art. 
         [0006]    Since the primary fluid contains radioactive materials and is isolated from the feedwater only by the U-tube walls, the U-tube walls form part of the primary boundary for isolating these radioactive materials. It is, therefore, important that the U-tubes be maintained defect free. It has been found that there are at least two causes of potential leaks in the U-tube walls. High caustic levels found in the vicinity of the cracks in tube specimens taken from operating steam generators and the similarity of these cracks to failures produced by caustic elements under controlled laboratory conditions, have identified high caustic levels as the possible cause of the intergranular corrosion, and thus possible cause of the tube cracking. 
         [0007]    The other cause of tube leaks is thought to be tube thinning. Eddy current tests of the tubes have indicated that the thinning occurs on tubes near the tube sheet at levels corresponding to the levels of sludge that has accumulated on the tube sheet. During operation of a pressurized water reactor steam generator, sediment is introduced on the secondary side as the water changes to steam. This sediment accumulates as sludge on the tube sheet. The sludge is mainly iron oxide particles and copper compounds along with traces of other minerals that have settled out of the feedwater onto the tube sheet and into the annulus between the tube sheet and the tubes. The level of sludge accumulation may be inferred by eddy current testing with a low frequency signal that is sensitive to the magnetite in the sludge. The correlation between sludge levels and the tube wall thinning location strongly suggests that the sludge deposits provide a site for the concentration of a phosphate solution or other corrosive agents at the tube wall that results in tube thinning. 
         [0008]    For the foregoing reasons, periodic cleaning of the sediment is desirable to maintain proper operation of the steam generator. Typically, spray nozzles are introduced along the center of the U-tubes (the tube lane) which move the sediment outward of the tube bundles. In the annulus, just outside the tube bundle, additional water flow is used to transport the sediment to a suction port where the sediment is carried outside the steam generator for disposal. 
         [0009]    For some steam generators, such as those formerly manufactured by Combustion Engineering, Inc., the normal access for sludge lancing from the center of the steam generator outward is limited by restrictions in the tube lane. A divider plate located directly in the center of the tube lane restricts the horizontal access to a nominal 1 5/16 inch (2.85 cms.). Due to manufacturing tolerances, the space between the divider plate and the inner row of tubes can be closer to one inch (2.54 cms.). The additional space restriction is mostly due to the divider plate not being placed parallel to the inner row of tubes. 
         [0010]    Since little space is available along the tube lane, presently cleaning is performed by sweeping high pressure and high volume water jets introduced along the periphery of the tube bundle of the steam generator. During cleaning, much of the spray is directed towards the center of the steam generator which pushes the sediment inward making it more difficult to remove. Another difficulty with spraying into the center of the steam generator is that the majority of the sludge deposits are further from the cleaning jets where the spray loses energy and focus. In addition, the jet spray is directed closer to being parallel to the tube sheet as opposed to being directed more perpendicular to the tube sheet where cleaning is more effective. 
         [0011]    A challenge for effective sludge lancing is the ability to align the cleaning jets with the tube gaps, i.e., the space between the tubes. For Combustion Engineering designed steam generators, the gap between the tubes is nominally 0.116 inch (0.295 cms.). For deep penetration into the tubes, an angular alignment accuracy of +/−0.02 degrees is desirable. Gap and angular alignment are more difficult when spraying inward from the periphery as the jets must be repositioned with the tube gaps each time the fixture is moved. 
         [0012]    Accordingly, it is an object of this invention to provide a sludge lance that can travel down the tube lane of a steam generator, between the divider plate and the first row of tubes without having its travel obstructed. 
         [0013]    It is a further object of this invention to provide such a sludge lance that can readily be spaced a predetermined distance from the first row of tubes while being angularly aligned with the gap. 
         [0014]    It is an additional object of this invention to provide such a sludge lance whose distance from the divider plate can be verified before set in operation. 
         [0015]    It is an added object of this invention to provide such a sludge lance whose alignment does not have to be recalibrated after each movement. 
         [0016]    It is a further object of this invention to provide support for a sludge lance nozzle that will counter any lateral reaction forces resulting from the high pressure fluid emanating from the nozzle jets. 
       SUMMARY 
       [0017]    These and other objects are achieved by a sludge lance for use in a steam generator having a shell enclosing a tube sheet and a plurality of substantially uniformly diametrically sized tubes extending from the tube sheet with the tubes disposed in a substantially regular pattern having substantially uniform narrow gaps between adjacent tubes. The regular pattern forms a generally central lane along which a divider plate extends along approximately the center of the center lane. The shell has at least one access opening in line with the central lane through which the sludge lance can access the central lane. The sludge lance includes a mounting assembly structured to support a drive assembly and a rail, with the drive assembly structured to move the rail along the central tube lane on one side of the divider plate, between the tubes and the divider plate. A nozzle assembly is coupled to the rail and has a body assembly defining a liquid passage. The nozzle assembly is sized to pass between the tubes and the divider plate. The nozzle body assembly has a plunger that is reciprocally movable in a cavity in the nozzle body assembly and biased in the direction to contact the divider plate when positioned in the center lane, to prevent movement of the nozzle in reaction to the spray of high pressure fluid from jets on the nozzle body assembly. 
         [0018]    In one embodiment, the cavity around the plunger is configured so that when high pressure fluid is sent through the nozzle assembly, the plunger is prevented from moving in the cavity. In the latter embodiment, the high pressure fluid clamps the plunger in position within the cavity. 
         [0019]    In another embodiment, the nozzle assembly body assembly has a plurality of jets, in fluid communication with the fluid passage, through which the fluid is sprayed through gaps between the tubes. In this embodiment, an alignment tool is attached to the rail for aligning the jets with the gaps. Preferably, the alignment tool is movable along the rail and determines the distance between the nozzle assembly and the closest tube to a pointer on the alignment tool. Desirably, the pointer swings laterally 90 degrees from a vertical orientation in at least one of two opposite directions, a first of the opposite directions to determine the distance between the nozzle assembly and the closest tube and a second of the opposite directions to determine the distance between the nozzle assembly and the divider plate. In an additional embodiment, the pointer swings in the first direction to align the jets with the gaps between the tubes. Preferably, a housing face from which the pointer is rotably supported includes markings on the housing face that translates the angular position of the pointer into linear distance from the nozzle assembly. 
         [0020]    The invention also contemplates an alignment tool for a steam generator sludge lance generally as just described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
           [0022]      FIG. 1  is an isometric, cutaway view of a steam generator; 
           [0023]      FIG. 2  is a partial cross sectional view of a steam generator of the type generally shown in  FIG. 1  with the cross sectional view taken above the tube sheet to show the divider plate extending along the central tube lane; 
           [0024]      FIG. 3  shows an enlarged sectional view of a portion of that shown in  FIG. 2  around the divider plate; 
           [0025]      FIG. 4  is a plan view of one embodiment of this invention mounted to the steam generator and passing through a hand hole; 
           [0026]      FIG. 5  is an elevational view of the portion of the steam generator shown in  FIG. 4 ; 
           [0027]      FIG. 6  is a cross sectional view of the spray head, rail and oscillator of the embodiment of this invention shown in  FIG. 5 ; 
           [0028]      FIG. 7  is an enlarged sectional view of the oscillator shown in  FIG. 4 ; 
           [0029]      FIG. 8A  is an elevational sectional view of the spray head illustrated in  FIG. 6 ; 
           [0030]      FIG. 8B  is a sectional view taken along the lines A-A shown in  FIG. 8A , through the head assembly; 
           [0031]      FIG. 8C  is an enlarged sectional view of a rear portion of the spray head assembly shown in  FIG. 8B ; 
           [0032]      FIGS. 9A , B and C are respectively front view, side view and bottom view of the mount assembly and intermediate plate shown in  FIGS. 4 and 5 ; 
           [0033]      FIGS. 10A and 10B  are respectively front and right side elevational views of the index drive assembly illustrated in  FIGS. 4 and 5 ; 
           [0034]      FIG. 11  is a plan view taken along lines A-A of  FIG. 10A ; 
           [0035]      FIG. 12  is a sectional view taken along the lines B-B of  FIG. 10A ; 
           [0036]      FIG. 13  is a sectional view taken along the lines C-C of  FIG. 11 ; 
           [0037]      FIG. 14  is a sectional view of the index drive taken along the lines of D-D of  FIG. 11 . 
           [0038]      FIG. 15  shows a sectional view of the alignment tool forming part of the sludge lance assembly of the preferred embodiment; 
           [0039]      FIGS. 16   a  and  16   b  respectively shows front and sectioned elevation views of the arm assembly illustrated in  FIG. 15 ; 
           [0040]      FIG. 17  is a sectional elevation view of the pointer assembly of  FIG. 15 ; 
           [0041]      FIG. 18  is a rear elevation view of the pointer assembly shown in  FIGS. 15 and 17 ; 
           [0042]      FIG. 19  is a schematic showing the swinger arm pointer at the tube gap alignment position; 
           [0043]      FIG. 20  is a schematic of a top and front view of the swing arm position for row  1  distance measurement; and 
           [0044]      FIG. 21  is a schematic of a top and front view of the swing arm position for divider plate distance measurement. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0045]      FIG. 1  shows a steam generator  10  associated with a pressurized water nuclear reactor (not shown). A more complete description of a steam generator  10  is set forth in U.S. Pat. No. 7,434,546, issued Oct. 14, 2008. Generally, the steam generator  10  includes an elongated, generally cylindrical shell  12  defining an enclosed space  14 , at least one primary fluid inlet port  16 , at least one primary fluid outlet port  18 , at least one secondary fluid inlet port  20 , at least one secondary fluid outlet port  22 , and a plurality of substantially uniformly, diametrically sized tubes  24  extending between, and in fluid communication with, the primary fluid inlet port  16  and the primary fluid outlet port  18 . The cylindrical shell  12  is typically oriented with the longitudinal axis extending substantially vertically. The tubes  24  are sealingly coupled to a tube sheet  38  that forms part of a manifold within the enclosed space that divides the fluid inlet port  16  and the fluid outlet port  18 . As seen in  FIG. 1 , the tubes  24  generally follow a path shaped as an inverted “U”. As seen in  FIGS. 2 and 3 , the tubes  24  are disposed in a substantially regular pattern having substantially uniform, narrow gaps  28  between adjacent tubes  24 . The tube gap  28  (shown in  FIG. 3 ) is typically between about 0.11 and 0.41 inch (0.30 and 1.04 cm.), and more typically about 0.116 inch (0.29 cm.). Also, as shown, the “U” shape of the tubes  24  creates a tube lane  26  extending across the center of the shell  12 . On both ends of the tube lane  26  there is a tube lane access opening  30 . The tube lane access opening  30 , which is usually round, typically has a diameter of between about five and eight inches (12.7 and 20.3 cms.), and more typically about six inches (15.2 cms.). 
         [0046]    During operation of the pressurized water nuclear reactor, heated, primary water from the reactor is passed through the tubes  24  via the primary fluid inlet port  16  and removed from the steam generator  10  via the primary fluid outlet port  18 . Secondary water, enters the steam generator  10  via the secondary fluid inlet port  20  and leaves the steam generator  10  via the steam outlet port  22 . As the secondary water is passed over the outer surface of the tubes  24 , the secondary water is converted to steam leaving sludge to collect between the tubes  24 , on the tube sheet  38 , and on other structures in the steam generator  10 . Typically, access for a full sized sludge lance is through the tube lane access opening  30 . 
         [0047]      FIG. 2  shows a partial cross sectional view of a steam generator taken along the lines  2 - 2  of  FIG. 1 . For certain steam generator designs, divider plate  32  restricts access for sludge lancing as the divider plate is approximately centered at the hand hole access opening  30 . For these types of steam generators, effective cleaning is accomplished by spraying high pressure water outward from the tube lane coupled with introducing peripheral water flow around the annular area between the shell  12  and the tubes  24  which follows a circumferential direction of flow as indicated by the arrow  34 , along with suction at location  36 , at an inspection port, to remove sediment/water from the steam generator (as explained in U.S. Pat. No. 4,079,701). The small gap “G” between the divider plate  32  and the inner row tubes severely limits the space available to introduce water jet spray which must be accurately aligned with the gaps between the tubes. The small gap “G” also restricts the use of opposing water jets to balance the reaction forces on a sludge lance nozzle. Without opposing balanced jets, a typical reaction force of 50 pounds (22.7 kilograms) is induced into the sludge lance nozzle. 
         [0048]      FIG. 3  shows an enlarged sectional view of the steam generator  10 , divider plate  32 , tubes  24  and hand hole access opening  30 . Due to the manufacturing tolerances of the steam generator, the divider plate  32  may not be parallel to the tubes. This angular misalignment results in a variation in the gap between the inner row of tubes and the divider plate. The difference between “G 1 ” and “G 2 ” may be as great as 0.25 inch (0.64 cms.) across the length of the divider plate. 
         [0049]      FIGS. 4 and 5  are respectively plan and elevational views of one embodiment of the invention claimed hereafter, shown mounted to the steam generator  10  and passing through the hand hole access opening  30 . Rotatable high pressure jets  40  introduce water flow into the steam generator, breaking loose and moving unwanted residue from between the tubes and towards the outer structure of the steam generator. In conjunction with the foregoing, a peripheral flow and suction system removes the residue from the steam generator. The jets  40  are part of the nozzle assembly  42  which is attached in the head assembly  44 . In  FIG. 5 , the jets  40  are shown pointing downward which is the normal starting position when the system is pressurized forcing high pressure water through the jets. In  FIG. 4 , the jets  40  are shown as rotated closest to the horizontal to direct water into the tube gaps  28 . As the jets rotate from a downward vertical position to near horizontal, the jet reaction forces the head assembly  44  towards the divider plate  32 . A locking plunger  46  (that will be described in more detail hereafter) maintains the head assembly  44  laterally fixed by reacting against the divider plate  32 , thus maintaining angular alignment of the cleaning spray to the tube gaps. Two or more rail assemblies  48 , which are joined together, are used to translate the head assembly  44  along the tube lane within the tube bundle. The rail assemblies  48  also provide the means for passage of high pressure flow water along with rotation of the nozzles. Fixed to the rear rail assembly is oscillator assembly  50 . The oscillator assembly provides the rotational drive for the sweeping motion of the jets  40 . Water introduced into quick coupling  52 , connected to swivel joint  54 , enables flexible motion of a water feed hose. Index drive assembly  56 , attached to intermediate plate  58  and supported by mount assembly  60 , provides precise translation of the rails  48  into or out of the steam generator  10 . The cross sectional geometry of the rail assemblies  48  provides sufficient flexible rigidity such that no additional supports are necessary to position the head assembly seven feet or more into the steam generator. Each assembly will be described hereafter. For cleaning to be effective jets  40  must be positioned at each tube gap. Proper index of the jets with the tube gaps can be reset or verified by the alignment marks  62  with adjustable pointer  64 . 
         [0050]      FIG. 6  shows a cross section of the head  44 , rail  48  and oscillator  50 . Passage  66  is used to deliver high pressure water (approximately 3,000 PSI) from the oscillator  50  to the head assembly  44 . Drive shaft  68  transfers rotation motion from the oscillator  50  to the head assembly  44 . Both the oscillator  50  and the rail  48  are similar to those disclosed in U.S. Patent Application Publication No. 2011/0079186. In the embodiment described herein, the drive shaft  68  is located below the water passage  66  such that the axis of rotation of the nozzle  40  is near the bottom of the head assembly  44 . This arrangement is desirable to place the nozzle  40  close to the steam generator tube sheet, support the nozzle, and allows placement of the components in the head assembly  44  that are required for its functionality. 
         [0051]      FIG. 7  is an enlarged sectional view of the oscillator  50 , also disclosed in U.S. Patent Application Publication No. 2011/0079186. Rotation of the drive shaft  68  is limited to +/−90 degrees by pin  70  in slot  72 . It is important to prevent the jets  40  from inadvertently rotating in an upward direction which may add excessive stress to the rail assemblies  48 . 
         [0052]      FIG. 8A  is an elevational sectional view of the head assembly  44  which provides the means to direct high pressure water spray accurately down the tube gaps. High pressure water enters passage  66  and is directed around annular opening  74  of the nozzle body  76 . Water then flows through angular port  78  into offset port  80 . Displacing port  80  from the nozzle rotational axis  82  provides clearance for the jets  40  to sweep in the limited space between the divider plate  32  and the inner row of tubes  24 . Sealed ball bearings  84  provide rigid rotational support for the approximately 50 pound radial load on the nozzle body  76 . Two seals  86  that contain the high pressure within annular opening  74  are leak limiting in order to provide minimal rotational friction. Since some water may leak by the seals, front openings  88  provide a leak path to prevent water pressure building up at the rear sealed bearing  84 . Low pressure seal  90 , fixed in place with pin  92 , provides a barrier to redirect high pressure seal leakage through port  94 . Without low pressure seal  90  water may pass along the drive shaft  68  and out of the steam generator. 
         [0053]    As mentioned earlier, a locking plunger  46  maintains the head assembly  44  laterally fixed by reacting against the divider plate  32 ; thus maintaining angular alignment of the cleaning spray to the tube gaps. The locking plunger  46  is integral to the head assembly  44 .  FIG. 8B  shows a cross section taken at the lines A-A through the head assembly  44  shown in  FIG. 8A .  FIG. 8C  is an enlarged sectional view which shows the locking plunger partially depressed by the divider plate  32 . Referring to  FIG. 8C , during translation of the head assembly  44  into or out of the steam generator, piston  96  is biased against the divider plate  32  with compression spring  98 . The force from the spring  98  is low enough (less than 0.5 pounds (0.23 kilograms)) to prevent excessive lateral deflection of the head assembly  44 . The piston  96  is constructed from a polymer such as Acetal to permit low friction to exist between the divider plate  32  and the piston  96  to protect the divider plate from damage. 
         [0054]    To increase rigidity of the outside diameter of the polymer piston  96 , stainless steel ring  100  is utilized and captured by end cap  102 . The stainless steel ring  100  is not susceptible to diameter changes due to hydroscopic swelling and provides a higher co-efficient of friction for the “locked” state. Surrounding stainless steel ring  100  is lock ring  104  and O-ring  106 . For high strength, moderate co-efficient of friction, lower modulus of elasticity, and lower water absorption, lock ring  104  is preferably constructed from PEEK (Polyether ether ketone). O-ring  106  and lock ring  104  are captured between the head assembly housing  108  and cover plate  110 . Seal ring  112  prevents loss of fluid so that the annular chamber  114  can be pressurized. 
         [0055]    Referring to  FIGS. 8A and 8C , the locking plunger functions as follows. The lance assembly is initially aligned to be parallel with the tube lane (as described hereafter) and close enough to the divider plate such that the lock plunger piston  96  will just touch or is depressed by the divider plate. A small amount of radial clearance between the outside diameter of ring  100  and the inside diameter of lock ring  104  provides a slidable interface for a spring  98  to keep piston  96  in intimate contact with the divider plate  32 . Prior to pressurized water flow, the lance head assembly is positioned within the steam generator with the jets facing downward as shown in  FIG. 8A . Increased water pressure initiates fluid flow into the head at port  66 . The smaller diameter of the jets  40  restricts water flow such that the pressure at port  66  is elevated to the system pumping pressure. A passage is available so the high pressure water can flow into port  116  and into the annular chamber  114 . Pressurized water in the annular chamber  114  forces O-ring  106  radially inward against lock ring  104  which also presses lock ring  104  around steel ring  100 . The radial clearance between the inside diameter of lock ring  104  and the outside diameter of steel ring  100  is small enough to maintain the deformation of the lock ring well within the elastic limit of the material which assures that when the system is depressurized the lock ring will force the O-ring  106  radially outward and permit free travel of the piston  96 . To prevent axial movement of the piston  96  when the system is pressurized, lock ring  104  is axially captured between housing  108  and cover plate  110 . As the system is pressurized with the jets facing downward water flow through the jets produces a reaction force that lifts the head in an upward direction (not laterally) that is restrained by the rail assembly  48 . With the system at pressure, piston  96  is held fixed with respect to the divider plate  32 . During cleaning, rotation of the jets into the tube bundle will create a horizontal reaction forcing the head assembly  44  in the direction of the divider plate  32 . Locked piston  96  prevents lateral movement of the head which maintains angular alignment of the jets  40  with the tube gaps. 
         [0056]      FIGS. 9A ,  9 B and  9 C show the mount assembly  60  and intermediate plate  58  attached to a steam generator  10 . The index drive assembly (not shown in  FIG. 9 ) is attached to intermediate plate  58  with bolts engaged in threaded holes  118  or  120  depending on the desired side of the divider plate the lance fixture is to traverse. Corresponding dowel pins  122  or  124  accurately position the index drive relative to the intermediate plate  58 . Once the intermediate plate position is adjusted, the index drive can be removed and positioned for either side of the divider plate  32  with little or no adjustment. Intermediate plate  58  is secured to mount assembly  60  with four clamp knobs  126 . Height adjusters  128  permit roll, pitch, and vertical position adjustment of the intermediate plate  58 . Lateral and angular position (yaw) of the intermediate plate  58  is adjustable with screws  130 . Slotted openings  132  in the mount assembly  60  permit lateral and angular motion. 
         [0057]    The index drive assembly  56  is shown in  FIGS. 10-14 . While the index drive assembly  56  is similar to that described in published patent application U.S. 2011/0079186, the differences are the addition of the lateral support mechanism and the bearing support for increase cantilever load from the rail assemblies  48 . Captured top mounting screws are also utilized. 
         [0058]    Front and side elevation views are respectively shown in  FIGS. 10A and 10B . The main parts of the index drive are the lower housing  134 , upper housing  136  and front cover  138 . Captured screws  140  are used to couple the lower housing to the intermediate plate  58  on the mount assembly  60 . Rail assembly  48  is shown in phantom as it would be located in the index drive  56 . 
         [0059]      FIG. 11  is a plan view of the index drive  56 . Access to the captured screws  140  is shown along with the adjustable pointer  64 . 
         [0060]      FIG. 12  is a sectional view taken along the lines B-B of  FIG. 10A  and shows the lateral clamp mechanism for the rail assemblies  48 . Two ball bearings  142  supported by shafts  144  position the rails  48  laterally a fixed distance relative to the lower housing  134  while enabling low friction translation of the rails into or out of the steam generator. A second set of ball bearings  146  supported on shafts  148  are attached to bracket  150 . Tightening of knob  152  on threaded shaft  154  moves bracket  150  along with bearings  146  toward the rails  48  which puts the rails in intimate contact with the bearings  142 . Dowel pins  156  press fit into bracket  150  have sufficient radial clearance to provide a slidable coupling with holes in the front cover  138 . It is desirable to provide a specific lateral clamping load on the rails with bearings  142  and  146 . Too much clamp force will increase rolling friction and possibly overstress bracket  150 . Too little clamp force may permit the rails  48  to move laterally causing misalignment of the jets  40 . At the point of contact of bearings  142  and  146  with the rail  48 , there is a predetermined gap  158  between the bracket  150  and front cover  138 . Further tightening of knob  152  closes gap  158  causing bracket  150  to act as a leaf spring with the correct lateral loading. 
         [0061]      FIG. 13  is a sectional view taken along the lines of C-C of  FIG. 11  and shows a rail section  48  positioned between bearings  142  and  146  such that the rail is laterally supported relative to the lower housing  134 . Vertical support of the rail  48  is achieved by drive wheel  160  rotatably fixed to the lower housing  134  with bearings  162  and  164 . A second idler (not shown) is also located in the lower housing. Two idler assemblies  166  in the upper housing  136  complete the vertical support mechanism. 
         [0062]      FIG. 14  is a sectional view taken along the lines D-D of  FIG. 11 . Upper housing  136  is slidably coupled to the lower housing  134  with twin shafts  168  passing through linear ball bearings  170 . Tightening of the threaded knob  172  forces the upper housing  136  towards the lower housing  134  providing rigid support of the rail  48  in the vertical direction. 
         [0063]    For effective sludge removal, it is important that the jets  40  are positioned at the tube gaps and the angle of the jets is parallel to the tube gaps. When reacting on the divider plate to limit lateral deflection, it is also important to verify the distance from the lance to the divider plate is within acceptable limits. The alignment tool performs these functions and works on either side of the divider plate.  FIG. 15  shows the alignment tool consisting of an arm assembly  174  and a pointer assembly  176  which may be attached to one or more rails  48 . Rail drive shaft  68  is used to communicate rotational motion between the arm  174  and the pointer  176 . 
         [0064]      FIGS. 16A and 16B  respectively show front and sectional, elevational views of the arm assembly  174 . Swing arm  178  attached to shaft  180  is rotatably coupled to housing  182  with a pair of ball bearings  184 . The ball bearings  184  are axially restrained to shaft  180  by means of nut  186  and inner race spacer  188 . Retaining screw  190  axially secures the rotatable assembly within the housing  182 . Tapered coupling  197  engages the rail drive shaft  68  which is axially loaded to eliminate backlash. Ball plunger  192  may engage anyone of three grooves  194  to hold the swing arm upward (as shown) or 90 degrees rotated clockwise or counterclockwise. During translation into or out of the steam generator, the swing arm  178  is positioned in the vertical position. The 90 degree position is used for setting the index pointer (described hereafter). Plastic guides  196  and  198  installed over mating “C” shaped profiles on the housing  182  are slidably fixed to the housing  182  with spring pins  200 . The plastic guides  196  and  198  prevent metal to metal contact with the steam generator tubes  24 . Lower plastic guide  198  contains holes  202  to permit free engagement with the drive pins  204  (shown in  FIG. 10   b ). 
         [0065]      FIGS. 17 and 18  are respectively rear and sectional, elevational views of the pointer assembly  176 . Rear block  206  is coupled to a rail section  48  with capture screws  208 . Dowel pins  210  provide accurate position of the rail/block assembly. Split bushings  212  provide a suitable rotational and translational coupling between the drive shaft  214  and the rear block  206 . Pointer  216  is rotatable coupled to the shaft  214  with a square drive  218 . A small clearance in the square drive permits translation of the shaft  214  within the pointer  216 . Compression spring  220  located between bushings  212  provides a separation force between the split bushings  212 . The rear bushing forces pointer  216  away from the block  206  (to prevent rubbing) and against thrust washer  222  which is held axially fixed by retainer  224 . The outside diameter of the shaft  214  is sufficiently larger than the installed inside diameter of the front split bushing  212  to prevent movement of the bushing on the shaft. Therefore, compression spring  220  provides an axial load to the shaft  214  to the left of the figure. The axial shaft load is then applied to each rail drive shaft and the arm assembly  174  to eliminate rotational backlash. 
         [0066]    Referring to  FIG. 18 , there are two sets of scribe lines. The top set labeled “DP” is for measuring the distance from the lance to the divider plate. The lower set labeled “R 1 ” is for measuring the distance from the row  1  tubes (row adjacent to the center tube lane) to the lance. Which set of scribe lines are used, i.e., left or right, depends on which side of the divider plate the lance is mounted. The alignment tool functions on either side. In order to provide a direct correlation between the radial translation of the swing arm  78  in  FIG. 16  and the actual linear displacement of the lance to the tubes (or the divider plate), the spacing between the scribe lines is scaled accordingly. Linear displacement values between the lance and the tubes permits a direct relation for calculated positioning of the lateral adjustment screws ( 130  in  FIG. 9 ). 
         [0067]      FIG. 19  shows the swing arm  178  at the tube gap alignment position. Initially, the swing arm  178  is rotated upward so the alignment tool can be translated into the steam generator. Once within the tube lane, the swing arm  178  is rotated towards the tubes while checking for interference with a tube  24 . If interference is realized, the alignment tool is translated along the tube lane until the swing arm  178  can be rotated 90 degrees. With the swing arm rotated 90 degrees, the tool is moved inward (to the left of  FIG. 19 ) until the front surface of the swing arm contacts a tube  24 . This is the position where the jets align with the tube gaps. Referring to  FIG. 5 , the index pointer  64  is then positioned to correspond to one of the marks  62  or the joint where two rails are connected together. 
         [0068]    To align the angle of the jets  40  parallel to the tube gaps, the swing arm  178  is rotated to the vertical position so the alignment tool can be moved into or out of the steam generator. If the alignment tool is moved to the adjacent rail mark  62 , or every other mark, the alignment tool will be positioned with respect to the tubes as shown in  FIG. 20 . Swing arm  178  is then rotated towards the tube  24  until edge  226  makes contact. As described earlier, the “R 1 ” distance is measured on the pointer assembly  176 . The swing arm  178  is then moved back to the vertical position so the alignment tool can be repositioned into or out of the steam generator to obtain further “R 1 ” measurements. Since the linear spacing of the rail marks  62  are known and the “R 1 ” readings correspond to linear displacement, the angular misalignment with respect to the tubes can be directly calculated. A corresponding correction can be made with the lateral adjustment screws described earlier. After making angular corrections, it may be necessary to reset the index pointer  64  with the swing arm in the position shown in  FIG. 19 . 
         [0069]    The final function of the alignment tool is to measure the distance to the divider plate  32 . As shown in  FIG. 21 , the swing arm is rotated until edge  228  contacts the divider plate  32 . The displacement is measured with the “DP” scale on the pointer assembly  176 . Corrections to lateral displacement are also made with the lateral adjustment screws described earlier. 
         [0070]    Although the sludge lance disclosed is specifically suited for a steam generator with a divider plate, the alignment tool can also be applicable to steam generators without a divider plate. 
         [0071]    While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Technology Category: 2