Abstract:
A tool is disclosed for remotely inspecting and/or treating welds, pipes, vessels and/or other components used in reactor coolant systems or other process applications to, among other things, mitigate stress corrosion cracking in the welds, pipes, vessels and/or other components. The tool is placed at the entrance to a pipe or vessel and walks into the pipe or vessel to a pre-selected weld, pipe or vessel location or other component. Upon reaching the pre-selected weld, pipe or vessel location or other component, the tool anchors itself, then advances an end effector to inspect and/or treat the pre-selected weld, pipe or vessel location or other component.

Description:
[0001]    The present invention relates to nuclear power plants, and, more particularly, to a tool for mitigating stress corrosion cracking in reactor coolant system welds, piping and/or other components in pressurized water reactor plants. 
       BACKGROUND OF THE INVENTION 
       [0002]    Primary water stress corrosion cracking (“PWSCC”) in SCC-susceptible metal welds, such as nickel-based welds (e.g., Alloy 600-type welds), in the piping and/or other components of reactor coolant systems (“RCS”) of pressurized water reactor (“PWR”) plants, or directly in the RCS piping and/or other components, is a significant challenge facing the nuclear power industry. Frequent occurrences of stress corrosion cracking have cost the nuclear industry significant amounts of money because of forced and extended outages, increased inspection requirements, repairs and replacements, and increased plant inspections by industry regulators. Managing degradation of RCS piping and other components in a PWR nuclear power plant is critical to the plant&#39;s continued safe operation and high reliability. The inspection and evaluation of susceptible areas of reactor coolant system piping and other components for the purpose of applying PWSCC mitigation strategies, especially in areas where inspections are difficult and repair and/or replacement options are prohibitively expensive, is desirable because the mitigation of PWSCC in nickel-based welds or other SCC-susceptible base or weld metals in RCS piping and/or other components may delay the repair and/or replacement of RCS piping and/or other components and possibly reduce inspection requirements. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    In an exemplary embodiment of the invention, a tool for inspecting and/or treating welds, pipes, vessels and/or other components used in reactor coolant systems or other process applications comprises a first unit for axially walking inside a pipe and/or vessel, the first unit having a first plurality of legs radially extendable from the first unit, a second unit for axially walking inside the pipe and/or vessel, the second unit having a second plurality of legs radially extendable from the second unit, a coupler extending between the first unit and the second unit, the coupler being axially movable into and out of the second unit, and an end effector unit connected to the first unit, the end effector unit being capable of delivering an end effector to a pre-selected weld, pipe or vessel location and/or other component and manipulating the end effector to inspect and/or treat the weld, pipe or vessel location and/or other component. 
         [0004]    In another exemplary embodiment of the invention, a tool for brushing welds, pipes, vessels and/or other components used in reactor coolant systems or other process applications to mitigate stress corrosion cracking in such welds, pipes, vessels and/or other components comprises a front unit for axially walking inside a pipe, the front unit having a first plurality of legs radially extendable from the front unit, a rear unit for axially walking inside the pipe, the rear unit having a second plurality of legs radially extendable from the rear unit, a coupler extending between and joining the front unit and the rear unit, the coupler being axially movable into and out of the rear unit, so as to move the front and rear units away and towards one another, respectively, and a brush unit connected to the front unit, the brush unit being capable of radially advancing a brush until the brush touches the inside circumference of the weld, rotating the brush circularly around the inside circumference of the weld, and indexing the brush axially along the pipe, to thereby mitigate any stress corrosion cracking that may be in the weld, the front unit including a plurality of first actuators for radially moving the first plurality of legs into and out of the front unit, the rear unit including a plurality of second actuators for radially moving the second plurality of legs into and out of the rear unit, the rear unit being an actuator and the coupler being movably disposed within the actuator, and the brush unit including a brush head on which is rotatably mounted the brush for brushing a pre-selected weld, pipe or vessel location and/or other component, the brush head being connected to a reversible screw drive for radially moving the brush head towards and away from the weld, pipe or vessel location and/or other component, and including a linear actuator for indexing the brush axially along the weld, pipe or vessel location and/or other component, to thereby mitigate stress corrosion cracking in, or that might otherwise occur in, the weld, pipe or vessel location and/or other component. 
         [0005]    In a further exemplary embodiment of the invention, a method of inspecting and/or treating welds, pipes, vessels and/or other components used in reactor coolant systems or other process applications comprises the steps of providing a tool comprising a front unit for axially walking inside a pipe, the front unit having a first plurality of legs radially extendable from and radially retractable into the front unit, a rear unit for axially walking inside the pipe, the rear unit having a second plurality of legs radially extendable from and radially retractable into the rear unit, a coupler extending between the front unit and the rear unit, the coupler being axially movable into and out of the rear unit, so as to move the front and rear units away from and towards one another, respectively, and an end effector unit rotatably connected to the front unit and including an end effector for inspecting and/or treating a pre-selected weld, pipe or vessel location and/or other component, placing the tool at the entrance to a pipe or vessel containing a pre-selected weld, pipe or vessel location and/or other component, causing the tool to walk into the pipe or vessel to the pre-selected weld, pipe or vessel location and/or other component, causing the tool, upon reaching the location of the pre-selected weld, pipe or vessel location and/or other component, to anchor itself inside of the pipe or vessel, causing the end effector unit to advance the end effector until it is delivered to the pre-selected weld, pipe or vessel location and/or other component, and causing the tool to manipulate the end effector to inspect and/or treat the pre-selected weld, pipe or vessel location and/or other component, to thereby mitigate any stress corrosion cracking that may be in the weld. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of the weld mitigation tool of the present invention. 
           [0007]      FIG. 2  is a side elevational view of the weld mitigation tool of the present invention. 
           [0008]      FIG. 3  is a partial cross-sectional view and partial perspective view of the weld mitigation tool of the present invention. 
           [0009]      FIG. 4  is a perspective view of the weld mitigation tool of the present invention positioned in the piping leading to a nozzle of a nuclear power plant. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]      FIG. 1  is a perspective view of the weld mitigation tool  10  of the present invention, while  FIG. 2  is a side elevational view of the weld mitigation tool  10 . 
         [0011]    Tool  10  shown in  FIGS. 1 to 4  is designed to be used to mitigate stress corrosion cracking in welds in the piping of reactor coolant systems by brushing the inside diameters of pipe welds in such systems. Thus, tool  10  includes and end effector in the form of a brush for brushing pipe welds. Tool  10  is typically placed at the entrance to a pipe, whereupon tool  10  walks into the pipe to a given weld, that is often remotely located. Upon reaching the weld location, the tool anchors itself, and then advances a brush radially until it touches the inside diameter of the weld. Tool  10  then sweeps the brush circularly around the inside diameter of the weld, while gradually indexing the brush along the axis of the pipe, to thereby mitigate any stress corrosion cracking that may be in the weld. 
         [0012]    It should be noted that the tool  10  could be used with different end effectors to perform other functions. The tool  10  could also be used to deliver an Electro-Discharge Machining (EDM) electrode to excavate existing SCC cracks or other type of defects, including pre-existing weld defects. The tool could also be used perform inspections of, for example, areas mitigated, using visual, ultrasonic and/or eddy-current examinations. The tool can be applied to PWR and BWR to provide access for, besides mitigation (brushing) and inspection activities, surface preparation and defect removal. The tool can be used in vessels and pipes used for other process applications, such as chemical processing vessels. 
         [0013]    Referring to the embodiment of tool  10  shown in  FIGS. 1 to 4 , to be able to walk to a weld area in a pipe, tool  10  includes a front axial walk unit  12  and a rear axial walk unit  14  that are joined together by a coupler  16  that extends between rear unit  14  and front unit  12 . The distal end  19  of coupler  16  is bolted to front axial walk unit  12 , while the proximal end of coupler  16  is movably disposed within rear unit  14 . Coupler  16  is capable of being extended from and retracted into unit  14  for the purpose of moving front unit  12  and rear unit  14  with respect to one another. For this purpose, rear unit  14  necessarily contains within it a suitable pneumatic-mechanical, electromagnetic and/or electromechanical arrangement for extending coupler  16  from and retracting it into unit  14 . 
         [0014]    In one embodiment, rear axial walk unit  14  is a linear pneumatic (or hydraulic) actuator. In this embodiment, energy in the form of compressed air is converted into linear motion. The pneumatic actuator consists of a piston, a cylinder and valves (not shown). The piston is covered by a diaphram (not shown), which keeps the air in the upper portion of the cylinder, allowing air pressure to force the diaphram downard, moving the piston underneath, which in turn moves a valve stem that is linked to the internal parts of a valve. Thus, the coupler  16  is like a piston rod, attached to the piston of the actuator, so as to be axially movable into and out of a housing  15  that is part of unit  14 . When the compressed air moves the piston within housing  15 , the coupler  16  is caused to either extend from or retract into housing  15  so that front unit  12  and rear unit  14  are caused to move with respect to one another. 
         [0015]    In another embodiment, rear axial walk unit  14  is a solenoid actuator with coupler  16  being the armature of the actuator so as to be axially movable into and out of the housing  15  that is part of unit  14 . In this embodiment, a plurality of electromagnets are mounted within housing  15 , while a plurality of corresponding magnets positioned at specified distances from each electromagnet are mounted on a portion of coupler  16 . When the electromagnets in housing  15  are activated, the coupler  16 , again, is caused to either extend from or retract into housing  15  so that front unit  12  and rear unit  14  are caused to move with respect to one another. 
         [0016]    In a further embodiment, coupler  16  can be axially movably disposed within housing  15  of rear axial walk unit  14  by means of a reversible motor, gearing and screw drive arrangement like the reversible motor  48 , belt drive  46  and screw drive  38  arrangement shown in  FIG. 3  and discussed in more detail below. 
         [0017]    Front axial walk unit  12  has a plurality of legs  18 A radially movable outward from or into unit  12 . Preferably, unit  12  has three radially movable legs  18 A. Similarly, rear axial walk unit  14  has a plurality of legs  18 B radially movable outward from or into unit  14 . Here again, preferably unit  14  has three radially movable legs  18 B. 
         [0018]    To radially move legs  18 A and  18 B, front unit  12  and rear unit  14  necessarily include suitable pneumatic-mechanical, electromagnetic and/or electromechanical arrangements for extending legs  18 A and  18 B from and retracting them into units  12  and  14 . 
         [0019]    In one embodiment, each of front unit legs  18 A is, in effect, a rod attached to a piston in a pneumatic (or hydraulic) linear actuator, which, when it moves, causes a corresponding leg  18 A to extend out of or retract into front unit  12 . Similarly, each of rear unit legs  18 B is, in effect, a rod attached to a piston within a pneumatic linear actuator  22 B which serves to extend and retract a corresponding leg  18 B into and out of rear unit  14 . 
         [0020]    In another embodiment, each of front unit legs  18 A is, in effect, an armature of a solenoid actuator  22 A which serves to extend and retract a corresponding leg  18 A into and out of front unit  12 . Similarly, each of rear unit legs  18 B is, in effect, an armature of a solenoid actuator  22 B which serves to extend and retract a corresponding leg  18 B into and out of rear unit  14 . 
         [0021]    In a further embodiment, legs  18 A and  18 B can be radially extended from and retracted into units  12  and  14  by means of a reversible motor, gearing and screw drive arrangement like the reversible motor  48 , belt drive  46  and screw drive  38  arrangement shown in  FIG. 3 . 
         [0022]    Each of front unit legs  18 A includes a foot  20 A attached to the distal end of the leg. Similarly, each of rear unit legs  18 B has a foot  20 B attached to the distal end of the leg  18 B. Preferably, each of foot  20 A and  20 B is curved so as to easily mesh with the curvature inside a pipe in which tool  10  will walk. 
         [0023]    The manner in which tool  10  walks to a weld location is as follows. If tool  10  is placed in the inside of a pipe in a state in which the armature coupler  16  is extending from rear unit  14 , the front unit  12  will cause each of the solenoid actuators  22 A to extend its corresponding leg  18 A until each leg engages the inside circumference of the pipe. At this point, each of the feet  20 A of the legs  18 A will be engaging the inside circumference of the pipe so as to lock the front unit  12  into position. Once front unit  12  is locked in position, rear unit  14  will cause each of the actuators  22 B on rear unit  14  to be activated so as to draw the radially extending legs  20 B of rear unit  14  into the housing  15  of rear unit  14 . Rear unit  14  will then cause armature coupler  16  to be retracted into the housing  15  of unit  14  so as to draw the rear unit  14  toward the front unit  12 . 
         [0024]    Once armature coupler  16  is completely contracted into housing  15  of rear unit  14 , rear unit  14  will be caused to move up against front unit  12 . At this point, rear unit  14  causes each of the actuators  22 B to cause their corresponding leg  18 B to extend radially outward from housing  15  of unit  14 , until the corresponding feet  20 B of each of legs  18 B engages the inside circumference of the pipe in which tool  10  has been placed. The radially extension of legs  18 B, so as to engage the feet  20 B with the inside circumference of the pipe, causes the rear unit  14  to be locked in place. At this point in time, rear unit  14  causes the coupler  16  to extend from housing  15  while front unit  12  causes each of actuators  22  to retract their corresponding legs  20 A into the housing  13  of front unit  12 . The retraction of each of radially extending legs  20 A unlocks front unit  12  from its position, and thereby allows front unit  12  to extend forward in a distance corresponding to the distance that coupler  16  extends outwardly from rear unit  14 . At the end of the stroke of coupler  16 , front unit  12  again causes each of the actuators  22 A to extend the corresponding leg  18 A out of housing  13  of front unit  12  until each of the corresponding feet  20 A of the legs  18 A engage the inside circumference of the pipe to again lock front unit  12  in position. Here again, once front unit  12  is locked in position, rear unit  14  causes each of actuators  22 B to retract corresponding legs  18 B into the housing  15  of rear unit  14  so as to unlock rear unit  14 . Thereafter, rear unit  14  is activated so as to cause coupler  16  to retract into housing  15  of rear unit  14 , thereby causing rear unit  14  to move forward in the direction of locked front unit  12 . This motion is repeated time and again until the tool  10  reaches the point in the pipe where the weld to be brushed is located. 
         [0025]    Front unit  12  includes a support collar  11  to which coupler  16  is bolted. Support collar  11  also serves as a structure for the mounting of housing  13  of front unit  12  and each of actuators  22 A, also mounted on housing  13 . Similarly, rear unit  14  includes a support collar  17  with a support ring  19  from which coupler  16  protrudes. Mounted on support collar  17  of rear unit  14  is housing  15  of unit  14  and each of the actuators  22 , also mounted on housing  15 . 
         [0026]    Connected to the front of front unit  12  is an end effector unit, which in the embodiment of the invention shown in  FIGS. 1 to 4  is a brush platform unit  24  on which is mounted a brush head  26  and a plurality of motors and gears used to move brush head  26  into position for purposes of brushing the inside diameter of a pipe weld. It should be noted that for other embodiments of the invention performing other tool functions, brush platform unit  24  would be replaced by a different end effector unit capable of delivering a different tool to a given location to perform a desired function. 
         [0027]    Turning again to the embodiment of the invention shown in  FIGS. 1 to 4 , brush platform  24  is attached to front unit  12  through a turn table  28  bolted to front unit  12 . Rotatably mounted by means of bearings on turn table  28  is an output gear  30 , which is driven by a drive gear  32  that is also rotatably mounted by bearings on turn table  28  and driven by a drive gear motor  34  mounted on housing  13  of front unit  12 . The combination of turn table  28 , output gear  30 , drive gear  32  and motor  34  constitutes a reversing rotary drive  36  to have reversible rotary motion, as shown in  FIG. 2 . 
         [0028]    Radial motion of the brush head  26  towards the inside circumference of a pipe is accomplished preferably by means of a screw drive  38  shown in  FIG. 3 , although it should be noted that an alternative arrangement like a linear actuator could be used. A first end  40  of the screw drive is attached to a platform  42  on which the brush head  26  is mounted. The opposite end of the screw drive  44  is attached to a belt drive  46 , which is driven by a reversible motor  48 . As the reversible motor  48  is rotated in one direction, the belt drive  46  causes the screw drive  38  to rotate in a first direction so that it moves up within a housing  50  to thereby raise platform  42  on which brush head  26  is mounted, and thereby radially extend out of housing  50  toward the inside circumference of a pipe. Conversely, when motor  48  is rotated in the opposite direction, belt drive  46  causes screw drive  38  to turn in the opposite direction so as to contract into housing  50 , thereby causing platform  42  on which brush head  26  is mounted to radially contract away from the inside circumference of the pipe. 
         [0029]    The brush head  26  includes a nylon brush  52  embedded with grit that engages and brushes a pipe weld for purposes of mitigating stress corrosion cracking. Brush  52  is driven by a reversible motor  54  that is attached to the armature  56  of a linear actuator  58  which provides brush head  26  with the axial indexing that is used to index the brush  52  along the axis of a pipe as it brushes a pipe weld. Also included in brush head  26  is a gearing arrangement  60  which allows brush  52  to be tilted up or down in connection with brush  52  brushing the weld of a pipe. 
         [0030]    It is the combination of gears, motors and drives that are part of brush head unit  24  that give brush head  26  the flexibility, upon tool  10  reaching a weld location, to advance the brush  52  radially outward until it touches the inside diameter of the weld and to sweep the brush circularly around the inside diameter of the weld while gradually indexing the brush along the axis of the pipe, to thereby mitigate stress corrosion cracking that may be in the weld. 
         [0031]      FIG. 4  shows an example of where tool  10  has been placed into a pipe  60 , and walked inside the pipe to a remotely located weld  62  for the purpose of brushing weld  62 . Upon reaching weld  62 , tool  10  anchors itself inside of pipe  60  by radially extending legs  18 A and  18 B until they engage the inside circumference of pipe  60 . Tool  10  then advances brush  52  radially outward until it touches the inside diameter of weld  62 . As shown in  FIG. 4 , Tool  10  then sweeps brush  52  circularly around the inside diameter of weld  62 , while gradually indexing brush  52  along the axis of the pipe using solenoid actuator  58  to move brush  52  axially, and thereby mitigate any stress corrosion cracking that may be in the weld  62 . 
         [0032]    Movement and on-sight operation of the tool can be controlled by a wireless control of the kind well known that typically include transceivers, both in the tool  10  and in a control unit held by an operator outside of a pipe. The tool is controlled with cables which carry electrical, pneumatic, hydraulic power, and control signals. The location of the tool/brush is monitored by a video camera mounted on the tool (not shown). 
         [0033]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.