Patent Application
20090307891
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.
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'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.
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.
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.
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.
Tool 10 shown in
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.
Referring to the embodiment of tool 10 shown in
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.
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.
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
Front axial walk unit 12 has a plurality of legs 18A radially movable outward from or into unit 12. Preferably, unit 12 has three radially movable legs 18A. Similarly, rear axial walk unit 14 has a plurality of legs 18B radially movable outward from or into unit 14. Here again, preferably unit 14 has three radially movable legs 18B.
To radially move legs 18A and 18B, front unit 12 and rear unit 14 necessarily include suitable pneumatic-mechanical, electromagnetic and/or electromechanical arrangements for extending legs 18A and 18B from and retracting them into units 12 and 14.
In one embodiment, each of front unit legs 18A is, in effect, a rod attached to a piston in a pneumatic (or hydraulic) linear actuator, which, when it moves, causes a corresponding leg 18A to extend out of or retract into front unit 12. Similarly, each of rear unit legs 18B is, in effect, a rod attached to a piston within a pneumatic linear actuator 22B which serves to extend and retract a corresponding leg 18B into and out of rear unit 14.
In another embodiment, each of front unit legs 18A is, in effect, an armature of a solenoid actuator 22A which serves to extend and retract a corresponding leg 18A into and out of front unit 12. Similarly, each of rear unit legs 18B is, in effect, an armature of a solenoid actuator 22B which serves to extend and retract a corresponding leg 18B into and out of rear unit 14.
In a further embodiment, legs 18A and 18B 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
Each of front unit legs 18A includes a foot 20A attached to the distal end of the leg. Similarly, each of rear unit legs 18B has a foot 20B attached to the distal end of the leg 18B. Preferably, each of foot 20A and 20B is curved so as to easily mesh with the curvature inside a pipe in which tool 10 will walk.
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 22A to extend its corresponding leg 18A until each leg engages the inside circumference of the pipe. At this point, each of the feet 20A of the legs 18A 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 22B on rear unit 14 to be activated so as to draw the radially extending legs 20B 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.
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 22B to cause their corresponding leg 18B to extend radially outward from housing 15 of unit 14, until the corresponding feet 20B of each of legs 18B engages the inside circumference of the pipe in which tool 10 has been placed. The radially extension of legs 18B, so as to engage the feet 20B 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 20A into the housing 13 of front unit 12. The retraction of each of radially extending legs 20A 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 22A to extend the corresponding leg 18A out of housing 13 of front unit 12 until each of the corresponding feet 20A of the legs 18A 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 22B to retract corresponding legs 18B 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.
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 22A, 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.
Connected to the front of front unit 12 is an end effector unit, which in the embodiment of the invention shown in
Turning again to the embodiment of the invention shown in
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
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.
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.
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).
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.
