Nondestructive inspection heads for components having limited surrounding space

An inspection head where non-destructive inspection is structured to fit into narrow spaces, and to accurately and repeatably move an inspection probe along a surface to be inspected. Movement of the inspection head along an X, Y, Z, Θ, and Φ-axis is precisely controlled by individual drive mechanisms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to non-destructive inspection of turbine components. More specifically, the invention provides inspection heads for positioning sensing elements on the surface of turbine rotor discs on either a fully assembled rotor or on discs that have been removed from the rotor in a controlled, repeatable manner.

2. Description of the Related Art

The blades of steam turbines are attached to discs and are subjected to significant stress due to the heat, pressure, and vibrations within their operating environments. It is therefore necessary to periodically inspect these discs for surface cracking, internal cracking, and pitting at the blade attachment area and the rotor attachment area, known as the disc bore. If such inspections locate indications of defects beginning to form that are not sufficient to take the disc out of service, it is desirable to ensure that later inspections focus on locations within the discs where the indications were found in the previous inspection.

Turbine discs are presently inspected using sensing elements such as ultrasonic probes and eddy current probes, the operation of which is well known in the art. Presently used probes are hand held, thereby limiting the positional accuracy of the inspection, and the repeatability with which the probes may be positioned.

Accordingly, there is a need for a means of accurately and repeatably positioning an inspection probe in a desired location with respect to a turbine disc. There is an additional need for such probes to fit within the small space available between discs within a typical turbine rotor assembly, thereby avoiding a need to remove the discs from the turbine for inspection.

SUMMARY OF THE INVENTION

The present invention provides a non-destructive inspection head that is particularly useful for inspecting the discs of turbines, and particularly the high stress areas, such as the blade attachment area and the disc bore area (where the disc is attached to the rotor using a “shrink fit” process for steam turbines.

For purposes of this description, the X-axis is defined as an axis substantially horizontal and substantially parallel to a disc being inspected. The Y-axis is defined as an axis that is substantially vertical, and also substantially parallel to a disc being inspected. The Z-axis is defined as an axis that is substantially horizontal, and substantially perpendicular to a disc being inspected. The Θ-axis is defined by rotation about the Z-axis. Lastly, the Φ-axis is defined by rotation around the X-axis.

The invention is structured to place an inspection probe, for example, an ultrasonic probe or an eddy current probe, adjacent to or against a disc to be inspected, while the disc remains mounted to a rotor. The turbine blades may or may not be attached to the disc during the inspection. The probe may be raised between the discs, and adjacent to the disc to be inspected, by presently available devices. As it is currently designed, one probe and head assembly is positioned on either side of the disc to be inspected. This provides a complete inspection without moving the base unit. Once the inspection head is properly positioned, the head itself is structured for movement along at least some of the X axis, Y axis, Z axis, Θ-axis and Φ-axis. Movement along each of these axes is controlled by a separate drive mechanism, so that the probe may move independently along any axis, or along more than one axis, as necessary to properly position the probe. The Θ-drive and consequentially the probe are free floating in a semi-spherical area atop the Z-drive, which allows for proper contact of the face of the probe to the disc over the various ranges of disc geometry and probe contact face contours.

If an ultrasound probe is used, a delivery/recirculation system for an ultrasonic coupling medium, for example, water, may also be provided. The delivery/recirculation system is figuratively illustrated inFIG. 17as137and139, respectively. The system is structured to dispense water between the propad and the component to be inspected, thereby providing effective ultrasonic coupling between the probe and the component. A catch basin139is located below the component, for catching the water so that it may be recirculated throughout the inspection process.

The inspection heads may be configured specifically to inspect specific discs on a turbine rotor assembly. For example, a linear drive head providing for movement along only the X and Y axes may be utilized for inspections near the blade attachment region, where the surfaces may be inspected along a straight line, and where the lack of Z and Θ drive mechanisms enables the inspection head to be smaller, better fitting within tight spaces. An arc drive head having an X axis drive and a Φ-axis drive may be utilized to inspect discs having a curved geometry. A standard head, having X-axis, Y-axis, Z-axis, and Θ-axis drives may be utilized to scan disc in the bore region, where the disc contacts the rotor, and is particularly useful for inspecting regions of turbine discs from the blade attachment area to the disc bore regions. Lastly, a low clearance head having X-axis, Y-axis, Z-axis, and Θ-axis drives, but with a more limited range of motion along the X-axis than the standard head, may be utilized where the minimum gap between discs is less than that which will accommodate a standard head. The use of an inspection head having precisely controlled positioning means ensures that the inspection head may be located accurately and repeatably where inspections are desired. For example, if an indication was found in a specific location in a prior inspection, but the indication was not sufficient to take the disc out of service, the inspection head may be accurately directed to the location where the indication appeared during a subsequent inspection.

Accordingly, it is an object of the present invention to provide an inspection head capable of accurately and repeatably positioning a non-destructive inspection probe against a component to be inspected.

It is another object of the invention to provide an inspection head having independently and precisely controlled drive systems for each axis of movement.

It is a further object of the invention to provide an inspection head that includes or omits specific drive mechanisms and specific directions, permitting construction of an inspection head that may fit within a narrow space in a desired location, while still providing the necessary range of motion to complete an inspection.

It is another object of the invention to provide an inspection head that may be utilized with one or two inspection probes.

It is a further object of the invention to provide an inspection head whose range of motion and precise control of positioning enable both straight on and angled directional inspections, thereby permitting an indication detected by a straight on inspection to be more precisely located using the angled inspection.

It is a further object of the invention to provide an inspection head that may be precisely positioned so that indications may be precisely located during pitch catch ultrasonic inspections.

It is a further object of the invention to provide an inspection head that may be used interchangeably with a wide variety of non-destructive inspection probes, for example, single ultrasonic, double ultrasonic, phased array ultrasonic, or eddy currents.

These and other objects of the invention will become more apparent through the following description and drawings.

Like reference characters denote like elements throughout the drawings.

DETAILED DESCRIPTION

The present invention provides an inspection head for delivering non-destructive inspection probes to locations having limited spaces for such probes, for example, between adjacent discs of a turbine rotor assembly for inspection of the surfaces of those discs.

Referring toFIGS. 1-6, the first embodiment of the inspection head is illustrated, hereinafter called a standard head10. Referring toFIGS. 1-2, the standard head10includes a base12(partially shown) structured for mounting on a presently available apparatus for raising the inspection head between adjacent discs. Although such devices are presently available, they will be briefly described below. A stand14extends upward from the base12. The stand14terminates in a rail support plate16. The rail support plate16supports a pair of rails18on either side of a drive screw20, with an endcap22on either end of the assembly. The drive screw20is rotably secured between the endcaps22, with an X-axis drive mechanism24, which will be described in greater detail below, operatively connected to one end of the drive screw20.

The stand14further includes a Y-axis drive mechanism26, including a fixed vertical rail28having a bracket30secured at its top end. A pair of sliders32are slidably mounted on the rail28, with an arm34extending upward from each slider32to the rail support plate16. In addition to the movement of the rail support plate16with respect to the base12, the individual probe assemblies36may move vertically with respect to the rail support plate16. A motor driven screw rail38, the operation of which will be described below, provides for vertical positioning adjustment of each probe assembly36.

The standard head10is illustrated in more detail inFIGS. 3-6. Referring specifically toFIGS. 2 and 5, the drive screw20is controlled by the X-axis drive motor40. The X-axis drive motor40is mounted to a motor mount42which is secured below one of the two end caps22. The motor40is connected through the bushing44to the pulley46, which drives the drive belt48, thereby turning the pulley50. The pulley50is connected to the drive screw20through the thrust bearings52and ball bearings54, thereby facilitating rotation within the hole56defined within the end cap22.

Referring toFIGS. 2 and 6, the Y-axis drive mechanism26is illustrated in more detail. The Y-axis motor58is secured to the motor mount60. The Y-axis motor58is operatively connected to the Y-axis drive screw38through the thrust bearing62, miter gear64, miter gear66, and thrust bearing68, with the interaction of the two miter gears64,66inverting the horizontal rotation imparted by the motor58to the vertical rotation necessary to rotate the drive screw38.

Referring toFIGS. 2-4, a probe assembly36is illustrated. The bottom of the probe assembly36includes a trolley plate70, which is threadedly engaged by the Y-axis drive screw38passing through the aperture72defined within the trolley plate70. The screw rail end74is located directly above the aperture72. A pair of trolleys76are secured to the lower side of the trolley plate70, and are structured to engage the rails18, thereby permitting the probe assembly36to slide along the rails18. A pair of pillow block assemblies78are disposed on either side of the trolley plate70, and define holes80therethrough, with the holes80being structured to receive a guide shaft82on either side of the Y-axis drive screw38. This portion of the probe assembly36remains adjacent to the rails18, with the remainder of the probe assembly36, described below, being structured for movement along the Y-axis as controlled by the motor58.

A shaft hangar84forms the lower portion of the movable part of the probe assembly36. Each end86of the shaft hangar84is structured to clamp around the guide shaft82. A bracket88is disposed above the shaft hangar84motor mounts90,92extend downward from the bracket88and upward from the shaft hangar84, respectively, and secure a Z-axis motor94therein. The Z-axis motor94turns the pulley96, which is operatively connected to the Z-drive arm98that is partially secured above the bracket88. The bracket88further defines a pair of upward extending end flanges100, with a mount102centered thereon, and a plurality of roller slides104between each side of the mount102and the corresponding flange100. An alignment plate106is pivotally mounted to each side of the mount102, and pivotally and slidably mounted across the roller slides104on that side and the upward extending flange100of the bracket88. Actuation of the Z-axis motor94thereby causes the Z-drive arm98to move the mount102along the Z-axis, with the roller slides104ensuring that the movement imparted by the Z-axis motor94remains substantially along the Z-axis. Movement of the mount102in the opposite direction is achieved by spring pressure on the Z-drive arm98.

A U-shaped bracket108is pivotally mounted on the mount102, with the ends of the U-shape extending upward. The upper ends of the U-shape define a pair of holes110, structured to receive a screw112passing through a thrust bearing114and ball bearing116, into either side of a probe plate118, thereby pivotally securing the probe plate118within the bracket108. A Θ-axis motor120is secured to the back of the probe plate118by the brackets122and clamps124. The Θ-axis motor120is operatively connected to the pulley126, which is operatively connected to the pulley128through the belt130. The pulley128is in turn connected to the worm gear shaft132, mounted on the front of the probe plate118, via the bearing134. The worm gear shaft132engages the worm gear136, to which the sensor138has been secured. The sensor138may be an ultrasound sensor, eddy current sensor, or other non-destructive inspection sensor. The sensor138may thereby be rotated around the Θ-axis by the Θ-axis motor120to change the angle at which a disc is inspected.

Referring toFIGS. 7-9, a low clearance head140is illustrated. The low clearance head140is similar to the standard head10in many respects. The low clearance head140includes the base142structured for mounting on a presently available apparatus for raising the inspection head between adjacent discs. A stand144extends upward from the base142. The stand144includes a fixed vertical rail146having a bracket148secured at its top end. A pair of sliders150are slidably mounted on the rail144, with an arm152extending upward from each slider150to either side of a top plate154. A pair of arms156extends outward from the top plate154, and may include rollers158pivotally secured to their ends. A second pair of arms160extends outward from the arms156, and include a pair of rollers162pivotally secured to their ends.

A Y-base plate164may be disposed on top of the top plate154. A pair of bolsters166are disposed atop either side of the Y-base plate164, with a thrust bearing168located between the top bolsters, on top of the Y-base plate. A Y-axis drive screw170extends upward through the Y-base plate164and thrust bearing168, terminating at its lower end with the end cap172. A pair of guide rods174are disposed on either side of the Y-axis drive screw170, passing through the Y-base plate164and top bolsters166. The above described portion of the low clearance head140remains stationary during movement in the Y-direction, while the following portion will move along the Y-axis.

A Y-drive base176is disposed at the top end of the guide rods174and Y-axis drive screw170. A support block178may be disposed below the Y-drive base, surrounding and providing additional support for each of the guide rods174. An endcap180surrounds and provides additional support for the Y-axis drive screw170. A Y-axis motor182is mounted on top of the Y-drive base176, and may be secured there by the motor bracket184. The Y-axis motor182is operatively connected to the drive screw170through the interaction of the miter gear186, connected to the Y-axis motor182, and the miter gear188, connected to the Y-axis drive screw170.

An X-axis motor183is mounted on a mounting plate185, at the top of the guide rods174. A dovetail slide187is mounted on the mounting plate185, being operatively connected to the X-axis motor183by the interaction of the miter gear189, attached to the motor183, and the miter gear191, attached to the leadscrew193of the dovetail slide187. The slider195, threadedly connected to the leadscrew193, is connected to the Z-drive base190.

A Z-drive base190is disposed above the Y-drive base176, and supports a Z-drive motor192thereon. The motor192is operatively connected to a pulley194. A slide mount plate196is disposed above the Z-drive base190and Z-drive motor192. The slide mount plate196defines a pair of upwardly extending flanges198at each end. The head mount plate200is centered on the slide mount plate196, with a plurality of roller slides202located between each side of the head mount plate200and the corresponding upward flange198. The roller slides202are all interconnected to the directly adjacent roller slides202, in a manner that permits only linear sliding motions in a Z direction with respect to each other. A Z-drive arm204is pivotally secured to the top surface of the slide mount plate196, and is operatively connected to the pulley194and the head mount plate200. Actuation of the Z-axis motor182thereby moves the pulley194, thereby causing the Z-drive arm204to move the head mount plate200along the Z-axis, with the roller slides202limiting the movement of the head mount plate200to within the Z-axis. A probe assembly36, identical to the probe assembly36described above, is mounted on top of the head mount plate200.

Referring toFIG. 10, an arc drive head206is illustrated. The arc drive head206sits atop a base plate208, which is similar to the top plate154, and which may be used to attach the arc drive head206to a base12and stand14, similar to those used for other inspection heads. The base plate208has an X-axis motor210secured thereto by the motor bracket portions212,214. The motor210turns a drive screw216mounted between a pair of end blocks218,220. A slider222is threadably secured to the drive screw216, and is rigidly attached to a slide base224. A pair of curved support arms226,228extend upward from the slide base224, pivotally securing a probe frame230between their top ends. A probe232is secured within the probe frame230by a plurality of screws234passing through the back236of the probe frame230, and then threadably engaging the probe232. Each of the screws232has a spring disposed thereon, thereby biasing the probe232away from the back236of the probe frame230. Rotation of the probe frame230about the Φ-axis is controlled by the Φ-axis motor240, which is mounted on the probe support arm226by the motor bracket242. The motor240is operatively connected to a worm gearshaft244, extending upward therefrom, and which engages the worm gear246mounted on the side248of the probe housing230.

Referring toFIGS. 11-12, a linear drive head250is illustrated. The linear drive head250includes a base plate252that is similar to the base plate208. An X-axis drive motor254is secured to the base plate between the brackets256,258. The motor254is operatively connected to a drive screw260housed within a slide262, mounted on the base plate252. A pulley262connected to the motor254is connected by a belt to a pulley264connected to the X-axis drive screw260. A slide base266is threadably secured to the X-axis drive screw260, so that the movement of the slide base266and the X-axis direction is controlled by the motor254.

A pair of generally L-shaped arms268are secured to the slide base266, and a slider276is secured between the L-shaped arms268, with the bracket278therebetween. The bracket278is biased away from the slide base266by the spring270. A cable272secured at one end to a bracket274which is itself secured to the bracket278may be used to pull the bracket278towards the slide base266. A Y-axis drive screw280is secured within the slider276, and has a pulley282at one end. A Y-axis motor284is secured to the top of the slider276by the bracket286, and is operatively connected to the pulley288. A belt between the pulleys282,288thereby permits the Y-axis motor284to control the Y-axis drive screw280. An outer probe frame290is threadably secured to the Y-axis drive screw280. An inner probe frame292is secured within the outer probe frame290by a plurality of screws294, each of which has a spring296disposed thereon between the outer probe frame290and inner probe frame292, thereby biasing the inner probe frame292away from the outer probe frame290. A probe298is housed within the inner probe frame292. As with all other inspection heads, on the probe298may be an ultrasonic inspection probe, an eddy current inspection probe, or other non-destructive inspection probe. A pair of rollers300are disposed near the top of the linear drive head250, and in the illustrated embodiment are secured to the arm302secured to the bracket286.

Referring toFIGS. 13-15, a probe insertion apparatus304is illustrated. The probe insertion apparatus304includes a base306having a stationary telescoping member308extending upward therefrom. A sliding telescoping member310fits around the stationary telescoping member308. Any of several inspection heads may be secured to the top of the sliding telescoping member310. The sliding telescoping member may be caused to move up and down with respect to the stationary telescoping member using any of several means that are well known in the art, for example, manually, through the use of hydraulic cylinders, through the use of an electric motor driving an appropriate pulley and/or gear system, etc. Because such systems are well known in the prior art, they will not be described further herein. When an inspection is desired, the sliding telescoping member may be raised with respect to the stationary telescoping member from the position ofFIG. 13to the position ofFIGS. 14-15, thereby locating the appropriate inspection head between a pair of turbine discs312,314. The inspection head may then be moved into engagement with the disc as described above. In the case of the linear drive head ofFIGS. 11-12, the spring270is allowed to bias the arms268to rotate the inspection head250against the disc318. In the case of the arc drive head ofFIGS. 10 and 16, the Θ-axis motor240will be actuated to orient the probe232along the surface of the disc318. In the case of the low clearance head ofFIG. 15, the inspection head140will be moved along the X, Y, and Z-axes until it properly engages the disc318. Depending upon the inspection to be performed, the disc may be rotated while the inspection head remains stationary, or the disc may remain stationary while the inspection head is moved along one of its axes of movements.

As another alternative, the standard head may be configured to place two probes on the same side or opposite sides of the disc.FIG. 1illustrates a pair of inspection heads36, each of which may move independently of the other along the X, Z, and/or Θ axis. As a further alternative, any head may be used in pairs, on opposite sides of a disc, either for pitch-catch inspection or merely to reduce the time required to perform an inspection as shown by the pair of linear drive heads250inFIG. 17. Each linear drive head250is supported by a stand318connected to a common base320, so that both heads250may be placed adjacent to opposite sides of a disk simultaneously. In a pitch-catch inspection, which is well-known in the art of nondestructive testing, one probe transmits an ultrasonic signal that is received by the other probe.

The present invention therefore provides an inspection head capable of accurately and repeatably positioning a non-destructive inspection probe against a component to be inspected. The inspection head has independently and precisely controlled drive systems for each axis of movement, and is constructed in a manner that permits the inspection head to fit within relatively inaccessible locations. The inspection head may be utilized with either ultrasound, eddy current, or other non-destructive inspection probes, may be utilized with individual or multiple probes, and enables both straight and angled directional inspections.