DUAL GUIDE TUBE FOR INSPECTION OF HEAT EXCHANGERS

DϋAL GUIDE TUBE FOR INSPECTION OF HEAT EXCHANGERS

BACKGROUND OF THE INVENTION Field Of The invention

The present invention relates to a method and apparatus for inspecting tubes, and more particularly, to a method and apparatus for inspecting the inner walls of two tubes simultaneously.

Description of the Prior Art

The in-service inspection of heat exchanger and steam generator tubing in nuclear power plants, as well as tubing in other applications, often requires that special probes be inserted and passed through individual tubes to detect flaws in the tubing. This testing is typically referred to as nondestructive testing because the inspection of the tubing takes place without altering the physical or chemical construction of the tubing. The test probes are able to detect any flaws in the tubing, which may be in the form of cracks, voids, holes, inclusions, pitting, corrosion and other inconsistencies in the tube wall, which would interfere with effective and safe operation of the tubing. When such flaws are detected, the tubing often must be either repaired or plugged at both ends and put out of service for safety reasons. Eddy current is a common nondestructive test method used to inspect nonferromagnetic tubing in heat exchangers and steam generators for both nuclear and non- nuclear applications. In a conventional testing procedure, an eddy current test probe is positioned underneath a tube to be tested and the probe is inserted into the tube by mechanical means until the probe exits the other side of the tube sheet. Data is collected when the probe is pulled back through the tube. Representative examples of such apparatuses including means for moving the probe within the tube are shown in U.S. Patent Nos. 4,876,506 to Brown et al., and 4,856,337 to Metala et al. However, existing equipment and technology allows only one tube to be inspected at a time.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and device for increasing the productivity of tube testing equipment and personnel.

It is a further object of the present invention to provide a method and device for increasing tube testing rate while decreasing time and costs. It is a further object of the present invention to provide a method and device for simultaneously testing two tubes which can be used with existing technology and equipment without significant modification to either.

It is a further object of the present invention to provide a device for guiding two test probes into two respective tubes simultaneously.

It is a further object of the present invention to provide a device for mounting to a robotic tool delivery system for guiding two test probes simultaneously. It is a further object of the present invention to provide an improved nondestructive test method for inspecting nonferromagnetic tubing in heat exchangers.

Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by the appended claims.

To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the dual guide tube inspection apparatus of this invention may comprise a base member for mounting to a positioning device, first and second guide tubes having free ends for guiding inspection probes into a set of tubes to be inspected, and means for fixing the first and second guide tubes to the base member with a predetermined distance between the free ends of the guide tubes. The first and second guide tubes provide simultaneous guiding of two inspection probes into the set of tubes. The base member of the apparatus may be made of a nonconductive material so as not to interfere with electronic testing procedures. The base member may also include upper and lower portions each having an opening therethrough for receiving the first and second guide tubes, and an intermediate portion connecting the upper and lower portions. The guide tubes may be mounted to the base member in such a manner that they are movable longitudinally, or are fixed securely in place. In a first embodiment, a clamping member and spacer bushings are provided along the guide tubes to fix the guide tubes against longitudinal movement with respect to the base member. The clamping member is adjustable to allow the guide tubes to be adjusted with respect to the base member to change the relative spacing between the free ends of the guide tubes. In a second embodiment, coil springs are provided in place of the spacer bushings of the first embodiment. The coil springs are fitted about the guide tubes to allow resilient movement of the guide tubes in a longitudinal direction with respect to the base member. The clamping collar may be adjusted in the second embodiment to allow the guide tubes to be adjusted with respect to the base member to change the relative spacing between the free ends of the guide tubes.

In a further aspect of the present invention, the tube inspection system may comprise a guide tube assembly, a robotic tool delivery system supporting the guide tube assembly for selectively positioning the guide tube assembly from a remote location, and an electronic inspection probe system operably connected to the guide tube assembly. The guide tube assembly comprises a base member mounted to the tool delivery system, and at least first and second guide tubes mounted to the base member, whereby at least two tube elements can be inspected simultaneously. The first and second guide tubes of the tube inspection system have open ends and are mounted to the base member with a predetermined distance between the open ends corresponding to a distance between the tube elements to be inspected. The electronic inspection probe system may comprise first and second eddy current probes selectively guided through the first and second guide tubes, respectively.

In yet a further aspect of the present invention, a method of inspecting a set of tubes is provided comprising the steps of providing a guide tube assembly having first and second guide tubes mounted to a common base, positioning the guide tube assembly adjacent to a set of tube elements to be inspected, simultaneously moving first and second inspection probes through the first and second guide tubes into a respective pair of tube elements to be inspected, and collecting data from the first and second inspection probes as they are simultaneously moved through the respective pair of tube elements. The method may further comprise the additional steps of constructing a map showing the location of all tube elements in the set of tube elements to be inspected, determining an optimum inspection pattern to maximize the locations where two tubes are inspected simultaneously, and programming a tool positioning device to automatically position the guide tube assembly according to the optimum inspection pattern.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in, and form part of, the specification, illustrate an embodiment of the present invention and, together with the description serve to explain the principles of the invention. In the drawings:

Fig. 1 is a front view of the dual guide tube assembly of the present invention; Fig. 2 is a side view of the dual guide tube assembly shown in Fig. 1;

Fig. 3 is a diagrammatic illustration showing the guide tube assembly supported by a tool positioning system and connected to a testing apparatus; Fig. 4 is a diagrammatic side view of the present invention in conjunction with a robotic tool delivery system;

Fig. 5 is a front view of an alternative embodiment of the dual guide tube assembly of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Reference will now be made in detail to the preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. The present invention comprises a dual guide tube assembly 10 for remotely holding two guide tubes 12 and 13 during a tube testing process, such as, but not limited to, an eddy current test process. The dual guide tube assembly includes a base member 11 into which the pair of guide tubes 12 and 13 are mounted in a fixed or suspension fashion, depending on the specific test performed. In the arrangement illustrated in Fig. 1, the tubes 12 and 13 are fixedly mounted to the base member 11 to maintain a fixed spacing d between the center of the tubes 12 and 13 at their top ends 18. This fixed spacing d corresponds to the spacing between tubes 61 in a tube sheet 60 of the heat exchanger or other equipment being tested (see Fig. 3) .

The base member 11, as best shown in the side view of Fig. 2, is formed in three pieces, including a top portion 15 and a bottom portion 14 each having openings therethrough for receiving the first and second guide tubes, and an intermediate portion 16 connecting the top and bottom portions. The base member 11 may, however, be formed in a single piece, such as by injection molding. When using the invention in conjunction with an eddy current probe or other form of electronic tester, it is preferable to make the fixture 11 of a nonconductive material so that it does not interfere with the test results.

The guide tubes 12 and 13, as shown in Fig. 1, are held in place within the base member 11 by clamping collars 21 which grip the outer surfaces of the guide tubes and abut against an inner wall of the base member. The clamping collars 21 may be loosened to enable adjustment of the first and second guide tubes with respect to the base member 11. A pair of spacer bushings 22 and 23 are positioned about the guide tubes adjacent each of the clamping collars 21 between the upper and lower portions 14 and 15 of the base member 11. The spacer bushings 22 and 23 act in cooperation with the claming collars 21 to prevent movement of the guide tubes in either direction.

In the illustrated embodiments, the guide tubes 12 and 13 are fixed to the base member 11 at an angle with respect to one another so that the top ends 18 are closer to each other than the lower ends 17. The angle of the guide tubes 12 and 13 enables the spacing d between the top ends 18 to be adjusted by changing the longitudinal position of the guide tubes with respect to the base member 11. The angle of the guide tubes 12 and 13 also helps provide sufficient room in the base member 11 for the clamping collars 21, 22 and 23, while enabling a close spacing between the top ends 18 to be maintained.

The guide tubes 12 and 13 include threaded portions 20 for mounting to respective flexible hoses 51 (see Fig. 3) . The flexible hoses 51 provide a conduit through which testing probes 52 and 53 are fed to the guide tubes and into the tube elements 61. The top ends 18 of the guide tubes 12 and 13 are preferably flared to facilitate positioning of the guide tubes in an abutting relationship to the tube elements 61 of the tube sheet 60. The guide tubes 12 and 13 themselves may be conventional guide tubes originally designed for individual use with well-known testing equipment and thus are not described in further detail.

As shown in Fig. 3, the present invention may be used in conjunction with a pair of eddy current testing systems 50 which are interconnected with the dual guide tube assembly 10 through flexible hoses 51. Testing probes 52 and 53 are connected to the flexible hoses 51 and are under the control of eddy current probe pushers 54 and a take-up reels 23 which are commercially available. A robotic tool delivery system 30 is used to position the dual guide tube assembly 10 during operation. The testing systems 50 and the tool delivery system 30 are both controlled and monitored by a control station 40. The robotic tool delivery system 30 may be in the form of a GENESIS manipulator by ABB Combustion Engineering. A positioning arm of the robotic system 30 is connected to the intermediate portion 16 of the fixture 11 such that the dual guide tube assembly can be remotely positioned in a specific orientation with a high degree of accuracy. Such a robotic tool delivery system may be important during testing of nuclear power plant equipment where radiation exposure is a concern.

The robotic system 30 preferably has three motion axes which provide a "wrist action" on the end of the robotic arm to maintain a specific orientation of the dual guide tube assembly with respect to the tube sheet of the heat exchanger or other equipment. As shown in Fig. 4, the robotic tool delivery system 30 includes a wrist 31, an elbow 32, a shoulder 33, and a leg 34, all of which are remotely controlled from a separate control station 40. With the robotic tool system 30 it is possible to simultaneously monitor and set the location and orientation of both guide tubes 12 and 13 with a high degree of accuracy.

An alternative arrangement 10' for mounting the guide tubes 12 and 13 within the base member 11 is shown in Fig. 5. In this arrangement, coil springs 24 are fitted about the guide tubes 12 and 13. The coil springs 24 allow resilient movement of the guide tubes 12 and 13 in a longitudinal up and down direction with respect to the base member 11. The guide tubes may be adjusted in this arrangement by loosening the clamping collars 21 and sliding the guide tubes to a new desired position with respect to the base member 11. Thus, the relative spacing between the free ends 18 of the guide tubes 12 and 13 may be changed by moving one or both guide tubes with respect to the base member 11 against the force of the spring 24, or by changing the position of the clamping collars 21.

In a typical heat exchanger or other equipment having a tube sheet, due to the geometry of the tube sheet and the location of the testing device, some tube elements often must be tested individually even with the dual guide tube device of the present invention. However, individual testing is minimized by predetermining the optimum inspection pattern prior to commencing the inspection. This can save considerable time especially where the tube sheet is in a standardized construction that has previously been tested at other locations. In determining the inspection pattern, a tube sheet map is constructed showing all tube plugs, sleeves and open locations. The map is then used to layout, orientate and sequence the inspection pattern. The robotic tool delivery system may then be programmed to follow the inspection pattern making the testing process fully automated.

In field inspections, the dual guide assembly and testing process have increased productivity by 30 to 40% and decreased costs by 10 to 15%. Furthermore, inspections using the present invention have been found to substantially reduce inspection time as compared to the time required when using a conventional single guide tube. This is especially important where tube repairs are required on large power generating equipment, such as nuclear power plants, where power outages may effect thousands of consumers.

The illustrated embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention only be limited by the claims appended hereto.