Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/954—Inspecting the inner surface of hollow bodies, e.g. bores

Definitions

• Fluorescent dye-penetrant inspection has been an established nondestructive testing method for many years.
• a component is prepared for inspection by exposing the surface to a low-viscosity fluid that acts as a carrier for a tracer material.
• the liquid penetrates into even the smallest surface-breaking cracks and voids.
• ultraviolet light 300 nm to 400 nm wavelength
• the tracer material fluoresces at a visible wavelength, thus revealing the presence of indications such as surface-breaking cracks and voids.
• the most common method for evaluating these indications is through visual observation.
• a significant benefit of liquid-penetrant testing is its sensitivity to very small cracks. Surface-breaking cracks as small as a few microns in length can be detected using this nondestructive testing method.
• Efforts have been undertaken to extend the process of fluorescent dye-penetrant testing to the internal surfaces of critical components such as nuclear steam-generator tubes. These devices use fiber-optic imaging probes and endoscopes, as described in Olympus Corporation, U.S. patent 5,115,136 and Commissariat a I'Energie Atomique, U.S. patent 4,791 ,293, with a right-angle mirror, which "pipe" the two-dimensional image from the tube surface to a remote viewing station using an optical fiber or fiber bundle. In order to rotate the observation assembly, the fiber-optic bundle must include a complex and signal-degrading optical siipring.
• An important aspect of this invention is its use of a non-rotating illumination source and a non-rotating photodiode assembly, cooperating with a rotating passive optical scanning mirror assembly, thus eliminating the need for complex, expensive and signal-degrading sliprings.
• the ultraviolet illumination source and photodiode are mounted on-axis and do not rotate. De-coupling these two elements from the rotating components of the scanning probe eliminates the need to use electrical or optical sliprings to "pipe" a complex two-dimensional visual image out of the probe via optical fibers.
• the preferred scanning system described herein provides an automated means of rapidly and accurately inspecting a tube, pipe, or other cylindrical or enclosed cavity that have been treated with a photoluminescent penetrant medium.
• the invention includes: 1) a means of delivering ultraviolet radiation to the test-part surface; 2) a passive rotary scanning means that includes a plurality of lenses, reflectors and an optical filter; 3) an offset rotary drive means that is capable of causing the scanning means to rotate at up to several thousand revolutions per minute; 4) a solid-state photodiode that receives fluorescent light and transmits electrical signals that correspond to the presence of photoluminescent penetrant; and 5) an instrumentation station that provides a means to post-process the signals and a means of evaluating and displaying the condition of the part being inspected.
• the passive optical scanning means is caused to rotate by the offset rotary drive means.
• Ultraviolet radiation from the illumination source is projected on-axis into the optical scanning means.
• a plurality of lenses focuses the radiation, and a reflecting prism directs the radiation onto the part surface.
• the result is a concentration of the ultraviolet radiation energy into a very small area (approximately 0.25 mm 2 ). If the ultraviolet radiation strikes dye-penetrant that has been adsorbed into a crack or void, the penetrant will be caused to fluoresce at a visible wavelength.
• the receiving lenses also contained in the passive optical scanning means, capture the fluorescent radiation emanating from the test-part surface and project it through an optical filter and onto the photodiode. A series of electrical pulses corresponding to the presence of surface flaws is generated from the photodiode. The electrical signals are then ported out of the probe to signal-processing instrumentation, via electrical wires, and digitized for further processing.
• the optical scanning assembly is rotated and translated along the axis of the tube or pipe that is being inspected, creating a helical map of the part surface. By encoding the linear and angular position of the scanning means, an accurate and quantitative map of the digitized flaw pattern can be constructed.
• FIG. 1 is a diagrammatic view of the dye-penetrant scanning system in accordance with the invention.
• FIG. 2 is a cross-sectional view showing the major components and subassemblies of the scanning probe used in the system of the invention.
• FIGS. 3A and 3B are cross-sectional views showing details of the scanning probe used in the system of the invention.
• FIG. 4 shows a basic diagram of the electronics and signal-processing details in the system of the invention.
• FIG. 5 shows another embodiment of the scanning probe used in the system of the invention.
• FIG. 1 is a diagrammatic view of the dye-penetrant scanning system in accordance with the invention.
• This device can be used for the inspection of a wide variety of critical applications, including nuclear steam-generator tubes, turbine rotor bores, aircraft landing gear and automotive parts.
• the scanning probe 1 can be configured in both straight and articulated forms, in order to facilitate the inspection of bent tubing, e.g. tubing commonly found in nuclear power-generating reactors.
• remotely operated dye-penetrant inspection systems have employed endoscopes or video probes that require subjective interpretation of the inspection results.
• the invention described herein provides a significant improvement by employing a high-speed, passive scanner that generates a digital stream of data that can be automatically processed in near real-time by computer means to generate a high-resolution and quantitative map of the test-part surface.
• the invention can be used on any tube, pipe and other cylindrical or enclosed cavity surface that has been properly treated with commercial photoluminescent, or other medium, that will adsorb into minute cracks and fluoresce at a wavelength that is different from that to which it has been exposed, e.g. ultraviolet light.
• Proper surface preparation methods are described in MIL-STD-6866: Military Standard Inspection Liquid-penetrant and ASTM -E- 1417:Practice for ⁇ quid-penetrant Examination.
• a preferred commercial penetrant delivery system is manufactured by iP-TEC of Varberg, Sweden.
• the penetrant scanning system shown in FIG. 1 includes a scanning probe 1 that is attached by means of a flexible delivery cable 2 to an electronic interface unit 3.
• the interface unit 3 is, in turn, attached via electrical cable to a computer 5, which provides control signals for scanning-probe 1 functions.
• the data storage and display computer 5 also receives, processes and stores inspection data that have been acquired by the scanning probe 1.
• An ultraviolet illumination source 4 is connected to the interface unit 3 via both electrical wires and an optical fiber (see FIG.'s 2 and 3). This optical fiber is then routed to the scanning probe 1 via the delivery cable 2 for the purpose of providing ultraviolet radiation to the optics assembly 18 (FIG. 2).
• a probe delivery system provides the axial locomotion for the scanning probe 1.
• probe pushers For applications such as tubing inspection, commercially available delivery systems, or so-called “probe pushers” may be used. The only requirement is that the probe pusher be compatible with the delivery cable 2 size and that an axial encoder signal be provided to the interface unit 3 in a compatible format via electrical cable. For non-standard applications a probe delivery system will be required that meets the aforementioned requirements.
• FIG. 2 shows a cross-sectional view of the major components and subassemblies of the preferred embodiment of the scanning probe 1 used in the system of the invention.
• Centering devices 23 keep the scanning probe 1 near the centerline of a cylindrical test-part.
• the centering devices 23 shown in FIG. 2 are composed of spring wires that are radially oriented about the probe housing 24; however, various types are known per se.
• the optical fiber 8 transmits ultraviolet radiation from the ultraviolet illumination source 4 to the optics assembly 18.
• the optics assembly 18 houses a plurality of optical components that are combined to form a means for transmission of optical radiation onto the test-part surface 16 and fluorescent radiation from the test-part surface 16 onto the photodiode 15.
• the optics assembly 18 is caused to rotate, relative to the optical fiber 8 and photodiode 15, by the drive motor 20 and offset drive 19 means.
• An angular encoder 21 monitors the angular position of the optics assembly 18.
• the offset drive 19 is instrumental in allowing the invention to function properly because the design relies on its ability to transmit ultraviolet radiation into the optics assembly 18 on-axis, and focus the resulting fluorescent radiation, on-axis, onto the photodiode 15.
• An amplifier circuit 22 in the scanning probe 1 converts the electrical current that is generated by the photodiode 15 to voltage signals, which are then amplified for transmission to the interface unit 3 via the delivery cable 2.
• Figs. 3A and 3B are cross-sectional views showing in more detail the components of the scanning probe 1 used in the system of the invention.
• Ultraviolet radiation 9 enters the optics assembly 18 via the optical fiber 8, along the mechanical centerline of the scanning probe 1.
• the ultraviolet radiation 9 is focused by the transmit lens 10 and then redirected through the transparent window 17 and onto the test-part surface 16 by the reflecting mirror 11.
• the reflecting mirror 11 is a single-element glass prism that has been coated on two surfaces with a suitable reflecting medium, such as gold. If any surface-breaking cracks or voids are present on the test-part surface
• the photoluminescent penetrant will respond to exposure to ultraviolet radiation 9 by fluorescing at a different wavelength.
• the optical filter 14 is designed to block any optical radiation that is the same wavelength as the illumination source 23, e.g. in this case 300 to 400 nm (ultraviolet). Only light resulting from the fluorescent reaction of the dye-penetrant, e.g. greater than 400 nm, can pass through to the photodiode 15.
• the photodiode 15 is mounted rigidly in the scanning probe 1 on its mechanical centerline and does not rotate. When photons, in the form of fluorescent radiation 12, strike the photodiode 15, minute electrical currents are generated that are proportional to the magnitude of the received energy.
• An amplifier circuit 22 in the scanning probe 1 converts the electrical currents to voltage signals, which are then amplified for transmission to the interface unit 3.
• Very fine wires (not shown) connect the photodiode 15 to the amplifier circuit 22. The wires are attached to the transparent window 17 and are not in the focal plane of the projected or received light. Therefore the wires do not negatively effect the transmitted or received light.
• FIG. 4 shows a block diagram of the electronics and signal-processing details in the system.
• the electrical signals that are generated from the photodiode 15 correspond to the presence of surface flaws. These electrical signals are then ported out of the scanning probe 1 via the delivery cable 2, to the electronic interface unit 3 and computer 5 for processing, analysis and display.
• the optics assembly 18 is not connected to any part of the scanning probe 1 by any means other than bearings 21 , it can be rotated at very high rates of speed. For example, depending on the application, the optics assembly 18 would be expected to rotate at speeds of 500 to 1 ,000 revolutions per minute.
• the scanning probe 1 is translated along the axis of the tube or pipe that is being inspected, creating a digital helical map of the test-part surface 16. Encoding the linear and angular position of the optics assembly 18 produces an accurate and quantitative map of the flaw pattern.
• FIG. 5 shows another embodiment of the scanning probe used in the system of the invention. This configuration eliminates the need to run fine wires through the optical path of the transmitted and received radiation.
• the optical fiber 8 is located off-axis and, using a transmit lens 10a, projects ultraviolet radiation 9 through a beam-splitter 25 on-axis through the receive lens 13a. The ultraviolet radiation 9 is then reflected by a 45° first-surface reflecting mirror 11a onto the test part surface 16.
• Fluorescent radiation 12 emanating from cracks or voids on the test-part surface 16 strikes the reflecting mirror 11a, and is redirected through the receive lens 13a, beam splitter 25, optical filter 14 and onto the photodiode 15.
• the optical filter 14, also described above, is designed to block any optical radiation that is the same wavelength as the illumination source 23, e.g. in this case 300 to 400 nm (ultraviolet).
• the electrical signals generated by the photodiode 15 are processed as described above.
• the apparatus according to the invention provides numerous unique advantages over conventional photoluminescent penetrant viewing devices, because: 1) it is capable of rapidly scanning a part surface and generating a digital stream of data that can be reconstructed by near real-time signal-processing instrumentation to generate a quantitative and accurate map of surface-breaking flaws; 2) the use of a passive rotating optics assembly eliminates the need for complex and costly optical sliprings; 3) the use of a solid-state photodiode and associated support circuitry provides a high-quality signal that is not subject to the attenuation that is inherent in optical fiber systems.
• the apparatus has numerous and varied applications that can be extended to industries including aerospace, chemical and petrochemical processing, nuclear and fossil power generation, automotive manufacturing and testing.
• the invention also has potential applications in the manufacture and testing of military items such as gun tubes.

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• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

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• 1999
  • 1999-08-31 WO PCT/US1999/019986 patent/WO2000017601A2/en not_active Application Discontinuation
  • 1999-08-31 EP EP99967061A patent/EP1133671A4/de not_active Withdrawn
  • 1999-08-31 JP JP2000571214A patent/JP2002525593A/ja active Pending
  • 1999-08-31 AU AU23418/00A patent/AU2341800A/en not_active Abandoned

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