US3117227A

US3117227A - Method of flow detection using visible light sensitive phosphors

Info

Publication number: US3117227A
Application number: US46885A
Authority: US
Inventors: Pollack Isidore
Original assignee: Purex Corp Ltd
Current assignee: Purex Corp Ltd
Priority date: 1960-08-02
Filing date: 1960-08-02
Publication date: 1964-01-07
Anticipated expiration: 1981-01-07

Description

United States Patent 3,117 ,227 METHOD OF FLGW DETECTION USING VISIELE LIGHT SENSITIVE PIIQSPHORS Isidore Pollack, Westminster, Calih, assignor, by mesne assignments, to Purex Corporation, Ltd, a corporation of California No Drawing. Filed Aug. 2, i960, er. No. 46,2i85 3 Claims. (Cl. 250-71) This invention relates to procedure for non-destructive testing of bodies which may be composed of metal, ceramic, plastic, and the like, to detect flaws and cracks in the surface of said bodies, and is particularly concerned with a novel method of fluorescent penetrant inspection employing visible light for activating the fluorescent dye.

In known penetrant inspection methods for rapid location and evaluation of surface flaws or cracks in parts, a penetrant composition containing a fluorescent dye and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition is then applied to the part surface. Such developer can be in the form of a light colored powder, which acts as a wick and causes the liquid penetrant containing the fluorescent dye which was retained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action. The part is then exposed to invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible light by the fluorescent penetrant dye which is retained in the cracks or flaws after the penetrant composition is removed from the surface of the part.

In such conventional fluorescent penetrant processes, a source of substantially invisible fluorescigenous light, usually ultra-violet, is employed for the excitation of the fluorescent dye to cause it to emit visible light to thereby locate the cracks and flaws. Such light sources may include mercury vapor discharge lamps, X-ray tubes and cathode ray tubes.

The use of such invisible fluorescigenous light and the light sources employed for its production, present certain serious problems. In the first place when for example, mercury vapor lamps are used, it is necessary to employ light filters which are transparent to ultra violet and essentially opaque to visible light. Not only are such filters often inefficient for producing the proper fluorescigenous light to obtain maximum contrast between the fluorescent penetrant dye and the surrounding area of the test body, but such equipment and the operation thereof are relatively expensive.

Another serious disadvantage to the use of invisible fluorescigenous light is that the inspection areas are of necessity highly confining enclosures or booths constructed to shut out extraneous visible light, and thus present unpleasant working conditions from the standpoint of the highly confining oppressive working area, the heat produced by the fluorescigenous light source, and the poor ventilation of such areas.

It is an object of this invention to provide a fluorescent penetrant inspection process, which eliminates the use of invisible or substantially invisible light for irradiation, such as ultraviolet light, and the necessity of special light sources for producing such light.

3,117,227 Patented Jan. 7, 1964 Another object is the provision of a fluorescent penetrant inspection process which requires only visible light for activation or excitation of the fluorescent penetrant dye, yet produces bright fluorescence.

A still further object is to afford a process of the above type employing visible light, and which is controlled so that the fluorescent dye is activated to produce maximum fluorescence.

Yet another object is to provide a fluorescent penetrant inspection process in which high contrast between the fluorescent penetrant dye and the background is achieved.

Other objects and advantages will appear hereinafter.

According to the invention, I have found that if a fluorescent penetrant dye, which is characterized by having an activating wave length within the visible spectrum, is used in penetrant inspection of a test body, the fluorescent penetrant retained in the cracks and flaws can be excited by exposure solely to visible light, to obtain excellent contrast between the fluorescent dye indicator present in the flaws and cracks of the test body and its surrounding area. According to a particular feature of the invention, best results are realized, in terms of brighter fluorescence of the penetrant dye and greater contrast between such fluorescence and the surrounding area of the test body, it such visible activating light contains light waves in the visible spectrum having the predominant activating wave length for producing maximum fluorescence at the fluorescent maximum wave length of the particular dye employed. Preferably the visible light employed is filtered to provide the required activating wave length.

The expression visible light or within the visible spectrum as employed herein is intended to denote wave lengths between about 4,000 A. and about 7,500 A., generally considered to be the wave length range of light to which the human eye is responsive or sensitive.

By activating wave length I mean that wave length which is within a major absorption band in the visible spectrum shorter than the Stokes radiation, i.e., a major band in the fluorescent emission spectrum of the dye which is of longer wave length than that of said absorption band.

By fluorescent maximum wave length I mean that wave length at the maximum of the band spectrum of the fluorescence which characterizes the visible color of the fluorescent dye. It is to be recognized that the band has width and will include wave lengths shorter and longer than the said maximum.

According to the invention I irradiate the test body with light within the visible spectrum containing wave lengths shorter than the wave lengths which charactize the fluorescent color of the fluorescent dye, and I preferably employ a radiation intensity of the irradiating source and a concentration of dye in the penetrant composition, such that the relative brightness of the fluorescent emission is substantially greater than the relative brightness of the background illumination produced by the irradiating light. This difference in brightness should be such that under inspection conditions there is a substantial contrast between the emitted fluorescence and the background light from the test body.

In one embodiment I select an intensity of the irradiating radiation and a concentration of the dye to produce substantially total absorption of the irradiating radiation so that the background appears matte black.

However, I may employ an intensity of irradiating radiation and/or dye concentration such that the relative brightness of the background is substantially less than the relative brightness of the fluorescent dye.

I may also employ an irradiating radiation of such intensity and dye concentration that the background radiation is of an intensity substantially greater than that of the fluorescent radiation and, in such case, I use a color separation between the irradiating radiation and the fluorescent radiation, e.g., by means of filters, which will selectively absorb the background light, and transmit the fluorescence.

The irradiation intensity and the concentration of fluorescent dye in the penetrant composition are preferably adjusted to produce a desired or maximum contrast between the fluorescent penetrant, at the location of the cracks and flaws, and the background. For each individual inspector, these values may vary to some extent for achieving maximum contrast. For example, if the background illumination is too great, the irradiating intensity may be reduced. It will also be understood that the optimum concentration of fluorescent dye employed will also depend on the particular dye utilized.

The invention process can be employed in connection with the use of a large 'variety of fluorescent dyes, but preferably those which emit a fluorescent color having wave lengths in the region ranging from green to red, and embracing, for example, fluorescent emittmg wave lengths of about 5,000 A. and greater.

Thus, for example, a yellow fluorescent penetrant dye emits radiation of 5,400 A. This dye can be activated by energy within the range between 3,500 and $700 However, I have found that it is possible to obtain maximum fluorescent emission by using an activating wave length which is substantially, although not necessarily, exclusively monochromatic, and which is in thC V1SlblC range of the spectrum. For this yellow dye, light of about 4,600 A., which is within the visible portion of the spectrum, gives good contrast and maximum fluorescence.

As is readily apparent, the instant process has the important advantage of eliminating the necessity for the use of invisible fluorescigenous or ultra violet light to activate the fluorescent penetrant dye. My processmakes it unnecessary to use the relatively expensive equipment employed as sources for such light, and significantly reduces the power costs of the inspection procedure. These advantages are obtained without sacrifice of efficient activation of the fluorescent penetrant to obtain good test results. Consequently, this technique el1minates the almost intolerable working conditions heretofore encountered by the inspectors, in avoiding the necessity for confined poorly ventilated enclosed test booths, and permits inspection under normal working conditions. Thus, for example, in the instant process, an ordinary tungsten lamp may be employed by screening its emission of substantially all wave lengths except the visible activating wave lengths including that required for maximum fluorescence from the fluorescent penetrant dye, according to the invention. Hence, in the specific example noted above, a tungsten lamp may be employed as a light source for irradiating the yellow dye, by placing over the lamp a suitable filter which has a maximum transmission at the visible approximately 4,600 A. required for maximum activation of the dye to provide maximum fluorescence. Such a filter may be one which transmits in the range of about 4,500 to about 4,700 A., with a maximum transmission at about 4,600 A.

In addition, the instant process is rendered more sensitive and pleasing to the eye, where the operator utilizes a pair of eyeglasses tinted with the color of the fluorescent dye or employs a suitable filter for viewing. Thus, in connection with the specific example of the use of a yellow fluorescent penetrant dye as above described, if the operator employs a pair of glasses tinted with a yellow dye or with a filter transmitting only yellow, this renders the surrounding background of the test body a matte black and intensifies the yellow fluorescence of the penetrant dye. Other filters may be utilized, if desired, to change the appearance and background of the test body without substantially altering the brightnes or contrast of the fluorescence produced by the fluorescent penetrant dye.

The penetrant composition employed in my invention may comprise a conventional solvent vehicle within which the fluorescent dye is soluble. The penetrant vehicle should be a liquid which is itself substantially nonfluorescent and having good wetting properties and the ability to penetrate fine surface cracks and imperfections readily. Satisfactory penetrant vehicles include, for example, petroleum solvents, kerosene, a mineral oil or spirit, or mixtures thereof, light fuel oils, and the like. Solvent vehicles found suitable may comprise, for example, a mixture of tributyl phosphate and toluene. Other solvents include, for example, ketones, esters and organic acids. The penetrant may also contain anemulsifying agent which renders the penetrant composition water emulsifiable. Such emulsifying agents may be, for example, oil-soluble soaps, detergents, and the like. The amount of fluorescent dye incorporated in the penetrant composition may range from about 0.05 to about 2.5%, preferably from about 0.1 to about 1.5%, by weight of such composition.

The dye penetrant composition is maintained on the surface of the part for a period suflicient to permit the composition to penetrate the cracks and imperfections in the part surface, e.g. for about 5 to 30 minutes.

The penetrant composition is then removed or washed oil the surface of the part being tested, without being removed from the openings of the surface cracks or flaws. This is accomplished by wiping with a cloth, or a solvent impregnated cloth, or with water where the penetrant composition has been rendered water-emulsifiable by addition thereto of an emulsifying agent, or by a post emulsifying agent where no emulsifying agent has been added to the penetrant composition itself. Such emulsifying agents may be, for example, oil soluble soaps, detergents, wetting agents, or the like, e.g. an al-kyl aryl sulfonate or an alkyl aryl polyether alcohol.

The part is preferably then sprayed with a developer composition. Such developer may be a dry developer which contains chalk, talc, silica aerogel, diatomaceous eartih, silica, a mixture of silica and talc, or other fine absorbent powdery material such as calcium or magnesium carbonate. Wet developers can also be used, in which a power such as talc or calcium carbonate in an amount ranging from about 2 to about 30%, e.g. about 12%, by weight, is suspended in a vehicle consisting, for example, of ethanol, isopropanol or any other aliphatic alcohol, a chlorinated hydrocarbon, or other sufiiciently volatile hydrocarbon. If desired, pigmentsv or dyes such as a phthalocy-anine dye of which one of the Heliogens is an example, may be incorporated in the developer composition, preferably producing a color, e.g. blue, which is in contrast with the color, e.g. yellow, of the fluorescent penetrant dye. When using a wet developer, such developer is allowed to dry, after application to the part surface, to form a continuous coating thereon.

The powdery material of the developing agent absorbs the penetrant and fluorescent dye therein, contained in the cracks and flaws of the part surface, by capillary action and forms a fluorescent smear adjacent the crack openings.

-While it is preferred to apply a developer in accordance with the procedure set forth above, this step is not essential for obtaining the improved results of my in vention. In the event that the developer is not used, flaw or cnack indication is not as vivid as when this step is used. However, for certain applications the decreased sensitivity may be tolerated or indicated because of increased economies of inspection and the lack of necessity for determining the location of surface flaws of sufficiently small size as not to impair the function of the part under test.

In either case the test part is then exposed to visible light according to the invention to obtain maximum fluorescence of the penetrant dye.

The following examples illustrate practice of my invention:

Example 1 A dye penetriant composition is prepared as follows:

ercent by weight Calcofluor Yellow HEB, Color Index, Fluorescent Brightening Agent No. 4 0.6 SAE No. 30 lubricating oil 30.0 Tributyl phosphate 69.4

The above penetrant composition is applied to the surface of a metal test body and maintained thereon for from 5 to 30 minutes, and the surface is then wiped clean of excess penetrant, or cleaned with Stoddard solvent or by use of an emulsifier composition as follows:

Percent by weight Light mineral oil 30.0

A developer having the following composition is then sprayed on the part surface.

Percent by weight Diatomaceous earth 90.0

Silica aerogel 10.0

Alternatively a liquid developer of the following composition can be employed:

Percent by weight Calcium carbonate 10.0

Ethanol 90.0

The test body surface including the cracks and defects therein, is exposed to visible blue light of wave length about 4,400 A. Such light is provided by 'an ordinary tungsten lamp over which is placed a filter having a maximum transmission generally corresponding to the predominant activating wave length of Oallcofluor Yellow HEB for producing maximum fluorescence that is, 4,400 A. Such filter may be a Oo-rning C.S.-5-75 or a Bausch and Lomb filter No. 33-78-44, having a maximum transmission at 4,650 A. The cracks and flaws in the test body are revealed at the location of the bright yellow fluorescence produced by the penetrant dye in the mouth of such cracks and flaws, on exposure to such visible blue light.

Example 2 Rhodamine 6 GDN, Color Index 45160 0.5 Toluene 69.5 Tributyl phosphate 30.0

The penetrant composition is applied to a test body, the excess penetrant removed fro-m the part surface by an emulsifier and a developer composition is applied to the surface, employing an emulsifier and a developer as described in Example 1. The part is then exposed to yellow light by means of an ordinary tungsten lamp, over which is placed a filter such as a B-ausch and Lomb No. 33-78-52, having a peak transmittance at 5,200 A. corresponding to the predominant activating wave length for maximum fluorescence at about 5,500 A. of the penetrant dye to produce a greenish yellow fluorescence at the locations of the penetrant dye in the cracks and flaws.

6 Example 3 The procedure of Example 1 is repeated through application of the developer, employing in place of the penetrant composition of Example 1 the following:

Percent by weight Uranine S.W.S., Color Index, Acid Yellow 73 1.0 Ethyl alcohol 99.0

The developed part is then irradiated using an ordinary tungsten lamp over which is placed a suitable filter such as Bausch and Lomb No. 33-78-46 which transmits light of the predominant activating wave length of about 4,500 A. to obtain maximum fluorescence of the dye at about 5,200 A., producing a greenish yellow fluorescence at the cracks and flaws in the part surface.

Example 4 The procedure of Example 1 is repeated, but employing in place of Oalcofluor Yellow HEB in the penetrant, the respective fluorescent dyes listed in the table below. In each case :an ordinary tungsten lamp is employed for irradiating the developed test body, employing a suitable filter to transmit light at the predominant activating wave length for obtaining maximum fluorescence for each of the dyes. The values of such predominant activating and maximum fluorescence wave lengths for the respective dyes, the type of filter employed in each instance, and the fluorescent color of each of the dyes produced at the location of the cracks and imperfections of the test body, are also listed in the table below.

Predom- Fluorescent mating Maximum Fluo- Fluoreseent Dye Activating Wave Filter rescent Wave Length, A. Color Length, A.

Rhodamine B, Color 5, 500 6,000 Bausch & Red.

Index 45,170. omb

Eosinc G. Color Index 5, 250 5, 800 Bauseh & Greenish 45,380. Lomb Yel 33-78- low. 52. Auramine, Color 4, 600 5, 200 Bausch & D0.

Index 41,000. Lomb 33-78- 46. Fluoral 7GA, Color 4, 600 5, do D0.

Index-Fluorescent brightening agent 75. Azosol Brilliant Yel- 4, 600 5, 100 do Do.

low GGF, Color Inilfx-SOlWIli; Yellow Brilliant Yellow 6G 4, 000 5, 100 do D0.

Base, Color Index- Solvent Yellow 44.

From the foregoing, it is seen that the invention provides a simple means employing visible light produced by common inexpensive light sources, for irradiating fluorescent penetrant dyes in penetrmt inspection methods, such visible light being selected preferably of a wave length corresponding to the predominant maximum activating wave length to obtain maximum fluorescence for the panticular dye employed. A further important advantage of the instant invention is that it permits inspection of test bodies to be carried out in relatively open work spaces, avoiding the cramped, poorly ventilated and oppressive enclosed inspection booths heretofore required for inspection employing fiuorescigenous light.

While I have described particular embodiments of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. The method for inspecting bodies for cracks and flaws, comprising applying a fluorescent penetrant dye composition containing a fluorescent dye to a test body,

said fluorescent dye having a predominant activating wave length for producing maximum fluorescence, within the visible spectrum, permitting said penetrant to remain on the test body for a period sufficient to cause said penetrant to enter cracks and flaws on the surface of said body, removing excess penetrant composition from the surface of said test body, applying a developing composition containing an absorbent powder to said test body, and inspecting such body solely under light waves inthe visible spectrum having a wave length corresponding to the predominant activating wave length for producing maximum fluorescence of said fluorescent dye, and producing a fluorescent emission from said fluorescent dye.

2. The method for inspecting bodies for cnacks and flaws, comprising applying a fluorescent penetnant dye composition containing a yellow fluorescent dye to a test body, said fluorescent dye having an activating wave length for producing fluorescence, within the visible spectrum, permitting said penetrant to remain on the test body for a period suflicient to cause said penetnant to enter cracks and flaws on the surface of said body, removing excess penetrant composition from the surface of said test body, applying a developing composition containing an absorbent powder to said test body, and inspecting such body solely under visible light containing light waves in the visible spectrum having a wave length corresponding to the activating wave length of said yellow fluorescent dye, and producing a fluorescent emission from said fluorescent dye.

3. The method for inspecting bodies for cracks and flaws, comprising applying a fluorescent penetrant dye composition containing a yellow fluorescent dye to a test body, said fluorescent dye having a predominant activating wave length for producing mmimum fluorescence, Within the visible spectrum, permitting said penetrant to remain on the test body for a period suficient to cause said penletnant to enter cracks and flaws on the surfam of said body, removing excess penetrant composition from the surface of said test body, applying a developing composition containing an absorbent powder to said test body, and inspecting such body solely under light waves in the visible spectrum having a wave length corresponding to the predominant activating wave length for producing maximum fluorescence of said yellow fluorescent dye, and producing a fluorescent emission from said fluorescent dye.

4. In a method for inspecting bodies for cracks and flaws, including the steps of applying a penetrant composition to a test body and removing excess penetrant from the test body, the improvement which comprises incorporating in said penetrant a fluorescent dye having an activating wave length for producing maximum fluorescence, within the visible spectrum, and irradiating said test body solely with light waves in the visible spectrum having a wave length corresponding to the predominant activating wave length for producing maximum fluorescence of said fluorescent dye, and producing a fluorescent emission from said fluorescent dye, the intensity of said visible light and the concentration of said fluorescent dye being such that a substantial contrast is obtained between the emitted fluorescence and the background light from the test body.

5. The method for inspecting bodies for cracks and flaws, comp-rising applying a fluorescent penetnant dye composition containing a fluorescent dye to a test body, said fluorescent dye having a predominant activating wave length for producing maximum fluorescence, within the visible spectrum, permitting said penetnant to remain on the test body for a period sufficient to cause said penetrant to enter cracks and flaws on the surface of said body, applying an emulsifier for said penetrant composition to said surface to remove excess penetrant composition from said surface, applying a developing composition containing an absorbent powder to said test body, and inspecting such body solely under light waves in the visible spectrum 8. having a Wave length corresponding to the predominant activating wavelength for producing maximum fluorescence of said fluorescent dye, and producing a fluorescent emission from said fluorescent dye.

6. The method for inspecting bodies for cracks and flaws, comprising applying a fluorescent penetnant dye composition containing a fluorescent dye to a test body, said fluorescent dye having a predominant activating wave length for producing maximum fluorescence, within the visible spectrum, permitting said penetrant to remain on the test body for a period suflicient to cause said penetuant to enter cracks and flaws on the surface of said body, removing excess penetrant composition from the surf-ace of said test body, applying a developing composition con,- taining an absorbent powder to said test body, and irradiating said body solely with light from a tungsten lamp source filtered to emit solely light waves in the visible spectrum having a wave length corresponding to the predominant activating wave length for producing maximum fluorescence of said fluorescent dye, and producing a fluorescent emission from said fluorescent dye, the intensity of said visible light and the concentration of said fluorescent dye being such that a substantial contrast is obtained between the emitted fluorescence and the background light from the test body.

'7. The method for inspecting bodies for cracks and flaws, comprising applying a fluorescent penetrant dye composition containing a yellow fluorescent dye to a test body, said fluorescent dye having a predominant activating Wave length for producing maximum fluorescence, within the visible spectrum, permitting said penetrant to remain on the test body for a period sumcient to cause said penetnant to enter cracks and flaws on the surface of said body, removing excess penetnant composition from the surface of said test body, applying a developing composition containing an absorbent powder to said test body,

. and irradiating said body solely with light from a tungsten lamp source filtered to emit solely blue light having a wave length corresponding to the predominant activating wave length fior producing maximum fluorescence of said yellow fluorescent dye, and producing a fluorescent emission from said fluorescent dye, the intensity of said visible light and the concentration of said fluorescent dye being such that a substantial contrast is obtained between the emitted fluorescence and the background light from the test body.

8. The method for inspecting bodies for cracks and flaws, comprising applying a fluorescent penetrant dye composition containing a fluorescent dye to a test body, said fluorescent dye having a predominant activating wave length for producing maximum fluorescence, within the visible spectrum, permitting said penetrant to remain on the test body for a period suflicient to cause said penetrant to enter cracks and flaws on the surlia'ce of said body, removing excess penetrant composition from the surface of said test body, and inspecting such body solely under light Waves in the visible spectrum having a wave length corresponding to the predominant activating wave length for producing maximum fluorescence of said fluorescent dye, and producing a fluorescent emission from said fluorescent dye.

References Cited in the file of this patent UNITED STATES PATENTS 2,478,951 Stokely Aug. 16, 1949 2,636,127 De Forest et al Apr. 21, 1953 2,920,203 Switzer et al. Jan. 5, 1960 2,953,530 Switzer Sept. 20, 1960 3,028,338 Parker Apr. 3, 1962 OTHER REFERENCES Luminescence of Solids of Leverenz, John Wiley & Sons, Inc, New York, 1950, Table 5 (between pages 72 and 73).

Claims

1. THE METHOD OF INSPECTING BODIES FOR CRACKS AND FLAWS, COMPRISING APPLYING A FLUORESCENT PENETRANT DYE COMPOSITION CONTAINING A FLUORESCENT DYE TO A TEST BODY, SAID FLUORESCENT DYE HAVING A PREDOMINAT ACTIVATING WAVE LENGTH FOR PRODUCING MAXIMUM FLUORESCENCE, WITHIN THE VISIBLE SPECTRUM, PERMITTING SAID PENETRANT TO REMAIN ON THE TEST BODY FOR A PERIOD SUFFICIENT TO CAUSE PENETRANT TO ENTER CRACKS AND FLAWS ON THE SURFACE OF SAID BODY, REMOVING EXCESS PENETRANT COMPOSITION FROM THE SURFACE OF SAID TEST BODY, APPLYING A DEVELOPING COMPOSITION CONTAINING AN ABSORBENT POWDER TO SAID TEST BODY, AND INSPECTING SUCH BODY SOLELY UNDER LIGHT WAVES IN THE VISIBLE SPECTRUM HAVING A WAVE LENGTH CORRESPONDING TO THE PREDOMINANT ACTIVATING WAVE LENGTH FOR PRODUCING MAXIMUM FLUORESCENCE OF SAID FLUORESCENT DYE, AND PRODUCING A FLUORESCENT EMISSION FROM SAID FLUORESCENT DYE.