GB1570911A

GB1570911A - Method for revealing leaks and cracks in fluid systems and compositions employed therein

Info

Publication number: GB1570911A
Application number: GB156577A
Authority: GB
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1976-01-15
Filing date: 1977-01-14
Publication date: 1980-07-09
Also published as: DE2701287A1

Description

(54) METHOD FOR REVEALING LEAKS AND CRACKS IN FLUID SYSTEMS AND COMPOSITIONS EMPLOYED THEREIN (71) We, ROCKWELL INTERNATIONAL CORPORATION, a Corporation organised and existing under the laws of the State of Delaware, United States of America, of 2230 East Imperial Highway, City of El Segundo, State of California, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: Method for detecting leaks and cracks in components of fluid-filled systems such as hydraulic systems, by applying to the exterior surface of a component of such system and suspected of having a leak, a dry powder indicator composition comprised of a suitable powder carrier, especially a mixture of silica and talc, containing a coloring agent, such as a fluorescent or non-fluorescent dye, the exuding fluid from the system activating the dye at the locations of any cracks to from colored indications, preferably removing excess powder composition from the component surface as by gentle air blowing, and viewing the colored, e.g. fluorescent, indications under suitable light, revealing the location of leaks and cracks on the component surface. The invention is also directed to the above-noted indicator composition employed in the process.

This invention relates to procedure and compositions for detecting leaks and cracks in components of fluid systems, and is particularly concerned with procedure and compositions for detecting leaks and cracks in components of fluid-filled systems under pressure, such as hydraulic systems and fuel lines, simply and economically without contaminating the fluidfilled system, and without removing the functional fluid of the system or removing the fluid-filled system from the vehicle with which it is employed.

Fluid-filled systems such as hydraulic, brake, transmission, or fuel lines and tanks often develop leaks due to cracks, pits, or improperly fitted parts. When leaks occur, these fluid-filled systems have to be removed from the vehicle, drained, and disassembled before they can be inspected for the defect causing the leak. The most common detection method used is dye penetrant inspection. In conventional dye penetrant inspection methods for location and evaluation of surface flaws, defects or cracks in test bodies or parts, a liquid penetrant composition containing a liquid carrier and 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 deveoper composition may then be applied to the part surface.Such developer can be in the form of a light coloured powder, which contrasts with the color of the dye and 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, and to "bleed" through the developer. Excess developer is removed and the part is then exposed to invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.

When applied to detection of cracks and leaks in a fluid-filled system, such conventional dye penetrant inspection methods can only be employed when the fluid used in the system has been totally removed in order for the penetrant solution to be purged into the system which had been previously filled with the hydraulic, brake, transmission, fuel or other fluids used in the system. Once the penetrant is allowed to pass through all the passages, lines, and tanks, it will exude through the defect after a developer coating is applied to aid in revealing the defect. The major drawback in using dye penetrants for locating defects in fluid-filled systems is that the original fluid in the system has to be drained, and the system has to be flushed with clean solvents.This task often also requires the removal of the system itself from the vehicle using it, and total disassembly of the system is often a requirement. The penetrant to be used must be compatible with all the seals and materials being used in the system. Since such compatibility is often impossible to determine in advance, the use of a penetrant often is prohibited. If a penetrant is used in the system, it has to be thoroughly flushed from the system after the inspection. Thus, current commercial dye penetrants and methods employed for locating leaks occuring in fluid-filled systems such as hydraulic systems, fuel lines and tanks are essentially not practical.

Exemplary prior art related to the problem of leak detection is noted below.

U.S. 3,287,156 to Griffith relates to a lacquer coating which is placed as a leak indicating coating for use with missiles and rockets, on the missile surface and which contains materials which will chemically react with any leaking fuel material. The reaction produces a distinctive color change which is readily visible. The patent disclosed a plurality of such organic coatings employing therein a combination of different coloring agents.

U.S. 2,878,392 to Polito discloses the use of an amine-containing leak detecting material which is put inside a tank or the like in order to determine where the leak exists. The patent indicates that the suspected leakage point may be dusted with a fine absorbent dust impregnated with a suitable indicator capable of changing color when it comes in contact with the amine solution. It is further indicated that the amine solution may also contain a fluorescent material.

A somewhat similar disclosure is found in U.S. 3,006,861 to Browning et al, which discloses the use of a leak detecting fluid containing a marker dye, which may be used in conjunction with a detection aid which is a dispersion of a material having good dye absorption properties such as clay, talc or chalk. The aqueous leakage simulating composition of this patent comprises a water base solution containing a surface active agent (a surfactant), an anti-foam agent and a marker dye.

U.S. 3,597,263 to Bancroft et al discloses various leak detectors including chemical indicators used in tapes or paints which change color on contact with steam or water.

However, the leak detection processes and systems of the above patents are subject to various disadvantages previously noted, such as contamination of the fluid-filled system by the leak detection medium, the requirement for removal of the functional fluid of the system being inspected, and the like.

As further illustrative of the prior art, U.S. 2,707,236 to De Forest discloses a method for detecting surface flaws in bodies by applying a liquid penetrant to the surface of the body and then applying to the surface an indicating powder which includes a carrier powder such as silica aerogel and a fluorescent or non-fluorescent pigment. Although in this method, the coloring matter or pigment is in the developer powder rather than in the liquid penetrant, this method is subject to the same disadvantages noted above for use of conventional dye penetrants for detection of leaks and cracks in fluid-filled systems, namely, it requires removal of the functional fluid from the system, the flushing of the system, and then refilling the system with functional fluid after the leak detection process has been carried out. U.S.

2,848,421 to De Forest has a disclosure similar to the 2,707,236 patent.

In copending application No. 36664/76 (Serial No. 1563017) there is disclosed a dry powder developer composition for dye penetrant inspection of cracks and flaws in a wor piece, consisting essentially of talc and silica.

It is an object of the present invention to provide novel procedure and compositions for locating cracks and leaks in fluid-filled systems. It is a particular object to provide simple, rapid and economical procedure and compositions for detecting leaks and cracks in fluidfilled systems particularly without requiring removal of the functional fluid from the system or contamination thereof by the crack detecting composition, the procedure and compositions being effective for use in systems employing a wide variety of functional fluids, both aqueous and non-aqueous.

The above objects are accomplished by a simple procedure employing a powder carrier of the types described in greater detail hereinafter, incorporating a coloring agent, e.g. a fluorescent or non-fluorescent dye, whereby leaks due to pits, cracks or improperly fitted joints in fluid-filled systems can be detected. The present invention employs as a basic feature, the fluid of the fluid-filled system as the vehicle for producing the colored indications of cracks causing leakage, in conjunction with a developer in the form of a suitable carrier powder which contains the coloring agent in the form of a dry, e.g. fluorescent or nonfluorescent, dye or tracer. Thus, the invention process employs the system's own fluid to advantage together with an indicator or developer powder which carries its own coloring agent or dye. The present invention is based on the principle that all common well known fluid-filled systems such as hydraulic, transmission, brake systems, fuel lines, and the like, employ as functional fluids liquids which readily dissolve various types of dyes, both fluorescent and non-fluorescent, and a suitable dye can be preselected and incorporated with a light colored carrier powder, for use with a particular functional fluid in which the dye is soluble.

According to the invention process, after the area of a component of the system which is suspected of having a leak or leaks is exteriorly cleaned of the leaking fluid, for example by either wiping with a volatile solvent or by flushing the area with a solvent and allowing it to dry, the powder composition is then applied to the suspected area by suitable means as by spraying, pouring or brushing. Almost immediately, the exuding fluid leaking from the system through cracks therein, is drawn into the indicator powder or composition adjacent the mouth of the cracks, and activates the fluorescent or non-fluorescent tracer which is carried in the powder composition.The colored indications thus produced reveal the location of the cracks causing such leakage, in the form of colored traces or as brilliantly fluorescent traces where fluorescent coloring agents or dyes are employed, while the excess developer powder on the surface of the part remains dull in color. The color contrast of the colored indications can be further increased by blowing off excess developer powder.

Thus, it is apparent that the invention process and composition permits detection of cracks and leaks in the fluid-filled systems without disturbing or contaminating the functional fluid in such system and without removing such fluid from the system or removing the system per se from the vehicle with which it is employed.

The invention process and compositions are applicable for use in a variety of fluid-filled systems including both oil based and aqueous fluid-filled systems. These include fluid-filled systems such as hydraulic, brake and transmission systems, and fuel lines, generally employing oil-based functional fluids which can include esters, both aliphatic and aromatic, hydrocarbons, analagous halogenated hydrocarbons, glycol ethers, and the like, described in detail hereinafter. Depending upon the particular application, the developer composition of the invention is tailored so that the coloring agent, e.g. the dye or dyes, employed in such indicator or revealer powder, dissolves in the particular non-aqueous or aqueous functional fluid of the system. The invention process is particularly designed for detecting cracks and leaks in oil-based fluid systems such as hydraulic fluids.

However, the invention process also can be employed for detecting cracks and leaks in water-based systems such as pressurized water lines. Further, ship hulls, for example, can be inspected by employing an indicator powder according to the invention, such as a combination of talc and silica powder, containing a water soluble dye. In this application the powder indicator or developer is applied to the inside of the hull for inspection of leaks. Indicator compositions suitable for use with water-based fluids can contain one or more dyes, either fluorescent or non-fluorescent, which are water soluble.

Thus, in a broad sense, the invention principles are applicable where the fluid of the fluid-filled system is on one side or surface of a component of such system having a crack, and the indicator powder hereof is placed on the opposite side or surface thereof to which the fluid has leaked.

Any known inert free flowing carrier powder generally employed as a developer powder in dye penetrant inspection processes can be employed. These are usually light colored or white powders providing high contrast for the colored indications when the fluid from the system is drawn from the cracks into the powder and dissolves the dye therein. Such powders include talc, silica, silica aerogel, magnesium carbonate, calcium carbonate, diatomaceous earth, clay, sawdust, powdered plastics, and the like. Generally there can be employed about 65 to about 99.9% of dry powder carrier and about 1 to about 35% of dye or other coloring agent, by weight of the total indicator composition. However, it has been found that most effective results are achieved employing a combination of talc and silica, particularly in the proportions noted below, and a dye.

The talc component of the developer composition is a fine white powder of small but irregular particle size. A commercially available material particularly suitable for purposes of the invention is that marketed as Desertalc Mikro 507, by Desert Minerals, Inc. of Los Angeles, California. The latter material is a semi-tremolitie-acicular-platey having a particle size distribution ranging from about 15 to less than 1 micron, and is essentially a calciummagnesium silicate. This white powder provides a unique combination of highly irregular particle sizes and shapes, leaving an almost invisible film deposit of microsize particles which provide a path for entrapment of fluid which exudes from cracks and microcracks in the surface to which the indicator composition is applied.Such fine powdery tale adheres to almost any type of surface including very fine or polished surfaces such as chrome plating.

Due to the irregular particle size content of such talc, it functions as an aid for depositing the indicator adjacent varying size cracks. Other suitable talcs include Desertalc Mikro 706,707 and 906. Desertalc Mikro 706 and 707 are ultra-fine micaceous particle structures of thin, soft translucent plates. Desertalc Mikro 906 is a steatic-platey, spherical material having a structure of fine small plateles and spheres of high uniformity. This material is low in carbonate and is non-abrasive. Particle sizes of Desertalc 706,707 and 906 are similar to 507, ranging from 15 to less than 1 micron.

The above described talcs, illustrated by Desertalc Mikro 507, 706, 707 and 906 have a different structure from conventional talc.

The second component of the preferred indicator composition is silica, employed also preferably in fine powder form of particle size ranging from about 0.007 to about 0.050 micron (about 70 to about 500 Angstroms), and is an extremely fluffy, snow-white powder of extremely low bulk density. A commercially available form of this component is marketed as Cab-0-Sil M-5 by Cabot Corporation. The Cab-0-Sil has an enormous external area, one gram of Cab-0-Sil M-5 having about 400 square meters of surface area. Cab-O-Sil M-5 is a sub-microscopic fire-dry fumed silica different in structure from precipitated silicas or silica gels or aerogels. This white silica powder imparts free-flowing, non-caking properties to the overall powder indicator or developer composition, and also aids in developing bright fluorescent indications from fluorescent dyes.

It has been found that in order to obtain most effective results with the indicator composition of the invention, the components thereof should be employed in certain proportions.

Thus, the talc component is generally employed in an amount ranging from about 5 to about 65%, preferably from about 25 to about 60%, and the silica component generally in an amount ranging from about 25 to about 85%, preferably from about 30 to about 70%, by weight of the overall composition, including the dry powder dye.

Any suitable dye generally employed in dye penetrant compositions can be incorporated into the developer powder. These include both fluorescent and non-fluorescent dyes, and dyes which are solvent soluble and those which are soluble in aqueous solutions or water.

Thus, various types of fluorescent dyes can be employed including for example the dye marketed as Fluorol 7GA and Morton Fluorescent Yellow G, as well as other fluorescent dyes such as those marketed as Calcofluor Yellow, Azosol Brilliant Yellow 6GF; Rhodanine B, Rhodanine 6 GDN, Calcofluor White RW, Blancophor White AW, Auramine and Eosine G, and water soluble fluorescent dyes such as Brilliant Sulfo Flavine FFA, Auramine B Extra S, and Blancophor FFG.

The dry powder developer or indicator composition employed in the invention process alternatively can contain non-fluorescent or daylight type dyes such as azo type dyes, e.g., xylenaezo-beta-naphthol, Mefford No. 322 dye, believed to be otoluene-azoxyleneazo-beta-naphthol, and the azo dyes marketed as Oil Red "0" and Sudan Red "0". These dyes conveniently can be employed where daylight or white light is only available. However, it is preferred to employ fluorescent dyes having greater sensitivity or detectability as result of the high contrast obtained by the fluorescent indications.

The amount of dye which is incorporated into the dry powder carrier to produce the indicator composition of the invention, can range from about 0.1 to 30%, preferably about 1 to about 20%, of the dye, or mixtures thereof, by weight, based on the total or overall weight of the dry indicator composition. In preparing the dry indicator composition employed in the invention process, the dye is simply added to the powder carrier, e.g. mixture of talc and silica, in the desired proportions.

Typical dry powder developer or indicator compositions containing a coloring agent or dye which can be employed in the invention process are set forth in Tables I, II and III below, Table I being directed to compositions in which the dye or dyes are fluorescent and solvent soluble, Table II to compositions containing fluorescent water soluble dyes and Table III to compositions containing non-fluorescent solvent soluble dyes. The proportions of components are in terms of percent by weight of the respective compositions.

TABLE I Fluorescent non-aqueous Solvent Soluble dyes COMPONENTS A B C D E F G H I J Desertalc Mikro 507 25 10 5 25 30 -- 25 25 60 9 Cab-O-Sil M5 60 75 80 59 55 90 60 60 25 90 Calcafluor White RW 10 10 10 8 10 5 -- 15 15 - Morton Fluorescent Yellow G 5 5 5 8 5 5 15 -- -- 10 TABLE II Fluorescent Aqueous Water Soluble Dyes COMPONENTS K L M N O P Q Desertalc Mikro 507 25 5 -- 40 -- 90 20 Cab-O-Sil M5 60 80 85 50 90 -- 60 Brilliant Sulpho Flavine FFA 15 15 15 10 10 10 20 in Table II above, the dye Brillian Sulph Flavine m;A can be replaced by Rhodanine B Extra S. In either case, employing such developer compositions in the invention process, indications of cracks or leaks will be revealed under either black or fluorescent light, or white light.Indications of cracks will show fluorescent red under black light and a bright red under white light.

TABLE III Non-fluorescent non-aqueous Solvent Soluble Dyes COMPONENTS R S T U V Desertale Mikro 507 25 30 10 -- 85 Cab-O-Sil M5 50 50 60 70 - Sudan Red "O" or Oil Red "0" 25 20 30 30 15 With respect to the compositions of Table III above, these formulations work well to reveal cracks and leaks according to the invention process if the part surface being inspected is light in color. Under these conditions the red indications will contrast well with the light background. However, if the surface being inspected is dark in color then the use of an indicator containing a fluorescent dye is preferred in order to increase the contrast between the fluorescent indications and the dark background.

It has been found that a particularly preferred dry powder developer containing a dye for use in the invention process and which is especially effective is composition A of Table I above.

As previously noted, fluid-filled systems, leaks and cracks in which can be detected or revealed employing the process and indicator compositions of the invention, can encompass the use of a wide variety of functional fluids. Thus, for example, hydraulic systems, particularly employed in aircraft, to which the process and developer compositions are applicable and in which the above noted solvent soluble dyes of the developer compositions are soluble, can include a wide variety of esters, both aliphatic and aromatic.Examples are esters of an acid of phosphorus, particularly phosphate esters including dialkyl aryl phosphates in which the alkyl groups are either straight chain or branched chain and contain from about 3 to about 10 carbon atoms, and the aryl radicals have from 6 to 8 carbon atoms, including dibutyl phenyl phosphate, butyl amyl phenyl phosphate, butyl hexyl phenyl phosphate, butyl heptyl phenyl phosphate, butyl octyl phenyl phosphate, triaryl phosphates in which the aryl radicals have from 6 to 8 carbon atoms, examples of such phosphates including tricresyl, trixylyl, phenyl dicresyl and cresyl diphenyl phosphates, trialkyl phosphates in which the akyl groups have from about 3 to about 10 carbon atoms, including tri-n-butyl phosphate, tri(2-ethyl hexyl) phosphate and tri-isononyl phosphate, and alkyl diaryl phosphates having the same definition for the alkyl and aryl radicals as for the dialkyl aryl phosphates, examples of which include butyl diphenyl, amyl diphenyl, hexyl diphenyl, heptyl diphenyl, octyl diphenyl, and 6-methyl heptyl diphenyl phosphates.

Other esters used as functional fluids which can be employed in hydraulic systems to which the invention is applicable are the di- and tricarboxylic acid esters, particularly the dicarboxylic acid esters. Preferred types of the latter compounds are the alkyl diesters of-adipic and sebacic acid, that is the diester adipates and sebacates. Such esters can contain alkyl groups, either straight chain or branched chain, containing from about 4 to about 12 carbon atoms. Specific examples of these fluids are dihexyl, di 2-ethylhexyl, dioctyl, dinonyl, didecyl and diisodecyl adipate, and the corresponding sebacates. Also, the diesters of the dicarbox ylic aromatic acids, particularly the diesters of phthalic acid, that is the phthalate diesters can be employed in fluid filled systems.The diesters of such acids can contain alkyl groups of from 4 to 12 carbon atoms, examples of which are di-n-butyl phthalate, dihexyl phthalate, dioctyl phthalate, dinonyl phthalate, didecyl phthalate, and di-isodecyl phthalate.

There can also be employed combinations of the above esters, such as a combination of a phosphate ester, e.g. dibutyl phenyl phosphate and a dicarboxylic acid ester, e.g. 2ethyl-hexyl adipate. Also there can be employed a combination of two or more phosphate esters or a combination of two or more dicarboxylic acid esters.

Another type of fluid useful as a functional fluid in fluid filled systems are the polyalkylene glycol materials, particularly polyalkylene glycol ethers containing oxyalkyl groups, the alkyl radicals of which can range from about 1 to about 8 carbon atoms in length. These glycol ethers can have molecular weights rangingfrom about 500 to about 25,000. Examples of such polyalkylene glycol materials include the n-butyl methyl, n-butyl ethyl, isobutyl ethyl, n-propyl ethyl and isopropyl ethyl diethers of polypropylene glycol, the monomethyl ether of polypropylene glycol and the copolymer of ethylene oxide and propylene oxide, monobutyl ether.

Functional fluids of fluid-filled systems which can be tested for leaks or cracks according to the invention can also include petroleum hydrocarbons, and which can contain carbon chains of from C10 to about C24 carbon atoms. Atypical example of such a petroleum hydrocarbon is the red petroleum hydrocarbon liquid according to military specification MIL-H-5606B, understood to contain carbon chains of about C10 to C20 carbon atoms, generally employed as a hydraulic fluid in military aircraft.

Also there can be employed in fluid-filled systems orthosilicate esters such as the tetraalkyl orthosilicates such as tetra(octyl)-orthosilicates, tetra(2-ethylhexyl)orthosilicates and the tetra(isooctyl) orthosilicates, and the (trialkoxysilico) trialkyl orthosilicates, otherwise referred to as hexa(alkoxy) disiloxanes, such as hexa(2-ethylbutoxy) di-siloxane and hexa(2)ethylhexoxy) disiloxane, the preferred orthosilicates being those in which the alkyl groups contain from 4 to 12 carbon atoms.

Other types of fluids employed in fluid-filled systems to which the present invention is applicable are halogenated organic compounds such as halogenated biphenyl compounds having from 20 to 61% by weight combined chlorine. Typical examples of halogenated biphenyl compounds are those which contain chlorine or bromine or combinations thereof in amounts corresponding to mono-, di-, tri-, tetra-, penta- and hexahalobiphenyl.

There can also be employed as functional fluids in such fluid-filled systems a mixture of halogenated alkylbenzenes such as the mixture of halogenated ethylbenzenes disclosed in U.S. Pat. No. 2,257,903, which contain an average of two atoms of bromine per mole of ethylbenzene.

The invention process and dry developer composition of the invention are also applicable for detecting cracks and leaks in fluid-filled systems based on aqueous functional fluids, including water alone. Thus, for example functional fluids which are water miscible or water soluble include glycols or glycol ethers having from 2 to about 14 carbon atoms such as ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol ethers such as the ethyl, methyl, propyl, and butyl ethers thereof, and similar ethers of diethylene and triethylene glycol.

Also, as previously noted, fluid-filled systems in which water alone is the functional fluid also are applicable for detection of cracks and leaks employing the invention process and powder indicator compositions.

In the method for detecting cracks and leaks in the surface of a component or components of a fluid-filled system, such as a hydraulic fluid-filled system, according to the invention, and as described in detail below, the various steps of the process are illustrated in Figs. 1 to 6 of the accompanying drawing. Referring to the drawing, numeral 10 represents a component, e.g. a line, of a fluid-filled system such as a hydraulic fluid system, which contains a defect or crack 12, which has permitted fluid, indicated at 14 within the system, to leak through crack 12 and to the outside surface of component 10, as indicated at 16.

The excess fluid 16 which is leaked to the outside is removed, as shown in Fig. 1, by means of a solvent wash or spray as indicated at 18. Such solvent wash can be any suitable fluid which essentially dissolves the fluid 16 and permits essentially complete removal of fluid 16 which has leaked to the outside surface of the part 10. Suitable solvent fluids for this purpose, depending upon the particular fluid employed in the fluid-filled system can include any suitable volatile type cleaning solvent or fluid such as naphtha, methyl ethyl ketone, acetone, trichloroethane, and the like.

After the surface has been permitted to dry and referring to Fig. 3 of the drawing, there is then applied to the surface of part 10, above and around the vicinity of the opening of crack 12 in the outer surface of the part, the dry indicator composition or crack revealer powder 20.

Usually the cracks or defects are so small that they are invisible to the naked eye. In the dry powder composition 20, the dye particles dispersed therein are indicated at 22.

Following application of the dry indicator powder 20 to the exterior surface of component 10, in a short period of time, e.g. of the order of about 5 to about 30 seconds, the fluid 14 in the crack 12 has begun to exude into the indicator powder 20 at the mouth of the crack and begun to dissolve the dye in the indicator powder adjacent the mouth of the crack, as indicated at 24 in Fig. 4, thus forming a colored indication opposite the mouth of the crack and along the length thereof.

Now referring to Fig. 5, excess indicator or developer powder 20 is removed as by gentle air blasting, as indicated at 26, without disturbing that portion of the developer powder at 24 adjacent the mouth of crack 12, and which has been wetted by the exuding fluid from the crack and which now contains the colored indication at such location. The remaining indicator powder at 24 which contains the leaking fluid adheres to the exterior surface of the component 10.

Referring to Fig. 6, the outer surface of the part 10 and containing the colored or dye indication 28 adjacent and along the mouth of the crack is viewed under suitable lighting conditions, for example black light as indicated at 29, where the dye in the developer composition is a fluorescent dye, producing a highly visible indication of 28 of the dissolved or liquefied dye, e.g. fluorescent dye, in the carrier powder, which preferably is a mixture of talc and silica. Fig. 6 also shows a slight migration of the dye into the mouth of the fluid-filled crack, as indicated at 30.

Although the invention is directed primarily to use of an indicator or developer composition in the form of a powder carrier containing a dry powder dye or dyes which when in contact with the fluid exuding from a crack in a fluid-filled system dissolves the dye contained in the powder carrier and forms a visible indication of the leak, the invention can also be practiced employing a fluorescent or non-fluorescent powder developer in which the entire powdered material is colored and which will adhere like a developer powder to the fluid exuding from the defect in the fluid-filled system, e.g. the housing of a hydraulic line or tank to give a coloured indication. Illustrative of such compositions are the materials marketed as "Dayglow" Registered Trade Mark fluorescent pigments, and commercially available nonfluorescent powdered pigments.However, such a variation of indicator composition according to the invention is not as sensitive as the powder composition containing a dry powder carrier and a dry powder dye.

Another modification of the powder indicator or developer of the invention is a combination of a carrier powder which is permanently pigmented or colored, either fluorescent or non-fluorescent, and which contains a dry dye which reacts with the fluid exuding from the system where the defect is located, forming a colored indication having a color which contrasts with the background color provided by the carrier powder. An example of such a developer material is "Dayglow" fluorescent pigment, e.g. fluorescent yellow, and a small amount of a red non-fluorescent dye. This modified form of developer has good sensitivity.

Also, instead of employing fluorescent or non-fluorescent dyes as coloring agents in the above carrier powders, inorganic or organic pigments can be employed as indicating material, examples of non-fluorescent pigments being metallic oxides, cobalt blue and "Permansa" red, and examples of fluorescent pigments being zinc sulfide or chrysene, fluorescent emerald green, and the like.

Illustrative examples of practice of the invention are set forth below.

EXAMPLE 1 The pressurized oil line for an aircraft turbine engine and containing as lubricating oil the fluid MIL-L-7808G, had a crack, causing lubricating oil to leak through the crack to the outside surface of the oil line. The lubricating oil MIL-L-7808G is understood to be comprised essentially of dioctyl sebacate.

The lubricating oil on the outer surface of the line was removed by a spray wash with naphtha solvent and the washed surface allowed to dry.

The indicator composition A of Table I above was applied by pouring over the area of the outer surface of the part from which the leaking oil had previously been removed. In about 5 seconds the lubricating oil exuding from the crack or defect had begun to dissolve the dyes in the powder developer composition, and excess powder on the surface of the part was removed by a gentle air blast.

The area of the part so treated with the developer powder was then subjected to black light (fluorescent) illumination, producing a highly visible brilliant fluorescent yellow-green indication of the crack which caused the leak.

During the test, the lubricating oil of the system remained inside the line.

EXAMPLE 2 The procedure of Example I above was repeated for detecting a leak in a pressurized hydraulic line in an aircraft system, containing the hydraulic fluid M-2-V. The latter fluid is understood as comprised essentially of hexa (2-ethyl-butoxy) disiloxane. Hydraulic fluid leaking to the outside surface of the line was removed by a spray of naphtha solvent. The outer surface was then permitted to dry.

Following application of the dry powder indicator composition A to the surface of the line suspected to contain the leak, and removal of excess powder, in a short time the hydraulic fluid exuding through the leak and passing to the outside into the indicator composition had dissolved the fluorescent tracer dye contained in the powdery carrier.

When the outer surface was subjected to fluorescent light, again a brilliant fluorescent indication was obtained, showing the location of the crack causing the leak.

EXAMPLE 3 The procedure of Example 1 is followed for detecting a lubricating oil leak for a lubricating oil of the type disclosed in Example 1, but employing the developer powder composition R of Table III above, containing the non-fluorescent dye Oil Red "0". In this case the surface of the metal line being inspected was of a light color.

Following treatment with the powder developer, the surface of the part was inspected under white non-fluorescent light, providing a red smear or indication of the location of the crack causing the leak.

EXAMPLE 4 A pressurized water line containing a leak, with water depositing on the outside surface at the location of the leak, was treated as follows.

The water leaking to the outside surface of the pipe was dried with a cloth and the powder developer composition K of Table II above, and containing the water soluble fluorescent dye, Brilliant Sulfo Flavine FFA, was applied to the surface of the line where the leak was located.

After about 5 seconds, during which time the fluorescent due had dissolved in the water exuding through the crack or leak in the pipe, excess powder was removed from the surface by a gentle air blast, and the area was subjected to fluorescent light, providing brilliant green fluorescent tracer indications of the cracks causing the leaks.

From the foregoing, it is seen that the invention provides a simple, rapid and economical procedure for readily detecting leaks due to pits, cracks or other imperfections in fluid-filled systems such as pressurized hydraulic, oil and fuel lines, as well as pressurized water systems, and which can employ a variety of fluids, while the system continues in operation, without contaminating the fluid-filled system or removing the system's fluid or removing the system from its normal location, by employing a powder indicator or developer incorporating a coloring agent or coloring means which in conjunction with the fluid leaking from the defect, provides a colored indication of the cracks or defects causing the leak.

WHAT WE CLAIM IS: 1. A method for detecting cracks and leaks through a wall having a surface in contact with a fluid, which method comprises applying to the opposite surface of the wall in an area suspected to contain a crack, a dry powder indicator composition containing a colouring agent capable of forming a coloured indication upon contact with the fluid, and viewing the opposite surface under appropriate lighting conditions to obtain visible coloured traces or indications of a crack where the fluid has passed through to said opposite surface.

2. A method for detecting cracks and leaks according to claim 1 wherein the wall is that of a component of a fluid-filled system and the said opposite surface is the exterior surface of said component.

3. A method as defined in claim 1 or 2 including the initial step of cleaning from the said opposite surface liquid which has leaked through one or more cracks, prior to applying the dry indicator composition.

4. A method as defined in claims 1,2 or 3 including the step of removing excess indicator composition from the said opposite surface while, leaving remaining any indicator composition clinging to the opposite surface at the location of cracks.

5. A method as defined in any one of claims 1 to 4 wherein the colouring agent is activated by the fluid to form the coloured indication and the indicator composition is maintained on the opposite surface at least for a period sufficient to cause fluid passing through cracks to activate the dye and form coloured indications of said cracks.

6. A method as defined in any one of claims 1 to 5 wherein the dry indicator composition comprises a carrier powder having a light colour, and said colouring agent is a dye or a pigment.

7. A method as defined in claim 6 the dye being soluble in the fluid.

8. A method as defined in claim 7 the dye being a fluorescent dye.

9. A method as defined in claim 7 the dye being a non-fluorescent dye.

10. A method as defined in claim 6 or a claim dependent thereon the carrier being one or more of talc, silica, silica aerogel, magnesium carbonate, calcium carbonate, diatomaceous earth, clay, sawdust or powdered plastics.

11. A method as defined in claim 10 the carrier being a light coloured powder comprised of a mixture of about 5 to about 65 % talc and about 25 to about 85 % silica, and 0.1 to about 30% dye, the percentages being by weight of the total composition.

12. A method as defined in any one preceding claim, the fluid being an oil-based fluid.

13. A method as defined in any one of claims 1 to 12 the fluid being an ester, hydrocar

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. suspected to contain the leak, and removal of excess powder, in a short time the hydraulic fluid exuding through the leak and passing to the outside into the indicator composition had dissolved the fluorescent tracer dye contained in the powdery carrier. When the outer surface was subjected to fluorescent light, again a brilliant fluorescent indication was obtained, showing the location of the crack causing the leak. EXAMPLE 3 The procedure of Example 1 is followed for detecting a lubricating oil leak for a lubricating oil of the type disclosed in Example 1, but employing the developer powder composition R of Table III above, containing the non-fluorescent dye Oil Red "0". In this case the surface of the metal line being inspected was of a light color. Following treatment with the powder developer, the surface of the part was inspected under white non-fluorescent light, providing a red smear or indication of the location of the crack causing the leak. EXAMPLE 4 A pressurized water line containing a leak, with water depositing on the outside surface at the location of the leak, was treated as follows. The water leaking to the outside surface of the pipe was dried with a cloth and the powder developer composition K of Table II above, and containing the water soluble fluorescent dye, Brilliant Sulfo Flavine FFA, was applied to the surface of the line where the leak was located. After about 5 seconds, during which time the fluorescent due had dissolved in the water exuding through the crack or leak in the pipe, excess powder was removed from the surface by a gentle air blast, and the area was subjected to fluorescent light, providing brilliant green fluorescent tracer indications of the cracks causing the leaks. From the foregoing, it is seen that the invention provides a simple, rapid and economical procedure for readily detecting leaks due to pits, cracks or other imperfections in fluid-filled systems such as pressurized hydraulic, oil and fuel lines, as well as pressurized water systems, and which can employ a variety of fluids, while the system continues in operation, without contaminating the fluid-filled system or removing the system's fluid or removing the system from its normal location, by employing a powder indicator or developer incorporating a coloring agent or coloring means which in conjunction with the fluid leaking from the defect, provides a colored indication of the cracks or defects causing the leak. WHAT WE CLAIM IS:

1. A method for detecting cracks and leaks through a wall having a surface in contact with a fluid, which method comprises applying to the opposite surface of the wall in an area suspected to contain a crack, a dry powder indicator composition containing a colouring agent capable of forming a coloured indication upon contact with the fluid, and viewing the opposite surface under appropriate lighting conditions to obtain visible coloured traces or indications of a crack where the fluid has passed through to said opposite surface.

7. A method as defined in claim 6 the dye being soluble in the fluid.

8. A method as defined in claim 7 the dye being a fluorescent dye.

9. A method as defined in claim 7 the dye being a non-fluorescent dye.

bon, halogenated hydrocarbon or glycol ether.

14. A method as defined in claim 13 the fluid being a phosphate ester, dicarboxylic acid ester or orthosilicate ester.

15. A method as defined in any one of claims 1 to 12 the fluid being a water-based fluid.

16. A method as defined in claim 3 or a claim dependent thereon, the cleaning being carried out by application of a solvent for said fluid.

17. A method as defined in claim 4 or a claim dependent thereon, the removal being carried out by blowing with a gentle air blast.

18. A method as defined in claim 11 the talc being present in an amount from about 25 to about 60%, the silica in an amount from about 30 to about 70two, and the dye in an amount from about 1 to about 20%, by weight of said composition.

19. A method as defined in claim 18 wherein the silica is fumed silica of low bulk density.

20. A method as defined in claim 19 wherein the particle size of the talc ranges from about 15 to less than 1 micron, said silica being fumed silica of low bulk density and having a particle size ranging from about 0.007 to about 0.050 micron.

21. A method as defined in any one of claims 18 to 20 wherein the silica has a particle size ranging from about 0.007 to about 0.050 micron.

22. A method as defined in any one of claims 18 to 21 wherein the talc is a semitremolitic-acicular-platey in the form of a white powder of irregular particle sizes and shapes.

23. A method as defined in claim 1 substantially as hereinbefore described.