US3538016A - Water dispersible high-sensitivity developer - Google Patents

Description

Int. Cl. G01n 33/00 US. Cl. 252-408 6 Claims ABSTRACT OF THE DISCLOSURE In the penetrant method of non-destructive testing for surface discontinuities wherein a developer serves to enhance a visible or fluorescent dye indication of a surface flaw or other discontinuity, the use of a water-wettable, finely divided clay having substantially no particles greater than about two microns in diameter and having a higher degree of brightness reflectness, a water-soluble, normally solid polyethylene glycol, a surfactant stable toward the other ingredients of the mixture and rendering the mixture readily dispersible in an aqueous liquid vehicle. In the method for use, such a developer is applied to a surface to which penetrant has previously been applied and from which the excess of the penetrant has been removed.

This invention relates to a water dispersible high-sensitivity developer, particularly adapted for use as a wet developer in the liquid pentrant method of nondestructive testing for the detection of surface flaws, discontinuitiesand the like. The developer may be used in either a dry state or in a wet state, and is applied to the surface of the workpiece undergoing test after the application of a liquid penetrant, usually but not necessarily containing a dye, and the removal of any of the excess of the penetrant from the surface.

In the penetrant method for the nondestructive testing of surfaces, using a liquid penetrant that is water or oil based and that contains a visible or fluorescent dye dissolved therein to detect the presence of surface flaws or other discontinuities, it has been proposed to use a lightcolorcd, finely divided developer powder, such as talc, titanium dioxide, clay, or other light-colored pigment, to enhance the visual contrast between the background surface and the residue of the penetrant appearing at the crack or other surface discontinuity. Developers have been used both in the dry, powdered form, and also in suspension in a volatile water miscible alcohol, or in water, or in a mixture of alcohol and water, all being herein termed aqueous type liquid vehicles.

In accordance with the present invention, a developer composition is supplied as a dry powder for dispersing at the time of use into an aqueous type liquid vehicle. The composition of my invention provides a substantially nonfoaming suspension in an aqueous liquid that has the following advantages over prior art wet developer compositions: it completely wets the surface, regardless of the particular material forming such surface, with no appreciable formation of rivulets or roll back from the edge of the surface tested; it has a whitish color and forms on drying a white or cream-colored coating that does not itself fluoresce but has high visible light reflectance; the residual developer coating can be easily and completely removed, as by flushing with water; the developer in the form of an aqueous suspension does not corrode aluminum or steel; and it is non-toxic and safe for industrial use. As a dry powder, my developer composition has a shelf life of indefinite length and in its wet state has a satisfactory tank life in that any settled out solids formed upon standing are very easily redispersed. Even more importantly, the developer of my invention,

.nited States Patent W Ice as compared with heretofore known developers, exhibits significantly greater sensitivity on extremely fine cracks, viz., those measurable down to 0.2 micron and even finer, although it does not appear any more sensitive than some known developers when applied over surfaces having large cracks, i.e., cracks of over 2.0 microns in width.

'It is therefore an important object of this invention to provide an improved developer composition for use as a dry or wet developer in the penetrant method of testing for surface discontinuities and other defects and which has the aforesaid advantageous properties and characteristics.

Other and further important objects of this invention will become apparent from the following description and the appended claims.

The developer composition of my invention preferably includes, in its dry state, a clay base of special properties; a dispersing agent; a film-forming ingredient that is water-washable and hence easily removable by water; a sequestering agent; a corrosion inhibitor; and a surfactant, or wetting agent, having good stability toward the other ingredients of the mixture. The wetting agent should be one that imparts excellent wetting properties to the mixture such that it is readily wetted by the liquid vehicle of the penetrant whether of an oily nature or of an aqueous type, but particularly where the liquid penetrant vehicle is a relatively nonvolatile hydrocarbon, or contains a relatively nonvolatile hydrocarbon in admixture with a relatively volatile diluent. In the case of a relatively nonvolatile, or oily type of colored penetrant that becomes entrapped in the surface discontinuity, my developer acts to draw it out of such discontinuity and thereby develop and enhance the visibility of the color indication by adsorption and absorption and by enlarging the same.

A suitable clay is one that is not water-swelling and is free from Water-soluble salts, that is, one containing 0.2% or less by weight of such salts. The clay consists of extremely finely divided particles, preferably including substantially no particles of greater than about 2 microns in diameter and having an verage particle size of around 0.5 micron. A number of clays that meet this requirement are Buca clay; proprietary clays, such as Catalpo clay, Al-Sil-Ate O, Al-Sil-Ate W, Al-Sil-Ate HO, and Al-Sil-Ate HO 2; Spray Satin clay and HT Predispersed clay.

All of these clays are normally nonswelling; are white, cream or light cream colored, of a brightness of around or higher (General Electric Refiectometer); are substantially free of Water soluble salts; and have a pH value of from 7.0 to 7.5, i.e., around the neutral point. While, as stated above, clays having an evareg particle size of around 0.5 micron are preferred, clays having a maximum range of particle size of between 0.04 and 7 microns have been found suitable. Such clays are easily dispersed in aqueous or organic systems, are extremely low in soluble salts, and have a high degree of purity and brightness. Additionally, all of these clays are substantially free of sulfur and chlorine and are therefore suitable for use in developers that are required to be free of sulfur and chlorine.

In order to impart anticorrosion properties to the developer of my invention, various compounds and compositions adapted for this purpose can be used, including sodium benzoate and sodium nitrite. Sodium benzoate performs a dual function in that it aids in the dispersion of the clay and also in providing a degree of rust inhibition. Primarily, the sodium benzoate acts as an antisludging and an anticaking agent for the clay particles. Accordingly, it is preferable to use an added corrosion inhibitor, particularly for ferrous metals, and for this purpose sodium nitrite is preferably used, in addition to 3 sodium benzoate. However, where no rust-preventative property is required, sodium nitrite may be omitted.

As the sequestering agent, sodium salts of ethylene diamine tetraacetic acid may be used. Such sequestering agents provide excellent dispersing properties that enable the developer powder to be dispersed without the need of high shear mixing equipment. Also, the sequestering agent enables the developer to be used satisfactorily in hard Water. The sodium salts of ethylene diamine tetraacetic acid are noncorrosive and free from sulfur and chlorine.

The film-forming ingredient of my developer that is preferred is a nonvolatile normally solid polyethylene glycol which is soluble in water and which is available as the proprietary product, Carbowax, and particularly Carbowax 4000 is preferred. Car'bowax 4000 has an average molecular weight of 3000 to 3700. However, any of the polyethylene glycols that is a medium-hard or hard, waxy solid, and that has a viscosity, Saybolt, sec. at 210 F. of at least 100, can be used satisfactorily. Such Water-soluble polyethylene glycols impart better coating characteristics to the developer and also improve its Water washability. The proportion of the polyethylene glycol used should be sufficient to impart water removability to the film formed but insufficient to form a nonporous film upon drying of the wet developer, since a porous film is required in order to provide the necessary capillary action for drawing the penetrant out of the surface discontinuities.

As the surfactant, it is preferable to use a sulfur-and chlorine-free, nonionic detergent that is low-foaming and that is substantially soluble in both Water and hydrocarbon oils or solvents. Particularly suitable surfactants, or detergents, are those available as Bio-Soft EA 8 and EA 10, which are water-soluble poly (C C alkoxylated fatty alcohols, and Makon NF-S, a water-soluble polyalkoxylated polyethylene ethanol. These are quite stable for the purposes of my developer and impart excellent wetting characteristics thereto. Other surfactants, such as Triton X-100, believed to be an octyl phenyl polyethoxy ethanol of 9 to 10 ethoxy groups, a nonionic surfactant, can be used satisfactorily. Where chlorine and sulfur free compositions are not required, surfactants such as the alkyl aryl sulfonates and many others can be used.

The following formulae of my developer composition illustrate my preferred compositions and the minimum and maximum variations of the ingredients used in making up the respective formulae:

Percentages by weight From the standpoint of an economic broad operative range where corrosion is not a factor, the proportions of essential ingredients are as follows:

For 100 parts by weight of clay- Parts Carbowax 4000 3-7 Versene powder 0.3-1.0 Surfactant 1.5-5

Where sodium benzoate is used, it can be employed within the range of from 7 to parts per 100 parts by Weight of clay. Larger proportions of these ingredients (other than clay) are, in general, unnecessary for the purposes of my invention and therefore uneconomical.

In the use of developer powders of the above formulations, the preferred operative range when made up as a wet developer is from A to 2 /2 lbs. of the powder to 1 gal. of water, preferably 1 /2 lbs. per gal. of water. A broader operative range is from A to 2 /2 lbs. of the powder to 1 gal. of water. Instead of water, an aqueous 4 alcohol liquid suspending medium can be used, the proportion of alcohol, such as ethanol or propanol, being varied in accordance with the degree of volatility desired.

In making up the dry powder for use as such or as a wet developer composition, the various ingredients, if all are dry, can all be added together and mixed in a ribbon type blender to insure a homogeneous dry powdered blend. If the surfactant, however, is a liquid wetting agent, it must first be thoroughly blended into the clay to provide a premix that will insure homogeneity of the final powder. In that case, the clay-wetting-agent premix can be made by mulling the liquid surfactant into some of the clay until a thorough blend has been obtained as a premix, and this premix is then combined with the remaining dry ingredients and the whole is blended for approximately 1 hour.

When the resulting homogeneous dry composition is to be used as a wet developer, it is suspended in an aqueous type liquid at the proper concentration for use. Preferably, the dry powder is mixed with hot or warm water for at least an hour prior to using, the water being gently agitated while the powder is slowly added thereto. If the wet developer has been standing for any length of time, it must first be stirred and brought into suspension so as to give the appearance of a cream before using any portion of it.

The parts that are to be tested, to which the penetrant has already been applied and from which the excess of penetrant has been removed, are submerged in the wet developer for a sufiicient length of time to Wet all of the surfaces to be inspected. After a short draining period, the surfaces are preferably dried in a hot air circulating drier.

Where an oil-based penetrant is used developing begins as the developer dries out on the surface, whereas if a water-penetrant is employed, development begins as soon as the wet developer is applied. The developing action that occurs after drying is due to the porosity of resulting coating and to its capillary attraction for the liquid penetrant left in any cracks in such surface. If drying is carried out at a temperature from 200 to 225 F., the drying time is quite rapid but will vary with the mass of the parts being tested and their temperature at the time of entering the drier. The parts are removed from the drier as soon as possible after the developer coatings are i completely dry, and are then inspected, either under white light if the dye used in the penetrant is a visible dye, or under black light if the dye used in the penetrant is a fluorescent dye.

The extreme state of subdivision of the clay particles increases the capillary force exerted by the dry developer coating toward the liquid penetrant residues in or about the cracks or other surface discontinuities and thus increases the sensitivity of the indications in the case of extremely fine surface discontinuities.

After inspection, the dried developer coating can be removed by means of a water rinse from a spray nozzle, but if not removed, the dry developer coating, being inert, will not harm the surface of the part undergoing test. The dried coating is substantially colorless, is free from fluorescence and is smooth and continuous, due to the use of a solid polyethylene glycol, such as Carbowax. However, also due to the water solubility of the polyethylene glycol used, the dried coating can be easily removed by water alone.

Where corrosion inhibition is not an essential characteristic of a wet developer of my present invention, it is not necessary to use either the sodium benzoate, or the sodium nitrite, for inhibiting corrosion of the surfaces of parts undergoing test. Neither is it necessary to use a Versene product, or its equivalent, if soft Water is used in making up the wet developer, but in the absence of any sequestering agent, sodium benzoate or other antifiocculent should be used in an aqueous type wet developer to aid in the dispersion of the clay and to break 5 up agglomerates, a function that is in part performed by the Versene product when such product is used.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of my present invention.

I claim:

1. A composition of matter for use as a wet developer in the penetrant method of nondestructive testing for surface discontinuities, consisting essentially of:

a water-wettable but nonwater-swelling, finely divided clay including substantially no particles greater than about 2 microns in diameter,

said clay having a pH from about 7.0 to 7.5 and a brightneses reflectance of at least about 85%,

a water-soluble normally solid polyethylene glycol having a viscosity Saybolt, sec. at 210 F. of at least 100, a relatively water-soluble, low-foaming surfactant selected from the group consisting of nonionic and anionic surfactants which is stable toward the other ingredients of said composition, and said composition being readily dispersible in an aqueous liquid vehicle.

2. A composition as defined by claim 1, wherein sodium benzoate is included as an antisludging and anticaking agent.

3. A wet developer consisting essentially of an aqueous liquid vehicle having dispersed therein from A to 2 /2 pounds per gallon of the composition defined by claim 1.

4. In a penetrant method of detecting surface discontinuities the step of applying to a surface to which a penetrant has been applied and from which the excess thereof has been removed, a wet developer as defined by claim 1.

5. A composition as defined by claim 2 wherein said clay is substantially free from sulfur and chlorine and has an average particle size of around 0.5 micron.

6. A wet developer consisting essentially of an aqueous liquid vehicle having dispersed therein from A1 to 2 /2 pounds per gallon of said mixture defined by claim 2.

References Cited UNITED STATES PATENTS 2,676,487 4/1954 Clarke 252408 XR 2,707,236 4/1955 De Forest 252408 XR 2,848,421 8/1958 De Forest 252408 3,028,338 4/ 1962 Parker 252408 X'R MAYER WEINBLATT, Primary Examiner US. Cl. X.R.