Water-washable inspection penetrant employing triglycerides and polyglycerides of fatty acids

Alburger December 30, 1

Patent Grant 3929664

U.S. patent number 3,929,664 [Application Number 05/513,084] was granted by the patent office on 1975-12-30 for water-washable inspection penetrant employing triglycerides and polyglycerides of fatty acids. Invention is credited to James R. Alburger.


United States Patent 3,929,664
Alburger December 30, 1975

Water-washable inspection penetrant employing triglycerides and polyglycerides of fatty acids

Abstract

A water-washable inspection penetrant composition and process in which a low-solubility fatty oil is used as the penetrant vehicle. The solvent liquids of the invention provide enhanced stability of penetrant entrapments in surface flaws, so as to increase the allowable time interval of wash water contact before an excessive depletion of the entrapment occurs. The flaw detecting capability of the water-washable penetrant is thereby improved.


Inventors: Alburger; James R. (La Canada, CA)
Family ID: 27047295
Appl. No.: 05/513,084
Filed: October 8, 1974

Related U.S. Patent Documents

Application Number Filing Date Patent Number Issue Date
482465 Jun 24, 1974

Current U.S. Class: 252/301.19; 73/104; 250/302; 252/960
Current CPC Class: G01N 21/91 (20130101); Y10S 252/96 (20130101)
Current International Class: G01N 21/91 (20060101); G01N 21/88 (20060101); C09K 011/06 (); G01N 019/08 (); G01N 021/16 ()
Field of Search: ;252/31.2P,408 ;250/302 ;73/104

References Cited [Referenced By]

U.S. Patent Documents
2871697 February 1959 Sockman
3386920 June 1968 Alburger
3716492 February 1973 Graham
Primary Examiner: Mack; John H.
Assistant Examiner: Weisstuch; Aaron

Parent Case Text



This application is a continuation-in-part of my copending application Ser. No. 482,465, filed June 24, 1974 for "Enhanced Stability Water-Washable Penetrant Composition and Process Therefor."
Claims



I claim:

1. In a water-washable inspection penetrant process in which a water-dispersible dyed liquid penetrant is applied to test parts, surface penetrant is removed by washing said test parts with water, and said parts are inspected for residual entrapments of penetrant liquid in surface flaws, the improvement wherein said water-washable penetrant consists essentially of the following formulation, stated in weight percentages:

said low-solubility solvent liquid being at least one member selected from the group consisting of:

Cottonseed oil,

Palm kernel oil,

Peanut oil,

Coconut oil,

Linseed oil,

Olive oil,

Soybean oil,

Castor oil,

Sunflower seed oil,

Rape seed oil,

Safflower oil,

Lard,

Tallow,

Fish oil,

Sardine oil, and

Whale oil,

and said solvent coupler being at least one member selected from the group consisting of:

Methanol,

ethanol,

butanol,

isopropanol,

1-propanol,

2-butanol,

ethylene glycol monobutyl ether,

ethylene glycol monoethyl ether,

ethylene glycol monomethyl ether,

diethylene glycol monomethyl ether,

diethylene glycol monoethyl ether,

diethylene glycol monobutyl ether,

butoxytriglycol,

methoxytriglycol,

ethoxytriglycol, and

1-butoxyethoxy-2-propanol,

said low-solubility solvent liquids being selectively employed singly and in combination.
Description



The invention relates to inspection penetrant materials. More particularly, the invention relates to water-washable inspection penetrant compositions which exhibit enhanced values of indication stability in the presence of wash water.

Heretofore, water-washable inspection penetrants have been comprised essentially of a water-dispersible liquid carrier containing a dissolved indicator dye. The liquid penetrant composition is selected or formulated so as to be readily soluble or self-emulsifiable in water. The indicator dye may be a visible-color dye or a fluorescent dye, but for high sensitivity usage, fluorescent dyes are most generally utilized.

In use, the water-washable penetrant is applied to parts to be tested for the presence of surface flaws. After a suitable dwell time, during which the penetrant enters any surface cracks which are present, the test parts are washed with water to remove surface penetrant, leaving entrapments of the tracer-dyed liquid in the surface cracks. Following the wash-remover step, the test parts are dried and sometimes they are treated with a fine-powder developer which acts to draw out penetrant entrapments to a point where they can be seen. In any event, the parts are inspected for the presence of surface flaw indications, using white light in the case of penetrants containing visible-color dye, or under black light in the case of penetrants containing fluorescent dyes. Entrapments of dyed penetrant which are retained or developed on a coating of powder particles are detected by their visible color or fluorescence, as the case may be. Normally, the step of development is considered to be part of the inspection step in the process.

In the past, it has been the practice to formulate water-washable penetrants in such a way that the compositions exhibit a feature of "good washability", such that the surface penetrant is easily removed when test parts are washed with water. Acceptable penetrant formulations have apparently been chosen for their ability to wash quickly so as to provide a relatively clean test surface with a minimum background of residues of dye penetrant. I have discovered that existing water-washable penetrants suffer from a serious drawback, in that they are characterized by an excessive degree of emulsifiability or solubility, such that in the process of wash-removal of surface penetrant, entrapments of penetrant in small, shallow surface flaws are also removed, or at least are depleted to an excessive degree.

I have endeavored to improve the retention of entrapments in flaws by various means. One method which I have devised involves the formulation of so-called gel-forming penetrants, as exemplified by the teachings of my U.S. Pat. Nos. 3,282,843, 3,349,041, and 3,429,826, and my copending application Ser. No. 127,681, filed Mar. 24, 1971, for "Inspection Penetrant Compositions and Processes Employing Balanced Surfactant/Synergist Detergent Systems."

I have also devised various methods of inhibiting the solubility of certain kinds of penetrants (particularly the gel-forming penetrants), by adjustment of the detergent balance of the composition, by introduction of certain solubility-inhibiting chemicals into the penetrant or into the wash water, or by raising the temperature of the wash water above a critical point of solubility inversion, as exemplified by the teachings of my copending application Ser. No. 163,643, filed July 19, 1971, for "Method and Means for Improving Flaw Entrapment Efficiency in Water-Washable Inspection Penetrants".

I have devised a technique for measuring the rate at which flaw indications are depleted by the action of wash water, and I have found it possible to assign values of "Indication Depletion Time Constants" to various materials such as water-washable penetrants, emulsifiers, and solvent removers. In essence, my method of evaluation involves the measurement by photoelectric means, of the loss of brightness of a standardized pattern of indications during the course of remover application, in the present case, the remover being water. The method yields, for each water-washable penetrant, a time constant which is a measure of the time in seconds of wash water contact required to deplete the effective magnitude of the flaw entrapment to 50% of its initial value. In some cases it may be preferred to state the time constant in terms of the time in seconds of wash water contact required to deplete the brightness of an indication to 50% of its initial value. Measurements of Indication Depletion Time Constants are made using a "standard" cracked panel having a pattern of closely spaced cracks or randomly distributed cracks of known effective magnitude.

I have found that the measured rate of indication depletion depends in part on the magnitude of the cracks in the testing panel. I have made and tested various kinds of testing panels in which I have been able to generate crack defects having effective magnitudes varying from less than a micron up to 20 or 30 microns, and where the depth-width ratio of the cracks may vary from about 3 up to 100 to 1. For many types of penetrant materials, it is practical to determine depletion time constants using a cracked anodic panel of the types described and claimed in my U.S. Pat. Nos. 3,785,936 and 3,791,198, in which the cracks are about 20 microns deep and 6 microns wide.

The significance of the Indication Depletion Time Constant is that in cases where processing conditions require a prolonged contact time of the wash water with the test surface, the Indication Depletion Time Constant must be large, otherwise indications may be lost. By using the methods which I have devised, and which have become standard procedures under Air Force MIL-Specifications and industrial specifications, I have been able to assign Indication Depletion Time Constants to penetrant process materials, and have thus been able to assign ratings of relative indication stability for such materials. It turns out that Indication Depletion Time Constants for typical water-washable penetrants (using a cracked anodic panel for example) fall in the range of from about 3 to 10 seconds, while for certain of the above-mentioned gel-forming penetrants, time constant values may be as high as 40 seconds.

While Indication Depletion Time Constant values in the range of 3 seconds up to about 40 seconds are suitable for most industrial inspection requirements, there are numerous cases where it is necessary to obtain a considerably higher degree of indication stability, as might be provided by water-washable penetrants having Indication Depletion Time Constants in the range of from about 40 seconds up to as much as 6000 seconds. One such inspection application is in the study of inter-crystalline separations in plated surfaces, or ceramics. Another application is in the testing of molybdenum disilicide heat resistant coatings for the presence of irregularities and discontinuities. In any of these applications, and others, which require extremely high flaw detection sensitivity combined with an extremely high degree of indication stability, it is essential that the water-washable penetrant shall resist the leaching of wash water during the time normally taken for the wash step.

The principal object of the invention, therefore, is to provide water-washable inspection penetrant compositions with features of enhanced flaw indication stability in the presence of wash water.

Another object of the invention is to provide a method of adjusting and controlling the Indication Depletion Time Constant value of a water-washable penetrant to a point within the approximate range of from about 40 seconds up to about 6000 seconds.

These and other objects of the invention will be in part be obvious and will in part become apparent from the following description thereof.

I have discovered a family of solvent liquids which satisfy the requirement of high values of Indication Depletion Time Constant, and I find that such solvent liquids may be suitably defined as solvent liquids which are soluble in water or compatible with water to the extent of from slightly less than 0.01% up to about 3%. If a solvent liquid has a water solubility or compatibility much lower than 0.01%, then penetrant formulations using such liquid may exhibit an unduly large depletion time constant, making wash removal of unwanted background indications excessively difficult. On the other hand, if the compatibility with water of the solvent liquid is much greater than 3%, then the depletion time constant becomes small, to the point where there is no advantage gained over materials already available which provide depletion time constants up to about 40 seconds.

It will be understood that the term "compatibility with water" refers to either the solubility of a liquid in water or the solubility of water in the liquid. It appears that the removal of penetrant entrapments from crack defects by washing with water takes place by a mechanism of diffusion of the two liquids, penetrant and water, into each other, and wash-removability of penetrant may take place at an acceptable rate provided that the solubility of water in the penetrant or penetrant in water fall within the above-stated percentage range. The percentage range of water compatibility of from slightly less than 0.01% up to 3% is given merely to indicate the physical-chemical property (with respect to water solubility) of the solvent liquids which are suitable for the purpose of the invention.

The penetrant compositions of the invention are comprised essentially of one or more low-solubility liquids drawn from the group to be described and identified below, the low-solubility liquids being selectively employed, singly and in combination. When so used, these liquids will provide Indication Depletion Time Constants within the range of about 40 to 6000 seconds. Among the various solvent liquids which are suitable as ingredients in the water-washable penetrants of the invention are:

Cottonseed oil,

Palm kernel oil,

Peanut oil,

Coconut oil,

Linseed oil,

Olive oil,

Soybean oil,

Castor oil,

Sunflower seed oil,

Rape seed oil,

Safflower oil,

Lard (grease),

Tallow,

Fish oil,

Sardine oil, and

Whale oil.

All of the foregoing oils, fats and greases fall in the same chemical category, being triglycerides or polyglycerides of fatty acids, such as oleic acid, linoleic acid, linolenic acid, etc. Some of the materials are solid at room temperature, but become liquid at slightly elevated temperatures. They are all considered to be water-insoluble, but I have discovered that they are in fact sufficiently soluble in water, particularly at elevated temperatures, so as to permit wash-removal in the water-washable inspection penetrant process.

I have found that it is possible to extend the polyglyceride oils of the invention with an inexpensive aliphatic mineral oil, for purposes of cost saving, or for purposes of reducing the viscosity of the penetrant composition. Normally, aliphatic mineral oils are not compatible with the polyglyceride oils of the invention, and yield hazy mixtures which separate on standing. However, I have discovered that a small amount of a suitable solvent coupler may act to couple the polyglyceride oil with the mineral oil to form a clear solution. For example, in testing mixtures containing 20 ml. of castor oil and 100 ml. of a light mineral oil (Chevron No. 2 Absorption Oil), I have found that clear mixtures are obtained by the addition of 5 ml. of diethylene glycol monobutyl ether, or 4.5 ml. of dibutyl phthalate, or 3 ml. of isodecanol. In all cases, where the polyglyceride oil of the invention is extended by means of a light mineral oil, I find that the flaw detection capability of the penetrant composition using such an extended vehicle is about the same as is obtained by use of pure polyglyceride oil. This feature of similarity is evident at concentrations of the mineral oil extender in the penetrant vehicle up to 80% or more. I have noticed that the actual value of Indication Depletion Time Constant which is characteristic of a given penetrant composition of the invention may vary as the concentration of indicator dye is varied. Since the flaw detection capability, or "sensitivity", of an inspection penetrant increases as the indicator dye concentration is increased, it follows that for a composition which utilizes a given solvent liquid of the invention, the Indication Depletion Time Constant will change as the sensitivity level (or dye concentration) is changed.

For example, if castor oil is utilized as the carrier liquid, and if different concentrations of fluorescent dye are tested, corresponding to relatively low up to relatively high sensitivity levels, as such levels are known in the art, then Indication Depletion Time Constant values may be obtained ranging from about 200 seconds for the low sensitivity composition up to about 10,000 seconds for the high sensitivity composition. It will be understood that the rate of solution, and the consequent Indication Depletion Time Constant, may be varied and adjusted by adjusting the temperature of the wash water. Depletion Time Constants are reduced as the water temperature is increased, partly because the solubility of the oil increases, and partly because the viscosity of the oil becomes lower and effects of diffusion become more rapid.

I have found that the Indication Depletion Time Constants of the compositions of the invention may be conveniently reduced and adjusted to desired values by the addition of an appropriate amount of a water-soluble solvent coupler. For the purpose of this specification, the designation "solvent coupler" shall be meant to include water-soluble alcohols and glycol-ethers. Among the various solvent couplers which are suitable for use as additives for reducing the Indication Depletion Time Constant are the following:

methanol,

ethanol,

butanol,

isopropanol,

1-propanol,

2-butanol,

ethylene glycol monobutyl ether,

ethylene glycol monomethyl ether,

ethylene glycol monoethyl ether,

diethylene glycol monoethyl ether,

diethylene glycol monomethyl ether,

diethylene glycol monobutyl ether,

butoxytriglycol,

methoxytriglycol,

ethoxytriglycol, and

1-butoxyethoxy-2-propanol.

Any of the above-identified solvent couplers may be included in the compositions of the invention at concentrations ranging from zero up to about 40% relative to the low-solubility solvent liquid of the invention, the proportional amount used depending on the dye sensitivity which pertains, the particular solvent which is used, and the desired Indication Depletion Time Constant.

Visible-color or fluorescent indicator dye concentrations in the compositions of the invention may range from about 0.2% up to about 30%, in accordance with known practices.

Accordingly, a water-washable inspection penetrant composition of the invention may be expressed by the following formulation, stated in weight percentages:

Low-solubility solvent liquid 30% to 99.8% Indicator dye .2% to 30% Solvent Coupler zero to 40%

Although the invention has been described with reference to particular embodiments thereof, it will be understood that various changes and modifications may be made therein without departing from the spirit of the invention nor the scope of the appended claim.

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