US3422670A - Cleaning process and compositions for post-emulsifier inspection penetrants - Google Patents

Description

3,422,670 EMULSIFIER Jan. 21, 1969 CLEANING PROCESS AND COMPOSITIONS FOR POST wwkukwtzmo Eamon; 0 I I INVENTOR. I y 62 Z United States Patent 3,422,670 CLEANING PROCESS AND COMPOSITIONS Filed June 16, 1965, Ser. No. 464,360 US. Cl. 73-104 Int. Cl. G01n 19/00 14 Claims ABSTRACT OF THE DISCLOSURE A cleaning method and applicable cleaning compositions for removing surface penetrant in inspection processes in which a low-activity wash liquid is applied to the surface to be cleaned, using agitation, the wash liquid being prepared by diluting an emulsifier-coupler with a suitable solvent-rinse liquid to a point where the solubilizing action of the mixture is at a low value sufficient to provide a minimum degree of stripping of defect entrapments of penetrant. The low activity of the diluted emulsifier-coupler prevents excessive solubilization of the penetrant, yet permits removal of penetrant with the assistance of mechanical agitation.

This invention relates to a process of and materials for cleaning or removing inspection penetrant materials from parts in post-emulsifier penetrant inspection processes. More particularly, the invention relates to a penetrant removal method which is intended to yield a high level of fiaw entrapment efiiciency in the detection of surface discontinuities by the post-emulsifier penetrant inspection method.

In general, the post-emulsifier penetrant inspection process employs a penetrant liquid containing a fluorescent or visible color tracer dye, said liquid being normally insoluble or non-washable in a wash medium as employed in the process. Parts to be inspected for surface discontinuities are immersed in the penetrant, whereupon the dyed penetrant enters any surface discontinuities or flaws which may be present and forms entrapments therein. Excess penetrant is allowed to drain from the parts, or is wiped off or blown off by an air blast. Thereupon, an emulsifier-coupler liquid is applied to the parts, said emulsifier-coupler having the ability to render the normally insoluble penetrant soluble in the wash medium.

Following a suitable emulsifier dwell time, during which the emulsifier-coupler blends with the film of penetrant remaining on the surface of a part being treated, the part is washed in a wash medium, thus flushing off the soluble or emulsified surface mixture and leaving any nonemulsified penetrant entrapments. These penetrant entrapments are then detected, usually by a visual inspection for their fluorescence or color.

The so-called post-emulsifier penetrant inspection process may take a variety of forms in that different kinds of penetrants, emulsifiers, and wash media may be employed. However, all post-emulsifier penetrant inspection processes have one feature in common, that being the use of an emulsifier or emulsifier-coupler which acts to render the normally insoluble penetrant washable in the wash medium.

The most commonly employed post-emulsifier inspection process is the so-called oil-phase P/ E process. In this process, the penetrant liquid is a water insoluble oil, the emulsifier is an oil-water coupler which has the ability to simultaneously dissolve the penetrant oil in itself and form a washable mixture in water, and the wash medium is water.

Another type of post-emulsifier penetrant process is "ice the so-called inverted system, which is described and claimed in my copending application, Ser. No. 452,861, filed May 3, 1965. In this inverted process, the penetrant is an oil-insoluble glycol liquid, the emulsifier-coupler is a glycol-oil coupler such as a glycol-ether or an alcohol, and the wash medium is a mineral thinner.

Regardless of the type of post-emulsifier penetrant inspection process which is employed, a cleaning step is always employed for removing surface penetrant on parts being processed, leaving only penetrant entrapments in surface flaws. This may be accomplished by the so-called solvent remover method, where a strong solvent is employed which flushes the surface clean. This method suffers from the drawback that it tends to strip penetrant out of shallow entrapments. The post-emulsifier method, using a penetrant-wash coupler, is much better and may be made to yield a controlled high level of flaw detec tion performance.

The flaw detection performances of post-emulsifier penetrant inspection systems depend chiefly on the emulsifier strength or activity and the rate at which the emusifier diffuses into flaw entrapments to render washable the penetrant contained therein. Even though post-emulsifier penetrant inspection processes have been developed to a high level of performance efiiciency, there are cases where these processes fail to meet the requirement of high sensitivity in the detection of micro-surface-fiaws. For example, where large parts are being inspected, it may take a relatively long time to apply an emulsifier and then wash off the surface mixture. In such cases, an excessive entrapment stripping action may occur, even with an emulsifier which is designed to a high level of flaw entrapment efficiency. Also, by virtue of the fact that a practical emulsifier formulation must have a reasonable penetrant contamination tolerance, the flaw entrapment efficiency must always be somewhat less than as described hereinafter. Hence, presently available penetrant cleaning or removing processes leave much to be desired in their ability to perform a cleaning function without at the same time causing an unwanted stripping out of the flaw entrapments.

It has been found that it is possible to provide a satisfactory surface cleaning function in a post-emulsifier type of a penetrant process without an unwanted removal of small penetrant entrapments.

The principal object of the invention, therefore, is to provide an improved method for cleaning normally insoluble and non-washable inspection penetrants from surfaces.

Another object of the invention is to provide an improved penetrant cleaning method which yields a high level of flaw entrapment efficiency.

Still another object of the invention is to provide a penetrant cleaning method which is economical to use.

A further object of the invention is to provide a penetrant cleaning process which provides a surface cleaning and scrubbing action without any deformation or damage to the surface being cleaned.

A still further object of the invention is to provide penetrant cleaning and emulsifying materials which yield high levels of flaw entrapment efficiency.

A better understanding of this invention may be had from the following detailed description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation in cross-section of the action of a conventional emulsifier cleaner in removing a surface penetrant in the region of a flaw entrapment;

FIG. 2 is a diagrammatic representation of the action of a cleaner material applied in accordance with this invention; and

FIG. 3 is a chart of emulsifier-cleaner activity plotted in terms of two parameters, penetrant contamination tolerance and viscosity.

In order to properly understand this invention and the embodiment thereof, it is first necessary to understand the mechanism of emulsifier action in removing surface penetrant by the conventional post-emulsifier process. Referring, now, to FIG. 1, a small surface flaw 1 is present in the surface 2 of a part being inspected for the presence of surface flaws. Following the application of a penetrant which contains a tracer dye, the penetrant enters the flaw 1 and forms an entrapment 3. The penetrant also leaves a film 4 of penetrant on the surface 2.

In the normal post-emulsifier procedure, an emulsifier is applied on the surface, either by spray or dipping, leaving a layer 5 of the emulsifier over the entire surface. This emulsifier layer 5 blends with the penetrant layer 4, forming a wash-removable mixture. However, the emulsifier layer 5 also diffuses down into the surface flaw 1 to a certain depth indicated by line 6. The depth of this diffusion by the emulsifier into the flaw entrapment depends on the emulsifier dwell time and its viscosity, and it is found that for presently employed emulsifiers, the diffusion will progress substantially to the bottom of very small surface flaws within a few seconds following application of the emulsifier. Even if the emulsifier does not diffuse completely into the penetrant entrapment, thereby rendering it completely washable, and assuming that it diffuses only part way to a point as indicated by line 6, then there will still be a substantial portion of the diffusion zone which will be rendered wash-removable. This portion is indicated as the emulsifier-penetrant mixture which lies outside of the washability break condition which occurs at line 7. The exact location of line 7 depends on the strength or activity of the emulsifier, and may be determined by measuring the penetrant contamination tolerance of the emulsifier as described in detail in my above-mentioned copending application, Ser. No. 492,676, now U.S. Patent No. 3,311,479, for Penetrant Inspection Process and compositions.

The flaw entrapment efliciency, or the percentile proportion of the entrapment which remains non-washable, is always somewhat less than 100% and is usually on the order of 70% or less for practical emulsifier materials. Up to the present time, there has been no practical way to remove the unwanted surface penetrant from parts without also stripping out a portion of the desired flaw entrapment.

It has been discovered that certain liquid materials which exhibit little or no solubilizing action on a penetrant material may be made to provide an efficient cleaning action on surface penetrant without removing any of the desired entrapped penetrant in surface flaws. Such trant material may be made to provide an efficient cleanwhich have been diluted or extended by the wash medium to a point where their coupling action has been reduced to an apparently negligible value. Furthermore, If such materials are applied to a surface with sufficient surface agitation, an effective cleaning action will take place. A suitable surface agitation may be obtained by a spray application of the cleaning material. Ultrasonic agitation of the surface could be employed, but this is not usually desirable for the reason that the ultrasonic energy does not confine itself entirely to the surface of the part and may tend to drive out some of the entrapment of penetrant from flaws.

Referring, now, to FIG. 2, a spray nozzle 10 delivers a stream of liquid spray 11 toward the surface 12 which contains a flaw 13. On the surface 12, there is a film of normally non-washable penetrant 14, and an entrapment of penerant 15 is in the flaw 13. As the liquid spray 11 strikes the surface film of penerant 14, it acts to scrub the surface clean. Individual droplets of the spray 16 are usually large with respect to the flaw 13, and they do not enter the flaw opening. Thus, the cleaning action of the spray is confined to the surface of the part, and

the desired penetrant entrapment remains substantially intact throughout the surface cleaning operation. Due to the liquid character of the spray-scrubbing mixture, there can be no deformation or damage to the surface being tested.

The essence of this invention lies in the surface scrubbing action which is obtained from a spray or stream of a liquid which has a small but finite solvent action on the surface penetrant. It will be seen at once that if the solvent or coupling action of the liquid spray is made too great, then there will be no particular gain in the flaw entrapment efficiency over the conventional postemulsifier and wash action as described above. On the other hand, if the solvent-coupling or emulsifier-coupling action of the cleaning liquid is made too small, then the cleaning action will progress at an excessively slow rate.

If a spray of plain water is applied on a surface film of an oil-phase post-emulsifiable penetrant, no cleaning action whatsoever will take place. However, the addition of a small amount of an oil-water coupling agent in the spray will permit the scrubbing action to take place, and the surface will be scrubbed clean.

Many materials may be employed as cleaning agents for use with the method of this invention. For example, if an oily water-insoluble penetrant is to be cleaned from a surface by the spray-scrubbing method of this invention, the coupler-cleaner may be a water-diluted soluble oil, or it may be a water-diluted penetrant inspection emulsifier of the type described and claimed in my copending application, Ser. No. 497,058, now U.S. Patent No. 3,349,041, for Gel-forming Inspection Penetrant and Emulsifier Compositions and Processes. Any one of a wide variety of surfactant materials may be employed in diluted and relatively inactive form for the sprayscrubbing cleaning method. Also, any one of a wide variety of liquid solvents such as alcohols, glycol eithers, dimethyl formamide, N-met hyl pyrrolidone, or other materials which have a degree of mutual solubility for both oil and water may be utilized in a more or less diluted form with water such that the coupler action is relatively small.

In the case of glycol-type penetrants, glycol-ethers, various alcohols, and a wide range of surfactant materials, and even soluble oils, may be used in diluted or extended mixtures in a mineral thinner, thereby providing a sprayscrubbing cleaning action on surface penetrants without an excessive removal of penetrant entrapments.

It has been found that any material which has a mutual solubility or compatibility with the penetrant and the wash medium may serve as a spray-scrubbing cleaner. The degree of flaw entrapment efiiciency which may be achieved depends on the penetrant contamination tolerance of the spray-scrubber mixture. In conventional emulsifier materials, a convenient method for measuring the penetrant contamination tolerance is to test the washability of sample smears of penetrant-emulsifier mixtures on a clean anodized aluminum panel, and thereby determine the percentage of added penetrant above which the washability of the mixture is destroyed.

Conventional emulsifier-couplers exhibit penetrant contamination tolerance values which may range from a few percent to 100% or more of added penetrant. In such materials, the percentile flaw entrapment efiiciency may be expressed as 100 T where T is the penetrant contamination tolerance expressed in terms of percent added penetrant. Thus, in an emulsifier-penetrant combination where the emulsifier will tolerate 15% added penetrant up to the washability break, the fiaw entrapment efiiciency is 100 -15 or Even this relatively high efiiciency factor does not necessarily lead to a good retention of flaw entrapments during the surface cleaning operation, for the reason that a prolonged contact of the emulsifier with a flaw entrapment may render the entire entrapment washable so that it is stripped out in the wash operation.

An empirical relationship which has been found for the behaviour of emulsifier-cleaner materials with respect to cleaning activity is illustrated in FIG. 3. Referring, now, to FIG. 3, the two Significant performance parameters of emulsifier-cleaners, namely, penetrant contamination tolerance and viscosity, are plotted on the axes of abcissas and ordinates, respectively. In this chart, the operating point of a given emulsifier-cleaner may be entered according to its parameter values, providing an Activity Quotient value with respect to the diagonal scale of the chart, this Activity Quotient value being the ratio of applicable values for penetrant contamination tolerance and viscosity.

A typical emulsifier-cleaner material which is employed extensively in penetrant inspection processes is the socalled E153 material, which is disclosed in my abovementioned US. Patent No. 3,311,479 which has a penetrant contamination tolerance rating of 25, meaning that it will tolerate 25% of added dioctyl phthalate reference oil up to the point where its washability is destroyed. This emulsifier also has a viscosity at 100 F. of about 50 centistokes. The activity quotient value for this product would be entered in the chart of FIG. 3 at point 20, where it is seen that the activity quotient value is .5.

Another typical emulsifier-cleaner material, similar to the above-mentioned E-153 emulsifier, which is used extensively in industry is the so-called E-157 product which has a penetrant contamination tolerance of 16% and a viscosity at 100 F. of 3.2 centistokes. The activity quotient value for this product would be entered in the chart at point 21, where it is seen that the activity quotient value is 5.0.

Another useful empirical relationship with respect to emulsifier action by normal contact diffusion has been found to be that two emulsifier-cleaners having different activity quotient values may be made to yield similar penetrant removal actions by adjusting their relative dwell times. It has been found that over a useful range of operating conditions, the relative dwell times for equivalent performance differ by a factor equal to the inverse square root ratio of the activity quotient values of the two materials. Line 22 in FIG. 3, and all lines parallel to it, represent locus lines of equivalent performance, such that points on a given locus line are related to one another in such a way that applicable ratios of equivalent performance dwell times are equal to the inverse square root ratios of applicable activity quotient values.

As an example, in comparing the performance behavior of the E153 product with that of the E157 material, a locus line 23 may be drawn on the chart such that point 24 represents a dwell time of two minutes as utilized for the E-153 emulsifier. 'This locus line intersects the activity quotient level of 5.0 for the E-157 material at point 25, which corresponds to a dwell time of .63 minute, or about 38 seconds. Comparison tests of the relative penetrant removal action of these two emulsifier products confirms that they do indeed yield equivalent results with dwell times of two minutes and 38 seconds, respectively.

Now, referring once again to the objects of this invention, it is desirable that the so-called spray-scrubber cleaners of the invention shall have extremely low activity quotient values such that a prolonged dwell time in contact with a penetrant entrapment will produce a negligible degree of solubilization of the entrapment. In practical terms, it is desirable that the spray-scrubber liquid, as employed in this invention, shall have a low level of activity such that a dwell time of about ten minutes in contact with a penetrant film will produce no more, and preferably less, solubilization action than will about one minute dwell time with a conventional contact emulsifier such as the E-153 material. In other words, the equivalent dwell time of a spray-scrubber must be greater than that of a conventional emulsifier by at least one order of magnitude.

It will be seen from an examination of the chart of FIG. 3 that in order to accomplish this result, it is necessary to have a very low activity quotient value for the spray-scrubber liquid. For example, if an equivalent performance locus line 26 is drawn on the chart, intersecting the activity quotient level of .5 for the E-153 product at point 27, corresponding to a dwell time factor of .05, then in order to achieve a condition where a sprayscrubber will yield similar performance characteristics with dwell times which are greater by one order of magnitude or more, an operating point for the spray-scrubber must be somewhere in the region of an activity quotient level of .005 or less, as indicated by the point 28. Hence, the activity quotient value for a practical spray-scrubber should be on the order of .005 or less. A useful range of equivalent values for spray-scrubbers has been found to be from about .00005 to about .05, but under certain special conditions of operation, where suitable adjustment may be made in dwell time or other factors, the sprayscrubbers may have activity quotient values ranging from about .0000005 to about .5.

Even though the activity quotient values of practical spray-scrubbers are quite low, the materials will remove surface penetrant to a very satisfactory degree of cleanliness, while at the same time relatively little stripping action takes place on flaw entrapments.

Inasmuch as oil-phase spray-scrubbers are diluted with water so that the resultant viscosity of the spray mixture is close to unity, and inasmuch as inverted system sprayscru bbers are most conveniently diluted with a mineral thinner such as kerosene so that the resultant viscosity of the spray mixture is in the range of unity or slightly less, it is seen from the chart that a spray-scrubber which is to have an activity quotient value of .005 in its diluted form will have an operating point in the region of point 29, and will exhibit a penetrant contamination tolerance of about .005 This level of penetrant contamination tolerance is too small to measure directly, but it is sutficient to permit a satisfactory cleaning removal of penetrant by the spray-scrubbing method of this invention.

It has been discovered that any emulsifier-coupler material, regardless of its chemical structure, may be diluted with its wash medium, and its penetrant contamination tolerance will drop to a relatively low value. In addition, it has been discovered that even though the penetrant contamination tolerance is reduced by such dilution to a value much smaller than 1%, the mixture will retain an ability to remove surface penetrant by a spray-scrubbing technique.

Example 1.To illustrate the phenomenon of sprayscrubber removal of surface penetrant, one part of a typical oil-phase emulsifier consisting of a 'mixture of sodium petroleum sulfonate, mineral oil and a combination of hydrophylic and lipophylic surfactants is diluted in ten parts water to form a milky emulsion. 'I he undiluted emulsifier has a mutual solubility for water and oily water insoluble penetrants. However, after dilution with water, the emulsified mixture has no discernible penetrant contamination tolerance, that factor being reduced to a value of a small fraction of a percent. Spray application of this mixture to a surface film of an oil-phase penetrant will scnub the surface clean by a slow erosion removal of the penetrant lil m, and will leave penetrant entrapments in flaws to a high level of flaw entrapment efiiciency.

Example 2.One part of an emulsifier-coupler intended for use as a water-washable penetrant-cleaner for parts which are to be wetted with liquid oxygen, said emulsifier being of the type described and claimed in my abovementioned US. Patent No. 3,349,041, is diluted with 20 parts water to form a milky emulsion. The undiluted emulsifier has in this case a mutual solubility for water and oily Water-insoluble penetrants. However, after dilution with water, the apparent solubility for oily penetrants falls to an apparently non-existent value. Even so, the diluted mixture will act as an effective spray-scrubber cleaner on surface fil-ms of oily penetrants without removing any of the desired flaw entrapments of penetrant.

Example 3.Equal parts of ethoxylated nonylpheno-l, having about 9 mols of ethylene oxide per mol of nonylphenol, and diethylene glycol monobutyl ether are mixed together to form a liquid concentrate. One part of this concentrate is diluted with about 50 parts water to form a spray-scrubber solution. Alternatively, the concentrate mixture is fed into a siphon type water-spray gun in such a way that the water dilution ratio is about 50 to 1. The undiluted concentrate exhibits a mutual solubility for water and oily penetrant materials; however, the diluted mixture has apparently no solubilizing action on oily penetrants. Even so, the diluted mixture provides an effective spray-scrubbing cleaner which is low in cost, convenient to use, and yields high levels of flaw entrapment efiiciencies.

Example 4.One part of diethylene glycol monobutyl ether is diluted with about 25 parts of kerosene to form a spray-scrubber mixture for a glycol type (inverted system) penetrant. Prior to dilution, the diethylene glycol monobutyl ether exhibits a mutual solubility for glycol penetrants and for mineral solvent wash media. However, the diluted mixture has no apparent solubility for glycoltype penetrants. Even so, the diluted mixture provides an effective spray-scrubbing cleaner which will remove surface glycol penetrant leaving flaw entrapments of penetrant substantially intact. In this example, the diethylene glycol monobutyl ether may be substituted with any one or a combination of a wide variety of glycol-ethers, alcohols and oil soluble surfactants.

The foregoing examples are representative of the many different penetrant-wash medium couplers which may be employed as spray-scrubber cleaners. All of the wide variety of suitable materials maybe used in the same way, yielding an effective spray-scrubber action, the only requirement being that the spray-scrubber mixture shall be prepared by diluting a. penetrant-wash medium coupler with the wash medium so as to reduce its Activity Quotient value to a satisfactory low level. The invention is, therefore, not limited to the materials or formulations given in the examples.

I claim:

1. In an inspection penetrant process involving the steps of penetrant application to test surfaces, removal of surface penetrant, and inspection for the presence of penetrant entrapments in surface defects, the step of applying an inspection penetrant to a surface to be inspected for surface discontinuities, and the step of applying a wash liquid to said surface, said wash liquid being an emulsifier-coupler diluted with a solvent rinse liquid, said emulsifier-coupler having a mutual solubility for said inspection penetrant and said solvent rinse liquid, and said solvent rinse liquid being nonsolvent for said inspection penetrant, said dilution being suflicient to provide an activity quotient of said wash liquid within the approximate range of .0000005 to .5, and said application of said wash liquid being carried out with vigorous agitation of said wash liquid against said test surfaces.

2. A process in accordance with claim 1 in which said inspection penetrant consists essentially of an oily, waterinsoluble liquid vehicle, said emulsifier-coupler is an oilwater coupler, and said solvent rinse liquid is water.

3. A process in accordance with claim 1 in which said penetrant entrapments in surface defects, the step of applying an inspection penetrant to a surface to be inspected for surface discontinuities, and the step of applying a wash liquid to said surface, said wash liquid being an emulsifiercoupler diluted with 'a solvent rinse liquid, said emulsifiercoupler having a mutual solubility for said inspection penetrant and said solvent rinse liquid, and said solvent rinse liquid being nonsolvent for said inspection penetrant, said dilution being sufiicient to provide an activity quotient 'of said wash liquid within the approximate range of .00005 to .05, and said application of said wash liquid being carried out with vigorous agitation of said wash liquid against said test surfaces.

6. A process in accordance with claim 5 in which said inspection penetrant consists essentially of an oily, waterinsoluble liquid vehicle, said emulsifier-coupler is an oilwater coupler, and said solvent rinse liquid is water.

7. A process in accordance with claim 5 in which said inspection penetrant consists essentially of a glycol liquid vehicle, said said emulsifier-coupler is a glycol-mineral thinner coupler, and said solvent rinse liquid is a mineral thinner.

8. A process in accordance with claim 5 in which said wash liquid is applied by spraying.

9. A spray-scrubbing cleaner composition for removing inspection penetrant in a cleaning step in an inspection penetrant process consisting essentially of an emulsifiercoupler diluted with a solvent rinse liquid, said emulsifiercoupler having a mutual solubility for said inspection penetrant and said solvent rinse liquid, and said solvent rinse liquid being nonsolvent for said inspection penetrant, said spray-scrubbing cleaner composition having an activity quotient value within the approximate range of .0000005 to .5.

10. A spray-scrubbing cleaner composition in accordance with claim 9 consisting essentially of an oil-water coupler diluted with water.

11. A spray-scrubbing cleaner composition in accordance with claim 9 consisting essentially of a glycol-mineral coupler diluted with mineral thinner.

12. A spray-scrubbing cleaner composition for removing inspection penetrant in a cleaning step in an inspection penetrant process consisting essentially of an emulsifiercoupler diluted with a solvent rinse liquid, said emulsifiercoupler having a mutual solubility for said inspection penetrant and said solvent rinse liquid, and said solvent rinse liquid being nonsolvent for said inspection penetrant, said spray-scrubbing cleaner composition having an activity quotient value within the approximate range of .00005 to .05.

13. A spray-scrubbing cleaner composition in accordance with claim 9 consisting essentially of an oil-water coupler diluted with water.

14. A spray-scrubbing cleaner composition in accordance with claim 9 consisting essentially of a glycol-mineral thinner coupler diluted with mineral thinner.

Zyglo and Zyglo-Pentrex: Brochure (73/104) Magnafiux Corporation, copyright 1957 pp. 12 and 13.

JAMES J. GILL, Primary Examiner.

R. S. SALZMAN, Assistant Examiner.

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