US3300642A

US3300642A - Method for changing and restoring the sensitivity characteristic of diluted penetrants

Info

Publication number: US3300642A
Application number: US342717A
Authority: US
Inventors: James R Alburger
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-02-05
Filing date: 1964-02-05
Publication date: 1967-01-24
Anticipated expiration: 1984-01-24

Description

Jan. 24, 1967 J. R. ALBURGER 3,300,642

- METHOD FOR CHANGING AND RESTORING THE SENSITIVITY CHARACTERISTIC OF DILUTED PENETRANTS Filed Feb. 5, 1964 INVENTOR. cflmss4wueaze Xrraemyy United States Patent 3,300,642 METHOD FOR CHANGING AND RESTORING THE SENSITIVITY CHARACTERISTIC 0F DILUTED PENETRANTS James R. Albnrger, 5007 Hillard Ave., La Canada, Calif. 91011 Filed Feb. 5, 1964, Ser. No. 342,717 Claims. (Cl. 25071) This invention relates to the detection of surface flaws in various types of material, particularly metal, and particularly to maintaining dimensional sensitivity in diluted inspection penetrants.

Penetrant inspection processes depend on the formation of entrapments of a penetrant material in surface flaws on parts being inspected. At the completion of the process, exuded flaw entrapments are observed as thin liquid films, being revealed by their color or fluorescence under black light. The ability of a given penetrant to detect small flaws depends on its so-called dimensional sensitivity, this being a function of the concentration of indicator dye in the penetrant.

In my issued patent, No. 3,107,298, there is described the effect of dimensional threshold of sensitivity, and it is shown how the threshold of sensitivity for a given dye solution depends on its concentration. Heretofore, where a certain penetrant sensitivity level has been wanted, it has been necessary to establish an appropriate dye concentration in the penetrant. In conventional penetrant processes, this dye concentration, of course, remains constant and provides a constant sensitivity characteristic for the penetrant.

In some inspection applications where very large tanks of penetrant are employed, it might be a natural desire to extend the penetrant process material by use of an inexpensive diluent. However, such steps have not been given serious consideration in the past for the reason that any dilution of the penetrant would alter the concentration of the dye, and, therefore, alter the dimensional sensitivity of the penetrant. On the other hand, dilution of the penetrant material could result in substantial cost saving.

The principal object of the invention, therefore, is to provide a method of and system for utilizing diluted penetrant inspection materials.

Another object of the invention is to provide an improved method of maintaining a desired dimensional sensitivity in the penetrant processes which utilize diluted penetrants.

A further object of the invention is to reduce the cost of inspection processes using flaw detection penetrants.

A better understanding of this invention may be had from the following detailed description when read in conjunction with the accompanying drawing in which a chart of two typical dilution curves is shown in the figure:

Referring, now, to the figure, the curves A and B show the behavior of dimensional thresholds of two typical penetrants as functions of their indicator dye concentrations. While various dye solutions exhibit differing specific dilution characteristics, all of such characteristics have the same general form in that the dimensional threshold of the dye solution is shifted upward by dilution.

It has been discovered that if a given non-volatile penetrant is diluted with a volatile solvent material, the dimensional sensitivity characteristic of the penetrant may be made to move upward in sensitivity along the dilution curve by a process of evaporation of the volatile diluent. In this way, a penetrant which is formulated to yield a dimensional threshold of 250 millimicrons, for example, may be diluted with a volatile solvent to a point where the dimensional threshold is greater than 2000 millimicrons, a sensitivity characteristic which is quite useless for the detection of surface flaws in parts. However, if the volatile solvent is allowed to evaporate from the mixture, the sensitivity threshold moves along the dilution curve back to the original value of 250 millimicrons.

A wide variety of conventional penetrant materials may be utilized in the method of this invention. Exemplary of such penetrant materials are those which are set forth in US. Patents Nos. 2,764,556; 2,871,697; 2,920,203; 2,953,530; 3,028,338; and in my copending application Ser. No. 492,676, originally filed as Ser, No. 254,487 on January 28, 1963, now abandoned. All of these prior art penetrant compositions, and in fact all presently used penetrant materials, be they water-washable or post-emulsifiable types, consist essentially of a relatively nonvolatile liquid vehicle in which there is dissolved a suitable fluorescent or visible color sensitizer dye. As I have pointed out in my now issued patent No. 3,107,298, the flaw detection capability or sensitivity of a given penetrant depends in part on the concentration of the sensitizer dye. Thus, any alteration in the effective concentration of an indicator dye in a given penetrant composi tion will result in an alteration of the effective flaw detection sensitivity.

As will be noted from the examples to be given below, the method steps of this invention may be carried out using any type or kind of inspection penetrant material and with virtually any relatively volatile solvent liquid which is compatible with the penetrant employed. For example, oil soluble or so-called oil-phase penetrants may be diluted with volatile solvents such as chlorinated hydrocarbons. On the other hand, many other kinds of volatile solvents may be employed in conjunction with appropriate compatible pentrants, one useful and inexpensive solvent being water, which may be used to dilute certain water-extendible penetrants.

It should be noted that certain diluents have been employed at times in prior art penetrants. For example, water has been utilized as a diluent for certain watermiscible glycol-type penetrant compositions. However, such materials have not previously been employed with the combination of method steps including dilution of the penetrant and subsequent exposure of test parts coated with the diluted penetrant so as to produce an evaporation or drying of the volatile diluent and a restoration of the sensitivity characteristic of the penetrant to a predetermined value.

In general, the prior art penetrants which have utilized water as a diluent are employed in a thus-diluted manner for the reason that the presence of water acts to inhibit an unwanted deleterious explosive reaction when the penetrant is used on parts which are to be wetted with liquid oxygen.

The present invention contemplates the use of a relatively volatile diluent which will remain as a relatively stable extender for an inspection penetrant, but which will evaporate to completion, if exposed to draining and drying, during the period of time required for penetration of the inspection penetrant liquid into surface flaws. Such solvents should be distinguished from aerosol propellant liquids which are extremely volatile and which do not remain with the penetrant for an appreciable time while in contact with test surfaces. Following the final step of exposure and drying of coated test surfaces to produce evaporation of volatile diluent material, as hereinafter described, subsequent process steps, such as emulsification, washing, development, and inspection may be carried out in accordance with conventional methods.

Referring, now, to the chart of the figure, curve A is a sensitivity curve of a conventional non-volatile fluorescent, oily penetrant having a dimensional threshold of fluorescence of 100 millimicrons at an equivalent dye concentration of grams per pint which has been diluted with v3 perchloroethylene in the proportion of 40 parts perchloroethylene to one part of penetrant. The initial sensitivity of this penetrant is illustrated at point 6 on the curve A in the figure. The diluted mixture has a dimensional threshold of fluorescence corresponding to point 7 or about 630 millimicrons.

With this penetrant, the parts being inspected are dipped in an open tank containing this diluted penetrant and are suspended over the tank to drain and dry. During a drain-dry period of about ten minutes, the volatile perchloroethylene evaporates from the film of liquid from the parts, whereupon the dimensional sensitivity of the liquid film is restored to its original value of 100 millimicrons. From an economical standpoint, the diluted penetrant might cost approximately $15.00 per gallon, whereas the perchloroethylene might cost about $2.00 per gallon. So with the diluted mixture costing about $2.32 per gallon, a cost saving for the tank of material would be of the order of 84.5%. In addition to the saving in cost of the material installation, an additional saving is effected by virtue of the fact that the perchloroethylene, being a very heavy vapor, pours back into the tank where it remains. Replenishment of the tank is accomplished by the addition of an appropriate amount of undiluted penetrant. v

Referring to curve B, a non-volatile water-miscible visible dye penetrant having a dimensional threshold of color of 500 millimicrons at a dye concentration of 10 grams per pint, is diluted with water in the proportion of 10 parts water to one part penetrant. The initial sensi tivity of the penetrant is illustrated by point 11 on the dilution curve B. The diluted mixture has a dimensional threshold of color corresponding to point 12, being about 1800 millimicrons.

Parts to be inspected are dipped in a tank containing the above-described diluted penetrant. Following a dwell time of 10 minutes, the parts are removed from the tank and allowed to drain and dry. During the drain-dry period of about 15 minutes, the water evaporates from the thin film of penetrant mixture on the parts and the sensitivity of the liquid film is restored to its original value of 500 millimicrons.

In this instance, the undiluted penetrant might cost $6.00 per gallon, while the diluted mixture costs only about $.60 per gallon, a cost saving for the tank mixture of about 90%.

In both of the above examples, a combination of method steps is employed wherein a penetrant of predetermined sensitivity is diluted with a relatively volatile diluent, and then test parts which have been dipped in the diluted penetrant are exposed in a drain-dry step such that the volatile diluent is allowed to evaporate from films of diluted penetrant applied to parts being inspected. An essential requirement for the proper performance of this method step is that the penetrant material, in its undiluted form, must be relatively non-volatile, so that it does not evaporae along with the volatile diluent.

The examples given are representative only, and the method step may be applied to any type of penetrant material so long as the step of evaporation of the volatile solvent does not carry withit a change in the characteristics or chemical balance of ingredients in the undiluted form of the penetrant. Even those penetrants which contain relatively volatile ingredients may be employed with the above-described method step, provided the volatility of the diluent material is substantially greater, and pro-v vided that azeotropic mixtures are not formed which cause a deviation in the sensitivity characteristic. A V

In the event that the undiluted penetrant contains in- V gredients which form azeotropic mixtures with the diluent material, and there are thousands of such combinations known to chemistry, then it is, of course, obvious that the initial undiluted penetrant could be formulated with an appropriate amount of diluent to provide an azeotropic mixture to start with. Then, by building adesired dimensional sensitivity into this azeotropic composition, dilution and subsequent evaporation of'diluent may be carried out as described above, yielding the desired result of restoration of sensitivity.

I claim:

1. In a penetrant inspection process employing a relatively nonvolatile liquid inspection penetrant containing at least one sensitizer dye, a method for changing and restoring the sensitivity characteristic of said inspection penetrant to its original value, comprising the steps of diluting said liquid inspection penetrant with a relatively volatile diluent, coating the surface to be inspected with a film of said diluted penetrant liquid, and drying said film to remove excess volatile diluent from said film.

2. The method steps in an inspection penetrant process in accordance with claim 1 in which said step of diluting said liquid inspection penetrant with a relatively volatile diluent is carried out during the initial formulation of said relatively nonvolatile liquid inspection penetrant.

3. A method in accordance with claim 1 in which said penetrant is a fluorescent oily penetrant and said relatively volatile diluent is chlorinated hydrocarbon.

4. A method in accordance with claim 1 in which said penetrant is a water-miscible visible dye penetrant and said relatively volatile diluent is water.

5. The method steps in an inspection penetrant process in accordance with claim 1 in which said penetrant is a water-miscible fluorescent penetrant and said relatively volatile diluent is water. I

6. The method steps in an inspection penetrant process in accordance with claim 1 in which said penetrant is an oily visible dye penetrant and said relatively volatile diluent is a chlorinated hydrocarbon.

7. The method steps in an inspection penetrant process in accordance with claim 1 in which said penetrant is compatible with water and said relatively volatile diluent is water.

8. The method steps in an inspection penetrant process in accordance with claim 1 in which said penetrant is compatible with chlorinated hydrocarbons and said diluent is a chlorinated hydrocarbon.

9. The method steps in an inspection penetrant process in accordance with claim 1 in which at least one of said sensitizer dyes is a visible color dye.

10. The method steps in an inspection penetrant process in accordance with claim 1 in which at least one of said sensitizer dyes is a fluorescent dye.

References Cited by the Examiner UNITED STATES PATENTS 2,953,530 9/1960 Switzer 250 71 x 3,028,338 4/1962 Parker 25071X 3,083,297 3/1963 Lockwood 250 71 3,215,839 11/1965 Anderson 250-10 RALPH G. NILSON, Primary Examiner. WALTER STOLWEIN, Examiner.

ELBAUM, Assistant Examiner.

Claims

1. IN A PENETRANT INSPECTION PROCESS EMPLOYING A RELATIVELY NONVOLATILE LIQUID INSPECTION PENETRANT CONTAINING AT LEAST ONE SENSITIZER DYE, A METHOD FOR CHANGING AND RESTORING THE SENSITIVITY CHARACTERISTIC OF SAID INSPECTION PENETRANT TO ITS ORIGINAL VALUE, COMPRISING THE STEPS OF DILUTING SAID LIQUID INSPECTION PENETRANT WITH A RELATIVELY VOLATILE DILUENT, COATING THE SURFACE TO BE INSPECTED WITH A FILM OF SAID DILUTED PENETRANT LIQUID, AN DRYING SAID FILM TO REMOVE EXCESS VOLATILE DILUENT FROM SAID FILM.