US 3735131 A
An Oil-Base Water-Absorbing Fluorescent Dyestuff Carrying Fluid used for testing metal which not only locates surface defects such as cracks but distinguishes between flaw depths and, consequently, flaw relevancy by means of combining different color water-soluble and oil-soluble fluorescent dyestuffs is disclosed in this invention. A process step in the use of this fluid is water washing of the surface to remove fluid which has not become entrapped in a surface discontinuity. During this step, fluid entrapped in shallow defects absorbs a relatively high percentage of water which activates the water-soluble dyestuff while fluid in deep defects remains substantially water free and the water-soluble dyestuff remains substantially inactive. Thus, shallow defects fluoresce the color of the water-soluble dyestuff and deep defects fluoresce the color of the oil-soluble dyestuff.
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Description (OCR text may contain errors)
United States Patent 91 Sherwin 5] May 22, 1973 [5 FLUORESCENT PENETRANT Primary Examiner-James W. Lawrence COMPOSITION AND METHOD Assistant Examiner-Harold A. Dixon  Inventor: Amos G. Sherwin, 8330 Gainford Street, Downey, Calif. 90240  ABSTRACT An Oil-Base Water-Absorbing Fluorescent Dyestuff  Flled' 1972 Carrying Fluid used for testing metal which not only  Appl. No.: 221,403 locates surface defects such as cracks but distinguishes between flaw depths and, consequently, flaw relevancy by means of combining different color water-solu-  U.S. Cl. ..250/71 T, 252/3012 ble and oil soluble fluorescent dyestuffs is disclosed in  I131. Cl. 21/16 this i i A process p the use of this fluid i  Field of Search ..250/71 T; 252/3012 water washing of the Surface to remove fluid which has not become entrapped in a surface discontinuity. References Cited During this step, fluid entrapped in shallow defects absorbs a relatively high percentage of water which ac- UNITED STATES PATENTS tivates the water-soluble dyestuff while fluid in deep 3,108,187 10/1963 Thombury ..250/71 T defects remains substantially water free and the water- 3,543,570 12/1970 Fijalkowski ..250/71 T soluble dyestuff remains substantially inactive. Thus, 3,456,110 7/1969 Diperstein ..250/71 T shallow defects fluoresce the color of the water-solu- 3,558,332 1/1971 j ble dyestuff and deep defects fluoresce the color of 2,635,329 4/1953 Deforest ..250/71 T the oil soluble dyestuffl 3,028,338 4/1962 Parker ..250/71 T 5 Claims, No Drawings FLUORESCENT PENETRANT COMPOSITION AND METHOD This invention is concerned with an improved fluorescent penetrant for finding flaws in metal and other insoluble surfaces. It provides a method of ascertaining the relevancy of a surface discontinuity in relation to the metal or material strength as revealed by the fluoresccnt penetrant process.
The fluorescent penetrant inspection process consists essentially of (1) application to the surface of a test body of a liquid composition in which has been dissolved fluorescent dyestuff, (2) removal of the liquid penetrant composition from the surface of the test body after sufficient time has elapsed for the liquid penetrant to work its way into and fill pores and other discontinuities such as cracks open to the surface in such a manner that the liquid penetrant in the discontinuities remains, and (3) examination of the surface, after drying (and after, in many cases, application of a developing agent), under an ultraviolet or black light in a darkened area for glowing points or lines or areas which mark locations of discontinuities.
Not all discontinuities are of consequence and, in
general, the inspector wants to find discontinuities of beyond a certain depth or flaws in a certain pattern or shape. However, regardless of depth, flaw marks glow in approximately the same magnitude of intensity. It is extremely difficult for the eye to distinguish any difference in intensity. A field of glowing pin points on the surface may or may not be cause for rejection of the part being inspected. If the inspector incorrectly judges them to be of a magnitude which justifies discarding a part, there is a financial loss. On the other hand, if he incorrectly judges them not of consequence and there is a subsequent breakdown of the part in service, the loss may be catastrophic.
My invention assists in distinguishing the relevant from the nonrelevant defect. It includes the use ofa water-free liquid which is nonetheless water-soluble and water-absorbing into which has been introduced watersoluble fluorescent dyestuff which is not in true solution but in a colloidal type suspension or beyond, as well as one or more oil-soluble fluorescent dyestuffs in solution which oil-soluble fluorescent dyestuffs are of a lighter shade than the water-soluble. This liquid is applied to the surface, flushed from the surface with water; the surface is dried and then inspected under black light. When the water from the wash mixes with the liquid, the water-soluble fluorescent dyestuff goes into solution and its color becomes evident. During the wash, there is some water absorption by the penetrant which has remained in the crack. This absorption is at the surface interface and the entrapped penetrant adjacent to the surface which has absorbed water places the water-soluble dyestuff into solution. If
the flaw is shallow and the bulk of the entrapped penetrant, therefore, close to the surface, the color of the water-soluble dyestuff will predominate, screening out or absorbing the emission of the oil-soluble dyestuff. However, if the flaw is deep, the water from the rinse step will not be absorbed into the lower level and the water-soluble dyestuff in the lower level will not be in solution and will not be fluorescing, and the oil-soluble dyestuff since it is in solution throughout all levels of the entrapped penetrant liquid will dominate.
A formula I have used with success to distinguish between hot tears and nonrelevant pores in turbine blades is 30 parts by volume of an ethoxylated linear alcohol having 7 moles of ethylene oxide, 20 parts by volume of Diethylene Glycol Monobutyl Ether, and 50 parts of an aliphatic petroleum solvent into which has been dispersed 2 percent by weight of Rhodamine B Extra Base, and into which has been dissolved V2 of 1 percent by weight of Fluorescent Brightening Agent and 1 /2 percent by weight of Fluorescent Brightening Agent 68.
What is claimed is:
1. A nonaqueous water-miscible penetrating liquid which includes an oil base and a water-soluble dye, which fluoresces under black light when in solution, dispersed therein and one or more oil-soluble dyes, which fluoresce under black light" when in solution, in solution therein, which oil-soluble dye(s) fluoresce either singly or in combination in a lighter shade than the water-soluble dye, which liquid will absorb water.
2. A water-free water-soluble penetrating liquid containing an oil base and a water-soluble fluorescent dye dispersed therein and an oil-soluble dye dissolved therein with the water-soluble dye having an absorptive spectra for the oil-soluble dye.
3. A liquid as in claim 2 but with more than one oilsoluble fluorescent dye.
4. A nonaqueous liquid containing 10 to 50 parts by volume of an ethoxylated linear alcohol having 6 to 10 moles of ethylene oxide in which a water-soluble dye has been dispersed therein and an oil-soluble dye dissolved therein with the water-soluble dye having an absorptive spectra for the oil-soluble dye.
5. A method in which a water-free water-miscible penetrating liquid with a water-soluble fluorescent dye suspended therein and one or more oil-soluble fluorescent dyes dissolved therein with the water-soluble fluobeen retained.