JPH035542B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a penetrant liquid for penetrant flaw detection and a penetrant flaw detection method using the penetrant liquid.

The present invention indicates the width, length, and shape of an opening defect existing on the surface of an object to be inspected using a defect indicating pattern that exhibits a clear red color under white light (visible light). Here, we have developed a penetrant liquid for penetrant testing that can indicate the depth of an open defect on the surface of an object to be inspected based on the brightness of the red to yellow fluorescent color exhibited by the defect indicating pattern. For the purpose of providing.

In addition, the present invention can detect the width, length, and shape of an opening defect existing on the surface of an object to be inspected and determine the depth of the opening defect by just applying one type of penetrating liquid once. The purpose of the present invention is to provide a penetrant testing method that can perform two types of inspections: detection and detection.

Furthermore, the main object of the present invention is to be able to accurately determine the relationship between the size (opening area) and the depth of the opening defect existing on the surface of the object to be inspected, and as a result, even if the opening area is large, It is an object of the present invention to provide a penetrating flaw detection method that can reliably screen out defects with shallow depths, defects with deep depths even if the opening area is minute, and the like.

The penetrant flaw detection method is a well-known flaw detection method that is generally well known as a typical non-destructive testing method. This flaw detection method is widely used to detect minute surface opening defects on the surfaces of cast products, machine parts, etc., and on the surfaces of welded parts of structures, etc. The typical operating modes are as follows.

In other words, in penetrant testing, first a penetrant liquid containing a solvent in which a visible dye (usually red) or a fluorescent dye (usually yellow to yellow-green under an ultraviolet lamp) is dissolved is applied to the surface of the object to be inspected. This operation is called a "penetration operation." −. Next, excess penetrating liquid that has not penetrated into the opening defect and remains on the surface of the object to be inspected is removed using water or a solvent - this operation is called a "cleaning operation".
It is called. −. At the end of this cleaning operation, the penetrating liquid remains only within the defect.
However, it is difficult to detect the presence of the penetrating liquid in this state, so next we apply a solution of white fine inorganic powder dispersed in water (called a "wet developer") or white A fine inorganic powder dispersed in a volatile solvent (called a "quick-drying developer") is applied, water or solvent is blown away,
A uniform layer of white fine inorganic powder is formed, and the penetrating liquid that has penetrated into the defect is sucked out by capillary action between the powder particles forming the layer, creating a blot pattern on the surface of the layer due to the penetrating liquid. By exposing the aperture defect, the aperture defect is enlarged and detected easily - this operation is called a "developing operation". −. The bled pattern, or defect indicator pattern, is then observed under white light in the case of visible dyes or under an ultraviolet lamp (called a "black light") in the case of fluorescent dyes. The presence or absence of an opening defect, the location of the opening defect,
Detecting the width, length, and shape of the opening defect - this operation is called an "inspection operation." - This is a flaw detection method that is performed by a series of operations.

Next, a well-known penetrant liquid used in the above penetrant testing method will be explained. Basically, a penetrating liquid consisting of a water-soluble visible dye or fluorescent dye and water in which it is dissolved, or an oil-soluble visible dye or fluorescent dye and an organic solvent in which it is dissolved. A penetrating solution consisting of a visible dye or a fluorescent dye that is an oil-soluble dye is dissolved in water or a water-alcoholic solvent using a surfactant.
There are several types. Usually, a surfactant for improving wettability and a rust preventive agent for preventing rust from forming on the test object are added.
There are two types of cleaning methods: those that are removed using a solvent (e.g. alcohol, acetone, gasoline, etc.) and those that are removed using water. It is blended. Rust inhibitors are also usually added. , is removed using water in the "washing operation". In addition, examples are known in which non-volatile aromatic hydrocarbons are added to those that are removed using water in order to improve washability.

Now, the penetrant flaw detection method is carried out using the various penetrating liquids mentioned above according to the operation mode described above, but conventionally, in general, the inspection operation is performed using white light using a penetrant containing a visible dye. The method in which the inspection is carried out under an ultraviolet lamp is called the "dye penetrant test method," and the method in which the test is performed under an ultraviolet lamp using a penetrant containing a fluorescent dye is called the "fluorescent penetrant test method." The former is used in cases where high precision is required (in cases where it is not necessary to detect even the smallest defects), and when simplicity is required without much accuracy (in cases where there is no need to detect even the smallest defects), the former The latter is applied in cases where it is necessary to do so.

However, the common drawback of "dye penetrant testing" and "fluorescent penetrant testing" is that although the width, length, and shape of the opening defect present on the surface of the object to be inspected can be detected almost accurately, The problem is that it is difficult to detect the depth of the defective part.
However, in both penetrant flaw detection methods, it is well known that the bleeding area of the defect indication pattern (bleeding pattern) increases approximately in proportion to the depth of the open defect, and this phenomenon can be used to detect the open defect. An attempt to determine the depth has also been proposed, in which two streak patterns of approximately the same width and length appear on the developer layer immediately after the "developing operation" (1 to 5 minutes after developer is applied). If the size of one rainbow pattern becomes larger than the other after a certain period of time, it is determined that the defect with the larger rainbow pattern is deeper than the other defect. This is a method to do so. However, although this method is theoretically possible, it has not been put into practical use. The reason is that the two rainbow patterns expand, one of the rainbow patterns stops expanding, and only the other rainbow pattern continues to expand, creating a clear size difference between them. It takes a very long time (usually 10
(~12 hours or more) As such dots and defect-indicating patterns expand due to bled, the color density of the bled pattern will naturally become lighter in "dye penetrant testing" and "fluorescent penetrant testing" The flaw detection method has two drawbacks: the luminance of the rainbow pattern's fluorescence decreases, making the instructions unclear.

On the other hand, when both penetrant testing methods are implemented, various benefits can be expected if the width, length, and shape of the opening defect as well as the depth of the defect can be accurately detected. For example, in our industry, as a result of penetrant testing on target products,
Even when an opening defect is detected, there are often cases where repairs are carried out by scraping off the defect without discarding the product.
In such cases, it is necessary to determine whether the opening defect detected by penetrant testing is a benign defect deep enough to be repaired by scraping, or a malignant defect so deep that it cannot be repaired. It becomes possible.

In view of the current situation as described above, the present inventor has discovered that it is possible to know the relationship between the width, length, and depth of an open defect existing on the surface of an object to be inspected by simply applying one type of penetrating liquid once. We have continued to study in search of a penetrating flaw detection method that can be used.

The present inventor has discovered that in a liquid in which a dye that exhibits a clear visible color under white light and exhibits fluorescence under an ultraviolet light is dissolved in a certain concentration or more, as the amount of the dye increases, the dye exhibits a clear visible color under white light. The visible color of the phosphor becomes darker, but the luminance of the fluorescent light under an ultraviolet lamp peaks at a certain amount and then decreases as the amount increases - this phenomenon is called the "concentration quenching phenomenon". It is called. As a result of systematic research and repeated experiments, the present invention was completed.

That is, the present invention provides a penetrant liquid for penetrant testing that contains a dye and a solvent in which the dye is dissolved as essential components, and which uses a dye that exhibits a red color under white light and a red to yellow fluorescence under an ultraviolet lamp. (hereinafter simply referred to as "red fluorescent dye"), a penetrant liquid for penetrant testing in which the dye is dissolved in a liquid with a concentration higher than that which causes the concentration quenching phenomenon, and a penetrant liquid using this penetrant liquid. This is a flaw detection method.

The configuration and effects of the present invention will be explained below.

First, the "concentration quenching phenomenon" will be explained in detail. This phenomenon is a known optical phenomenon,
Although it has been discussed theoretically from various angles, a concrete explanation using an experimental example is as follows.

Experimental example Oil Scarlet #308 as red fluorescent dye - Product name: Orient Chemical Co., Ltd.: CIName
Using Solvent Red 18-, add this to a solvent consisting of 30 parts of isopropyl alcohol (meaning parts by weight. The same applies hereinafter) and 70 parts of ethyl carbitol.
A solution in which 1 part was dissolved is designated as Solution A, a solution in which 5 parts were similarly dissolved is designated as Solution B, and a solution in which 10 parts was similarly dissolved is designated as Solution C.

White fine inorganic powder - Powder used in commercially available quick-drying developers (DN-600S: Product name: Special paint
Co., Ltd.: Aerosol type: Particle size used in
A measurement sample was prepared in which the above solutions A to C were present (adsorbed) in various amounts in a mixed powder of basic magnesium carbonate powder and anhydrous silicic acid powder in the range of 0.05 to 0.5μ. The fluorescence brightness of each sample under ultraviolet light was measured using a Yagi type fluorophotometer (the filter used was _O2 : yellow), and the red density of each sample under white light was measured using a colorimeter: The amount of absorbed light was measured using an electronic photovolt photometer manufactured by Tokyo Denshoku Kogyo Co., Ltd. (red filter was used). Further, the saturated adsorption amount of each liquid to the above powder was about 1 ml/g.

Note that the saturated adsorption amount is a concept similar to "oil absorption amount," and in the present invention, when the penetrant is gradually added to a certain amount of developer powder (dry), the amount of the penetrant is adsorbed. There is no mixture of adsorbed powder particles and non-adsorbed powder particles, and there is no penetrating liquid that cannot be absorbed by all powder particles, and all powder particles are uniformly and sufficiently absorbed. The state in which the permeate is adsorbed is called "saturated adsorption," and the amount of permeate used at this time is called the "saturated adsorption amount." It is expressed as the amount of permeated liquid in ml per 1 g of powder.

Figure 1 shows the results regarding fluorescence brightness;
The figure shows the above experimental results for red density.

In Figure 1, the horizontal axis shows the amount of adsorption of each liquid on the powder (ml/g), and the vertical axis shows the fluorescence brightness (%, however,
The peak value shown at C in the figure is expressed as 100%. ) to show the relationship between dye concentration, adsorption amount (abundance), and fluorescence brightness.

As shown in Figure 1, in the case of liquid A (one part of dye dissolved), the fluorescence brightness increases as the amount of adsorption increases, and in the case of saturated adsorption, liquid B,
The fluorescence brightness is much higher than that in the case of the saturated adsorption amount of liquid C.

In the case of Solution B (5 parts of dye dissolved), the fluorescence brightness is highest when the adsorption amount is relatively small, and when the adsorption amount increases beyond this amount, the fluorescence brightness decreases slightly, and after that, the fluorescence brightness is the highest. Even when the amount of adsorption increases, the fluorescence brightness shows a flat state, and even when the amount of adsorption is saturated, there is almost no change, and there is little change in the fluorescence brightness overall.

In the case of liquid C (dissolving 10 parts of dye), the fluorescence brightness is highest when the amount of adsorption is very small, and when the adsorption amount increases beyond this amount, the fluorescence brightness decreases rapidly, and then the adsorption decreases. As the amount increases, the fluorescence brightness gradually decreases, and in the case of a saturated adsorption amount, the fluorescence brightness decreases to about 1/4 of the maximum fluorescence brightness.

In Figure 2, the horizontal axis shows the amount of adsorption of each liquid on the powder (ml/g), and the vertical axis shows the amount of absorbed light (%, however,
The peak value shown at C in the figure is expressed as 100%. ) to show the relationship between dye concentration, adsorption amount, and amount of absorbed light (red density).

As shown in FIG. 2, in the case of liquid A (one part of the dye dissolved), as the amount of adsorption increases, the amount of absorbed light increases linearly up to the saturated amount of adsorption. The amount of absorbed light in the case of saturated adsorption amount is approximately 50%.

In the case of liquid B (5 parts of dye dissolved), as the amount of adsorption increases, the amount of absorbed light also increases linearly up to the saturated amount of adsorption. The amount of absorbed light at saturated adsorption amount is approximately 75
%.

In the case of liquid C (dissolving 10 parts of dye), the amount of absorbed light increases linearly as the amount of adsorption increases, but approximately
When it exceeds 80%, the amount of absorbed light increases slowly. The amount of absorbed light in the case of saturated adsorption amount is 100%.

As seen in the above experimental results, when the dye concentration in the liquid becomes higher (1 part, 5 parts, 10 parts), the red color density of the liquid itself under white light also becomes higher. (Refer to the amount of absorbed light for the saturated adsorption amount of each solution.) At the same time, at any dye concentration, as the adsorption amount increases, the red density increases linearly and becomes darker. . However, regarding the fluorescent brightness under an ultraviolet lamp, when the dye concentration in the liquid increases to 1 part, 5 parts, and 10 parts,
On the contrary, the fluorescent brightness of the liquid itself is decreasing (see the fluorescent brightness of the saturated adsorption amount of each liquid), and furthermore, the change in fluorescent brightness as the adsorbed amount increases is due to the dye concentration of the liquid. They are completely different depending on the situation. That is, in the case of 1 part, the change in red density is almost the same as under white light, but in the case of 5 parts, even though the amount of adsorption increases, the change in fluorescence brightness is almost the same throughout the entire process. In the case of 10 parts, the fluorescence intensity peaks at a very small amount of adsorption, and then decreases as the amount of adsorption increases. This phenomenon in the case of 10 parts is the concentration quenching phenomenon referred to in the present invention.

That is, the red fluorescent dye Oil Scarlet #308 is a dye that causes a concentration quenching phenomenon in a liquid in which it is dissolved in a concentration above a certain level (10 parts in the above experimental example).

The present inventor also conducted tests on currently commercially available red fluorescent dyes, and found that the red fluorescent dyes, in other words, exhibit red color under white light and red to yellow under ultraviolet light. It was confirmed that all dyes that exhibit fluorescence cause the concentration quenching phenomenon, and surprisingly, the numerical values of the dye concentration and adsorption amount were almost the same as those in the above experimental example. I confirmed that it was.

Note that dyes that cause concentration quenching are not limited to red fluorescent dyes, but include dyes that exhibit yellow under white light and yellow to yellow-green fluorescence under ultraviolet light, and dyes that exhibit yellow-green fluorescence under white light. The concentration quenching phenomenon also occurs in the case of dyes that exhibit blue color under ultraviolet light and blue to blue-green fluorescence under ultraviolet light, but in the present invention, from the viewpoint of contrast during detection, etc., the dye that emits red fluorescence Specific to dyes.

The following are various dyes that the present inventor has confirmed through tests to have the same effect as the above-mentioned Oil Scarlet #308.

Water-soluble dyes Rhodamine G: CIName Basic 8 Rhodamine 6G: CIName Basic 1 Rhodamine B: CIName Basic Violet 10 Sulforhodamine BG: Manufactured by Hoechst Fluorescein: CIName Acid Yellow
73 Fuchsin: CIName Basic Violet
14 Eosin Y: CIName Assured 87 Food Red No. 105: Rose Bengal: CIName Assured 94 Watered E: Futaba Kagaku Kenkyusho Co., Ltd. Water Pink 2: Orient Chemical Co., Ltd. Watered 2: 〃 Watered 9: 〃 Alcohol-soluble dye Edible Red No. 201: Dibromo phreoresenii:
CIName Pigment Orange 51 Food Red No. 206: Iodine/Fluorescein: C.
I.Name Assit Red 95 Food Red No. 215: Rhodamine B Stearate: CIName Solvent Red 49 Food Red No. 223: Tetrachloro Tetrabromo Fluorescein: CIName Assit Red 64 Opuras Thread #330: CIName Dispered 9 Daito Acrylic Brill Pink R: Daito Kagaku Co., Ltd.
Manufactured by Solvent Red FR: Manufactured by Futaba Kagaku Kenkyusho Co., Ltd. Rhodamine Base FB: CIName Solvent Red 49 Oil-soluble dye Oil Pink #312: Manufactured by Orient Chemical Co., Ltd. Oil Pink OP: Manufactured by Orient Chemical Co., Ltd. This invention utilizes the concentration quenching phenomenon described above.

That is, the penetrant liquid for penetrant flaw detection according to the present invention is a liquid that causes a concentration quenching phenomenon.In other words, it is a liquid that causes a concentration quenching phenomenon. is a penetrant liquid for penetrant flaw detection, which is made of a liquid in which the dye is dissolved at a concentration higher than that which causes the concentration quenching phenomenon.

Therefore, the penetrating liquid according to the present invention is formulationally similar to the conventional penetrating liquids of types 2 to 3 described above, except for the dissolved concentration of the various red fluorescent dyes used, and contains surfactants, surfactants, It is exactly the same as in the conventional case that rust inhibitors, nonvolatile aromatic hydrocarbons, etc. may be added.

However, in the penetrating liquid according to the present invention, it is difficult to determine whether the penetrating liquid causes a concentration quenching phenomenon or not, in other words, whether or not the red fluorescent dye is dissolved in the penetrating liquid at a concentration higher than that which causes a concentration quenching phenomenon. This clearly distinguishes it from conventional penetrating fluids.

That is, none of the conventionally known penetrant liquids causes the concentration quenching phenomenon, and of course, there is no penetrating liquid in which the red fluorescent dye is dissolved at a concentration higher than that at which the concentration quenching phenomenon occurs.

Incidentally, the dye used in the conventional dye penetrant liquid used in the above-mentioned "dye penetrant flaw detection method" is a non-fluorescent dye that exhibits a bright red color under white light but does not exhibit fluorescence under ultraviolet light. Light red dyes (e.g. CIName Solvent Red 19, 23, 24, 27, etc.)
is selected, and approximately 1 to 3 parts are dissolved in 100 parts of the penetrant. This penetrating liquid shows a pattern that is almost the same as the change in line C in FIG. Furthermore, the dye used in the conventional penetrant liquid used in the above-mentioned "fluorescent penetrant testing" exhibits a white or yellow color under white light, and a clear yellow to yellow-green color under an ultraviolet lamp. Fluorescent dyes that emit fluorescence (e.g.
CIName Fluorescent Brightening Agent 63, 68, 75, etc.) are selected, and in the case of general-use penetrants, about 0.1 to 1 part is dissolved in 100 parts of penetrant, and in the case of high-sensitivity penetrants, Penetrant 100
About 1 to 3 parts are dissolved in each part. The former permeate shows a pattern that is almost the same as the change in line A in FIG. 1, and the latter shows a pattern that is almost the same as the change in line B in FIG.

However, this does not mean that there are no examples of penetrating liquids using red fluorescent dyes, and as far as the present inventors are aware, the following several examples have been proposed recently.

In other words, “Rocol” released by the British company Rocol
Flow Finder Penetrant” and “Spotcheck” released by the American Magnaflux company.
Penetrant Type SKL-4-B" is a penetrant liquid, and these penetrant liquids are said to be applicable to both "dye penetrant testing" and "fluorescence penetrant testing". It exhibits red fluorescence under white light and red-yellow fluorescence under ultraviolet light. However, of course, it does not cause the concentration quenching phenomenon, and under an ultraviolet lamp it exhibits approximately uniform fluorescent brightness regardless of its amount. In fact, when we conducted an experiment similar to the above example using these penetrants, we found that the pattern was almost the same as the change in line B in Figure 1 and the change in line C in Figure 2. It has been confirmed that there are dyes, and these penetrants are formulated to avoid changes in fluorescent brightness due to changes in the amount present (amount adsorbed to the developer layer) under ultraviolet lamps as much as possible. The concentration is estimated to be about 3 to 5 parts dissolved in 100 parts of the penetrant.

Next, the penetrant testing characteristics of the penetrant liquid according to the present invention will be explained.

As mentioned above, during the "developing operation", a layer of white fine inorganic powder with a substantially uniform thickness is formed on the surface of the object to be inspected, and defects are removed by capillary action between the powder particles forming the layer. The penetrating liquid that has permeated the inside of the layer is sucked out and a bleed pattern (defect indicating pattern) is formed by the penetrating liquid on the surface of the layer, and defects are detected by observing this defect indicating pattern during the "inspection operation". However, in this case, the relationship between the adsorption amount of the penetrating liquid to the powder forming the layer and the defect indication is
The various conventional penetrants and the penetrant according to the present invention are as follows.

(1) The conventional penetrating solution using the above-mentioned non-fluorescent red dye shows the same pattern as the change in line C in Figure 2, so the penetration of the penetrating solution into the powder under white light is The larger the amount of adsorption, the darker and clearer the defect indication will be obtained, and the smaller the amount of adsorption of the penetrant to the powder, the weaker and less clear the defect indication will be. Therefore, for defects with a small opening area and depth, the amount of penetrating liquid in the defect is small, so the defect indication becomes faint and may be overlooked and cannot be detected, and even if the defect is deep, the opening area is small. For defects with a very small size, the penetrating liquid in the defect is not sufficiently sucked out to the surface of the layer, so the defect indication becomes faint and may be overlooked and cannot be detected.

(2) Conventional general-use penetrants using the above-mentioned fluorescent dyes show the same pattern as the change in line A in Figure 1, so under an ultraviolet lamp, the penetrants are adsorbed to the powder. The larger the amount, the brighter and clearer the defect indication will be obtained, and the smaller the amount of penetrating liquid adsorbed to the powder, the defect indication will be dark and unclear.
Therefore, even in this case, defects with very small opening areas may not be detected even if the opening area and depth are both small or deep, but since fluorescence is used, it is possible to detect defects near the surface of the layer. Since the fluorescence can be recognized from the penetrating liquid that has been sucked out up to the point but has not yet reached the surface of the layer, it is possible to detect even smaller defects compared to (1).

(3) The conventional high-sensitivity penetrant using the above-mentioned fluorescent dye shows the same pattern as the change in line B in Figure 1, so it is possible that the penetrant is adsorbed to the powder under an ultraviolet lamp. Regardless of the amount, the defect indication exhibits a nearly constant brightness. Therefore, in this case, even if the opening area and depth are both small or deep, even if the opening area is very small, the defect indication is similar to that of a defect with a large opening area and depth. It is possible to detect defect indicators that exhibit the same brightness.

(4) The conventional special penetrating solution is made by dissolving about 5 parts of the above red fluorescent dye in 100 parts of the penetrating solution.
Under white light, it shows the same pattern as the change in line C in Figure 2. Naturally, under white light, it shows the same pattern as (1), and under ultraviolet light, it shows the same pattern as line C in Figure 1.
It shows the same pattern as the line change, and is naturally the same as (3) under ultraviolet light.

(5) On the other hand, since the penetrating liquid according to the present invention shows the change as shown in line C in Figure 2 under white light,
Under white light, it is the same as (1), but under ultraviolet light, it shows the change of line C in Figure 1, so it is completely different from (2) to (4), and it is a concentration quenching phenomenon. As a result, the larger the amount of penetrating liquid adsorbed to the powder, the darker the defect indication will be obtained, and the smaller the amount of penetrating liquid adsorbed to the powder, the brighter and brighter the defect indication will be. Therefore, under an ultraviolet lamp, defects with small opening area and depth have a small amount of penetrating liquid in the defect, so the defect indication is bright and clear and can be detected without being overlooked, and even deep defects can be detected. Even if there is a defect with a very small opening area, at the time when the penetrating liquid in the defect has not been sufficiently sucked out to the surface of the layer, the amount of penetrating liquid adsorbed to the powder is small, so the defect indication will be bright and clear. When the defect can be detected without being overlooked, and the penetrating liquid in the defect has been sufficiently sucked out to the surface of the layer, the defect indication becomes dark because the amount of penetrating liquid adsorbed to the powder increases. Note that a change from bright to dark or dark to bright in the defect indicating pattern under an ultraviolet lamp can be clearly detected because it is a change in fluorescent luminance.

That is, under white light, the penetrating solution according to the present invention exhibits a higher adsorption rate under white light, just as in the case of the penetrating solution using a conventional non-fluorescent red dye. Then, the larger the amount of penetrant in the defect,
In other words, the larger the defect capacity (opening area x depth), the darker and clearer the defect indication becomes, and conversely, the smaller the defect capacity, the fainter and more indistinct the defect indication becomes.
Under an ultraviolet lamp, unlike the case of penetrants using conventional fluorescent dyes or red fluorescent dyes, the smaller the amount of penetrant adsorbed to the powder, in other words, the smaller the amount of penetrant in the defect. The smaller the quantity, or in other words, the smaller the capacity of the defect, the brighter and clearer the defect indication becomes, and conversely, the larger the capacity of the defect, the darker the defect indication becomes. Using this characteristic, it is possible to detect the width, length, and opening shape of the defect under white light, and to detect the capacity of the defect, or in other words, the depth, under ultraviolet light. This is possible. Moreover, as will be described later, by overlapping and analyzing the inspection results under white light and the inspection results under ultraviolet light, it is possible to know even the nature of the defective portion.

Next, the formulation of the penetrating liquid according to the present invention will be explained in more detail.

The formulation of the penetrating liquid according to the present invention basically consists of a red fluorescent dye and a solvent in which it is dissolved, and the red fluorescent dye must be dissolved in the penetrating liquid at a concentration higher than that which causes the concentration quenching phenomenon. Must be.

As the red fluorescent dye, any dye that exhibits red color under white light and red to yellow fluorescence under ultraviolet light can be used. More specifically, there are the various commercially available red fluorescent dyes listed above. One or more types may be selected from those listed above.

It goes without saying that the solvent for dissolving the red fluorescent dye must be a liquid that has sufficient ability to dissolve the dye used, but since it is the main ingredient of the penetrating liquid, there are other factors besides dissolving ability. The following items should be selected as criteria.

Low surface tension. (preferably 32dyne/cm
Below) Low viscosity. (Preferably 10 centiStokes/25°C or less) Low volatility.

Furthermore, it is desirable to select one that is low toxicity, nonflammable, and inexpensive.

Specifically, water, alcohols such as ethyl alcohol or isopropyl alcohol, esters such as ethyl acetate and butyl acetate, cellosolves such as ethyl cellosolve and butyl cellosolve, carbitols such as ethyl carbitol and butyl carbitol, and dioctyl. Depending on the type of dye, one or more types may be selected from polymer esters such as phthalate, tricresyl phosphate, dibutyl sebacate, and diethyl phthalate.

The concentration at which the penetrating liquid in which the red fluorescent dye is dissolved causes the concentration quenching phenomenon varies depending on the type of dye used, but if more than 10 parts per 100 parts of the penetrating liquid are dissolved, Regardless of the type of red fluorescent dye, the concentration quenching phenomenon as shown in the above experimental example occurs significantly. Furthermore, it is not advisable to use too large a quantity of dye, as it increases the viscosity of the liquid and increases costs, so in practical terms, the amount should be limited to about 30 parts.

By appropriately combining the above-mentioned red fluorescent dye and solvent, and adding surfactants, rust preventives, non-volatile aromatic hydrocarbons, etc. as necessary, the above-mentioned conventional penetrating liquid of the type ~ can be obtained. . For example, rhodamine
Combine FB and water, add surfactant if necessary,
If you add a rust preventive agent, it becomes a type of penetrating liquid.
For example, a type of penetrating liquid can be obtained by combining Oil Scarlet #308 with isopropyl alcohol and ethyl carbitol, and adding a non-volatile aromatic hydrocarbon if necessary.

In addition, it is preferable to use a nonionic or anionic surfactant, and the amount added is as follows:
It is determined depending on the type of ~, but a range of 5 to 40 copies is good for all types. If the amount is less than 5 parts, it is difficult to provide sufficient wettability or washability, and if the amount is more than 40 parts, the viscosity of the liquid increases, which is not preferable.

In addition, the non-volatile aromatic hydrocarbons that are removed using water and the non-volatile aromatic hydrocarbons that are mixed in the type of are bisphenol, diphenyl, alkylbenzene with carbon number of 18 or more, carbon number of 11 or more.
The above-mentioned alkylnaphthalenes and the like are preferred, and the amount added is preferably in the range of 5 to 20 parts. If it is less than 5 parts, it is difficult to improve the washability and prevent the oil-soluble dye in the penetrant composition from remaining after washing, and if it is more than 20 parts, it tends to worsen the washability. So I don't like it.

Next, a penetrant testing method using the penetrating liquid according to the present invention as explained above will be described. Its operating mode is similar to the typical operating mode of the conventional penetrant testing method described above.

That is, it is a penetrant flaw detection method that is performed by a series of operations consisting of "penetrating operation,""cleaningoperation,""developingoperation," and "inspection operation," as in the conventional method.

As a penetrating liquid, the above-mentioned characteristics can be restated: under white light, the larger the defect volume, the darker and clearer the defect indication becomes; conversely, the smaller the defect volume, the fainter the defect indication becomes; under ultraviolet light, the defect indication becomes darker and clearer. Due to the use of the penetrant liquid according to the present invention, which has the characteristic that the smaller the defect volume is, the brighter and clearer the defect indication becomes, and conversely, the larger the defect volume is, the darker the defect indication is. It is performed in two settings: under white light and under ultraviolet light. By comparing the inspection results in these two places, it is possible to accurately know the relationship between the opening area of the defective part and its depth, and also to know the nature of the defective part. This is its biggest feature. This will be explained in detail below.

FIG. 3 is a partially omitted enlarged cross-sectional explanatory diagram schematically showing various typical shapes of opening defects. The figure shows five types of open defects from ~ to ~, and for each one, 5 minutes have elapsed after the cleaning operation (A in the figure) and after the development operation (in the figure) when the penetrant flaw detection method according to the present invention is carried out. B) also shows the state of defective areas 1, 21, penetrating liquids 2, 22, developer powder layers 3, 23, 15 minutes after the development operation (C in the figure).

Now, when the penetrating liquid according to the present invention is applied to the surface of the object to be inspected, a "penetrating operation" is performed according to a conventional method, and then a "cleaning operation" is performed to remove excess penetrating liquid, the state shown in Example A in the figure is obtained. Next, when a "developing operation" is performed to form a developer layer made of white fine inorganic powder, a defect indicating pattern due to the penetrating liquid appears on the surface of the layer, and after about 5 minutes, the state as shown in example B in the figure is reached. After a few minutes, the state of Example C will be reached. Next, we perform "inspection operations" on this condition in two places: under white light and under ultraviolet light.

In the "developing operation", the above-mentioned "quick-drying developer" is used. The penetrant testing method of the present invention can also be carried out using the above-mentioned "wet developer," but in this case, a drying process to remove water is essential. This is because if the conditions differ for each opening defect, it will have an adverse effect on comparative observation of defect indication patterns, which will be described later. As is well known, "quick-drying developer" is ethanol,
A fine white inorganic powder is dispersed in a volatile solvent such as isopropyl alcohol, 1-1-1 trichloroethane, or Freon-113, and if a certain amount is sprayed onto the surface of the object to be inspected, a certain thickness corresponding to the amount of spray will be created. A developer layer made of uniform white fine inorganic powder can be easily formed, and when the solvent evaporates (volatizes), the gaps between the powder particles forming the layer become almost vacuum-like. Therefore, it has the effect of strongly sucking up the penetrating liquid inside the defect. Therefore, when implementing the penetrant flaw detection method according to the present invention, a "quick-drying developer" is used.
It is desirable to select

Figure 3 shows an opening defect modeled after a scratch, a dent, a blowhole, etc., and the defect 1
Since the opening area (width) is set to be large and its depth is set to be shallow, the defect capacitance is small.

In addition, is an open defect modeled on a relatively large crack, and the defect 21 has a large opening area and a deep depth, so the defect capacity is larger than in the case of. .

, under white light, in the state B, the defect indicating patterns corresponding to the opening areas of the defective parts 1 and 21 are both marked in deep red.

However, when observed under an ultraviolet lamp, in condition B, the defect indication pattern of defect area 1 is uniformly bright and large over the entire pattern, but that of defect area 21 is dark and large throughout the pattern. There is.

From the above observation results, the inspector can empirically reliably determine that, even if the opening area is large, the defect 1 is shallow in depth, whereas the defect 21 is deep. When the flaw detection method is actually carried out, the open defect will be determined to be a benign defect that can be repaired by scraping or a malignant defect that cannot be repaired.

In addition, in state C, the defect indicator pattern of the defective part 1 is enlarged by blurring under white light, and the color density becomes lighter and shows a pale red color, and under an ultraviolet light, it becomes fluorescent. Although the brightness has increased, the defect indicator pattern of the defective area 21 has been enlarged by blurring under white light, but there has been little change in color density, and it has a slightly lighter red color, and under ultraviolet light it shows a slight change in color density. At the bottom, the fluorescence brightness only at the periphery increases and becomes brighter, but the center remains dark.

Figure 3 shows an open defect modeled after a crack.The defect 31 has a small opening area, a deep depth, and a branched shape, so the defect capacity is large. It's summery.

When the state of B is observed under white light, a small defect indicating pattern corresponding to the opening area of the defective portion 31 is indicated in dark red. When observed under an ultraviolet light, the entire pattern appears dark. In state C, the defect indicator pattern of the defective part 31 is enlarged by blurring under white light, but remains deep red without any change in color density, and under ultraviolet light it shows no fluorescence. There is no increase in brightness and it is still dark.

From the above observation results, the inspector can reliably know from experience that the defect 31 has a small opening area but a very deep depth. Then, it can be determined that this is a fatal malignant defect that is even worse than the above-mentioned open defect.

That is, although the defect is shown enlarged in FIG. 3, the opening area of the defect that is actually the target of penetrant testing is often very small, on the order of microns. If a defect with such a minute opening area is extremely deep compared to the opening area, even if a developer layer is formed, all of the penetrating liquid in the defect area 31 will be absorbed in a short period of time. Although it is not sucked out, the powder in the developer layer near the opening is sufficiently filled with the penetrating liquid (state B in Figure 3).
For this reason, the defect indicating pattern corresponding to the opening area is indicated in deep red under white light, and dark under ultraviolet light. Then, as time passes, the entire amount of the penetrating liquid in the defective part 31 is sucked out, but until the entire amount of the penetrating liquid is sucked out, the penetrating liquid is not allowed to flow between the powders in the developer layer. Since the bleeding (diffusion) speed and the supply of the penetrating liquid from inside the defective part 31 are balanced, the powder in the developer layer is still sufficiently filled with the penetrating liquid (state C in Fig. 3). Therefore, the color density of the enlarged defect indicating pattern does not decrease under white light, and the fluorescence brightness does not increase under ultraviolet light.
Incidentally, after a long period of time has elapsed and the entire amount of the penetrating liquid in the defective part 31 has been sucked out, only the diffusion of the penetrating liquid continues, and the penetrating liquid becomes diluted, and the fluorescence brightness increases.

The above phenomenon is more pronounced as the opening area is smaller and the depth is deeper, so if the inspector is aware of this phenomenon, it will be easier to screen out malignant defects. be.

FIG. 3 shows an open defect modeled on a pinhole, and since the defect portion 41 has a small opening area and a shallow depth, the defect capacitance is small.

Further, is an opening defect modeled on a micro-crack, and since the defect portion 51 has a minute opening area and a shallow depth, the defect capacity is smaller than in the case of .

, under white light, in state B, the defect indicating pattern corresponding to the opening area of the defective part 41 is indicated as a small red dot, and the defect indicating pattern of the defective part 51 is too minute to be seen with the naked eye. That's not acceptable. When observed under an ultraviolet lamp, in state B, the defect indicating pattern of the defective part 41 is indicated darkly, but that of the defective part 51 is indicated as a bright small dot. In state C, the defect indicator pattern of the defective part 41 expands due to blurring under white light, and the color density becomes lighter, taking on a light red color, and under an ultraviolet lamp, the fluorescence brightness increases. There is. On the other hand, the defect indication pattern of the defective part 51 is
Although it is slightly larger due to blurring, it has a pale pink color density and is easy to overlook, and under an ultraviolet lamp the fluorescence brightness increases slightly and is indicated as a bright spot.

From the above observation results, the inspector can know from experience that an opening defect is a defect with a small opening area and shallow depth, and can be ignored as a pinhole, and that it is possible to overlook a minute opening defect. It is a micro crack that can be reliably detected without any defects, and has a small opening area and shallow depth, and cannot be used in applications where fatigue expansion is a problem (for example, when used in power parts). You can learn that.

As is clear from the above-mentioned cases, the penetrant flaw detection method according to the present invention allows the depth of the detected opening defect to be determined based on the difference in fluorescent brightness between "dark and bright" as well as the "dark →
This can be determined by the change in the brightness. Moreover, since it utilizes the concentration quenching phenomenon, minute defects that are easily overlooked during inspection operations are indicated by bright and clear fluorescent light, and large defects that cannot be overlooked are indicated by dark fluorescent light. Since it is directed by
This allows for more accurate testing.

In addition, the "inspection operation" of the penetrant testing method according to the present invention is performed in two places, one under white light and the other under an ultraviolet lamp, and the test results under white light and those under an ultraviolet lamp are compared. In some cases, a television camera is used instead of the inspector's visual inspection, and a well-known video system records the observation results under white light and then under ultraviolet light, thereby recording both results. By employing a method of overlapping the results, efficient and accurate testing can be performed. In this case, when recording under an ultraviolet lamp, changes in fluorescence brightness are recorded with a television camera, so an extremely clear image can be obtained. Furthermore, instead of the Tervi camera used under an ultraviolet lamp, a well-known optical sensor can be used to treat changes in fluorescence brightness as electrical signals.

Furthermore, it is also possible to automatically identify defects by applying an automatic flaw detection system using the ITV method, which has already been put into practical use in the magnetic particle flaw detection method for square billets, etc., to the penetrant flaw detection method according to the present invention. , the above-mentioned features of the penetrant flaw detection method according to the present invention can be particularly effectively utilized.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 (1) Penetrant liquid formulation Oil Scarlet #308 15 parts Isopropyl alcohol 30 parts Ethyl carbitol 55 parts When the relationship between the amount of adsorption and the fluorescence brightness value was measured using a Yagi type fluorophotometer as in the previous experimental example, it was found that the amount of adsorption was
The highest fluorescence brightness was exhibited at 0.03 ml/g. FIG. 4A shows the relationship between the adsorption amount of the penetrant and the fluorescence brightness, with the horizontal axis representing the adsorption amount (ml/g) to the powder and the vertical axis representing the fluorescence brightness (%, However, the fluorescence brightness is expressed as 100% when 0.03ml/g is adsorbed to the powder.)

(2) Penetrant testing A "2024S-Al quench crack test piece" was used as the object to be inspected, and the above penetrating liquid was uniformly applied to the surface of the test piece, and the test piece was left for 10 minutes.

Next, the surface of the test piece was wiped with a rag soaked in isopropyl alcohol to remove excess penetrating liquid.

Next, a quick-drying developer - commercial product: DN-600S, product name: manufactured by Tokushu Toyo Co., Ltd., aerosol type: a mixture of isopropyl alcohol and acetone is used as a solvent - was applied to the surface of the above test piece. This was sprayed to form a developer powder layer with a uniform thickness. Five minutes after spraying, the samples were observed under white light and ultraviolet light (black light).

Under white light, multiple clear red defect indicator patterns of various sizes, large, medium, and small, depending on the open area of the multiple open defects scattered on the surface of the test piece were observed. Subsequently, when we performed follow-up observation under an ultraviolet lamp for defect indicator patterns that were approximately the same size from among these defect indicator patterns, we found that even though the defect indicator patterns were approximately the same in size, they were dark. Two types of indicator patterns were recognized: one with red fluorescence and one with bright orange fluorescence.

Pratt &
Measurement was performed using a photomulti system using an optical sensor specified in the inspection standard specification equipment of Whitney (an American aircraft manufacturer). The results are shown below. In addition, the fluorescence brightness standard is based on the amount of adsorption of the above-mentioned penetrant.
Fluorescent brightness at 0.03ml/g is set as 100.

Fluorescent brightness of the dark red fluorescent indicator pattern: 37% Fluorescent brightness of the bright orange fluorescent indicator pattern: 95% From the above results, the test piece surface has open defects with various open areas. Although the existence and opening area are almost the same, the depth is
It was possible to detect the existence of shallow defects and deep defects.

Incidentally, when the fluorescence brightness was measured 15 minutes after spraying, the fluorescence brightness at 37% had increased to 40%, but the brightness at 95% remained unchanged.

Example 2 (1) Penetrant liquid formulation Food red No. 215 10 parts Butyl cellosolve 55 parts Nonylphenol ethoxylate (10 mole ethylene oxide adduct) 30 parts Bisphenol 5 parts The above penetrant liquid was used in the penetrant test described below. Figure 4 shows the maximum fluorescence brightness at an adsorption amount of 0.03 ml/g for the developer powder.
This is a graph showing the relationship between the adsorption amount of the penetrating liquid and the fluorescence brightness, similar to FIG.

(2) Penetrant testing The test object is a nickel/chrome plating bending crack test piece as described in Utility Model Publication No. 56-35815, with a depth of 20μ and a width of 2μ on the plating surface.
The opening defect is set (A) and the depth is 50μ,
Two test pieces (B) with an opening defect of 5 μ in width were used, and the above-mentioned penetrating solution was evenly applied to the plating surface of each test piece and left for 15 minutes.

Next, the plated surface of each test piece was wiped with a cloth soaked in water to remove excess penetrating liquid.

Next, apply a quick-drying developer to the surface of each test piece - Commercial product: UD-St: Product name: Tokushu Toyo Co., Ltd.: Aerosol type: Basic magnesium carbonate with a particle size within the range of 0.05 to 0.5μ. A mixed powder of powder and silicic anhydride powder was used, and a mixed solution of normal heptane and ethanol was used as a solvent.- was sprayed to form a developer powder layer of uniform thickness. 10 minutes after spraying, observations were made under white light and ultraviolet light.

Under white light, no defect indicating pattern could be observed for test piece (A), but a red defect indicating pattern corresponding to the aperture width was observed for test piece (B). Next, when each test piece was observed under an ultraviolet lamp, a defect indicating pattern exhibiting bright orange-yellow fluorescence corresponding to the aperture width was observed for test piece (A), and for test piece (B), the defect indicator pattern was observed as described above. It was observed that the defect indicating pattern exhibited a rather dark orange-yellow fluorescence.

When the fluorescence brightness of each defect indicating pattern described above was measured in the same manner as in the example, it was 98% for test piece (A);
In the case of test piece (B), it was 86%.

Furthermore, when the fluorescence brightness was measured 15 minutes after spraying, no change was found in either case.

Example 3 (1) Prescription of penetrating liquid Watered E 20 parts Ethyl alcohol 10 parts Newcol 290B: Product name: Nippon Nyukazai Co., Ltd.
Manufactured by: Sulfosuccinate type surfactant 20 parts Water 50 parts The above penetrant liquid exhibits the highest fluorescence brightness at an adsorption amount of 0.03ml/g for the developer powder used in the penetrant inspection below. , Figure 4C
1 is a graph showing the relationship between the adsorption amount of the penetrating liquid and the fluorescence brightness, similar to FIG.

(2) Penetrant testing A ``weld wire hot cracking test piece (a test piece with many cracks similar to the shape shown in Figure 4)'' is used as the object to be inspected. The above penetrant solution was evenly applied to the surface and left for 15 minutes. Next, the surface of the above test piece was washed with water at a pressure of 1 Kg/cm and 10
Excess penetrant was removed by spraying water for 2 seconds.

Next, the above test piece was coated with powder for wet developer for dye penetrant testing - commercially available product: D-LW: product name: special paint.
Co., Ltd.: Soaked in a 15% aqueous dispersion of basic magnesium carbonate powder with a particle size of 0.2 to 0.5μ, immediately removed, dried at 65℃ for 5 minutes, and developed a uniform thickness on the surface of the test piece. A powder layer was formed. After drying, 10
After a few minutes had elapsed, the samples were observed under white light and ultraviolet light.

Under white light, multiple clear red defect indicator patterns of various sizes depending on the opening area of multiple open defects scattered on the surface of the test piece were observed.
Subsequently, when the test was observed under an ultraviolet lamp, it was observed that the larger defective indicator patterns exhibited very dark red-orange fluorescence, and the smaller indicator patterns exhibited dark red-orange fluorescence. .

The results of measuring the fluorescence brightness of each defect indicating pattern described above in the same manner as in Example 1 are shown below.

Fluorescent brightness of very dark red-orange fluorescent indicator pattern:
40% Fluorescence brightness of indicator pattern with dark red-orange fluorescence: 60% When observed under an ultraviolet lamp again 15 minutes after drying, the large indicator pattern still exhibited very dark red-orange fluorescence. The small indicator pattern exhibited bright orange fluorescence, and the difference in brightness between the former and the latter was extremely remarkable.

In this case, the fluorescence brightness of each defect indication pattern is 40%.
Those who were at 60% rose to 92%.

From the above results, it is clear that the surface of the specimen is scattered with cracks with a relatively large opening area and a relatively deep depth, and cracks with a relatively small opening area and a relatively shallow depth. I was able to detect it.

It should be noted that the defect indicating patterns formed in the penetrant testing of Examples 1 to 3 above can not only be clearly recognized by the naked eye of the inspector, but also extremely clearly by an ordinary video television camera. It was something that could be recorded.

[Brief explanation of drawings]

1 and 2 are for explaining the concentration quenching phenomenon in the present invention, and FIG. 1 is a graph showing the relationship between dye concentration and adsorption amount and fluorescence brightness. FIG. 2 is a graph showing the relationship between the dye concentration, the amount of adsorption, and the amount of absorbed light. In both figures, line A is when 1 part of dye is dissolved in 100 parts of solvent, line B is when 5 parts of dye is dissolved in 100 parts of solvent, and line C is when 1 part of dye is dissolved in 100 parts of solvent. This is the case when 10 parts of the dye is dissolved. FIG. 3 is a partially omitted enlarged cross-sectional explanatory diagram schematically showing various shapes of opening defects. Furthermore, the same figure shows the state when the penetrant flaw detection method according to the present invention is carried out, in which column A is the state after the cleaning operation, column B is the state after 5 minutes after the development operation, and column C is the state after the development operation. The state after 15 minutes is shown. 1, 21, 3 in Figure 3
1, 41, 51 are defective parts, 2, 22, 32, 4
2, 52 is penetrating liquid, 3, 23, 33, 43, 53
indicates a developer powder layer. FIG. 4 is a graph showing the relationship between the adsorption amount and fluorescence brightness of each of the penetrants listed as examples of the penetrant according to the present invention, where A is Example 1, B is Example 2, C is shows the case of Example 3.

Claims (1)

[Claims] 1. A penetrant liquid for penetrant flaw detection that contains a dye and a solvent in which the dye is dissolved as essential components; exhibits a red color under white light and red to yellow fluorescence under an ultraviolet lamp. Concentration quenching phenomenon occurs when the liquid in which the dye is dissolved exhibits a concentration quenching phenomenon (in a liquid in which the dye is dissolved above a certain concentration, the visible color under white light becomes darker as the amount of the dye dissolved increases, but the visible color under white light becomes darker; The luminance of fluorescent light under a lamp peaks when the amount is at a certain level, and then decreases as the amount increases.This phenomenon is called the "concentration quenching phenomenon."The same applies hereinafter. ) A penetrant liquid for penetrant testing that is characterized by being dissolved at a concentration higher than that which causes . 2. The penetrant liquid for penetrant flaw detection according to claim 1, wherein 10 to 30 parts by weight of the dye is dissolved in 100 parts by weight of the penetrant liquid. 3. The penetrant liquid for penetrant flaw detection according to claim 1 or 2, wherein the dye is a water-soluble red fluorescent dye. 4. The penetrant liquid for penetrant flaw detection according to claim 1 or 2, wherein the dye is an oil-soluble red fluorescent dye. 5. The penetrant liquid for penetrant flaw detection according to any one of claims 1 to 4, to which a surfactant is added. 6. After applying a penetrant liquid for penetrant testing, which contains a dye and a solvent in which the dye is dissolved as essential components, to the surface of the object to be inspected and allowing the penetrant liquid to penetrate into the surface opening defect, The excess penetrating liquid remaining on the surface of the object to be inspected is removed, and then a layer of penetrant developer made of white fine inorganic powder is formed on the surface of the object to be inspected, and capillary action between the powders is applied. In the penetrant testing method, the penetrant liquid that has penetrated into the defect is sucked out and a defect indicating pattern appears on the surface of the developer layer, and then the defect is detected by detecting the defect indicating pattern; A penetrating liquid for flaw detection that contains a dye that exhibits a red color under white light and a red to yellow fluorescence under an ultraviolet light at a concentration higher than that which causes the concentration quenching phenomenon in the liquid in which the dye is dissolved. When detecting the defect indicating pattern, the size of the defect indicating pattern corresponding to the opening area of the defect indicated by the defect indicating pattern is detected under white light, and the size of the defect indicating pattern corresponding to the opening area of the defect indicated by the defect indicating pattern is detected under white light. A penetrant flaw detection method characterized by detecting the brightness and darkness of an indicator pattern corresponding to the depth of the defect indicated by the fluorescent brightness of the indicator pattern. 7. The penetrant flaw detection method according to claim 6, wherein the defect indicating pattern is detected under white light and under an ultraviolet lamp using a television camera. 8. The penetrant flaw detection method according to claim 6, wherein the defect indicating pattern is detected under a white light using a television camera and under an ultraviolet light using an optical sensor. 9 After applying a penetrant liquid for penetrant testing, which contains a dye and a solvent in which the dye is dissolved as essential components, to the surface of the object to be inspected and allowing the liquid to penetrate into the surface opening defect, The excess penetrating liquid remaining on the surface of the object to be inspected is removed, and then a layer of penetrant developer made of white fine inorganic powder is formed on the surface of the object to be inspected, and capillary action between the powders is applied. In the penetrant testing method, the penetrant liquid that has penetrated into the defect is sucked out and a defect indicating pattern appears on the surface of the developer layer, and then the defect is detected by detecting the defect indicating pattern; A penetrating liquid for flaw detection that contains a dye that exhibits a red color under white light and a red to yellow fluorescence under an ultraviolet light at a concentration higher than that which causes the concentration quenching phenomenon in the liquid in which the dye is dissolved. In forming the developer layer for penetrant testing, a fine white inorganic powder dispersed in a volatile solvent is sprayed onto the surface of the object to be inspected to form a layer with a uniform thickness; In detecting the defect indicating pattern, the size of the defect indicating pattern corresponding to the opening area of the defect indicated by the defect indicating pattern is detected under white light, and the fireflies of the defect indicating pattern are detected under an ultraviolet light. A penetrant flaw detection method that is characterized by detecting the brightness and darkness of an indication pattern that corresponds to the depth of the defect indicated by light intensity.