JPH0252987B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a dispersant for magnetic powder liquid used in wet magnetic flaw detection, which maintains dispersion and defoaming effects for a long time even at high temperatures of approximately 40°C to 50°C. It is an object of the present invention to provide a dispersant for magnetic powder liquid that has the ability to maintain over a long period of time.

In general, magnetic flaw detection is well known as a typical non-destructive testing method for magnetic materials. In this method, when a defect such as a crack or a pinhole exists on the surface of a magnetic material (for example, a square piece of steel) or in a relatively shallow part below the surface, when a current is passed through the magnetic material, the magnetic resistance of the defective part is reduced. Because the area is larger than other healthy parts, magnetic flux drifts in that area and leaks into the air. This phenomenon is utilized, and iron powder, stainless steel powder, etc. magnetically conductive powder (generally called "magnetic powder").
Magnetic powder coated with fluorescent material is
It is called "fluorescent magnetic powder." ), the magnetic particles are collected in the area of leakage magnetic flux mentioned above, and the defective part of the object to be inspected is detected by the magnetic particle pattern.When scattering the magnetic particles on the surface of the object to be inspected,
There is a method in which magnetic particles are directly dispersed in the air and sprinkled on the surface of the object to be inspected (generally referred to as "dry magnetic flaw detection"). Disperse it at a concentration of 1 part water to create a magnetic powder dispersion (generally called ``magnetic powder liquid'').
There is a method (called ``wet magnetic flaw detection'') in which this magnetic powder liquid is sprinkled on the surface of the object to be inspected.
The latter wet magnetic flaw detection method is particularly widely used in the steel industry, and is used to detect flaws in steel materials such as square billets and round billets.

The present invention relates to a "dispersant for magnetic powder liquid" used in the preparation of magnetic powder liquid in the above-mentioned wet magnetic flaw detection method.
This is related to.

As mentioned above, the magnetic particle concentration of the magnetic powder liquid is usually 1 to 3.
g/water 1, but this is 1g/water 1
In the following cases, the amount of magnetic particles that collect on the defective part of the surface of the object to be inspected becomes so small that practical flaw detection accuracy cannot be obtained, and in the case of 3 g/water 1 or more, magnetic particles also collect in parts other than the defective part. Attached to "background"
This is because this phenomenon occurs and the flaw detection accuracy decreases.

As is well known, when spraying magnetic powder liquid with a magnetic particle concentration of 1 to 3 g/water 1, it is required that the magnetic particles are sufficiently dispersed and that the magnetic particle liquid uniformly wets the surface of the object to be inspected. .

Furthermore, the dispersed magnetic powder liquid is collected and reused, and in this industry, normally, a magnetic powder liquid stirring device as shown in Fig. 1 is used, the magnetic powder liquid is poured into a tank 1, and a pump 2 is used from the tank 1. transport the magnetic powder liquid to a predetermined spraying location and spray it on the inspection object A, collect the sprayed magnetic powder liquid into tank 1, and transport the collected magnetic powder liquid from tank 1 again to the predetermined spraying location using pump 2. The method is to repeat the cycle of transporting and dispersing. This aspect is described in detail in, for example, Japanese Utility Model Publication No. 47-41518. That is, the magnetic powder liquid is always used in a stirred state, and the magnetic powder liquid during use is in a state where it is very easy to foam. It will be easily understood that if there is a lot of foaming, foaming will occur on the surface of the object to be inspected, interfering with flaw detection, or the foam will overflow from the tank 1. Therefore, in addition to the above, it is required that the magnetic powder liquid during use does not cause any bubbling phenomenon.

In the industry, dispersants for magnetic powder liquids are used in preparing magnetic powder liquids in order to meet the above requirements.

A typical formulation of dispersants for magnetic powder liquids currently on the market is 1 to 3% by weight of silicone antifoaming agent (hereinafter, all % by weight is simply referred to as %), 2 to 3% of surfactant.
6% and the balance water, to which 3 to 5% of a rust preventive agent is added as necessary.

To explain in more detail, the silicone antifoaming agent in the formulation is a polyethylene glycol type non-foaming agent with an HLB value of 10 to 11, which is dimethylpolysiloxane oil, which is considered to be the best antifoaming agent to be added to dispersants for magnetic powder liquids. Oil-in-water (O/
W) A silicone antifoaming agent in the form of an emulsion, the blending ratio of which is 10-30% dimethylpolysiloxane oil, 5-10% surfactant, and the balance water, and this ratio is an oil-in-water that is stable during use. It is said to be the optimum ratio for maintaining the mold emulsion.
In addition, as a commercially available product, "Silicone antifoaming agent KM68-
1F'', ``KM-70'', and ``KM-72F'' (all product names: manufactured by Shin-Etsu Chemical Co., Ltd.) are well known.

The silicone antifoaming agent mentioned above is, of course, blended to meet the above requirements.

Next, the surfactant in the formulation has an HLB value of 10 to
13 polyethylene glycol type nonionic surfactant. It is said that in order to keep the oil-in-water emulsion of the silicone antifoaming agent stable during use, it is necessary to use a surfactant with properties similar to those of the surfactant used in the silicone antifoaming agent. Selected based on viewpoint.

The above surfactant is blended to meet the above requirements. As mentioned above, the silicone antifoaming agent also contains a surfactant, but it is completely impossible to sufficiently disperse the magnetic particles with just the amount of surfactant contained in the silicone antifoaming agent. As mentioned above, 2 to 6% of surfactant is blended as the amount of surfactant necessary to sufficiently disperse the magnetic powder and satisfy wettability during spraying. ~
The specified amount of 6% does not include the amount of surfactant pre-blended in the silicone antifoaming agent. ).

Next, the rust preventive agent added as necessary is sodium nitrite, triethanolamine, etc., and is added when it is necessary to prevent rust from forming on the test object.

The commercially available dispersant for magnetic powder liquid used in the wet magnetic flaw detection method (hereinafter referred to as "known dispersant"), which has the above-mentioned formulation, is currently considered to have the highest performance. A magnetic powder solution prepared by adding magnetic powder to water at a concentration of 1 to 3 g/water at a concentration of 1%/water is as follows.
It is guaranteed that sufficient flaw detection accuracy can be obtained for practical use by meeting the above requirements, and that the defoaming effect is maintained for 10 to 20 hours after the start of use of the magnetic powder liquid. ing.

In addition, the concentration of the known dispersant used is 1 to 3%/1 part water.
This is because, in order to satisfy the above requirements, a concentration of at least 1%/water 1 or more is required, and even if the concentration is 3%/water 1 or more, this dispersion and wetting effect will be significant. This is because no significant improvement can be recognized. In addition, the defoaming effect maintenance time mentioned above is
The concentration of dispersant added to the magnetic powder liquid was 3%/1 water.
There is almost no difference even with the above, and when the magnetic powder liquid starts to foam after the antifoaming effect maintenance time has elapsed, even if you add a known dispersant or the silicone antifoaming agent itself, no additional Sometimes, the foaming phenomenon is only temporarily suppressed, and the foaming phenomenon occurs again after about 3 to 4 hours.

The known dispersants described above have the following drawbacks. That is, when the liquid temperature of the magnetic powder liquid prepared using a known dispersant is room temperature (20° to 30°C), it exhibits high performance that satisfies the above requirements without any problems, but when the liquid temperature is about When the temperature exceeds 40°C, the dispersion effect and antifoaming effect are suddenly lost, which leads to an extremely low flaw detection accuracy and severe bubbling.

Of course, a situation in which the temperature of the magnetic powder liquid exceeds 40°C during wet magnetic flaw detection usually rarely occurs.

However, when wet magnetic flaw detection is applied to a square billet that has undergone heat treatment such as rolling or annealing to room temperature in the summer, the temperature of the magnetic powder liquid is 40°C. It is not rare for the dispersant to exceed the above range, and in such cases, the known dispersants exhibit the above-mentioned drawbacks.

As far as the present inventors know, there is no magnetic powder dispersant available in Japan or other countries that can maintain the dispersion effect and antifoaming effect when the temperature of the magnetic powder liquid exceeds about 40°C.

Therefore, in this industry, the liquid temperature of magnetic powder liquid is approximately
There is a strong desire for a dispersant for magnetic powder liquids that does not lose its dispersing and antifoaming effects even at temperatures exceeding 40°C.

In view of the current situation as described above, the present inventor has repeatedly conducted systematic tests and research in order to achieve the intended purpose.

The present inventor has discovered that a known dispersant has a liquid temperature of about 40°C.
As a result of thorough investigation into the factors that cause the rapid loss of dispersion and antifoaming effects when the temperature exceeds ℃, we found that the surfactants contained in known dispersants (including the surfactants in the silicone antifoaming agents mentioned above) were found. I learned that the reason for this is the cloud point of .

To be more specific, as mentioned above, known dispersants include 1-
Contains 3% of the above silicone antifoaming agent,
The silicone antifoaming agent is HLB, which uses dimethylpolysiloxane oil as an oil-in-water emulsion.
Contains a polyethylene glycol type nonionic surfactant with a value of 10-11. As is well known, the optimal HLB value for making dimethylpolysiloxane oil into an oil-in-water emulsion is 10.5.
In manufacturing the above silicone antifoaming agent,
Use a polyethylene glycol type nonionic surfactant with an HLB value of 10.5 alone, or
Multiple polyethylene glycol type nonionic surfactants of 10 to 11 are used in combination to give an HLB value of 10.5, and it is generally believed that more stable oil-in-water emulsions can be obtained by relying on the latter. .

By the way, the cloud point of a polyethylene glycol type nonionic surfactant with an HLB value of 11 or less is about 40°C or less.

As is well known, polyethylene glycol type nonionic surfactants have the property of being hydrophobic and soluble in water at temperatures below the cloud point, but not soluble in water at temperatures above the cloud point.

In other words, known dispersants always contain a polyethylene glycol type nonionic surfactant with an HLB value of 10 to 11, and their cloud point is 40°C or lower, so magnetic powder liquids using known dispersants cannot be used. When the liquid temperature exceeds 40°C, the surfactant separates from water and dimethylpolysiloxane oil. The separated surfactants adhere to each other to form hydrophobic oil droplets, to which the magnetic particles adhere, and the dimethylpolysiloxane oil separated from the surfactant naturally separates from water as well, forming hydrophobic oil droplets. Oil droplets are formed, to which the magnetic particles also adhere, and thus the magnetic particles are no longer uniformly dispersed. At the same time, the dimethylpolysiloxane oil separates from the water, resulting in a foaming phenomenon.

As mentioned above, when the liquid temperature of the magnetic powder liquid exceeds approximately 40°C, the dispersion effect and antifoaming effect of known dispersants are lost. contained in the drug
This is due to the fact that the cloud point of a polyethylene glycol type nonionic surfactant with an HLB value of 10 to 11 is about 40°C or lower.

Therefore, as a solution, it is natural to think that the surfactant contained in the above-mentioned silicone antifoaming agent should have a high clouding point, for example, one with a clouding point of about 50°C or higher. It will be done. However, in order to maintain dimethylpolysiloxane oil as a stable oil-in-water emulsion during use, it is necessary to use a polyethylene glycol type nonionic surfactant with an HLB value of 11 or less and a cloud point of 40°C or less. , cloud point approximately 50℃ (in this case
If a polyethylene glycol-type nonionic surfactant with an HLB value of 12 to 15) is used, the silicone antifoaming agent will allow dimethylpolysiloxane oil to remain stable in water during use, even if the liquid temperature is below 40°C. This results in a product that cannot be maintained as an oil emulsion.

In addition, if we focus only on the dispersion effect of magnetic powder, we can compare polyethylene glycol type nonionic surfactants with an HLB value of 10 to 13, which are blended in 2 to 6% in known dispersants, to a cloud point of approximately 50 with an HLB value of 12 to 15. ℃ or higher, but in this case, even if a dispersion effect is obtained, an antifoaming effect cannot be obtained, and even if the temperature of the magnetic powder liquid is below 40℃, severe foaming occurs. That's what happens. (This is because when blending a polyethylene glycol type nonionic surfactant with an HLB value of 12 to 15 and a cloud point of approximately 50°C or higher, its properties are vastly different from the surfactant contained in the silicone antifoaming agent. This is because the oil-in-water emulsion of the silicone antifoaming agent is destroyed during use, and the dimethylpolysiloxane oil separates from the water.Also, the higher the cloud point, the more hydrophilic groups there are in the surfactant. (This is also due to poor compatibility with hydrophobic dimethylpolysiloxane.) The present inventor sought a solution that could be achieved without changing the surfactant contained in known dispersants. Through research, we have found that when using Setsuken in addition to known dispersants, even when the liquid temperature of the magnetic powder liquid exceeds 40°C, the same dispersion and antifoaming effects as when the liquid temperature is room temperature can be maintained for a long time. can be maintained,
Moreover, the present invention was completed based on the remarkable fact that the above-mentioned method does not have any adverse effects.

That is, the present invention provides silicone antifoaming agents 1 to 1 which are made of dimethylpolysiloxane oil as an oil-in-water emulsion using a polyethylene glycol type nonionic surfactant with an HLB value of 10 to 11 and a cloud point of 40°C or less.
3%, 2-6% polyethylene glycol type nonionic surfactant with an HLB value of 10-13 and a cloud point of 50°C or less,
This is a dispersant for magnetic powder liquid (hereinafter referred to as improved dispersant) used in wet magnetic flaw detection, consisting of 1 to 40% solids and the balance water.

The most distinctive feature of the present invention is the addition of a liquid to the above-mentioned typical formulation of a known dispersant. The soap used in the present invention is the well-known sodium soup and potassium soup. Examples of the former include:

Sodium laurate (C ₁₁ H ₂₃ COONa), sodium myristate (C ₁₃ H ₂₇ COONa), sodium palmitate (C ₁₅ H ₃₁ COONa), sodium stearate (C ₁₇ H ₃₅ COONa), sodium oleate (C ₁₇ H ₃₃ COONa) and sodium beef tallow fatty acid (NS soap: Product name: Kao Soap Co., Ltd.)
manufactured by).

Examples of the latter include:

Potassium Laurate (C ₁₁ H ₂₃ COOK), Potassium Myristate (C ₁₃ H ₂₇ COOK), Potassium Palmitate (C ₁₅ H ₃₁ COOK), Potassium Stearate (C ₁₇ H ₃₅ COOK), Potassium Oleate (C ₁₇ H ₃₃ COOK), beef tallow fatty acid potassium (FR−
14: Product name: Kao Soap Co., Ltd.) and castor oil potassium (FR-25: Product name: Kao Soap Co., Ltd.).

The amount of Setsuken added is important, at least 1
% or more, the temperature of the magnetic powder liquid will be about 40℃.
It is not possible to maintain the dispersion effect and the antifoaming effect when the amount exceeds the above range. In addition, if the content is 40% or more, the viscosity of the improved dispersant itself becomes very high, making it difficult to handle, for example, when adding the improved dispersion to water. Therefore, the amount of soap added should be selected within the range of 1 to 40%.

The formulation of the improved dispersant other than the ingredients is exactly the same as the above-mentioned representative formulation of the known dispersant.

Further, as in the case of known dispersants, a rust preventive agent such as sodium nitrite or triethanolamine may be added in a range of 3 to 5%, if necessary.

The method for using the improved dispersant is exactly the same as that for known dispersants; 1-3% magnetic powder is added to water to which the improved dispersant has been added at a concentration of 1-3%/1 water.
A magnetic powder solution is prepared by adding so that the concentration is 1 g/water. This magnetic powder liquid has a temperature of about 50℃ not only when the liquid temperature is 20 to 30℃, but also when the liquid temperature exceeds 40℃.
It can be guaranteed that the above requirements are met and that sufficient flaw detection accuracy is obtained for practical use.
Even when the liquid temperature exceeds 40°C, it is guaranteed that the antifoaming effect will be maintained for about 12 hours after the start of use, up to about 50°C. It should be noted that there is almost no possibility that the temperature of the magnetic powder liquid will exceed approximately 50℃, and if it exceeds 50℃, the wet magnetic flaw detection method itself may become impossible due to burns on the inspector. It becomes possible.

Next, the manufacturing method of the improved dispersant is extremely easy; first, a predetermined amount of each compound and water are weighed out, and then a predetermined amount of each compound is added to a predetermined amount of water, and the The desired product can be obtained by mixing and stirring. When mixing and stirring, it is desirable to heat the mixture to about 50 to 70°C in order to dissolve the liquid in a short time.

Unfortunately, the theoretical elucidation of the effect of adding Setsuken in the present invention has not yet been carried out.
The present inventor believes that Setsuken does not have a cloud point and remains dissolved even when the liquid temperature exceeds 40℃. It suppresses the separation of the above-mentioned polyethylene glycol type nonionic surfactant with an HLB value of 10 to 11 and a cloud point of 40℃ or less, water, and dimethylpolysiloxane oil, which occurs when the temperature exceeds We believe that the foaming of the dissolved Setsuken itself is suppressed by the presence of the silicone antifoaming agent.

The above-mentioned various soaps all exhibit the effects of the present invention, but from the viewpoint of solubility in a wide temperature range, they contain various fatty acids such as lauric acid, palmitic acid, and stearic acid in their ingredients. It is preferable to use sodium beef tallow fatty acid or castor oil potassium.

Next, the structure and effects of the present invention will be explained using Examples and Comparative Examples.

Example 1 <Formulation> Silicone antifoaming agent KM-68-1F (product name: Shin-Etsu Chemical Co., Ltd.) 3% polyoxyethylene nonyl phenyl ether (3 mole adduct) HLB6.1, cloud point 10°C or less
1% polyoxyethylene lauryl ether (6.5 mol adduct) HLB11.6 Cloud point 38℃ 4% Sodium myristate 10% Sodium nitrite 5% Water 77% Mix and stir thoroughly while heating to 60℃. A translucent improved dispersant was obtained.

<Preparation of magnetic powder liquid> Add 60 ml of water to tank 1 (volume 100) shown in Figure 1.
and add the above improved dispersant to it at a ratio of 1%/1 water.
Add 600 c.c. to a concentration of 600 c.c., then add magnetic powder (fluorescent magnetic powder) to a concentration of 2 g/1 water.
A magnetic powder solution was prepared by adding 120 g.

<Implementation of wet magnetic flaw detection method> Pump 2 in Figure 1 was activated to circulate the magnetic particle liquid as indicated by the arrow in the figure, and while the magnetic particle liquid was maintained at approximately 40°C, a defect with a depth of 0.88 mm was detected. A square billet of medium 65 low carbon steel is used as the object to be inspected, and the axial energization method DC
Apply current at -1000A, spread the magnetic powder liquid, and visually judge the flaw detection accuracy at each point 5 minutes, 8 hours, and 12 hours after the start of circulation of the magnetic particle liquid under black light irradiation. . As a result, defects were clearly observable at all times, and at approximately 40°C.
It was determined that the magnetic particles in the magnetic powder liquid were sufficiently dispersed not only after 5 minutes, but also after 12 hours, even at a liquid temperature of .

Furthermore, even 12 hours after the start of circulation of the magnetic powder liquid, there were no bubbles overflowing from the top of tank 1, and it was determined that sufficient antifoaming effect was maintained at a liquid temperature of approximately 40°C. Ta.

Next, for comparison, except for the above prescription, 87
The same operation as above was performed using a comparative formulation expressed as %.

As a result, no defects could be confirmed 5 minutes after the start of circulation of the magnetic powder liquid, and it was determined that the magnetic particles in the magnetic powder liquid had agglomerated. (In fact, it was visually confirmed that the magnetic particles had aggregated in the form of flocs.) In addition, 5 minutes after the start of circulation of the magnetic powder liquid,
Bubbles were overflowing from the top of tank 1.

In addition, even in the case of the comparative formulation, the liquid temperature of the magnetic powder liquid is approximately 30℃.
If the temperature was below ℃, wet magnetic flaw detection could be carried out without any problems.

Example 2 <Formulation> Silicone antifoaming agent KM-72F (Product name: Shin-Etsu Chemical
Co., Ltd.) 1% Polyoxyethylene nonyl phenyl ether (5 mole adduct) 1.8% HLB10.0 Cloud point 10°C or less.

Polyoxyethylene dovanol ether (4.5 mole adduct) 4.2% HLB10.7 Cloud point 50°C.

Sodium beef tallow fatty acid (NS Soap: product name: Kao Soap Co., Ltd.) 1% Sodium nitrite 5% Water 86.5% ~ were mixed and stirred thoroughly while heated to 50°C to form a translucent improved dispersion. obtained the drug.

Example 1 Using the above improved dispersant, <preparation of magnetic powder liquid> was carried out in exactly the same manner as in Example 1, except that the magnetic powder liquid was used and the temperature of the magnetic powder liquid was maintained at 42°C. In the same manner as above, wet magnetic flaw detection was carried out.

As a result, as in Example 1, defects can be clearly observed at any time point, and the magnetic particles in the magnetic powder liquid are still sufficiently dispersed even after 12 hours, even at a liquid temperature of approximately 42°C. I was able to determine that.

Furthermore, even 12 hours after the start of circulation of the magnetic powder liquid, there were no bubbles overflowing from the top of tank 1, and it was determined that sufficient antifoaming effect was maintained at a liquid temperature of approximately 42°C. .

Next, for comparison, except for the above formulation,
The same operation as above was performed using a comparative formulation of 87.5%.

As a result, no defects could be confirmed 5 minutes after the start of circulation of the magnetic powder liquid, and it was determined that the magnetic particles in the magnetic powder liquid had agglomerated.

Further, 5 minutes after the start of circulation of the magnetic powder liquid, bubbles began to overflow from the upper surface of the tank 1.

Example 3 <Formulation> Silicone antifoaming agent KM-70 (Product name: Shin-Etsu Chemical
Co., Ltd.) 2% Polyoxyethylene nonyl phenyl ether (8.5 mol adduct) 2% HLB12.5, cloud point 44°C.

Potassium castor oil (FR-25: Product name: Kao Soap Co., Ltd.) 32% Sodium nitrite 3% Water 61% ~ were mixed and thoroughly stirred at 50°C to improve translucency. A dispersant was obtained.

Example 1 Using the above improved dispersant, <preparation of magnetic powder liquid> was carried out in exactly the same manner as in Example 1, except that the magnetic powder liquid was used and the temperature of the magnetic powder liquid was maintained at 43°C. In the same manner as above, wet magnetic flaw detection was carried out.

As a result, as in Example 1, defects can be clearly observed at any time point, and the magnetic particles in the magnetic powder liquid are still sufficiently dispersed even after 12 hours, even at a liquid temperature of about 43°C. I was able to determine that.

Furthermore, even 12 hours after the start of circulation of the magnetic powder liquid, there were no bubbles overflowing from the top of tank 1, and it was determined that sufficient antifoaming effect was maintained at a liquid temperature of approximately 43°C. .

Next, for comparison, except for the above prescription, 93
The same operation as above was performed using a comparative formulation expressed as %.

As a result, no defects could be confirmed 5 minutes after the start of circulation of the magnetic powder liquid, and it was determined that the magnetic particles in the magnetic powder liquid had agglomerated.

Further, 5 minutes after the start of circulation of the magnetic powder liquid, bubbles began to overflow from the upper surface of the tank 1.

The silicone antifoaming agents used in Examples 1 to 3 all have HLB values of 10 to 11, which are considered optimal as antifoaming agents for use in dispersants for magnetic powder liquids, and cloud points of 40°C.
A commercially available silicone antifoaming agent made of dimethylpolysiloxane oil as an oil-in-water emulsion using the following polyethylene glycol type nonionic surfactant, dimethylpolysiloxane oil 10
~30% surfactant, 5~10% surfactant, and the balance water.

[Brief explanation of drawings]

FIG. 1 is a partial longitudinal cross-sectional explanatory view showing a magnetic powder liquid stirring device commonly used in wet magnetic flaw detection. In the figure, 1 is a tank, 2 is a pump, and A is an object to be inspected. Note that the arrows in the figure indicate the circulation system path of the magnetic powder liquid.

Claims (1)

[Claims] 1. 1 to 3% by weight silicone antifoaming agent made of dimethylpolysiloxane oil as an oil-in-water emulsion using a polyethylene glycol type nonionic surfactant with an HLB value of 10 to 11 and a cloud point of 40°C or less. ,
A dispersant for magnetic powder liquid used in wet magnetic flaw detection, consisting of 2-6% by weight of a polyethylene glycol type nonionic surfactant with an HLB value of 10-13 and a cloud point of 50°C or less, 1-40% by weight of soap, and the balance water. 2. The dispersant for magnetic powder liquid used in the wet magnetic flaw detection method according to item 1, to which 3 to 5% by weight of a rust preventive agent is added. 3. The first product whose settsuken is sodium beef tallow fatty acid
A dispersant for magnetic powder liquid used in the wet magnetic flaw detection method according to item 1 or 2. 4. A dispersant for magnetic powder liquid used in the wet magnetic flaw detection method according to item 1 or 2, wherein the liquid is potassium castor oil.