JP2008224241A - Magnetic powder flaw detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic powder flaw detection method capable of obtaining good visibility, even if the surface of an inspection target is discolored by the effect of the time elapse or heat treatment after welding, to enhance the detection accuracy of flaws, in non-fluorescent type magnetic powder flaw detection to which a black magnetic powder is applied. <P>SOLUTION: The black magnetic powder is used as a magnetic powder and, before the magnetic powder is scattered over the surface of the inspection target 1, the inspection target 1 is coated with coating 3, having a color brighter than the surface color of the inspection target 1. The coating 3, preferably, is white color. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic particle flaw detection method used for detecting defects on or near the surface of an inspection object made of a magnetic material.

  For example, when manufacturing a large cylindrical container, the integrity of the welded part is checked by checking whether or not there is a defect (scratch) in the welded part before and after each step such as welding, heat treatment, pressure resistance test. A flaw detection test to confirm is necessary. As a method for nondestructively inspecting whether or not a defect exists in such a welded portion of a steel material, a magnetic particle flaw detection method is widely used (for example, see Patent Document 1 below).

  The magnetic particle flaw detection method is one of the methods for flaw detection on the surface of the ferromagnetic material and defects near the surface. An appropriate magnetic field is applied to the test body, and the magnetic powder is magnetized by the leakage magnetic flux generated in the defect portion, resulting in the defect. The magnetic powder pattern is formed by magnetizing the magnetic powder by the leakage magnetic flux and adsorbing it on the defective portion. And it is the test method which tries to know the presence or absence of a defect by observing this formed magnetic powder pattern. According to this magnetic particle flaw detection method, a magnetic powder pattern several to several tens of times larger than the actual defect width is formed by the magnetic particles adhering to the defective part, so that the defect can be easily detected by visual observation. Can do.

The magnetic particle flaw detection method includes a fluorescent method using fluorescent magnetic powder and a non-fluorescent method using ordinary magnetic particles such as white, black, and red used under visible light. The fluorescent method is currently mainstream because the magnetic powder itself emits fluorescence and has excellent visibility, but the non-fluorescent method has not been used so far.
However, since the fluorescent method can clearly identify the magnetic powder pattern by using an ultraviolet irradiation lamp (black light) in a dark place, the dark place is set by covering the examination site with a dark curtain or the like during the examination. It is necessary, and it is difficult to observe the magnetic powder pattern, hold the dark screen, and irradiate the ultraviolet irradiation lamp alone, which requires at least two inspection personnel, which is disadvantageous from the viewpoint of cost.
On the other hand, since there is no need to set a dark place in the non-fluorescent system, only one inspector is required, which is advantageous in terms of cost.

Japanese Patent Laid-Open No. 2001-21540

As a magnetic particle flaw detection method by a non-fluorescence method, three types of magnetic powders currently on the market were used, and a trial test on a test piece (polished surface) was performed. Table 1 shows the magnetic powder used in the test and the evaluation of its detectability and visibility. Note that “detectability” means sensitivity to defects (capability of forming a magnetic powder pattern), and “visibility” means ease of recognizing a magnetic powder pattern by visual observation.

As a result of this test, it was confirmed that if flaw detection with black magnetic powder was adopted, the detection performance was comparable to that of the fluorescence method. The reason why black magnetic powder has better detectability than other color magnetic powders is that the magnetic particles of other colors are colored with black pigment because of the pigment, and the black magnetic powder has a smaller particle size. It is done. Further, in the case of black magnetic powder, it was confirmed that there was no problem in terms of visibility if it was before or just after welding.
However, rusting due to the passage of time after welding and the influence of heat treatment, the background (surface of the object to be inspected) becomes a brownish color or bluish black, especially in the final test after pressure resistance test Large discoloration due to heat effect. When the black magnetic powder is applied to the background changed in this way, it is difficult to visually identify the magnetic powder pattern, and there is a problem that the visibility is lowered and the defect detection accuracy is lowered.

  The present invention has been made in view of the above problems, and in non-fluorescent magnetic particle flaw detection using black magnetic powder, even if the surface of the object to be inspected discolors due to the passage of time after welding or the influence of heat treatment, good visual recognition is achieved. It is an object of the present invention to provide a magnetic particle flaw detection method that can improve the accuracy of defect detection.

In order to achieve the above object, the magnetic particle flaw detection method of the present invention employs the following means.
(1) The present invention provides a magnetic particle inspection method in which magnetic particles are dispersed on the surface of a test object made of a ferromagnetic material, and defects are detected based on a magnetic powder pattern shown on the surface of the magnetized test object. The black magnetic powder is used as a coating material, and before the magnetic powder is dispersed on the surface of the object to be inspected, a paint having a lightness higher than the color of the surface of the object to be inspected is applied to the object to be inspected. .

(2) Moreover, in the said magnetic particle flaw detection method, the said coating material is white.

(3) Moreover, in the said magnetic particle flaw detection method, the surface of the said to-be-inspected object before apply | coating the said coating material is a brown color or bluish black.

(4) In the magnetic particle flaw detection method described above, the time when the flaw detection inspection is performed is performed after the rust is generated on the surface of the inspection object after the inspection object is welded or on the inspection object. After discoloration due to the effect of heat treatment after welding.

According to the present invention, since black magnetic powder is applied, good detectability can be obtained. In addition, the discoloration due to the effects of rusting and heat treatment is brown (brown, reddish brown, blue-brown, etc.) or blue-black color, so a paint with a higher brightness than these colors is applied to the surface of the object to be inspected. By applying, the contrast between the background and black (the color of magnetic powder to be applied) is increased. Therefore, the visual discrimination of the magnetic powder pattern is enhanced and the visibility is improved.
Further, by applying a white paint having the largest lightness difference from black as the paint, the visibility can be greatly improved.
Therefore, according to the present invention, even when the surface of the object to be inspected changes to a brownish color or blue-black color due to rusting due to the passage of time after welding or the effect of heat treatment, it is equivalent to the case of fluorescent flaw detection. Visibility is obtained, and an excellent effect that the detection accuracy of defects can be improved is obtained.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a diagram for explaining a magnetic particle flaw detection method according to an embodiment of the present invention. The present invention is a non-fluorescent magnetic particle flaw detection method using black magnetic particles. Therefore, unlike the fluorescent method, there is no need to set a dark place, so only one inspector is required, which is advantageous in terms of cost.

In the magnetic particle flaw detection method of the present invention, for example, in the manufacture of a large cylindrical vessel (such as a reactor pressure vessel), is there a defect (scratch) in the welded part before and after each step such as welding, heat treatment, pressure test, etc. Applied to check for no. However, the present invention is not limited to this, and can be widely applied to the defect detection of an inspection object made of a ferromagnetic material such as a steel material.
In FIG. 1 (A), a test object 1 to be inspected and a welded part 2 on the test object 1 are shown. The device under test 1 is made of a ferromagnetic material such as a steel material, and is, for example, a side wall portion or a bottom portion of a large cylindrical container.

  When the magnetic particle flaw detection method is performed on the object 1 to be inspected, first, dirt and oil and the like adhering to the surface of the inspection site of the object 1 to be inspected are removed as pretreatment. As described above, in the inspection after welding, there is discoloration due to rusting with the passage of time, and in addition, in the inspection after heat treatment (in the case where a pressure resistance test is performed, in particular the final inspection after the pressure resistance test) In addition to discoloration due to rust, there is also discoloration due to heat effects. As a result, the background (surface of the object 1 to be inspected) changes to a brown color (brown, reddish brown, blue brown, etc.) or blue-black. The discoloration to brown is mainly due to rust, and the discoloration to blue-black is mainly due to the influence of heat treatment. The heat treatment referred to in this specification means a post-weld heat treatment (PWHT) in which a welding site is heated to a specified temperature for the purpose of removing harmful effects such as residual stress.

  Thus, when black magnetic powder is applied in a state where the surface of the device under test 1 is discolored, it is difficult to visually identify the magnetic powder pattern. Therefore, in the present invention, as shown in FIG. 1 (A), before spraying magnetic powder on the surface of the object 1 to be inspected, the paint 3 having a higher brightness than the color of the surface of the object 1 is inspected. Apply to the surface of the body 1 examination site. As described above, since the discoloration due to the effects of rusting or heat treatment is a brown color (brown, reddish brown, blue brown, etc.) or blue-black, the paint 3 having a lightness higher than these colors is inspected. By applying to the surface of the body 1, the contrast between the background and black (the color of magnetic powder to be applied) is increased. The color of the paint 3 is preferably as bright as possible as compared with the color of the surface of the object 1 to be inspected, and white, yellow, ivory, beige, and other colors having lightness comparable to these are preferable. In particular, white is optimal because it has the largest brightness difference from black.

  If the coating material 3 is applied too thickly, fine defects on the surface of the object to be inspected 1 may be embedded with the coating material 3 and the defect may not be detected. Therefore, the application means may be brush application, but it is preferable to apply by spray (aerosol) 4 as shown in FIG. After applying the paint 3, it is sufficiently dried.

  Next, as shown in FIG. 1B, an appropriate magnetic field is applied to the device under test 1 using the magnetizer 5 to magnetize the device under test 1. The dotted line arrow in the figure indicates the magnetic flux. In the present embodiment, an example in which a flaw detection inspection is performed on the welded part 2 is shown. Therefore, an interpole method in which the inspection part is magnetized by placing it between the magnetic poles of the magnetizer is applied, but depending on the shape of the inspection object 1 Of course, other appropriate magnetization methods (axial conduction method, brood method, current penetration method, etc.) may be applied. The magnetizer 5 is composed of an electromagnet or a permanent magnet.

  Next, black magnetic powder is sprayed on the surface of the inspection site of the magnetized inspection object 1. In the magnetic particle inspection method, there are a dry type in which the magnetic powder is dispersed in powder form, and a wet method in which the magnetic powder is dispersed using a magnetic powder liquid dispersed in a liquid such as water or oil. Although this method is also applicable, it is preferable to apply a wet method capable of uniformly dispersing magnetic powder. In the case of the wet type, the magnetic powder can be dispersed by applying the magnetic powder liquid to the surface of the inspection object 1 using a dropper or a spray.

  When the magnetic powder is dispersed on the surface of the object 1 to be inspected, as shown in FIG. 1C, the magnetic powder is magnetized by the leakage magnetic flux generated in the defect to become a micro magnet and adsorbed on the defective portion. Is formed. Since the magnetic powder pattern is formed with a width several to several tens of times larger than the actual width of the defect, the defect can be detected visually by observing the magnetic powder pattern.

According to the magnetic particle flaw detection method of the present invention described above, the discoloration due to the influence of rusting or heat treatment is a brownish color (brown, reddish brown, blue brown, etc.) or blue-black color, and thus has a higher brightness than these colors. By applying the color paint 3 to the surface of the object 1 to be inspected, the contrast between the background and black (the color of the magnetic powder to be applied) is increased. Therefore, the visual discrimination of the magnetic powder pattern is enhanced and the visibility is improved.
Therefore, according to the present invention, even when the surface of the inspected object 1 is changed to a brown color or blue-black color due to rusting due to the passage of time after welding or the influence of heat treatment, it is equivalent to the case of fluorescence flaw detection. And the excellent effect that the detection accuracy of defects can be improved.

[Example]
In order to verify the effect of the present invention, a verification test was performed using the test piece under the following test conditions.
(1) Magnetic powder: Black magnetic powder (Eijin Chemical / MK-10)
(2) White paint: AOTAKESOL
(3) Surface condition: smooth grinding + white paint (4) Magnetizer: Handy Magna A-2 manufactured by Eishin Chemical
(5) Magnetization method: Inter-pole method (6) Magnetization time: 5 sec. (7) Magnetization interval: 105 mm
(8) Magnetization current AC
(9) Magnetic powder concentration: 1.8 ml (magnetic powder precipitation volume) / 100 ml (unit volume)
(10) Inspection method: ASME Code Sec. V, ARTICLE 7, 2004 Edition without Addenda

As a result of this verification test, it was confirmed that the magnetic powder pattern appeared in black against the white background, and sufficient visibility was obtained.
In addition, as shown in FIG. 2, holes are provided at positions of 0.5 mm, 1.0 mm, 2.0 mm, 3.0 mm, and 4.0 mm from the surface of the test piece, respectively, and the magnetic powder pattern appears up to the number of holes. The detection sensitivity was judged depending on whether it increased. As a result, the formation of a magnetic powder pattern was recognized up to the third one (depth 2.0 mm from the surface), and it was confirmed that the same detectability as that of conventionally used fluorescent magnetic powder was obtained.

  It should be noted that the present invention can also be applied to dark painted surfaces. It was confirmed by a separate test that even if the inspection site was a coated surface covered with a relatively thick coating film (thickness 0.2 mm), it had sufficient detectability.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

It is a figure explaining the magnetic particle flaw detection method concerning embodiment of this invention. It is a figure explaining the Example of this invention.

Explanation of symbols

1 Inspected object 2 Welded part 3 Paint 4 Spray 5 Magnetizer

Claims (4)

In the magnetic particle flaw detection method for detecting defects based on the magnetic powder pattern shown on the surface of the magnetized object to be inspected by spreading magnetic powder on the surface of the object to be inspected made of a ferromagnetic material.
Using black magnetic powder as the magnetic powder,
A magnetic particle flaw detection method, comprising: applying a paint having a lightness higher than the color of the surface of the test object to the test object before spraying the magnetic powder on the surface of the test object.   The magnetic particle flaw detection method according to claim 1, wherein the paint is white.   3. The magnetic particle inspection method according to claim 1, wherein the surface of the object to be inspected before applying the paint is a brown color or bluish black.   The time at which the flaw detection inspection is carried out after rusting occurs on the surface of the object to be inspected after welding of the object to be inspected, or after discoloration due to the effect of heat treatment after welding performed on the object to be inspected The magnetic particle flaw detection method according to any one of claims 1 to 3.

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