JPH08145922A - Method for inspecting defect of painting and coating material - Google Patents

Abstract

PURPOSE: To provide a method for inspecting a defect of a painting and coating material for detecting the defect such as an air void produced on a steel tube coated with the painting and coating material. CONSTITUTION: A site welding joint part 2c of a coated steel tube 2 is coated with an anticorrosion painting and coating layer material 1 through a bonding agent layer, and heated by a heat source such as a gas burner 6. The anticorrosion painting and coating layer material 1 is contracted thermally, and after the anticorrosion painting and coating layer material 1 is cooled, it is heated. The temperature distribution is observed by an infrared ray camera 3, and a method for inspecting a defect of the painting and coating material for detecting a defect part such as an air void from a part of slow cooling speed is provided by supplying an image processor with a heat image signal of the infrared ray camera 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting defects in an anticorrosion coating material for coating a welded joint portion of a coated steel pipe, and more particularly,
The present invention relates to a defect inspection method for inspecting defects such as floating and swelling of the anticorrosion coating covering material of a welded joint.

[0002]

2. Description of the Related Art Generally, at a piping site using a coated steel pipe such as a polyethylene coated steel pipe, a heat shrinkable tube or sheet made of a synthetic resin material such as cross-linked polyethylene is welded to prevent corrosion of the on-site welded joint. After covering the part,
The heat-shrinkage is performed to bring the steel pipe and the heat-shrinkable tube into close contact with each other to prevent corrosion of the welded joint. As shown in FIG. 6, the anticorrosion coating covering material for performing the anticorrosion treatment on the on-site welded joint portion of the coated steel pipe is prepared by mixing various additives into the anticorrosion layer 2b made of a heat shrinkable synthetic resin material and a mixture of asphalt and rubber. When the on-site welded joint portion of the coated steel pipe 2a is heat-shrinked and coated with the anticorrosion layer 2b, the anticorrosion treatment is performed.
If a large number of air voids 9 are present between the steel pipe 2a and the adhesive 2d, the reliability of the steel pipe 2a with respect to anticorrosion will decrease.

In order to solve such a problem, in the work process of the anticorrosion coating treatment, it is inspected whether the outer periphery of the welded joint portion is normally covered with the anticorrosion coating covering material. There is a process called. The inspection method is usually performed by visual inspection, touching with a finger, or the like. There is also a method of peeling a part of the anticorrosion coating material and inspecting for the presence of air voids. In this peeling and inspection method, the portion must be repaired after peeling.

A method for inspecting air voids with an infrared camera has not existed in the past, but a method for inspecting the wall thickness of the anticorrosion coating on the inner surface of a steel pipe is described in Japanese Patent Laid-Open No. 12045/1990. . However, this method is for detecting a thin defect portion of the anticorrosion coating and is a method for detecting while cooling and a temperature difference remains, and spatially differentiating the temperature distribution to detect the defect portion. However, this detection method has no concept of differentiating the temperature distribution with respect to time. Further, a method of detecting the water-containing portion of the covered pipe from the surface temperature distribution obtained by taking a thermal image is disclosed in Japanese Patent Laid-Open No. 6-11840. In this method, since the heat transfer coefficient greatly differs between the air layer and the water-containing portion, the water-containing portion is detected by the temperature distribution generated by the difference. However, the water is not detected by specially heating the pipe.

[0005]

Conventionally, the on-site welded joint portion of the coated steel pipe has been subjected to the anti-corrosion treatment by covering the on-site welded joint portion by heat-shrinking the anticorrosion coating material. At that time, if a large number of air voids are generated between the anticorrosion coating material and the steel pipe, the reliability of the coating material against corrosion is reduced. Conventionally, a method of visually inspecting an air void or touching it with a finger can detect a relatively large one. However, if it is small, it is difficult to confirm its existence, and
The method of inspecting the entire covering portion by touching the finger is extremely troublesome for the operator. Furthermore, when the number of air voids is large, it is difficult to specify the position and size thereof. Further, when abnormality was felt by visual inspection or finger touch, a part of the anticorrosion coating was peeled off and inspected. This peeled portion needs to be repaired, and this repair takes time, resulting in a high cost.

In view of the above, in the anticorrosion treatment, it is desired to develop a method for detecting defects such as air voids generated between the steel pipe and the anticorrosion coating material by the nondestructive inspection method. As a conventional nondestructive inspection method, there is a method of detecting a water-containing portion from a temperature distribution using an infrared camera. However, when detecting the water-containing portion in the pipe covered with the heat insulating material, the pipe is not externally heated. Therefore, there is a drawback that it is difficult to inspect a defective portion such as a very small air void or a defective adhesion portion.

The present invention has been made in view of the above problems, and provides a method for inspecting a coating material defect for detecting defects such as air voids generated in a steel pipe coated with the coating material. The purpose is to do.

[0008]

In order to solve the above-mentioned problems, a method for inspecting a coating-covering material defect according to the present invention comprises heating a coating-covering material covered on a field welded joint of a coated steel pipe. The method is characterized by cooling the temperature of the coating and covering material and observing the temperature distribution with an infrared camera to detect the occurrence of air voids from a location with a slow cooling rate. In the defect inspection method for the coating / covering material, the temperature distribution of the coating / covering material is observed by an infrared camera for infrared rays reflected by a mirror. Further, in the defect inspection method for the coating / covering material, the heating temperature of the coating / covering material is set to be higher than the initial temperature by 1 to 200 ° C.
Further, in the defect inspection method for the coating and covering material, the cooling temperature distribution of the coating and covering material is differentiated with respect to time, and the size of the air void is inspected from the distribution.

[0009]

According to the above-mentioned means, the defect inspection method for the coating material according to the present invention comprises the steps of heating the anticorrosion coating material for coating the on-site welded joint of the coated steel pipe, and then heating the steel pipe and the anticorrosion coating material. If a defective part such as an air void or a poorly adhered part occurs between the parts, the air in the defective part becomes a heat insulating layer, and the cooling speed of this part is slow This is a detection method for detecting a relatively small defective portion by detecting the temperature distribution due to. Moreover, the defect inspection method of the coating / covering material according to the present invention is a detection method in which infrared rays radiated from the anticorrosion coating / covering material using a mirror are reflected and measured in the direction of the infrared camera, and the temperature distribution is detected. Defects can be detected even in difficult areas. Furthermore, the temperature detected by the infrared camera is lower than the actual surface temperature, but by obtaining the thermal image signal obtained by reflection by time differentiation, the difference in relative cooling rate is made clearer and the air void is made clearer. It is to confirm the existence of a defect such as a contact failure portion or the like.

Further, in the defect inspection method for the coated covering material according to the present invention, the detection of the defective portion such as the air void or the defective adhesion portion is obtained by time-differentiating the thermal image signal obtained by the infrared camera by the image processing device. The contour of the defective portion is made clear from the information, and its size is accurately detected. Also,
The defect inspection method of the coating / covering material according to the present invention, after performing a step of heating and shrinking the coating / coating material by heating during the anticorrosion coating / coating treatment, it is naturally cooled to cause a partial difference in temperature drop. Since it is possible to detect the presence of the air voids, it is possible to detect the defective portion without performing a heating step for nondestructive inspection.

[0011]

Embodiments of the present invention will be described below with reference to FIGS.
Will be described with reference to. (Embodiment 1) FIG. 1 is a diagram for explaining an embodiment of a defect inspection method for a coated covering material according to the present invention. In the figure, a coated steel pipe coated with an anticorrosion coating material, a measuring device and a heat source are shown, and welding and anticorrosion treatment of the coated steel pipe 2 are carried out in a local piping process. Referring to the figure,
The piping process of the coated steel pipe 2 will be briefly described. First,
After the coating material 2b is peeled off to expose the steel pipe 2a, the steel pipes 2a are welded to each other. The welded joint portion 2c and the covering material 2b are covered with the anticorrosion coating material 1, and then the anticorrosion coating material 1 is heated and shrunk by a heat source such as a gas burner 6 to expose the welding portion 2c and the steel pipe 2a. The portion and the covering material 2b are brought into close contact with each other. The anticorrosion coating material 1 is in the form of a heat-shrinkable resin tube or sheet, and the back surface thereof is provided with, for example, an adhesive layer in which various additives are mixed in a mixture of asphalt and rubber. . The adhesive layer is melted by heating and becomes viscous.

After the above-described anticorrosion treatment process is performed, the process proceeds to a defect inspection process for the presence / absence of a defect such as an air void or a poor adhesion portion, which is one embodiment of the defect inspection method for the coating material. First, after the portion heated in the anticorrosion treatment step is once cooled to room temperature, a new infrared lamp, laser light,
The anticorrosion coating material 1 is heated by a gas burner or an electric heater. Then, the heat-shrinked anticorrosion coating material 1 is naturally cooled and the temperature distribution is measured. The temperature distribution is measured by the infrared camera 3, the thermal image signal thereof is input to the image processing device 4 such as a computer to perform image processing, and the temperature distribution on the surface of the anticorrosion coating material 1 is observed to detect the air voids. Detecting defective parts such as or defective adhesion. As another inspection method, after the portion heated in the anticorrosion treatment step is cooled for a predetermined time, the infrared camera 3 may measure the temperature distribution of the surface portion to detect the defective portion. The surface temperature of the anticorrosion coating material in each processing step of the anticorrosion processing step and the defect inspection step is observed while being observed by the infrared radiation thermometer 7.

The effectiveness of measuring the temperature distribution by an infrared camera in the defect inspection method for air voids and poor adhesion will be described below based on experimental results. This will be described with reference to FIG. In this experiment, a 750A polyethylene-coated steel pipe 2 was welded, and its weld joint portion 2c was coated with an anticorrosion coating covering material 1 (for example, heat-shrinkable resin for 750A, thickness 3mm) to artificially increase the diameter to 6mm. A 20 mm air void was formed. After the anticorrosion coating material 1 was heat-shrinked, it was once cooled to room temperature, and again the anticorrosion coating material 1 was heated with an infrared lamp or the like to measure the surface temperature distribution to detect air voids. The inspection result is shown in FIG. In FIG. 2, the horizontal axis shows the heating temperature from the heating from the initial surface temperature of the anticorrosion coating material, and the vertical axis shows the number of judgments in 10 air voids. The broken line (a) in the figure has a diameter of 6
The number detected for each surface temperature of the air void of mm is shown, and the solid line (b) shows the number detected for each surface temperature of the air void having a diameter of 20 mm.

As is apparent from FIG. 2, about 3 ° C. to about 3 ° C.
In the range of 5 ° C., 100% (10/10) of the air voids indicated by the broken line (a) and the solid line (b) are both detected.
In the case of the broken line (a), 70% (7 pieces /
10) were detected, 80% (8/10) air voids were detected in the range from about 35 ℃ to 130 ℃, and 1
The detection rate gradually decreases in the range of 30 ° C to 200 ° C. On the other hand, in the case of the solid line (b), it is 8 when it is about 1 ° C.
0% (8/10) detected, about 35 to 160
90% (9/10) of air voids are detected in the range up to ° C, and the detection rate gradually decreases in the range from 160 ° C to 200 ° C.

From this result, the most suitable surface temperature range for detecting air voids is 3 to 3 from the initial surface.
It has been shown that a temperature of 5 ° C. higher is suitable. But,
If the detection rate is reduced to 50%, it depends on the diameter of the air void, but when the diameter is 20 mm, the surface temperature is 1 to 1
It is possible to detect up to 80 ° C higher temperature. Furthermore, even an air void having a large diameter can be detected up to 200 ° C. As described above, the detection rate depends on the diameter of the air void, but generally the surface temperature of the anticorrosion coating material is 1 ° C or higher and 20
Air voids can be detected in the range up to 0 ° C.
It is also clear that this detection rate also depends on the thickness of the anticorrosion coating material. Further, in FIG. 2, the detection rate decreases when the heating temperature is set to 1 ° C. This is because the detection rate decreases because the temperature difference itself between the sound portion and the defective portion also decreases.

Next, Tables 1 and 2 show the difference in detection rate between the conventional inspection method and the inspection method of the embodiment. Table 1 shows that the anticorrosion coating material was heat-shrinked to adhere to the steel pipe, and after cooling to room temperature,
The heating temperature of the anticorrosion coating material is 20 from the initial surface temperature.
The detection rate is shown by an experimental result of inspecting a defective portion by setting the temperature higher by ℃, and the conventional inspection method is visual inspection or finger touch. Table 2 shows the results of an experiment in which, during the anticorrosion coating treatment, the anticorrosion coating covering was heated and shrunk, and then naturally cooled to perform detection.

[0017]

[Table 1]

According to the experimental results shown in Table 1, an air void having a diameter of 6 mm could not be detected by the conventional visual or finger touch method. However, in the method of Example 1, 10
0% detection was possible. Further, in the case of an air void having a diameter of 10 mm, 30% (3/10
However, in Example 1, 100% could be detected. In addition, in the experimental results shown in Table 2, the detection rates when the diameters of the air voids are 10 mm and 20 mm were compared between the method by visual observation and finger touch and the method according to the example.

According to the experimental results shown in Table 2, when the diameter of the air void is 10 mm, 10% (1 piece /
The detection rate was 10), but 90% in the method of the example.
The detection rate was (9/10). Further, when the diameter of the air void is 20 mm, the detection rate was 30% (3/10) in the conventional method, but 100% in Example 1.
The detection rate was (10 pieces / 10 pieces). The position of the air void was confirmed by a peeling test. Further, as shown in Tables 1 and 2, it is shown that some errors occur in the inspection, as is clear from the results when the air void diameter is 10 mm.

Next, the measurement conditions for detecting defects such as air voids will be described in detail with reference to FIG. The vertical axis of FIG. 3 represents the surface temperature of the anticorrosion coating, and the horizontal axis represents the cooling time. In the figure, a indicates the initial surface temperature of the anticorrosion coating material of the coated steel pipe coated with the anticorrosion coating material. b
Indicates the heating temperature, and c indicates the measurement temperature range.
(A) is a temperature cooling curve of a portion that is soundly bonded, and (B) is a temperature cooling curve of a defective portion such as an air void.

Explaining the measurement conditions shown in FIG. 3, the anticorrosion coating material covering the on-site welded joint of the coated steel pipe is heated so that its surface temperature is 10 ° C. to 2 ° C. higher than the initial surface temperature a.
Heated to 0 ° C. higher temperature. After that, the result of natural cooling and measurement of the temperature distribution at every predetermined elapsed time is shown.
The measurement temperature was 1.8 to 4.2 ° C. higher than the surface temperature, and the sensor sensitivity was 0.3 ° C. When the sensitivity of the sensor is high, the color distribution showing the temperature distribution fluctuates drastically with time, which causes a decrease in the detection efficiency. The change of the color showing the temperature distribution becomes gentle with respect to the change,
It was found that the detection efficiency is good when detecting air voids. That is, the detection efficiency can be improved by arbitrarily setting the temperature sampling time.

However, since these results affect the material and thickness of the anticorrosion coating material, these values differ depending on the specific heat and thickness of the material and the heating temperature. The air in the air voids or the poorly adhered portion serves as a heat insulating device, and the temperature distribution is inspected by focusing on the slow cooling rate to detect defective portions such as air voids. The temperature cooling curves (a) and (b) of the defective portion (air void) and the sound portion in FIG. 3 are shown as a model in order to facilitate understanding of the present invention.

(Embodiment 2) FIG. 4 is a view for explaining another embodiment of the defect inspection method for the coating covering material. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals. In the figure, the heat shrinkage of the anticorrosion coating covering material 1 is performed using a gas burner, and the anticorrosion coating covering material 1 covers the on-site welded joint 2c, the exposed portion of the steel pipe 2a and the covering material 2b to prevent corrosion. Processing is being done. After the temperature of the heat-shrinked anticorrosion coating material 1 is naturally cooled, the anticorrosion coating material 1 is heated using an infrared heater (or panel heater) 8. Then, after a lapse of a predetermined time obtained from the cooling curve of FIG. 3, the infrared camera 3 measures the temperature distribution of the surface portion. An image signal from the infrared camera 3 is input to the image processing device 4 such as a computer through the cable 5 to detect defective portions such as a void or a defective adhesion portion. In this case as well, the detection rate of defective portions such as a void and a poorly adhered portion is as described above. In addition, by heating the anticorrosion coating material 1 using a sheet-shaped heater (infrared heater or panel heater), a large area can be heated at one time.
The temperature distribution can be easily observed, which is good for improving the detection efficiency.

(Embodiment 3) FIG. 5 is a view for explaining another embodiment of the defect inspection method for the coating covering material. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals. In the same figure, as in the second embodiment, the anticorrosion coating material 1 is heated and contracted by using the infrared heater 8, and the anticorrosion coating material 1 is welded to the welded portion 2c and the exposed portion of the steel pipe 2a to the coating material 2b. Covering.
Then, the anticorrosion coating material 1 is heated and shrunk and once cooled, then the anticorrosion coating material 1 is heated and the infrared camera 3 measures the temperature distribution of its surface portion through the mirror 10. To measure the temperature distribution, infrared rays emitted from the anticorrosion coating layer material 1 are reflected by a mirror 10 and the infrared rays are taken by an infrared camera 3, and an image signal from the infrared camera 3 is processed by a computer such as a computer through a cable 5. Input to the device 4. The surface temperature of the coating material 1 at the time of heat treatment is measured by the infrared radiation thermometer 7. Next, Table 3 shows a comparison of air void detection rates according to the conventional example of Example 3j.

[0025]

[Table 2]

Table 3 shows the results of inspecting by artificially forming 10 air voids by the method according to the example and the conventional example. When compared with the conventional visual inspection and finger touch inspection, detection was not possible when the air void diameter was 6 mm, but according to Example 3, 90% (9/10) detection was possible. there were. When the diameter was 20 mm, the conventional inspection method had 30% (3/10 pieces), while the inspection methods of Examples 1 and 2 detected 100%. In this embodiment, when the diameter is 6 mm as compared with the method of directly detecting the temperature distribution, the detection rate of the defective portion is slightly lowered as compared with the case of directly detecting the surface temperature of the anticorrosion coating material 1. There is. However, by using a mirror to detect the defective portion, inspection can be facilitated even in a portion where measurement is difficult.

(Embodiment 4) Next, another embodiment of the method for inspecting defects of a coated covering material according to the present invention will be described. Incidentally, the arrangement of the object to be inspected, the measuring device and the like is based on the same method described in FIGS. In this embodiment, a defect such as an air void is detected based on an image signal obtained by time-differentiating the temperature distribution of the anticorrosion coating material.

As shown in the above embodiment, after artificially forming air voids having diameters of 6 mm and 15 mm in the anticorrosion coating material, the anticorrosion coating material is heated to obtain an image signal obtained from the cooling process. Is time-differentiated to detect a defective portion. In the image obtained by differentiating with time, the outline of the defect becomes clearer and the size of the air void becomes clearer. Therefore, after detecting the temperature distribution of the anticorrosion coating using a mirror,
Even if the detection efficiency is slightly lowered by performing the time differentiation, the boundary can be made clearer, so that the detection rate can be increased. Further, by performing time differentiation processing on the image signal, it is possible to obtain a better detection result than the above-described detection result.

[0029]

[Table 3]

This measurement result indicates that the measurement error is small as compared with the conventional inspection method by differentiating the image signal with respect to time. In the conventional inspection method, when the air void diameter is 6 mm, a measurement error of 19% occurs, whereas in the inspection method of the present invention, a measurement error of only 7% occurs. Further, when the diameter of the air void is 15 mm, a measurement error of 12% occurs, whereas in the inspection method according to the present invention, a measurement error of only 5% occurs. As is clear from this result, the method of differentiating the thermal image signal of Example 4 with respect to time increases the accuracy of detecting a defective portion. Furthermore, the result is
The same applies to the first to third embodiments described above. Therefore, by differentiating the thermal image signal with time, it means that the measurement conditions are relaxed, and the detection rate can be further increased. Further, since the contour of the defective portion becomes clear and the position can be easily specified, the defective portion can be repaired in a short time.

[0031]

As described above, according to the present invention, it is possible to easily detect the presence and position of defects such as floating and swelling of the anticorrosion coating covering material that covers the on-site welded joint portion of the coated steel pipe. Is. Conventionally, a defective portion such as an air void has been detected by visual inspection or touch with a finger, but the defective portion is not sufficiently detected, and the reliability of anticorrosion is not perfect. However, according to the inspection method of the present invention, defects such as small aevoids can be detected in about 10
It is possible to detect 0%, and since the position can be easily specified, there is an advantage that repairing the defect does not take time and the defect can be easily repaired. There is an advantage that the reliability of anticorrosion is further enhanced.

Further, in the defect inspection method for the anticorrosion coating material, the defect is relatively detected by detecting the infrared ray reflected by the mirror to detect the temperature distribution on the surface of the anticorrosion coating material. There is an advantage that even a difficult part can be easily detected. Further, there is an advantage that the detection rate can be further increased by subjecting the thermal image signal to the time differential processing in the image processing apparatus. In addition, the anti-corrosion coating is formed by heat treatment during the anti-corrosion construction of the on-site welded joint.By cooling this heated anti-corrosion coating and measuring its temperature distribution, it is possible to detect aevoid, etc. It is possible, and it is possible to omit the step of newly heating when performing the inspection after the anticorrosion construction.

[Brief description of drawings]

FIG. 1 is a diagram showing an arrangement of an object to be inspected and a measuring device in a defect inspection method for a coating covering material according to the present invention.

FIG. 2 is a diagram showing the number of defects determined with respect to the heating temperature in the defect inspection method for a coated covering material according to the present invention.

FIG. 3 is a diagram showing, as a model, a temperature cooling curve of a defective portion and a sound portion of the coating material covering the field welded joint.

FIG. 4 is a diagram showing another arrangement of the object to be inspected and the measuring device in the defect inspection method for the coating covering material according to the present invention.

FIG. 5 is a diagram showing another arrangement of the object to be inspected and the measuring device in the defect inspection method for the coating covering material according to the present invention.

FIG. 6 is a cross-sectional view showing an air void.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Anticorrosion coating material 2 Coating steel pipe 2a Steel pipe 2b Coating material 2c Weld joint part 2d Adhesive layer 3 Infrared camera 4 Image processing device 5 Cable 6 Gas burner 7 Infrared radiation thermometer 8 Infrared heater 10 Mirror

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Tadashi Kawamura, 1-2, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Motofumi Hirata, 1-2, Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. An on-site welded joint of a coated steel pipe is heated by heating a coating material comprising an adhesive layer and anticorrosion equipment, the temperature of the coating material is cooled, and the temperature distribution is observed by an infrared camera. Then, a method for inspecting defects of a coated covering material is characterized in that the occurrence of air voids is detected from a location having a slow cooling rate. 2. The defect inspection method for the coating and covering material according to claim 1, wherein the temperature distribution of the coating and covering material is observed by an infrared camera for infrared rays reflected by a mirror. 3. The heating temperature of the coating and covering material is set to be 1 to 200 ° C. higher than the initial temperature.
The method for inspecting defects of the coating and covering material according to. 4. The defect of the coating material according to claim 1, wherein the temperature distribution of the coating material is differentiated with respect to time and the size of the air void is inspected from the distribution. Inspection methods.