JPS599502A - Method for inspecting pipe whose inner surface is painted - Google Patents

Abstract

PURPOSE:To inspect the quality of a painted film along the entire length by a nondestructive means, by providing an inspecting brush at the inner surface of a pipe, whose inner surface is painted, providing a current collecting ground part at the outer surface of the pipe, applying a DC voltage across both parts, and detecting the potential difference. CONSTITUTION:A metallic inspecting brush 6, which is connected to a positive electrode side, is inserted into the inner surface of a pipe 5, whose inner surface, is painted. A current collecting ground part 7, which is connected to a negative electrode, is provided at the outer surface of the painted pipe 5. A low DC voltage, which is 50V or less, is applied across the brush and the ground part. Said brush 6 and the ground part 7 are made to move in the direction of the axis of the pipe, and the potential difference is obtained and recorded by a specified control part. When a defective part is present in the painted film formation, the potential becomes small and the defective part is located. Thus completeness of the painted film can be inspected along the entire length by a nondestructive means.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inspection method for internally coated pipes, and in particular to a method for determining whether the coating condition of the painted part on the inner surface of the pipe is good or bad without destroying the pipe. It is about how it can be done.

BACKGROUND ART Internally coated pipes, in which the inner surface of the pipe is coated with a predetermined coating, have been used in various fields for the purpose of preventing rust and corrosion. For example, in thermal and nuclear power plants,
High-temperature, high-pressure steam is used as power in steam turbines for power generation, but in order to increase turbine efficiency, improve the thermal efficiency of the plant, and further condense and recover turbine steam, the steam outlet of the steam turbine is A condenser is installed on the side.

The condenser is equipped with a large number of small-diameter pipes, and cools the turbine steam outside the pipes by passing cooling water such as seawater through the condenser.
The water condenses and reduces the back pressure of the turbine.

Therefore, the condenser tube is required to have excellent corrosion resistance such as rust prevention and corrosion resistance against cooling water such as steam and seawater. In order to improve the corrosion resistance against cooling water such as seawater, the inner surfaces of heat exchanger tubes are coated, or pre-coated tubes are used.

Since the purpose of this type of heat exchanger tube is to efficiently exchange heat, it is necessary to paint it to improve corrosion resistance so that heat conduction is significantly reduced. It is necessary to control the thickness of the paint film so as not to impair heat transfer performance. For example, when painting the inner surface of a condenser pipe, the thickness of the paint film must be approximately 5 to 10 μm. There is.

As described above, in the various fields in which internally coated pipes are used, it is necessary to control the thickness of the coating film applied to the inner surface, the condition of the coating film, etc. in various ways.

By the way, in the past, various methods have been proposed for inspecting painted products. For example, when inspecting the coating thickness on the outer surface of plate products and pipes, eddy current flaw detection has been used as a non-destructive testing method. Methods have been adopted, and samples have been actually inspected to achieve the intended purpose. However, the thickness of the coating film formed on the inner surface of the pipe cannot be measured by the method of destructively inspecting the entire length. Since it is difficult to insert this, it has rarely been proposed, and currently no method has been found that is worthy of being practically adopted.

The present invention has been made in view of the above circumstances, and its purpose is to inspect the integrity of the coating film applied to the inner surface of a metal pipe over its entire length using a non-destructive method. The purpose of the present invention is to provide a practical method for inspecting the inner surface of a metal pipe whose inner surface is coated with a predetermined coating. moving the first contacting means in the axial direction of the tube while making contact, while attaching the second contacting means to the outer surface of the painted tube, and applying a predetermined DC voltage between the two contacting means, By detecting the potential difference between the first contact means and the second contact means, the condition of the painted portion on the inner surface of the painted tube is evaluated.

As described above, in the present invention, by utilizing the insulation properties of the coating film applied to the inner surface of the tube and the conductivity of the metal tube itself, the change in the potential difference between them is applied to the inner surface of the tube. Since the objective is to evaluate the thickness of the painted surface and the health of the paint film, there is no need to destroy the tube to expose the inner surface of the tube, and the entire length of the tube is skillfully inspected. This made it possible to test for In particular, the method of the present invention can be effectively employed to non-destructively inspect the integrity of the ultra-thin insulating coating of about 5 to 50 microns applied to the inner surface of the heat exchanger tube over its entire length. It is.

In order to carry out the method of the present invention, an apparatus having a power supply section 1, a control section 2, a detection section 3, and a recording section 4 is used, for example, as shown in FIG. The result is that

The power source l in this device is a device that supplies a predetermined direct current voltage at a constant voltage, and the power source voltage is practically variable.

Note that the voltage input from this power supply section l is generally a low voltage or
It is desirable to employ a voltage of usually about 50V or less, preferably 30V or less, particularly preferably 20V or less. Furthermore, by adopting such a low voltage, there is the advantage that dielectric breakdown of the coating film can be effectively prevented, and such an advantage is particularly effective in heat exchanger tubes where the coating film thickness is approximately 5 to 50μ. It is demonstrated effectively. Further, the lower limit of the voltage is related to the length of the inner-coated pipe to be inspected, the material of the pipe, etc., but generally a value of 1 V or more is adopted.

Further, the control unit 2 is a device that controls the detection unit 8 and the recording unit 4 according to the voltage supplied from the power supply unit l,
A predetermined voltage is applied to the detection section 3, the signal from the detection section 3 detected as a potential difference is processed, and the processed result is output to the recording section 4.

Furthermore, the detection unit 3 includes a first contact means that is moved in the axial direction of the inner surface of the pipe to be inspected while contacting the inner surface of the pipe, and a second contact means that is attached to the outer surface of the coated pipe. are connected to the control section 2 so that a predetermined DC voltage is applied between the two contact means.

Specifically, as shown in FIG. 2, an inspection brush used for inspecting the inner surface coating film is connected to the anode side and is inserted and moved into the inner surface coated tube 5 to be inspected. 6, and a current collecting ground 7 which is fixedly attached to the outer surface of the painted tube 5 to transmit voltage and is connected to the cathode side. The potential difference between them is grasped by the control unit 2, and predetermined processing is performed. In particular, this inspection brush 6 has a large size that makes it possible to contact the inner surface of the inner-coated pipe 5 over the entire circumference in the pipe circumferential direction, and to satisfactorily evaluate the state of the coating film at the position in the pipe where the brush 6 is located. It has characteristics.

Note that this inspection brush 6 is of course made of metal and has good conductivity, but its material and structure do not adversely affect the coating film formed on the inner surface of the painted tube 5 due to the strength of the coating film. These will be selected as appropriate. Of course, it is also possible to use other suitable contact means in place of such an inspection brush. In addition, the terminals to which the inspection brush 6 and the current collecting ground 7 are connected may be reversed from the upper side in some cases, and the inspection brush 6 may be connected without fixing the current collecting ground 7. Similarly, it is also possible to move it in the tube axis direction while making contact with the tube outer surface.

Then, the recording section 4 records the signal from the control section 2, that is, the signal output from the control section 2 according to the potential difference detected at the detection section 8, and records the signal from the control section 2, It is designed to judge the quality of the painted part at the position of the brush 6) in the inner surface painting tube 5, such as the thickness of the paint film and its health.

Therefore, according to this configuration, the electrical insulation properties of the paint in the coating film formed on the inner surface of the painted tube to be inspected allow the first contact means (6) and the second contact means (7
) is suppressed or blocked, and a large potential difference is generated between the two, and the state of the coating film is evaluated based on the value of that potential difference.

If a coating film is not formed on the inner surface of the painted tube 5 due to a coating defect, the first contact means (6) reaches the uncoated portion and comes into contact with the inner wall (base) of the tube. A good electrical continuity is established between the first contact means (6) and the second contact means (7), so that the potential difference between them becomes small, and therefore such a small potential difference By detecting the formation of a coating defect on the inner surface of the tube, the presence of a coating defect is discovered.

As described above, in the present invention, the thickness and health of the coating on the inner surface of the tube are detected and evaluated as changes in the potential difference using the electrical insulation properties of the coating, so it can be effectively and non-destructively measured. This method makes it possible to inspect the entire length of the inner-coated pipe, and this is where the great industrial significance of the present invention lies.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an apparatus for carrying out the method of the present invention, and FIG. 2 is an explanatory diagram showing an example of the structure of a detection section in the apparatus of FIG. 1. 1: Power supply section 2: Control section 3: Detection section 4: Recording section 5: Inner surface coating tube 6; Inspection brush 7: Current collecting ground Applicant Sumitomo Light Metal Industries, Ltd. = l〇-

Claims (3)

[Claims] (1) While the first contact means is moved in the axial direction of the pipe while bringing the inside of the pipe to be inspected into contact with the inside of the pipe whose inner surface is coated with a predetermined coating, the outside of the painted pipe is moved. By attaching a second contact means to the surface, applying a predetermined DC voltage between the two contact means, and detecting the potential difference between the second contact means and the second contact means. A method for inspecting an inner surface coated pipe, characterized in that the condition of a painted part on the inner surface of the coated pipe is evaluated. (2) The first contact means is an inspection brush connected to the anode side, and the second contact means is a ground for the painted tube connected to the cathode side.
The method described in section. (3) The method according to claim 1 or 2, wherein the DC voltage is a low voltage of about 50V or less.