JPS5823563B2 - Corrosion wear detection method - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for detecting the degree of corrosion damage, particularly for boilers,
The location of the corroded part of the inner wall of the heat exchanger pipe, the underground pipe,
This invention relates to an optimal detection method for detecting the degree of corrosion and wear.

Heat exchangers with many tubes are often used in oil refining and other chemical industries, and many of these tubes are in a corrosive atmosphere, so periodic open inspections are performed to ensure their safety. δ It is necessary to check the durability, lifespan, etc. As a conventional non-destructive method for detecting the degree of wear of such pipes, there is the so-called eddy current flaw detection method, which is often used for austenitic stainless steel pipes, brass pipes, etc. .

This method uses an excitation coil and a detection coil to detect pipe flaws based on pulse signals from the detection coil, but the output pulses do not correspond to the depth of the corroded area and there is a limit to detection accuracy. There is.

In addition, the pipe material to be inspected must be a non-magnetic material, and therefore there are drawbacks such as the need for magnetic saturation measures for magnetic materials such as steel pipes.

Furthermore, there is a method of measuring tube wall thickness using radiation irradiation.
Disadvantages include that measurements are limited to one direction and that measurements are impossible when tubes are piled up in a bundle.

In addition, recently, inner surface observation using a fiberscope method has been used, but it has drawbacks such as being inefficient and easily overlooking worn parts.

In view of this, as a more reliable means of detecting wear and tear, for equipment with a large number of tubes, such as heat exchangers, by removing a representative tube and conducting a destructive inspection, it is possible to detect corrosion and wear on other tubes. At present, we are speculating about the situation.

However, such a sampling inspection is only a guess-based measurement, and is inefficient and uneconomical.

On the other hand, there are methods such as ultrasonic wall thickness method and direct measurement using a depth gauge, but these methods have the disadvantage that they are inefficient and cannot provide highly accurate measurements.

As a method for detecting the degree of corrosion damage without the above-mentioned drawbacks, the first method is
The system shown in the figure has been proposed.

That is, by arranging the conductor disks 1 and 2 at right angles to the longitudinal direction of the tube 3 to be inspected and with their circumferential surfaces close to the inner wall of the tube, and holding them with a cylindrical member, for example, the conductor disks 0
, 2 in the longitudinal direction while keeping the distance d constant.

For example, it is moved in the pipe from position (I) to position (II) as shown in the figure.

However, when the conductor discs 1 and 2 are charged with charges of opposite signs, the electric lines of force generated between the two discs are not all straight lines, but arcuate curves are drawn at the peripheral edge of the discs. ) The dielectric constant ε differs between an intact position such as position (II) and a position where a corroded portion 4 exists such as position (II) because the inner diameter of the tube is different.

As a result, the conductor disk 1 at the (I) position and the (n) position,
Since the capacitance CX between the two discs will be different, the parts of the discs 1 and 2 are incorporated into a bridge circuit 5 as shown in FIG.
A high frequency voltage is applied to the bridge circuit 5 by a high frequency oscillator 6, the unbalanced voltage is rectified by a rectifying diode 7, and the rectified output is amplified by an amplifier 8 and displayed by a voltmeter 9. Therefore, it is possible to detect the degree of

That is, at position (I), the reference capacitor Cs or the reference inductance coil L0. If L2 is selected, the capacity Cx when the disks 1 and 2 are moved to the position of the corrosion wear part 4
The output of the bridge circuit 5 increases due to a change in the output, and the degree of output change changes depending on the degree of corrosion and wear. Therefore, it is possible to know the degree of corrosion and wear by obtaining a calibration curve using the standard pipe material in advance. will be possible.

By the way, in order to detect the degree of corrosion loss based on the change in capacitance between the disks 1 and 2, a resonant circuit including the disks 1 and 2 is constructed instead of the bridge circuit 5 as described above, and the circuit is configured to detect the degree of corrosion due to the change in capacitance between the disks 1 and 2. It is possible to detect corrosion wear and tear based on the collapse of the resonance state.

FIG. 3 is a circuit diagram showing an example of this, where L3 is a primary coil connected to the high frequency oscillator 6, L is a secondary coil electromagnetically coupled to this primary coil, and this secondary coil and the above circle - The circuits of plates 1 and 2 constitute a resonant circuit, and the resonant voltage is rectified by a diode 7 and displayed by a voltmeter 9 via an amplifier 8.

If the circuit is adjusted so that the maximum resonant voltage is obtained at position (1) in Figure 1, then at position (II), the resonance relationship is broken due to the change in capacitance Cx, and the output voltage decreases, and since the degree of decrease changes depending on the degree of corrosion wear and tear, it is possible to know the degree of corrosion wear.

Therefore, this invention was made with the aim of realizing a simpler method for detecting the degree of corrosion wear by improving the detection method, and its feature is that Rather than using a conductive plate, the degree of corrosion and wear is detected by detecting the capacitance between the conductive material and the tube.

An embodiment of the present invention will be described below with reference to FIG.

10 is a cylindrical member made of an insulating material having an outer diameter slightly smaller than the inner diameter of the tube 3, and 11 is a ring made of a conductive material fixed to the outer circumference thereof.

Reference numeral 12 designates the bridge circuit shown in FIG. 2 fixedly housed within the cylindrical member 10, for example, by molding.

Note that the resonant circuit shown in FIG. 3 may be used instead of this bridge circuit.

Further, 14 is a lead wire connecting the tube 3 and the bridge circuit 1.2, and 15 is a display device provided outside the tube, which includes the above-mentioned amplifier 8 and voltmeter 9.

Note that a rectifying diode (not shown) is inserted and connected within the cylindrical member 10 to a lead wire 16 that connects the display device 15 and the bridge circuit 12.

This detection method detects the corroded portion 4 by detecting the capacitance between the inner surface of the tube 3 and the ring 11 as Cx in FIG.

That is, for example, the rings 11 are attached to both ends of the cylindrical member 10.
The detection probe 19 is completed by providing rings 17 and 18 made of insulating material with a larger diameter or a slightly smaller diameter than the inner diameter of the P tube 3. For example, compressed air is sent from the Q direction shown in the figure to move the detection probe 19 into the P tube. When moving in the direction, when the ring 11 made of conductive material is in a position where there is no wear on the inner surface of the tube 3, the capacitance between the tube 3 and the II song 1 is constant;
When the ring 11 is located at the corrosion wear part 4, the ring 1
1 and the inner surface of the tube becomes a dog, reducing the capacity.

Therefore, by incorporating the connection between the tube 3 and the ring 11 into one arm of the bridge circuit 5 shown in FIG. 2 instead of the electrodes 1 and 2, it becomes possible to detect the degree of corrosion and wear based on the above-mentioned principle.

In other words, if a pipe with corrosion damage is prepared in advance and the relationship (calibration curve) between the output voltage of the bridge circuit 5 and the degree of corrosion damage is determined, the degree of corrosion damage can be determined from the reading of the voltmeter 9. Can be done.

In place of the bridge circuit 5 in FIG. 2, the resonant circuit in FIG. 3 is used, and the capacitance Cx between the tube 3 and the ring 11 and the coil L are
It goes without saying that it is possible to detect the degree of corrosion damage even if a resonant circuit is formed with 4.

By detecting the capacitance between the tube 3 and the ring in this way, the configuration of the detection element is simplified.

Furthermore, compared to the method using a 1.degree. 2 disk as shown in FIG. 1, it is possible to detect a sharper degree of corrosion wear, that is, to detect corrosion wear on smaller and medium scales.

In addition, in the above-mentioned device, one ring 11 is formed on the entire circumferential surface of the cylindrical member 10 constituting the detection probe, so it is difficult to accurately determine the state of the pipe against localized corrosion and wear. It is also possible that it cannot be detected.

To solve this problem, as shown in FIG.
are provided, and bridge circuits 24 to 27 are configured for each of these conductive materials.

Therefore, each bridge circuit 24 to
28 is excited, and the outputs from each bridge circuit are converted into direct current by diodes CR1 to CR, and then the direct current signals are transmitted and read by voltmeters 30, respectively.

In this way, it is possible to reliably detect the state of corrosion and wear at the position in the pipe that faces the plurality of conductive materials 20 to 23.

On the other hand, in addition to such a plurality of conductive materials 20 to 23 and bridge circuits 24 to 27, a ring 11, a bridge circuit 31, and a bridge circuit 28 similar to those described above are arranged side by side, and the overall state of corrosion and wear is measured using a voltmeter 32. It can also be detected by

In the embodiment shown in Fig. 5, the output of each bridge circuit is detected by a voltmeter, but in reality, this is not necessary and only the largest output among them (resonant circuit shown in Fig. 3) is detected. When using , it is necessary to detect only the smallest output).

In such a case, for example, the output of each bridge circuit may be rectified and converted into direct current, and then the maximum voltage may be detected using an OR circuit.

In this case, if the signal is converted to direct current within the detection probe and then transmitted, the wiring for the output signal of the probe can be simplified.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the conventional detection method, Figures 2 and 3
The figure is a circuit diagram showing an example of a detection circuit related to the present invention.
The figure shows an apparatus used for carrying out one embodiment of the detection method according to the present invention, and FIG. 5 is a diagram showing an apparatus used for carrying out another embodiment of the present invention. 3...Pipe, 4...Corrosion and wear and tear, 5...
...Bridge circuit, 6...High frequency oscillator,
7. CR1~CR5... Rectifier diode, 8
...Amplifier, 9...Voltmeter, 10...
... Cylindrical member, 11 ... Conductive material ring, 1
2... Bridge circuit, 13, 14, 16...
...Relead wire, 15...Display device, 17.
18... Insulating material ring, 19... Detection probe, 20-23... Conductive material, 24-28
...Bridge circuit, 29...Power supply, 3
0, 32... Voltmeter, 31... Conductive material ring.

Claims (1)

[Claims] 1. A band-shaped conductive material extending in the circumferential direction is attached around a member made of an insulating material having an outer diameter slightly smaller than the inner diameter of the pipe to be inspected and has a circular cross section, and this member is attached in the longitudinal direction of the pipe. A method for detecting the degree of corrosion wear and tear, characterized in that the state of corrosion wear and tear existing on the inner surface of the tube is detected by a change in capacitance between the conductive material and the tube during movement.