JPS5818602B2 - 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 and wear, and particularly to a method for detecting the degree of corrosion and wear, particularly the location of the corrosion and wear on the inner wall of a boiler, a heat exchanger tube, and other hollow tubes.
This invention relates to an optimal detection method for detecting the degree of corrosion and wear and tear.

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. It is necessary to check safety, lifespan, etc.

Conventionally, as a detection method for such a pipe, there is a so-called eddy current flaw detection method, which is a non-destructive method and 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 detection of corroded parts and there is a limit to detection accuracy. .

Also, the tubing must be non-magnetic and therefore
For magnetic materials such as steel pipes, there are drawbacks such as the need for magnetic saturation flux.

Furthermore, there is a method of measuring tube wall thickness using radiation irradiation.
There are disadvantages such as the measurement being limited to one direction and the measurement being impossible when the 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, a more reliable means of detection is to remove a representative tube from a heat exchanger or other equipment that has a large number of tubes, and perform a destructive inspection to estimate the state of corrosion and wear and tear on other tubes. This is the current situation.

However, 1. O) Such sampling inspections are only measurements based on estimates, and are 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.

Therefore, an object of the present invention is to provide a method for detecting the degree of corrosion and wear that does not have the above-mentioned drawbacks.

This invention will be explained below.

In this invention, as shown in FIGS. 1A and 1B, opposing conductor disks 1 and 2 are disposed at right angles to the longitudinal direction of the tube 3 to be measured, and their circumferential surfaces are close to the inner wall of the tube. conductor disk 1,
2 while keeping the distance d constant while moving the tube 3 in the longitudinal direction.

For example, the pipe is moved from the mountain position shown in the figure (like the loss position).

Here, the area of each of the conductor disks 1 and 2 is A1
If the dielectric constant between the conductor disks 1 and 2 is ε, then the conductor disk 1
, 2 is the electrostatic capacitance C formed between.

Therefore, when the conductive disks 1 and 2 are charged with charges of opposite signs, the lines of electric force generated between the two disks are not all straight lines,
An arcuate curve is drawn at the peripheral edge of the disc.

Therefore, the dielectric constant ε differs between an intact position such as the illustrated peak position and a position where a corroded wear portion 4 exists, due to the difference in the inner diameter of the pipe.

That is, if the permittivity at the peak position is ε1, then (nJ
The dielectric constant at the position is s2 (\ε1), the capacitance C1 formed between the conductor disks 1 and 2 at the position (II) is expressed as, and the capacitance C2 at the position (II) is expressed as It will be done.

In this case, the dielectric constant at that time is determined by the degree of corrosion damage on the tube wall.

Thus, when the conductor disks 1 and 2 are moved in the longitudinal direction within the tube while keeping the distance d constant, if there is a corroded part on the tube wall, the capacitance generated between these conductors will change. With this, it is possible to detect the position of corrosion damage in the pipe, the degree of corrosion damage, etc.

In accordance with the above-mentioned detection principle, in actual detection, as shown in FIGS. A pair of conductor pieces i i and 12 are wound to form one detection capacitor Cx.

This detection capacitor Cx includes a reference capacitor Cs with a predetermined capacity, a reference inductance coil L1. L2 are connected in series to form an impedance bridge circuit 13.

In this case, the reference capacitor C3 and the reference inductance coils L1 and L2 are both disposed within the cylindrical member 10 so as not to interfere with each other, and are fixed, for example, by molding.

Note that such an impedance bridge circuit may be formed using only a capacitor or a resistor.

Thus, the conductor pieces 1 are wound around both ends of the cylindrical member 10.
1. Additional side plates 14゜15 with a diameter slightly larger than the outer diameter of 12 and slightly smaller than the inner diameter of the tube 3 to be measured are added, and excitation leads connected from one side plate to a pair of terminals of the bridge circuit 13. The output lead wire 1γ connected to the wire 16 and the other pair of terminals of the bridge circuit 13 is drawn out.

Thus, the detection probe 18 for detecting corrosion wear
is configured.

Here, an AC power source 20 is connected to the excitation lead wire 16, and a voltmeter 22 is connected to the output lead wire 17 via an amplifier 21.

In this connected state, the detection probe 18 is inserted into the tube 3 whose degree of corrosion wear is to be detected, and is moved at a constant speed.

For example, if compressed air is blown from one of the Q directions, the detection probe 18 will move in the R direction, so the detection probe 18 can be moved over the entire area of the tube 3.

When the detection probe 18 moves within the tube 3 in this way, only the capacitance of the detection capacitor Cx changes in accordance with the degree of corrosion and wear existing in the tube 3, so the electrical balance of the invader bridge circuit 13 changes. This voltage change is amplified by an amplifier 21 and displayed on a voltmeter 22.

In this way, the state of corrosion and wear inside the pipe 3 can be easily detected.

Here, before detecting corrosion and wear, the capacitance or inductance L, L2 of the capacitor Cs is adjusted in accordance with the frequency of the AC power supply 20, etc. so that the output voltage is at a minimum.

Moreover, if a predetermined unevenness is provided on the preliminary tube and the inside of the tube is scanned with a detection probe to obtain a calibration curve as shown in FIG. 4, reliable measurements can be made during actual detection.

Figure 4 shows the case where the frequency of the AC power supply is 144■Z, but if a voltage as shown in Figure 5A is obtained from this calibration curve, the state of corrosion and wear as shown in Figure 5B can be estimated. obtain.

Note that in order to improve measurement accuracy, it is better to have a higher frequency of the AC power source.

As described above, according to the detection method of the present invention, it is possible to accurately detect the degree and position of corrosion and wear even with a relatively simple configuration.

Furthermore, since detection is performed based on changes in dielectric constant, there are no restrictions on the material of the tube, and rapid measurement is possible, making it extremely efficient.

In addition, in the above method, one detection capacitor is formed on the entire circumferential surface of the cylindrical member that constitutes the detection probe, so it is difficult to accurately prevent pitting-like corrosion damage that exists locally within the pipe. It is also conceivable that certain conditions may not be detected.

To solve this problem, as shown in FIG. 6, a plurality of detection capacitors are arranged axially symmetrically within the cylinder so that the angular distance between the center angles formed locally is even over the entire surface of the cylindrical member. 30 to 33 are provided, and bridge circuits 34 to 36 are configured corresponding to each of these capacitors.

Therefore, each bridge circuit 34 to
37 is excited, and the change in output voltage from each bridge circuit is read with a voltmeter 39.

In this way, each of the plurality of capacitors 30 to 33Q
It is possible to reliably detect the state of corrosion and wear at the opposing positions in the pipe.

On the other hand, in addition to the plurality of capacitors 30 to 33 and bridge circuits 34 to 37, a detection capacitor 40 and a bridge circuit 41 similar to those described above are arranged in parallel, and the overall state of corrosion and wear is detected by a voltmeter 42. You can also do this.

Further, when detecting pitting-like corrosion wear, it is actually not necessary to detect output changes of all impedance bridge circuits as described above, and it is sufficient to detect only the largest one among them.

In such a case, for example, the output of each impedance 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, converting the signal into direct current within the detection probe and transmitting it later has the advantage of simplifying the wiring for the output signal of the probe.

[Brief explanation of the drawing]

FIG. 1A is a diagram for explaining the invention in detail, FIG. 1B is a field of view at the X-Y position of FIG. 1A, and FIG. 2 is a diagram showing an example of the configuration for implementing the principle. , Fig. 3 is its electrical circuit diagram, Fig. 4 is a calibration curve measured by applying this invention, Fig. 5 A and B are diagrams showing actual measurement results, and Fig. 6 is an expanded example of another configuration. FIG. 1.2... Conductor disk, 3... Tube, 4...
... Corrosion wear part, 10 ... Cylindrical member, l
L12...Conductor piece, 13...Bridge circuit, 20...AC power supply, 21...Amplifier, 22...Voltmeter.

Claims (1)

[Scope of Claims] 1. Opposing conductors are wound around a cylindrical member made of an insulator so as to be perpendicular to the longitudinal direction of the tube, and placed within the tube, and the conductors with a constant spacing are placed inside the tube. A method for detecting the degree of corrosion damage, characterized in that the state of corrosion damage existing in the pipe is detected by a change in capacitance that occurs between the conductors based on the movement in the longitudinal direction. 2 A pair of opposing conductors are wound around a cylindrical insulating member at right angles to the longitudinal direction of the tube and placed inside the tube to form one detection capacitor, and a reference capacitor and/or An impedance bridge circuit is configured together with a reference inductance, and while this impedance bridge circuit is excited with a high frequency signal, the detection capacitor is moved in the longitudinal direction of the tube, and the change in the output voltage of the bridge circuit that occurs at this time causes A method for detecting the degree of corrosion and wear and tear, characterized in that the state of corrosion and wear that exists in the pipe is detected. 3. The plurality of pairs of conductors facing each other are arranged so that the angular distance between their center angles is uniform locally over the entire surface of the cylindrical member of the insulator so that the conductors are perpendicular to the longitudinal direction of the pipe, and A plurality of detection capacitors are arranged symmetrically to form a plurality of impedance bridge circuits corresponding to each of the detection capacitors together with a reference capacitor and/or reference inductance, and each of these impedance bridge circuits is connected to a high frequency Exciting with a signal and moving each of the detection capacitors in the longitudinal direction within the tube,
A method for detecting the degree of corrosion wear and tear, characterized in that the state of corrosion wear existing in the tube is detected by the change in the output voltage of each of the impedance bridge circuits that occurs at this time.