KR101202078B1 - Monitoring method for the defect of conducting, structural material using switching DCPD - Google Patents

Abstract

The present invention relates to a non-destructive method for detecting a defect including a thickness reduction of a complex structure made of an electrically conductive material. When a current is applied to both ends of the inspection object, the voltage drop varies according to the electrical resistance of the inspection object. If a defect such as thickness thinning occurs in the structure, the resistance changes, and the voltage drop value changes even under a constant current value. In this way, defects in the structure under inspection can be monitored.

At present, nuclear power plants and thermal power plants are equipped with carbon steel pipes, and their lengths are considerable, so that all locations cannot be quickly inspected by conventional ultrasonic tests. Due to the deterioration of nuclear power plants, the problem of thinning of carbon steel pipes is serious. Therefore, by using electric resistance change in all locations, it is possible to sort out the areas of concern in a short period of time. This allows you to inspect all locations in a short time.

In the present invention, when the switching DCPD technique is to be applied to a complex interconnected pipe, the theoretical circuit for the defect shape of each pipe part is performed, and then the measurement circuit is configured in units of straight pipe, curved pipe, and T-shaped branch. By devising a special measuring device, it is possible to measure the occurrence of thinning defects for long-term pipes longer than 1 meter in length by changing the electrical resistance.

In the case of complicated entanglement of piping, such as power plants, current application can cause short-circuit to the inspection site as well as to the electrically connected outside, causing safety problems. In order to prevent this, the present invention constitutes a circuit as shown in the representation.

In order to prove the practicality of the present invention, after measuring by applying the Switching DCPD technique to the artificially thinned pipes, the verification of the conformity was verified using an ultrasonic test.

Description

Monitoring method for the defect of conducting, structural material using switching DCPD}

1 and 2 are diagrams for measuring the potential difference with respect to the curved portion and the T-shaped branch according to the present invention;

3, 4a, b and 5 show the application according to the structure form;

6 is a diagram showing a voltage drop appearing in accordance with a defect form of a structure such as a pipe.

7 is a diagram showing a voltage drop effect.

8 is a diagram comparing the results with the finite enzyme analysis method.

9 shows a comparison with an ultrasonic wave measurement result.

10a, b, and c are graphs showing the calculation results according to the thinning angles, respectively, when the degree of thinning of the tube is represented by a resistance model and when modeled by a finite element analysis technique.

11A, B, and C are diagrams for comparing the results of measuring the voltage drop with the ultrasonic test method while mechanically cutting the actual pipe to verify the degree of error of the symmetrical DC potential difference method.

Fig. 12 is a diagram showing an algorithm for efficiently classifying the voltage drop per position with the minimum number of measurements.

In the case of pipes made of carbon steel in power plants, this is vulnerable to flow accelerated corrosion, which can lead to continuous thinning leading to pipe failure. In particular, as generation facilities such as nuclear power plants are aging, many problems are caused. In addition, continuous monitoring of major vulnerable areas is required.However, if a general ultrasonic inspection is performed during a short preventive maintenance period when a power plant is stopped, many monitoring points are required. It is difficult to inspect effectively. In addition, in the case of ultrasonic equipment, there is a disadvantage that it is difficult to measure the thickness thinning or defect of a non-uniform cross section, such as a complex structure or a welded area, which is prone to problems, and in fact, such a site is known to be more vulnerable to defects. This problem can be overcome by using the eddy current flaw detection method, but this method does not apply to materials such as carbon steel pipes.

It is an object of the present invention to provide a method for measuring the thickness and flaw of a piping structure by a relatively simple method without using ultra-short wave equipment or the like to achieve the above object.

It is also an object of the present invention to provide a method that can be applied over a wide area rather than a simple point.

In order to achieve the object as described above, the present invention provides a method for inspecting a thinning defect of an electrically conductive structure over a wide area.

A method for inspecting thinning defects of an electrically conductive structure for a wide area,

Designating at least two checkpoints in the structure;

Sending a current to the designated checkpoint;

Measuring a voltage drop at the checkpoint;

How to inspect thinning defects in electrically conductive structures over a wide area

In addition, a method for inspecting a wide range of thinning defects of an electrically conductive structure in which a current flows in one direction by adjusting the magnitude and direction of the current flowing between the inspection points.

In addition, a method for inspecting a thinning defect of an electrically conductive structure for a wide area by measuring the thinning of the thickness by moving the position of the inspection point and measuring the voltage drop.

In addition, when the structure forms a branching point, three inspection points are designated around the branching point, and a thinning defect of the electrically conductive structure, in which a current flows to flow toward any one of the three inspection points, is provided. How to check for wide area

In addition, when the structure is a closed loop,

Selecting at least two measurement sites;

Selecting inspection points at both ends of the measurement part;

The current flows to the inspection point, but adds a resistance before and after the current source that generates the current to make the equipotential surface between the measurement sites so that there is no current flow so that the closed loop structure can be seen as the open structure. It may further comprise a.

The present invention is a method for safely monitoring a defect of an electrically conductive structure such as a pipe connected intricately in a short time without risk of leakage. The target structure must be electrically conductive because it is a method of monitoring faults in the structure as a change in electrical resistance. Ultrasonic testing of structures, such as long pipes, requires enormous time because only a small area can be measured once. In this case, it is difficult to inspect all the desired ranges due to time constraints such as the inspection period of the equipment. Therefore, in the present invention, the inspection site is regarded as a circuit composed of electrical resistance, and devised a technique capable of inspecting a large area, not a point, in a short time by using a resistance change measurement method, and an electrical leak in application according to the shape of a complicatedly connected piping structure. We devised a technique to solve the safety problem.

Fig. 1 is a diagram showing a state in which a potential difference is measured by applying a symmetrical direct current to both ends with respect to the curved pipe part. After the inspection point is set, the current that is supplied to the inspection site through the current source from one inspection point to the other inspection point again flows toward the current source, so no leakage to the outside occurs and the voltage drop at each inspection point In certain cases, this may be indicated by a change in resistance. In the case of piping structures, damage in the depth or width direction from inside the pipe may be indicated by such a change in resistance, so damage in the depth and width direction of the pipe can be measured. have.

FIG. 2 is a circuit diagram configured to perform inspection on all portions by applying a current of three stages to a T-type branch at an appropriate ratio, and to prevent leakage of current outside the inspection region. In Fig. 2, the current flowing through the current source at the left and the bottom is turned to the right to the current source, so that leakage to the outside of the inspection site does not occur.

Figure 3 shows the applicability according to the complicated pipe shape, the electrical circuit is configured to prevent the short circuit caused by the electrical ground of the pipe and the theoretical result (solid line) is shown.

4A and 4B show the results of the analysis of application difficulties according to the structure type, in which two independent circuits are designed so that there is no leakage to the outside of the measurement site when the pipe is configured as a closed loop, and this is actually a closed loop. Experimental results verifying that the leakage is zero by adjusting the current source applied to the pipe. If the pipe forms a closed loop, two or more inspection points can be determined, and after selecting the inspection points, any two inspection points connected to each other can be inspected as if they are not closed loops. We measure the voltage drop and the change of resistance.

Figure 5 shows the results of the analysis of the application difficulties according to the structure type, if the pipe is branched in three or more directions by applying the current at an appropriate distribution ratio for the defect measurement of the desired position to be collected in a specific direction by flowing The method of examining the site is shown.

In Figure 6, the voltage drop appears in a different form depending on the defect form of the structure, such as piping, in particular, it shows that the measurement efficiency is better in thickness reduction, etc. than when applied to the conventional crack measurement.

In the same volume change, when the thickness thinning progresses in the depth direction, the voltage drop effect increases faster than the progress in the width direction in the electrical model, and is represented by a formula.

Where R is the resistance, a is the depth of thinning, and b is the length of thinning in the width direction.

FIG. 8 shows the result of showing that the equivalent resistance circuit equations coincide with each other by comparing the voltage drop value calculated by the electric resistance circuit formula and the result calculated by the finite element analysis method.

FIG. 9 compares the DC potential difference measurement result and the ultrasonic measurement result with respect to the pipe defect, and shows mutual agreement.

10a, b, and c show that the results of the thinning angle correspond to the thinning degree of the pipe as a resistance model and the finite element analysis method. FIG. 10a shows the thinning degree of the pipe as a resistance model, FIG. 10b shows the result of modeling by the finite element analysis technique, and FIG. 10c compares the two calculation results. It can be seen that there are no significant differences in the results of the two techniques.

11a, b and c show the results of measuring the voltage drop while mechanically scraping the actual pipe to verify the degree of error of the symmetrical DC potentiometric method compared with the results of the ultrasonic test method. FIG. 11A shows a photograph of measuring a voltage drop of a pipe by a direct current potential difference method and directly cutting a pipe.

In FIG. 11B, the thickness measured while cutting the pipe by the ultrasonic measuring sensor is shown in a graph. In FIG. 11C, the ultrasonic measurement results are compared with the DCPD measurement results. As a result, it can be confirmed that the ultrasonic measurement result and the measurement error of the DC potential difference method are relatively precisely fit within 1%.

Fig. 12 shows the design of an algorithm and a measuring device for efficiently classifying the voltage drop for each location with the minimum number of measurements. Figure 12 shows the design of the measuring device module, by which it is possible to easily measure the voltage drop in both the wide and narrow areas while applying a current to the measurement position. For example, if the measured voltage drop of a large part is a + b + c + d and the measured voltage drop of a narrow part is b + c through one measurement with a measuring device module, four variables and two equations are used for one measurement. Appears. At this time, if you move a little later and measure one more time, you know the values of b + c + d + e and c + d, and one variable is added. Finally, one more measurement adds two equations, c + d + e + f and e + f, and adds the unknown variable f. In this way, three voltage measurements of a, b, c, d, e, and f showed six voltage drops, indicating that the voltage drop due to thickness reduction in a wider area can be measured more efficiently. . In addition, by changing the length of the narrow area, it is possible to accurately determine whether the desired thin area thickness is reduced.

The monitoring technique proposed in the present invention divides a complex pipe system into a region by applying a switching DCPD technique, prevents the risk of a short circuit through the grounding part, and monitors defects occurring in the entire region at one point instead of at a point, so that Since the area can be monitored and is not affected by high temperature, radiation, etc., it is expected to be applied to a nuclear power plant or other pipes requiring inspection to greatly improve the pipe reliability.

Claims (5)

A method for inspecting thinning defects of an electrically conductive structure for a wide area, Designating at least two checkpoints in the structure; Sending a current to the designated checkpoint; Measuring a voltage drop at the checkpoint;  The current flows in one direction by adjusting the magnitude and direction of the current flowing between the inspection points. By measuring the voltage drop by moving the position of the test point and measuring the thickness of the thickness  When the structure forms a branching point, three inspection points are designated around the branching point, and a current flows so that a current flows toward any one of the three inspection points.  If the structure is a closed loop, Selecting at least two measurement sites; Selecting inspection points at both ends of the measurement part; The current flows to the inspection point, but adds a resistance before and after the current source that generates the current to make the equipotential surface between the measurement sites so that there is no current flow so that the closed loop structure can be seen as the open structure. A method for inspecting a wide area for thinning defects of an electrically conductive structure using a direct current potentiometric method, the method further comprising: delete delete delete delete

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