JP2006170754A - System for monitoring wall thickness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To construct a system for measuring defect remotely when necessary on the basis of defect detection technology with an established guide wave and predict future thinning from thinning speed considering former thinning speed and property of metal material and predict exchange time of a pipe. <P>SOLUTION: Ultrasonic signal output from an ultrasonic signal converter is introduced in a pipe and the reflection wave transmitted as a guide wave in the pipe and reflected at the pipe wall are measured with the ultrasonic signal converter. By this, correlation between the height of the reflection wave and the cross section reduction rate of the pipe is obtained in advance in a thickness monitoring system measuring the thickness of the pipe, thinning quantity of the pipe is estimated from the height of the reflection wave measured with the ultrasonic signal converter by utilizing the correlation. When the estimated thinning quantity exceeds a reference value, alert is issued. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wall thickness monitoring system. Specifically, the present invention relates to a system using a measuring instrument that measures a wall thickness by a guide wave.

A flaw detection technique shown in FIG. 10 is known as a measuring instrument (hereinafter referred to as a guide wave measuring instrument) for measuring the thickness of a pipe by propagating an ultrasonic signal as a guide wave to the pipe (see Patent Document 1). .
As shown in FIG. 10, this guided wave measuring instrument arranges an ultrasonic signal converter 120 together with a sample 110 that is a pipe in a pressure vessel 100, and an ultrasonic signal from the ultrasonic signal converter 120 toward the sample 110. S _i is output to propagate the ultrasonic signal S _r as a guide wave in the sample 110, and the ultrasonic signal S _r is reflected by the tube wall and received by the ultrasonic signal converter 120.

When the ultrasonic signal S _i to be output toward the sample 110 forms the angle of incidence theta _i to the normal direction N _P samples 110, the ultrasonic signal S _r incident on the sample 110 within the laws of the sample 110 In order to make the refraction angle θ _r with respect to the line direction N _P and detect the vertical crack 111 in the tube wall of the sample 110, the incident angle θ _i is aligned and the refraction angle θ _r is 45 °. Adjust so that Further, in order to measure the thickness d ₂ of the sample 110, adjustment is made so that the incident angle θi = the refraction angle θr = 0 °.

A rectangular wave pulser 130, a magnetic diplexer circuit 140, and a high input impedance receiver amplifier 150 are used to generate and receive an ultrasonic signal by the ultrasonic signal converter 120 and to set its conditions. In addition, a digital storage oscilloscope (DSO) 160 and a personal computer 170 are used to record the signal waveform received by the ultrasonic signal converter 120. In the figure, 180 is a preamplifier, 190 is an amplifier, and 200 is a translation stage.
Japanese Patent No. 30553352

In a thermal power plant, pipe thickness measurement is generally performed by stopping the plant and removing the pipe heat insulation before an operator enters the plant and attaches a measuring device.
However, assuming that a pipe blast accident occurs in a thermal power plant, it becomes very difficult to enter the plant during operation, and it is desirable to be able to measure wall thickness and cracks remotely and when necessary.

The object of the present invention is to solve the above-mentioned problems by using the flaw detection technique.
In other words, based on the already established guide wave flaw detection technology, a system for remote flaw detection and measurement is constructed when necessary.
Furthermore, it is possible to predict the future thickness reduction and the pipe replacement timing from the current thickness reduction speed and the thickness reduction speed considering the characteristics of the metal material.

  The thickness monitoring system according to claim 1 of the present invention that achieves such an object makes an ultrasonic signal output from an ultrasonic signal converter incident on a pipe, propagates in the pipe as a guide wave, and passes through the pipe wall. In the thickness monitoring system for measuring the thickness of the pipe by measuring the reflected wave reflected by the ultrasonic signal converter, the correlation between the height of the reflected wave and the cross-sectional reduction rate of the pipe is previously determined. Obtaining and estimating the thinning amount of the pipe from the height of the reflected wave measured by the ultrasonic signal converter using the correlation, and when the estimated thinning amount exceeds a reference value, a warning It is characterized by performing.

  The wall thickness monitoring system according to claim 2 of the present invention that achieves the above object causes an ultrasonic signal output from an ultrasonic signal converter to enter a pipe, propagates in the pipe as a guide wave, and passes through the pipe wall. In a thickness monitoring system that measures the thickness of the pipe by measuring the reflected wave reflected by the ultrasonic signal converter, a correlation between the height of the reflected wave and the cross-sectional reduction rate of the pipe is obtained in advance. In addition, the temporal transition of the cross-section reduction rate is obtained in advance, and the piping of the pipe at the next periodic inspection is calculated from the height of the reflected wave measured by the ultrasonic signal converter using the correlation and temporal transition. The thickness is estimated, and when the estimated thickness reduction of the pipe is equal to or less than the allowable minimum thickness, a stop plan and countermeasure arrangement are performed.

  The wall thickness monitoring system according to claim 3 of the present invention that achieves the above object is characterized in that, in the wall thickness monitoring system according to claim 1 or 2, the pipe is disposed in a thermal power plant.

  The wall thickness monitoring system according to claim 4 of the present invention that achieves the above object is the wall thickness monitoring system according to claim 3, wherein the ultrasonic signal converter is used in a throttle element having a fluid temperature in the tube of 300 ° C. or less. It is characterized by being installed in a plurality of places where there is a possibility of swirling downstream.

  The wall thickness monitoring system according to claim 5 of the present invention that achieves the above object is the wall thickness monitoring system according to claim 3, wherein the ultrasonic signal converter is disposed on the downstream side of the condensate flow meter of the thermal power plant, the high pressure Feed water heater drain level control valve downstream side, feed water flow rate control valve downstream side, feed water flow meter downstream side, superheater spray control valve downstream side, superheater spray flow meter downstream side, reheater spray control valve downstream side, reheat It is characterized in that it is installed in plural at least one of the downstream side of the sprayer flow meter and the downstream side of the steam separator drain valve.

  A thickness monitoring system according to a sixth aspect of the present invention that achieves the above object is the thickness monitoring system according to the first, second, third, fourth, or fifth aspect, wherein the reflection is measured by the ultrasonic signal converter. A crack in the pipe is detected from the wave.

  In the wall thickness monitoring system according to claim 1, based on the already established guide wave flaw detection technology, a correlation between the height of the reflected wave and the cross-sectional reduction rate of the pipe is obtained in advance, and this is used to operate the system. It is possible to measure the wall thickness remotely and when necessary in places where it is very difficult to enter.

  In the thickness monitoring system according to claim 2, on the basis of the already established guide wave flaw detection technology, the correlation between the height of the reflected wave and the cross-section reduction rate of the pipe and the temporal transition of the cross-section reduction rate are obtained in advance. By using these, it is possible to predict the wall thickness remotely and when necessary, at places where it is very difficult to enter during operation.

  In the wall thickness monitoring system according to claim 3, in addition to the effects of claim 1 or 2, it is possible to measure and predict the wall thickness remotely and when necessary in a thermal power plant that is very difficult to enter during operation. Become.

  In the wall thickness monitoring system according to the fourth aspect, in addition to the effects of the third aspect, it is possible to measure and predict the wall thickness remotely and when necessary, at a plurality of locations where the thinning is most likely to occur in the thermal power plant.

  In addition to the effects of claim 4, the wall thickness monitoring system according to claim 5 is capable of measuring wall thickness remotely and when necessary at nine locations that most require thinning monitoring in large thermal power plants. Become.

  In the wall thickness monitoring system according to claim 6, in addition to the effects of claim 1, 2, 3, 4 or 5, crack measurement can be performed remotely and at a necessary place in a place where it is very difficult to enter during operation. It becomes possible.

  Hereinafter, the best mode when the present invention is applied to a multi-flaw detection monitoring system using a guided wave of a thermal power plant will be described with reference to FIGS.

<Prediction over time of thinning amount>
The above-described guide wave measuring instrument (see FIG. 10) is installed at a plurality of locations in the piping of the thermal power plant, the ultrasonic signal output from the guide wave measuring instrument is propagated as a guide wave to the pipe, and the reflected wave reflected from the pipe wall is reflected. When it is received by the guide wave measuring instrument, the measurement result display screen shown in FIG. 2 is obtained.
FIG. 2 shows the relationship between the echo height of the reflected wave and the distance.

The echo height of the reflected wave has a correlation shown in FIG. 3, for example, with the cross-sectional area reduction rate (S ₁ / S ₀ ). Such data is acquired in advance and stored in a database.
FIG. 3 shows a correlation in which the cross-sectional area reduction rate (S ₁ / S ₀ ) increases as the echo height increases, although there is some variation.
Here, the cross-sectional area reduction rate (S ₁ / S ₀ ) means the ratio of the current cross-sectional area reduction amount S _{1 to} the initial cross-sectional area S ₀ , and increases as time progresses as shown in FIG. It is estimated that it changes. Here, it is desirable to estimate in consideration of the characteristics of the metal material used for the piping.

Further, the cross-sectional area reduction amount S ₁ shown in FIG. 6 can be approximated as the product of the thinning amount d and the thinning width W in the pipe 1 as shown in the following equation (1).
Cross-sectional area reduction amount S ₁ ≈d × W (1)
However, when the relationship between the thinning amount d and the thinning width W is obtained in advance and stored in the database, as shown in FIG. 7, the distribution increases so that the thinning amount d increases as the thinning width W increases. .
That is, when the relationship between the thinning amount d and the thinning width W is mathematically expressed, the above equation (1) is obtained. If the relationship has a distribution width, the result shown in FIG. 7 is obtained.

As described above, the cross-sectional area reduction rate (S ₁ / S ₀ ) changes so as to increase as time progresses as shown in FIG. 4, and the thinning width W increases as shown in FIG. In this case, since the thickness reduction d increases, it is estimated that the thickness reduction d increases as time progresses as shown in FIG.
Therefore, in this embodiment, as shown in FIG. 5, two reference values 1 and 2 are set for the thickness reduction d.

<Setting reference value>
In the present embodiment, the reference value 1 and the reference value 2 are set as follows.
Reference value 1; when X ₂ reaches X _cr (thickness <tsr (allowable minimum thickness) with a probability of 1%)
Reference value 2; when X ₃ reaches X _cr (thickness <tsr (allowable minimum thickness) with a probability of 50%)

As described above, the cross-sectional reduction amount S ₁ ≈d × W, and the ratio (database) of the thinning width W and the thinning amount d has a certain distribution.
Here, as shown in FIG. 8, the probability density with respect to the thinning amount d is bilaterally symmetric, and this distribution moves to the right with the progress of time (destruction of demolition).
X ₁ and X ₂ in FIG. 8 are the lower limit and upper limit of the 99% confidence interval, as shown by the following equation (2).
d = X _{1 to} X ₂ (2)

The confidence interval is defined between the lower limit value and the upper limit value of a signal that can be determined to be incarnation from the flaw detection result.
Therefore, X ₁ is the lower limit value of the confidence interval, and if it is a signal higher than this, it is a value that is judged to be ruined, and X ₂ is the upper limit value of the confidence interval, and if the signal is less than this, it decreases. It is a value to judge meat.
X ₃ means the average value of X ₁ and X ₂ .
X _cr = limit thickness reduction (refers to the thickness when reaching tsr)
tsr (Thickness shell required) refers to the minimum allowable wall thickness of piping.

<Flow reduction prediction evaluation flow>
FIG. 1 shows a flow chart for predicting thinning of a multi-flaw detection monitoring system using a guide wave of a thermal power plant.

First, a monitoring location is selected based on the design temperature, flow velocity calculation, material, D0 measurement result, and Fe ion measurement result of the thermal power plant (step S1).
The monitoring location refers to the location of the piping where the above-described guide wave measuring instrument is installed to measure the wall thickness. For example, as will be described later, in the piping of the thermal power plant, the throttle element whose fluid temperature is 300 ° C. or less. It is preferable to install a plurality of vortices at places where there is a possibility of vortexing downstream.

Next, the above-described guide wave measuring device is installed at the monitoring location, and monitoring by the guide wave is performed (step S2).
That is, an ultrasonic signal output from the guide wave measuring instrument is propagated as a guide wave in the pipe, and a reflected wave reflected by the pipe wall is received by the guide wave measuring instrument.

Here, in order to measure the thickness of the pipe, the incident angle and the refraction angle of the ultrasonic signal with respect to the normal direction of the pipe are adjusted so that the incident angle = the refraction angle = 0 °. In order to detect vertical cracks (cracks) in the tube wall, the incident angle is aligned and the refraction angle is adjusted to 45 ° with respect to the normal direction.
Thus, the echo height of the reflected wave received by the guide wave measuring instrument has the correlation shown in FIG. 3 with respect to the cross-sectional area reduction rate (S ₁ / S ₀ ), and such correlation is acquired in advance. And accumulated in the database.

Subsequently, the correlation between the echo height of the reflected wave accumulated in the database and the cross-sectional area reduction rate (S ₁ / S ₀ ), and the cross-sectional area reduction amount S ₁ ≈d × W shown in Expression (1) Is used to estimate the thinning amount d from the echo height of the reflected wave received by the guide wave measuring device, and determine whether the estimated thinning amount d exceeds the reference value 1 (step S3).
Here, when the thinning amount d exceeds the reference value 1, the lower limit value X1 of the 99% confidence interval reaches X _cr , that is, the thickness <tsr (allowable minimum thickness) with a probability of 1%. Means that

When it is determined that the estimated thinning amount d does not exceed the reference value 1, the process returns to step S2, while when it is determined that the estimated thinning amount d exceeds the reference value 1 (thickening amount). > Reference value 1) gives an alarm warning (step S4).
The warning by the alarm here is assumed to be a mild one that calls attention in consideration of the fact that the wall thickness becomes the allowable minimum wall thickness tsr with a probability of 1%.

Further, by using the relationship shown in FIG. 5 in which the thinning amount d increases with time, the average thickness until the next periodic inspection is estimated, and the estimated average thickness is tsr (allowable minimum thickness). ) Is evaluated whether or not the remaining life is exceeded (step S5).
When the estimated average wall thickness becomes smaller than tsr (allowable minimum wall thickness), when the remaining life is evaluated, a plant stop plan is executed (step S6), and countermeasures are arranged (step S7).

The plant stop plan here is a plan to stop the plant before the next periodic inspection, and the countermeasure arrangement at that time is an arrangement to advance the replacement time of the piping.
On the other hand, when it is evaluated that the estimated average thickness is tsr (allowable minimum thickness) or more, the monitoring is continued (step S8).

Thereafter, the correlation between the echo height of the reflected wave accumulated in the database and the cross-sectional area reduction rate (S ₁ / S ₀ ), and the cross-sectional area reduction amount S ₁ ≈d × W shown in Equation (1) Is used to estimate the thinning amount d from the echo height of the reflected wave received by the guide wave measuring device, and determine whether the estimated thinning amount d exceeds the reference value 2 (step S9).
Here, when the thinning amount d exceeds the reference value 2, the upper limit value X2 of the 99% confidence interval reaches _Xcr , that is, the thickness <tsr (allowable minimum thickness) with a probability of 50%. Means that

And when it determines with the estimated thickness reduction d not exceeding the reference value 2, it returns to step S8.
On the other hand, when it is determined that the estimated thinning amount d exceeds the reference value 2 (thickening amount> reference value 2), an alarm warning is given (step S10), and the plant stop plan is executed (step S11). ), Measures are arranged (step S12).
Here, the warning by the alarm is assumed to be of a severe level in consideration of the fact that the wall thickness becomes the allowable minimum wall thickness tsr with a probability of 50%.
The plant stop plan here is a plan to stop the plant quickly, and the countermeasure arrangement at that time is an arrangement to replace the pipes promptly.

Although omitted in the flowchart shown in FIG. 1, when a vertical crack (crack) is detected in the pipe by the guide wave measuring instrument, the extent is the same as when the thinning amount d exceeds the reference values 1 and 2. Depending on the situation, alarm warnings, plant shutdown plans and countermeasure arrangements will be made.
Further, accompanying the flowchart shown in FIG. 1, a thickness monitoring system installation work using a guide wave, a flaw detection measurement work using the above system, a pipe renewal work when the pipe is thinned, and the like are also performed.

<Functional specifications of multi-flaw monitoring system using guided waves>
The functional specifications of the “multi-flaw inspection system” that inputs signals from multiple sensors (guide wave measuring instruments) installed for the purpose of pipe thinning measurement and crack measurement in a thermal power plant are described below.

(1) Up to 50 detection points are currently possible. As shown in the system diagram of Fig. 9, there are nine possible locations that require thinning monitoring in large thermal power plants.
However, up to 50 points are possible in consideration of the existence of a plant having a plurality of systems and future expandability.

(2) Maintaining system health through continuous monitoring Since system health is always confirmed through continuous monitoring, flaw detection measurements can be performed reliably when monitoring is necessary. .
Also, early recovery can be performed by issuing an alarm in the event of an abnormality.
This makes it possible to monitor without human beings entering the site.

(3) Scanning at a predetermined interval Considering the pipe thinning rate, a short scan time is not required.
The scan time can be set arbitrarily. For example, once / day, once / week, once / month.

(4) Input data display method The present value, comparison with past data, etc. may be displayed in a table format, or a trend monitoring method may be used.

(5) Alarm display An alarm is issued when a preset threshold value (reference value 1, 2) is exceeded.

(6) Thinning prediction function Calculates the thinning speed from changes in input data based on <Thinning prediction flow chart>, <Prediction of time transition of thinning amount>, and <Standard value setting> To make a thinning prediction.

(7) Maintenance guidance Maintenance guidance, such as pipe repair, is performed from the above (6) thinning prediction result.

<Guide wave measuring instrument installation location of multi-flaw monitoring system using guide wave>
In a thermal power plant, a plurality of installations are provided at locations where a vortex may flow downstream in a throttle element having a fluid temperature of 300 ° C. or lower as shown in (a) to (i) below.

(a) Downstream side of the condensate flow meter The condensate flow meter is installed in order to confirm whether an appropriate flow rate is secured in the condensate system.

(b) High-pressure feedwater heater drain level control valve downstream The high-pressure feedwater heater level control is a drain-belel control valve, and a control valve is necessary to perform heat exchange properly.

(c) Water supply flow rate control valve downstream side A control valve is required to control the water supply required for the boiler.

(d) Downstream side of feed water flow meter A feed water flow meter is necessary to control the feed water flow rate to an appropriate level.

(e) Superheater (SH) spray control valve downstream The superheater spray control valve is necessary to control the steam temperature at the outlet of the superheater to an appropriate temperature. However, the transformer once-through boiler exceeds 300 ° C, so it is excluded.

(f) Superheater spray flow meter downstream A flow meter is necessary to monitor whether the superheater spray amount is appropriate. However, the transformer once-through boiler exceeds 300 ° C, so it is excluded.

(g) Reheater (RH) spray control valve downstream The reheater spray control valve is necessary to control the steam temperature at the outlet of the reheater to an appropriate temperature.

(h) Reheater spray flow meter downstream The flow meter is necessary to monitor whether the reheater spray amount is appropriate.

(i) Steam / water separator drain valve downstream The drain valve is the necessary valve to control the steam / water separator to an appropriate level.

  The present invention can be used as a multi-wall thickness monitoring system for monitoring the wall thickness of a plurality of pipes in a thermal power plant, but is not limited to a thermal power plant. It is possible to measure the thickness and predict the thickness when necessary.

It is a flowchart which shows thinning prediction evaluation. It is explanatory drawing which shows a measurement result display screen. It is a graph which shows the relationship between echo height and a cross-section reduction rate. It is a graph which shows the time change of a cross-section reduction rate. It is a graph which shows the time change of the amount of thinning. It is explanatory drawing which shows the thinning amount and thinning width of piping. It is a graph which shows the relationship between the thinning amount and the thinning width. It is a graph which shows the relationship between probability density and thickness reduction width. It is the thermal power plant system diagram which attached | subjected the guide wave measuring device installation location. It is the schematic which shows the conventional guide wave measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piping 120 Ultrasonic signal converter 130 Pulsar 140 Diplexer 150 Amplifier 160 Oscilloscope 170 Personal computer 180 Preamplifier 190 Amplifier 200 Translation stage d Thinning amount W Thinning width

Claims (6)

  The ultrasonic signal output from the ultrasonic signal converter is incident on the pipe, and the reflected wave reflected on the pipe wall by propagating through the pipe as a guide wave is measured by the ultrasonic signal converter. In the wall thickness monitoring system for measuring the wall thickness, the correlation between the height of the reflected wave and the cross-section reduction rate of the pipe is obtained in advance, and measured by the ultrasonic signal converter using the correlation. A wall thickness monitoring system that estimates a thinning amount of the pipe from the height of a reflected wave, and warns when the estimated thinning amount exceeds a reference value.   The ultrasonic signal output from the ultrasonic signal converter is incident on the pipe, and the reflected wave reflected on the pipe wall by propagating through the pipe as a guide wave is measured by the ultrasonic signal converter. In the thickness monitoring system for measuring the wall thickness of the pipe, the correlation between the height of the reflected wave and the cross-section reduction rate of the pipe is obtained in advance and the temporal transition of the cross-section reduction rate is obtained in advance. The thickness of the pipe at the next periodic inspection is estimated from the height of the reflected wave measured by the ultrasonic signal converter using the transition, and the estimated thickness reduction of the pipe is the allowable minimum thickness. A wall thickness monitoring system that performs stop planning and countermeasure arrangement when:   The wall thickness monitoring system according to claim 1, wherein the pipe is disposed in a thermal power plant.   4. The wall thickness monitoring system according to claim 3, wherein a plurality of the ultrasonic signal converters are installed at a location where a swirl element having a fluid temperature in the pipe of 300 [deg.] C. or less may swirl downstream.   The ultrasonic signal converter includes a condensate flow meter downstream side of the thermal power plant, a high pressure feed water heater drain level control valve downstream side, a feed water flow rate control valve downstream side, a feed water flow meter downstream side, and a superheater spray control valve downstream side. And a plurality of them installed on at least one of the downstream side of the superheater spray flow meter, the downstream side of the reheater spray control valve, the downstream side of the reheater spray flow meter, and the downstream side of the steam / water separator drain valve. Item 3. The thickness monitoring system according to item 3.   The wall thickness monitoring system according to claim 1, 2, 3, 4, or 5, wherein a crack of the pipe is detected from a reflected wave measured by the ultrasonic signal converter.

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