JP5734789B2 - Damage estimation method for structures made of conductive materials - Google Patents

Description

  The present invention relates to a method for estimating damage such as thinning that occurs in a structure made of a conductive material, and more particularly to a method for estimating damage to a structure made of a conductive material that can be estimated nondestructively with high accuracy using a potential difference method. . In the present invention, among structures such as pipes of an oil refinery plant, for example, the structure itself is buried in embankments, embankments, etc., or a covering material is applied, and they are dismantled and removed. Otherwise, damage that occurs in places where inspections are difficult to perform will be targeted.

  In oil refining plants, equipment and pipes made of metal materials such as steel materials (hereinafter also referred to as pipes) are often exposed to a strong corrosive environment or erosion environment. Therefore, metal materials that make up structures such as pipes In some cases, damage such as flaws, cracks, cracks, and thickness reduction due to corrosion may occur. Since damages to these metal materials often cause destruction of structures such as pipes, it is necessary to detect them from the viewpoint of ensuring the safety of pipes and the like.

  Conventionally, nondestructive inspection methods such as an ultrasonic flaw detection method and an X-ray transmission method have been proposed as methods for detecting damage to piping and the like. However, these detection methods have limitations on the measurement location that measurement is not possible if there is a bend or a weld, and it is difficult to obtain the degree of damage and the amount of change with high accuracy, or the measurement is complicated. However, since analysis is difficult, there were problems such as requiring the cooperation of qualified personnel in the implementation of measurement and analysis.

  Further, there is a potential difference method as a nondestructive inspection method that can obtain information on the size and shape of defects such as cracks with relatively high accuracy. When a current is passed through a material to be measured including a defect such as a crack, the defect has an electrical resistance corresponding to its size, and a potential difference corresponding to this occurs on both sides of the defect. In the potentiometric method, a current is passed through the object to be measured, the potential difference at the position where this defect is sandwiched is measured, and information on the shape and size of the defect contained in the object to be measured is obtained using a calibration curve obtained in advance from the result. Is going to get.

  For example, Patent Document 1 proposes a nondestructive inspection method for flaws using a potential difference method. In the technique described in Patent Document 1, a plurality of potential difference measuring terminals are arranged in a matrix at a predetermined interval on the surface of the object to be measured, and each potential difference is measured while supplying current to the object to be measured. Obtain the potential difference or potential difference change rate distribution generated between the terminals, and refer to the relationship between the potential difference distribution or potential difference change rate distribution associated with the preliminarily related dimension shape and the position of the flaw included in the object to be measured, the size shape It is said that the progress of flaws can be detected.

  Patent Document 2 describes a method for detecting damage to a structure made of a conductive material using a potential difference method. In the technique described in Patent Document 2, a plurality of potential difference measurement terminals are linearly arranged in the longitudinal direction of the conductive material structure on the surface of the conductive material structure, which is the object to be measured, at predetermined intervals. A first step of measuring the potential difference between the terminals, measuring the potential difference between the terminals, obtaining the potential difference distribution in the measurement region, and evaluating the occurrence of damage is performed. If it is determined that there is damage in the first step and it is determined that more detailed measurement is necessary, a plurality of potential difference measurement terminals are arranged in a straight line at a narrower measurement interval in the area. The second step is performed to measure the potential difference occurring in the measurement area, obtain the potential difference distribution in the measurement region, and measure the presence or absence of damage more accurately. If it is evaluated that there is damage in this second step, a plurality of potential difference measurement terminals are arranged in a grid pattern at narrower intervals in the region as a third step, and the type and degree of damage are determined. evaluate. Furthermore, if necessary, a plurality of potential difference measurement terminals are arranged in a grid pattern at a further narrow interval, the potential difference generated between each terminal is measured, the potential difference distribution in the measurement region is obtained, and the degree of damage is measured with higher accuracy. A fourth step may be added. According to the technique described in Patent Document 2, it can be used as a rough screening test for an actual structure, and the type and degree of damage can be detected with high accuracy as required.

  Patent Document 3 describes a method for detecting damage to a structure made of a conductive material. In the technique described in Patent Document 3, a plurality of potential difference measurement terminals are arranged at a predetermined interval so as to surround a region to be measured of a structure made of a conductive material, and a pair of potential difference measurement terminals are sandwiched therebetween. Between the respective potential difference measurement terminals that surround the region to be measured of the conductive material structure and are opposed to each other while supplying current in a specific direction of the conductive material structure through the pair of electrode terminals. Conductive material is measured while measuring a potential difference generated, and then supplying a current in a direction different from the specific direction through another pair of electrode terminals sandwiching a plurality of potential difference measurement terminals separately from the pair of electrode terminals. The potential difference generated between the respective potential difference measurement terminals surrounding the measurement area of the manufactured structure is measured, and the damage state in the measurement area is evaluated. As a result, even in the measurement area where the potential difference measurement terminal cannot be directly installed, the damage occurrence area can be specified. Further, in the technique described in Patent Document 3, it is possible to specify the damage occurrence region with higher accuracy by narrowing the interval between the potential difference measurement terminals.

  Recently, attempts have been made to inspect pipes and the like using guide waves. For example, Non-Patent Document 1 describes a pipe corrosion inspection technique using a guide wave. This technique is to inspect a defect by applying a long-distance propagation ultrasonic wave (guide wave) from a sensor installed on the outer surface of a pipe. The ultrasonic wave (guide wave) applied from the surface of the pipe propagates in the axial direction of the pipe, and detects the presence of a defect using a change in cross-sectional shape existing on the path as a reflection source. According to this technique, it is possible to inspect several tens of meters from the measurement position regardless of the installation position of the pipe.

JP 2005-208039 A JP 2008-83038 A JP 2009-74923 A

Hiroyuki Shanishi et al .: NKK Technical Report, No.177 (2002.6), p.38-42

  In the techniques described in Patent Documents 1 to 3, with respect to an object to be measured in which a potential difference measurement terminal can be set in the vicinity of a damage occurrence location, damage can be identified relatively accurately with non-destructiveness even while the plant is in operation. I can say that. However, for example, in piping covered with embankments, walls, embankments, etc. as shown in FIG. 1, a plurality of potential difference measurement terminals cannot be set directly in the vicinity of the damage occurrence location, and thus described in Patent Documents 1 to 3 There is a problem that the technology cannot be applied as it is.

In the past, the damage caused to the pipes covered with embankments, embankments, etc. as shown in FIG. 1 was investigated by directly disassembling the embankments, embankments, etc., and ultrasonic flaw detection, X-ray inspection, etc. . However, there is a problem that a large amount of cost is incurred in a survey that presupposes the dismantling of such embankments and embankments.
Moreover, in the inspection technique using the guide wave described in Non-Patent Document 1, there is an advantage that inspection of piping and the like can be performed without dismantling the embankment, bank, heat insulating material, etc., but the measurement section is When the length is longer, there is a problem that the ultrasonic wave is attenuated and it becomes difficult to ensure a predetermined inspection accuracy, and a desired inspection accuracy cannot be obtained due to the influence of an anticorrosion tape attached to the outside of a pipe or the like.

  Therefore, the present invention solves such a problem of the prior art, and among the damages that occur in the structure made of conductive material, such as thinning that occurs in places that require a large amount of cost for inspection and that are difficult to perform the inspection. It is an object of the present invention to propose a damage estimation method for a structure made of a conductive material that can easily and non-destructively estimate damage.

  In order to achieve the above-described object, the present inventors first applied non-destructive and simple measurement, applying a potentiometric method, and inspecting a structure such as a pipe. Even in difficult locations, we have intensively studied how to measure the degree of damage with high accuracy without dismantling the embankment, bank, and insulation. As a result, it has been conceived that it is effective to set a region having the same structure in the same structure (pipe) as a region (potential difference measurement region) where damage is to be measured as a reference potential difference measurement region. Then, a plurality of reference potential difference measurement terminals are set in the reference potential difference measurement area, and the electrode pair is sandwiched between the potential difference measurement area and the reference potential difference measurement area so that the potential difference measurement terminals set in the potential difference measurement area are in series. It was found that the damage in the potential difference measurement region can be measured with high accuracy by measuring the potential difference in each region and comparing the potential difference per unit length.

  This is because the reference potential difference measurement region having the same structure as the potential difference measurement region can easily measure the degree of damage without requiring any special work even if damage has not occurred or has occurred, If the potential difference per unit length between the reference potential difference measurement terminals set in such a region is set as a reference potential difference, and the potential difference change rate between the potential difference measurement terminals in the potential difference measurement region with respect to the reference potential difference is calculated, Therefore, it is possible to easily estimate whether or not there is any damage and how much.

The present invention has been completed on the basis of such findings and further studies. That is, the gist of the present invention is as follows.
(1) Damage using a potentiometric method to estimate the degree of damage in a region to be inspected that is difficult to inspect for damage in a structure made of a conductive material by directly setting a plurality of potential difference measurement terminals in the vicinity of the damage occurrence site In the estimation method, the conductive material structure is a pipe, the inspection target part has a tube shape including a straight pipe part, the inspection target part is defined as a potential difference measurement section, and both sides sandwiching the potential difference measurement section as the pair in, arranged at least one pair of potentiometric terminal, further, in the region other than the previous SL inspected portion, a portion having the same tubular shape as the inspection target region, in the vicinity of the inspected portion wherein when present in piping, a site with of identity Ji pipe shape is set as the reference potential difference measuring period,該参 so that the pair at the ends on both sides of the irradiation potential difference measuring section, at least a pair of reference potential measuring terminal Arrange In addition, a pair of electrodes is installed in the conductive material structure so as to sandwich the potential difference measurement section and the reference potential difference measurement section, and the potential difference measurement section and the reference potential difference measurement section are connected in series via the pair of electrodes. The potential difference per unit length between the pair of reference potential difference measurement terminals obtained by measuring a potential difference between the at least one pair of potential difference measurement terminals and the at least one pair of reference potential difference measurement terminals From the potential difference V _3i per unit length between the pair of potential difference measurement terminals obtained with reference to V _2i , the following equation (1) ΔV ₃ (%) = {(V _3i / V _2i ) −1} × 100 (1)
(Where ΔV _{3 is} the potential difference change rate (%) of the site to be examined, V _{3i is} the potential difference per unit length between the pair of potential difference measurement terminals, and V _{2i is} per unit length between the pair of reference potential difference measurement terminals. Potential difference)
The potential difference change rate ΔV ₃ of the site to be inspected defined in (1) above is calculated, and the degree of damage to the site to be inspected is estimated based on the potential difference change rate ΔV _3. Estimation method.

(2 ) In (1), instead of the case where the inspection target part has a tube shape including a straight pipe part , the inspection target part has a pipe shape including a straight pipe part and a bent part, and the inspection when the site with more same length in the same tubular shape as the target site is present in the pipe in the vicinity of the inspected portion is a portion having the same length in of identity Ji tube shape, as said reference potential measure section A damage estimation method for a structure made of a conductive material, characterized by comprising:

(3) (1), the examination target region is in place if it has a tubular shape consisting of straight pipe section, before Symbol examination target region is composed of a straight pipe portion and the n-number of bends, the test object When a portion having the same tube shape as the portion is present in the pipe in the vicinity of the potential difference measurement section, the reference potential difference measurement section is a straight pipe portion having the same tube shape as the straight pipe portion, and further, the bending portion. the at least one bend portion having the same tube shape, set respectively, the potential difference change rate [Delta] V ₃ of the inspected portion, instead of the equation (1), the following equation (2) [Delta] V 3 _(%) = (V ₃ / (V _2E × n + V _2S × L) −1) × 100 (2)
(Where ΔV _{3 is} the potential difference change rate (%) of the site to be examined, V _{3 is} the potential difference between the pair of potential difference measurement terminals in the potential difference measurement section (test target section), and V _{2S is the} reference potential difference measurement section in the straight tube section. Potential difference per unit length between a pair of reference potential difference measurement terminals, V _2E : Potential difference between a pair of reference potential difference measurement terminals in a bent portion reference potential difference measurement section, n: Number of bent portions in the potential difference measurement section, L: Potential difference Straight pipe length in the measurement section)
The damage estimation method of the structure made from an electrically-conductive material characterized by calculating using this.

( 4 ) In any one of (1) to ( 3 ), the potential difference change rate ΔV ₃ (%) of the site to be inspected and the average thickness ts (mm) of the reference potential difference measurement section obtained by an ultrasonic flaw detection method The following equation (3) tm (mm) = (ts) × (1−ΔV ₃ / (100 + ΔV ₃ )) (3)
(Where tm: estimated average thickness (mm) of the site to be examined, ts: standard average thickness (mm) of the reference potential difference measurement section, ΔV ₃ : potential difference change rate (%) of the site to be examined)
A method for estimating damage to a structure made of a conductive material, comprising calculating an estimated average thickness tm of the inspection target part using a.

( 5 ) In any one of (1) to (4), when the potential difference change rate ΔV ₃ (%) of the inspection target region exceeds a preset threshold value, the potential difference change rate ΔV of the inspection target region is further increased. _A method for estimating damage to a structure made of a conductive material, wherein the minimum thickness is estimated from ₃ (%) and a master curve obtained in advance.

  According to the present invention, it is possible to easily and non-destructively estimate damage such as thinning that occurs in a place (inspection target part) that requires a great deal of cost for measurement and is difficult to carry out the measurement. Play. In addition, according to the present invention, there is an effect that it is possible to estimate the degree of local damage as well as the gentle thinning.

It is explanatory drawing which shows typically an example of the test object site | part which this invention makes object. It is explanatory drawing which shows typically schematic structure of the potentiometric device used by this invention. It is explanatory drawing which shows typically an example of the installation condition of the electric potential difference measurement terminal pair and the reference electric potential difference measurement terminal pair in the test object part which consists of a straight pipe part. It is a graph which shows the relationship (master curve) between an estimated minimum thickness and a potential difference change rate. It is explanatory drawing which shows typically an example of the installation condition of the electric potential difference measurement terminal pair in the test object site | part which has a straight pipe part and one bending part. It is explanatory drawing which shows typically an example of the installation condition of the electric potential difference measurement terminal pair in the test object site | part which has a straight tube | pipe part and two bending parts. It is explanatory drawing which shows typically the test object site | part measured in the Example with a measurement terminal position. It is explanatory drawing which shows the procedure of damage estimation in this invention.

For example, in oil refining plants, oil barriers such as embankments, walls, and banks are installed around the storage tanks to prevent the outflow of dangerous materials from the storage tanks, etc. There is a place where some piping penetrates them. Furthermore, not only an oil refining plant but also a pipe that is a structure made of a conductive material may be buried in the ground or the like.
Even in such a place, damage may be a problem, and it is necessary to inspect the degree of damage periodically or as necessary. In order to directly inspect the degree of damage at such a location, for example, in a breakwater, it is necessary to install a temporary breakwater and dismantle the embankment, etc. It is becoming difficult to inspect directly the degree of. In addition, inspection of piping buried in the ground requires excavation work of the buried portion, which requires a great deal of cost.

The present invention is a damage estimation method for a structure made of a conductive material, which can easily and non-destructively estimate the degree of damage to such a difficult-to-inspect site using a potential difference method.
In the present invention, the region to be inspected is set as the measurement area W and is set as a potential difference measurement section, and at least a pair of potential difference measurement terminals are disposed so as to be paired on both sides thereof. Measure the potential difference of the pair. The apparatus used for measuring the potential difference is not particularly limited. However, as shown in FIG. 2, the power source 1 and at least a pair of electrodes 11 for applying a current from the power source 1 to the measurement region W, 11, a device having a plurality of potential difference measuring terminals 2, a potential difference measuring means 3, a calculating means 4, and a data storing means 5.

A pipe in an oil refinery plant will be described as an example of the conductive material structure. Needless to say, the present invention is not limited to this.
The structure shown in FIG. 3 is a pipe having a pipe shape formed only from a straight pipe portion. As schematically shown in FIG. 3, a portion of the piping covered with a bank is a portion to be inspected.
In FIG. 3, four potential difference measurement terminals are installed at each position in the circumferential direction of the pipe, for a total of eight positions, and four potential difference measurement terminal pairs, 2a-2b, 2c-2d, 2e- The installation is such that 2f, 2g-2h can be formed.

In the present invention, in a region other than the potentiometric measurement interval, a reference potential difference measurement section provided, so that the pair at the ends on both sides of the section, at least a pair disposed a reference potential measurement terminal. The installation position of the reference potential difference measurement terminal is the same position as the installation position of the potential difference measurement terminal, for example, the same circumferential direction position of the pipe as shown in FIG. The reference potential difference measurement terminal is provided to erase a resistance change (change in potential difference) other than damage, such as a material of the structure, a shape of the structure, and a temperature change of the structure. In FIG. 3, four reference potential difference measuring terminals are installed in the circumferential direction, which is the same circumferential position of the pipe corresponding to the potential difference measuring terminal, for a total of eight locations, and four pairs of reference potential differences are measured in the reference potential difference measuring section. The measurement terminal pairs 2b-i, 2d-j, 2f-k, and 2h-l are installed.

The potential difference measuring terminal and the reference potential difference measuring terminal are preferably a terminal of a method in which the surface is measured with a spring or the like and sufficiently brought into contact with the surface of the conductive material measurement object. You may join and arrange | position by joining means, such as welding, crimping | bonding, and adhesion | attachment. Bonding is not particularly limited as long as the contact resistance does not change.
In the present invention, a pair of potential difference measurement sections and reference potential difference measurement sections are sandwiched between the above-described potential difference measurement sections and reference potential difference measurement sections, that is, in FIG. Electrodes 11 and 11 are installed. A current supply power source is wired to the pair of electrodes 11 and 11 so that a current can be supplied from the power source 1. The applied current is preferably a direct current or a direct current pulse current. Note that the value of the applied current is not particularly limited as long as the potential difference can be measured in the measurement region.

  In the present invention, while current is supplied between the electrode pair, it occurs between at least a pair of potential difference measurement terminals and at least a pair of reference potential difference measurement terminals installed at corresponding circumferential positions in the reference potential difference measurement section. Each potential difference is measured. Obtain the potential difference per unit length from the obtained potential difference between the pair of potential difference measurement terminals and the potential difference between the pair of reference potential difference measurement terminals, and use the potential difference per unit length between the reference potential difference measurement terminals as a reference. The rate of change in potential difference between potential difference measurement terminals is calculated.

It should be noted that the potential difference change rate (electric field fingerprint coefficient) ΔV ₃ between the potential difference measurement terminals, that is, the potential difference change rate of the region to be examined is expressed by the following equation (1) ΔV ₃ (%) = {(V _3i / V _2i ) −1 } × 100 (1)
Here, V _3i : Potential difference per unit length between a pair of potential difference measurement terminals (inspection site),
V _2i : A value defined by a potential difference per unit length between a pair of reference potential difference measurement terminals.

In the present invention, based on the potential difference change rate ΔV ₃ of the inspection target part, the degree of damage of the inspection target part is estimated. In addition, the present inventors have already confirmed that the potential difference change rate ΔV ₃ of the site to be examined is proportional to the degree of damage in the section. For example, if the damage is a decrease in thickness, if the potential difference change rate ΔV ₃ increases, the decrease in thickness increases. If the damage is local pitting corrosion, the pitting corrosion depth increases as the potential difference change rate ΔV ₃ increases.

If damage is reduced wall thickness is the thickness of the reference potential difference measuring section are not inspected portion, by measuring as a reference thickness by ultrasonic flaw detection and the like, the average wall of the reference potential difference measuring section Using the thickness ts (mm) as a reference, from the potential difference change rate ΔV _{3 of the} site to be inspected, the following equation (3): tm (mm) = (ts) × (1−ΔV ₃ / (100 + ΔV ₃ )) (3)
(Where tm: estimated average thickness (mm) of the site to be examined, ts: standard average thickness (mm) of the reference potential difference measurement section, ΔV ₃ : potential difference change rate (%) of the site to be examined)
Can be used to calculate the estimated average thickness tm (mm) of the region to be examined. In addition, the value measured separately by the ultrasonic flaw detection method in the reference potential difference measurement terminal shall be used for the standard average thickness of the reference potential difference measurement section.

When the conductive material structure is a pipe, the potential difference change rate V ₃ (%) is measured at each position in the circumferential direction, and the maximum value is obtained. Since the potential difference change rate is proportional to the thickness reduction amount, the maximum thickness reduction occurs at the circumferential position where the maximum value occurs. Therefore, from the viewpoint of safety, when the structure is a pipe, it is preferable to estimate the degree of damage using the thickness reduction amount (minimum thickness) at the position where the maximum potential difference change rate occurs.

  Depending on the structure to be inspected, the potential difference change rate may vary by about 5% due to the influence of manufacturing errors and the like. When the obtained potential difference change rate in the potential difference measurement section is larger than the potential difference change rate due to an error at the time of manufacturing, it can be estimated that corrosion (thickness reduction) occurs in the section. For this reason, it is preferable to set a threshold value including an error during manufacturing in order to detect the occurrence of the thickness reduction. As an example of one threshold value, a potential difference change rate of 5% can be used. Further, a value obtained by calculation based on a standard or a tolerance of the mill sheet may be used as the threshold value. If the potential difference change rate does not exceed the threshold value, it can be determined that the corrosion in the section is minor, and if the threshold value is exceeded, it is assumed that corrosion has occurred and there is damage. It is necessary to confirm the degree of damage. In addition, the progress of the damage can be monitored.

The master curve measures a number of damages (thickness reduction) and the degree of potential difference change in the damage (thickness reduction) that actually occurs in structures exposed to the same type of environment. Then, based on the obtained data, for example, as shown in FIG. 4, the correlation between the potential difference change rate ΔV ₃ and the estimated minimum thickness (maximum thickness reduction amount) may be determined in advance. preferable.

Such a pre-determined as a master curve, based on the correlation between the potential difference change rate [Delta] V ₃ and the estimated minimum wall thickness (maximum thickness reduction), the potential difference change rate [Delta] V ₃ obtained, of the inspection target section The estimated minimum wall thickness can be estimated and the degree of damage (corrosion) can be determined (confirmed).
In addition, when the inspection target part is a pipe having a pipe shape including a straight pipe part and a bent part, it is necessary to consider that the bent part has a different influence on the potential difference measured from the straight pipe part. There is.

  For example, as shown in FIG. 5, when there is a part having the same tube shape and the same length as the inspection target part in the vicinity of the inspection target part in the pipe, the same length and the same length are used. It is preferable to set the part which has as a reference electric potential difference measurement area. The above-described (1) is the same as in the case of the tube shape of only the straight tube portion by setting a portion having the same tube shape and the same length as the examination target portion that is the potential difference measurement section as the reference potential difference measurement section. The formula can be used, and the potential difference change rate in the potential difference measurement section can be calculated from the potential difference between the obtained potential difference measurement terminals based on the potential difference between the reference potential difference measurement terminals. In this case, since the length between the reference potential difference measurement terminals and the potential difference measurement terminals are the same, it is not necessary to convert the potential difference per unit length when using the equation (1).

Further, as shown in FIG. 6, the inspection target part is composed of a straight pipe part and n bent parts, and the part having the same pipe shape including the inspection target part and the length is connected to the pipe near the inspection target part. If there is a bent part with the same tube shape in the nearby pipe, the reference potential difference measurement section is set to a straight pipe part with the same tube shape as the straight pipe part of the difficultly inspected part, and the bent part of the difficultly inspected part It is preferable to set at least one bent portion having the same tube shape. Also in this case, similarly to the equation (1), the rate of change of the potential difference of the examination target site is expressed by the following equation (2) ΔV ₃ (%) = ((V ₃ / (V _2E × n + V _2S × L) -1) × 100 (2)
(Where ΔV _{3 is} the potential difference change rate (%) of the site to be examined, V _{3 is the} potential difference of the potential difference measurement section (test target site), and V _{2S is} the straight pipe per unit length of the straight pipe portion of the reference potential difference measurement section. Part reference potential difference, V _2E : reference potential difference per bent part of the reference potential difference measurement section, n: number of bent parts in the potential difference measurement section, L: length of straight pipe part in the potential difference measurement section)
It is preferable to calculate using By using the equation (2), it is possible to easily estimate the degree of damage in the potential difference measurement section including the straight pipe portion and the plurality of bent portions, including damage to the straight pipe portion and the bent portion. become.

FIG. 8 shows a flow of a procedure for estimating the degree of damage using the potentiometric method when the structure is a pipe and the inspection target part to be measured has various pipe shapes.
First, the inspection object is selected. If the object to be inspected is a straight pipe-shaped pipe, the measurement terminal is set as shown in FIG. When the inspection object includes a bent portion (component) other than the straight pipe, if there is a portion having the same shape and the same length in the vicinity, the measurement terminal is set as shown in FIG. When the inspection object is other than that, the measurement terminal is set as shown in FIG. 6, that is, the reference potential difference measurement section is set to the straight pipe portion and the bent portion, respectively. When the setting of the measurement terminals is completed, a current is passed through the electrode pair, the potential difference between the measurement terminals is measured, and the potential difference change rate in the potential difference measurement section is obtained. If the potential difference change rate is less than or equal to a predetermined threshold, the degree of corrosion in the potential difference measurement section is determined to be minor, and if it exceeds the threshold, the estimated minimum wall thickness is determined using a predetermined master curve. It is preferable to determine the degree of corrosion (damage) from the value.

  Hereinafter, based on an Example, this invention is demonstrated further.

Example 1
The damage state of the penetrating part (part to be inspected) penetrating the oil barrier as shown in FIG. 3 was measured using a potentiometric method in an oil refinery plant pipe (made of carbon steel pipe). A plurality of potential difference measurement terminals were provided so as to be paired on both sides of the penetrating portion (inspection target site), thereby forming a potential difference measurement section. The plurality of potential difference measurement terminals were installed at four positions (0 °, 90 °, 180 °, 270 °) in the circumferential direction of the pipe. In addition, the reference potential difference measurement section was installed adjacent to the penetrating part (part to be inspected). In the reference potential difference measuring section, a plurality of reference potential difference measuring terminals were installed so as to be paired on both ends of the section. The plurality of reference potential difference measurement terminals were installed at four positions (0 °, 90 °, 180 °, and 270 °) in the circumferential direction of the pipe, similarly to the potential difference measurement terminals.

The pair of electrodes 11 and 11 were installed so as to sandwich the potential difference measurement section and the reference potential difference measurement section. Then, the potential difference of the potential difference measurement pair and the potential difference of the reference potential difference measurement pair at each position in the circumferential direction of the pipe were measured while supplying a DC pulse current through the pair of electrodes.
Using the obtained potential difference, the potential difference change rate ΔV ₃ (%) of the difficult-to-test site was calculated by the above-described equation (1). Next, using the obtained ΔV ₃ , the estimated average thickness tm of the difficult-to-inspect part was calculated from the above equation (3). The thickness at each reference potential difference measurement terminal was measured by an ultrasonic flaw detection method to obtain a standard average thickness ts. When different values were measured between the reference potential difference measurement terminals at the same position in the circumferential direction, the average value was used on the assumption that the wall thickness changed linearly between them.

  The obtained results are shown in Table 1.

The position of 270 ° in the circumferential direction shows the largest potential difference change rate of 3.6%. The minimum estimated average wall thickness was 6.0 mm (thickness reduction: 0.4 mm) at the 90 ° position in the circumferential direction. If the thickness was reduced to this extent, it was determined that there was no corrosion at the inspection target site.
(Example 2)
With a pipe (made of carbon steel pipe) of an oil refinery plant, as shown in FIG. 6, a penetrating part (part to be inspected) composed of two bent parts and a straight pipe part is used as a potential difference measuring section. In the same manner as in Example 1, the potential difference was measured. Note that the reference potential difference measurement section was set to a bent portion other than the through portion and a straight pipe portion. In the same manner as in Example 1, the measurement terminals in each section were arranged at four locations in the circumferential direction. As in the first embodiment, a pair of electrodes 11 and 11 are arranged so as to sandwich the potential difference measurement section and the reference potential difference measurement section, and a DC pulse current is supplied to each potential difference measurement terminal pair, and The potential difference generated in the reference potential difference measuring terminal pair was measured.

Using the obtained potential difference, the potential difference change rate ΔV ₃ of the penetrating portion (examination target site) was calculated using the above-described equation (2). From the obtained potential difference change rate ΔV ₃ and the average thickness ts between the reference potential difference measurement terminals measured by the ultrasonic flaw detection method, the estimated average thickness tm of the penetrating portion (examination target site) is calculated using equation (3). Asked.
The obtained results are shown in Table 2.

The 180 ° position in the circumferential direction shows the largest potential difference change rate of −1.0%. Moreover, the minimum estimated (average) thickness was 3.8 mm (thickness reduction: 0.4 mm) at a 180 ° position in the circumferential direction. If the thickness was reduced to this extent, it was determined that there was no corrosion at the inspection target site.
(Example 3)
In the pipe of an oil refinery plant (made of carbon steel pipe), as shown in Fig. 7, the potential difference method is used for the through-hole (inspection target part) having a straight pipe shape with a sheath pipe connected to the outlet side of the through-hole. The damage state was measured. Since the sheath tube exists, the reference potential difference measurement section was installed without being adjacent to the position away from the penetrating portion, and the measurement terminals were provided on both sides of the end portion of the reference potential difference measurement section. In the same manner as in Example 1, the measurement terminals in each section were arranged at four locations in the circumferential direction. As in the first embodiment, a pair of electrodes 11 and 11 are arranged so as to sandwich the potential difference measurement section and the reference potential difference measurement section, and a DC pulse current is supplied to each potential difference measurement terminal pair, and The potential difference generated in the reference potential difference measuring terminal pair was measured.

Using the obtained potential difference, similarly to Example 1, the potential difference change rate ΔV ₃ (%) of the penetrating portion (examination target site) was calculated by the above-described equation (1). Next, using the obtained ΔV ₃ , the estimated average thickness tm of the site to be inspected was calculated from the above equation (3). The thickness at each reference potential difference measurement terminal was measured by an ultrasonic flaw detector to obtain the standard average thickness ts. When different values were measured between the reference potential difference measurement terminals at the same position in the circumferential direction, the average value was used on the assumption that the wall thickness changed linearly between them.

  The obtained results are shown in Table 3.

  The position of 270 ° in the circumferential direction shows the largest potential difference change rate, which is 5.4%, and the estimated average thickness is 5.9mm (thickness reduction: 0.5mm) at the position of 90 ° in the circumferential direction. It was determined that scale corrosion had occurred. The degree of corrosion was estimated from the obtained maximum potential difference change rate and the master curve shown in FIG. 4 that the estimated minimum thickness was about 70% of the original thickness. However, since the required wall thickness of the pipe is 60% of the original thickness, it was judged that no urgent measures were necessary.

1 Power supply
11, 12 Electrode 2 Potential difference measurement terminal 3 Potential difference measurement means 4 Calculation means 5 Data storage means

Claims (5)

Damage estimation method that uses the potentiometric method to estimate the degree of damage in a part to be inspected that is difficult to inspect for damage in a structure made of a conductive material by directly setting a plurality of potential difference measurement terminals in the vicinity of the damage occurrence part Because
The conductive material structure is a pipe, and the inspection target part has a pipe shape including a straight pipe part,
At least a pair of potential difference measurement terminals are arranged so that the examination target site is a potential difference measurement section, and a pair is formed on both sides across the potential difference measurement section,
Furthermore, an area other than the pre-Symbol inspected portion, a portion having the same tubular shape as the inspection target region, if present in the pipe in the vicinity of the inspected portion is a portion having a of identity Ji tube shape, Set as reference potential difference measurement section,
Disposed at least one pair of reference potential measuring terminal such that the pair at the ends on both sides of the 該参 irradiation potential difference measuring section,
Furthermore, a pair of electrodes is installed in the conductive material structure so as to sandwich the potential difference measurement section and the reference potential difference measurement section, and a current is connected in series to the potential difference measurement section and the reference potential difference measurement section via the pair of electrodes. Measuring the potential difference between the at least one pair of potential difference measuring terminals and between the at least one pair of reference potential difference measuring terminals,
On the basis of the potential difference V _2i per unit length between the pair of reference potential measurement terminals obtained, the potential difference V _3i per unit length between the pair of potential difference measurement terminals obtained from the following (1) A potential difference change rate ΔV ₃ of the site to be inspected defined by the equation is calculated, and a degree of damage of the site to be inspected is estimated based on the rate of change in potential difference ΔV ₃ . Damage estimation method.
ΔV ₃ (%) = {(V _3i / V _2i ) −1} × 100 (1)
Where ΔV ₃ : potential difference change rate (%) of the site to be examined
V _3i : Potential difference per unit length between a pair of potential difference measurement terminals,
V _2i : _Potential difference per unit length between a pair of reference potential difference measurement terminals Instead of the case where the inspection target part has a tube shape made of a straight pipe part, the inspection target part has a pipe shape made of a straight pipe part and a further bent part, and further has the same tube shape as the inspection target part. If the sites having the same length are present in the pipe in the vicinity of the inspected portion is claims and sets the sites having the same length in of identity Ji tube shape, as said reference potential measure section Item 2. A method for estimating damage to a structure made of a conductive material according to Item 1. Instead of the case where the inspection target part has a tube shape including a straight pipe part, the inspection target part includes a straight pipe part and n bent parts, and a part having the same tube shape as the inspection target part is provided. When present in the pipe in the vicinity of the potential difference measuring section, the reference potential difference measuring section has at least one straight pipe portion having the same tube shape as the straight pipe portion, and further having the same pipe shape as the bent portion. in a bend, respectively set, a potential difference change rate [Delta] V ₃ of the inspected portion, instead of the equation (1), according to claim 1, characterized in that calculated using the following formula (2) Of estimating damage to a structure made of conductive material.
ΔV ₃ (%) = (V ₃ / (V _2E × n + V _2S × L) −1) × 100 (2)
Where ΔV ₃ : potential difference change rate (%) of the site to be examined
V ₃ : Potential difference between a pair of potential difference measurement terminals in a potential difference measurement section (examination target site),
V _2S : Potential difference per unit length between a pair of reference potential difference measurement terminals in the straight pipe portion reference potential difference measurement section,
V _2E : Potential difference between a pair of reference potential difference measurement terminals in the bent portion reference potential difference measurement section, n: Number of bent portions in the potential difference measurement section,
L: Straight pipe length in the potential difference measurement section Based on the potential difference change rate ΔV ₃ (%) of the site to be inspected and the average thickness ts (mm) of the reference potential difference measurement section obtained by the ultrasonic flaw detection method, the following equation (3) is used as a reference. The estimated average thickness tm (mm) of a target part is calculated, The damage estimation method of the structure made from a conductive material in any one of Claim 1 thru | or 3 characterized by the above-mentioned.
Tm (mm) = (ts) × (1−ΔV ₃ / (100 + ΔV ₃ )) (3)
Where tm: estimated average thickness (mm) of the site to be examined
ts: standard average thickness (mm) of the reference potential difference measurement section,
ΔV ₃ : Potential difference change rate (%) of the site to be examined When the potential difference change rate ΔV ₃ (%) of the inspection target region exceeds a preset threshold, the potential difference change rate ΔV ₃ (%) of the inspection target region is further calculated from the master curve obtained in advance. The method of estimating damage to a structure made of a conductive material according to claim 1, wherein the thickness is estimated.

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