JP5876745B2 - Method for evaluating the degree of corrosion of steel pipe columns - Google Patents

Description

  The present invention relates to a method for evaluating the degree of corrosion of a steel pipe column.

  Conventionally, steel pipe columns are endured by galvanization on the inner and outer surfaces, the lower end portion is buried in the ground, and are built as electric poles in mountainous areas and narrow spaces.

  However, in such a steel pipe column, the boundary between the buried portion buried in the ground and the ground surface and the buried portion in the vicinity of the boundary (hereinafter collectively referred to as a ground portion) due to long-term use. There is a case where the thickness becomes thin due to corrosion, and when such a corrosion defect occurs, the steel pipe column may collapse. Therefore, it is required to detect a corrosion defect of the steel pipe column at the submarine part, reinforce the corroded portion of the steel pipe column, or rebuild the corroded steel pipe column.

  As a method for detecting such a corrosion defect of a steel pipe column, for example, a probe of an ultrasonic flaw detector is attached to the ground of a steel pipe column whose lower part is buried in the ground, and ultrasonic waves are transmitted to the underground part by the probe. From the echo received by the probe and received by the probe, in the first evaluation means, the ratio of the total echo height from the edge of the steel pipe column and the total echo height from the end surface of the steel pipe column In the second evaluation means, the ratio of the total echo height from the steel pipe column base and the total echo height from the entire middle part of the steel pipe column is evaluated in multiple stages, and the third evaluation is performed. In the means, the defect of the steel pipe column boundary part is evaluated by evaluating the defect of the steel pipe column boundary part in a plurality of stages from the evaluation of the plurality of stages of the first evaluation means and the evaluation of the plurality of stages of the second evaluation means. A method has been proposed (see, for example, Patent Document 1).

JP 2009-36531 A

  However, the method described in Patent Document 1 can be used for a steel pipe column having a relatively thin thickness (for example, a thickness of 2 to 4 mm), while a steel pipe having a relatively thickness (for example, a thickness of 6 to 10 mm). When used on a column, the ultrasonic wave is attenuated by its thickness. In such a case, depending on the length of the steel pipe column, the echo from the end surface portion of the steel pipe column may not be received, and there is a problem that the defect cannot be accurately evaluated.

  An object of the present invention is to provide a method for evaluating the degree of corrosion of a steel pipe column, which can more accurately evaluate the degree of corrosion by a simple operation.

  In order to achieve the above object, the method for evaluating the degree of corrosion of a steel pipe column according to the present invention is a method for evaluating the degree of corrosion at the underground part of a steel pipe column whose lower end is buried in the ground, An arrangement step of arranging a pair of a probe for transmitting an ultrasonic flaw detector and a receiving probe for an ultrasonic flaw detector on a surface of a steel pipe column so as to be separated from the ground surface by a predetermined distance; A transmitting step of transmitting an ultrasonic beam from the probe; a direct receiving step of directly receiving an echo of the transmitted ultrasonic beam by the receiving probe during a predetermined beam path; and the transmitting An indirect receiving step of indirectly receiving the echo of the ultrasonic beam transmitted from the probe for the probe and reflected at the location of the corrosion by the receiving probe during a predetermined beam path; Received ultrasonic beam And an echo area, is characterized in that it comprises a area ratio calculation step of calculating the ratio of the echo area of indirectly received ultrasound beams.

  Further, in the method for evaluating the degree of corrosion of the steel pipe column of the present invention, in the area ratio calculation step, the echo area of the ultrasonic beam directly received and the echo area of the ultrasonic beam received indirectly are calculated. It is preferable to correct the ratio according to the temperature condition.

  In the method of evaluating the degree of corrosion of the steel pipe column according to the present invention, it is preferable that the end point of the beam path is set in the indirect reception step in accordance with the start point of the beam path of the echo of the ultrasonic beam.

  The method for evaluating the degree of corrosion of a steel pipe column according to the present invention further includes an echo area of an ultrasonic beam directly received and an echo of an ultrasonic beam received indirectly after the area ratio calculating step. It is preferable to provide a thinning rate estimation step of estimating an average thinning rate of the steel pipe column due to the corrosion from the ratio with the area.

  According to the method for evaluating the degree of corrosion of a steel pipe column according to the present invention, a transmission probe of an ultrasonic flaw detector and a reception probe of an ultrasonic flaw detector are used as a pair, and an ultrasonic wave directly received is received. The degree of corrosion of the steel pipe column is evaluated by the ratio of the echo area of the acoustic beam and the echo area of the ultrasonic beam received indirectly.

  Therefore, according to the method for evaluating the degree of corrosion of the steel pipe column of the present invention, it is not necessary to receive an echo from the end surface portion of the steel pipe column, and the ultrasonic wave is relatively attenuated (for example, a thickness of 6 to 10 mm). With regard to the steel pipe column of), the degree of corrosion can be more accurately evaluated by a simple operation.

(A) shows the schematic of the steel pipe column by which one Embodiment of the evaluation method of the corrosion degree of the steel pipe column of this invention is employ | adopted, (b) is one of the evaluation methods of the corrosion degree of the steel pipe column of this invention. An example of the chart obtained by embodiment is shown. It is the schematic of the steel plate at the time of preparation of a surface temperature-sensitivity difference graph. The surface temperature-sensitivity difference graph is shown. FIG. 6 is an arrangement diagram of probes when setting a reference sensitivity. It is the schematic of the steel pipe column at the time of preparation of a reflective echo evaluation range graph, Comprising: (a) is the top view schematic diagram of a steel pipe column, (b) shows the side view schematic diagram of a steel pipe column, respectively. The reflection echo evaluation range graph is shown. FIG. 6 is a layout diagram of probes when creating an area ratio temperature correction graph. An area ratio temperature correction graph is shown. It is the schematic of the steel pipe pillar at the time of preparation of an average thinning rate estimation graph, (a) is a form in which a notch is formed in a steel pipe pillar, (b) is a through-hole formed in a steel pipe pillar. Each form is shown. An average thinning rate estimation graph is shown. The measurement result regarding the direction 1 is shown. The measurement result regarding the direction 1-2 is shown. The measurement result regarding the direction 2 is shown. The measurement result regarding the direction 2-3 is shown. The measurement result regarding the direction 3 is shown. The measurement result regarding the direction 3-4 is shown. The measurement result regarding the direction 4 is shown. The measurement result regarding the direction 4-1 is shown. An appearance photograph in direction 1 is shown. An appearance photograph of direction 1-2 is shown. An appearance photograph in direction 2 is shown. An appearance photograph in direction 2-3 is shown. An appearance photograph in direction 3 is shown. An appearance photograph of direction 3-1 is shown. An appearance photograph in direction 4 is shown. An appearance photograph in direction 4-1 is shown.

  FIG. 1 (a) shows a schematic view of a steel pipe column in which an embodiment of the method for evaluating the degree of corrosion of the steel pipe column of the present invention is adopted, and FIG. 1 (b) shows the degree of corrosion of the steel pipe column of the present invention. An example of the chart obtained by one Embodiment of an evaluation method is shown.

  In FIG. 1 (a), the steel pipe pillar 1 consists of a well-known steel pipe which has predetermined thickness, and a lower end part is embed | buried in the ground and is constructed so that a vertical direction may be followed.

  The thickness (wall thickness) of the steel pipe column 1 is, for example, 6 to 10 mm, preferably 6 to 8 mm.

  Moreover, the outer diameter of the steel pipe column 1 is 216.3-267.0 mm, for example, Preferably, it is 216.3 mm.

  In such a steel pipe column 1, the buried portion (land portion) near the surface of the earth causes corrosion defects due to long-term use, for example, a through hole may be formed, or the wall may be thin, for example. FIG. 1 (a) schematically shows a portion 6 where corrosion occurs.

  When such a corrosion defect occurs, the steel pipe column may collapse. Therefore, it is required to detect a corrosion defect of the steel pipe column at the submarine part, reinforce the corroded portion of the steel pipe column, or rebuild the corroded steel pipe column.

  Hereinafter, a method for evaluating the degree of corrosion at the underground portion of the steel pipe column 1 will be described in detail.

  In this method, first, as shown in FIG. 1 (a), on the surface of the steel pipe column 1, the transmitting probe 3 of the ultrasonic flaw detector 2 and the receiving probe 4 of the ultrasonic flaw detector 2 are provided. Are disposed as a pair so as to be separated from the ground surface 5 (arrangement step).

  Specifically, the transmitting probe 3 is disposed at a predetermined distance from the ground surface 5 so that an ultrasonic beam (see arrow u in FIG. 1A) can be transmitted toward the ground surface 5 side. .

  The receiving probe 4 can directly receive the scattered echo (incident echo) (see arrow a in FIG. 1A) of the ultrasonic beam transmitted from the transmitting probe 3, In order to receive indirectly the reflected echo (corrosion echo) (see arrow x in FIG. 1 (a)) reflected at the location 6 where corrosion occurs, it is arranged at a predetermined distance from the ground surface 5.

  Preferably, the transmitting probe 3 and the receiving probe 4 are arranged at the same distance from the ground surface 5.

  The transmitting probe 3 and the receiving probe 4 are preferably arranged so as to be adjacent to each other along the circumferential direction of the steel pipe column 1 and in close contact with each other.

  The distance from the ground surface 5 of the probe 3 for transmission and the probe 4 for reception is 150-600 mm, for example, Preferably, it is 250-400 mm, More preferably, it is 300 mm.

  Next, in this method, an ultrasonic beam is transmitted from the transmitting probe 3 as schematically indicated by an arrow u in FIG. 1A (transmitting step).

  Examples of the ultrasonic beam include an ultrasonic beam generally used in the ultrasonic flaw detector 2, and specific examples include a T wave (longitudinal wave) and an S wave (transverse wave), and preferably , S wave. Examples of the S wave include an SH wave and an SV wave. From the viewpoint of reflectivity, an SH wave is preferable.

  The frequency of the ultrasonic beam is, for example, 0.2 to 1.0 MHz, preferably 0.5 MHz.

  Further, the flaw detection sensitivity of the ultrasonic beam is appropriately selected according to the purpose and application, and is further corrected by a known method according to, for example, the temperature condition (for example, the surface temperature of the steel pipe column 1).

  Next, in this method, as schematically shown by an arrow a in FIG. 1A, the echo of the transmitted ultrasonic beam is directly transmitted by the receiving probe 4 between predetermined beam paths. Receive (direct reception process).

  That is, in this method, since the transmitting probe 3 and the receiving probe 4 are provided separately on the steel pipe column 1, the ultrasonic beam transmitted from the transmitting probe 3 generates corrosion. Even if it is not reflected at the location 6 or the like, it is received by the receiving probe 4 as the scattered echo a.

  Thereby, the peak of the scattered echo a is detected so that A (described later) in FIG.

  The starting point of the beam path of the scattered echo a is a point where the ultrasonic beam is transmitted from the transmitting probe 3, and the end point of the beam path is appropriately set according to the purpose and application.

  The beam path of the scattered echo a is specifically, for example, 0 to 100 mm as a distance read by the ultrasonic flaw detector 2.

  Next, in this method, as schematically shown by an arrow x in FIG. 1A, an echo of an ultrasonic beam transmitted from the transmitting probe 3 and reflected at the corrosion occurrence site 6 is converted into a predetermined value. During the beam path, the signal is indirectly received by the receiving probe 4 (indirect reception process).

  That is, in this method, when a through-hole is formed in the steel pipe column 1 at the ground due to corrosion, or when the steel pipe column 1 is thin, ultrasonic waves are generated at the corrosion occurrence location 6. The beam is reflected, and the reflected echo x is received by the receiving probe 4.

  Thereby, the peak of the reflected echo x is detected so that X (described later) in FIG.

  The beam path of the reflected echo x is a distance from the rising start point of the peak of the reflected echo x to the peak end point of the reflected echo x and is observed as a distance read by the ultrasonic flaw detector 2.

  In actual measurement, for example, when the peak end point of the reflected echo x is unclear, the beam path of the reflected echo x may not be determined accurately.

  Therefore, in this method, preferably, after the start point of the beam path of the reflected echo x is observed, the end point of the beam path is set according to the start point.

  That is, in this method, there is a correlation between the start point of the beam path of the reflected echo x (the rising start point of the peak of the reflected echo x) and the end point (the peak end point of the reflected echo x). The distance from the start point to the end point becomes longer as the distance that becomes the start point of the beam path is longer.

  Therefore, in this method, the relationship between the start point and end point of the beam path of the reflected echo x is sampled in advance, and the start point and end point are determined based on the sampling result.

  More specifically, for example, first, a steel pipe column 1 in which a corrosion defect is generated at a predetermined position is prepared, and the transmission probe 3 and the reception probe 3 are separated from the corrosion defect at various predetermined intervals. The tactile element 4 is arranged. Then, the ultrasonic beam is transmitted and received, and the relationship between the start point of the beam path of the reflected echo x (the rising start point of the peak of the reflected echo x) and the end point (the peak end point of the reflected echo x) is sampled. Then, a graph showing the relationship between them (see FIG. 6, reflection echo evaluation range graph) is created.

  In actual measurement, using this reflection echo evaluation range graph, the end point of the beam path is determined according to the start point of the beam path of the reflection echo x (the rising start point of the peak of the reflection echo x), Thereby, the beam path is determined.

  Thus, if the end point of the beam path is set according to the start point of the beam path of the reflected echo x, the degree of corrosion of the steel pipe column 1 can be more accurately evaluated.

  Next, in this method, the echo area of the ultrasonic beam directly received in the direct reception step (that is, the peak area of the scattered echo a) and the ultrasonic wave indirectly received in the indirect reception step are described. A ratio with the echo area of the beam (that is, the peak area of the reflected echo x) is calculated (area ratio calculating step).

  The peak area of the scattered echo a is defined as the sum of the heights of the received echoes in the beam path (for example, 0 to 100 mm) of the scattered echo a, and is indicated by the letter A.

  The peak area of the reflected echo x is defined as the sum of the heights of the received echoes along the beam path (start point to end point) of the reflected echo x, and is indicated by the letter X.

  In this method, the peak area A of the scattered echo a and the peak area X of the reflected echo x are obtained, and the ratio of the peak area X of the reflected echo x to the peak area A of the scattered echo a (area ratio X / By calculating A), the degree of corrosion at the submerged portion of the steel pipe column 1 is evaluated.

  More specifically, in this method, it is determined that the greater the calculated area ratio, the greater the degree of corrosion of the steel pipe column 1, and the smaller the area ratio, the smaller the degree of corrosion of the steel pipe column 1.

  In addition, when the corrosion degree of the steel pipe column 1 is very small, or when the steel pipe column 1 is not corroded, the reflection echo x may not be received and the area ratio may be zero. In such a case, it is determined that the steel pipe column 1 is not corroded.

  On the other hand, the area ratio calculated as described above may vary depending on the surface temperature of the steel pipe column 1.

  Specifically, in this method, there is a correlation between the area ratio (X / A) calculated as described above and the surface temperature of the steel pipe column 1, and the lower the surface temperature of the steel pipe column 1, the more the area ratio ( X / A) increases.

  Therefore, in this method, from the viewpoint of more accurately evaluating the degree of corrosion, preferably, the relationship between the surface temperature of the steel pipe column 1 and the area ratio (X / A) is sampled in advance, and based on the sampling result. In the area ratio calculation step, the area ratio calculated as described above is corrected according to the temperature condition.

  More specifically, for example, first, a steel pipe column 1 in which a corrosion defect is generated at a predetermined position is prepared, and the ratio of the peak area X of the reflected echo x to the peak area A of the scattered echo a is measured for the steel pipe column 1. (X / A) is calculated at a reference temperature (for example, the surface temperature of the steel pipe column 1 is 18 ° C.).

  Then, in other temperature ranges (for example, the surface temperature of the steel pipe column 1 is 8 to 35 ° C.), the ratio of peak areas (X / A) is similarly calculated, and the surface temperature and the area ratio of the steel pipe column 1 (X / A) ) And a graph showing the relationship is created.

  Further, from the slope of this graph, the area ratio (X / A) calculated under the temperature condition at the time of measurement (for example, a temperature other than 18 ° C.) is the area calculated at the reference temperature (for example, 18 ° C.). A correction coefficient for correcting the ratio (X / A) is calculated, and a graph (see FIG. 8, area ratio temperature correction graph) showing the relationship between the correction coefficient and the temperature condition is created.

  In actual measurement, the area ratio temperature correction graph is used to obtain a correction coefficient corresponding to the temperature condition at the time of measurement, and the area ratio calculated as described above is corrected according to the obtained correction coefficient.

  Thereby, an area ratio can be standardized and the corrosion degree of the steel pipe pillar 1 can be evaluated more correctly.

  Moreover, the range (flaw detection range) evaluated by such a method is 30-100 mm as a length (flaw detection width) along the circumferential direction of the steel pipe column 1, for example, Preferably, it is 60 mm.

  Further, when the flaw detection width is less than the circumferential length of the steel pipe column 1, the steel pipe column 1 is preferably arranged in a plurality of regions along the circumferential direction in order to more reliably evaluate the degree of corrosion. Divide and evaluate the degree of corrosion in each area.

  Specifically, for example, as shown in FIG. 5A, the steel pipe column 1 is equally divided into a plurality of parts (for example, eight equal parts) along the circumferential direction, and at each of the equally divided points, By evaluating the degree of corrosion, the degree of corrosion of the steel pipe column 1 as a whole can be evaluated.

  Further, in this method, the area ratio (X / A) calculated as described above and the average thickness reduction rate due to corrosion of the steel pipe column 1 (average of the thickness reduction degree of the steel pipe column 1 within the flaw detection range (flaw detection width)) Value), and specifically, the greater the area ratio (X / A), the greater the average thickness reduction rate due to corrosion.

  Therefore, in this method, from the viewpoint of more accurately evaluating the degree of corrosion, preferably, after the area ratio calculation step, the echo area of the ultrasonic beam directly received (peak area A of the scattered echo a), and From the ratio (X / A) with the echo area (peak area X of the reflected echo x) of the ultrasonic beam received indirectly, the average thinning rate of the steel pipe column 1 due to corrosion is estimated (thickening rate estimation step) ).

  As such a method, for example, the relationship between the average thickness reduction rate due to corrosion of the steel pipe column 1 and the above-mentioned area ratio (X / A) is sampled in advance, and actually based on the sampling result, The method of estimating the average thickness reduction rate of the steel pipe column 1 by corrosion from the area ratio (X / A) calculated is mentioned.

  More specifically, for example, first, a steel pipe column 1 in which a corrosion defect is generated at a predetermined position and reduced in thickness at various average thickness reduction ratios is prepared, and the above-described area ratio (X / A) ) Is calculated. Then, the relationship between the average thinning rate and the area ratio (X / A) is sampled, and a graph showing the relationship (see FIG. 10, average thinning rate estimation graph) is created.

  And in an actual measurement, the average thinning rate of the steel pipe column 1 is estimated from the area ratio (X / A) calculated by using the average thinning rate estimation graph.

  Moreover, in this method, the range of the average thickness reduction rate and the range of the area ratio (X / A) can be made to correspond.

  That is, in the same manner as described above, for example, when the average thickness reduction rate is 0% or more and 25% or less, what range the area ratio (X / A) is, for example, the average thickness reduction rate is What is the range of the area ratio (X / A) when it exceeds 25% and is 50% or less, for example, when the average thickness reduction rate exceeds 50% and is 100% or less, the area The range of the ratio (X / A) is obtained by sampling, and the range of the area ratio (X / A) is set according to the range of the average thickness reduction rate.

  In the actual measurement, the steel pipe column is obtained from the area ratio (X / A) calculated as described above by applying the correspondence relationship between the range of the average thickness reduction ratio and the range of the area ratio (X / A). An average thinning rate of 1 can be estimated.

  Thus, if the average thickness reduction rate is estimated from the area ratio, the degree of corrosion of the steel pipe column 1 can be more accurately evaluated.

  And according to the evaluation method of the degree of corrosion of the steel pipe column 1 of the present invention, the transmitting probe 3 of the ultrasonic flaw detector 2 and the receiving probe 4 of the ultrasonic flaw detector 2 are used as a pair, The ratio of the echo area of the ultrasonic beam received directly (peak area A of the scattered echo a) and the echo area of the ultrasonic beam received indirectly (peak area X of the reflected echo x) (X / According to A), in order to evaluate the degree of corrosion of the steel pipe column 1, it is not necessary to receive an echo from the end surface portion of the steel pipe column 1, and the ultrasonic wave is relatively attenuated (for example, a thickness of 6 to 10 mm). The steel pipe column 1 can also evaluate the degree of corrosion more accurately by a simple operation.

Next, although this invention is demonstrated based on an Example, this invention is not limited by the following Example.
[Preparation for flaw detection]
<Creation of surface temperature-sensitivity difference graph>
FIG. 2 is a schematic view of a steel plate when creating a surface temperature-sensitivity difference graph.

  As shown in FIG. 2, a through hole having a diameter of 10 mm was formed as an artificial defect in a steel plate having a thickness of 5 mm, and a standard test specimen was produced.

  Next, a probe of the ultrasonic flaw detector 2 (model number: UI-25, manufactured by Ryoden Shonan Electronics Co., Ltd.) was placed at a position 300 mm away from the artificial defect. Then, while changing the surface temperature of the standard specimen from 8 to 35 ° C., an ultrasonic beam (SH wave, 0.5 MHz) is transmitted by the probe under each temperature condition, and the reflected echo reflected from the artificial defect The sensitivity at which x was received and the echo height was 80% was measured.

By repeating this, the change in sensitivity due to the surface temperature of the standard test specimen is sampled, and the difference in sensitivity due to the surface temperature of the standard test specimen is graphed based on the sensitivity at 18 ° C. Got. The obtained surface temperature-sensitivity difference graph is shown in FIG.
<Setting reference sensitivity>
FIG. 4 is a layout diagram of the probes when the reference sensitivity is set.

As shown in FIG. 4, in a steel pipe column 1 (thickness 6 mm, outer diameter 216.3 mm, surface temperature 18 ° C.) in which the lower part is buried in the ground, the transmitting probe of the ultrasonic flaw detector 2 is used. 3, and the receiving side probe 4 was arranged to face the transmitting side probe 3 so as to be spaced by 100 mm along the tube axis direction of the steel pipe column 1. Then, an ultrasonic beam was transmitted from the transmission side probe 3 and the transmission echo was received by the reception side probe 4 and the height of the transmission echo was adjusted to 80%. The sensitivity at this time was measured as the reference sensitivity and found to be 33.4 dB.
<Determination of flaw detection sensitivity>
In order to clarify the waveform display of the ultrasonic flaw detector, 51.4 dB, which is 18 dB larger than the standard sensitivity 33.4 dB, is used. Further, referring to the above-mentioned surface temperature-sensitivity difference graph, the steel pipe column that is the object of flaw detection The sensitivity was corrected according to the surface temperature (14 ° C.) at the flaw detection position of 1.

  According to the above surface temperature-sensitivity difference graph, the sensitivity difference between the sensitivity at 14 ° C. and the sensitivity at 18 ° C. was 1.5 dB, so that 52.9 dB obtained by adding 1.5 dB to 51.4 dB is flaw detection sensitivity. As determined.

In the actual measurement, in order to further clarify the waveform display of the ultrasonic flaw detector, a value larger than 52.9 dB is detected with a sensitivity of 63.4 dB obtained by adding 12 dB to 51.4 dB. The obtained waveform was converted into a waveform when flaw detection was performed with a sensitivity of 52.9 dB by a known method.
<Creation of reflection echo evaluation range graph>
FIG. 5 is a schematic view of a steel pipe column at the time of creating a reflection echo evaluation range graph, where (a) is a schematic top view of the steel pipe column, and (b) is a schematic side view of the steel pipe column. Show.

  As shown in FIG. 5 (b), the steel tube column 1 (thickness 6 mm, outer diameter 216.3 mm) has an artificial defect having a maximum length of 100 mm, a maximum depth of 3 mm, and a substantially letter-shaped notch in cross section. 7 was formed from the outer peripheral surface side.

  Next, as shown in FIG. 5 (a), marks for arranging the probes were set at equal dividing points where the steel pipe column 1 was equally divided into eight in the circumferential direction.

  Specifically, first, the steel pipe column 1 was divided into four equal parts, and the respective equal dividing points were defined as direction 1, direction 2, direction 3, and direction 4. The intermediate point between direction 1 and direction 2 is direction 1-2, the intermediate point between direction 2 and direction 3 is direction 2-3, the intermediate point between direction 3 and direction 4 is direction 3-4, and direction 4 is An intermediate point with respect to direction 1 was defined as direction 4-1.

  Next, as shown in FIG. 5 (b), the transmitting probe 3 and the receiving probe 4 of the ultrasonic flaw detector 2 are arranged at the respective mark positions, and the notch 7 is cut out from these probes. The ultrasonic beam (SH wave, flaw detection sensitivity 63.4 dB, 0.5 MHz) is emitted while changing the distance to the maximum depth portion of 10 mm pitch in the range of 150 to 450 mm, and the reflected echo due to artificial defects x was measured.

  At this time, the distance display of the peak rising start point of the reflected echo x coincided with the distance from the probe to the maximum depth of the artificial defect.

Then, the distance display of the rising start point of the peak of the reflection echo x and the distance display of the peak end point of the reflection echo x are sampled, the distance from the start point to the end point is obtained, and the relationship is graphed. By doing so, a reflection echo evaluation range graph was obtained. The obtained reflection echo evaluation range graph is shown in FIG.
<Creation of area ratio temperature correction graph>
FIG. 7 is a layout diagram of the probes when creating the area ratio temperature correction graph.

  As shown in FIG. 7, a through-hole 8 having a width of 10 mm was formed as an artificial defect in a steel pipe column (thickness 6 mm, outer diameter 216.3 mm).

  Next, the transmission side probe 3 and the reception side probe 4 of the ultrasonic flaw detector 2 are arranged on the surface of the steel pipe column 1, and the distance from the probe to the through hole 8 is in the range of 250 to 350 mm, While changing at a pitch of 50 mm, an ultrasonic beam (SH wave, flaw detection sensitivity 63.4 dB, 0.5 MHz) was transmitted, and a scattered echo a and a reflected echo x due to an artificial defect were received. Then, the ratio (X / A) between the peak area A of the scattered echo a and the peak area X of the reflected echo x was calculated.

  And said operation was repeated changing the surface temperature of the steel pipe pillar 1 in the range of 8-35 degreeC, and the relationship between area ratio (X / A) and the surface temperature of the steel pipe pillar 1 was sampled. In addition, the area ratio (X / A) was shown so low that the surface temperature of the steel pipe column 1 was low.

Thereafter, an area ratio temperature correction graph is calculated by calculating a correction coefficient of the area ratio (X / A) depending on the surface temperature of the steel pipe column 1 based on the case where the surface temperature of the steel pipe column 1 is 18 ° C. Got. The obtained area specific temperature correction graph is shown in FIG.
<Creation of average thinning rate estimation graph>
FIG. 9 is a schematic diagram of a steel pipe column at the time of creating an average thinning rate estimation graph, where (a) is a form in which a notch is formed in the steel pipe column, and (b) is a through hole in the steel pipe column. The form in which is formed is shown respectively.

  As shown in FIG. 9 (a), a steel pipe column 1 (thickness 6 mm, outer diameter 216.3 mm, surface temperature 18 ° C.) has an artificial defect with a maximum length of 100 mm and a maximum depth of 1.5 mm (average thickness reduction). The cutout 7 having a substantially square shape in cross section was formed from the outer peripheral surface side.

  Next, the transmitting side probe 3 and the receiving side probe 4 of the ultrasonic flaw detector 2 are arranged on the surface of the steel tube column 1, and the distance from these probes to the maximum depth portion of the notch 7 is set. The ultrasonic wave (SH wave, flaw detection sensitivity 63.4 dB, 0.5 MHz) was transmitted while changing at a pitch of 50 mm in the range of 200 to 600 mm, and the scattered echo a and the reflected echo x due to the artificial defect were received. . Then, the ratio of the peak area A of the scattered echo a and the peak area X of the reflected echo x was calculated.

  Further, as the artificial defect, the peak area A of the scattered echo a is similar to the above except that the cutout portion 7 having a substantially square shape in cross section with a maximum depth of 3 mm (average thickness reduction rate of 50%) is formed. The ratio of the reflection echo x to the peak area X was calculated.

  In addition, the peak area of the scattered echo a is the same as the above except that the artificial defect has a cutout portion 7 having a maximum depth of 4.5 mm (average thickness reduction rate of 75%) and a substantially square shape in cross section. The ratio between A and the peak area X of the reflected echo x was calculated.

  Further, as shown in FIG. 9 (b), the steel tube column 1 (thickness 6 mm, outer diameter 216.3 mm) was formed as an artificial defect, except that a through hole 8 having a width of 10 mm was formed. The ratio of the peak area A of the scattered echo a and the peak area X of the reflected echo x was calculated. In this case, since the artificial defect width of 10 mm is 16.7% of the flaw detection width of 60 mm, the average thickness reduction rate is 16.7%.

  Further, the ratio between the peak area A of the scattered echo a and the peak area X of the reflected echo x is calculated in the same manner as described above except that a through-hole having a width of 20 mm (average thinning ratio 33.3%) is formed. did.

  Further, the ratio of the peak area A of the scattered echo a and the peak area X of the reflected echo x was calculated in the same manner as described above except that a through hole having a width of 30 mm (average thickness reduction rate of 50%) was formed.

  And the average thinning rate estimation graph was obtained by graphing the relationship between said average thinning rate and area ratio. The obtained average thinning rate estimation graph is shown in FIG.

The following estimation criteria could be read from the average thinning rate estimation graph.
・ When the area ratio exceeds 0.0 and less than 3.0, the average thickness reduction rate is 0% or more and 25% or less ・ When the area ratio exceeds 3.0 and is less than 7.5, the average thickness reduction When the rate exceeds 25% and is less than 50% ・ When the area ratio exceeds 7.5, the average thickness reduction rate exceeds 50% and is less than 100% (penetration) [Example 1]
The degree of corrosion of steel pipe columns (wall thickness 6 mm, outer diameter 216.3 mm, surface temperature 15 ° C.) that was used for a long time and removed was evaluated by the method described below.

  That is, first, a mark for arranging the probe was set at an equally dividing point where the steel pipe column was equally divided into eight in the circumferential direction.

  Specifically, the steel pipe column was divided into four equal parts, and the respective equal dividing points were defined as direction 1, direction 2, direction 3, and direction 4. The intermediate point between direction 1 and direction 2 is direction 1-2, the intermediate point between direction 2 and direction 3 is direction 2-3, the intermediate point between direction 3 and direction 4 is direction 3-4, and direction 4 is An intermediate point with respect to direction 1 was defined as direction 4-1 (see FIG. 5A).

  Next, in the direction 1 described above, the transmitting probe and the receiving probe of the ultrasonic flaw detector are positioned 300 mm above the position corresponding to the boundary between the steel pipe column 1 and the surface of the steel column 1 in the building column state. The tentacles were respectively arranged (arrangement step (see FIG. 1A)).

  Next, an ultrasonic beam (SH wave, flaw detection sensitivity 63.4 dB, 0.5 MHz) was transmitted from the transmitting probe (transmitting step).

  Then, the echo of the transmitted ultrasonic beam is directly received by the receiving probe (direct reception process) in the beam path (distance) 0 to 100 mm, and transmitted from the transmitting probe. The echo of the ultrasonic beam reflected at the location where corrosion occurred was indirectly received by the receiving probe within the beam path length (distance) of 320 to 468 mm (indirect reception step).

  Since the start point of reception of the reflected echo x was confirmed at 320 mm, the end point of the beam path of the reflected echo x was determined to be 468 mm with reference to the reflected echo evaluation range graph (FIG. 6).

  Next, the ratio of the echo area of the ultrasonic beam directly received (peak area A of the scattered echo a) and the echo area of the ultrasonic beam received indirectly (peak area X of the reflected echo x) ( X / A) was calculated (area ratio calculation step).

  The echo area of the directly received ultrasonic beam (peak area A of the scattered echo a) is 224, and the echo area of the indirectly received ultrasonic beam is (peak area X of the reflected echo x) 1545, Their ratio (X / A) was 6.9.

  Next, the calculated area ratio (X / A) was corrected according to the temperature condition.

  Specifically, with reference to the area ratio temperature correction graph (FIG. 8), the correction coefficient of the area ratio (X / A) measured when the surface temperature of the steel pipe column is 15 ° C. is 0.87. The area ratio 6.9 actually measured was multiplied by 0.83. Thereby, the area ratio (X / A) after correction was set to 6.0.

  Thereafter, the average thickness reduction rate in direction 1 was estimated from the corrected area ratio (X / A). As a result, since the area ratio exceeded 3.0 and was less than 7.5, the average thickness reduction rate was estimated to be 25% or more and less than 50%.

  The measurement results for direction 1 are shown in FIG.

  Further, in the same manner as described above, the area ratio (X after correction) for each of the direction 1-2, the direction 2, the direction 2-3, the direction 3, the direction 3-4, the direction 4 and the direction 4-1 of the steel pipe column. / A) was calculated, and the average thinning rate was estimated.

FIG. 12 shows the measurement results for the direction 1-2, FIG. 13 shows the measurement results for the direction 2, FIG. 14 shows the measurement results for the direction 2-3, FIG. 15 shows the measurement results for the direction 3, and FIG. The results are shown in FIG. 16, the measurement results for direction 4 are shown in FIG. 17, and the measurement results for direction 4-1 are shown in FIG.
[Evaluation]
In each of the above-mentioned direction 1, direction 1-2, direction 2, direction 2-3, direction 3, direction 3-4, direction 4 and direction 4-1 of the steel pipe column, the maximum thinning depth and the maximum thinning rate. Then, the minimum thickness reduction depth and the minimum thickness reduction rate were measured, and the thickness reduction rate was compared with the average thickness reduction rate estimated as described above. The results are shown in Table 1.

  Further, the appearance photograph of direction 1 is shown in FIG. 19, the appearance photograph of direction 1-2 is shown in FIG. 20, the appearance photograph of direction 2 is shown in FIG. 21, the appearance photograph of direction 2-3 is shown in FIG. The photograph is shown in FIG. 23, the appearance photograph in the direction 3-4 is shown in FIG. 24, the appearance photograph in the direction 4 is shown in FIG. 25, and the appearance photograph in the direction 4-1 is shown in FIG.

  As shown in Table 1, the thinning rate estimated by the above method corresponds well to the actually measured thinning rate, and therefore the degree of corrosion of the steel pipe column is evaluated well by the above method. can do.

DESCRIPTION OF SYMBOLS 1 Steel pipe pillar 2 Ultrasonic flaw detector 3 Transmitting probe 4 Receiving probe 5 Ground 6 Corrosion occurrence place

Claims (3)

It is a method for evaluating the degree of corrosion at the underground part of a steel pipe column whose lower end is buried in the ground,
An arrangement step of arranging a pair of a probe for transmitting an ultrasonic flaw detector and a receiving probe for an ultrasonic flaw detector on a surface of a steel pipe column so as to be separated from the ground surface by a predetermined distance;
A transmitting step of transmitting an ultrasonic beam from the transmitting probe;
A direct reception step of directly receiving an echo of the transmitted ultrasonic beam by the reception probe during a predetermined beam path;
An indirect receiving step of indirectly receiving the echo of the ultrasonic beam transmitted from the transmitting probe and reflected at the location where the corrosion has occurred, by the receiving probe during a predetermined beam path;
An area ratio calculating step for calculating a ratio between an echo area of the ultrasonic beam directly received and an echo area of the ultrasonic beam received indirectly ;
In the area ratio calculation step,
A steel pipe column characterized by correcting a ratio of an echo area of a directly received ultrasonic beam and an echo area of an indirectly received ultrasonic beam according to a temperature condition Evaluation method of the degree of corrosion. In the indirect reception step,
The method for evaluating the degree of corrosion of a steel pipe column according to claim 1 , wherein an end point of the beam path is set according to a start point of a beam path of an echo of the ultrasonic beam. Furthermore, after the area ratio calculating step,
A thinning rate estimation step of estimating an average thinning rate of the steel pipe column due to the corrosion from a ratio between an echo area of the ultrasonic beam directly received and an echo area of the ultrasonic beam received indirectly. The method for evaluating the degree of corrosion of a steel pipe column according to claim 1 or 2 , characterized by comprising: