JP4840951B2 - Defect evaluation method for steel pipe column boundary and method for deducing estimated fracture load of steel tube column using the method - Google Patents

Description

  The present invention relates to a method for evaluating a defect in a steel pipe column bottom part, which is evaluated by ultrasonic flaw detection, and a steel pipe against a bending load using the method. More particularly, the present invention relates to a simplified and highly reliable evaluation method and derivation method.

  Thin and light assembled steel pipe columns with a thickness of about 2 to 4 mm used in mountainous areas and confined spaces are corroded and deteriorated due to long-term use in buried parts buried in the ground.

Therefore, the conventional method for evaluating defects in a steel pipe column embedded part is to attach a probe to the ground part of the steel pipe column where the lower part is embedded in the ground, transmit an ultrasonic wave toward the ground part, receive an echo, This is a method of normalizing echo waveform data, detecting a rising angle from a predetermined level of the normalized waveform data to a peak value, and evaluating the degree of defects based on the detected angle (for example, Patent Documents) 1).
JP-A-2004-361321 (first page, FIG. 1)

  In the case of the conventional method, the rising angle from the predetermined level of the normalized waveform data of the echo to the peak value is detected, and the degree of the defect is evaluated based on the detected angle, which is complicated. And when the whole underground part is a moderate corrosion defect, there exists a possibility that a corrosion defect may be evaluated to the lighter one different from an actual thing, and there exists a problem that reliability is low.

  The present invention takes into account the above points and aims to provide a simple and reliable defect evaluation method for a steel pipe column boundary without being evaluated to a lighter one that is different from actual corrosion defects, It is another object of the present invention to provide a simple and reliable method for deriving an estimated fracture load of a steel pipe column.

In order to solve the above problems, the defect evaluation method for the steel pipe column boundary portion of the present invention is as follows.
Attach the probe of the ultrasonic flaw detector to the ground part of the steel pipe column where the lower part is buried in the ground, transmit the ultrasonic wave to the ground part by the probe, and receive the echo,
From the echo received by the probe,
In the first evaluation means, the ratio A of the total echo height from the steel pipe column edge and the total echo height from the steel pipe column end surface is less than A1, A1 to less than A2, A2 to less than A3, A3 to less than A4, A4 and more than multiple stages of evaluation , and evaluation value a1, a2, a3, a4, a5 that sequentially increase the evaluation value a of the plurality of stages, and configured to score,
2nd evaluation means WHEREIN: Ratio B of the echo height sum total from the said steel pipe pillar base part and the echo height sum total from the said steel pipe pillar center whole part is less than B1, B1 to less than B2, B2 to less than B3 , B3 and higher grades are evaluated , and the evaluation values b of the multiple steps are sequentially scored into evaluation points b1, b2, b3, b4,
In the third evaluation means, the added value C of the evaluation score of the first evaluation means and the evaluation score of the second evaluation means is less than a plurality of stages C1 and C1 to C2 that are configured by dividing the increasing points sequentially. , C2 or more is collated, and the defect of the steel pipe column boundary part is finally evaluated in a plurality of stages (Claim 1).

  In the third evaluation means, it is desirable that the evaluation in a plurality of stages classifies the degree of thinning or remaining meat (claim 2).

further,
A1 is 0.25, A2 is 0.50, A3 is 0.75, A4 is 1.00,
a1 is 0, a2 is 1, a3 is 2, a4 is 3, a5 is 4,
B1 is 0.5, B2 is 0.6, B3 is 0.8,
b1 is 0, b2 is 1, b3 is 2, b4 is 3,
Less than C1 is 3 or less, C1 to less than C2 is 4, C2 or more is 5 or more,
When C is 3 or less, 4 or 5 or more, it is preferable to make sound / micro corrosion, mild corrosion, and severe corrosion, respectively (Claim 3).

In addition, the steel pipe column boundary part is a distance on the display screen of the ultrasonic flaw detector, and is a range between 50 mm above the ground and 100 mm underground from the surface of the steel pipe column,
Steel column end surface portion, at a distance on the display screen of the ultrasonic flaw detector, and more preferably in the range between the upper 100mm and the lower 200mm from steel column end surface (claim 4).

And the estimated fracture load derivation method of the steel pipe column using the defect evaluation method of the steel pipe column ground part of the present invention is:
Defect evaluation of the steel pipe column of the steel pipe column boundary part defect evaluation method is performed at a plurality of locations on the peripheral surface of the steel pipe column,
From the outer diameter of the steel pipe column and the maximum remaining thickness and the minimum remaining thickness of the plurality of locations, respectively, the direction with the weakest strength against bending load and the section modulus in the direction are derived,
The maximum estimated breaking load and the minimum estimated breaking load are derived (Claim 5 ).

According to the method for evaluating defects at the bottom of a steel pipe column according to the present invention, a probe of an ultrasonic flaw detector is attached to the ground part 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 echoes received by the probe and received by the probe, the first evaluation means WHEREIN: The total echo height from the steel pipe column base and the total echo height from the end surface of the steel pipe column Are evaluated in a plurality of stages of less than A1, A1 to less than A2, A2 to less than A3, A3 to less than A4, and A4 or more, and evaluation points a1 and a2 that sequentially increase the evaluation value a of the plurality of stages , A3, a4, and a5, and in the second evaluation means, the ratio B of the total echo height from the steel pipe column base and the total echo height from the central part of the steel pipe column less than B1, than from B1 B2, than from B2 B3, above B3 With evaluating the several stages, and configure scored evaluation points b1, b2, b3, b4 sequentially increasing the evaluation value b of the plurality several stages, in the third evaluation means, the evaluation point of the first evaluation means The added value C of the evaluation points of the second evaluation means is compared with a plurality of grades of less than C1, less than C1 to less than C2, and more than C2, which are configured by dividing the number of points that increase sequentially. Since the final evaluation is performed in a plurality of stages, the defect evaluation of the steel pipe column boundary portion can be easily and highly reliably evaluated (claim 1).

  Moreover, in the said 3rd evaluation means, the defect of a steel pipe pillar border part can be evaluated clearly by classifying the grade of a thinning or a remaining meat by multiple steps | paragraphs of evaluation (Claim 2).

further,
A1 is 0.25, A2 is 0.50, A3 is 0.75, A4 is 1.00,
a1 is 0, a2 is 1, a3 is 2, a4 is 3, a5 is 4,
B1 is 0.5, B2 is 0.6, B3 is 0.8,
b1 is 0, b2 is 1, b3 is 2, b4 is 3,
Less than C1 is 3 or less, C1 to less than C2 is 4, C2 or more is 5 or more,
When C is 3 or less, 4 or 5 or more, it can be easily and clearly evaluated by sound / micro-corrosion, mild corrosion, and severe corrosion, respectively (claim 3).

Further, the steel pipe column boundary part is a distance on the display screen of the ultrasonic flaw detector and is in a range between 50 mm above the ground and 100 mm underground from the surface of the steel pipe column, and the steel pipe column end surface part is super It is practical that the distance on the display screen of the acoustic flaw detector is in the range between the upper 100 mm and the lower 200 mm from the end surface of the steel pipe column (claim 4 ).

And the estimated failure load derivation method of the steel pipe column using the defect evaluation method of the steel pipe column boundary part of the present invention is the following. Performed at a plurality of locations of the surface, from the outer diameter of the steel pipe column, the maximum remaining thickness and the minimum remaining thickness of the plurality of locations, respectively, to derive the direction of the weakest strength against bending load, and the section modulus in the direction, Since the maximum estimated fracture load and the minimum estimated fracture load are derived, the estimated fracture load of the steel pipe column can be derived easily and reliably (Claim 5 ).

The best mode for carrying out the defect evaluation method for a steel pipe column boundary according to the present invention will be described with reference to FIGS. 1 to 3.
Fig. 1 shows the connection of multiple thin-walled steel pipe columns 1 with a wall thickness of about 2 to 4 mm. The lowermost steel pipe column 1 is buried in the ground, and the second steel pipe column 1 from the bottom is buried in the ground. In the vicinity of the ground of the second steel pipe column 1 from the bottom, that is, the corrosion defect of the ground portion S is subjected to ultrasonic flaw detection using an ultrasonic flaw detector.

  In the figure, reference numeral 2 denotes a probe of an ultrasonic flaw detector attached to the ground portion of the steel pipe column 1, and its attachment position is on the ground in order to secure a distance greater than the short distance limit of the probe 2. About 300 mm above 3 is desirable, and in this embodiment, it is attached 300 mm above the ground 3.

  Upon ultrasonic flaw detection, an SH wave is transmitted from the probe 2 toward the ground, and the echo is received. The sum of echo heights from the ground surface S near the ground surface 3 of the steel tube column 1, the steel tube column The total echo height from the end surface portion T near the end surface 4 of 1 and the total echo height from the entire underground portion U of the steel pipe column 1 are obtained.

  The ground portion S is a distance on the display screen of the ultrasonic flaw detector and ranges from the ground surface 3 of the steel pipe column 1 to several tens of millimeters and 50 mm to 200 mm in the ground. The end face T is a distance on the display screen of the ultrasonic flaw detector and is about 100 mm above and 100 mm below from the end face 4 of the steel pipe column 1 from the ground 3 to 50 mm above the ground and 100 mm below the ground. Or a range between 300 mm, preferably between 100 mm above the end face 4 and 200 mm below.

  And if it expands beyond the said range as the range of the edge part S and the end surface part T, respectively, or if it reduces without satisfying the said range, it will become inadequate or inadequate as a document.

  In the present embodiment, the ground portion S is in the range between the ground surface 3 to 50 mm above the ground and 100 mm in the ground, and the end surface portion T is in the range between 100 mm above the end surface 4 and 200 mm below, The entire underground part U of the steel pipe column 1 is a range between the ground part S, the end face part T, and the ground part S and the end face part T, between the ground part 3 to the ground 50 mm and the end face 4 to the bottom 200 mm. It is a range.

  FIG. 2 shows an example of the corrosion state and the monitoring waveform of the ultrasonic flaw detector. FIG. 2A is a partial cross-sectional view of the steel pipe column 1 and the distance from the ground surface 3 to the end face 4 of the steel pipe column 1. Is 500 mm, and the distance from the ground surface 3 to the probe 2 is 300 mm, indicating corrosion of the underground portion of the steel pipe column 1.

  (B), (C), and (D) of the same figure show the example of the display screen of the echo of an ultrasonic flaw detector, (B) is when the embedding part of the steel pipe pillar 1 is healthy, (C) is the ground When the portion S is corroded, (D) is a case where the ground portion S is close to mild corrosion.

  In the scale of the distance from the probe in FIGS. 5B, 5C, and 3D, 0 is the position of the probe 2, 300 mm is the position of the base 3 of the steel pipe column 1, and 800 mm is the steel pipe column 1. As shown in FIG. 4D, the ground portion S is between the ground surface 3; 300 mm to the upper 50 mm, 250 mm, and the ground surface 3; 300 mm to the lower 100 mm, 400 mm. The range, the end surface portion T is the range between the end surface 4; 700 mm from 800 mm to the upper 100 mm and the end surface 4; the range from 800 mm to the lower 200 mm is 1000 mm, and the entire underground portion U is the range between the 250 mm and 1000 mm.

Then, the first evaluation means, the second evaluation means, and the third evaluation means are performed based on the echo of the ultrasonic flaw detector. First, in the first evaluation means, as the corrosion becomes deeper, from the steel pipe column boundary S. Focusing on the point that the echo from the steel pipe column end surface portion T becomes small, as shown in Table 1,
The total echo height from the border S
Ratio A with the total echo height from the end face T
Are evaluated in a plurality of stages, and the evaluation value a of each stage is scored to obtain an evaluation score.

  That is, when the ratio A is less than A1, less than 0.25, from A1 to less than A2, from 0.25 to less than 0.50, from A2 to less than A3, and from 0.50 to less than 0.75, A3 From A to less than A4; 0.75 to less than 1.00, A4 or more; and 1.00 or more, the evaluation value a and the evaluation point are a1; 0, a2; 1, a3; 2, a4; a5;

Next, in the second evaluation means, the surface of the ground is rough, or the ultrasonic wave is attenuated while propagating through the underground due to the degree of contact with the soil, and the echo at the end face T is very small and may not appear. In order to avoid overevaluation by only the ratio A of the first evaluation means , as shown in Table 2,
The total echo height from the border S
Ratio B with the total echo height from the entire underground U
Are evaluated in a plurality of stages, and the evaluation value b of each stage is scored to obtain an evaluation score.

  That is, when the ratio B is less than B1; less than 0.5, B1 to less than B2; 0.5 to less than 0.6; B2 to less than B3; Above, in the case of 0.8 or more, the evaluation points b are set to b1; 0, b2; 1, b3; 2, b4;

  Next, in the third evaluation means, as shown in Table 3, the final evaluation is performed by adding the evaluation score C of the evaluation value a of the first evaluation means and the evaluation score of the evaluation value b of the second evaluation means. For steel pipe columns, a three-stage evaluation of sound / micro-corrosion, mild corrosion, and severe corrosion is adopted.

  That is, when the added value C is less than C1; 3 or less, C1 to less than C2; 4, C2 or more; and 5 or more, final evaluations are indicated by ◯: sound / micro-corrosion, Δ: mild corrosion, × Mark: Severe corrosion and thickness reduction rate is less than 25%, 25% to less than 50%, 50% or more, and remaining thickness rate is more than 75%, less than 75% to 50%, 50 %, And evaluate the defects at the steel pipe column boundary in multiple stages.

Next, an ultrasonic flaw detection is performed on the steel pipe column in the standing column state, and an example of the defect evaluation of the present invention will be described.
In the case of the ultrasonic echo of the ultrasonic flaw detection result shown in FIG.
The total echo height from the border S (range between 50mm above the ground and 100mm below the ground)
Ratio A to the total echo height from the end face (range between the top 100mm and the bottom 200mm from the end face of the steel pipe column)
Is 0.344, the evaluation value a is a2, and the evaluation score is 1.

Next, in the second evaluation means,
The total echo height from the border
Ratio B with the total echo height from the whole underground part B
Is 0.209, the evaluation value b is b1, and the evaluation score is 0.

  Next, in the third evaluation means, the added value of the evaluation point 1 of the first evaluation means and the evaluation point 0 of the second evaluation means is 1, which falls under 3 or less, and the final evaluation is marked with a circle. -Corresponds to micro-corrosion, thickness reduction rate of 0% to less than 25%, and residual thickness rate of 100% to 75%.

  The actual drilling results show that there is a pitting corrosion group with a maximum depth of 0.3 mm for the original wall thickness of 2.1 mm of the steel pipe column, which corresponds to micro-corrosion with a thickness reduction rate of less than 25%. The final evaluation by the defect evaluation method agrees with the actual measurement result.

Next, in the case of the ultrasonic echo of the ultrasonic flaw detection result shown in FIG.
The total echo height from the border S
Ratio A with the total echo height from the end face T
Is 2.111, the evaluation value a is a5, and the evaluation score is 4.

Next, in the second evaluation means,
The total echo height from the border S
Ratio B with the total echo height from the entire underground U
Is 0.467, the evaluation value b is b1, and the evaluation score is 0.

  Next, in the third evaluation means, the added value of the evaluation score 4 of the first evaluation means and the evaluation score 0 of the second evaluation means is 4, which falls into 4 categories, and the final evaluation is Δ mark; mild corrosion The thickness reduction rate is 25% to less than 50%, and the remaining thickness rate is less than 75% to 50% or more.

  And the actual measurement result of excavation shows that there is a pitting corrosion group with a maximum depth of 0.6mm against the original wall thickness of 2.1mm of the steel pipe column, and it corresponds to mild corrosion with a thickness reduction rate of 25% to less than 50%, The final evaluation by the defect evaluation method of the present invention matches the actual measurement result.

Next, in the case of the ultrasonic echo of the ultrasonic flaw detection result shown in FIG.
The total echo height from the border S
Ratio A with the total echo height from the end face T
Is 5.467, the evaluation value a is a5, and the evaluation score is 4.

Next, in the second evaluation means,
The total echo height from the border S
Ratio B with the total echo height from the entire underground U
Is 0.750, the evaluation value b is b3, and the evaluation score is 2.

  Next, in the third evaluation means, the added value of the evaluation score 4 of the first evaluation means and the evaluation score 2 of the second evaluation means is 6, which falls into 5 or more categories, and the final evaluation is marked with x. Corresponds to corrosion, thickness reduction rate of 50% or more, and residual thickness rate of less than 50%.

  And the actual measurement result of excavation shows that there is a pitting corrosion group with a maximum depth of 1.5 mm against the original wall thickness of 2.1 mm of the steel pipe column, which corresponds to severe corrosion at a thickness reduction rate of 50% or more. The final evaluation by the defect evaluation method agrees with the actual measurement result.

  Next, 10 steel pipe columns from 1976 to 1984 and 9 steel pipe columns from 1972 to 1984 in the 1976-1984 and 9 steel pipe columns from 1972 to 1984, respectively. Defect evaluation according to the present invention is performed for the flaw detection direction at 16 equally spaced locations, and among the 16 evaluations of each steel pipe column, 3 consecutive poorly evaluated locations are excavated to a depth of about 20 cm to confirm the corrosion state in appearance. did.

Table 4 shows the results of the final three-stage flaw detection of the present invention for 10 of the zone A and Table 5 for the 9 of the zone B.
○ mark: Sound / micro corrosion (thickness reduction rate less than 25%),
Δ: Mild corrosion (thickness reduction rate: 25% to less than 50%),
X: Severe corrosion (thickness reduction rate: 50% to 100%)
And the result of appearance observation is shown.

  Further, Table 6 shows the result of evaluation by ultrasonic flaw detection according to the present invention and the degree of corrosion by excavation confirmation.

  As shown in Table 6, in 55 places except the following 2 places, the evaluation of the present invention and the excavation confirmation coincide with each other, and the evaluation of the present invention is mild corrosion at the position a 2 of the steel pipe column. On the other hand, in the excavation confirmation, it is sound and micro-corrosion, and in the position D2 of the steel pipe column D, it is severe corrosion in the evaluation of the present invention, whereas in the excavation confirmation, it is mild corrosion. However, it is better than the lighter one and there is no problem in reality.

  Note that the number of stages of evaluation in the first evaluation means, the second evaluation means, and the third evaluation means, the method of scoring the evaluation points of the first evaluation means and the second evaluation means, and the classification of the points of the third evaluation means Of course, the method is not limited to the above-described embodiment, and may be increased, decreased, or changed.

Next, the best mode for carrying out the estimated failure load derivation method for steel pipe columns using the defect evaluation method of the present invention will be described.
Defect evaluation is performed by the defect evaluation method at a plurality of locations on the peripheral surface of the steel pipe column. The plurality of locations are preferably equally spaced positions on the circumferential surface of the steel pipe column, and are preferably 8 locations, 16 locations, and preferably 32 locations, but in reality, 16 locations are sufficient.

From the outer diameter of the steel pipe column and the maximum remaining thickness and the minimum remaining thickness according to the remaining thickness ratio in Table 3 at a plurality of locations based on the initial thickness, the direction with the weakest strength against the bending load, respectively, The section modulus is derived, and the maximum estimated failure load and the minimum estimated failure load are derived.
This maximum and minimum estimated breaking load can be used as data for studying the necessity of steel pipe column replacement.

  Next, an example of deriving the estimated breaking load will be described with reference to FIG. The final evaluation of the defect of the present invention, that is, ◯: sound / micro-corrosion (remaining wall thickness rate 100% to 75%), Δ: mild corrosion (remaining wall thickness rate less than 75% to 50%), × mark: severe The results of three-stage evaluation of corrosion (remaining wall thickness ratio of less than 50% to 0%) in 16 directions of steel pipe columns in the standing column, and the maximum remaining thickness and the minimum remaining thickness based on the results are shown in Table 7 shows.

The table shows the case where the original thickness of the steel pipe column is 2.24 mm, and the remaining thickness is represented by a numerical value of 75%, for example, less than 75%.
○ mark; (100% to 75%) Maximum 2.24 Minimum 1.68
Δ: (less than 75% to 50%) Maximum 1.68 Minimum 1.12
X mark (less than 50% to 0%) Maximum 1.12 Minimum 0

  4A shows the cross section of the steel pipe column at the ground when the maximum remaining thickness is shown in Table 7, and FIG.

First, a weak axis that gives the minimum moment of inertia of the cross section is obtained from the cross sectional view of the minimum remaining thickness in FIG.
And the direction with the weakest intensity | strength of the steel pipe column with respect to a bending load is calculated | required from the weak axis.
Next, the section modulus about the weak axis is obtained.

  Then, the product of the tensile or compressive strength of the material and the section modulus at the minimum remaining thickness is divided by the distance from the load point applied to the steel pipe column on the ground in parallel with the ground to the ground to obtain the minimum residual Derive the minimum estimated failure load for wall thickness.

  Next, from the cross-sectional view of the maximum remaining wall thickness in FIG. 4A, similarly, the section coefficient relating to the weakest direction and the weak axis of the steel pipe column with respect to the bending load is obtained.

  Then, the product of the tensile or compressive strength of the material and the section modulus at the maximum remaining thickness is divided by the distance from the load point applied to the steel pipe column on the ground in parallel to the ground to the ground to obtain the maximum residual Deriving the maximum estimated failure load in the case of wall thickness.

In the case of this example, the direction of the weakest strength of the steel pipe column with respect to the bending load is south-southeast.
In the case of the maximum estimated breaking load, the tensile or compressive strength of the material is 540 N / mm ² , the maximum remaining thickness in FIG. 4A and the section coefficient of 196 cm ³ derived from the outer diameter of the steel pipe column of 405.8 mm ^3. The maximum estimated breaking load of 9.7 kN (69%) is derived from the distance from the ground to the load point of 10.86 m.
Next, in the case of the minimum estimated breaking load, the minimum estimated breaking load of 4.5 kN (32%) is similarly derived from the section modulus of 90 cm ³ derived from the minimum remaining thickness in FIG.

In addition, in the case of a healthy steel pipe column having the same outer diameter of 405.8 mm, the section modulus is 285 cm ³ and the estimated fracture load is 14.1 kN.

It is a schematic diagram of an embodiment of the present invention. (A) shows a partial cross-sectional view of a steel pipe column and a probe, and (B), (C) and (D) are display diagrams of echoes of an ultrasonic flaw detector. (A), (B) and (C) are display diagrams of echoes of the ultrasonic flaw detector. (A) And (B) is a horizontal cross-sectional view of the steel pipe column at the time of the maximum remaining thickness and the minimum remaining thickness.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel pipe pillar 2 Probe 3 Ground surface 4 End face S Ground part T End surface part U The whole underground part

Claims (5)

Attach the probe of the ultrasonic flaw detector to the ground part of the steel pipe column where the lower part is buried in the ground, transmit the ultrasonic wave to the ground part by the probe, and receive the echo,
From the echo received by the probe,
In the first evaluation means, the ratio A of the total echo height from the steel pipe column edge and the total echo height from the steel pipe column end surface is less than A1, A1 to less than A2, A2 to less than A3, A3 to less than A4, A4 and more than multiple stages of evaluation , and evaluation value a1, a2, a3, a4, a5 that sequentially increase the evaluation value a of the plurality of stages, and configured to score,
2nd evaluation means WHEREIN: Ratio B of the echo height sum total from the said steel pipe pillar base part and the echo height sum total from the said steel pipe pillar center whole part is less than B1, B1 to less than B2, B2 to less than B3 , B3 and higher grades are evaluated , and the evaluation values b of the multiple steps are sequentially scored into evaluation points b1, b2, b3, b4,
In the third evaluation means, the added value C of the evaluation score of the first evaluation means and the evaluation score of the second evaluation means is less than a plurality of stages C1 and C1 to C2 that are configured by dividing the increasing points sequentially. A method for evaluating a defect in a steel pipe column boundary part, wherein the defect is finally evaluated in a plurality of stages in comparison with C2 or higher . 3. The method for evaluating defects in a steel pipe column boundary according to claim 1, wherein in the third evaluation means, the evaluation in a plurality of stages classifies the degree of thinning or remaining meat.   A1 is 0.25, A2 is 0.50, A3 is 0.75, A4 is 1.00,
  a1 is 0, a2 is 1, a3 is 2, a4 is 3, a5 is 4,
  B1 is 0.5, B2 is 0.6, B3 is 0.8,
  b1 is 0, b2 is 1, b3 is 2, b4 is 3,
  Less than C1 is 3 or less, C1 to less than C2 is 4, C2 or more is 5 or more,
  2. The method for evaluating defects in a steel pipe column according to claim 1, wherein when C is 3 or less, 4 or 5 or more, sound / micro-corrosion, mild corrosion, and severe corrosion are used. The steel pipe column boundary is a distance on the display screen of the ultrasonic flaw detector, and is a range between 50 mm above the ground and 100 mm underground from the surface of the steel pipe column,
Steel column end surface portion, at a distance on the display screen of the ultrasonic flaw detector according to claim 1, which is a range between the upper 100mm and the lower 200mm from tubular columns end face, claim 2 or claim 3 Defect evaluation method of steel pipe pillar border part of description. The defect evaluation of the steel pipe column in the defect evaluation method of the steel pipe column boundary part according to claim 1, claim 2, claim 3 or claim 4 is performed at a plurality of locations on the peripheral surface of the steel pipe column,
From the outer diameter of the steel pipe column and the maximum remaining thickness and the minimum remaining thickness of the plurality of locations, respectively, the direction with the weakest strength against bending load and the section modulus in the direction are derived,
An estimated failure load derivation method for steel pipe columns, characterized by deriving a maximum estimated failure load and a minimum estimated failure load.

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