JPH06258034A - Method and apparatus for measuring outer diameter of tubular body - Google Patents

Abstract

PURPOSE:To measure the outer diameter of a tubular body susceptible to flexure due to large diameter and heavy weight highly accurately. CONSTITUTION:A pair of distance meters 13a, 13b movable up and down on the opposite sides of the cross-section of a tubular body 10 to be measured are positioned at the cross points Y, or the vicinity thereof, of a right circle and a curve having profile defined by the attributes, e.g. material and dimension, of the tube 10. The distance meters 13a, 13b measure the horizontal distances La, Lb upto the tubular body 10 at each position and then the outer diameter D of the tubular body 10 is calculated based on the horizontal distances thus measured and the geometrical positions of the distance meters 13a, 13b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring an outer diameter of a tubular body and an outer diameter of the tubular body for accurately measuring the outer diameter of the tubular body which is liable to bend due to its large diameter and large weight. Regarding measuring device.

[0002]

2. Description of the Related Art Spiral steel pipes are often used in pipelines for transporting oil and various fluids because of their large outer diameters. The manufacturing method of this spiral steel pipe is shown in FIG. That is, the strip-shaped steel plate 1 is bent in a spiral shape, and the inner surface and the outer surface of the contact portion on the side surface of the bent strip-shaped steel plate 1 are welded to form a steel pipe 2 having a predetermined outer diameter D as shown in the drawing. In this case, the outer diameter D of the steel pipe 2 is determined by the equation (1) using the plate width W of the strip steel plate 1, the introduction angle θ of the strip steel plate 1 and the plate thickness t of the strip steel plate 1. D = W / (π ・ sinθ) + t (1)

As can be understood from the equation (1), the steel pipe 2
The outer diameter D of is greatly dependent on the introduction angle θ of the strip steel plate 1.
Therefore, a slight deviation of the introduction angle θ appears in the dimensional error of the outer diameter D as it is.

For this reason, in the apparatus for manufacturing the steel pipe 2, the operator measures the outer diameter by winding a steel tape measure or the like on the steel pipe 2 in a rotationally moving state during the pipe manufacturing. Then, when the measured outer diameter is out of the allowable range with respect to the target outer diameter, the introduction angle adjustment or the like in the manufacturing apparatus is performed.

However, since the measuring work is a manual work using a tool such as a steel tape measure, the measuring work can be executed only at regular intervals in the axial direction of the steel pipe 2. Therefore, it is not possible to detect a local variation in outer diameter. Further, the work of winding the steel tape measure around the steel pipe 2 which is rotating and moving in the axial direction is dangerous, and therefore only a skilled worker can perform it.

In order to eliminate such inconvenience, FIG.
The outer diameter measuring device shown in FIG.
15994 publication). A steel band 5 twisted into a figure 8 is wound between a fixed pulley 3 and a movable pulley 4 that is movable in the horizontal direction, and a pipe 6 to be measured is inserted into the lower ring of the hanging steel band 5. To do. The movable pulley 4 is biased rightward in the drawing by a weak spring member so that the steel band 5 does not loosen. The vertical distance H from the lower end position of the pipe 6 to be measured to the positions of the pools 3 and 4 is fixed.

In the outer diameter measuring device having such a structure,
Fixed pulley 3 and movable pulley 4 in a state where a reference tube 6a having a known outer diameter Da is attached to a steel band 5 in advance.
The distance S between and is measured. Then, when the measured pipe 6 is attached to the steel band 5, the movable pulley 4 is
If it is moved to the right by S, this amount of movement ΔS is proportional to the difference ΔD between the outer diameter D of the pipe 6 to be measured and the outer diameter Da of the reference pipe 6a. ΔD = (Da−D) = K · ΔS (2) Note that K is a constant determined by the positional relationship such as the outer diameter of each pulley 3, 4 and the distance H. Further, FIG. 8A shows the outer diameter D of the steel pipe.
FIG. 3 is a schematic configuration diagram of an outer diameter measuring device that measures N.

As shown in the figure, a pair of laser rangefinders 7 are arranged on the axis 7 of the pipe to be measured 6 so as to face the pipe 6 to be measured.
a and 7b are provided. And each laser range finder 7
The distances L _A and L _B to the pipe 6 to be measured are measured with a and 7b. Since the distance L ₀ between the laser rangefinders 7a and 7b is fixed, the outer diameter D of the pipe 6 to be measured can be obtained by the following equation (3). _{D = L 0 - (L A} + L B) ... (3)

[0009]

However, the above-mentioned outer diameter measuring devices also have the following problems to be improved.

First, in the outer diameter measuring device shown in FIG. 7, in order to measure the outer diameter D accurately, the steel band 5 is used.
Needs to be strongly wound around the pipe 6 to be measured in a rotationally moving state. Therefore, there is a concern that the pipe 6 to be measured may be damaged or, conversely, the outer diameter measuring device or the steel pipe manufacturing device may be damaged. That is, there is a problem caused by the contact measurement method in which the steel band 5 is wound around the pipe 6 to be measured in the rotational movement state.

Further, in the outer diameter measuring device shown in FIG. 8A, the outer diameter of the pipe 6 to be measured is measured in a non-contact manner.
The problem caused by contact measurement in the outer diameter measuring device of FIG. 7 is solved. However, in this outer diameter measuring device, the outer diameter D is not calculated from the outer peripheral value, but is calculated only from the measured values at two points. In this method, the outer diameter D can be accurately measured when the outer diameter D is small, the measured pipe 6 does not bend due to its own weight, and has a constant circular cross-sectional shape.

However, a spiral steel pipe generally used for a pipeline has a large diameter such as 600 mm to 2500 mm and is heavy in weight. Therefore, as shown in FIG. 8A, when the measured pipe 6 is supported in a cantilever state,
As shown in (b), the cross-section changes from a perfect circle indicated by the alternate long and short dash line to an elliptical shape indicated by the solid line by bending due to its own weight.

As described above, when the measured pipe 6a whose cross-sectional shape is changed to the elliptical shape is measured by using the upper and lower laser distance meters 7a and 7b, the outer diameter is smaller than the outer diameter of the perfect circle. Therefore, if the steel pipe manufacturing apparatus is controlled by the outer diameter D that is measured small, the outer diameter of the spiral steel pipe that is actually manufactured becomes larger than the specified outer diameter. When the spiral steel pipe is actually laid, it is laid in the ground without being applied with its own weight.

Further, in the outer diameter measuring device of FIG. 8A, since the outer diameter of the pipe 6 to be measured changes greatly as described above, the laser rangefinders 7a and 7b are separated from the pipe 6 to be measured. Need to be installed. Therefore, the pipe to be measured 6
The measurement error increases as the outer diameter D of N decreases.

The present invention has been made in view of the above circumstances, and utilizes that the cross-sectional shape when the pipe to be measured is bent in a flat shape intersects with a perfect circle on the assumption that there is no slack. Then, by setting the measurement position with respect to the pipe to be measured to the optimum position, even if the cross-sectional shape is bent, it is an object to provide an outer diameter measuring method of a pipe body and a device therefor that can always measure a correct outer diameter. And

[0016]

In order to solve the above-mentioned problems, the method for measuring the outer diameter of a tubular body according to the present invention comprises a pair of rangefinders that are movable up and down with a cross section of the tubular body to be measured interposed therebetween. The bending curve of the cross-sectional shape determined by attributes such as the material and dimensions of the measuring pipe is positioned at each of the vertically spaced intersections between the curved lines and the perfect circle, or at each vertical position in the vicinity of each intersection, and at each of these positioned positions. Each horizontal distance to the pipe to be measured is measured, and the outer diameter of the pipe to be measured is calculated from the measured horizontal distance and the geometric position of each distance meter.

Further, the outer diameter measuring apparatus of the present invention is supported movably up and down across the cross section of the pipe to be measured, and a pair of distance meters for measuring the horizontal distance to the pipe to be measured, and each distance. A reference position determining means for determining the reference position at which the measured value shows the lowest value while moving the meter up and down, and a reference from the intersection of the bending curve and the perfect circle of the sectional shape determined by the attributes such as the material and size of the pipe to be measured. The moving distance determining means for determining the vertical moving distance to the position, the distance meter positioning means for moving each distance meter in the opposite direction from the reference position by the vertical moving distance, and the measured distance by each distance meter An outer diameter calculating means for calculating the outer diameter of the pipe to be measured from each horizontal distance and the geometrical position of each distance meter is provided.

An outer diameter measuring device of still another invention is a pair of rangefinders, which are movably supported up and down across a cross section of a pipe to be measured and which measure a horizontal distance to the pipe to be measured. Reference position determining means for deciding the reference position where the measured value shows the lowest value while moving the distance meter up and down, and vertical movement from the position where the error of the measured value shows the lowest value to the reference position while moving each distance meter up and down Moving distance determining means for determining the distance, distance meter positioning means for moving each distance meter from the reference position in opposite directions by a vertical movement distance, and each horizontal distance measured by each of the positioned distance meters. The outer diameter calculation means for calculating the outer diameter of the pipe to be measured from the geometrical position of the range finder, and the outer diameter dimension calculated by this outer diameter calculation means are used to determine the material, dimensions, etc. of the pipe to be measured. Deflection curve of cross-sectional shape determined by attributes and each measured value Those having an outer diameter correction means for correcting the correction amount determined by the position.

[0019]

First, the operation principle of the outer diameter measuring method and the outer diameter measuring device of the present invention will be described with reference to the schematic diagram of FIG.

The cross-sectional shape of the tube, assuming that no deflection due to its own weight has occurred, is a perfect circle shape A shown by the solid line in the figure.
Is. Then, the same tubular body is bent by its own weight, and the cross-sectional shape is elliptical shapes B ₁ , B ₂ . Suppose it has been transformed into B ₃ . And
Each elliptical shape ₁ , B ₂ . B ₃ has different flatness rates. The degree of flatness is determined by the weight, material, wall thickness, and other attributes of the tube. In addition, in FIG. 2, the movement of the center position due to its own weight is regarded as a relative movement, and is drawn so as to coincide with the center O of the perfect circular shape A.

In this case, each elliptical shape B ₁ , B ₂ . B ₃ always intersects with the perfect circular shape A. Then, at each intersection P ₁ .
The distance from P ₂ and P ₃ to the center O is the radius of the perfect circular shape A. Therefore, each intersection P ₁ . P ₂ , P ₃ and the intersection points P ₁ . Each intersection Q ₁ which is a point symmetric position with respect to the center O of P ₂ and P ₃ . Each distance L ₁ , L ₂ , between Q ₂ and Q ₃
L ₃ are all equal and have an outer diameter D of a perfect circular shape A.

Therefore, the intersection points P of the deflection curve (elliptical shape B) and the perfect circular shape A, which are elliptically deformed with an arbitrary flatness,
If the two-dimensional position of Q is determined, the correct outer diameter D can be easily calculated by geometrical consideration.

As described above, the deflection curve (elliptical shape)
Is determined by the material and dimensions of the pipe to be measured. Therefore, this flexure curve is obtained in advance, and the intersection point P (P ₁ .P ₂ ,
P ₃ ) vertical movement distance Y (Y ₁ , Y ₂ ,
Y ₃ ) is determined, a pair of rangefinders are positioned at the positions facing the intersections P and Q in the horizontal direction, and the horizontal distances from these positions to the pipe to be measured are measured. P. The two-dimensional position of Q is determined. Therefore, the correct outer diameter D is calculated from the geometric position of each rangefinder.

Further, in the outer diameter measuring device of the present invention,
Define the reference position as the vertical position of the horizontal line passing through the center O,
While moving each measuring meter up and down, the position where the measured value shows the minimum value is detected as the reference position.

Further, in another invention, the measurement position in each distance meter is obtained by measurement. That is, as described above, the deflection curve (elliptical shape B) and the perfect circular shape A
If the relationship with is previously obtained, the value on the deflection curve at the measurement position can be specified even if each distance meter does not exactly face the intersection points P and Q. Therefore, the difference between the outer diameter D calculated from each horizontal distance measured at the measurement position and the truly correct outer diameter can be specified using the deflection curve. Therefore, an accurate outer diameter can be obtained by correcting the calculated outer diameter using this difference as a correction amount.

This means that if the measurement position of each distance meter is set to a position where the variation (error, standard deviation) of measured values is minimized, the measurement accuracy is improved as a whole.

When the horizontal distances at a plurality of positions in the axial direction at the same height position (y) of one pipe to be measured are measured, the position where the degree of variation (standard deviation) in the measured horizontal distance is the smallest is It has been experimentally confirmed that the position is at the intersection P, Q position or its vicinity.

Therefore, in the present invention, the vertical position showing the smallest variation in the measured values is set as the measuring position, the outer diameter is calculated from each measured horizontal distance, and then the correction amount at the corresponding measuring position is set. Is calculated from the relationship between the deflection curve (elliptical shape B) and the perfect circle shape A, and the measured outer diameter is corrected.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an outer diameter measuring device for a pipe according to an embodiment. The measured pipe body 10 is, for example, a spiral steel pipe manufactured by the method shown in FIG. 6, and moves in the axial direction orthogonal to the paper surface while rotating.

A pair of upper and lower linear guides 11a, which are parallel to each other on both sides of the pipe 10 to be measured and which extend in the vertical direction,
11b is laid. Each upper and lower linear linear guide 1
Laser rangefinders 13a and 13b are attached to 1a and 11b via horizontal linear guides 12a and 12b. Then, the two-dimensional positions (Xa, Ya), (Xb, Yb) of the laser rangefinders 13a, 13b are controlled to move independently of each other by the linear guide control units 14a, 14b.

The laser distance meters 13a and 13b respectively measure the horizontal distances La and Lb to the pipe 10 to be measured without contact. The horizontal distances La and Lb measured by the laser rangefinders 13a and 13b are the signal processing circuits 15a and 1b, respectively.
After being converted into a digital value by 5b, the arithmetic processing unit 1
6 is input.

The arithmetic processing unit 16 is composed of, for example, a computer, and is connected with an input / output device 17 including a display 17a and a keyboard 17b. Further, the arithmetic processing section 16 indirectly controls the positions of the laser rangefinders 13a and 13b via the linear guide control sections 14a and 14b.

First, assume a reference tube 18 having the same standard as that of the pipe 10 to be measured as shown in FIGS. 3 (a) and 3 (b). Then, the correct outer diameter D _S of the perfect circular shape A on the assumption that the deflection due to its own weight does not occur in the reference pipe 18
When the deflection due to its own weight is generated and it is deformed into the elliptical shape B as shown in FIG. 2, the laser distance meters 13a and 13b are arranged at an arbitrary distance y from the reference position and the horizontal distances La, by measuring Lb, the measurement value La, calculates the difference between the outer diameter D calculated from _{Lb ΔD (= D S -D)} . The reference position is defined as the vertical position of a horizontal line passing through the center 0 of the reference tube 13 as shown in FIG.

Then, the difference .DELTA.D when the vertical distance y is changed from the reference position is obtained respectively, and FIG.
The correction curve C of (b) is determined. Therefore, the vertical position Y where the correction curve C crosses the reference position (y = 0) is the intersection point P position where the elliptical shape B described above intersects with the perfect circular shape A. Therefore, the correction curve C corresponds to the deflection curve when the deflection is generated. The correction curve C thus measured for the reference tube 18 is preset in the storage unit of the arithmetic processing unit 16. Next, the measurement operation in the arithmetic processing unit 16 will be described step by step.

(1) The laser rangefinders 13a and 13b are moved to the lower end positions of the upper and lower linear guides 11a and 11b. In this case, the horizontal positions Xa and Xb of the laser rangefinders 13a and 13b are the same as those of the laser rangefinders 13a and 13b.
When b is moved up and down, it is brought close enough not to contact the pipe to be measured 10.

(2) The laser rangefinders 13a, 13b are continuously moved upward from the lower end position along the upper and lower linear guides 11a, 11b. In the course of this movement, the laser rangefinders 13a, 13b obtain the respective values. Horizontal distance La, L
Read a. In this case, each laser range finder 13a, 13b
The horizontal distances La and Lb are measured a plurality of times at the same height position y by slowing down the moving speed of, and the average value [La] me,
[Lb] me and standard deviations σ [La] and σ [Lb] are calculated. (3) The upper and lower positions at which the smallest average values [La] me and [Lb] me are obtained are determined as the reference positions Ra and Rb. Theoretically Ra = Rb.

(4) The smallest standard deviation σ [La],
The upper and lower positions at which σ [Lb] is obtained are measured positions Ya and Yb.
To decide. Then, the moving distance Y (= Ya−Ra = which is the difference between the respective measurement positions Ya and Yb and the reference positions Ra and Rb).
Yb-Rb) is calculated.

(5) Next, one laser rangefinder 13a
Is moved upward from the reference position Ra by the movement distance Y to be positioned at the measurement position (Xa, Ya). At the same time, the other laser distance meter 13b is moved downward from the reference position Ra by the movement distance Y to be positioned at the measurement position (Xb, Yb). (6) In this state, the laser distance meters 13a and 13b measure the horizontal distances La and Lb to the pipe 10 to be measured.

(7) Measured horizontal distances La and Lb
And the two-dimensional position of each laser rangefinder 13a, 13b (Xa,
The outer diameter D of the pipe 10 to be measured is calculated by using the equation (4) from the geometrical relationship of (Ya) and (Xb, Yb). D = [{(Xa-La)-(Xb + Lb)} ² + (Ya-Yb) ² ] ^1/2 …(Four)

(8) The correction amount Δ at the vertical position (y = Y) moved by the movement distance Y from the reference position (y = 0) in the correction curve C shown in FIG. 3B stored in the storage unit.
Read D _Y. (9) Using the read correction amount ΔD _Y , the outer diameter D previously calculated by the equation (4) is corrected by the equation (5) to obtain the correct outer diameter D _C. D _C = D−ΔD _Y (5)

In the outer diameter measuring device for a pipe having such a structure, it corresponds to the deflection curve (elliptical shape B) due to its own weight from the perfect circular shape A in the reference pipe 18 of the same standard as the pipe 10 to be measured. The correction characteristic C is registered in the storage unit in advance. Then, the correction value ΔD _Y corresponding to the installation position (moving distance Y) of each of the laser rangefinders 13a and 13b is read out, and the measured value La. Correct the outer diameter D obtained from Lb by this correction value ΔD _Y to obtain the correct outer diameter D _C.
Is getting Therefore, even if the measured pipe body 10 is bent by its own weight, the correct outer diameter D _C is always obtained.

Further, once the measurement position (moving distance Y) is determined, the outer diameter can be continuously measured at the same position and in a non-contact state. Therefore, as compared with the case where the steel tape 5 shown in FIG.
The measured pipe body 10 is not damaged, and the rotational speed and axial movement speed of the measured pipe body 10 can be increased. That is, even if the outer diameter is continuously measured, the safety can be sufficiently ensured, so that the manufacturing efficiency of the spiral steel pipe does not decrease.

Further, as shown in FIG. 3 (b), since the measurement position (moving distance Y) is set to the position where the variation (standard deviation) of the measured values La and Lb is minimized, the final outer diameter is determined. Measurement accuracy can be further improved. 4 and 5
Shows the measured value.

FIG. 4 is an actual measurement diagram showing the relationship between the horizontal distances La and Lb obtained from the laser rangefinders 13a and 13b and the vertical position y when the laser rangefinders 13a and 13b are moved up and down. As shown in the figure, the minimum positions of the horizontal distances La and Lb are set as the reference positions Ra and Rb.

FIG. 5 shows the variation of the corrected measured value D _C at each measuring position in the axial direction when continuously measuring the outer diameter of the pipe 10 to be measured which is rotating and the steel tape measure is used. It is a figure showing comparison with the amount of fluctuation when measuring the outer circumference and calculating the outer diameter from the outer circumference. As shown in the figure, it was proved that in the example apparatus, the measured value substantially corresponding to the manual measured value using the steel tape measure was obtained. Next, a pipe outer diameter measuring device of another embodiment will be described. The hardware configuration of this embodiment apparatus is the same as that of the above-described embodiment apparatus shown in FIG. The different point is the software-like measurement operation in the arithmetic processing unit 16. The measurement operation of the apparatus of this embodiment will be described. The measurement operation of (1) is the same as the measurement operation of (1) in the previous embodiment.

(2) The laser rangefinders 13a and 13b are continuously moved upward from the lower end position along the upper and lower linear guides 11a and 11b, and in the course of this movement, the laser rangefinders 13a and 13b obtain each. Horizontal distance La, L
Read a. (3) The vertical positions at which the smallest horizontal distances La, La are obtained are determined as the reference positions Ra, Rb. (4) The moving distance Y _P across the reference position (y = 0) in the correction curve C shown in FIG. 3B stored in the storage unit is read.

(5) Next, one laser rangefinder 13a
Is moved upward from the reference position Ra (y = 0) by the movement distance Y _P to be positioned at the measurement position (Xa, Ya). At the same time, the other laser range finder 13b is moved downward from the reference position Ra by the movement distance Y _P to be positioned at the measurement position (Xb, Yb). (6) In this state, the laser distance meters 13a and 13b measure the horizontal distances La and Lb to the pipe 10 to be measured.

(7) Measured horizontal distances La and Lb
And the two-dimensional position of each laser rangefinder 13a, 13b (Xa,
The outer diameter D of the pipe body 10 to be measured is calculated using the equation (6) from the geometrical relationship of (Ya) and (Xb, Yb). D = [{(Xa-La)-(Xb + Lb)} ² + (Ya-Yb) ² ] ^1/2 … (6)

In this case, since the horizontal distances La and Lb face the intersection points P and Q of the perfect circle shape A and the elliptical shape B in FIG. 2, it is necessary to execute the correction calculation process in the above-mentioned embodiment. Absent.

Even in the outer diameter measuring device for a tubular body constructed as described above, the tubular body 10 to be measured in a state of being bent by its own weight.
Since it is possible to accurately measure the correct outer diameter when it is assumed that the deflection does not occur, it is possible to obtain substantially the same effect as the above-described embodiment.

[0052]

As described above, according to the method for measuring the outer diameter of a pipe and the apparatus for measuring an outer diameter of a pipe of the present invention, the bending of the cross-sectional shape curve when the pipe to be measured is bent flat Utilizing the fact that it intersects with a perfect circle that has not occurred,
The installation position of the range finder for measuring the outer diameter of the pipe to be measured is set to a position where the influence of deflection is small. Therefore, even if the cross-sectional shape is bent, it is possible to accurately measure the correct outer diameter when it is assumed that the measured pipe body is not bent due to its own weight.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an outer diameter measuring device for a tube to which an outer diameter measuring method for a tube according to an embodiment of the present invention is applied.

FIG. 2 is a diagram for explaining the operating principle of the measurement method.

FIG. 3 is a diagram showing a correction curve stored in the apparatus of the embodiment.

FIG. 4 is a diagram showing a measurement result in each laser range finder of the apparatus of the embodiment.

FIG. 5 is a view showing a comparison between a variation amount of the outer diameter measured by the apparatus of the embodiment and a variation amount manually measured.

FIG. 6 is a schematic view showing a method for manufacturing a general spiral steel pipe.

FIG. 7 is a schematic diagram showing a schematic configuration of a conventional outer diameter measuring device.

FIG. 8 is a diagram for explaining a schematic configuration of a conventional outer diameter measuring device and its problems.

[Explanation of symbols]

10 ... Tube to be measured, 11a, 11b ... Vertical linear guide, 12a. 12b ... Horizontal linear guides, 13a, 13
b ... Laser rangefinder, 14a. 14b ... Linear guide control unit, 15a, 15b ... Signal processing unit, 16 ... Arithmetic processing unit,
17 ... I / O device, 18 ... Reference tube.

Claims (3)

[Claims] 1. A pair of rangefinders, which can move up and down across the cross section of the pipe to be measured, are provided between a bending curve and a perfect circle of a cross sectional shape determined by attributes such as material and size of the pipe to be measured. Positioned at each vertical position of each intersection or its vicinity, which is separated from each other vertically, and measure each horizontal distance to the pipe to be measured at each of these positioned positions. A method for measuring an outer diameter of a tubular body, which comprises calculating the outer diameter of the tubular body to be measured from the geometrical position of the meter. 2. A pair of distance meters, which are movably supported up and down across the cross section of the pipe to be measured, and which measure a horizontal distance to the pipe to be measured, and measurement while vertically moving each distance meter. Reference position determining means for determining the reference position showing the minimum value, and vertical movement from the intersection of the perfect curve and the bending curve of the cross-sectional shape determined by the properties such as the material and size of the pipe to be measured to the reference position. Moving distance determining means for determining a distance, distance meter positioning means for moving each of the distance meters in the opposite directions from the reference position by the vertical movement distance, and each horizontal position measured by each of the positioned distance meters. An outer diameter measuring device for a tubular body, comprising: an outer diameter calculating means for calculating an outer diameter of the tubular body to be measured from a distance and a geometrical position of each distance meter. 3. A pair of distance meters, which are movably supported up and down across the cross section of the pipe to be measured, and which measure the horizontal distance to the pipe to be measured, and measurement while vertically moving each distance meter. A reference position determining means for determining a reference position showing a minimum value, and a moving distance for determining a vertical movement distance from the position where the error of the measurement value shows the minimum value while vertically moving each distance meter to the reference position. Determining means, distance meter positioning means for moving each of the distance meters in the opposite directions from each other by the vertical movement distance, each horizontal distance measured by each of the positioned distance meters, and each distance meter. The outer diameter calculation means for calculating the outer diameter of the pipe to be measured from the geometrical position of, and the outer diameter dimension calculated by this outer diameter calculation means Deflection curve of cross-sectional shape determined by attributes and each of the above An outer diameter measuring device for a tubular body, comprising an outer diameter dimension correcting means for correcting the measured value with a correction amount determined by the measurement position.