JP7236373B2 - Reverse strain calculation method for welded steel pipe and its program - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reverse strain calculation method and program for a welded steel pipe.

A welded steel pipe is a steel pipe formed by welding seams. Due to the distortion caused by welding, the shape of the inner and outer circumferences of the welded steel pipe deviates from a perfect circle (an example of the shape before welding). This tendency is particularly large in large-diameter welded steel pipes.

In order to reduce the distortion due to welding, that is, to make the welded shape closer to a perfect circle, it has been proposed to apply reverse distortion to the welded steel pipe before welding (see, for example, Patent Document 1). . The method described in Patent Document 1 can estimate the deformation due to welding of a steel structure to which reverse strain is applied.

Japanese Unexamined Patent Application Publication No. 2011-101900

By the way, the method described in Patent Document 1 is based on the premise that reverse strain is applied to the entire range in which strain is generated by welding. If this method is applied to a welded steel pipe, reverse strain will be applied to the entire circumference of the welded steel pipe, so it is theoretically ideal, but not realistic. This is because the inner and outer perimeters of the welded steel pipe to which reverse strain is applied to the entire circumference are elliptical or oval, and the welded steel pipe (specifically, the components of the welded steel pipe) is deformed to have such a shape. This is because it is difficult to do so in terms of construction.

On the other hand, although it is realistic to apply reverse strain to a certain range instead of the entire circumference of the welded steel pipe, it is difficult to estimate the appropriate amount and range of reverse strain.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a reverse strain calculation method for a welded steel pipe and a program therefor, which are capable of obtaining an appropriate reverse strain amount and range.

In order to solve the above-mentioned problems, a method for calculating reverse strain in a welded steel pipe according to a first invention is a welded steel pipe formed by welding a seam in the axial direction. A reverse strain calculation method for a welded steel pipe, which calculates the amount and range that provides
a first welding strain calculation step of calculating the steel type, plate thickness and inner diameter of the welded steel pipe, and the shape of the strain due to welding corresponding to the groove shape of the welding, based on a prepared database;
a backdistortion calculation step of setting the amount and range of the backdistortion as variables and calculating the shape of the backdistortion at the amount and range;
a second welding strain calculation step of calculating a shape of distortion due to welding in consideration of the reverse strain by adding the shape calculated in the reverse strain calculation step to the shape calculated in the first welding strain calculation step;
an integrating step of calculating an integrated value of the shape calculated in the second welding distortion calculating step with respect to a shape in which distortion due to welding does not occur;
The first With the variable and the second variable being the amount and range of the backdistortion, and the target value being the integrated value, each fixed value of the amount and range of the backdistortion when the integrated value is equal to or less than a threshold. and taking one of each calculated fixed value as the formal backdistortion amount and range.

A method for calculating reverse strain in a welded steel pipe according to a second invention is the method for calculating reverse strain in a welded steel pipe according to the first invention, wherein the threshold value in the optimization method utilization step is the minimum integrated value in the integration step. It is a method that is a value.

Further, a method for calculating reverse strain in a welded steel pipe according to a third aspect of the invention is the method for calculating reverse strain in a welded steel pipe according to the first or second aspect of the invention, wherein the database prepared in the first welding strain calculation step is stored This is a method of calculating the shape of distortion due to welding by interpolating data.

In addition, a method for calculating reverse strain in a welded steel pipe according to a fourth aspect of the invention is the method for calculating reverse strain in a welded steel pipe according to any one of the first to third inventions, wherein the reverse strain calculated in the reverse strain calculating step is A method in which the shape is an arc in a circle with a smaller diameter than the welded steel pipe.

Further, the method for calculating reverse strain in a welded steel pipe according to a fifth aspect of the invention is the method for calculating reverse strain in a welded steel pipe according to any one of the first to fourth inventions, wherein the reverse strain set as a variable in the step of calculating the reverse strain is is the method involving welded steel pipe seams.

A method for calculating reverse strain in a welded steel pipe according to a sixth aspect of the invention is the method for calculating reverse strain in a welded steel pipe according to any one of the first to fifth aspects of the invention, wherein the joint of the welded steel pipe is divided into a plurality of welded steel pipes. are equally divided,
In this method, the range of reverse strain set as a variable in the reverse strain calculation step includes the middle of the adjacent seams of the welded steel pipe.

A program according to a seventh invention is a program for causing a computer to execute the reverse strain calculation method for a welded steel pipe according to any one of the first to sixth inventions.

According to the method and the program for calculating the reverse strain in the welded steel pipe, it is sufficient to apply the reverse strain only in a certain range instead of the entire circumference of the welded steel pipe, and the amount and range of the reverse strain in which the strain due to welding is reduced is calculated. Therefore, an appropriate backdistortion amount and range can be obtained.

1 is a perspective view showing a welded steel pipe for which a reverse strain calculation method according to an embodiment of the present invention is used, showing a state before welding; FIG. It is a perspective view which shows the same welded steel pipe, and shows the state after welding. It is a two-dimensional orthogonal coordinate system showing the same welded steel pipe in a cross section perpendicular to its axis. It is the first quadrant of the orthogonal coordinate system, and shows a welded steel pipe to which reverse strain is applied in a range including the weld. The first quadrant of the orthogonal coordinate system shows a welded steel pipe that is reverse strained in a range that includes an intermediate portion between adjacent welds. FIG. 5 is a graph showing the amount of deformation from the shape before welding with no reverse strain given in the case of FIG. 4 ; FIG. FIG. 6 is a graph showing the amount of deformation from the shape before welding with no reverse strain given in the case of FIG. 5 ; FIG. 4 is a flow chart showing a procedure of a reverse strain calculation method for the same welded steel pipe.

A reverse strain calculation method for a welded steel pipe according to an embodiment of the present invention will be described below.

First, a brief description will be given of a welded steel pipe for which the reverse strain calculation method is used.

As shown in FIGS. 1 and 2, the welded steel pipe 1 is a steel pipe formed by welding a seam 2 in the axial center O direction. The welded steel pipe 1 is not limited to a steel pipe or tube, and may be any diameter and length as long as it is a cylindrical steel material such as a cylinder. FIG. 1 shows the state before welding, and FIG. 2 shows the state after welding. Although FIGS. 1 and 2 show two examples in which the seams 2 are located at upper and lower positions, the number of seams 2 may be one or three or more. When there are a plurality of seams 2, it is preferable that the adjacent seams 2 are equidistant from the viewpoint of the structure of the welded steel pipe 1. The welding of the seam 2 is performed on the inner peripheral side of the welded steel pipe 1 (an example in which the groove 3 is formed on the inner peripheral side of the welded steel pipe 1). may be constructed on In addition, below, the welded part is called the welding part 4. As shown in FIG.

In FIG. 2, the welded steel pipe 1 after welding is indicated by a solid line, and the front end portion of the welded steel pipe 1 before welding is indicated by a phantom line. As is clear from comparing the solid line and the phantom line in FIG. 2, the welded steel pipe 1 after welding (solid line) expands in diameter at each position above and below the welded portion 4 from the shape before welding (phantom line). , and the diameter is reduced at each of the left and right positions between the adjacent welded portions 4 . Such deformation due to diameter expansion and diameter reduction is called welding distortion because it is caused by the welding.

A cross section in a direction perpendicular to the direction of the axis O is shown in a two-dimensional orthogonal coordinate system in FIG. In this two-dimensional orthogonal coordinate system, the inner circumference of the welded steel pipe 1 before welding is indicated by a virtual line, and the inner circumference after welding is indicated by a solid line (thin line). Due to welding distortion, the inner circumference changes from a virtual line to a solid line (thin line) shape. That is, compared to the virtual line, the solid line (thin line) expands in the upper and lower positions where the welded portion 4 is located (that is, expands in the y-axis direction), and the left and right positions between the adjacent welded portions 4 It shrinks in diameter (that is, shrinks in the x-axis direction). In order for the shape of the inner circumference after welding to be the shape indicated by the imaginary line in FIG. 3 instead of the shape indicated by the solid line (thin line) in FIG. It is ideal to distort in the opposite direction by the amount of distortion, that is, to apply reverse distortion over the entire circumference. The shape of the inner periphery to which this ideal reverse strain is applied is indicated by a thick line in FIG. That is, compared to the virtual line, the diameter of the thick line is reduced at the upper and lower positions (y-axis direction) where the diameter is expanded by welding, and the diameter is expanded at the left and right positions (x-axis direction) where the diameter is reduced by welding.

As shown in FIG. 3 , in order to obtain the ideal shape of the inner circumference (thick line) to which the reverse strain is applied, the shape (virtual line) before the reverse strain is applied to the entire circumference of the welded steel pipe 1. It is necessary to provide counter-distortion over the entire length. Such construction is practically difficult, and is extremely difficult especially when the welded steel pipe 1 has a large diameter (inner diameter of 1800 mm or more). Therefore, it is realistic that the reverse distortion is applied in a certain range instead of the entire circumference.

By the way, as shown in FIG. 3, the shape of the inner circumference to which the ideal reverse strain is applied (bold line) is changed to the shape (virtual line) before the reverse strain is applied due to the welding distortion, or (virtual line). On the other hand, the shape of the inner periphery to which the reverse strain is applied within a certain range does not become the shape (virtual line) before the reverse strain is applied due to the welding distortion. In the present embodiment, reducing the distortion due to welding does not mean reducing the welding distortion itself, but the shape of the inner circumference after being subjected to reverse distortion and being welded. It means that it is close to the inner peripheral shape (virtual line) before welding.

As shown in FIG. 3, the first quadrant (x is positive, y is positive) and the second quadrant (x is negative, y is positive) are symmetrical with respect to the y-axis, and the first quadrant (x is positive, y is positive) and the third quadrant (x is negative, y is negative) are symmetrical with respect to the origin, and the first quadrant (x is positive, y is positive) and the fourth quadrant (x is positive and y is negative) is symmetrical with respect to the x-axis. Therefore, if the shape of the first quadrant can be grasped, it is possible to grasp the shapes of the second to fourth quadrants. Therefore, FIGS. 4 and 5 show only the first quadrant (where x is positive and y is positive), and the second to fourth quadrants are omitted.

4 and 5 both show the shape of the inner circumference before welding, the shape before the reverse strain is given by a virtual line, and the reverse strain is in a certain range (circular arc with a central angle θ). The given shape is shown in bold. That is, the reverse distortion is given only within a certain range (arc with central angle θ) and is not given outside the certain range (arc with central angle θ). The amount of reverse distortion δ is the maximum value of the difference between the shape before the reverse strain is applied (virtual line) and the shape after the reverse strain is applied (thick line). FIG. 4 shows a case where the welded portion 4 (a position near 90° from the x-axis where x>0) falls within the above range, and FIG. position near 0°) falls within the above range. The fixed range in which the reverse distortion is applied is the arc of the central angle θ, but since this arc is proportional to the central angle θ, the above range will be described below as the central angle θ (angle) for convenience.

As shown in FIGS. 4 and 5, the reverse strain applied to the welded steel pipe 1 is, for example, an arc having a radius r2 smaller than the inner diameter r1 of the welded steel pipe 1 before the reverse strain is applied. Once the amount δ and the range θ of reverse strain applied to the welded steel pipe 1 are determined, the center coordinates (α, β) and the radius r2 of the circle forming the arc (hereinafter referred to as a small circle) are calculated. Specifically, in both cases shown in FIG. 4 and FIG. , the center coordinates (α, β) and the radius r2 are calculated.

In the graphs shown in FIGS. 6 and 7, the horizontal axis is the angle, and the vertical axis is the deformation amount from the inner circumference before welding without reverse strain (positive is diameter expansion, negative is diameter reduction). do. 6 and 7, the inner circumference before being reverse-strained and welded is indicated by a thick line, and the inner circumference after welding without being reverse-strained is indicated by a solid line (thin line), The inner perimeter after being counterstrained and welded is shown in bold dashed lines. In other words, the thick dashed line is obtained by adding the thick line and the solid line. FIG. 6 is a graph corresponding to FIG. 4 (the welded portion 4 falls within the reverse strain range θ), and FIG. 7 corresponds to FIG. 5 (the intermediate portion of the adjacent welded portions 4 falls within the range θ). It is a graph that

In FIGS. 6 and 7, the thick line (the inner circumference before being reverse-strained and welded) is determined by the amount δ and the range θ of the reverse strain. be. In addition, since the solid line (the inner circumference after welding without giving reverse strain) is the default value called from the database, the thick dashed line obtained by adding the thick line and the solid line is also a function of the amount of reverse strain δ and the range θ. is. Therefore, since the integrated value of the thick dashed line is also a function of the amount δ and the range θ of the reverse distortion, it is expressed as S(δ, θ) below. This integral value S (δ, θ) is the inner circumference (thickness dashed line). Therefore, the smaller the integrated value S(δ, θ) is, the more the inner circumference (bold dashed line) after reverse strain is applied and welded is the same as that before reverse strain is applied and welded. It can be said that it is close to the inner circumference (on the horizontal axis) as a whole. That is, the smaller the integrated value S(δ, θ), the less the distortion due to welding. Therefore, the case where the distortion due to welding is reduced is the case where the function S(δ, θ) is equal to or less than the threshold. That is, if the function S (δ, θ) is equal to or less than the threshold, the inner circumference (thick dashed line) after being welded with the reverse strain given by the amount δ and the range θ is It can be said that it is generally close to the inner circumference (on the horizontal axis) before it is applied and welded.

An optimization method is employed to calculate the backdistortion amount δ and the range θ within which the function S(δ, θ) is equal to or less than the threshold. This optimization method is a method of calculating each fixed value of the first variable and the second variable when the objective value obtained from the function of the first variable and the second variable which are mutually independent is equal to or less than the threshold value. The optimization method employed is not particularly limited, but includes, for example, a method using a solver, a method using a genetic algorithm, or a method using a mathematical solution. Specific examples of such methods include the solver function of Excel (registered trademark), which is Microsoft's spreadsheet software, the optimization application of MATLAB (registered trademark), which is numerical analysis software of Mathworks, and Python ( (Registered Trademark) library functions, R language library functions, or the like may be used. As the method, instead of using the existing functions described above, a subroutine incorporating the method may be created and used. The method using the mathematical solution approximates the objective value to an independent two-variable (first and second variable) Nth-order equation (where N is an even number), and the independent two-variable Nth-order equation is below a threshold value. This is a method of mathematically obtaining the first variable and the second variable in a certain case as a solution.

In the optimization method, the first variable and the second variable, which are independent of each other, are the amount δ and the range θ of the reverse distortion, respectively, and the target value is the function S(δ, θ). That is, by this optimization method, fixed values of the amount δ and the range θ of the backdistortion are calculated when the function S(δ, θ) is equal to or less than the threshold. Since the smaller the function S(δ, θ), the better, the threshold is preferably the minimum value of the function S(δ, θ). In other words, it is preferable to calculate each fixed value of the backdistortion amount δ and the range θ when the function S(δ, θ) takes the minimum value.

As described above, the method for calculating the reverse strain in the welded steel pipe 1 according to the embodiment of the present invention is to calculate the reverse strain when the function S(δ, θ) is equal to or less than the threshold value, that is, the reverse strain at a predetermined amount δ and range θ Calculating the amount δ and range θ of the reverse strain when the inner periphery after welding is applied and welded is generally close to the inner periphery without reverse strain and before welding It is a way to In other words, the method of calculating the reverse strain in the welded steel pipe 1 is a method of calculating the amount δ and the range θ of reverse strain to reduce the strain due to welding. The method will be described below by dividing it into steps with reference to FIG.

As shown in FIG. 8, the reverse strain calculation method for the welded steel pipe 1 includes a first welding strain calculation step S10, a reverse strain calculation step S20, a second welding strain calculation step S30, an integration step S40, and an optimization method use step S50. Prepare.

In the first welding distortion calculation step S10, the steel type, plate thickness and inner diameter r1 of the welded steel pipe 1, and the shape of the distortion due to welding corresponding to the groove shape of the welding are calculated based on a prepared database. It is a process. This process includes Step S11 in which the steel type, plate thickness and inner diameter r1 of the welded steel pipe 1, and the groove shape of the welding are input as conditions, and the welding strain corresponding to the input conditions is calculated based on the database. It is divided into step S12. The database stores the data indicated by the solid lines (thin lines) in FIGS. 3, 6 and 7, that is, the shape data of the inner circumference of the welded steel pipe 1 after being welded without being given reverse strain. . The data correspond to various steel grades, plate thicknesses and inner diameters of the welded steel pipe 1 (before reverse strain is applied and welded), and the groove shape of the weld. The data stored in the database is data obtained in advance by an analysis method, for example, data obtained by thermal elastic plasticity by the finite element method (FEM), or data obtained by the inherent strain method. be. If the stored data does not correspond to the input condition, the database interpolates data corresponding to the input condition from the stored data. This interpolation is preferably a linear interpolation, for example to reduce the time for the calculation.

The reverse distortion calculation step S20 is a step of setting the amount δ and the range θ of the reverse distortion as variables, and calculating the shape of the reverse distortion with the amount δ and the range θ. That is, the reverse distortion calculation step S20 is a step of calculating the shape indicated by the thick lines in FIGS. 4 to 7 as a function of the amount δ and the range θ of the reverse distortion.

The second welding strain calculation step S30 adds the shape calculated in the reverse strain calculation step S20 to the shape calculated in the first welding strain calculation step S10, thereby calculating the distortion due to welding in consideration of the reverse strain. This is the step of calculating the shape. That is, the second welding strain calculation step S30 adds the shape indicated by the thick line to the shape indicated by the solid line in FIGS. and the step of calculating as a function of the range θ.

The integration step S40 is a step of calculating an integral value of the shape calculated in the second welding distortion calculation step S30 with respect to a shape in which distortion due to welding does not occur. That is, the integration step S40 is a step of calculating the integrated value S(δ, θ) of the function indicated by the thick dashed line in FIGS. 6 and 7 as a function of the amount δ and the range θ of the reverse distortion.

The optimization method using step S50 includes optimization for calculating each fixed value of the first variable and the second variable when a target value obtained from a function of the first variable and the second variable that are independent of each other is equal to or less than a threshold value. Using the method, the amount δ and the range θ of the reverse distortion set with the first variable and the second variable as variables, and the target value is the integrated value S (δ, θ), and the Each fixed value of the backdistortion amount δ and the range θ when the integrated value S(δ, θ) is equal to or less than the threshold is calculated, and one of the calculated fixed values is used as the formal backdistortion amount δfix and This is a step for setting the range θfix. That is, the optimization method use step S50 is a step of calculating, by using the optimization method, the fixed values of the amount δ and the range θ of the inverse distortion when the function S(δ, θ) is equal to or less than the threshold value.

A computer may be caused to execute the first welding strain calculation step S10, the reverse strain calculation step S20, the second welding strain calculation step S30, the integration step S40, and the optimization method use step S50 described above. In this case, the steel type, plate thickness and inner diameter of the welded steel pipe 1 and the weld groove shape input in the first welding distortion calculation step S10 are input by input means such as a keyboard and/or a mouse. is preferred. Further, the formal amount δfix and the range θfix of the back distortion calculated in the optimization method using step S50 are preferably displayed by display means such as a display.

As described above, according to the method for calculating the reverse strain in the welded steel pipe 1, it is sufficient to apply the reverse strain only in a certain range θ instead of the entire circumference of the welded steel pipe 1, and further, the reverse strain amount δfix that reduces the strain due to welding. and the range θfix are calculated, it is possible to obtain an appropriate backdistortion amount δfix and range θfix.

Further, since the threshold value in the optimization method use step S50 is the minimum value of the integrated value in the integration step S40, the most appropriate amount δfix and the range θfix of the backdistortion are each determined to be one. The amount of backdistortion δfix and extent θfix can be obtained.

Furthermore, the database prepared in the first welding distortion calculation step S10 calculates the shape of distortion due to welding by interpolating the stored data, thereby calculating a more appropriate shape of distortion due to welding. The amount of backdistortion δfix and extent θfix can be obtained.

In addition, since the shape of the reverse strain calculated in the reverse strain calculation step S20 is an arc of a circle having a diameter smaller than that of the welded steel pipe 1, it becomes easier to apply the reverse strain to the welded steel pipe 1, so that the reverse strain is more appropriate. We can obtain the quantity .delta.fix and the extent .theta.fix of .

In addition, since the range θ of the reverse strain set as a variable in the reverse strain calculation step S20 includes the joint 2 of the welded steel pipe 1, it becomes easier to apply the reverse strain to the welded steel pipe 1. δfix and range θfix can be obtained.

Moreover, since the joint 2 of the welded steel pipe 1 equally divides the welded steel pipe 1 into a plurality of pieces, the welded steel pipe 1 can be structurally stabilized after being welded. Furthermore, the range θ of reverse strain does not include the welded portion 4 by including the middle of the adjacent seams 2 of the welded steel pipe 1 . This makes it possible to obtain a more appropriate backdistortion amount δfix and range θfix.

By the way, in the above-described embodiment, as shown in FIGS. 6 and 7, when there are two welded portions 4 and the adjacent welded portions 4 are equidistant, integration is performed only in the angle range of 0° to 90°. Although the value S (δ, θ) has been described as being calculated, the other angles 90° to 180°, 180° to 270° and 270° to 360° have the same integrated values, so other It is not necessary to calculate the integral value at the angle. That is, when there are two welded portions 4 and the adjacent welded portions 4 are equidistant, the angle for calculating the integral value S (δ, θ) is sufficient in the range of 0° to 90°. δfix and range θfix can be calculated in a short time. When the number of welded portions 4 is M (M is a positive number), the range of 180°/M is sufficient for the angle for calculating the integrated value S (δ, θ). However, if M is 2 or more, it is assumed that adjacent welded portions 4 are equidistant.

Further, in the above-described embodiment, the data stored in the database has not been described for cases other than the number of welded portions 4 being two. prepare.

Furthermore, in the above embodiment, the shape of the welded steel pipe 1 is described based on the inner circumference of the welded steel pipe 1, but the outer circumference (or the middle between the inner circumference and the outer circumference) of the welded steel pipe 1 may be used as the reference.

In addition, in the above embodiment, the groove 3 is formed in the seam 2, but the groove 3 may not be formed and the seam 2 may be directly joined by welding.

Further, in the above embodiment, the welded portions 4 shown in FIGS. Although the cases where the welded portion 4 and the intermediate portion fall into different reverse strain ranges have been described separately. Of course, neither the welded portion 4 nor the intermediate portion may enter the range of reverse distortion.

Moreover, the above-described embodiments are illustrative in all respects and are not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims. Of the configurations described in the above embodiments, the configuration other than the configuration described as the first invention in "Means for Solving the Problems" is an arbitrary configuration, and can be deleted and changed as appropriate.

O Axis center δ Amount of reverse strain θ Range of reverse strain 1 Welded steel pipe 2 Seam 3 Groove 4 Welded part

Claims (7)

A method for calculating reverse strain in a welded steel pipe formed by welding a seam in the axial direction, the method for calculating the amount and range of reverse strain to reduce the strain due to welding, the method comprising:
a first welding strain calculation step of calculating the steel type, plate thickness and inner diameter of the welded steel pipe, and the shape of the strain due to welding corresponding to the groove shape of the welding, based on a prepared database;
a backdistortion calculation step of setting the amount and range of the backdistortion as variables and calculating the shape of the backdistortion at the amount and range;
a second welding strain calculation step of calculating a shape of distortion due to welding in consideration of the reverse strain by adding the shape calculated in the reverse strain calculation step to the shape calculated in the first welding strain calculation step;
an integrating step of calculating an integrated value of the shape calculated in the second welding distortion calculating step with respect to a shape in which distortion due to welding does not occur;
The first With the variable and the second variable being the amount and range of the backdistortion, and the target value being the integrated value, each fixed value of the amount and range of the backdistortion when the integrated value is equal to or less than a threshold. and setting any of the calculated fixed values as the official amount and range of the reverse strain. 2. The method for calculating reverse strain in a welded steel pipe according to claim 1, wherein the threshold value in the optimization method utilization step is the minimum integrated value in the integration step. 3. The reverse strain in the welded steel pipe according to claim 1 or claim 2, wherein the database prepared in the first welding strain calculation step calculates the shape of the strain due to welding by interpolation of the stored data. calculation method. 4. The method for calculating reverse strain in a welded steel pipe according to claim 1, wherein the shape of the reverse strain calculated in the reverse strain calculating step is an arc of a circle having a diameter smaller than that of the welded steel pipe. . 5. The method for calculating reverse strain in a welded steel pipe according to claim 1, wherein the range of reverse strain set as a variable in the reverse strain calculation step includes seams of the welded steel pipe. The seam of the welded steel pipe divides the welded steel pipe into a plurality of equal parts,
6. The reverse strain in the welded steel pipe according to any one of claims 1 to 5, wherein the range of reverse strain set as a variable in the reverse strain calculation step includes a midpoint between adjacent seams of the welded steel pipe. calculation method. A program for causing a computer to execute the reverse strain calculation method for the welded steel pipe according to any one of claims 1 to 6.

Images