JP2011027493A - Apparatus, method and program for destructive evaluation of piping - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a realistic and rational technique for destructive evaluation of piping, by excluding excess conservativeness when evaluating the soundness of piping. <P>SOLUTION: A piping destructive evaluation apparatus includes a setter 24 for setting any cross-section to be evaluated, a setter 26 for setting a crack region present in the cross-section, a setter 28 for setting a neutral axis to a bending moment acting on the piping, an alteration part 29 for altering the orientation of the neutral axis, a computation part 30 for computing a fracture mechanics parameter along the front edge of the crack when a bending moment corresponding to the neutral axis acts, a detection unit 32 for detecting a local maximum value of a distribution curve of the fracture mechanics parameter, a selection part 33 for selecting a neutral axis for evaluation in which the local maximum value can take a maximum value, and an evaluation part 33 for evaluating fracture due to the action of the bending moment corresponding to the neutral axis for evaluation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pipe fracture evaluation technique, and more particularly to a fracture strength evaluation technique for a pipe having a crack.

  When cracks due to stress corrosion cracks occur and propagate in piping of boiling water reactors, the development of structural integrity assessment methods to estimate the fracture strength and the advancement of accuracy are being promoted. In fact, cracks in pipes due to stress corrosion cracking have a complex shape, and pipe fracture evaluation is generally performed by modeling this crack into a single simple shape. .

With reference to FIG. 11, a simple modeling method in conventional fracture evaluation will be described.
FIG. 11 (A) shows a cross section 2 of the pipe, and a plurality of cracks S1 to S6 opened on the inner peripheral surface are displayed. And these cracks S1-S6 are normalized to the cracks H1-H6 of the fan-shaped surface each shown with the broken line.
The standardized cracks H1 to H6 are defined as a circumferential length c1 to c6 and a radial depth a1 to a6, respectively.

Further, the plurality of standardized cracks H1 to H6 are shifted in the circumferential direction as shown in FIG. 11B to obtain a circumferential length Σc (= c1 + c2 +... + C6) and a radial depth a _max. (The crack H1-H6 having the maximum depth (in the figure, a _max = a4)) is integrated into the sector model 3.
Assuming that the sector 2 includes a crack in the cross section 2, the fracture strength characteristics of the pipe in which a bending moment acts around the X axis orthogonal to the symmetry axis Y have been studied (for example, Non-patent document 1).

  Furthermore, a fracture evaluation method for only the plastic collapse mode has been proposed as a fracture mode of a pipe having a plurality of circumferential surface cracks.

Structural Health Assessment Handbook (2005); Kyoritsu Shuppansha

However, as described above, evaluating the fracture strength of a pipe with a simple model in which a plurality of cracks existing in a cross section are integrated into a fan shape is an overly conservative evaluation.
In addition, in pipe fracture assessments targeting only the plastic collapse mode, brittle fracture or elastoplastic fracture with ductile crack growth may dominate depending on the pipe material. It is not enough to assess the soundness of

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a practical and rational piping destruction evaluation technique by eliminating excessive maintainability in evaluating the soundness of piping. And

  The pipe fracture evaluation apparatus according to the present invention includes an evaluation cross-section setting unit that sets any cross section in the pipe as an evaluation target, and a crack area setting that sets a crack area existing in the set cross-section. A neutral axis setting unit that sets a neutral axis with respect to a bending moment acting on the pipe on the cross section, an axis direction changing unit that changes and sets the direction of the neutral axis, and the set neutral axis A fracture mechanics parameter calculation unit for calculating a fracture mechanics parameter along the front edge of the crack when a bending moment corresponding to the pressure acts, and detecting a local maximum value of the distribution curve of the fracture mechanics parameter with respect to the position of the front edge Evaluation is performed on a local maximum value detection unit, a selection unit that selects a neutral axis for evaluation in which the maximum value can take a maximum value, and destruction due to the action of the bending moment corresponding to the neutral axis for evaluation. Those comprising a valence unit.

  According to the pipe fracture evaluation apparatus, method, and program of the present invention, a practical and rational pipe fracture evaluation technique is provided by eliminating excessive maintainability in evaluating pipe soundness.

The functional block diagram which shows embodiment of the destruction evaluation apparatus of piping which concerns on this invention. The perspective view of piping to which the present invention is applied. The cross-sectional view including a plurality of circumferential surface cracks in the pipe to which the present invention is applied. (A) And (B) is a figure which shows the computing equation which derives | leads-out the fracture mechanics parameter of a crack, respectively. The figure which shows the distribution curve of the fracture mechanics parameter along the front edge of the crack of piping. (A) is an image diagram in which the orientation of the neutral axis with respect to the bending moment is changed by Δφ from the initial setting, and (B) is a graph showing the change in the distribution curve of the fracture mechanics parameter after changing the orientation of the neutral axis from the initial state by Δφ. . The cross-sectional view of the piping which standardized the shape of the crack in the fan shape. The cross-sectional view of the piping which normalized the shape of the crack to the semi-ellipse shape. The flowchart which shows embodiment of the destruction evaluation method of piping which concerns on this invention. The flowchart which shows other embodiment of the destruction evaluation method of piping which concerns on this invention. (A) is sectional drawing including the crack of the piping to which the conventional fracture evaluation is applied, (B) is the image figure of the crack modeled simply in the conventional fracture evaluation.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in the functional block diagram of FIG. 1, a pipe fracture evaluation system to which the present invention is applied includes a crack detection device 11, a bending moment calculation device 12, an input terminal 13, a display body 14, and a fracture evaluation. The apparatus 20 is comprised.
The pipe failure evaluation system constructed in this way detects the risk of initial defects such as cracks contained in pipes of plant systems such as nuclear power plants growing over time and leading to large-scale damage at an early stage. It provides information necessary to take effective measures.

The crack detection device 11 measures the cracks S1, S2,... (FIG. 3) included in the pipe 1 (FIG. 2). As a detection principle of the crack, penetration detection, fluorescence detection, magnetic particle detection, and overcurrent detection are performed. Known methods such as radiation transmission and ultrasonic flaw detection can be employed.
The bending moment calculation device 12 calculates a bending moment acting on an arbitrary cross section Wn in the pipe 1 from the layout of the pipe 1, the support method of the pipe 1, the assumed acceleration specified in the earthquake resistance, and the like.

  The fracture evaluation device 20 includes an interface 21 that exchanges data with the crack detection device 11, the bending moment calculation device 12, and the input terminal 13, a data storage unit 22, and data acquired from the crack detection device 11. Based on the three-dimensional information forming unit 23 for converting the form and position of the crack in the pipe 1 into three-dimensional information, the evaluation cross-section setting unit 24, the cross-section setting changing unit 25, the crack region setting unit 26, and the crack region Normalization unit 27, neutral axis setting unit 28, axial orientation changing unit 29, fracture mechanics parameter calculation unit 30, distribution curve generation unit 31, maximum value detection unit 32, selection unit 33, and evaluation unit 34 It consists of and.

Further, the destructive evaluation apparatus 20 is a computer including such an execution means, and includes a case in which an operation or data processing designated based on a program is executed.
The fracture evaluation apparatus 20 configured as described above outputs information related to the pipe fracture evaluation to the display body 14 based on information input from the crack detection apparatus 11, the bending moment calculation apparatus 12 and the input terminal 13.

  The data storage unit 22 temporarily stores external input data and internal processing data, and particularly stores a database such as the relationship between stress and strain of the constituent material of the pipe 1 necessary for calculating fracture mechanics parameters. Is.

The evaluation cross-section setting unit 24 sets one of the planar (XY coordinate system) cross-sections Wn that is cut at right angles to the center line (Z axis) as the evaluation target. That is, the pipe 1 converted into the three-dimensional information by the three-dimensional information conversion unit 23 has a plurality of cracks S (S1, S2,...) As shown in FIG. To two-dimensional information.
The cross section Wn converted into the two-dimensional information is displayed on the display body 14 and is switched to another cross section by operating the input terminal 13 and the function of the cross section setting changing unit 25.
Here, the cross-sectional view of FIG. 3 schematically shows a cross section having a plurality of cracks S on the inner surface in the circumferential direction of the pipe 1, but the number of cracks may be single. The position of the crack may be on the outer surface.

The crack region setting unit 26 defines the region of the crack S existing in the set cross section Wn, particularly the leading edge where the crack S propagates.
Further, the present invention is not limited to the case where the entire surface area of the crack S is included in the cross section Wn. When the surface area intersects the cross section Wn at a shallow angle, this surface area is projected onto the cross section Wn. The crack S may be handled.
Of the cracks S contained in the pipe 1, those whose surface area is perpendicular to the cross section Wn does not affect the fracture strength characteristics of the pipe 1 on which a bending moment acts.

The crack region normalization unit 27 approximates the region of the crack S to the shape of a sector D or a semi-ellipse E as shown in FIGS.
That is, since the crack S displayed on the cross section Wn has a complicated shape, as shown in FIG. 7, each crack S is enveloped by a sector D having the same depth and surface length. And Alternatively, as shown in FIG. 8, each crack S is enveloped by a semi-ellipse E having the same depth and surface length.
This modeling makes it possible to make a conservative evaluation because the crack area is greatly estimated, and because the crack shape is simple, an analytical model can be created for numerical analysis of fracture mechanics parameters. It becomes easy.

The neutral axis setting unit 28 sets the neutral axis for the bending moment M acting so as to bend the pipe 1 on the cross section Wn. Here, the neutral axis is a boundary line that divides strain in the Z direction into a compression side and a tension side in a cross section Wn on which a bending moment acts.
In FIG. 3, since the center of the cross section Wn is the origin through which the Z axis passes with respect to the bending moment M, the neutral axis is made coincident with the X axis, and the bending direction of the pipe 1 is the negative direction of the Y axis, the XY coordinates The system is compressed in the first quadrant and the second quadrant, and is tensioned in the third and fourth quadrants.
Here, it is clear that the tensile strain in the pipe 1 increases and the crack S tends to progress as the distance from the neutral axis X to the negative direction of the Y axis increases in the cross section Wn. Therefore, the initial setting of the neutral axis with respect to the cross section Wn is desirably set so that the Y axis penetrates the center in the circumferential direction with respect to the maximum crack depth (reference numeral S4 in FIG. 3).

The fracture mechanics parameter calculation unit 30 is a fracture mechanics along the leading edge of the crack S when a bending moment corresponding to the neutral axis X initially set and reset by the neutral axis setting unit 28 and the axial direction changing unit 29 is applied. The parameter is calculated.
Examples of the fracture mechanics parameters include a stress intensity factor, a J integral, and a crack tip opening displacement, and FIG. 4 illustrates a general formula for calculating them.
Note that the fracture mechanics parameter may be obtained strictly from numerical analysis by the finite element method, or may be obtained approximately from various proposed simple equations. In addition, it is assumed that various constants used for the calculation are stored in the data storage unit 22 in advance.

In the stress field σ _ij at the crack tip shown in FIG. 4A, when the stress intensity factor is K, the x axis is parallel to the crack surface, the y axis is perpendicular, and the tangent of the crack inner edge is the z axis. By defining a rectangular coordinate system defined as follows, it is expressed as shown in Equation (1).
Here, the stress intensity factor K is the mode II or mode III among the three independent deformation modes (mode I (opening), mode II (in-plane shear), mode III (out-of-plane shear)) at the crack tip. Since the contribution ratio is small in the bending deformation of the pipe 1, only the mode I is examined.

As shown in FIG. 4B, the J-integral is a surface force defined by a path Γ surrounding the crack tip, a strain energy density W, a normal vector n along the path Γ, and T _i = σ _ij n _j. If the vector T, the displacement vector u on the path Γ, and the minute line element ds on the path Γ are set, the following expression (2) is obtained.
Further, the relationship between the stress intensity factor K and the J integral is expressed as a formula (3) as Young's modulus E and Poisson's ratio ν.
The crack tip opening displacement Ψ is expressed as a yield stress σ _Y and a Young's modulus E as shown in Expression (4).

The distribution curve generation unit 31 generates a distribution curve (FIG. 5) of fracture mechanics parameters with respect to the orientation δ of the position P of the leading edge of the crack S in the XY coordinate system set in FIG.
The maximum value detector 32 detects the maximum value of the distribution curve of fracture mechanics parameters along the crack leading edge shown in FIG. In FIG. 5, it can be seen that the direction of the maximum value is deviated by Δδ from the direction (δ = 0) where the maximum stress acts due to the bending moment M.
Then, the detected maximum value and the value of the azimuth deviation Δδ are temporarily stored in the data storage unit 22.

The axial direction changing unit 29 changes the setting of the direction of the neutral axis X by causing the XYZ coordinate system to be angularly displaced Δφ around the Z axis relative to the cross section Wn, thereby acting on the pipe 1. The direction (Y-axis) of the bending moment M to be changed is virtually changed.
Each time the direction of the neutral axis X is set and changed by the axis direction changing unit 29, the fracture mechanics parameter calculating unit 30, the distribution curve generating unit 31, and the maximum value detecting unit 32 operate to newly detect the maximum value. The value of the orientation deviation Δδ is stored in the data storage unit 22.

  The selection unit 33 selects an evaluation neutral axis based on the information accumulated in the data accumulation unit 22 so that the maximum value of the distribution curve of the fracture mechanics parameter can take the maximum value. Two examples of such a method for selecting a neutral axis for evaluation are illustrated.

A first evaluation neutral axis selection method will be described with reference to FIG.
FIG. 6A is an image diagram in which the azimuth of the neutral axis X with respect to the bending moment is changed from the initial setting, and an angular displacement Δφ around the Z axis corresponding to the azimuth deviation Δδ in FIG. 5 is given.
Accordingly, as shown in FIG. 6B, the distribution curve of the fracture mechanics parameter before the change represented by the alternate long and short dash line is shifted to the position where the maximum value is δ = 0 as represented by the solid line. In general, the value K2 of the fracture mechanics parameter when the maximum value is obtained at the position of δ = 0 as described above generally takes the maximum value with respect to the value K1 when the maximum value is obtained at other positions. (K1 <K2).

Note that, when the azimuth of the maximum value of the fracture mechanics parameter does not coincide with the position of δ = 0 by the angular displacement Δφ around the Z-axis by the axis azimuth changing unit 29, it is converged by repeated trials.
In this manner, the selection unit 33 selects the tilted neutral axis X as the evaluation neutral axis based on the azimuth deviation Δδ having the maximum value corresponding to the initially set neutral axis X.
That is, when the XYZ coordinate system is set by adjusting the rotation angle Δφ so that the direction of the maximum value of the fracture mechanics parameter coincides with δ = 0, the X axis becomes the neutral axis for evaluation, and the bending in the Y axis direction is The pipe 1 is destroyed with the weakest bending moment.

Next, a second evaluation neutral axis selection method will be described.
In this case, the axis azimuth changing unit 29 performs step rotation of the neutral axis X at predetermined azimuth intervals (step displacement for each rotation angle Δφ of the XYZ coordinate system), and in each case, the distribution curve generation unit 31 performs fracture mechanics. A parameter distribution curve may be generated, and an output value from the local maximum detection unit 32 may be stored in the data storage unit 22.
At this time, the selection unit 33 selects the X axis of the XYZ coordinate system that gives the maximum value among the plurality of maximum values stored in the data storage unit 22 as the neutral axis for evaluation. Then, the Y-axis direction is the direction in which the pipe 1 is broken with the weakest bending moment.
In this case, Δφ is an XYZ coordinate at which the Y axis intersects the crack (reference numeral S4 in FIG. 3) that is the most critical for fracture because the accuracy improves as it becomes finer, but avoids long calculation time. It is desirable that the number of systems is set to be about 10 to 100.

The evaluation unit 34 evaluates the breakage of the pipe due to the action of the bending moment M corresponding to the neutral shaft for evaluation described above. That is, when the pipe 1 is bent and deformed in the direction perpendicular to the neutral axis for evaluation (Y-axis direction), the fracture strength is the weakest. Therefore, the mechanical strength only in the weakest direction is examined. It is reasonable to do.
Then, the evaluation unit 34 breaks when the local maximum value of the fracture mechanics parameter distribution curve when the bending moment corresponding to the neutral axis for evaluation is applied to the pipe 1 exceeds the fracture limit value of the constituent material of the pipe 1. And evaluate.
Specifically, when the stress intensity factor K exceeds the fracture toughness value Kc of the pipe material, it is evaluated that the pipe breaks, and the fracture evaluation of the pipe is compared with a value obtained by multiplying the fracture toughness value Kc by a safety factor. It becomes possible to carry out easily.

With reference to the flowchart of FIG. 9 (refer FIG. 1 suitably), embodiment of the piping fracture evaluation method of this invention is described.
First, the position and form of the internal crack are detected by the crack detection device 11 for the pipe 1 installed in the plant, and inspection data is input to the fracture evaluation device 20 (S11). Next, information such as the dimensions, material, and layout of the pipe 1 is input to the bending moment calculation device 12 (S12), and the bending moment M acting on the cross section Wn is calculated and input to the fracture evaluation device 20. (S13). These input data are stored in the data storage unit 22.

  Next, the data obtained from the crack detection device 11 is modified in the three-dimensional information conversion unit 23 so that an arbitrary cross section Wn can be displayed on the display body 14 or predetermined data processing can be performed. Then, the operator operates the input terminal 13 while referring to the display body 14 to set any cross section Wn in the pipe as an evaluation target (S14). This operation involves the cross-section setting changing unit 25 and the evaluation cross-section setting unit 24, and the selection of the cross-section Wn to be evaluated is arbitrary depending on whether it is a manual operation by an operator or an automatic setting.

  Next, a two-dimensional region of a crack existing in the cross section Wn set for evaluation is set (S15). The inner edge of the crack S for which the fracture mechanics parameter is calculated may have a complicated boundary and may be difficult to identify. Therefore, normalization is appropriately performed (FIGS. 7 and 8). This operation involves the crack region setting unit 26 and the crack region normalizing unit 27, and it is arbitrary whether the setting is based on a complete manual operation by the operator or automatic setting.

  Next, an XY coordinate system in which the X axis coincides with the neutral axis is set on the cross section Wn (S16). Thus, the Y-axis direction coincides with the direction of the bending moment that acts so that the pipe 1 bends. This operation involves the neutral axis setting unit 28 and the axial direction changing unit 29, and the initially set XY coordinate system is the center of the circumferential length of the most critical crack (reference numeral S4 in FIG. 3) with respect to the fracture. Is preferably set so that the Y axes intersect.

  Next, fracture mechanics parameters along the leading edge of the crack when a bending moment corresponding to the neutral axis X of the cross section Wn in the set XY coordinate system acts are calculated (S17). In this operation, the fracture mechanics parameter calculation unit 30 is involved, and it is selected from the input terminal 13 as to which of the stress intensity factor, the J integral, and the crack tip opening displacement is to be adopted. Various necessary constants are acquired from the data storage unit 22.

  Then, a distribution curve of the stress intensity factor K (fracture mechanics parameter) along the crack leading edge is created (FIG. 5) (S18). Further, the local maximum value Kp of the fracture mechanics parameter with respect to the position of the leading edge is detected in the created distribution curve (S19). In this operation, the distribution curve generation unit 31 and the maximum value detection unit 32 are involved, and the range of the distribution curve to be created is at both ends of the front edge of the crack where the Y axis intersects in the third and fourth quadrants. It is preferable to include the leading edge of several cracks including at least the orientation δ and on both sides thereof.

Next, the azimuth deviation Δδ with respect to the bending direction (δ = 0) of the pipe 1 is examined for the maximum value Kp (S20). When there is almost no azimuth deviation Δδ (S20; Yes), the bending moment corresponding to the neutral axis X of the set XY coordinate system gives the weakest breaking strength in the pipe 1 among all the bending directions. It will be.
If this azimuth deviation Δδ is significant (S20; No), the axis azimuth changing unit 29 changes the azimuth of the neutral axis by Δδ, and the routine from S16 to S20 is turned again to evaluate S20; Yes. Guide the vertical axis.
In this way, the local maximum value Kp corresponding to the neutral axis for evaluation derived based on the azimuth deviation Δδ of the local maximum value Kp corresponding to the initially set neutral axis is the maximum value among the calculated fracture mechanics parameters. Can take.

Next, the fracture toughness value Kc of the material of the pipe 1 is acquired from the data storage unit 22 (S21) and compared with the maximum value Kp of the stress intensity factor K (fracture mechanics parameter) corresponding to the derived neutral axis for evaluation. (S22).
Here, if the maximum value Kp of the stress intensity factor is equal to or greater than the fracture toughness value Kc, it is evaluated that there is a possibility that the pipe will break immediately if the maximum bending moment assumed for the pipe is applied. The conclusion is that they will be exchanged (S22; No, S23).

On the other hand, if the maximum value Kp of the stress intensity factor is smaller than the fracture toughness value Kc, it is evaluated that there is no possibility of immediate fracture even if the maximum assumed bending moment acts on the pipe (S22; Yes).
Further, other cross sections Wn are evaluated in the same manner (S24), and if it is evaluated that there is no possibility of immediate breakage even if the maximum assumed bending moment acts on the pipe, it is judged that the operation is continued. (S25).

  With reference to the flowchart of FIG. 10 (refer to FIG. 1 as appropriate), another embodiment of the pipe fracture evaluation method according to the present invention will be described. Here, S31 to S35 in FIG. 10 are respectively common with S11 to S15 in FIG.

  After the two-dimensional region of the crack is set with respect to the cross section Wn (S35), a plurality of XYZ coordinate systems having the neutral axis as the X axis are set while being angularly displaced around the Z axis at predetermined intervals Δφ (S36). ).

Next, for each of a plurality of set XYZ coordinate systems, fracture mechanics parameters along the leading edge of the crack S in the cross section Wn when a bending moment corresponding to the neutral axis X acts are calculated (S37).
Then, a distribution curve of the fracture mechanics parameter K is created for each of a plurality of set XYZ coordinate systems, and each local maximum value Kp is detected (S38, S39). In this way, the maximum values Kp of the distribution curves corresponding to the plurality of neutral axes X set at regular intervals in the circumferential direction of the transverse section Wn are accumulated in the data accumulation unit 22 (S40).

Next, the fracture toughness value Kc of the material of the pipe 1 is acquired from the data storage unit 22 (S41) and compared with the maximum (Kp) max among the plurality of maximum values Kp stored in the data storage unit 22 ( S42).
Here, if the maximum value (Kp) max of the stress intensity factor is equal to or greater than the fracture toughness value Kc, it is evaluated that there is a possibility that the pipe will break immediately when the maximum bending moment assumed in the pipe is applied. (S42; No, S43).

If the maximum value (Kp) max of the stress intensity factor is smaller than the fracture toughness value Kc, it is evaluated that even if the maximum assumed bending moment acts on the pipe, there is no possibility of immediate fracture (S42; Yes). ).
Further, other cross sections Wn are evaluated in the same manner (S44), and if it is evaluated that there is no possibility of immediate fracture even if the maximum assumed bending moment acts on the pipe, it is judged that the operation is continued. (S45).

  DESCRIPTION OF SYMBOLS 1 ... Piping, 11 ... Crack detection device (external device), 12 ... Moment calculation device (external device), 13 ... Input terminal, 14 ... Display body, 20 ... Destruction evaluation device for piping, 21 ... Interface, 22 ... Data Accumulation unit, 23 ... three-dimensional information conversion unit, 24 ... evaluation section setting unit, 25 ... section setting change unit, 26 ... crack region setting unit, 27 ... crack region normalization unit, 28 ... neutral axis setting unit, 29 DESCRIPTION OF SYMBOLS Axis change part 30 ... Fracture mechanics parameter calculation part 31 ... Distribution curve generation part 32 ... Maximum value detection part 33 ... Selection part 34 ... Evaluation part K, K1, K2 ... Stress intensity factor (Fracture mechanics) Parameters), S (S1, S2, S3, S4, S5, S6)... Crack, Wn.

Claims (6)

An evaluation cross-section setting unit that sets any cross-section in the pipe as an evaluation target;
A crack region setting unit for setting a region of a crack existing in the set cross section;
A neutral axis setting unit for setting a neutral axis on the transverse section with respect to a bending moment acting on the pipe;
An axis direction changing unit for changing and setting the direction of the neutral axis;
A fracture mechanics parameter calculation unit for calculating a fracture mechanics parameter along the leading edge of the crack when a bending moment corresponding to the set neutral axis acts;
A maximum value detecting unit for detecting a maximum value of a distribution curve of the fracture mechanics parameter with respect to the position of the leading edge;
A selection unit for selecting a neutral axis for evaluation in which the maximum value can take a maximum value;
A pipe fracture evaluation apparatus comprising: an evaluation unit that evaluates breakage due to the action of the bending moment corresponding to the neutral shaft for evaluation.   2. The pipe fracture evaluation apparatus according to claim 1, wherein the selection unit selects, as the neutral axis for evaluation, an inclination of an initially set neutral axis based on a direction of the corresponding maximum value.   The evaluation unit evaluates that when the maximum value of the distribution curve when a bending moment corresponding to the neutral axis for evaluation acts exceeds a fracture limit value of a constituent material of the pipe, the fracture is reached. The pipe fracture evaluation apparatus according to claim 1 or 2.   4. The data storage unit according to claim 1, further comprising a data storage unit configured to store, as a database, a relationship between stress and strain of the constituent material necessary for calculating the fracture mechanics parameter. 5. Pipe breakage evaluation equipment. A step of setting any cross section in the pipe as an evaluation target;
Setting a region of a crack present in the set cross section;
Setting a neutral axis for the bending moment acting on the pipe on the cross section;
Calculating fracture mechanics parameters along the front edge of the crack when a bending moment corresponding to the set neutral axis acts;
Detecting a local maximum of a distribution curve of the fracture mechanics parameter with respect to the position of the leading edge;
Selecting a neutral axis for evaluation, which is set by changing the orientation of the neutral axis and the maximum value can take a maximum value;
Evaluating the fracture due to the action of the bending moment corresponding to the evaluation neutral shaft. Computer
Means for setting any cross-section in the pipe as an evaluation target;
Means for setting a region of a crack existing in the set cross section;
Means for setting on the transverse section a neutral axis for a bending moment acting on the pipe;
Means for changing and setting the direction of the neutral axis;
Means for calculating fracture mechanics parameters along the front edge of the crack when a bending moment corresponding to the set neutral axis acts;
Means for detecting a maximum value of a distribution curve of the fracture mechanics parameter with respect to the position of the leading edge;
Means for selecting a neutral axis for evaluation in which the maximum value can take a maximum value;
A pipe fracture evaluation program that functions as means for evaluating breakage due to the action of the bending moment corresponding to the evaluation neutral shaft.

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