JP4808110B2 - Damage assessment method - Google Patents

Description

  The present invention relates to a damage evaluation method, and more particularly to a damage evaluation method for a pipe having a long path length such as a steam pipe of a power plant.

  Pipes through which high-temperature fluid flows, such as steam pipes in power plants, are susceptible to creep damage due to thermal stress and internal pressure. In order to be able to repair and replace such steam pipes in advance, it has traditionally been possible to grasp the fatigue state of the pipes through periodic inspections, and to increase the remaining life of the pipes through simulation using numerical analysis. Evaluating.

As a simulation method using such numerical analysis, for example, in Patent Document 1, a displacement at a restraint support portion of a pipe is measured, and based on this displacement, a stress analysis of a pipe inspection portion is performed using a finite element method. The method of performing and calculating | requiring the damage condition of piping is described. Further, for example, in Patent Document 2, the displacement at a plurality of points before and after the bent portion of the pipe is measured, the bending moment acting on the bent portion is calculated based on the measured displacement, and the creep is calculated based on the calculated bending moment. A method for determining damage is described.
JP 2002-62199 A JP 2003-232719 A

By the way, the steam pipe of the power plant relaxes the thermal stress caused by the high-temperature steam, so that the total length reaches several hundred meters, for example. On the other hand, in the method described in Patent Document 1, since the entire steam pipe is subjected to a three-dimensional elastic analysis, the calculation amount becomes enormous, a high-performance computer is required, and the numerical analysis takes a very long time. Take it.
In addition, in the method described in Patent Document 2, the damage state at the bent portion can be obtained, but the damage state of the entire steam pipe cannot be evaluated.

  The present invention has been made in view of the above problems, and an object thereof is to provide a damage evaluation method capable of accurately evaluating damage in the entire steam pipe by numerical analysis with a small calculation load.

  The damage evaluation method of the present invention is an evaluation method of damage to a pipe through which a high-temperature fluid flows, and the displacement in a state where the high-temperature fluid is flowing with respect to a state where the high-temperature fluid is not flowing in a predetermined portion of the pipe. A displacement measuring step for measuring, a shell model creating step for modeling the entire pipe by shell elements, and creating a shell model, and setting the measured displacement as a boundary condition, and performing shell analysis using the created shell model A shell analysis step to be performed; a site specifying step for selecting a site to be analyzed based on the result of the shell analysis; a solid model creating step for modeling the site to be analyzed with a solid model; and a displacement obtained by the shell analysis And setting the stress to the boundary value of the solid model, and the modeled solid For 3-dimensional elastic creep analysis using Dell, characterized in that it comprises a three-dimensional analysis step of evaluating the damage.

  In the damage evaluation method, the site specifying step includes a maximum principal stress or an equivalent stress that includes a weld line and acts in a tensile direction in a direction perpendicular to the weld line in the analysis result obtained in the shell analysis step. May be selected as the analysis target part.

  Further, the previous displacement measuring step measures a displacement at a position where the structure supporting the pipe end and the pipe is provided, and the shell analyzing step determines the displacement of the pipe end and the type of the supporting structure. The displacement selected based on the boundary condition may be used.

  According to the present invention, it is possible to grasp the damage status of the entire pipe by shell analysis. In addition, the damage situation of the entire pipe is examined by shell analysis, and the three-dimensional elastic analysis is performed only on the portion where damage is progressing in the analysis result, so the calculation load in the numerical analysis can be reduced.

Hereinafter, an embodiment of a damage status determination method of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an example of a steam pipe 10 of a generator that is a target of application of the damage determination method of the present embodiment. As shown in the figure, the steam pipe 10 of the generator is provided so as to connect the boiler and the turbine, and reaches a length of several hundred meters in order to relieve the thermal stress caused by the high-temperature steam. During operation of the generator, high-temperature steam flows through the steam pipe 10, and thermal stress acts on the steam pipe 10, so that creep damage is likely to occur in the steam pipe 10.

Further, in order to support the steam pipe 10, various types of support structures are used according to the performance required for the place to be supported. As will be described in detail later, in the damage determination method of the present embodiment, the motion state (that is, the high-temperature fluid is flowing) with respect to the generator stop state (that is, the state where the high-temperature fluid is not flowing) at a predetermined location of the steam pipe. State) is measured, and the measured displacement is used as a boundary condition in the shell analysis. At that time, the boundary condition is selected according to the type of the support structure. First, the main support structure used to support the steam pipe will be described.
FIG. 2 is a diagram showing the types of main support structures used to support the steam pipe 10 of the power plant. As shown in the figure, the support structure of the steam pipe 10 can be classified into a rigid hanger, a constant hanger, a vibration isolator support, a restraint hanger, and a spring hanger. And ring support.

  FIG. 3 is a diagram showing the configuration of the rigid hanger 50. As shown in the figure, the rigid hanger 50 supports the steam pipe 10 with a non-stretchable hanger 51 extending vertically from the ceiling or the like. For this reason, the steam pipe 10 is restricted from moving in the vertical direction, but may move in the horizontal direction.

The constant hanger is a support structure that always supports the steam pipe 10 with a constant load even when the steam pipe 10 moves up and down. In this embodiment, bolt support, U-belt support, and ring support are used. Yes. 4A and 4B are diagrams showing the configuration of the constant hanger. FIG. 4A shows the bolt support 100, FIG. 4B shows the U-belt support 200, and FIG. 4C shows the ring support 300.
As shown in FIG. 2A, the bolt support 100 is provided with a plate-like mounting member 11 having an opening at the upper part of the steam pipe 10, and a bolt 12 is inserted through the opening of the mounting member 11 so that the vertical The steam pipe 10 is supported by being fixed to a support member 13 extending in the direction. The support member 13 is always supported vertically upward with a constant load. Here, the opening for inserting the bolt 12 provided in the attachment member 11 is larger than the bolt diameter. For this reason, the steam pipe 10 may move in the horizontal direction.

  Further, as shown in FIG. 5B, the U-belt support 200 is provided by providing a support member 22 so as to contact the steam pipe 10 and fixing the steam pipe 10 to the support member 22 by the U-belt 21. ing. Further, although the support member 22 is always supported vertically upward with a constant load, the U belt 21 may be deformed in accordance with the movement of the steam pipe 10.

  Further, as shown in FIG. 5C, in the ring support 300, a ring 31 is attached so as to be wound around the outer periphery of the steam pipe 10, and this ring 31 is always supported vertically upward with a constant load. Yes. In the ring support 300, the steam pipe 10 may slide in the axial direction.

FIG. 5 is a diagram showing the configuration of the vibration isolator support 400. As shown in the figure, in the vibration isolator support 400, a ring 41 is wound around the steam pipe 10, and the ring 41 is supported by a pipe 43 extending obliquely from the vibration isolator 42 to support the steam pipe 10. Yes. Since the steam pipe 10 is supported by the ring 41 and slides in the pipe axial direction, the axial displacement is not reliable. Furthermore, when measuring the displacement, since the displacement is measured on the pipe 43 that is obliquely inclined, even if the steam pipe 10 is rotating, the measurement value does not reflect the influence.
Further, in the restraint hanger, the steam pipe 10 is attached to the support member by welding or the like, and the movement in the axial direction is completely fixed, but there is a possibility of movement in other directions.
FIG. 6 is a view showing the configuration of the spring hanger 500. As shown in the figure, the spring hanger 500 supports the steam pipe 10 via the coil spring 52, and the vertical displacement changes according to the load acting on the steam pipe 10.

  As described in the section of the prior art, in order to predict such creep damage of the steam pipe, a simulation using numerical analysis such as a finite element method has been performed. However, since the steam pipe 10 has a very long length of several hundred meters, the numerical analysis using the finite element method has a problem that it takes a long calculation time.

  On the other hand, the damage status determination method of the present embodiment is for determining the damage status of the steam pipe, and measures the displacement or the like at the position of the support member at the time of stopping and at the time of starting. Based on the analysis, the shell model that modeled the entire steam pipe with the shell element is used to identify the part of the steam pipe where the damage is progressing, and the three-dimensional elastic creep analysis is performed on this part. It identifies the situation.

Hereinafter, the damage status determination method of the present embodiment will be described in detail.
FIG. 7 is a flowchart showing the flow of the damage status determination method of the present embodiment.
As shown in the figure, first, in step 100, the state of motion with respect to the stop state of the generator at the position where the end of the steam pipe 10 and the support structure are installed (that is, the state where the high-temperature fluid is not flowing) ( That is, the displacement in a state where a high-temperature fluid is flowing is measured. At the same time, the type of support structure is also examined.

  Here, as described above, even in the position where the support structure of the steam pipe 10 is installed, a displacement occurs in a specific direction, which may not be suitable for use as a boundary condition in shell analysis in step 106 described later. is there. Therefore, in step 102, the displacement used as the boundary condition in the shell analysis is selected as described below.

As described above, when supported by the rigid hanger 50, the steam pipe 10 is restricted from moving in the vertical direction, but may move in the horizontal direction. For this reason, only the displacement in the vertical direction (that is, the displacement is set to zero) is used.
In the constant hanger bolt support 100, the steam pipe 10 may move in the horizontal direction. For this reason, only the displacement in the vertical direction is used.
Further, in the U belt support 200, the U belt 21 is deformed. In the U-belt support 200, since the displacement is measured by the support member 22, the displacement measured in the U-belt support 200 is not used in all directions.
In the ring support 300, since the steam pipe 10 may slide in the pipe axis direction, a displacement in a direction other than the pipe axis direction is used.

  Further, in the vibration isolator support 400, the steam pipe 10 may slide in the pipe axis direction. Furthermore, since the displacement is measured on the pipe 43 that is inclined, the influence of the rotation of the steam pipe 10 cannot be measured. For this reason, the measured displacement is not used in the vibration isolator support 400.

In the restraint hanger, the steam pipe 10 is completely fixed in movement in the axial direction, but may move in other directions. For this reason, only the displacement in the pipe axis direction is used (that is, the displacement in the pipe axis direction is set to zero).
The spring hanger 500 is supported in the vertical direction via the coil spring 52. For this reason, the design value of the coil spring 52 is used as the spring constant in the vertical direction.
Moreover, the entrance / exit of the steam piping 10 shall fix the coordinate of the piping center (namely, a displacement shall be zero).
The displacement selected as described above and the displacement at the end of the steam pipe are used as boundary conditions in step 106 described later.

Next, in step 104, the entire steam pipe is modeled by a shell element and a beam element to create a shell model.
Next, in step 106, a shell analysis is performed by using the created shell model and giving the displacement selected in step 102 as a boundary condition.

Next, in step 108, an analysis target portion that needs to be subjected to a three-dimensional elastic creep analysis described later is specified.
Here, the creep damage rate increases as the maximum principal stress or equivalent stress increases. Further, in the welded portion, cracks are likely to occur when a large tensile stress acts in a direction perpendicular to the weld line. For this reason, in the present embodiment, the site where the maximum principal stress and the equivalent stress are high in the result of the shell analysis and where a large tensile stress acts in the direction perpendicular to the weld line is the target site for evaluating creep damage. It was decided to.

Next, in step 110, the part to be analyzed is modeled by a three-dimensional solid element and a beam element to create a solid model.
Next, in step 112, the displacement and stress acting on the analysis target part obtained by the shell analysis are set as the boundary value of the solid model.
Next, in step 114, a three-dimensional elastic creep analysis is performed by the finite element method using the created solid model.

  Next, in step 116, based on the strain obtained by the three-dimensional elastic creep analysis, the creep damage rate of the site to be analyzed is calculated. By the above process, the damage situation in the whole steam pipe and the creep damage in the damaged part can be obtained.

  Here, in order to confirm that the creep damage can be accurately evaluated by the damage determination method of the present embodiment described above, the strain obtained by the damage determination method and the pipe temperature in the steam pipe 10 of the actual power plant are stable at a high temperature. The strain measured during the comparison was compared. FIG. 8 is a table comparing the measured values of the actual machine on the circumference of the elbow (pipe of the bent portion), the strain obtained as a result of the shell analysis, and the strain obtained as a result of the three-dimensional elastic analysis. As shown in the figure, both the strain obtained by the shell analysis and the strain obtained by the three-dimensional elastic creep analysis are close to 80% of the strain in the actual steam pipe, and are calculated very accurately. You can see that it is made. Thereby, according to the damage evaluation method of this embodiment, it was confirmed that a highly accurate analysis can be performed.

  Further, according to the damage determination method of the present embodiment, since the entire steam pipe is calculated by shell analysis, the analysis time can be greatly shortened as compared with the case where the entire steam pipe is subjected to three-dimensional elastic creep analysis. Further, since shell analysis is used for the analysis of the entire steam pipe, the stress state of the entire steam pipe can be calculated, and the site where damage has occurred can be reliably detected. In addition, since the range to be subjected to the three-dimensional elastic creep analysis is small and detailed analysis can be performed, the creep damage rate can be calculated for each part on the outer surface and inside in mm units, and the damage situation is high. Can be evaluated with accuracy.

  In the present embodiment, the case where the steam pipe 10 is supported by a rigid hanger, a constant hanger, a vibration isolator support, a restraint hanger, and a spring hanger has been described. Should just be used. In such a case, only a reliable one of the displacements measured in the support structure may be used as the boundary condition.

It is a figure which shows an example of the steam piping of the power plant used as the object of application of the damage determination method of this embodiment. It is a figure which shows the kind of main support structure currently used in order to support the steam piping of a power plant. It is a figure which shows the structure of a rigid hanger. It is a figure which shows the structure of a constant hanger, The figure (A) shows the support structure of a bolt support, (B) shows the support structure of a U belt support, (C) shows the support structure of a ring support. It is a figure which shows the structure of a vibration isolator support. It is a figure which shows the structure of a spring hanger. It is a flowchart which shows the flow of the determination method of the damage condition of this embodiment. It is a table | surface which compares the measured value of the actual machine in the elbow circumference, the distortion in the result of a shell analysis, and the distortion obtained as a result of a three-dimensional elastic analysis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Steam piping 11 Protrusion part 12 Bolts 13, 22, 32, 51 Support member 21 U belt 31, 41 Ring 42 Vibration isolator 50 Rigid hanger 52 Coil spring 100 Bolt support 200 U belt support 300 Ring support 400 Vibration isolator support 500 Spring hanger

Claims (3)

A method for evaluating damage to piping through which a high-temperature fluid flows,
A displacement measuring step for measuring a displacement in a state where the high-temperature fluid is flowing with respect to a state where the high-temperature fluid is not flowing in a predetermined portion of the pipe;
A shell model creating step of modeling the entire pipe by shell elements and creating a shell model;
A shell analysis step of setting the measured displacement as a boundary condition and performing a shell analysis using the created shell model;
Based on the result of the shell analysis, a site specifying step for selecting a site to be analyzed;
A solid model creating step of modeling the analysis object part by a solid model;
Setting the displacement and stress obtained by the shell analysis to the boundary value of the solid model;
A damage evaluation method comprising: a three-dimensional analysis step of performing damage analysis by performing three-dimensional elastic creep analysis using the modeled solid model. The damage evaluation method according to claim 1,
The site specifying step includes
In the analysis result obtained in the shell analysis step, a portion including a weld line and having a maximum principal stress or equivalent stress acting in a tensile direction perpendicular to the weld line in a tensile direction is selected as the analysis target portion. A damage evaluation method characterized by: The damage evaluation method according to claim 1 or 2,
The displacement measuring step measures a displacement at a position where a structure for supporting the pipe end and the pipe is provided,
The shell analysis step uses a displacement selected based on the displacement of the pipe end and the type of structure to be supported as a boundary condition.

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