JP5187483B2 - Pipe evaluation method and pipe evaluation program - Google Patents

Description

  The present invention relates to a method for evaluating the state of a tube based on the thickness of the tube and a program for realizing the method.

When describing the thickness evaluation method of heat transfer tubes such as feed water heaters, as one of such wall thickness measurement techniques, a technique for measuring wall thickness from the inside of a heat transfer tube by ultrasonic flaw detection is known ( For example, Patent Document 1). In a normal evaluation method, the thickness of each part of the tube is measured by ultrasonic flaw detection, and if the thickness at any point is below a predetermined threshold considering the strength of the tube, It can be determined that there is an abnormality (for example, the corrosion of the tube has progressed). If it is determined to be abnormal, the heat transfer tube is repaired or replaced.
Japanese Patent Publication No. 5-8780

  However, even if the wall thickness at any point is below a predetermined threshold value, the heat transfer tube strength is often sufficiently maintained in the vicinity of the wall thickness data in consideration of the surrounding wall thickness data. If the normal judgment method as described above is adopted, even a heat transfer tube that still has sufficient strength is judged to be abnormal, and extra repair work or replacement work is performed.

By the way, in the technical field of ultrasonic inspection of pipes, the planar spread (area) of a thickness defect is obtained without evaluating only by the thickness of a single point, and the defect is evaluated based on it. It is known (for example, Patent Document 2 and Patent Document 3).
JP-A-2-208554 JP 2002-350407 A

  Although these patent documents 2 and patent documents 3 can obtain the spread (planar area) of the thickness defect, how to determine whether the thickness defect having such a spread is normal or abnormal. Whether or not to determine is not disclosed.

  The present invention has been made to solve the above-described problems, and the object thereof is to comprehensively evaluate the thickness data at a plurality of points and automatically determine whether or not the tube is normal. It is in providing the evaluation method of such a pipe. Another object of the present invention is to provide a program for executing such an evaluation method.

  The first embodiment of the pipe evaluation method according to the present invention comprises the following stages: axial evaluation, circumferential evaluation, minimum wall thickness stress evaluation, and pitting corrosion evaluation. Steps (a) to (f) are provided. (A) A recording stage in which the thickness of the tube is measured at a predetermined measurement pitch in each of the axial direction and the circumferential direction of the tube, and the thickness data is recorded. (A) A reading stage for reading the recorded thickness data. (C) With regard to the thickness data that is below the predetermined thickness threshold value, whether the axial direction is evaluated based on the plurality of axial thickness data, is normal or need to be re-evaluated? Determine the axial evaluation stage. (D) With regard to the thickness data that falls below the predetermined thickness threshold value, whether the circumferential direction is evaluated based on the plurality of circumferential thickness data, is normal or need to be re-evaluated? The circumferential evaluation stage to determine the. (E) The minimum thickness that determines whether the data is normal or needs to be re-evaluated by evaluating the thickness data that is below the predetermined thickness threshold based on the stress of the minimum thickness portion Stress evaluation stage. (F) By performing pitting corrosion evaluation on the thickness data that needs to be re-evaluated in at least one of the axial direction evaluation stage, the circumferential direction evaluation stage, and the minimum thickness portion stress evaluation stage. The pitting corrosion evaluation stage to determine whether the tube is normal or abnormal.

  The present invention can be applied to any pipe capable of measuring a wall thickness, for example, a pipe called “pipe” or a pipe called “tube”. is there.

  The evaluation method of the present invention basically determines whether or not the tube has a sufficient thickness from the viewpoint of maintaining the strength at which the tube does not break. Therefore, the viewpoint of whether leakage occurs due to the presence of minute through-holes is not taken into consideration.

  The second embodiment of the pipe evaluation method according to the present invention includes the following stages: axial evaluation, circumferential evaluation, and stress evaluation of the minimum thickness portion. (E) Stages are provided. (A) A recording stage in which the thickness of the tube is measured at a predetermined measurement pitch in each of the axial direction and the circumferential direction of the tube, and the thickness data is recorded. (A) A reading stage for reading the recorded thickness data. (C) With respect to the wall thickness data that has entered a predetermined wall thickness threshold value, the axial direction is evaluated based on the plurality of wall thickness data in the axial direction to determine whether it is normal or abnormal. Axial evaluation stage. (D) With respect to the thickness data that has entered the predetermined thickness threshold, the circumferential direction is evaluated based on the plurality of circumferential thickness data to determine whether it is normal or abnormal. Circumferential evaluation stage. (E) Minimum wall thickness stress evaluation that evaluates based on the stress of the minimum wall thickness, and determines whether it is normal or abnormal with respect to the wall thickness data that has entered the predetermined wall thickness threshold Stage.

  In any of the above-described invention forms, is the axial direction evaluation step normal based on the axial length of the portion that has interrupted the thickness threshold in a cross section cut by a plane including the axis of the tube? Determining whether or not can be included.

  In any of the above-described invention forms, whether or not the axial direction evaluation stage is normal based on a cross-sectional area of a portion where the thickness threshold is interrupted in a cross section cut by a plane including the axis of the tube. A step of determining can be included.

  In the first embodiment described above, an area in which the thickness data that has interrupted the thickness threshold value is defined as an interrupt area, and the effective area for reinforcing the hole in the interrupt area Based on this, the pitting corrosion can be evaluated.

  In the first embodiment described above, the hole diameter of the equivalent hole is determined for the cross-sectional area of the portion where the thickness threshold is cut in the cross section cut along the plane including the axis of the pipe, and the hole diameter is equal to the inner diameter of the pipe. The pitting corrosion evaluation can be performed based on whether or not the ratio is not more than a predetermined ratio (for example, not more than a quarter).

  In any of the above-described invention forms, the thickness data can be measured from the inside of the tube by an ultrasonic flaw detection method.

  A third aspect of the present invention is an invention of a pipe evaluation program, which causes a computer to realize the following functions (a) to (e). (A) A reading function for reading the thickness data recorded by measuring the thickness of the tube at a predetermined measurement pitch in each of the axial direction and the circumferential direction of the tube. (B) With regard to the thickness data that is below the predetermined thickness threshold value, whether the axial direction is evaluated based on the plurality of axial thickness data, is normal or need to be re-evaluated? Axis direction evaluation function to determine. (C) With regard to the thickness data that is below the predetermined thickness threshold value, whether the circumferential direction is evaluated based on the plurality of circumferential thickness data, is normal or need to be re-evaluated? The circumferential evaluation function to determine the. (D) Minimum wall thickness that determines whether normal or re-evaluation is required by evaluating the wall thickness data that is below the predetermined wall thickness threshold based on the stress at the minimum wall thickness Stress evaluation function. (E) By performing pitting corrosion evaluation on the wall thickness data that needs to be re-evaluated in at least one of the axial direction evaluation function, the circumferential direction evaluation function, and the minimum wall thickness portion stress evaluation function. Pitting corrosion evaluation function to determine whether the tube is normal or abnormal.

  A fourth aspect of the present invention is an invention of a pipe evaluation program, which causes a computer to realize the following functions (a) to (d). (A) A reading function for reading the thickness data recorded by measuring the thickness of the tube at a predetermined measurement pitch in each of the axial direction and the circumferential direction of the tube. (A) With respect to the thickness data that has entered a predetermined thickness threshold, the axial direction is evaluated based on the plurality of axial thickness data to determine whether it is normal or abnormal. Axial evaluation function. (C) With respect to the wall thickness data that has entered a predetermined wall thickness threshold value, the circumferential direction is evaluated based on the plurality of wall thickness data in the circumferential direction to determine whether it is normal or abnormal. Circumferential evaluation function. (D) Minimum wall thickness that determines whether normal or re-evaluation is required by evaluating the wall thickness data that is below the predetermined wall thickness threshold based on the stress at the minimum wall thickness Stress evaluation function.

  According to the present invention, it is possible to automatically determine whether or not the pipe is normal by comprehensively evaluating the thickness data at a plurality of points.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1A is a partial cross-sectional view of a measuring apparatus in an example in which the evaluation method of the present invention is applied to “evaluation of a heat transfer tube by an internal ultrasonic flaw detection method”. The heat transfer tube 10 is filled with water, and the ultrasonic flaw detector 12 is inserted therein. The ultrasonic wave 16 emitted from the ultrasonic probe 14 travels along the center of the heat transfer tube 10, is reflected at a right angle by the ultrasonic reflection mirror 18, and strikes the inner surface 20 of the heat transfer tube 10. The ultrasonic wave reflected by the inner surface 20 or the outer surface 22 of the heat transfer tube 10 returns along the same path and is detected by the ultrasonic probe 14. By measuring the time difference between the firing time and the detection time, the thickness of the heat transfer tube can be measured.

  The ultrasonic reflection mirror 18 rotates at a high rotation speed (for example, 12000 rpm), and thereby ultrasonic waves are scanned in the circumferential direction on the inner surface 20 of the heat transfer tube 10. The ultrasonic probe 14 emits ultrasonic waves 16 at a predetermined repetition frequency (for example, 10000 Hz). Therefore, the measurement pitch in the circumferential direction is determined by the combination of the rotation of the ultrasonic reflection mirror 18 and the repetition frequency of the ultrasonic wave 16, and for example, the thickness can be measured at 50 points per round. The ultrasonic flaw detector 12 moves in the axial direction of the heat transfer tube 10 at a predetermined translation speed (for example, 150 mm per second). The measurement pitch in the axial direction of the heat transfer tube 10 is determined by a combination of the translation speed and the rotation speed of the ultrasonic reflection mirror 18. For example, the thickness can be measured at a measurement pitch of 0.75 mm.

  FIG. 1B is a graph schematically showing echo data when one point is measured with ultrasonic waves. The horizontal axis is the elapsed time from the time of ultrasonic wave emission to the time of detecting the echo, and the vertical axis is the echo height. The echo T is an echo reflected by the ultrasonic reflection mirror 18, the echo S is an echo reflected by the inner surface 20 of the heat transfer tube 10, and the echo B is an echo reflected by the outer surface 22 of the heat transfer tube 10. FIG. 1A schematically shows the state of these echoes T, S, and B. In FIG. 1B, the time difference between the echo S and the echo B corresponds to the thickness. This measured time difference can be converted into the thickness of the heat transfer tube.

  FIG. 2 is a part of an arrangement diagram of the thickness recording data. The thickness data at each point of the heat transfer tube measured by the ultrasonic flaw detection method is stored in a storage device. The number of data of the wall thickness is large. For example, assuming that 50 points are measured per circumference in the circumferential direction of the inner circumference of the heat transfer tube and are measured at a pitch of 0.75 mm in the axial direction, a length of 10 m In the case of the heat transfer tube, 50 × (10000 / 0.75) = 667,000 wall thickness data is stored in the recording device as a whole. FIG. 2 schematically shows the recording data arranged two-dimensionally in the circumferential direction and the axial direction. This figure corresponds to the distribution of the wall thickness data when the inner surface of the heat transfer tube is developed in a plane. One section 24 corresponds to one measurement point, and wall thickness data is attached to each point. The points indicated by hatching are interrupt points to be described later, and the points filled in black are re-evaluation points to be described later. In the case of the above-described example, there are points 1 to 50 in the circumferential direction, and starts from point 1 and reaches 13000 or more in the axial direction.

  Next, referring to the flowcharts of FIGS. 3 to 6 and the explanatory diagrams of FIGS. 7 to 9, the heat transfer tube evaluation procedure will be described in detail. FIG. 3 is a flowchart showing the overall flow of an embodiment of the evaluation method of the present invention. FIG. 4 is a flowchart of the subroutine for “total thinning evaluation” shown in the flowchart of FIG. FIG. 5 is a flowchart of the subroutine “Stress evaluation of minimum thickness portion” shown in the flowchart of FIG. FIG. 6 is a flowchart of the “pitting corrosion evaluation” subroutine shown in the flowchart of FIG. 3.

In FIG. 3, evaluation is started, and first, conditions are input (step S1). Examples of conditions input by the user include the following items.
(1) The outer diameter (D) of the heat transfer tube. This example assumes 15.88 mm.
(2) Initial wall thickness (ta) of the heat transfer tube. In this embodiment, it is assumed that the distance is 2.2 mm. Accordingly, the inner diameter (d) is 11.48 mm.
(3) Maximum operating pressure (P) applied to the inside of the tube.
(4) Wall thickness threshold (tsr). This tsr is the thickness required to maintain the strength of the heat transfer tube with respect to the use conditions (temperature, pressure, etc.) of the heat transfer tube, and is a value smaller than the initial wall thickness. When this thickness is interrupted, it is determined in the prior art that the thickness is abnormal. In this embodiment, tsr = 1.6 mm. tsr can be obtained by, for example, equation (1) described in FIG. In equation (1), P is the maximum operating pressure (MPa) applied to the inside of the pipe, D is the outer diameter (mm) of the pipe, σa is the allowable tensile stress (N / mm ² ) of the material, and η is the efficiency of the longitudinal joint (Η = 1.0 when there is no longitudinal joint).
(5) Translation speed of the ultrasonic flaw detector. In this embodiment, it is assumed that it is 150 mm per second.
(6) The rotational speed of the ultrasonic reflecting mirror. In this embodiment, it is assumed that 12000 rpm.
(7) Ultrasonic repetition frequency. In this embodiment, it is assumed that the frequency is 10,000 Hz.

  When the above conditions are entered, the measurement pitch is automatically determined. That is, the measurement pitch (p1) in the axial direction is 0.75 mm. The measurement pitch (p2) in the circumferential direction is 0.72 mm on the inner surface of the tube, and measurement is performed at 50 points per circumference.

  Based on the above conditions, the thickness of the heat transfer tube is measured as shown in FIG. Then, the measurement data (which is time difference data) is recorded in the storage device. Since a large amount of measurement data is recorded in the storage device, the wall thickness measurement and subsequent data analysis can be performed separately. Since the operations described below are all executed inside the computer, unless otherwise specified, the operations are described in the computer. The recorded data is read from the storage device. This corresponds to “data reading” in the flowchart of FIG. This data is time difference data as shown in FIG. This is converted into wall thickness data. Then, the wall thickness data is arranged so as to have an arrangement as shown in FIG. The steps so far correspond to “data processing” in the flowchart of FIG. Data reading and data processing are step S2.

  Next, in step S3, the presence / absence of an interrupt point is determined. The “interruption point” is a measurement point at which measured wall thickness data (hereinafter sometimes referred to as a remaining wall thickness) has interrupted (that is, fell below) the above-described wall thickness threshold value tsr. . If the remaining thickness exceeds the thickness threshold at all measurement points, the determination in step S3 is “NO”. At this time, there is no problem at all, and the evaluation procedure is “normal and completed”. . “Normally completed” means that the normality is output and the evaluation procedure is terminated. If even one interrupt point exists, the process proceeds to step S4 and subsequent steps. This invention is characterized by extracting only the situation where the strength of the heat transfer tube is not really maintained by continuing the evaluation procedure without making an abnormality immediately even if an interruption point exists. .

  If at least one interruption point exists in the determination in step S3, the process proceeds to step S4, and it is determined whether or not the wall thickness (remaining wall thickness) is 0 mm for all the interruption points. If there is even one point where the wall thickness is 0 mm, “ends abnormally”. The meaning of “terminated with an abnormality” is that the abnormality is output and the evaluation procedure is terminated. That the wall thickness is 0 mm means that there is a through-hole that connects the inner surface and the outer surface of the heat transfer tube.

  If “NO” is determined in the step S4, the process proceeds to a step S5 to display all interrupt points on the screen. FIG. 2 shows a display example of interrupt points. The hatched point is the interrupt point. In this example, it is “displayed” so that the user can see the interruption point on the screen. However, from the viewpoint of automatically evaluating the heat transfer tube, it is not always necessary to “display” and within the computer It is sufficient if the interrupt point is specified.

  Next, the first interruption point is selected (step S6). In FIG. 2, “first” refers to the interruption point having the smallest axial point number and the smallest circumferential point number. Then, a subroutine for “total thickness reduction evaluation” (step S7) and a subroutine for “stress evaluation of the minimum thickness portion” (step S8) are executed for the interruption point. In these subroutines, it is determined whether the interruption point is problematic in terms of strength in consideration of the surrounding wall thickness data (details of this point will be described later). If there is a problem interruption point, it is stored as a point that needs to be re-evaluated (re-evaluation point). When such work is completed for one interrupt point, it is determined whether or not there is a next interrupt point (step S9). If the next interrupt point exists, the next interrupt point is selected. (Step S10), the subroutine of “total thickness reduction evaluation” and “stress evaluation of the minimum thickness portion” is repeated. In this manner, when the subroutine for overall thinning evaluation and the stress evaluation for the minimum thickness portion is completed for all interrupt points, it is determined whether or not the re-evaluation points are stored in the middle of those subroutines (step S11). . If the re-evaluation point is not stored, there is no problem in strength among the interruption points, so “normally end” is performed as it is. If there is a re-evaluation point, the routine proceeds to a “pitting corrosion evaluation” subroutine (step S12). And pitting corrosion evaluation is performed about the interruption area | region containing a reevaluation point, and it is determined whether it is really abnormal. If it is abnormal, the evaluation procedure ends with “Ended abnormally” in the “pitting corrosion evaluation” subroutine. If you successfully exit the pitting corrosion evaluation subroutine, you will be “normally finished”.

  FIG. 4 is a flowchart of a subroutine for comprehensive evaluation of thinning. At the time of entering the subroutine for overall thinning evaluation, as described above, any one interruption point is selected. This overall assessment of thinning is divided into an axial evaluation and a circumferential evaluation. The evaluation in the axial direction is further performed based on the evaluation based on the “axial length” for the region where the interruption points are continuous, and the “interruption region in the cross section (vertical cross section) cut along the plane including the axis of the tube. Includes evaluation based on “area” (evaluation by area compensation method).

  In step S13 of FIG. 4, the area | region where the interruption point is continuing from the interruption point to the axial direction is specified about the said interruption point. Here, an area where interrupt points are continuous is defined as an interrupt area. And about the interruption area | region containing the said interruption point, it is determined whether the axial direction range of an interruption area | region is settled within the outer diameter D of a heat exchanger tube centering on the said interruption point. This will be described with reference to the graph of FIG. FIG. 7A is a graph showing a part of the axial distribution of the thickness data. The horizontal axis is the position in the axial direction, and the vertical axis is the wall thickness. The measurement pitch in the axial direction is p1. The thickness data of the interrupt point (the interrupt point selected when entering the subroutine for overall thinning evaluation) is indicated by a black circle. ta is the initial thickness of the heat transfer tube, and tsr is the thickness threshold value. The black circle data naturally interrupts tsr (therefore, the process moves to a subroutine for overall thinning evaluation). An area 26 where interrupt points continue from the black circle data is an interrupt area. Whether the interruption area 26 is within the outer diameter D around the interruption point of the black circle, in other words, whether it is within (1/2) D on both sides in the axial direction, as described above. It is determined at 13. If “NO”, the safety indicator has been interrupted, so this black circle interrupt point is an interrupt point that requires re-evaluation, and this interrupt point is stored as a “re-evaluation point” (see FIG. Step S14 in the flowchart of FIG. Then, the overall evaluation for thinning is finished. That is, neither the area compensation method determination nor the circumferential evaluation is performed. This is because the interruption point is stored as the “re-evaluation point” without performing the determination and evaluation. If “YES” in the step S13, the process proceeds to the determination by the next area compensation method (step S15).

  The grounds for determining that the axial range of the interruption region is “within the outer diameter D” of the heat transfer tube as described above are as follows. In the case of a normal tube having a cylindrical cross section (outer diameter is 1520 mm or less), a hole having a size that is 1/2 the maximum outer diameter (however, 508 mm or less) can be provided. Range is from the center of the hole to the range of the hole diameter (1/2 of the outer diameter) in the axial direction (ASME standard Sec. I PG-32.3.2 or the corresponding Japan (Based on the definition of PG-32.3.2 (hole diameter) of JSME S TA1 of the Japan Society of Mechanical Engineers). Based on this, it is a question whether the axial range of the interrupt area is within the effective range (within the outer diameter D) for reinforcing the largest allowable hole (1/2 of the outer diameter). ing.

  Step S15 evaluates the heat transfer tube based on the cross-sectional area of the interrupt region in the longitudinal section with the interrupt point as the center. This will be described with reference to the graph of FIG. FIG. 7B shows the distribution of the thickness data in the axial direction, similarly to FIG. 7A. In this graph, the cross-sectional area of the interrupt area in the vertical cross section is a problem. The area of the region that interrupts tsr is A1. On the other hand, within the range of the outer diameter D with the black circle interruption point as the center, the sum of the cross-sectional areas at the points where tsr is not interrupted is A21 + A22 = A2. Whether A1 is smaller than A2 is determined in step S15 of the flowchart of FIG. If “NO”, the safety indicator has been interrupted, so this black circle interrupt point is an interrupt point that requires re-evaluation, and this interrupt point is stored as a “re-evaluation point” (see FIG. Step S14 in the flowchart of FIG. Then, the overall evaluation for thinning is finished. That is, the circumferential evaluation is not performed. This is because the interruption point is stored as a “re-evaluation point” without performing the evaluation. If “YES” in the step S15, the process proceeds to the next circumferential evaluation.

  Steps S16 and S17 are circumferential evaluations. First, regarding the interruption point, in the cross section including the interruption point (cross section perpendicular to the axial direction of the heat transfer tube), the remaining thickness is less than (1/2) tsr at some point in the circumferential direction. It is determined whether or not (step S16). This will be described with reference to the graph of FIG. FIG. 7C shows a part of the distribution in the circumferential direction of the thickness data. The horizontal axis is the circumferential position, and the vertical axis is the wall thickness. The measurement pitch in the circumferential direction is p2. The black circle is the interruption point. Obviously, the black circle data interrupts tsr. In this embodiment, there are 50 measurement points in the circumferential direction, and it is determined whether or not the remaining wall thickness is less than (1/2) tsr only at 8 points obtained by dividing the circumferential direction into 8 equal parts. To do. Although determination may be made for all points in the circumferential direction (50 points), in this embodiment, the processing speed is preferentially limited to 8 points. If none of the measurement points is below, the determination in step S16 in the flowchart of FIG. 4 is “NO”, and the overall thinning evaluation is terminated. In this case, since the safety of the interruption point is ensured, the overall evaluation for thinning is terminated without being stored as a re-evaluation point.

  If “YES” is determined in the step S16, the determination in the next step S17 is further executed. The reason is that even if the remaining thickness is less than (1/2) tsr at any of the circumferential points, if the average remaining thickness in the circumferential direction is equal to or greater than a predetermined value, there is a risk of insufficient strength. Because there is no. That is, in step S17, it is determined whether or not the average remaining thickness in the circumferential direction is equal to or greater than (1/2) tsr. In this case, the average of the above-mentioned eight points is the average remaining thickness in the circumferential direction. Of course, an average of 50 points can be adopted. If step S17 is “NO”, the safety indicator has been interrupted, so that the interrupt point becomes an interrupt point that requires re-evaluation, and this interrupt point is stored as a “re-evaluation point” ( Step S14). Then, the overall assessment of thinning is completed. If step S17 is "YES", since the safety | security of the said interruption | blocking point is ensured, it will be memorize | stored as a re-evaluation point, and will complete | finish comprehensive thinning.

  FIG. 5 is a flowchart of a subroutine for stress evaluation of the minimum thickness portion. In this subroutine, it is determined whether or not the stress at the minimum thickness portion is lower than the allowable tensile stress of the material.

  As described with reference to FIG. 7A, since the interrupt area 26 has already been specified, the point having the minimum thickness data in the interrupt area 26 is the minimum thickness portion. First, in the axial direction of the tube, the range of the outer diameter D centering on the minimum thickness portion is divided into a plurality of evaluation regions (step S18). This will be described with reference to the graph of FIG. FIG. 8A is a graph showing a part of the axial distribution of the thickness data. The horizontal axis is the position in the axial direction, and the vertical axis is the wall thickness. The thickness data of the minimum thickness portion is indicated by black circles. A region within the range of the outer diameter D is specified with the minimum thickness portion as the center. Then, the range of the outer diameter D is divided into a plurality of regions with a point where the axial distribution of the thickness data crosses the thickness threshold value tsr as a boundary point. In FIG. 8A, it is divided into a region, b region and c region. The b region is a region where the thickness is less than tsr, and the a region and the c region on both sides thereof are regions where the thickness is greater than tsr.

  Next, in step S19 in the flowchart of FIG. 5, the stress (σn) of each evaluation region is calculated. This will be described with reference to the graph of FIG. In the a region, the average value of the wall thickness is assumed to be tn. The stress σn in the region a can be calculated by the equation (2) described in the flowchart of FIG. In the formula (2), P is the maximum working pressure applied to the inside of the pipe, D is the outer diameter of the pipe, and tn is the average value of the wall thickness. Similarly, the stress σn can be calculated for the c region. For the b region below tsr, the stress σn is obtained by using the minimum thickness tmin as tn in the equation (2).

  Next, the load Fn of each evaluation region is calculated in step S20. The load Fn can be calculated by equation (3) in the flowchart of FIG. In equation (3), σn is the stress obtained in step S19, and An is the cross-sectional area of each evaluation region. As shown in FIG. 8B, the cross-sectional area An of the a region can be obtained by multiplying the average thickness tn by the axial length of the a region. The same applies to the c region. For the b region, the minimum wall thickness tmin is multiplied by the axial length of the b region to obtain a cross-sectional area An.

  Next, in the flowchart of FIG. 5, in step S21, a corrected load Fnm based on the minimum wall thickness tmin is calculated for each evaluation region. The corrected load Fnm can be calculated by equation (4). In the equation (4), Fn is the load obtained in step S20, tmin is the minimum thickness, and tn is the average value tn of the thickness in each region. For the b region below tsr, substituting tn = tmin, Fnm is equal to Fn. This corrected load corresponds to the load obtained by subtracting the load of the cross-sectional area regions 38 and 40 indicated by the hatching of the broken line from Fn in Fnm and the regions a and c in FIG.

  Next, in the flowchart of FIG. 5, in step S22, the applied stress σ1 at the minimum wall thickness tmin is calculated. The applied stress σ1 can be calculated by equation (5). In the equation (5), the numerator on the right side is the sum of the correction loads Fnm of the respective regions. The denominator on the right side is a cross-sectional area of a member having a thickness of tmin extending from the a region to the c region.

  Next, in step S23, it is determined whether or not the applied stress σ1 is lower than the allowable tensile stress σa of the tube material. If the determination in step S23 is “NO”, a safety index is interrupted, and this minimum thickness portion is stored as a “re-evaluation point” (step S24). And the stress evaluation of the minimum thickness part is complete | finished. If the determination in step S23 is “YES”, the minimum wall thickness portion is secured in terms of strength, so the stress evaluation of the minimum wall thickness portion is completed without being stored as a re-evaluation point. To do.

  FIG. 6 is a flowchart of a pitting corrosion evaluation subroutine. At the time of entering the pitting corrosion evaluation subroutine, as described above, there is at least one re-evaluation point. First, an interrupt area including “at least one re-evaluation point” (this is defined as a re-evaluation area) is created (step S25). This reevaluation area is created for all the reevaluation points stored. In FIG. 2, an interrupt area 28 including a re-evaluation point is shown, and this is the re-evaluation area 28. The other interrupt areas 30 and 32 shown in FIG. 2 do not include a re-evaluation point, and thus are not re-evaluation areas.

  In FIG. 6, the first reevaluation area is selected (step S26). Next, in step S27, a range L effective for hole reinforcement is calculated for the reevaluation region. Further, a range L effective for hole reinforcement is also calculated for the interrupt area adjacent to the re-evaluation area. This will be described with reference to FIG. FIG. 9A is a longitudinal sectional view of the heat transfer tube. In this drawing, a hole 34 exists on the inner surface of the heat transfer tube. This hole 34 is recognized by the axial distribution of the thickness data. Of the cross-sectional shape of the hole 34, the cross-sectional area A3 of the portion where tsr is interrupted is obtained. Next, the range L is calculated based on the equation (6) described in FIG. The meaning of the range L is as follows. When it is assumed that the cross-sectional area A3 of the part where tsr is interrupted is reinforced by the surrounding "part where tsr is not interrupted", the range L of the reinforcing part so that the total cross-sectional area of the reinforcing part becomes A3. Is stipulated. That is, the idea is to reinforce the hole portion that has weakened by interrupting tsr with the “portion that does not interrupt tsr” around the hole. If the “part where tsr is not interrupted” is sufficiently widened around the hole, it is determined that the hole has no problem in strength. Therefore, when there is an adjacent hole near the hole, it is important that the reinforcing range L of the hole and the reinforcing range of the adjacent hole do not overlap. It is step S28 in the flowchart of FIG. 6 that determines such a situation, and step S27 calculates the reinforcement range L for that purpose. The determination in step 28 corresponds to determining whether or not the hole is a “single hole”.

  In FIG. 2, a range L <b> 1 effective for reinforcing the reevaluation region 28 is shown below the reevaluation region 28. Further, an effective range L2 for reinforcing the interrupt area 30 is shown above the interrupt area 30 adjacent to the reevaluation area 28. If the ranges L1 and L2 overlap, step S28 in the flowchart of FIG. 6 is “YES”. In this case, “ends abnormally”. At that point, the evaluation procedure ends. If “NO” in the step S28, the process proceeds to the next equivalent hole diameter determining step S29.

  In the above description, the presence / absence of overlap between the ranges L1 and L2 has been described only with respect to whether or not there is overlap in the axial direction of the tube, but in reality, the circumferential direction of the tube and the oblique direction (axial and circumferential directions). (A direction that forms an angle of 45 degrees with respect to), the presence or absence of overlap between the ranges L1 and L2 is determined.

  In step S29, it is determined whether or not the re-evaluated region has an equivalent pore diameter of (1/4) d or less. This will be described with reference to FIG. In the longitudinal cross-sectional view of the heat transfer tube, the cross-sectional area A3 of the portion where tsr is cut in the cross-sectional shape of the hole 34 is obtained. This A3 has already been obtained in step S27. Next, a linear through hole 36 in which the cross-sectional area of the portion equal to or less than tsr is A3 is assumed. This through hole 36 is an equivalent hole of the hole 34. The hole diameter of the equivalent hole 36 is d3. This d3 can be obtained by equation (7) in FIG. That is, A3 is divided by tsr. It is determined in step S29 in the flowchart of FIG. 6 whether this equivalent hole diameter d3 is equal to or less than one quarter of the inner diameter d of the heat transfer tube. If step 29 is “NO”, “ends abnormally”. At that point, the evaluation procedure ends. If “YES”, it is determined whether or not there is a next reevaluation area (step S30). If there is a next reevaluation area, the next reevaluation area is selected (step S31), and the process returns to step S27. If there is no next reevaluation area, the pitting corrosion evaluation is terminated. In this case, the process returns to the flowchart of FIG.

The present invention is not limited to the above-described embodiments, and the following modifications are possible.
(1) Although the above-mentioned embodiment is applied to the wall thickness measured by the ultrasonic flaw detection method, the present invention can also be applied to the wall thickness obtained by other measurement methods. For example, the present invention can be applied to a wall thickness obtained by a potential difference method. Measuring the wall thickness of a tube using the potentiometric method is disclosed, for example, in Patent Document 4 below.
JP, 2005-308544, A (2) In Step S13 of the flow chart of Drawing 4, the judgment condition of "within outer diameter D" can be made tighter (to the safe side). For example, a condition such as “within 0.8D of the outer diameter” can be set. (3) In step S16 of the flowchart of FIG. 4, the determination condition “remaining wall thickness <(1/2) tsr” can be made tighter (safe side). For example, a condition such as “remaining wall thickness <(2/3) tsr” can be set. (4) In step S29 of the flowchart of FIG. 6, the determination condition that “the equivalent hole diameter is (1/4) d or less” can be tightened (to the safe side). For example, a condition such as “equivalent pore diameter of 0.2 d or less” can be set.

(A) is a partial cross-sectional view of a measuring apparatus in an example in which the evaluation method of the present invention is applied to the evaluation of a heat transfer tube by an internal ultrasonic flaw detection method. (B) is a graph schematically showing echo data when one point is measured by ultrasonic waves. It is a part of arrangement | sequence diagram of recording data of thickness. It is a flowchart which shows the whole flow of one Example of the evaluation method of this invention. It is a flowchart of the subroutine of a thinning comprehensive evaluation. It is a flowchart of the subroutine of the stress evaluation of the minimum thickness part. It is a flowchart of a subroutine for pitting corrosion evaluation. It is a graph which shows distribution of the axial direction or circumferential direction of thickness data. It is a graph which shows distribution of the axial direction of thickness data, Comprising: It is a graph for demonstrating the stress evaluation of a minimum thickness part. It is a longitudinal cross-sectional view of the heat exchanger tube explaining the method of pitting corrosion evaluation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Heat transfer tube 12 Ultrasonic flaw detector 14 Ultrasonic probe 16 Ultrasonic 18 Ultrasonic reflection mirror 20 Inner surface 22 Outer surface 28 Re-evaluation area 30, 32 Interruption area

Claims (9)

A tube evaluation method comprising the following steps (a) to (f):
(A) A recording stage in which the thickness of the tube is measured at a predetermined measurement pitch in each of the axial direction and the circumferential direction of the tube, and the thickness data is recorded.
(A) A reading stage for reading the recorded thickness data.
(C) With regard to the thickness data that is below the predetermined thickness threshold value, whether the axial direction is evaluated based on the plurality of axial thickness data, is normal or need to be re-evaluated? Determine the axial evaluation stage.
(D) With regard to the thickness data that falls below the predetermined thickness threshold value, whether the circumferential direction is evaluated based on the plurality of circumferential thickness data, is normal or need to be re-evaluated? The circumferential evaluation stage to determine the.
(E) The minimum thickness that determines whether the data is normal or needs to be re-evaluated by evaluating the thickness data that is below the predetermined thickness threshold based on the stress of the minimum thickness portion Stress evaluation stage.
(F) By performing pitting corrosion evaluation on the thickness data that needs to be re-evaluated in at least one of the axial direction evaluation stage, the circumferential direction evaluation stage, and the minimum thickness portion stress evaluation stage. The pitting corrosion evaluation stage to determine whether the tube is normal or abnormal. A tube evaluation method comprising the following steps (a) to (e):
(A) A recording stage in which the thickness of the tube is measured at a predetermined measurement pitch in each of the axial direction and the circumferential direction of the tube, and the thickness data is recorded.
(A) A reading stage for reading the recorded thickness data.
(C) With respect to the wall thickness data that has entered a predetermined wall thickness threshold value, the axial direction is evaluated based on the plurality of wall thickness data in the axial direction to determine whether it is normal or abnormal. Axial evaluation stage.
(D) With respect to the thickness data that has entered the predetermined thickness threshold, the circumferential direction is evaluated based on the plurality of circumferential thickness data to determine whether it is normal or abnormal. Circumferential evaluation stage.
(E) Minimum wall thickness stress evaluation that evaluates based on the stress of the minimum wall thickness, and determines whether it is normal or abnormal with respect to the wall thickness data that has entered the predetermined wall thickness threshold Stage.   3. The evaluation method according to claim 1, wherein the axial direction evaluation step is normal based on an axial length of a portion where the thickness threshold value is cut in a cross section cut by a plane including an axis of a tube. The evaluation method characterized by including the step which determines whether it is.   The evaluation method according to any one of claims 1 to 3, wherein the axial direction evaluation step is performed on a cross-sectional area of a portion where the thickness threshold value is cut in a cross section cut along a plane including an axis of a pipe. An evaluation method characterized by including a step of determining whether or not it is normal based on.   2. The evaluation method according to claim 1, wherein an area in which the thickness data that has interrupted the thickness threshold value is defined as an interrupt area, and an effective range for reinforcing a hole in the interrupt area The pitting corrosion evaluation is performed based on the evaluation method.   2. The evaluation method according to claim 1, wherein a hole diameter of an equivalent hole is obtained for a cross-sectional area of a portion where the thickness threshold is cut in a cross section cut along a plane including an axis of the pipe, and the hole diameter is an inner diameter of the pipe. The pitting corrosion evaluation is performed based on whether or not the ratio is less than or equal to a predetermined ratio.   The evaluation method according to any one of claims 1 to 6, wherein the thickness data is measured from the inside of a tube by an ultrasonic flaw detection method. A pipe evaluation program for causing a computer to realize the following functions (a) to (e).
(A) A reading function for reading the thickness data recorded by measuring the thickness of the tube at a predetermined measurement pitch in each of the axial direction and the circumferential direction of the tube.
(B) With regard to the thickness data that is below the predetermined thickness threshold value, whether the axial direction is evaluated based on the plurality of axial thickness data, is normal or need to be re-evaluated? Axis direction evaluation function to determine.
(C) With regard to the thickness data that is below the predetermined thickness threshold value, whether the circumferential direction is evaluated based on the plurality of circumferential thickness data, is normal or need to be re-evaluated? The circumferential evaluation function to determine the.
(D) Minimum wall thickness that determines whether normal or re-evaluation is required by evaluating the wall thickness data that is below the predetermined wall thickness threshold based on the stress at the minimum wall thickness Stress evaluation function.
(E) By performing pitting corrosion evaluation on the wall thickness data that needs to be re-evaluated in at least one of the axial direction evaluation function, the circumferential direction evaluation function, and the minimum wall thickness portion stress evaluation function. Pitting corrosion evaluation function to determine whether the tube is normal or abnormal. A pipe evaluation program for realizing the following functions (a) to (d) on a computer.
(A) A reading function for reading the thickness data recorded by measuring the thickness of the tube at a predetermined measurement pitch in each of the axial direction and the circumferential direction of the tube.
(A) With respect to the thickness data that has entered a predetermined thickness threshold, the axial direction is evaluated based on the plurality of axial thickness data to determine whether it is normal or abnormal. Axial evaluation function.
(C) With respect to the wall thickness data that has entered a predetermined wall thickness threshold value, the circumferential direction is evaluated based on the plurality of wall thickness data in the circumferential direction to determine whether it is normal or abnormal. Circumferential evaluation function.
(D) Minimum wall thickness that determines whether normal or re-evaluation is required by evaluating the wall thickness data that is below the predetermined wall thickness threshold based on the stress at the minimum wall thickness Stress evaluation function.

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