JPWO2005124315A1 - Comprehensive evaluation method of creep remaining life - Google Patents

Abstract

Provided is a method capable of accurately evaluating the remaining life of a device member subjected to creep damage regardless of a fine grain portion and a coarse grain portion. This is a method for evaluating the remaining life represented by the time until creep destruction of a device member that has undergone creep damage. On the surface of the equipment member, find the number of connecting voids that exist over 1/2 of each length of at least two grain boundaries within the range of 1 mm2, and the number of specific voids for the area of 1 mm2 Is the L parameter. Further, on the surface of the device member, the ratio of the total length of all voids on the grain boundary to the length of one grain boundary within the range of 1 mm 2 is obtained for each grain boundary as the void boundary occupation ratio, The maximum value is set as the M parameter. The remaining life of the equipment member is evaluated based on the L parameter and the M parameter, respectively, and the result of the shorter evaluation is defined as the remaining life of the equipment member.

Description

  The present invention relates to a technique for evaluating the remaining life of a device member that has undergone creep damage.

  For example, in the case of equipment members that are used for a long time under high temperature and high pressure, such as high-temperature members used in thermal power generation boilers and steam turbines, especially in the vicinity of welds (welded metal parts, weld heat-affected parts, and base materials) ), Deterioration due to creep damage progresses as time passes, and minute voids or voids called voids or cavities (collectively referred to as “voids”) are generated in the metal structure. As the void grows, it joins and coalesces, eventually forming a microcrack of about 1 (crystal) grain boundary length, and the microcrack further repeats propagation and connection, destroying the entire member. (Creep destruction). Therefore, in order to stably operate the thermal power generation unit over a long period of time, it is possible to accurately grasp the time until the equipment member creeps or the remaining life represented by the “creep life consumption rate” described later. It is necessary.

  According to the following non-patent document 1, more than 80% of commercial thermal power generation units in Japan currently have a cumulative operating time of over 100,000 hours, and the other 20% have exceeded 200,000 hours. It is a situation. For this reason, during periodic inspections, for the thermal power generation unit boiler, etc., select the part under the most severe conditions from the past remaining life diagnosis history, structure, stress, temperature, weight, etc., and progress of creep deterioration It is important to accurately grasp the situation and repair it appropriately.

  Non-Patent Document 2 below shows a conventional creep remaining life evaluation method focusing on voids generated in actual machine members. The surface of the member is polished and corroded, and a film made of acetylcellulose or the like is applied to copy the surface of the member. An evaluation method using what was taken (hereinafter referred to as “replica”) is described. The remaining life or creep damage evaluation method using this replica is evaluated by various parameters such as A parameter, structure contrast, void area ratio (Non-patent Document 3), void area density, grain boundary damage (Non-Patent Document 4), etc. The method is known.

  In these methods, parameters representing the state of creep deterioration of actual machine members are obtained, and the “creep life consumption rate” expressed as the ratio of the actual usage time to the total time (life) from the time of new material to creep failure is obtained. Thus, the remaining life of the actual machine member is estimated. Specifically, in any of the above methods, first, a creep test is performed to create a master curve that represents the relationship between the parameters of each method and the creep life consumption rate. Then, a creep life consumption rate of the actual machine member can be estimated by collecting a replica from the surface of the target actual machine member and comparing the parameter obtained on the replica with the master curve. Furthermore, based on the actual use time and the creep life consumption rate at the time of evaluating the remaining life of the actual machine member, the time representing the remaining life of the actual machine member can be estimated. Specifically, when the creep life consumption rate at the time of evaluation is “A” and the actual use time is “B”, the remaining life t is calculated by the equation “t = B × {(1−A) / A}”. Can be sought.

  In addition, Non-Patent Document 5 described below describes a method for estimating the remaining creep life by nondestructive inspection such as an ultrasonic noise energy method and an ultrasonic spectroscopy method. Non-Patent Documents 6 and 7 below clearly show the physical meaning of the creep damage parameter for “void occupancy on the grain boundary line” (Non-Patent Document 8), which is used as an index focusing on voids at grain boundaries. It is described that.

  Among the above evaluation methods, the “A-parameter method” draws a straight line parallel to the stress axis in a determined region, and the parameter is the ratio of the grain boundary line where voids occupy the number of intersections between the straight line and the grain boundary line. And is generally called “A parameter for measurement”. However, since the A parameter is based on the idea that if there is even one void at the grain boundary, the grain interface is severely damaged and the whole grain boundary is regarded as a microcrack, so it is generally used. The physical meaning of the measured A parameter is sparse.

The “void area ratio method” uses the void area ratio per unit area within a specified area as a parameter, and the “void area density method” exists per unit area (usually 1 mm ² ). This is an evaluation method using the number of voids as a parameter. This void area density method is easy to measure because it is only necessary to determine the number of voids, but this parameter (void area density) is proportional to the radius and number of voids and inversely proportional to the crystal grain size. There is a problem in that it does not directly represent the number of voids actually present in the member.

  “Void occupancy method on the grain boundary line” is a method for determining the length of each void on the grain boundary line with respect to the length of the grain boundary line for each grain boundary line within a predetermined range appearing on the cut surface or surface of the member. In this evaluation method, the total ratio is obtained and the average value is used as a parameter. This parameter is equal to the void area ratio on the grain interface, which is the path of creep fracture, and has a one-to-one correspondence with the effective cross-sectional area used in conventional damage mechanics, so the physical meaning is clear. However, there is a problem that measurement is difficult as compared with other methods.

  Patent Document 1 below describes a creep (remaining) life evaluation method that can easily and accurately estimate the “creep life consumption rate” of a creep-degraded equipment member. In this method, the ratio of the total length of voids on the grain boundary to the length of one grain boundary of the member is obtained for each grain boundary, and the maximum value is used as a parameter (referred to as “M parameter”). Since it is an evaluation method, it is called the “M parameter method”. In this M parameter method, the closer the M parameter is to “1”, the higher the creep life consumption rate and the shorter the remaining life, that is, the higher the risk of creep destruction.

International Publication WO02 / 014835 Keiichi Iwamoto, Thermal Power Generation, 48-8 (1997), 14 Japan Iron and Steel Institute, Creep and Creep Fatigue Damage Manual by Replica Method “Structural Materials Reliability Evaluation Technology Subcommittee High Temperature Strength WG Research Results Report (separate volume manual), (1991), 1 Isamu Nonaka, Keigo Sonoie, Masashi Nakashiro, Hiroshi Yoneyama, Masaki Kitagawa, Ishikawajima-Harima Technical Report, 32-5 (1992), 313 Kenji Kikuchi, Yoshiyuki Kaji, Materials, 44-505 (1995), 1244 The Japan Society of Mechanical Engineers, Power Plant / Structure Remaining Life Evaluation Technology, (1992), 89, Gihodo Publishing Naoya Tada, Satoshi Fukuda, Takayuki Kitamura, Ryuichi Otani, Materials 46-1, (1997), 39 Naoya Tada, Takayuki Kitamura, Ryuichi Otani, Materials 45-1, (1996), 110 Tsuneyuki Ejima, Zhou, Ryuichi Otani, Takayuki Kitamura, Naoya Tada, 32nd High Temperature Strength Symposium Preprint, (1994), 94

  However, in the above-mentioned equipment members, the metal structure of the weld metal part and the weld heat-affected zone is mainly about 100 micrometers (μm) in particle size in order from the weld metal side (some have 200 μm or more). The point is composed of a coarse-grained portion made of a crystal and a fine-grained portion made of a crystal having a particle size of about 1 μm to 10 μm, and one void is almost the same size as one crystal grain boundary in the fine-grained portion. In light of the fact that growth has been found in recent experiments, when the “fine-grained portion” is evaluated by the above-mentioned M-parameter method, the M-parameter reaches “1” at the beginning of the creep life. May lead to an evaluation that the risk is high.

  In addition, as described above, the main cause of creep fracture is the formation of microcracks by the growth, connection and coalescence of voids generated on the grain boundaries. In view of the fact that it occurs intensively in the latter half of the case, even if one void becomes the same size as one grain boundary in the fine grain part, it cannot be said that the risk of creep fracture is high immediately. In the parameter method, it is difficult to accurately evaluate the creep life for the “fine-grained portion”.

  On the other hand, according to the results of various creep tests, the portion that reaches the creep fracture in the coarse grain portion and the fine grain portion differs depending on various conditions such as differences in welding methods such as longitudinal welding and circumferential welding, and stress conditions. In view of the fact that the actual machine members are subjected to various types of welding and placed in a multiaxial stress field, it is also important to accurately evaluate the creep life in the fine-grained portion.

  Further, when evaluating a fine grain part, for example, in the conventional A-parameter method, the grain boundaries that are damaged to be measured are unclear and the number of grain boundaries becomes very large. It is practically difficult to evaluate the grain.

  In view of the above situation, an object of the present invention is to provide a method capable of accurately evaluating the remaining life of a device member that has undergone creep damage regardless of whether the portion is a fine-grained portion or a coarse-grained portion. .

  The present invention relates to a method for evaluating the time until creep destruction of an equipment member that has undergone creep damage or the remaining life represented by a creep life consumption rate, within a predetermined range on the surface of the equipment member. The number of specific voids existing across a plurality of crystal grain boundaries is obtained, and the ratio of the number of specific voids to the area of the predetermined range is defined as a specific void density, and 1 in the predetermined range on the surface of the device member. The ratio of the total length of all voids on the grain boundary to the length of the grain boundary is obtained for each grain boundary as a void grain boundary occupation ratio, and the maximum value is defined as the maximum void boundary occupation ratio. The remaining life of the device member is evaluated based on the void density and the maximum void boundary occupancy rate, respectively, and the result of the shorter evaluation is defined as the remaining life of the device member.

  In an embodiment of the invention, the specific void is an extended void that exists over at least half of each length of at least two crystal grain boundaries, or voids generated on a plurality of crystal grain boundaries are combined. It is the connection void formed by doing.

  The maximum void grain boundary occupancy is obtained by the following equation.

Here, m is the number of grain boundaries where voids are present, n is the number of voids present on each grain boundary, and l _αi is the length of the i-th void existing on the α-th grain boundary in the grain boundary direction. , L _α is the length of the α-th grain boundary where the void exists.

  Furthermore, the evaluation of the remaining life is performed by referring to each evaluation standard obtained from the creep test for the relationship between the specific void density and the remaining life and for the relationship between the maximum void grain boundary occupancy and the remaining life. It is to estimate the time. Or, in addition to the above evaluation criteria for the specific void density and the maximum void grain boundary occupancy rate, the remaining life is evaluated by the ratio of the number of all voids within the range to the number of voids in the range. The evaluation criteria for the other parameters are also referred to, and the shortest time estimated by the evaluation criteria for each parameter is set as the remaining life.

  In a more specific embodiment, the voids present on the surface of the fine-grained portion formed of crystals having a particle size of 10 μm or less of the device member are targeted.

  Further, the surface of the device member is imaged, and the number of voids is obtained on the image. In this case, the surface of the equipment member is polished and corroded, and then a film made of acetylcellulose or the like is pasted to copy the surface, or the equipment member is imaged using an imaging means, It is possible to image the surface of

  According to the present invention, the number of specific voids existing over a plurality of crystal grain boundaries within a predetermined range on the surface of the device member is obtained, and the specific void represented by the ratio of the number of specific voids to the area of the range By obtaining the density, it is possible to evaluate the remaining life of the equipment member that has undergone creep damage. This evaluation method can be evaluated more quickly and easily than the conventional void number density method because it is only necessary to detect not all of the voids within a predetermined range but only specific voids. In addition, since the specific voids that exist across a plurality of crystal grain boundaries are voids that have grown beyond one grain boundary to span two or more grain boundaries, the number of creeps on the surface of the device member It becomes an index indicating the degree of progress of deterioration. Therefore, by using the parameter “specific void density” described above, it is possible to correctly grasp the state of creep deterioration, specifically the remaining life, and at least two grain boundaries even in a “fine grain part” where the grain boundary is small. By paying attention to the voids extending over, it is possible to accurately evaluate the remaining life in the fine-grained portion, which is difficult with the conventional evaluation method such as the A-parameter method.

  According to a specific aspect, as the specific void, an extended void existing over 1/2 or more of each length of at least two crystal grain boundaries, or a void generated on a plurality of crystal grain boundaries is combined. By detecting the connection void formed by the above, the degree of progress of creep deterioration can be grasped more accurately.

  Further, as a specific evaluation method of the remaining life, by referring to or collating an evaluation standard (for example, a master curve described later) obtained by a creep test for the relationship between the specific void density and the remaining life as described above, It is possible to estimate the time (or creep life consumption rate) until the equipment member creeps.

  Furthermore, in addition to the evaluation criteria for the above-mentioned “specific void density”, reference is also made to the evaluation criteria for “void number density” and other parameters. By making it the remaining life of, it is possible to evaluate from a safer side. As these evaluation criteria, as will be described later, a master curve representing the relationship between each parameter and the creep life consumption rate, and other functions and data representing the relationship between the two can be used.

  In addition, according to the present invention, as described above, the surface of the fine-grained portion formed of crystals having a particle size of 10 μm or less can be selected as a location for obtaining the number of voids within a predetermined range.

  Furthermore, when the method of the present invention is implemented, if the surface of the device member is imaged as a means for measuring the voids existing on the surface of the device member, the specific void is automatically recognized by a machine such as a computer, and those voids are displayed on the image. The number can be obtained quickly and easily. In this case, the image of the surface of the equipment member is obtained by polishing the surface of the equipment member and then corroding the surface of the equipment member to copy the surface, or by using an imaging means. Is obtained by imaging.

The main flowchart of the creep remaining life evaluation method of an Example. The figure which shows the test body and void observation position which were used for the creep test. The figure which shows the test body and void observation position which were used for the creep test. The figure which shows the test body and void observation position which were used for the creep test. The figure which shows the position which extract | collected the test piece in the actual machine waste material of a thermal power plant. An electron micrograph showing the occurrence of voids during each interruption of the internal pressure creep fracture test. The figure which shows the void generation | occurrence | production state of the observation position at the time of each halfway stop of an internal-pressure creep fracture test (actual machine acceleration test). The figure which shows the basic view of L parameter. The figure which shows the basic view of M parameter. A master curve representing the relationship between the L parameter and the creep life consumption rate. A master curve representing the relationship between the M parameter and the creep life consumption rate. The figure which shows the basic concept of the void number density which is a parameter of the void number density method. Master curve for void number density method.

  FIG. 1 is a main flowchart of the creep remaining life evaluation method of the present invention.

  In the embodiment, a method of evaluating the remaining life represented by the time until creep rupture or the creep life consumption rate of a member that is used at high temperature and high pressure in a power plant boiler and is damaged by creep will be described. .

  In this creep remaining life evaluation method, a predetermined parameter based on a microscopic void called a void existing on the surface of an actual machine member is obtained, and this is compared with a previously created evaluation criterion representing the relationship between the parameter and the remaining life. Thus, the remaining life of the member is evaluated. Therefore, in order to create the above evaluation criteria, a creep test is performed using various specimens, and the void linkage density (Voids Linking Density Parameter [hereinafter referred to as L parameter]), which will be described later, is used as the above parameter while appropriately stopping the test. A maximum void grain boundary occupation ratio (Maximum Fraction of Voids on the Grain boundary Line Parameter [hereinafter referred to as M parameter]) is obtained (step [hereinafter referred to as ST] 1).

  2 to 4 show a specimen used for the creep test and a void observation position in each specimen.

  The specimen shown in FIG. 2 is a test piece 1 taken from a weld that has been damaged by creep in a high-temperature reheat steam pipe in operation. Using this specimen, a creep rupture test can be performed while stopping appropriately. Do. Test conditions are shown below.

(1) Test temperature is 883.15K
(2) Test stress (tensile) is 68.6MPa.

  Also, as shown in the figure, the metal structure near the welded portion 2 of the test piece 1 includes a coarse-grained portion 3 formed of crystals with a particle size of about 100 μm or less and crystals with a particle size of about 1 μm to 10 μm from the weld metal side. It is comprised with the fine grain part 4 formed by. In the creep remaining life evaluation method of the example, the M parameter is obtained based on the void observation result in the coarse grain part 3, and the L parameter is obtained based on the void observation result in the fine grain part 4.

  The specimen shown in FIG. 3 is, for example, a test piece 5 made of a welded joint pipe which is welded to a solid round bar (φ40 × t8 × L430) made of 2.25Cr-1Mo steel and is hollowed in the center. . The peripheral weld 6 of the test piece 5 is preferably made as close as possible to the weld of the actual machine member by 1 to 4 layers of covered arc welding and heat-treated at 993 K × 1.3 hr. The test piece 5 is subjected to a pipe internal pressure creep rupture test. Specifically, while heating the test piece 5 in an electric furnace, pressurized water is injected into the test piece 5 to form high-pressure steam and to apply the internal pressure. Also in this test, the suspension is appropriately stopped, the voids in the coarse grain portion and the fine grain portion are observed at each suspension, and each parameter is obtained by the method described later. Test conditions are shown below.

(1) Test temperature is 903K
(2) The circumferential stress is 61.3 MPa (according to the average diameter formula).

  The specimen 7 in FIG. 4 is a waste material of a high temperature reheat steam pipe elbow made of, for example, 2.25Cr-1Mo steel, and the welded portion 8 of the specimen 7 is a tubular pair of plates bent with the same curvature. After being combined, the submerged arc welding is performed in the longitudinal direction. The specimen 7 is subjected to an internal pressure creep rupture test (actual machine acceleration test) while appropriately stopping the test. Specifically, after the sample 7 is surrounded by a plate heater and heated, pressurized water is injected into the sample 7 to form high-pressure steam and an internal pressure is applied. In this test, for example, at the two observation positions 9a and 9b determined on the surface near the welded portion 8, the voids of the coarse grain portion and the fine grain portion at each halfway stop are observed, and each parameter is obtained. Test conditions are shown below.

(1) Test temperature is 923K
(2) Test stress is Uchisho 3.0MPa
(3) The maximum principal stress at the center of the elbow abdomen is 39.2 MPa
(4) The actual usage time until the specimen 7 is discarded is about 1475 hours.

  FIG. 5 shows a position where a test piece is collected from the actual waste material of the thermal power plant in order to perform another creep test. In the SH pipe T piece pipe of (a) and the RHY piece pipe of (b), voids were observed on the surface in the vicinity of the peripheral welds 10 and 11, and a diameter of 10 mm was observed from the cross section near the site where the presence of voids was observed. Take a round bar specimen with a distance between the gauges of 50mm. In the RH pipe stub of (c), a miniature creep round bar test piece having a diameter of 2 mm is taken from the cross section in the vicinity of the pipe stub weld 12 where the presence of a void is recognized. For these test pieces, a uniaxial creep rupture test in an inert gas atmosphere was performed while appropriately stopping the suspension, and voids were observed in the coarse and fine portions at each suspension, and each parameter was Ask for. The following table shows the usage conditions of each waste material.

  FIG. 6 shows the occurrence of voids during each halfway stop of the pipe internal pressure creep rupture test using the test piece 5 (FIG. 3). In void observation, for example, the surface of the test piece 5 may be directly imaged using a scanning electron microscope (hereinafter referred to as “SEM”) as shown in the figure, or the surface of the test piece 5 is polished and corroded. A replica obtained by applying a predetermined film (for example, an acetylcellulose film) and copying the surface of the member can be imaged and observed with an SEM.

  In collecting replicas, the surface of the test piece 5 can be polished by, for example, rough polishing with a grinder, polishing sequentially with a grinding wheel of No. 120 to No. 1000, and then buffing with diamond particles of about 3 μm to 1 μm. Polishing should be done sequentially and mirror finish should be done.

  Furthermore, in order to corrode the surface of the test piece 5, for example, after polishing the surface as described above, the corrosive liquid is soaked into absorbent cotton and applied to the polished surface, thereby identifying the crystal grain boundaries in the metal structure. Can be possible. The following two types of corrosive liquids can be used for the corrosion.

(1) Picric acid: saturated picric acid (dissolved in methanol) + surfactant
(2) Nitric acid (5 ml) + methanol (95 ml).

  As the surfactant, for example, sodium dodecylbenzenesulfonate is preferably used and mixed at a rate of 1 g with respect to 100 ml of saturated picric acid.

  In order to collect a replica, a replica softening material (for example, methyl acetate) is applied to the surface of the corroded test piece 5, an acetylcellulose film is attached, and the replica softening material is sufficiently dried. If the film is peeled off, the surface of the test piece 5 can be copied. Thereby, the void generated on the surface of the test piece 5 appears as a protrusion on the replica.

In addition, in the observation of voids, the state of occurrence of voids in a predetermined range (for example, 30 mm ² ) is observed in advance with an optical microscope or the like, and the place where the damage is most advanced (void generation / connection is concentrated) After confirming the above, if the portion is observed with an SEM (for example, observed at a magnification of 1000), void observation can be performed without missing the portion where the damage has progressed.

Returning to FIG. 6 again, it can be seen that the number of voids increases on the surface of the test piece 5 with the passage of time in the pipe internal pressure creep rupture test. For example, as shown in the figure,
(1) When the creep life consumption rate (t / tr) = 0.49, a void of about 1 μm is generated.
(2) At t / tr = 0.73, multiple voids occur at the same grain boundary,
(3) At t / tr = 0.97, void connection is observed,
(4) At t / tr = 1.0, a microcrack was formed.

  Here, each halfway stop time was expressed as a creep life consumption rate (t / tr), which is a value obtained from the result of the pipe internal pressure creep rupture test until the test piece 5 reached the creep rupture. is there.

  As described above, voids are initially randomly generated on a plurality of grain boundaries, but thereafter are intensively generated at specific positions, and these are eventually connected to form a microcrack.

  FIG. 7 shows the occurrence of voids at the observation positions 9a and 9b when the internal pressure creep rupture test (actual machine acceleration test) using the specimen 7 (FIG. 4) is stopped halfway. In this test as well, it can be seen that voids start to be generated randomly on a plurality of grain boundaries, then increase in a concentrated manner at specific positions, and eventually connect to form a microcrack.

  FIG. 8 shows a basic concept of the L parameter for evaluating the remaining life of the equipment member by the creep remaining life evaluation method of the embodiment.

The L parameter is represented by the ratio of the number of voids existing across a plurality of crystal grain boundaries within the predetermined area of the void observation position surface. Specifically, first, voids (hereinafter referred to as “below”, which exist within a predetermined range (for example, 1 mm ² ) on the surface of the observation position and over 1/2 of each length of at least two grain boundaries. Number of connected voids).

  For example, as shown in the figure, when there are three voids 16a, 16b, and 16c on the crystal grain boundary 15 in a certain range, the uppermost void 16a exists only on one crystal grain boundary. Therefore, it is not counted as a connecting void and can be ignored.

  Next, since the central void 16b exists on the three crystal grain boundaries 15 and completely covers the two crystal grain boundaries 15, this is counted as a connecting void.

  The void 16c exists on the three crystal grain boundaries 15, and there is no crystal grain boundary 15 that completely covers the void 16c, but exists over more than half of each length of the two crystal grain boundaries 15. Therefore, this is also counted as a connecting void.

By determining the number of connecting voids within a predetermined range (for example, 1 mm ² ) on the surface of the observation position by the above method at the midpoint of each creep test, this number is calculated as the area of the evaluation target range (for example, The L parameter expressed by the value divided by 1 mm ² ) is obtained. Therefore, the L parameter is defined by the following equation.

  FIG. 9 shows the basic concept of the M parameter, which is another parameter.

The M parameter is the ratio of the total length of all voids on the grain boundary to the length of one grain boundary within a predetermined range (for example, 1 mm ² ) on the void observation position surface. It calculates | requires about each crystal grain boundary and is represented by the maximum value. That is, the M parameter can be obtained by the following equation.

Where m is the number of grain boundaries where voids exist,
n is the number of voids present on each grain boundary,
l _αi is the grain boundary length of the i th void existing on the α th grain boundary,
L _α is the length of the α-th grain boundary where a void exists.

Therefore, as shown in the figure, if there are two voids 18 on a certain grain boundary 17, the length of each void 18 in the grain boundary direction is l ₁ and l ₂ , and the length of the grain boundary is L, The void grain boundary occupation ratio in this grain boundary can be calculated | required by the following formula | equation.

  Thus, by obtaining the void grain boundary occupation ratio for each grain boundary within a predetermined range, the maximum value can be obtained as the M parameter.

  Returning to the main flow chart (FIG. 1) again, after completing the above various creep tests, each master curve is created as an evaluation criterion for the remaining creep life based on the L parameter obtained at each halfway stop (ST2, ST3).

  FIG. 10 is a master curve showing the relationship between the L parameter and the creep life consumption rate.

  The creep life consumption rate is represented by the ratio of the total time “t” of the time used for the creep test and the actual use time with respect to the total time “tr” from the time of the new material to creep rupture. Therefore, when the specimen reaches creep fracture, it is “t / tr = 1”, and it can be evaluated that the smaller this value is, the closer to the state of the new material, that is, the longer the remaining life.

According to this master curve, the L parameter is substantially “0” in the first half of the life of the equipment member, and increases in the second half of the life. Thus, the master curve based on this L parameter is
(1) The main cause of creep fracture is that voids generated on grain boundaries grow, coalesce and connect to form microcracks,
(2) Microcracks are concentrated in the latter half of the creep life,
(3) The connection void is well reflected in that it exists over at least half of the length of at least two grain boundaries, that is, it is formed by connecting a plurality of voids. Recognize.

  FIG. 11 is a master curve showing the relationship between the M parameter and the creep life consumption rate.

  According to this master curve, the M parameter increases while drawing a downward convex smooth curve over the entire creep life, and the master curve according to the L parameter (FIG. 10) and other conventional master curves (for example, A rapid increase in the late stage of life as shown in FIG. 13) is not recognized. In addition, since the M parameter evaluates the creep life by focusing only on the localized damaged portion, that is, the maximum damaged portion, it can be seen that the M parameter shows a certain value even at the initial stage of the life. From the above, the master curve based on this M parameter indicates that the growth and connection of voids proceed intensively on a specific grain boundary on the grain boundary in the coarse region of the weld heat affected zone. It can be seen that this directly reflects the mechanism of creep rupture, which grows and breaks.

  Next, in order to evaluate the remaining life of a member that is actually used in a boiler of a power plant and is creep damaged, various parameters are obtained from the actual machine member to be evaluated (ST4). Here, in the creep remaining life evaluation method of the example, in order to evaluate the creep remaining life of the actual machine member with higher accuracy, each evaluation result based on the aforementioned L parameter and M parameter, and the estimation result by the conventional remaining life evaluation method And compare. For example, a void number density method can be employed as a conventional remaining life evaluation method.

  The specific method for obtaining various parameters from actual machine members is to determine the most severe conditions by comprehensively considering the past remaining life diagnosis history, structure, stress, temperature, load, etc. Pick a spot below and take a replica from the surface of that spot. When the member surface copied on the replica is enlarged and displayed by SEM, various parameters in a predetermined range can be obtained.

  The method for obtaining the L parameter and the M parameter is as described in ST1 of the main flowchart. Hereinafter, a method for obtaining the void number density which is a parameter of the void number density method will be described.

FIG. 12 shows the basic concept of void number density, which is a parameter of the void number density method. The void number density is a ratio of the number of all the voids 20 existing in a predetermined area (for example, 1 mm ² ), and is specifically defined by the following equation.

  Specifically, when there are six voids 20 within a certain range shown in the figure, the number of all these voids is counted regardless of the size of each void 20. This operation is performed within a predetermined range, and the void number density is obtained by dividing by this area.

Also, when obtaining the void number density, as described in ST1, a predetermined range (for example, 30 mm ² ) is observed in advance with an optical microscope or the like, and a location where damage is most advanced is selected. It is better to observe with SEM.

  FIG. 13 is a master curve of the void number density method. This master curve can be created by itself by various creep tests described in ST1 of the main flowchart (FIG. 1), and the master curve by the void number density method and other conventional remaining life evaluation methods has been made public. It is also possible to use this.

  Returning to the main flowchart (ST1) again, various parameters obtained from the actual machine members are collated with the master curves (FIGS. 10, 11, and 13) corresponding to the respective parameters (ST5), and until the actual machine members are creep-destructed. Time is estimated (ST6).

Specifically, for example, if the L parameter obtained from the replica of the actual machine member is “67 pieces / mm ² ”, the creep life consumption rate is “t / tr” by comparing this with the master curve (FIG. 10). ≒ 0.94 "can be estimated. That is, according to this master curve, the remaining life of the member can be estimated to be 6% of the total life.

  The time corresponding to “6% of the total lifetime” can be obtained by the following formula, assuming that the actual use time of the actual machine member to be evaluated is “t≈7000 hr”.

  If the M parameter obtained from the replica of the actual machine member is “0.87”, the creep life consumption rate can be estimated as “t / tr≈0.97” by comparing this with the master curve (FIG. 11). . That is, according to this master curve, the remaining life of the member is a time corresponding to 3% of the total life, and can be obtained by the following equation.

Furthermore, if the void number density obtained from the replica of the actual machine member is “650 / mm ² ”, the creep life consumption rate is “t / tr≈0.92” by comparing this with the master curve (FIG. 13). Can be estimated. Therefore, according to the master curve of the void number density method, the remaining life of the member is a time corresponding to 8% of the total life, and can be obtained by the following equation.

Finally, the shortest time obtained as the remaining life estimation result by each method is estimated as the time until the actual machine member to be evaluated reaches the creep failure (ST7). That is,
(1) The remaining life calculated based on the L parameter is “447hr”
(2) The remaining life calculated based on the M parameter is "216hr"
(3) Remaining life by void number density method is “609hr”
Therefore, the remaining life of the member can be estimated to be “216 hr” obtained based on the M parameter.

  As described above, according to the creep remaining life evaluation method of the present invention, the L parameter method suitable for the remaining life evaluation of the fine grain part and the M parameter method (M parameter method) suitable for the remaining life evaluation of the grand grain part. Can be used to evaluate the remaining creep life at any location of the actual machine member, regardless of whether the evaluation target site in the actual machine member is a fine-grained portion or a coarse-grained portion. Furthermore, the remaining life evaluation with higher reliability can be performed by comparing with the estimation result by the conventional remaining life evaluation method such as the void number density method.

  The method for evaluating the remaining life of the actual machine member by the creep remaining life evaluation method of the embodiment has been described above, but the reliability of the L parameter in the creep life evaluating method of the present invention will be mentioned. The reliability of the creep life evaluation refers to how close the evaluation result (remaining life or creep life consumption rate) by the adopted parameters is to the result of the creep test. Therefore, not all parameters that can be considered can be used as they are in the remaining life evaluation of actual machine members, and it is necessary to confirm in advance the reliability of the parameters to be employed in the remaining life evaluation. Hereinafter, an example of the accuracy confirmation test result for confirming the reliability of the L parameter is shown.

  (1) For the real scale high temperature reheat steam pipe simulated fracture test (creep test using a 15mm square x L50mm specimen), the rupture time is 147hr, and the creep life consumption rate obtained from the creep test is "t /Tr=0.93 ". On the other hand, the creep life consumption rate as a result of applying the L parameter to the surface of the fine grain part of the specimen was also “t / tr = 0.93”.

  (2) With regard to the actual machine waste material creep test (creep test using φ20mm × L50mm specimen), the rupture time is 85hr, and the creep life consumption rate obtained from the creep test is “t / tr = 0.96” there were. On the other hand, the creep life consumption rate as a result of applying the L parameter on the surface of the fine grain part of the specimen at this time was “t / tr = 0.98”.

  In this way, the creep test result and the result by the L parameter (creep life consumption rate) are almost the same (an error of about 1%), confirming that the reliability of the L parameter is very high. can do.

  Further, in the embodiment, the connection void formed by combining the voids generated on the plurality of crystal grain boundaries with the extended voids existing over at least half of each length of the two crystal grain boundaries. However, if it is possible to clearly distinguish between expanded voids that grow and grow from one void and those that combine multiple voids, those that are connected and those that are not And may be counted separately.

  In the example, when calculating the time as the remaining creep life, a master curve is created by a computer based on data representing the relationship between each parameter obtained from various creep tests of ST1 and the creep life consumption rate. By doing so, it is possible to immediately obtain the creep life consumption rate and the remaining life based on the above-described calculation formulas only by inputting various parameters obtained from actual machine members.

  As described above, the method of evaluating the remaining life of the actual machine member by the creep remaining life evaluation method of the embodiment has been described, but the present invention is not limited to this. For example, in the embodiment, the estimation result by the conventional void number density method is also compared. Although it was set as a target, estimation results by an evaluation method based on other parameters can be set as comparison targets. As other methods, for example, an A parameter method, a tissue contrast method, a void area ratio method, or a void area density method can be employed.

  Further, in the examples, each master curve representing the relationship between the L parameter or the M parameter and the creep life consumption rate was adopted as the remaining life evaluation standard of the actual machine member, but a database representing the relationship between the two was created, The remaining life can also be evaluated by comparing this with various parameters obtained from actual machine members. In any of the methods, the remaining life can be automatically calculated by inputting the L parameter obtained from the actual machine member using a computer.

Further, in the embodiment, when obtaining the L parameter from the actual machine member, a replica of the member surface is collected, and the replica is enlarged by SEM or the like and the void is visually observed. After imaging, it is also possible to automatically recognize the connected voids by a machine such as a computer and quickly and easily obtain the number of them on the image.

Claims (8)

In the method for evaluating the time until the creep failure of the equipment member subjected to creep damage or the remaining life represented by the creep life consumption rate,
On the surface of the device member, the number of specific voids existing across a plurality of grain boundaries within a predetermined range is obtained, and the ratio of the number of specific voids to the area of the predetermined range is defined as the specific void density,
On the surface of the device member, a ratio of the total length of all voids on the grain boundary to the length of one grain boundary within a predetermined range is determined for each grain boundary as a void grain boundary occupation ratio, Let the maximum value be the maximum void grain boundary occupancy,
Creep characterized by evaluating the remaining life of the device member based on the specific void density and the maximum void grain boundary occupancy, respectively, the result of which one of the shorter evaluation is the remaining life of the device member Remaining life evaluation method.   The creep remaining life evaluation method according to claim 1, wherein the specific void is an extended void existing over at least half of each length of at least two grain boundaries. Method.   The creep remaining life evaluation method according to claim 1 or 2, wherein the specific void is a connected void formed by combining voids generated on a plurality of crystal grain boundaries. The creep remaining life evaluation method according to any one of claims 1 to 3, wherein the maximum void grain boundary occupancy is obtained by the following equation.

Where m is the number of grain boundaries where voids exist,
n is the number of voids present on each grain boundary,
l _αi is the grain boundary length of the i th void existing on the α th grain boundary,
L _α is the length of the α-th grain boundary where a void exists.   5. The creep remaining life evaluation method according to claim 1, wherein the remaining life is evaluated with respect to a relationship between the specific void density and the remaining life and a relationship between the maximum void boundary occupancy and the remaining life. A creep remaining life evaluation method which is to estimate the time by referring to each evaluation standard obtained from a creep test.   6. The creep remaining life evaluation method according to claim 5, wherein the remaining life is evaluated within the range with respect to the area of the predetermined range in addition to the evaluation criteria for the specific void density and the maximum void grain boundary occupancy. Creep remaining life evaluation, which is to refer to evaluation criteria for void number density and other parameters, which is the ratio of the number of all voids, and to set the shortest time estimated by the evaluation criteria for each parameter as the remaining life. Method.   The creep remaining life evaluation method according to any one of claims 1 to 6, wherein a surface of the device member is imaged, and the number of the specific voids and the void grain boundary occupation ratio are obtained on the image. Remaining life evaluation method. 8. The creep remaining life evaluation method according to claim 7, wherein the image of the surface of the device member is obtained by polishing the surface of the device member and then corroding the surface of the device member, and then copying the surface by applying a predetermined film. A creep remaining life evaluation method characterized by being obtained by imaging the surface of the equipment member using means.

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