WO2005124315A1

WO2005124315A1 - Method of comprehensively evaluating creep life expectancy or life span

Info

Publication number: WO2005124315A1
Application number: PCT/JP2005/011268
Authority: WO
Inventors: Hidetaka Nishida
Original assignee: The Chugoku Electric Power Co., Inc.
Priority date: 2004-06-21
Filing date: 2005-06-20
Publication date: 2005-12-29
Also published as: JPWO2005124315A1; JP4054834B2

Abstract

A method of accurately evaluating the life expectancy or the life span of a creep-damaged device member irrespective of whether the grained part is fine grained or coarse grained. The life expectancy or the life span is represented by the time until the creep-damaged device member creep-ruptures. The number of linked voids present over a half or more of each length of two or more grain boundaries in areas of up to 1 mm2 of the surface of the device member is determined. The ratio of the number of the specific linked voids to the area of 1 mm2 is used as L parameter. As the void grain boundary occupancy ratio, the ratio of the total of the lengths of all the voids present at the grain boundaries in the surface of the device member to the length of one grain boundary within the area of 1 mm2 is determined for each grain boundary, and the maximum value is used as M parameter The life expectancies or life spans of the device member based on the L and M parameters are evaluated, and the shorter one is determined as the life expectancy or life span of the device member.

Description

Comprehensive evaluation method of remaining life of tallies

Technical field

TECHNICAL FIELD [0001] The present invention relates to a technology for evaluating a remaining life of a device member subjected to creep damage.

[0002] 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 welded parts (welded metal parts, welding heat affected parts). And the base material), the deterioration due to creep damage progresses over time, and minute voids or voids called voids or cavities (collectively referred to as “voids”) are generated in the metal structure. The voids grow, connect, coalesce, and eventually form microcracks of the length of 1 (crystal) grain boundary, and the microcracks further repeat propagation and connection, resulting in the entire member. To destruction (creep destruction). Therefore, in order to operate the thermal power generation unit stably for a long period of time, the time required for the equipment members to undergo creep rupture or the remaining life represented by the “creep life consumption rate” described below must be accurately determined. It is necessary to understand.

[0003] According to Non-Patent Document 1 below, at present, more than 80% of commercial thermal power generation units in Japan have accumulated operation hours exceeding 100,000 hours, and the remaining 20% The situation is over 200,000 hours. For this reason, at the time of periodic inspection, for the boiler of the thermal power generation unit, the location under the harshest conditions is selected from the past life-span diagnosis history, structure, stress, temperature, weighting, etc., and the creep deterioration progresses. It is important to understand the situation accurately and repair appropriately.

In Non-Patent Document 2 below, as a conventional method for evaluating the remaining creep life, which focuses on voids generated in actual machine members, the surfaces of the members are polished and corroded, and a film made of acetyl cellulose is attached. An evaluation method using a copy of the surface of the member (hereinafter referred to as “replica”) is described. Methods for evaluating the remaining life or creep damage using this replica include A-meter, microstructure comparison, void area ratio (Non-Patent Document 3), void area density, grain boundary damage (non- An evaluation method using various parameters such as Patent Document 4) is known.

[0005] In these methods, a parameter indicating the state of creep deterioration of a real machine member is obtained, and the "creep life consumption rate" is expressed as a ratio of the actual use time to the total time (life) from the time of new material to creep rupture. To estimate the remaining life of the members of the actual machine. Specifically, in any of the above methods, first, a creep test is performed to create a master curve representing the relationship between the parameters of each method and the creep life consumption rate. Then, a replica of the surface force of the target actual machine member is sampled, and the parameter obtained on the replica is compared with the master curve, whereby the creep life consumption rate of the actual machine member can be estimated. Further, the time indicating the remaining life of the actual machine member can be estimated 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. Specifically, assuming that the creep life consumption rate at the time of evaluation is "A" and the actual usage time is "B", the remaining life t is obtained by the formula "t = BX {(1—A) ZA}". be able to.

[0006] In addition, Non-Patent Document 5 below describes a method for estimating the remaining creep life by a non-destructive inspection such as an ultrasonic noise energy method or an ultrasonic statroscopy method. Non-Patent Documents 6 and 7 below describe the physical meaning of the “void occupancy on the grain boundary line” (Non-Patent Document 8) used as an index focusing on voids at grain boundaries as a creep damage parameter. It is stated that it is clear.

[0007] Among the above evaluation methods, the "A-parameter method" draws a straight line parallel to the stress axis within a predetermined region, and determines the number of intersections between the straight line and the grain boundary line. The ratio is a parameter, and is generally called the "A parameter for measurement". However, the A parameter is based on the idea that if at least one void exists at the grain boundary, the grain interface is considered to be severely damaged and the entire grain boundary is regarded as a small crack. However, the physical meaning of the commonly used measurement A parameter is considered to be sparse.

[0008] The "void area ratio method" uses the ratio of the void area per unit area in a predetermined region as a parameter, and the "void area density method" uses the unit area (usually lmm ² ). This evaluation method uses the number of voids per hit as a parameter. Since this void area density method only needs to find the number of voids, measurement is easy. 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 that it does not directly represent the number of voids actually existing inside.

[0009] "Void occupancy on grain boundary line method" is a method for each grain boundary line within a predetermined range appearing on a cut surface or a surface of a member, for each void on the grain boundary line with respect to the length of the grain boundary line. This is an evaluation method that calculates the ratio of the total length and uses the average value as a parameter. This parameter has a one-to-one correspondence with the effective area used in conventional damage mechanics, which is equivalent to the area ratio of voids at the grain interface, which is the path of creep rupture. There is a problem that the force is difficult to measure compared to other methods.

[0010] Patent Document 1 below describes a creep (remaining) life evaluation method capable of easily and accurately estimating the "creep life consumption rate" of a creep-degraded device member. In this method, the ratio of the total length of voids on a grain boundary to the length of one grain boundary of a member is determined for each grain boundary, and the maximum value is determined as a parameter (“M parameter” t). This method is referred to as the “M-parameter method”. According to the M-parameter method, it is possible to obtain an evaluation that the creep life consumption rate is high and the remaining life is short, that is, the risk of creep fracture is high, as the M-parameter force is closer to 1 ".

Patent Document 1: International Publication WO02Z014835

Non-patent Document 1: Keiichi Iwamoto, Thermal and Nuclear Power, 48-8 (1997), 14

Non-Patent Document 2: Japan Iron and Steel Association, Creep and Creep-Fatigue Damage Manual by Replica Method "Structural Material Reliability Evaluation Technology Subcommittee High-Temperature Strength WG Research Results Report (separate volume manual), (1991), 1

Non-Patent Document 3: Isamu Nonaka, Keiji Sonoya, Masashi Nakashiro, Hiroshi Yoneyama, Masaaki Kitagawa, Harima Ishikawajima Harima Technical Report, 32-5 (1992), 313

Non-patent Document 4: Kenji Kikuchi, Yoshiyuki Kaji, Materials, 44-505 (1995), 1244

Non-Patent Document 5: Japan Society of Mechanical Engineers, Power Plant 'Remaining Life Evaluation Technology for Structures, (1992)

, 89, Gihodo Publishing

Non-Patent Document 6: Naoya Tada, Tetsushi Fukuda, Takayuki Kitamura, Ryuichi Otani, Materials 46-1, (1997), 39

Non-patent document 7: Naoya Tada, Takayuki Kitamura, Ryuichi Otani, Materials 45-1, 1, (1996), 110 Non-patent document 8: Tsuneyuki Ejima, Zhou, Ryuichi Otani, Takayuki Kitamura, Naoya Tada, The 32nd high temperature strength system Preprints of Non-Podium, (1994), 94

Disclosure of the invention

[0012] In the above-mentioned device members, the metal structures of the weld metal portion and the heat affected zone of the weld, in particular, have a particle size of about 100 micrometers (m) in order from the weld metal side (200 μm). m) and a fine-grained part consisting of crystals with a grain size of about 1 μm to 10 μm. Considering that recent experiments have shown that the grain grows to almost the same size as one crystal grain boundary in the above, when the `` fine grain part '' is evaluated by the above M-parameter method, the creep life There is a possibility that the M-parameter force reaches 1 "in the early stage, that is, the risk of creep rupture is high.

[0013] As described above, creep rupture is mainly attributable to the fact that voids generated on grain boundaries grow, connect, and coalesce to form microcracks. In particular, considering that intensive cracks occur in the second half of the creep life, even if one void has the same size as one grain boundary in the fine grain part, there is a high risk of creep rupture immediately. Therefore, it is difficult for the M-parameter method to accurately evaluate the creep life of “fine-grained parts”.

[0014] On the other hand, according to the results of various creep tests, the portions that lead to creep rupture in the coarse-grained portion and the fine-grained portion are determined by various conditions such as differences in welding methods such as longitudinal welding or girth welding and the degree of application of stress. It is important to accurately evaluate the creep life of fine-grained parts in view of the fact that they differ from each other and that the actual parts are subjected to various types of welding and are placed in a multiaxial stress field.

[0015] In the case of evaluating a fine grain portion, for example, in the conventional A-parameter method, the damaged grain boundary to be measured is unclear and the number of grain boundaries becomes extremely large. Therefore, it is practically difficult to evaluate fine-grained parts.

The present invention has been made in view of the above circumstances, and provides a method capable of accurately evaluating the remaining life of a device member subjected to creep damage irrespective of a fine grain portion and a coarse grain portion. The purpose is.

[0017] The present invention relates to a time or a time until a creep-damaged device member undergoes creep rupture. In a method for evaluating the remaining life represented by the creep life consumption rate, the number of specific voids existing over a plurality of crystal grain boundaries within a predetermined range on the surface of the above-mentioned component is determined. The ratio of the number of the specific voids to the area of the predetermined range is defined as a specific void density, and the length of one crystal grain boundary within the predetermined range on the surface of the device member is defined by the total voids on the grain boundaries. The ratio of the total length is determined as void grain boundary occupancy for each crystal grain boundary, and the maximum value is defined as the maximum void grain boundary occupancy, based on the specific void density and the maximum void grain boundary occupancy! / Evaluate the remaining life of each of the device members, and use the result of the shorter evaluation of V ヽ as the remaining life of the device members.

[0018] In the embodiment of the invention, the specific void is an extended void existing over at least 1/2 of each length of at least two grain boundaries, or generated on a plurality of grain boundaries. It is a connecting void formed by merging the voids.

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

[0020] [Equation 1] Maximum void grain boundary occupancy (MP) =

Here, m is the number of grain boundaries where voids exist, n is the number of voids present on each grain boundary, 1

α ι is the length of the i-th void on the α-th grain boundary in the direction of the grain boundary, and L is the length of the α-th grain boundary where the void exists.

[0022] Further, the evaluation of the remaining life is based on the evaluation criteria obtained from the creep test on the relationship between the specific void density and the remaining life and on the relationship between the maximum void grain boundary occupancy and the remaining life. Estimating said time by reference. Alternatively, the evaluation of the remaining life is the ratio of the number of all voids within the predetermined range to the area of the predetermined range in addition to the above evaluation criteria for the specific void density and the maximum void grain boundary occupancy. With reference to the evaluation criteria for the void number density and other parameters, the shortest time estimated by the evaluation criteria for each parameter is defined as the remaining life.

[0023] A more specific embodiment is directed to a void present on the surface of a fine grain portion formed of a crystal having a grain size of 10 µm or less of an equipment member. 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 device member is polished and corroded, and then a film made of acetyl cellulose or the like is attached to the device member. In addition, it is possible to image the surface of the device member.

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 an equipment member is determined, and is represented by the ratio of the number of specific voids to the area of the range. By determining the specific void density, the remaining life of equipment components that have undergone creep damage can be evaluated. In this evaluation method, it is necessary to detect only a specific void among all voids within a predetermined range, and therefore, the evaluation can be performed more quickly and easily than the conventional void number density method. In addition, the specific void existing over a plurality of crystal grain boundaries is a void that has grown from one grain boundary to two or more grain boundaries. It is an index that indicates the degree of progress of creep deterioration. Therefore, by using the above-mentioned parameter of “specific void density”, the state of creep deterioration, specifically, the remaining life can be accurately grasped, and even in the “fine grain part” where the crystal grain boundary is small, two or more By paying attention to voids extending across the grain boundaries, it is possible to accurately evaluate the remaining life of fine-grained parts, which is difficult with conventional evaluation methods such as the A-parameter method.

[0026] According to a specific mode, as the specific void, an extended void existing over at least 1/2 of each length of at least two crystal grain boundaries, or a void generated on a plurality of crystal grain boundaries. By detecting the connection voids formed by merging, the degree of progress of creep deterioration can be grasped more accurately.

As a specific method for evaluating the remaining life, an evaluation criterion (for example, a master curve described later) obtained by a creep test based on the relationship between the specific void density and the remaining life as described above is used. By referring or collating, it is possible to estimate the time (or tallip life consumption rate) until the equipment member undergoes creep rupture.

[0028] Further, in addition to the evaluation criterion for the "specific void density", the evaluation criterion for the "void number density" and other parameters is also referred to, and the time estimated by the evaluation criterion of each parameter is referred to. By setting the shortest of these as the remaining life of the equipment members, it is possible to make evaluations from a safer side. These evaluation criteria include parameters and creep life as described below. A master curve indicating the relationship with the consumption rate, a function or data indicating the relationship between the two, and the like can be used.

Further, according to the present invention, as described above, the surface of the fine-grain portion formed of a crystal having a grain size of 10 μm or less is selected as a portion for determining the number of voids within a predetermined range. Can be.

Further, when implementing the method of the present invention, as a means for measuring the voids present on the surface of the equipment member, if the surface of the equipment member is imaged, the specific void is automatically recognized by a machine such as a computer, and the image is obtained. Above, their number can be determined quickly and easily. In this case, the image of the surface of the device member may be obtained by polishing and corroding the surface of the device member and then attaching a film made of acetyl cellulose or the like, or photographing the surface of the device member using imaging means. Obtained by imaging the surface of.

Brief Description of Drawings

FIG. 1 is a main flowchart of a creep remaining life evaluation method of an embodiment.

FIG. 2 is a diagram showing a specimen and a void observation position used in a creep test.

FIG. 3 is a diagram showing a specimen and a void observation position used in a creep test.

FIG. 4 is a diagram showing a specimen and a void observation position used in a creep test.

FIG. 5 is a diagram showing a position where a test piece is collected from actual waste wood of a thermal power plant.

FIG. 6 is an electron micrograph showing the occurrence of voids at each interruption in the creep rupture test for pipe internal pressure.

FIG. 7 is a diagram showing a state of void generation at an observation position at each interruption during an internal pressure creep rupture test (actual machine acceleration test).

FIG. 8 is a view showing a basic concept of an L parameter.

FIG. 9 is a diagram showing a basic concept of M parameters.

[Figure 10] Master curve showing the relationship between L parameter and creep life consumption rate.

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

FIG. 12 is a diagram showing a basic concept of a void number density which is a parameter of the void number density method.

[Figure 13] Master curve of void number density method.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 is a main flowchart of the remaining creep life evaluation method of the present invention.

[0033] In the embodiment, the remaining life of a member that is used under high temperature and high pressure in a boiler of a power plant and undergoes creep damage and evaluates the time until creep fracture or the creep life consumption rate is evaluated. I will explain how to do it.

[0034] In this creep remaining life evaluation method, predetermined parameters based on minute holes called voids existing on the surface of the actual machine member are obtained, and the obtained parameters are evaluated based on an evaluation criterion representing the relationship between parameters created in advance and remaining life. To evaluate the remaining life of the member. Therefore, in order to create the above evaluation criteria, a creep test is performed using various test specimens, and a void linking density parameter (hereinafter referred to as an L parameter) is used as the above parameter while appropriately stopping the test. And the maximum void fraction on the grain boundary line parameter [hereinafter referred to as M-noise meter] is determined (step [hereinafter referred to as ST] 1).

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

[0036] The test piece shown in Fig. 2 is a test piece 1 taken from a welded part that has been subjected to creep damage by a high-temperature reheated steam pipe in operation, and the test piece 1 is used while appropriately stopping the test piece. Conduct a creep rupture test. The test conditions are shown below.

[0037] (1) The test temperature was 883.15K

(2) The test stress (tensile) is 68.6MPa.

[0038] As shown in the figure, the metallographic structure near the welded portion 2 of the test piece 1 includes, from the weld metal side, a coarse-grained portion 3 formed of crystals having a grain size of about 100 µm or less, It is composed of fine-grained parts 4 formed of crystals of about μm to 10 μm. In the creep remaining life evaluation method of the embodiment, the M parameter is obtained based on the void observation result in the coarse-grained part 3, and the L parameter is obtained based on the void observation result in the fine-grained part 4.

[0039] For example, the test specimen shown in Fig. 3 is a test in which girth welding is performed on a solid round bar (φ40Xt8XL430) made of 2.25Cr-lMo steel, and the pipe force of the weld joint penetrating the center is also obtained. Piece 5 The girth weld 6 of the test piece 5 is preferably prepared by 1 to 4 layers of covered arc welding so as to be as close as possible to the weld of the actual machine member, and is preferably heat-treated at 993KX for 1.3 hours. 5 specimens In addition, an internal pressure creep rupture test is performed. Specifically, while heating the test piece 5 in an electric furnace, pressurized water is injected into the test piece 5, and high pressure steam is applied to apply internal pressure. In this test as well, interruption is performed appropriately, voids in the coarse-grained part and fine-grained part are observed at each interruption, and each parameter is obtained by the method described later. The test conditions are shown below.

[0040] (1) The test temperature was 903K

(2) Circumferential stress is 61.3MPa (according to the formula of average diameter).

[0041] The specimen 7 in Fig. 4 is, for example, a waste material of a high-temperature reheated steam pipe elbow made of 2.25Cr-lMo steel, and a welded portion 8 of the specimen 7 has a pair of bent pieces having the same curvature. After assembling the plates into a tube, they are formed by submerged arc welding performed in the longitudinal direction. For this specimen 7, an internal pressure creep rupture test (acceleration test on actual equipment) is performed with appropriate interruption. Specifically, after heating the specimen 7 by surrounding it with a plate-shaped heater, water under pressure is injected into the specimen 7, and high-pressure steam is applied to apply internal pressure. In this test, for example, at two observation positions 9a and 9b defined on the surface in the vicinity of the welded portion 8, voids in the coarse-grained portion and the fine-grained portion at each interruption are observed, and each parameter is obtained. The test conditions are shown below.

[0042] (1) The test temperature was 923K

(2) Test stress is 3.0MPa

(3) The maximum principal stress at the center of the elbow abdomen is 39.2MPa

(4) Approximately 1475 hours of actual use time until disposal of specimen 7

FIG. 5 shows a position where a test piece was taken from a waste material of an actual thermal power plant to perform another creep test. In the T piece pipe near the SH pipe in (a) and the RHY piece pipe in (b), voids were observed on the surfaces near the circumferential welds 10 and 11, and the diameter was 10 mm from the cross section near the part where the presence of voids was recognized. Collect a round bar specimen with a gauge length of 50 mm with. In the RH stub-side stub of (c), a 2mm diameter miniature creep round bar specimen is taken from the cross section near the stub welded part 12 where the presence of voids has been recognized. For these test pieces, a uniaxial creep rupture test was performed in an inert gas atmosphere while appropriately stopping them. Parameter Ask for data. The usage conditions for each waste material are shown in the table below.

[Table 1]

[0045] Fig. 6 shows the state of void generation at each interruption in the pipe internal pressure creep rupture test using test piece 5 (Fig. 3). In the void observation, for example, the surface of the test piece 5 may be directly imaged using a scanning electron microscope (hereinafter, “SEM” t) as shown in the figure, and the surface of the test piece 5 may be It can also be polished and corroded, and a replica obtained by attaching a predetermined film (for example, an acetyl cellulose film) and copying the surface of the member can be observed with a SEM.

In replica sampling, the surface of the test piece 5 is polished by, for example, rough polishing with a grinder, successively polishing with a grindstone of No. 120-No. It is better to sequentially perform puff polishing with diamond particles and perform mirror finishing.

[0047] Further, in order to corrode the surface of the test piece 5, for example, after polishing the surface as described above, the corrosive liquid is impregnated into absorbent cotton and applied to the polished surface to form a bond in the metal structure. Grain boundaries can be made identifiable. The following two types of corrosive liquids can be used for corrosion.

[0048] (1) Picric acid: Saturated picric acid (dissolved in methanol) + surfactant

(2) Nitric acid (5 ml) + methanol (95 ml).

[0049] As the above surfactant, for example, sodium dodecylbenzenesulfonate is preferably used and mixed at a ratio of 1 g to 100 ml of saturated picric acid.

[0050] Then, 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 and an acetyl cellulose film is stuck thereon, so that the replica softening material is sufficient. If the acetyl cellulose film is peeled off after drying, the surface of the test piece 5 can be copied. As a result, voids generated on the surface of the test piece 5 appear as protrusions on the replica.

In void observation, a predetermined range (for example, 30 mm ² Observing the void generation status in (), confirming the location where damage is most aggressive (voids are generated and connection is concentrated), and then observing that location by SEM (e.g., observation at 1000x) ), It is possible to perform a void observation without missing a spot where damage has progressed.

Referring back to FIG. 6, it can be seen that the number of voids increases on the surface of the test piece 5 with the elapse of time in the pipe internal pressure creep rupture test. For example, as shown in the figure, the state of void generation at each stop

(1) When the creep life consumption rate (tZtr) = 0.49, a void of about 1 μm is generated,

(2) At tZtr = 0.73, multiple voids occur at the same grain boundary,

(3) At t / tr = 0.97, void connection is observed,

(4) At tZtr = 1.0, microcracks were formed!

[0053] Here, the above interruptions are represented by the creep life consumption rate (tZtr), which is obtained as a result of a pipe internal pressure creep rupture test until the test piece 5 reaches creep rupture. Value.

[0054] Thus, it can be seen that voids are initially generated randomly on a plurality of grain boundaries, and then concentrated at specific positions, and eventually connect to form microscopic cracks. .

FIG. 7 shows the state of void formation at observation positions 9a and 9b at the time of each interruption in the internal pressure creep rupture test (actual machine acceleration test) using specimen 7 (FIG. 4). In this test as well, voids began to form randomly on multiple grain boundaries, then increased intensively at specific locations, and eventually joined to form microcracks. You.

FIG. 8 shows the 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.

[0057] The L parameter is represented by a ratio of the number of voids present over a plurality of crystal grain boundaries within a predetermined range on the surface of the void observation position to a predetermined range. First, a void (hereinafter, referred to as “half the length of at least two crystal grain boundaries” within a predetermined range (for example, 1 mm ² ) on the surface of the observation position is used. Find the number of connected voids “t”.

[0058] For example, as shown in the figure, when there are three voids 16a, 16b, and 16c on a grain boundary 15 in a certain range, the uppermost void 16a exists only on one grain boundary. Also Therefore, it is not counted as a connection void and can be ignored.

Next, the center void 16b exists on the three grain boundaries 15 and the two voids 1b

Since it completely covers 5, this is counted as a connecting void.

[0060] The voids 16c are present on the three grain boundaries 15 and do not completely cover the grain boundaries 15. However, the voids 16c are more than 1/2 of each length of the two grain boundaries 15. Because it exists throughout

, This is also counted as a connected void.

[0061] By the above method, at the time of stopping each creep test, the number of connected voids within a predetermined range (for example, 1 mm ² ) on the surface of the observation position is determined, and this number is used as an evaluation target. Find the L parameter expressed as the value divided by the area of the range (for example, 1 mm ² ). Therefore, the L parameter is defined by the following equation.

[0062] [Equation 2]

L parameter = m / A

A is the area of the evaluation range (for example, 1 mm ² )

m is the number of connected voids within the evaluation target range

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

[0064] The M parameter is a ratio of the total length of all voids on the grain boundary to the length of one crystal grain boundary within a predetermined range (for example, lmm ² ) on the surface of the void observation position. It is obtained for each grain boundary as the field occupancy, and is expressed by the maximum value. That is, the M parameter can be obtained by the following equation.

[Equation 3] Maximum void grain boundary occupancy-

(ΜParameter) ―

Here, m is the number of grain boundaries where voids exist,

n is the number of voids present on each grain boundary,

1 is the length of the i-th void on the α-th grain boundary in the direction of the grain boundary,

α ι

L is the length of the α-th grain boundary where the void exists

It is. Therefore, as shown in the figure, if there are two voids 18 on a certain grain boundary 17 and the length force SI, 1 of each void 18 in the direction of the grain boundary, and the length of the grain boundary is L, , Void grain boundary occupation at this grain boundary

1 2

The percentage can be obtained by the following equation.

[Equation 4] void grain boundary occupancy = _τ " ²

As described above, by obtaining the void grain boundary occupancy for each grain boundary within a predetermined range, the maximum value can be obtained as the Μ parameter.

[0070] Returning again to the main flowchart (Fig. 1), after completing the various creep tests described above, based on the L parameter obtained at the time of each suspension, each master curve was created as an evaluation standard of the remaining creep life. (ST2, ST3).

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

[0072] The creep life consumption rate is represented by the ratio of the total time "t" to the total time "tr" to the time to the creep rupture of the new material and the total time "t" of the time subjected to the creep test and the actual use time. . Therefore

On the other hand, when the specimen strength S creep rupture is reached, "t / tr = l". The smaller the value, the closer to the state of the new material, that is, the longer the remaining life, it can be evaluated.

According to this master curve, the L parameter is substantially “0” in the first half of the life of the device member, and increases in the second half of the life. Thus, the master curve based on this L parameter is

(1) Creep rupture is mainly due to the fact that voids generated on grain boundaries grow, coalesce and join to form micro cracks.

(2) Microscopic cracks occur intensively, especially in the second half of creep life,

(3) Connected voids exist over at least 1/2 of each length of at least two grain boundaries, that is, are formed by connecting a plurality of voids.

It reflects well and helps you.

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

[0075] According to this master curve, the M parameter increases in a smooth downwardly convex curve over the entire creep life, and the L-parameter master curve (Fig. 10) and other conventional master curves Sudden increase in late life (e.g., Figure 13) It is not allowed. In addition, since the M parameter evaluates the creep life by focusing only on the localized damaged part, that is, only the maximum damaged part, it can be seen that the M parameter shows a certain value even at the beginning of the life. Based on the above, the master curve based on this M parameter shows that the growth and connection of voids proceed intensively on a specific grain boundary on the crystal grain boundary in the weld heat affected zone coarse grain region, and the crack It can be seen that this directly reflects the mechanism of cleaved fracture, which leads to growth and destruction.

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 also obtained for the actual machine member to be evaluated (ST4). Here, in the method for evaluating the remaining creep life of the embodiment, in order to more accurately evaluate the remaining creep life of the actual machine member, the evaluation results based on the above-described L parameter and M parameter and the estimation based on the conventional remaining life evaluation method are used. Compare the result. For example, a void number density method can be adopted as a conventional remaining life evaluation method.

[0077] The actual method of obtaining the various member parameters is as follows. Among the welded parts of the member, a comprehensive consideration is given to the conditions of the past remaining life diagnosis history, structure, stress, temperature, load, etc. Select a location under severe conditions and collect a surface force replica of the location. By enlarging and displaying the surface of the member copied on this replica 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 of 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 the 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 range to the area (for example, 1 mm ² ) of the range, and is specifically defined by the following equation.

[0080] [Equation 5]

Void number density = nZA

A is the area of the evaluation enclosure (for example, 1 mm ² )

n is the number of all poids within the evaluation range

[0081] Specifically, when there are six voids 20 in a certain range shown in the figure, Count the number of all these voids, regardless of the size of each void 20. This operation is performed within a predetermined range, and divided by the area of the range to obtain a void number density.

[0082] Further, even when obtaining the void number density, as described in ST1, previously prescribed range by an optical microscope or the like (e.g., 30 mm ²⁾ were observed to select the location where the most progress of damage, It is advisable to magnify and observe the location with SEM.

FIG. 13 is a master curve of the void number density method. This master curve can be created by the various creep tests described in ST1 of the main flowchart (Fig. 1), and the master curve based on the void number density method and other conventional methods for evaluating the remaining life is publicly available. It is also possible to use this.

Returning to the main flowchart (ST1) again, the various parameters obtained from the actual machine parts are compared with the master curves (FIGS. 10, 11, and 13) corresponding to the respective meters (ST5), and the actual machine parts are compared. Estimate the time until creep rupture (ST6).

[0085] Specifically, for example, actual L parameters obtained from replica members "67 pieces / mm ^2" and Then, by comparing this with the master curve (FIG. 10), the creep life consumption rate " t

Ztr 0.94 ". That is, according to this master curve, the remaining life of the member can be estimated to be 6% of the total life.

[0086] The time corresponding to "6% of the total life" can be obtained by the following equation, assuming that the actual use time of the actual machine member to be evaluated at the time of the evaluation is "t ^ 7000hr".

[0087] [Equation 6]

7 0 0 0 X (0.06 / 0.94) = 4 4 7 (hr)

[0088] Further, assuming that the M parameter obtained from the replica of the actual machine member is "0.87", by comparing this with the master curve (Fig. 11), the creep life consumption rate can be estimated to be "tZtr ^ 0.97". it can. That is, according to the 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.

[0089] [Equation 7]

7 0 0 0 X (0.03 / 0.97) = 2 16 (hr)

Further, assuming that the void number density determined from the replica of the actual machine member is “650 / mm ² ”, Is compared with the master curve (Fig. 13), the creep life consumption rate can be estimated as "tZtr ^ 0.92". 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.

[0091] [Number 8]

7 0 0 0 X (0.08 / 0.92) = 6 0 9 h r

[0092] Finally, the shortest time obtained as a result of the remaining life estimation by each method is estimated as the time until the actual machine member to be evaluated reaches creep rupture (ST7). That is,

(1) The remaining life calculated based on the L parameter is "447hr",

(2) The remaining life obtained based on the M parameter is "216 hours",

(3) The remaining life by the void number density method is "609hr"

Therefore, the remaining life of the member can be estimated to be “216 hours” obtained based on the M parameter.

[0093] As described above, according to the creep remaining life evaluation method of the present invention, the L parameter method suitable for evaluating the remaining life of fine grains and the M parameter method (M Combined with the parameter method, the residual creep life can be evaluated at any point on the actual machine member, regardless of whether the evaluation target site on the actual machine member is a misalignment of the fine grained part or the coarse grained part. can do. Furthermore, by comparing the result of estimation with a conventional remaining life evaluation method such as the above-mentioned void number density method, more reliable remaining life evaluation can be performed.

[0094] The method of evaluating the remaining life of the actual machine member using the method for evaluating the remaining creep life of the embodiment has been described above. The reliability of the creep life evaluation means how close the evaluation result (remaining life or creep life consumption rate) based on the parameters adopted is to the result of the creep test. Therefore, not all conceivable parameters can be used as they are for the evaluation of the remaining life of actual components, but it is necessary to confirm in advance the reliability of the parameters to be adopted for the evaluation of the remaining life. . The following shows an example of the accuracy confirmation test results for confirming the reliability of the L parameter. (1) The rupture time was 147 hours in a simulated fracture test (15 mm square X L50 mm specimen) of a real machine scale high-temperature reheated steam pipe, and the rupture time was 147 hours. The rate was "tZtr = 0.93". On the other hand, the creep life consumption rate as a result of applying the L parameter on the surface of the specimen fine grain portion at this time was also "tZtr = 0.93".

[0096] (2) The creep test of the actual waste material creep test (using a φ20mm X L50mm specimen and a tarp test) was 85 hours, and the creep test force was obtained. Ztr = 0.96 ". On the other hand, the creep life consumption rate as a result of applying the L parameter on the surface of the specimen fine grain at this time was "tZtr = 0.98".

[0097] As described above, the result of the creep test and the result by the L parameter (creep life consumption rate) are almost the same (error of about 1%), and the reliability of the L parameter is very high. It can be confirmed that there is.

[0098] Further, in the embodiment, expanded voids existing over at least 1/2 of each length of at least two grain boundaries are formed by uniting voids generated on a plurality of grain boundaries. If the expanded voids can be clearly distinguished from those that have grown larger due to the growth of one void and those that have combined multiple voids, the expanded voids are considered to be connected. Well, you can count them separately.

[0099] Further, in the embodiment, when obtaining the time as the remaining creep life, the various types of ST1 test force of ST1 were calculated based on the data representing the relationship between each parameter obtained and the creep life consumption rate. By creating the master curve with, the creep life consumption rate and the remaining life can be immediately obtained based on the above formulas simply by inputting various parameters for the actual machine member force. .

[0100] As described above, the method of evaluating the remaining life of the actual machine member using the creep remaining life evaluation method of the embodiment has been described. However, the present invention is not limited to this. For example, in the embodiment, the estimation based on the conventional void number density method is performed. Although the results were also compared, the results of estimation based on other parameter-based evaluation methods can also be compared. 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.

[0101] In the embodiment, the L parameter or the M parameter Each master curve was used to represent the relationship between the data and the life consumption rate of talyp.However, a database was created to show the relationship between the two, and the remaining life was evaluated by comparing this with the parameters obtained for the actual machine components. You can also. In either method, it is possible to automatically calculate the remaining life by inputting the obtained L parameters using the computer.

Further, in the embodiment, when obtaining the L parameter, the actual machine member also obtains a replica of the member surface, enlarges the replica by SEM or the like, and visually observes the voids. After connecting the images, the connected voids can be automatically recognized by a machine such as a computer, and the number thereof can be quickly and easily obtained on the image.

Claims

The scope of the claims

[1] A method for evaluating the time until creep damage occurs or the remaining life represented by the creep life consumption rate after creep damage occurs.

On the surface of the device member, the number of specific voids existing over a plurality of crystal grain boundaries within a predetermined range is determined, and the ratio of the number of the specific voids to the area of the predetermined range is defined as a specific void density,

On the surface of the device member, the ratio of the total length of all the voids on the grain boundary to the length of one grain boundary within a predetermined range is defined as the void grain boundary occupancy, and the ratio of each grain boundary is The maximum value is defined as the maximum void grain boundary occupancy,

Based on the specific void density and the maximum void grain boundary occupancy, the remaining life of the equipment member is evaluated, and the result of V, which is shorter or shorter, is determined as the remaining life of the equipment member. And a creep remaining life evaluation method.

[2] The method for evaluating a remaining creep life according to claim 1, wherein the specific void is an extended void existing over at least 1/2 of each length of at least two crystal grain boundaries. Creep remaining life evaluation method.

[3] The method for evaluating a remaining creep life according to claim 1 or 2, wherein the specific void is a connected void formed by uniting voids generated on a plurality of crystal grain boundaries. Evaluation method.

[4] The method for evaluating a remaining creep life according to any one of claims 1 to 3, wherein the maximum void grain boundary occupancy is determined by the following equation.

[Equation 1] Largest boat occupancy —Rate—

(M parameter) One ^M

Where m is the number of grain boundaries where voids exist,

n is the number of voids present on each grain boundary,

1 is the length of the i-th void on the α-th grain boundary in the direction of the grain boundary, L is the length of the α-th grain boundary where the void exists

It is.

[5] In the creep remaining life evaluation method according to any one of claims 1 to 4, the evaluation of the remaining life is based on the relationship between the specific void density and the remaining life and the maximum void grain boundary occupancy. A creep remaining life evaluation method for estimating the time by referring to each evaluation criterion for which the creep test force was also obtained for the relationship between the creep test life and the remaining life.

[6] In the method for evaluating a remaining creep life according to claim 5, the evaluation of the remaining life is based on the specific void density and the maximum void grain boundary occupancy, For the void number density and other parameters, which are the ratio of the number of all voids in the range to the area of the predetermined range, also refer to the evaluation criteria for all parameters, and estimate the time estimated by the evaluation criteria for each parameter. A creep remaining life evaluation method in which the shortest one is the remaining life.

[7] According to the method for evaluating a remaining creep life according to any one of claims 1 to 6, an image of a surface of the device member is formed, and the number of the specific voids and the void grain boundary occupancy on the image. And a creep remaining life evaluation method characterized by:

[8] According to the remaining creep life evaluation method according to claim 7, the image of the surface of the device member is obtained by polishing and corroding the surface of the device member, and then attaching a predetermined film to the surface. A creep remaining life evaluation method, which is obtained by taking a picture or taking an image of the surface of the device member using an image pickup means.