FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention: CREEP LIFE EVALUATION METHOD
2. Applicant(s)
NAME NATIONALITY ADDRESS
MITSUBISHI POWER, LTD. Japanese 3-1, Minatomirai 3-Chome, Nishiku,
Yokohama-shi, Kanagawa
2208401, Japan
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it
is to be performed.

TECHNICAL FIELD
[0001] This disclosure relates to a creep life evaluation method.
5 BACKGROUND
[0002] Some tubes used in a heating device such as a boiler, for example heattransfer
tubes, are used at high temperature and high pressure. This type of tube
is inspected to evaluate the remaining life by periodic inspections in order to
check the integrity.
10 For example, in the creep damage estimation method disclosed in Patent
Document 1, the hardness of heat-resistant steel surface is measured to determine
the creep strain amount of the heat-resistant steel from a predetermined created
relationship between hardness and creep strain amount, and the creep damage rate
is determined by comparison with a separately determined creep strain curve.
Citation List
Patent Literature
[0003] Patent Document 1: JP4737512B
SUMMARY
Problems to be Solved
[0004] In the creep damage estimation method disclosed in Patent Document
1, the creep strain curve for determining the creep damage rate is calculated from
material data such as steady creep rate experimentally obtained, temperature, and
stress conditions. That is, it is considered that the creep damage estimation
method disclosed in Patent Document 1 uses data from an accelerated test in order
to obtain a master curve for determining the creep damage rate.
Since it is difficult to reproduce creep damage in an environment exceeding
100,000 hours (11.4 years), which is the operating time of an actual boiler, due to
time constraints or the like, generally, necessary data is obtained by performing an
accelerated test as in the 5 creep damage estimation method disclosed in Patent
Document 1.
For example, in an accelerated test relating to material creep, a sample is
caused to creep in a short time by making the acting stress and the temperature
larger than those in the actual operating environment.
However, since the material creep behavior depends on the acting stress and
the temperature, there is a difference between the data obtained in the accelerated
test and the creep behavior in the actual machine. Therefore, it is difficult to
improve the accuracy of the master curve for determining the creep damage rate,
and it is difficult to improve the accuracy of the creep damage rate determined by
the master curve.
[0005] In view of the above, an object of at least one embodiment of the
present invention is to improve the accuracy of evaluation of the creep life.
Solution to the Problems
[0006] (1) A creep life evaluation method according to at least one
embodiment of the present invention comprises: a damage index acquisition step
of acquiring a damage index of each of a first portion of a boiler tube used in a
boiler and a second portion of the boiler tube in a different position from the first
portion, the second portion being made of a same material as the first portion; a
life consumption rate evaluation step of evaluating a life consumption rate of each
of the first portion and the second portion; a correlation acquisition step of
acquiring a correlation between the damage index and the life consumption rate,
based on the damage index of each of the first portion and the second portion and
the life consumption rate of each of the first portion and the second portion; an
evaluation damage index acquisition step of acquiring a damage index of an
evaluation target tube; 5 and an evaluation step of evaluating a life consumption rate
of the evaluation target tube, based on the correlation and the damage index of the
evaluation target tube.
[0007] In the above method (1), the damage index of each of the first portion
and the second portion of the boiler tube is acquired. Further, in the above
method (1), the correlation between the damage index and the life consumption
rate is acquired, based on the acquired damage index, and the life consumption
rate of each of the first portion and the second portion. That is, with the above
method (1), since the correlation between the damage index and the life
consumption rate is acquired using the damage index of the boiler tube actually
used in the boiler, it is possible to eliminate the influence of dependency on the
temperature and the acting stress in the material creep behavior, and improve the
accuracy of the correlation.
Further, with the above method (1), since the life consumption rate of the
evaluation target tube is evaluated based on the damage index of the evaluation
target tube and the correlation, the life consumption rate of the evaluation target
tube can be evaluated based on the correlation of high accuracy, so that it is
possible to improve the evaluation accuracy of the creep life.
[0008] (2) In some embodiments, in the above method (1), an acting stress
acting on the second portion during operation of the boiler can be regarded as the
same as an acting stress acting on the first portion, and a temperature of the
second portion during operation of the boiler is higher than a temperature of the
first portion.
[0009] With the above method (2), since the first portion and the second
portion, which can be regarded as the same in acting stress but differ in
temperature during operation of the boiler, have different degrees of damage, two
different damage indexes can be acquired. 5 As a result, since data of two
different points on the correlation between the damage index and the life
consumption rate can be acquired, it is possible to improve the accuracy of the
correlation.
[0010] (3) In some embodiments, in the above method (1) or (2), a plurality of
heat exchangers including the boiler tube is disposed inside a furnace of the boiler.
The second portion is included in a same heat exchanger as the first portion, and
the second portion is in a different position from the first portion in a furnace
width direction.
[0011] Generally, in the furnace of the boiler, due to the temperature
distribution of the combustion gas, the strength of radiation, and the flow of the
combustion gas, the temperature of the heat-transfer tube varies with the position
in the furnace width direction or the front-back direction of the boiler. Thus,
with the above method (3), since the first portion and the second portion are
included in the same heat exchanger but disposed in different positions in the
furnace width direction, the first portion and the second portion have acting
stresses that can be regarded as the same, but different temperatures during
operation of the boiler. Accordingly, with the above method (3), since the first
portion and the second portion have different degrees of damage, two different
damage indexes can be acquired. As a result, since data of two different points
on the correlation between the damage index and the life consumption rate can be
acquired, it is possible to improve the accuracy of the correlation.
[0012] (4) In some embodiments, any one of the above methods (1) to (3)
further comprises a temperature measurement step of measuring a temperature of
the first portion and a temperature of the second portion during operation of the
boiler from outside a furnace. The life consumption rate evaluation step includes
evaluating the life consumption 5 rate of each of the first portion and the second
portion, using the temperature of the first portion and the temperature of the
second portion obtained by measurement in the temperature measurement step.
[0013] With the above method (4), since the temperature of the first portion
and the temperature of the second portion during operation of the boiler obtained
by measurement in the temperature measurement step are used, it is possible to
improve the evaluation accuracy of the life consumption rate of each of the first
portion and the second portion. Thus, it is possible to improve the accuracy of
the correlation.
[0014] (5) In some embodiments, in any one of the above methods (1) to (4),
the life consumption rate evaluation step includes: an average particle size
acquisition step of obtaining an average particle size of each of deposits of the
first portion and the second portion; a temperature calculation step of obtaining a
temperature of each of the first portion and the second portion during operation of
the boiler, based on a relationship between an average particle size of a deposit of
a structure of a heat-resistant material made of the same material as the first
portion and the second portion and a first parameter related to a temperature and a
usage time of the heat-resistant material, the average particle size of each of the
deposits of the first portion and the second portion, and a usage time of the first
portion and the second portion; a second parameter value acquisition step of
25 obtaining a value of a second parameter related to a temperature and a rupture
time of each of the first portion and the second portion, based on a relationship
between an acting stress of the heat-resistant material and the second parameter of
the heat-resistant material, and a stress of each of the first portion and the second
portion; and a rupture time acquisition step of obtaining a rapture time of each of
the first portion and the second portion, based on the value of the second
parameter of each of the 5 first portion and the second portion, and the temperature
of each of the first portion and the second portion during operation of the boiler.
[0015] With the above method (5), the temperature of each of the first portion
and the second portion during operation of the boiler can be obtained, based on a
relationship between the average particle size of the deposit of the structure of the
heat-resistant material and the first parameter, the average particle size of each of
the deposits of the first portion and the second portion, and the usage time of the
first portion and the second portion. Further, with the above method (5), the
value of the second parameter of each of the first portion and the second portion
can be obtained, based on a relationship between the acting stress and the second
parameter of the heat-resistant material, and the stress of each of the first portion
and the second portion. With the above method (5), the rapture time of each of
the first portion and the second portion can be obtained, based on the value of the
second parameter of each of the first portion and the second portion, and the
temperature of each of the first portion and the second portion during operation of
the boiler.
Consequently, with the above method (5), the life consumption rate of each
of the first portion and the second portion can be easily obtained from the rupture
time obtained as described above and the operating time of the boiler.
[0016] (6) In some embodiments, in the above method (1), a temperature of
the second portion during operation of the boiler can be regarded as the same as a
temperature of the first portion, and an acting stress acting on the second portion
during operation of the boiler is greater than an acting stress acting on the first
portion.
[0017] With the above method (6), since the first portion and the second
portion, which can be regarded as the same in temperature but differ in acting
stress during operation of the boiler, have 5 different degrees of damage, two
different damage indexes can be acquired. As a result, since data of two
different points on the correlation between the damage index and the life
consumption rate can be acquired, it is possible to improve the accuracy of the
correlation.
[0018] (7) In some embodiments, in the above method (1) or (6), the second
portion is included in a same circumferential weld of the boiler tube as the first
portion, and the second portion is in a different position from the first portion in a
circumferential direction.
[0019] Generally, when the bending stress acts on the boiler tube due to the
influence of thermal expansion and own weight of the boiler tube, even with the
same circumferential weld, the stress varies with the position in the
circumferential direction. Thus, with the method (7), since the first portion and
the second portion are included in the same circumferential weld but disposed in
different positions in the circumferential direction, the first portion and the second
portion have temperatures that can be regarded as the same, but different acting
stresses during operation of the boiler. Accordingly, with the above method (7),
since the first portion and the second portion have different degrees of damage,
two different damage indexes can be acquired. As a result, since data of two
different points on the correlation between the damage index and the life
consumption rate can be acquired, it is possible to improve the accuracy of the
correlation.
[0020] (8) In some embodiments, in any one of the above methods (1), (6), or
(7), the life consumption rate evaluation step includes: a second parameter value
acquisition step of obtaining a value of a second parameter related to a
temperature and a rupture time of each of the first portion and the second portion,
based on a relationship between a stress 5 of a heat-resistant material made of the
same material as the first portion and the second portion and the second parameter
of the heat-resistant material, and a stress of each of the first portion and the
second portion; and a rupture time acquisition step of obtaining a rapture time of
each of the first portion and the second portion, based on the value of the second
parameter of each of the first portion and the second portion, and a temperature of
each of the first portion and the second portion during operation of the boiler.
[0021] With the above method (8), the value of the second parameter, related
to the temperature and the rupture time, of each of the first portion and the second
portion can be obtained, based on a relationship between the stress of the heat15
resistant material and the second parameter of the heat-resistant material, and the
stress of each of the first portion and the second portion. Further, with the above
method (8), the rapture time of each of the first portion and the second portion can
be obtained, based on the value of the second parameter of each of the first
portion and the second portion, and the temperature of each of the first portion and
the second portion during operation of the boiler.
Consequently, with the above method (8), the life consumption rate of each
of the first portion and the second portion can be easily obtained from the rupture
time obtained as described above and the operating time of the boiler.
[0022] (9) In some embodiments, in any one of the above methods (1) to (8),
the damage index is any of a void number density, a tube deformation, or a
hardness.
[0023] With the above method (9), since the damage index is any of the void
number density, the tube deformation, or the hardness, it is possible to easily
acquire the damage index.
Advantageous Effects
[0024] According to at least one embodiment of the present invention, it is
possible to improve the accuracy of evaluation of the creep life.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 is an overall configuration diagram of a power generation plant
according to an embodiment.
FIG. 2 is a schematic configuration diagram of a super-heater.
FIG. 3 is a schematic diagram showing relationships of metal temperature
and creep damage rate (life consumption rate) with position in a furnace width
direction of the same device.
FIG. 4 is a flowchart showing a process of a creep life evaluation method
according to some embodiments.
FIG. 5 is a flowchart showing an example of a schematic procedure of a life
consumption rate evaluation step.
FIG. 6 is a graph showing a relationship between average particle size of a
specific deposit and first parameter of a heat-resistant material.
FIG. 7 is a graph showing a relationship between acting stress and second
parameter.
FIG. 8 is a diagram showing an example of a master curve represented by a
relationship between damage index and life consumption rate.
FIG. 9 is a schematic diagram of a super-heater when viewed in a furnace
width direction.
FIG. 10 is a flowchart showing an example of a schematic procedure of a
life consumption rate evaluation step according to another embodiment.
FIG. 11 is a diagram showing the vicinity of a bend portion of a pipe such as
a main steam pipe or a re-heated steam pipe.
FIG. 12 is a flowchart showing an example of a schematic procedure of a
life consumption rate evaluation step according to another embodiment.

DETAILED DESCRIPTION
[0026] Embodiments of the present invention will now be described in detail
with reference to the accompanying drawings. It is intended, however, that
unless particularly identified, dimensions, materials, shapes, relative positions,
and the like of components described in the embodiments shall be interpreted as
illustrative only and not intended to limit the scope of the present invention.
For instance, an expression of relative or absolute arrangement such as “in a
direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric”
and “coaxial” shall not be construed as indicating only the arrangement in a strict
literal sense, but also includes a state where the arrangement is relatively
displaced by a tolerance, or by an angle or a distance whereby it is possible to
achieve the same function.
For instance, an expression of an equal state such as “same” “equal” and
“uniform” shall not be construed as indicating only the state in which the feature
is strictly equal, but also includes a state in which there is a tolerance or a
difference that can still achieve the same function.
Further, for instance, an expression of a shape such as a rectangular shape or
a cylindrical shape shall not be construed as only the geometrically strict shape,
but also includes a shape with unevenness or chamfered corners within the range
in which the same effect can be achieved.
On the other hand, an expression such as “comprise”, “include”, “have”,
“contain” and “constitute” are not intended to be exclusive of other components.
[0027] FIG. 1 is an overall configuration 5 diagram of a power generation plant
according to an embodiment.
In an embodiment, a power generation plant 1 includes a turbine group
including a high-pressure turbine 4, an intermediate-pressure turbine 6, and a lowpressure
turbine 8, a generator 9 driven by the turbine group, and a boiler 10 for
generating steam supplied to the turbine group.
The shafts of the high-pressure turbine 4, the intermediate-pressure turbine 6,
and the low-pressure turbine 8 are coaxially connected to each other, and may also
be connected to the shaft of the generator 9.
[0028] The high-pressure turbine 4 is supplied with main steam produced by a
super-heater 12 disposed on the boiler 10 via a main steam pipe 13. The main
stream flowing into the high-pressure turbine 4 is, after expansion work,
discharged from the high-pressure turbine 4 and flows into a re-heater 14 disposed
on the boiler 10. The steam re-heated by the re-heater 14 flows into the
intermediate-pressure turbine 6 via a re-heated steam pipe 15. The re-heated
stream flowing into the intermediate-pressure turbine 6 is, after expansion work,
discharged from the intermediate-pressure turbine 6 and flows into the lowpressure
turbine 8 via a crossover pipe 18. The stream flowing into the lowpressure
turbine 8 is, after expansion work, discharged from the low-pressure
turbine 8, condensed into water by a condenser 20, and returned to the boiler 10
by a boiler feedwater pump 22.
[0029] In the power generation plant 1 having the above configuration, the
main steam supplied to the high-pressure turbine 4 via the main steam pipe 13 and
the re-heated steam supplied to the intermediate-pressure turbine 6 via the reheated
steam pipe 15 are at 550°C or higher (for example, about 600°C). The
main steam pressure is set to 20 MPa or more, for example 25 MPa.
[0030] FIG. 2 is a schematic configuration 5 diagram of the super-heater 12.
The configuration of the re-heater 14 is the same as the super-heater 12 and thus
will not be described in detail.
The super-heater 12 includes an inlet header 12A, an outlet header 12C, and
a plurality of super-heater tubes (heat-transfer tubes) 12B. In the super-heater 12
shown in FIG. 2, a plurality of heat-transfer tubes 12B are arranged in a
substantially U-shape in a plane to form a heat-transfer tube panel 12D, and a
plurality of the heat-transfer tube panels 12D are arranged in the extending
direction of the headers 12A and 12C.
[0031] Since the heat-transfer tube of the super-heater 12 or the re-heater 14 is
used for a long period at high temperature and high pressure as described above,
the tube is inspected to evaluate the remaining life by periodic inspections in order
to check the integrity of the tube.
Further, in addition to the steam at high temperature and high pressure
flowing therethrough, stress due to factors other than internal pressure, such as
thermal stress and pipe reaction force, acts on the pipe such as the main steam
pipe 13 and the re-heated steam pipe 15 due to the influence of thermal expansion
and own weight of the pipe. A welded portion such as a circumferential weld of
the pipe or a header tube weld generally has a low creep strength compared with a
base material of the pipe. Thus, since the welded portion having a large acting
stress tends to creep significantly, the welded portion is inspected to evaluate the
remaining life by periodic inspections in order to check the integrity.
[0032] The remaining life evaluation method in periodic inspections includes,
for example, evaluating the remaining life based on the number density of creep
voids caused with creep damage, evaluating the remaining life based on the
deformation of a tube such as creep extension and strain, or evaluating the
remaining l 5 ife based on the hardness of the evaluation target.
In the remaining life evaluation method as described above, the creep life is
evaluated by focusing on the fact that the damage index such as the physical
property value and the morphology of the target to be evaluated for the remaining
life, including the number density of creep voids, the deformation of tube, and the
hardness, changes with the creep damage. Specifically, in the remaining life
evaluation method as described above, a correlation between the damage index
and the life consumption rate is previously acquired as a master curve, and the
creep life of the evaluation target is evaluated based on this master curve and the
damage index of the evaluation target.
[0033] Since it is difficult to reproduce creep damage in an environment
exceeding 100,000 hours (11.4 years), which is the operating time of an actual
boiler, due to time constraints or the like, generally, data necessary for acquiring
the master curve is obtained by performing an accelerated test.
For example, in an accelerated test relating to material creep, a sample is
caused to creep in a short time by making the acting stress and the temperature
larger than those in the actual operating environment.
However, since the material creep behavior depends on the acting stress and
temperature, there is a difference between the data obtained in the accelerated test
and the creep behavior in the actual machine. Therefore, it is difficult to
improve the accuracy of the master curve for determining the creep damage rate.
[0034] Thus, in some embodiments described below, the master curve, which
is a correlation for evaluating the creep life, is acquired based on the damage
index acquired from a boiler to be evaluated for the creep life, in order to improve
the accuracy of the master curve. Details will be described. In the following,
tubes used in the boiler 10, such as the heat-transfer tube 12B of the super-heater
, the heat-transfer tube of the re-5 heater 14, the main steam pipe 13, and the reheated
steam pipe 15, are also simply referred to as a boiler tube 30. Further, in
the following, the super-heater 12 and the re-heater 14 are also collectively
referred to as a heat exchanger 25.
[0035] First, the overview of the method of acquiring the master curve of the
boiler tube according to some embodiments will be described. In the following,
the correlation between damage index and life consumption rate for evaluating the
life consumption rate of the evaluation target tube to be evaluated for the life
consumption rate is also referred to as a master curve.
Generally, in a furnace of the boiler 10, due to the temperature distribution
of the combustion gas, the strength of radiation, and the flow of the combustion
gas, for example, even with the heat-transfer tube 12B of the same super-heater 12,
as shown in FIG. 3, the temperature (metal temperature) of the heat-transfer tube
12B varies with the position in the furnace width direction or the front-back
direction of the boiler. On the other hand, with the same super-heater 12, even if
the position in the furnace width direction or the boiler front-back direction differs,
the internal pressure of the heat-transfer tube 12B can be regarded as the same,
and the usage time is the same. That is, as shown in FIG. 2, for example among
the plurality of heat-transfer tubes 12B of the super-heater 12, a first portion 31
and a second portion 32 disposed in different positions in the furnace width
direction are different in temperature during the operation of the boiler 10 but the
same in acting stress and usage time. Further, the material of the heat-transfer
tube 12B of the same super-heater 12 is generally the same regardless of the
position in the furnace width direction.
Accordingly, the degree of creep damage differs between the first portion 31
and the second portion 32 due to the difference in temperature. In other words,
since the first portion 31 and 5 the second portion 32 have the same acting stress
and usage time, the difference in creep damage degree between the first portion 31
and the second portion 32 is due to the difference in temperature. Here, FIG. 3 is
a schematic diagram showing relationships of metal temperature and creep
damage rate (life consumption rate) with position in the furnace width direction of
the same device, for example the super-heater 12.
[0036] In the method of acquiring the master curve of the boiler tube
according to some embodiments, damage indexes of at least two portions with
different creep damage degrees due to the difference in temperature, such as the
first portion 31 and the second portion 32 described above, are acquired. Further,
in the method of acquiring the master curve according to some embodiments, the
life consumption rate of each of the at least two portions is evaluated, and a
master curve M represented by a relationship between the damage index and the
life consumption rate is acquired based on the evaluated life consumption rate and
the acquired damage index as described above.
In this way, in the method of acquiring the master curve according to some
embodiments, since the master curve M is acquired using the damage index of the
boiler tube 30 used in the boiler 10, it is possible to eliminate the influence of
dependency on the temperature and the acting stress in the material creep behavior,
and improve the accuracy of the master curve M.
Hereinafter, the creep life evaluation method according to some
embodiments will be described.
[0037] FIG. 4 is a flowchart showing a process of the creep life evaluation
method according to some embodiments. The creep life evaluation method
according to some embodiments includes a damage index acquisition step S10 to
acquire the master curve, a life consumption rate evaluation step S20, a
correlation acquisition step S30, 5 an evaluation damage index acquisition step S40,
and an evaluation step S50.
The method of acquiring the master curve of the boiler tube according to
some embodiments is a method of acquiring the master curve of the boiler tube 30
used in the boiler 10, and includes the damage index acquisition step S10, the life
consumption rate evaluation step S20, and the correlation acquisition step S30.
Specifically, in the creep life evaluation method according to some
embodiments, the master curve M is acquired by performing the damage index
acquisition step S10, the life consumption rate evaluation step S20, and the
correlation acquisition step S30 as described below. Further, in the creep life
evaluation method according to some embodiments, the damage index of the
evaluation target tube to be evaluated for the life consumption rate is acquired by
performing the evaluation damage index acquisition step S40 as described below.
Further, in the creep life evaluation method according to some embodiments, the
life consumption rate of the evaluation target tube is evaluated by performing the
evaluation step S50.
[0038] (Damage index acquisition step S10)
The damage index acquisition step S10 according to some embodiments is a
step of acquiring the damage index of each of a first portion of the boiler tube 30
and a second portion of the boiler tube 30 in a different position from the first
portion, made of the same material as the first portion. For example, in the case
of the super-heater 12, in the damage index acquisition step S10, the damage
index of each of the first portion 31 of the heat-transfer tube 12B and the second
portion 32 of the heat-transfer tube 12B in a different position from the first
portion 31 is acquired.
In the following, the first portion 31 and the second portion 32 of the heattransfer
tube 12B of the super-heater 12 will 5 be described as an example, but the
same should apply to the re-heater 14.
[0039] The damage index acquired in the damage index acquisition step S10
according to some embodiments may be, for example, void number density, tube
deformation, or hardness. In the following, the case where the damage index is
void number density will be described.
In the damage index acquisition step S10 according to some embodiments,
for example, as shown in FIG. 3, if a relationship between the position in the
furnace width direction and the metal temperature is previously known, it is
desirable to acquire the numbers of voids in at least two positions, one in the
vicinity of a position P1 where the metal temperature is the minimum and the
other in the vicinity of a position P2 where the metal temperature is the maximum.
Thereby, with respect to the master curve M acquired as described later, it is
possible to expand the range in which the master curve M can be acquired by
interpolation. In other words, by acquiring the void number densities in at least
two positions in the vicinity of the position P1 and the vicinity of the position P2,
it is possible to narrow the range in which the master curve M can be acquired by
extrapolation. Thus, it is possible to improve the accuracy of the master curve M.
[0040] Further, it is desirable to acquire the void number density in a position
where the temperature is intermediate between the maximum metal temperature
Tmax and the minimum metal temperature Tmin. Thereby, it is possible to
improve the accuracy of the master curve M.
Even if the positions to acquire the void number density are randomly
determined, the master curve M can be created unless two positions that are
separated in the furnace width direction but have the same metal temperature are
accidentally selected.
[0041] The following 5 description will be given on the premise that the first
portion 31 and the second portion 32 of the heat-transfer tube 12B of the superheater
12 have different metal temperatures. s
[0042] (Life consumption rate evaluation step S20)
The life consumption rate evaluation step S20 according to some
embodiments is a step of evaluating the life consumption rate of each of the first
portion and the second portion. That is, for example, in the case of the superheater
12, in the life consumption rate evaluation step S20, the life consumption
rate of each of the first portion 31 and the second portion 32 of the heat-transfer
tube 12B is evaluated. In the life consumption rate evaluation step S20, if there
is a portion other than the first portion 31 and the second portion 32 of the heattransfer
tube 12B where the damage index has been acquired in the damage index
acquisition step S10, the life consumption rate of this portion is also evaluated.
Specifically, in the life consumption rate evaluation step S20 according to some
embodiments, the life consumption rate is evaluated as follows.
[0043] FIG. 5 is a flowchart showing an example of a schematic procedure of
the life consumption rate evaluation step S20.
In the life consumption rate evaluation step S20, the life consumption rate of
the portion where the damage index has been acquired in the damage index
acquisition step S10 is evaluated by the following steps S201 to S209.
The life consumption rate evaluation step S20 includes an average particle
size acquisition step S201, a temperature calculation step S203, a second
parameter value acquisition step S205, a rupture time acquisition step S207, and a
life consumption rate calculation step S209.
[0044] The average particle size acquisition step S201 is a step of obtaining
the average particle size of each of deposits of the first portion and the second
portion. For example, in the case of the super-5 heater 12, in the average particle
size acquisition step S201, the average particle size of each of deposits of the first
portion 31 and the second portion 32 of the heat-transfer tube 12B is obtained.
In the average particle size acquisition step S201, for the portion where the
damage index has been acquired in the damage index acquisition step S10, a
replica of the structure is obtained by a method such as the replica method.
Further, the average particle size of a specific deposit in the portion where the
damage index has been acquired, i.e., the portion where the replica has been
obtained, is calculated from the obtained replica. For example, in the case of the
super-heater 12, in the average particle size acquisition step S201, replicas of the
structures of the first portion 31 and the second portion 32 of the heat-transfer
tube 12B are obtained. Then, the average particle size of a specific deposit in
each of the first portion 31 and the second portion 32 is calculated from the
obtained replicas of the first portion 31 and the second portion 32.
For calculating the average particle size of the specific deposit of the portion
where the damage index has been acquired in the damage index acquisition step
S10, it is not necessarily required to obtain the replica. For example, the tube
may be removed to collect a sample of the structure, and the average particle size
of the specific deposit may be calculated from the sample.
[0045] The temperature calculation step S203 is a step of obtaining the
temperature of each of the first portion and the second portion during operation of
the boiler 10, based on a relationship between the average particle size of a
deposit of a structure of a heat-resistant material made of the same material as the
first portion and the second portion and a first parameter λ1 related to the
temperature and the usage time of the heat-resistant material, the average particle
size of each of the deposits of the first portion and the second portion, and the
usage time of the first portion and the second portion.
[0046] FIG. 6 is a graph showing a relationship between the average particle
size of a specific deposit of the heat-resistant material and the temperature-time
parameter (first parameter) λ1 related to the temperature and the usage time of the heat-resistant material. It is known that there is a relationship as shown in FIG. 6
between the average particle size of a specific deposit and the first parameter λ1
related to the temperature and the usage time of the heat-resistant material,
according to the material of the heat-resistant material used in the boiler tube 30.
The specific deposit is a deposit that has a high correlation between the average
particle size and the first parameter λ1 and can accurately calculate the value of the first parameter λ1 from the value of the average particle size.
The first parameter λ1 is, for example, a Larson-Miller parameter,
represented by the following expression (1), where T is the temperature (unit: K)
when the heat-resistant material is heated, t (unit: h) is the heating time, and C is
the material constant of the heat-resistant material.
λ = T×(C+log(t))/1000 (1)
[0047] From the graph 41 representing the relationship between the average
particle size of the specific deposit and the first parameter λ1 shown in FIG. 6, the value of the first parameter λ1 corresponding to the average particle size of the specific deposit of each of the replica-obtained portions can be acquired. Further, by substituting the acquired value of the first parameter λ1 and the operating time of the boiler 10 into the expression (1), the metal temperature of each replica- obtained portion during operation of the boiler 10 can be determined.
For example, in the case of the super-heater 12, the metal temperature T1 of
the first portion 31 of the heat-transfer tube 12B during operation of the boiler 10
is calculated from the average particle size of the specific deposit of the first
portion 31 as described above, 5 and the metal temperature T2 of the second portion
32 during operation of the boiler 10 is calculated from the average particle size of
the specific deposit of the second portion 32 as described above.
[0048] The second parameter value acquisition step S205 is a step of
obtaining a value of a second parameter λ2 related to the temperature and the
rupture time of each of the first portion and the second portion, based on a
relationship between the acting stress of the heat-resistant material and the second
parameter λ2 of the heat-resistant material, and the stress of each of the first
portion and the second portion.
It is known that there is a relationship as shown in FIG. 7 between the acting
stress and the temperature-time parameter (second parameter) λ2 related to the
temperature and the rupture time of the heat-resistant material, according to the
material of the heat-resistant material used in the boiler tube 30. The second
parameter λ2 is, for example, a Larson-Miller parameter.
[0049] From the graph 42 representing the relationship between the acting
stress and the second parameter λ2 shown in FIG. 7, the value of the second
parameter λ2 corresponding to the acting stress of each of the replica-obtained
portions can be acquired.
As described above, if the replicas are obtained from the heat-transfer tube
of the same dimension in the same device, the acting stresses of the replica25
obtained portions can be regarded as the same, so that the acting stress can be
determined from the internal pressure of the heat-transfer tube. Accordingly, if
the replicas are obtained from the heat-transfer tube in the same device, the values
of the second parameters λ2 of the replica-obtained portions are the same.
For example, in the case of the super-heater 12 described above, the values
of the second parameters λ2 of the first portion 31 and the second portion 32 of the heat-transfer tube 12B can be acquired 5 from the graph 42 shown in FIG. 7 and
the acting stress of the first portion 31 and the second portion 32.
[0050] The rupture time acquisition step S207 is a step of obtaining the
rapture time of each of the first portion and the second portion, based on the value
of the second parameter λ2 of each of the first portion and the second portion, and the temperature of each of the first portion and the second portion during
operation of the boiler 10.
Specifically, in the rupture time acquisition step S207, for each of the
replica-obtained portions, by substituting the value of the second parameter λ2
acquired in the second parameter value acquisition step S205 and the metal
temperature during operation of the boiler 10 determined in the temperature
calculation step S203 into the expression (1), the rupture time of each replicaobtained
portion is obtained.
For example, in the case of the super-heater 12, in the rupture time
acquisition step S207, the rapture time of each of the first portion 31 and the
second portion 32 of the heat-transfer tube 12B is obtained by substituting the
value of the second parameter λ2 of each of the first portion 31 and the second
portion 32 acquired in the second parameter value acquisition step S205, and the
metal temperature of the first portion 31 and the second portion 32 during
operation of the boiler 10 determined in the temperature calculation step S203 into
the expression (1).
[0051] The life consumption rate calculation step S209 is a step of calculating
the life consumption rate of each of the first portion and the second portion, based
on the rupture time of each of the first portion and the second portion, and the
usage time of each of the first portion and the second portion.
Specifically, in the life consumption rate calculation step S209, the life
consumption rate of each of 5 the replica-obtained portions is obtained by dividing
the usage time of each of the replica-obtained portions by the rupture time
obtained in the rupture time acquisition step S207 for each of the replica-obtained
portions.
As described above, if the replicas are obtained from the heat-transfer tube
in the same device, the usage times of the replica-obtained portions are the same.
For example, in the case of the super-heater 12, in the life consumption rate
calculation step S209, the life consumption rate of each of the first portion 31 and
the second portion 32 of the heat-transfer tube 12B is obtained by dividing the
usage time of the first portion 31 and the second portion 32, i.e., the usage time of
the super-heater 12 by the rupture time of each of the first portion 31 and the
second portion 32 obtained in the rupture time acquisition step S207.
[0052] As described above, in the life consumption rate evaluation step S20
according to some embodiments, the temperature of each of the first portion 31
and the second portion 32 during operation of the boiler 10 can be obtained, based
on a relationship between the average particle size of the deposit of the structure
of the heat-resistant material and the first parameter λ1, the average particle size
of each of the deposits of the first portion 31 and the second portion 32, and the
usage time of the first portion 31 and the second portion 32. Further, in the life
consumption rate evaluation step S20 according to some embodiments, the value
of the second parameter λ2 of each of the first portion 31 and the second portion
32 can be obtained, based on a relationship between the acting stress and the
second parameter λ2 of the heat-resistant material, and the stress of each of the
first portion 31 and the second portion 32. In the life consumption rate
evaluation step S20 according to some embodiments, the rapture time of each of
the first portion 31 and the second portion 32 can be obtained, based on the value
of the second parameter λ2 of each 5 of the first portion 31 and the second portion
32, and the temperature of each of the first portion 31 and the second portion 32
during operation of the boiler 10.
Consequently, in the life consumption rate evaluation step S20 according to
some embodiments, the life consumption rate of each of the first portion 31 and
the second portion 32 can be easily obtained from the rupture time obtained as
described above and the operating time of the boiler 10.
[0053] (Correlation acquisition step S30)
The correlation acquisition step S30 according to some embodiments is a
step of acquiring a correlation between the damage index and the life consumption
rate, based on the damage index of each of the first portion and the second portion,
and the life consumption rate of each of the first portion and the second portion.
That is, in the case of the super-heater 12, in the correlation acquisition step S30,
the master curve M represented by a relationship between the damage index and
the life consumption rate is acquired, based on the damage index of each of the
first portion 31 and the second portion 32 of the heat-transfer tube 12B acquired in
the damage index acquisition step S10, and the life consumption rate of each of
the first portion 31 and the second portion 32 acquired in the life consumption rate
evaluation step S20.
FIG. 8 is a diagram showing an example of the master curve M represented
by a relationship between the damage index and the life consumption rate. The
point a1 on the master curve M of FIG. 8 is, for example, a plot indicating the
damage index and the life consumption rate of the first portion 31 of the heattransfer
tube 12B, and the point a2 is, for example, a plot indicating the damage
index and the life consumption rate of the second portion 32 of the heat-transfer
tube 12B.
[0054] In this way, in some embodiments, 5 the damage index of each of the
first portion 31 and the second portion 32 of the boiler tube 30 is acquired.
Further, in some embodiments, the master curve M represented by a relationship
between the damage index and the life consumption rate is acquired, based on the
acquired damage index, and the life consumption rate of each of the first portion
31 and the second portion 32. That is, in some embodiments, since the master
curve M is acquired using the damage index of the boiler tube 30 actually used in
the boiler 10, it is possible to eliminate the influence of dependency on the
temperature and the acting stress in the material creep behavior, and improve the
accuracy of the master curve M.
[0055] In some embodiments, during operation of the boiler 10, the acting
stress acting on the second portion 32 used for creating the master curve M can be
regarded as the same as the acting stress acting on the first portion 31 used for
creating the master curve M. Further, in some embodiments, during operation of
the boiler 10, the temperature of the second portion 32 used for creating the
master curve M is higher than the temperature of the first portion 31 used for
creating the master curve M.
Since the first portion 31 and the second portion 32, which can be regarded
as the same in acting stress but differ in temperature during operation of the boiler
10, have different degrees of damage, two different damage indexes can be
acquired. As a result, since data of two different points on the master curve M
represented by a relationship between the damage index and the life consumption
rate can be acquired, it is possible to improve the accuracy of the master curve.
[0056] In some embodiments, in a furnace of the boiler 10, a plurality of heat
exchangers 25 including the boiler tube 30 is disposed. Further, in some
embodiments, the second portion 32 is included in the same heat exchanger 25 as
the first portion 31, and the second 5 portion 32 is in a different position from the
first portion 31 in the furnace width direction.
[0057] As described above, generally, in the furnace of the boiler 10, due to
the temperature distribution of the combustion gas, the strength of radiation, and
the flow of the combustion gas, etc., the temperature of the heat-transfer tube
varies with the position in the furnace width direction or the front-back direction
of the boiler. Thus, in some embodiments, since the first portion 31 and the
second portion 32 are included in the same heat exchanger 25 but disposed in
different positions in the furnace width direction, the first portion 31 and the
second portion 32 have acting stresses that can be regarded as the same, but
different temperatures during operation of the boiler 10. Accordingly, in some
embodiments, since the first portion 31 and the second portion 32 have different
degrees of damage, two different damage indexes can be acquired. As a result,
since data of two different points on the master curve M represented by a
relationship between the damage index and the life consumption rate can be
acquired, it is possible to improve the accuracy of the master curve M.
[0058] (Evaluation damage index acquisition step S40)
The evaluation damage index acquisition step S40 according to some
embodiments is a step of acquiring the damage index of an evaluation target tube
to be evaluated for the life consumption rate. The type of the damage index
acquired in the evaluation damage index acquisition step S40 is the same as the
type of the damage index acquired in the damage index acquisition step S10
described above. That is, if the damage index acquired in the damage index
acquisition step S10 is the void number density, in the evaluation damage index
acquisition step S40, the void number density of the evaluation target tube is
acquired.
In some embodiments, since the damage index acquired in the damage index
acquisition step S10 and the evaluation damage index acquisition step S40 is any
of the void number density, tube deformation, or hardness, it is possible to easily
acquire the damage index.
[0059] The tube from which the damage index is acquired in the evaluation
damage index acquisition step S40 is another tube in the device that includes the
tube from which the damage index has been acquired in the damage index
acquisition step S10 for acquiring the master curve M in the master curve
acquisition step S10 to S30. If the master curve M has been acquired from the
heat-transfer tube 12B of the super-heater 12 in the master curve acquisition step
S10 to S30, the evaluation target tube is another heat-transfer tube 12B of the
super-heater 12. If the master curve M has been acquired from the heat-transfer
tube of the re-heater 14 in the master curve acquisition step S10 to S30, the
evaluation target tube is another heat-transfer tube of the re-heater 14.
[0060] For example like the super-heater 12 and the re-heater 14, even if the
devices differ, and the internal pressures in the heat-transfer tubes differ, there is a
case that the acting stresses can be regarded as the same. That is, even with
different devices, if the materials used in the devices are the same, the acting
stresses in design may be designed to be substantially the same.
Therefore, if the used materials are the same, the acting stresses can be
regarded as the same, and the usage times are the same, the device that includes
the tube from which the damage index has been acquired in the damage index
acquisition step S10 in order to acquire the master curve M may differ from the
device that includes the evaluation target tube, i.e., the device to be evaluated for
the life consumption rate.
[0061] Here, a case will be described in which the acting stress in one portion
(hereinafter referred to as first acting 5 stress) and the acting stress in the other
portion (hereinafter referred to as second acting stress) can be regarded as the
same. In some embodiments, the case where the first acting stress can be
regarded as the same as the second acting stress includes, in addition to that the
first acting stress is the same as the second acting stress, that the creep life of the
other portion on which the second acting stress acts is, for example, within a range
of twice or half the creep life of one portion on which the first acting stress acts.
In this case, the range of possible values of the second acting stress with respect to
the first acting stress is in a range of minus 15% to plus 15% of the first acting
stress.
[0062] (Evaluation step S50)
The evaluation step S50 according to some embodiments is a step of
evaluating the life consumption rate of the evaluation target tube, based on the
damage index of the evaluation target tube and the master curve M. Specifically,
in the evaluation step S50, the life consumption rate of the evaluation target tube
is evaluated, based on the damage index acquired in the evaluation damage index
acquisition step S40 and the master curve M as shown in FIG. 8 acquired in the
correlation acquisition step S30.
[0063] Thus, in some embodiments, since the life consumption rate of the
evaluation target tube is evaluated based on the damage index of the evaluation
target tube and the master curve M described above, the life consumption rate of
the evaluation target tube can be evaluated based on the master curve M of high
accuracy, so that it is possible to improve the evaluation accuracy of the creep life.
[0064] (Case where usage temperature is measurable)
FIG. 9 is a schematic diagram of the super-heater 12 when viewed in the
front-back direction of the boiler. In the super-heater 12, the inlet header 12A
and the outlet header 12C are disposed in a furnace 5 exterior 10B above a ceiling
11 in the boiler 10, and most of the plurality of heat-transfer tubes 12B is disposed
in a furnace interior 10A below the ceiling 11 of the boiler 10. A thermometer
51 for measuring the temperature of the heat-transfer tube 12B is difficult to place
in the furnace interior 10A through which the combustion gas flows, but easy to
place outside the furnace. Depending on the boiler 10, the thermometer 51 may
be arranged in advance in a portion of the heat-transfer tube 12B in the furnace
exterior 10B for the purpose of operating the boiler.
For convenience of explanation, the thermometer 51 attached to the heattransfer
tube 12B of the heat-transfer tube panel 12D including the first portion 31
shown in FIG. 2 may be referred to as a first thermometer 51A. Similarly, the
thermometer 51 attached to the heat-transfer tube 12B of the heat-transfer tube
panel 12D including the second portion 32 shown in FIG. 2 may be referred to as
a second thermometer 51B. The thermometer 51 may be, for example, a
thermocouple.
[0065] In the case where the temperature of the heat-transfer tube 12B can be
measured by the thermometer disposed in a portion of the heat-transfer tube 12B
in the furnace exterior 10B, for example, instead of obtaining the temperature of
the replica-obtained portion in the temperature calculation step S203, the
temperature of the heat-transfer tube 12B measured by the thermometer 51 during
operation of the boiler 10 may be acquired. The replica-obtained portion is
desirably near the installation position of the thermometer 51. However, since
the temperature of the replica-obtained portion and the temperature of the
installation position of the thermometer 51 are substantially equal to the
temperature of the steam flowing inside, the replica-obtained portion may be apart
from the installation position of the thermometer 51.
[0066] FIG. 10 is a flowchart 5 showing an example of a schematic procedure
of the life consumption rate evaluation step S20 according to another embodiment,
i.e., an embodiment in which the temperature of the heat-transfer tube can be
measured during operation of the boiler 10.
The life consumption rate evaluation step S20 of the embodiment shown in
FIG. 10 includes a temperature measurement step S211, a second parameter value
acquisition step S205, a rupture time acquisition step S207, and a life
consumption rate calculation step S209.
[0067] The temperature measurement step S211 is a step of measuring the
temperature of the first portion and the temperature of the second portion during
operation of the boiler 10 from outside the furnace. That is, for example in the
case of the super-heater 12, in the temperature measurement step S211, as shown
in FIGs. 2 and 9, the temperature of the first portion 31 and the temperature of the
second portion 32 during operation of the boiler 10 are measured by the first
thermometer 51A and the second thermometer 51B.
[0068] The temperature of the first portion during operation of the boiler 10
may be the temperature on the surface of the first portion, or the temperature of a
fluid flowing through the tube including the first portion may be used as the
temperature of the first portion. Similarly, the temperature of the second portion
during operation of the boiler 10 may be the temperature on the surface of the
second portion, or the temperature of a fluid flowing through the tube including
the second portion may be used as the temperature of the second portion.
[0069] In the embodiment shown in FIG. 10, the process of the second
parameter value acquisition step S205 is the same as that of the second parameter
value acquisition step S205 shown in FIG. 5.
[0070] In the embodiment shown in FIG. 10, in the rupture time acquisition
step S207, for each of 5 the replica-obtained portions, by substituting the value of
the second parameter λ2 acquired in the second parameter value acquisition stepS205 and the temperature (metal temperature) during operation of the boiler 10
measured in the temperature measurement step S211 into the expression (1), the
rupture time of each replica-obtained portion is obtained. That is, in the case of
the super-heater 12, in the rupture time acquisition step S207, the rapture time of
each of the first portion 31 and the second portion 32 of the heat-transfer tube 12B
is obtained by substituting the value of the second parameter λ2 of each of the First
portion 31 and the second portion 32 acquired in the second parameter value
acquisition step S205, and the temperature of the first portion 31 and the second
portion 32 during operation of the boiler 10 measured in the temperature
measurement step S211 into the expression (1).
[0071] In the embodiment shown in FIG. 10, the process of the life
consumption rate calculation step S209 is the same as that of the life consumption
rate calculation step S209 shown in FIG. 5.
[0072] Thus, the embodiment shown in FIG. 10 includes the temperature
measurement step S211. Further, in the embodiment shown in FIG. 10, in the
life consumption rate evaluation step S20, the life consumption rate of each of the
first portion and the second portion is evaluated using the temperature of the first
portion and the temperature of the second portion obtained by measurement in the
temperature measurement step S211.
Thus, in the case where the usage temperature is measurable, since the
temperature of the first portion and the temperature of the second portion during
operation of the boiler 10 obtained by measurement in the temperature
measurement step S211 can be used, it is possible to improve the evaluation
accuracy of the life consumption rate of each of the first portion and the second
portion. Thus, it is possible 5 to improve the accuracy of the master curve M.
[0073] (Case where first portion and second portion have different acting
stresses)
In the above-described embodiments, the master curve M represented by a
relationship between the damage index and the life consumption rate is acquired
based on the damage indexes of at least two portions with different creep damage
degrees due to the difference in temperature, such as the first portion 31 and the
second portion 32 shown in FIG. 2. However, in the boiler 10, as described later,
two different portions may have metal temperatures regarded as the same during
operation of the boiler, but different acting stresses during operation of the boiler.
[0074] FIG. 11 is a diagram showing the vicinity of a bend portion 27 of a
pipe 26 such as the main steam pipe 13 or the re-heated steam pipe 15. The pipe
has a portion connecting two pipes 26A, 26B extending in different directions
by a bend 26C, as shown in FIG. 11. The pipe 26A, 26B and the bend 26C are
connected by circumferential welding at ends. In the following, the portion at
which the ends of the pipe 26A, 26B and the bend 26C are connected is referred to
as a circumferential weld 60.
For example, as shown by the arrow F, when the pipe 26 receives a force
other than the internal pressure due to thermal expansion or own weight of the
pipe 26, bending stress is generated in the pipe 26, and even with the same
circumferential weld 60, the acting stress varies with the position in the
circumferential direction. Thus, even with the same circumferential weld 60, the
degree of damage may vary with the position in the circumferential direction.
For example, in FIG. 11, with respect to a first portion 61 and a second
portion 62 of the circumferential weld 60 in different circumferential positions,
the acting stress acting on the second portion 62 is greater than the acting stress
acting on the first portion 61, and the first 5 portion 61 and the second portion 62
have different degrees of damage.
[0075] However, in the same circumferential weld 60, regardless of the
circumferential position, the metal temperature is substantially the same as the
temperature of the internal steam in contact with the circumferential weld 60, and
the usage time is the same.
Then, in another embodiment of the creep life evaluation method described
below, damage indexes of at least two portions with different creep damage
degrees due to the difference in acting stress, such as the first portion 61 and the
second portion 62 described above, are acquired. Further, in the creep life
evaluation method according to the embodiment described below, the life
consumption rate of each of the at least two portions is evaluated, and a master
curve M represented by a relationship between the damage index and the life
consumption rate is acquired based on the evaluated life consumption rate and the
acquired damage index as described above.
In this way, in the creep life evaluation method according to the other
embodiment, since the master curve M is acquired using the damage index of the
boiler tube 30 used in the boiler 10, it is possible to eliminate the influence of
dependency on the temperature and the acting stress in the material creep behavior,
and improve the accuracy of the master curve M.
[0076] Hereinafter, the creep life evaluation method according to the other
embodiment will be described. In the following, differences from the creep life
evaluation method according to the above-described embodiments will be mainly
described. In the following, when the same process as the creep life evaluation
method according to above-described embodiments is performed, the same step
number as used in FIGs. 4 and 5 is used for the process, and detailed description
may be omitted.
[0077] (Damage index acquisition step S10)
In the damage index acquisition step S10 according to the other embodiment,
damage indexes of at least two portions with the same temperature and usage time
but different creep damage degrees due to the difference in acting stress, such as
the first portion 61 and the second portion 62 described above, are acquired.
[0078] (Life consumption rate evaluation step S20)
FIG. 12 is a flowchart showing an example of a schematic procedure of the
life consumption rate evaluation step S20 according to the other embodiment.
In the life consumption rate evaluation step S20 according to the other
embodiment, the life consumption rate of the portion where the damage index has
been acquired in the damage index acquisition step S10 is evaluated by the
following steps S205 to S209. In the following, the portion where the damage
index has been acquired in the damage index acquisition step S10 is also simply
referred a damage-index-acquired portion.
The life consumption rate evaluation step S20 of the other embodiment
includes a second parameter value acquisition step S205, a rupture time
acquisition step S207, and a life consumption rate calculation step S209.
[0079] In the second parameter value acquisition step S205 according to the
other embodiment, from the graph 42 representing the relationship between the
acting stress and the second parameter λ2 shown in FIG. 7, the value of the second
parameter λ2 corresponding to the acting stress of each damage-index-acquired
portion is acquired.
The acting stress of each damage-index-acquired portion can be obtained by
stress analysis considering operating conditions such as the steam temperature and
the steam pressure in the boiler 10.
For example, in the embodiment 5 shown in FIG. 11, in the second parameter
value acquisition step S205, the acting stress of each of the first portion 61 and the
second portion 62 of the circumferential weld 60 is obtained by stress analysis,
and the value of the second parameter λ2 of each of the first portion 61 and the
second portion 62 is acquired from the obtained acting stress and the graph 42
shown in FIG. 7.
[0080] In the rupture time acquisition step S207 according to the other
embodiment, for each of the damage-index-acquired portions, by substituting the
value of the second parameter λ2 acquired in the second parameter value
acquisition step S205 and the metal temperature during operation of the boiler 10
into the expression (1), the rupture time of each damage-index-acquired portion is
obtained.
The metal temperature of each damage-index-acquired portion may be
determined from the operating conditions of the boiler 10. Alternatively, if the
steam temperature in the pipe 26 such as the main steam pipe 13 and the re-heated
steam pipe is measured during operation of the boiler 10, this measurement
value may be used as the metal temperature of each damage-index-acquired
portion.
That is, for example in the embodiment shown in FIG. 11, in the rupture
time acquisition step S207, the rapture time of each of the first portion 61 and the
second portion 62 of the circumferential weld 60 is obtained by substituting the
value of the second parameter λ2 of each of the first portion 61 and the second
portion 62 acquired in the second parameter value acquisition step S205, and the
metal temperature of the first portion 61 and the second portion 62 during
operation of the boiler 10 determined as described above into the expression (1).
[0081] In the life consumption rate calculation step S209 according to the
other embodiment, the life consumption 5 rate of each of the damage-indexacquired
portions is obtained by dividing the usage time of each of the damageindex-
acquired portions by the rupture time obtained in the rupture time
acquisition step S207 for each of the damage-index-acquired portions.
As described above, if the damage indexes are obtained from the same
circumferential weld 60, the usage times of the damage-index-acquired portions
are the same.
For example, in the embodiment shown in FIG. 11, in the life consumption
rate calculation step S209, the life consumption rate of each of the first portion 61
and the second portion 62 of the circumferential weld 60 is obtained by dividing
the usage time of the first portion 61 and the second portion 62, i.e., the usage
time of the boiler 10 by the rupture time of each of the first portion 61 and the
second portion 62 obtained in the rupture time acquisition step S207.
[0082] Thus, in the life consumption rate evaluation step S20 according to the
other embodiment, the value of the second parameter λ2, related to the
temperature and the rupture time, of each of the first portion 61 and the second
portion 62 can be obtained, based on a relationship between the stress of the heatresistant
material and the second parameter λ2 of the heat-resistant material, and
the stress of each of the first portion 61 and the second portion 62. Further, in
the life consumption rate evaluation step S20 according to the other embodiment,
the rapture time of each of the first portion 61 and the second portion 62 can be
obtained, based on the value of the second parameter λ2 of each of the first
portion 61 and the second portion 62, and the temperature of each of the first
portion 61 and the second portion 62 during operation of the boiler 10.
Consequently, in the life consumption rate evaluation step S20 according to
the other embodiment, the life consumption rate of each of the first portion 61 and
the second portion 62 can be 5 easily obtained from the rupture time obtained as
described above and the operating time of the boiler 10.
[0083] In the other embodiment, during operation of the boiler 10, the
temperature of the second portion 62 can be regarded as the same as the
temperature of the first portion 61. Further, in the other embodiment, the acting
stress acting on the second portion 62 during operation of the boiler 10 is greater
than the acting stress acting on the first portion 61.
Since the first portion 61 and the second portion 62, which can be regarded
as the same in temperature but differ in acting stress during operation of the boiler
have different degrees of damage, two different damage indexes can be
acquired. As a result, since data of two different points on the master curve M
represented by a relationship between the damage index and the life consumption
rate can be acquired, it is possible to improve the accuracy of the master curve M.
[0084] In other embodiment, the second portion 62 is included in the same
circumferential weld 60 of the pipe 26 as the first portion 61, and the second
portion 62 is in a different position from the first portion 61 in the circumferential
direction.
[0085] As described above, generally, when the bending stress acts on the
pipe 26 due to the influence of thermal expansion and own weight of the pipe 26,
even with the same circumferential weld 60, the stress varies with the position in
the circumferential direction. Thus, in the other embodiment, since the first
portion 61 and the second portion 62 are included in the same circumferential
weld 60 but disposed in different positions in the circumferential direction, the
first portion 61 and the second portion 62 have temperatures that can be regarded
as the same, but different acting stresses during operation of the boiler 10.
Accordingly, in the other embodiment, since the first portion 61 and the second
portion 62 have different degrees of damage, 5 two different damage indexes can be
acquired. As a result, since data of two different points on the master curve M
represented by a relationship between the damage index and the life consumption
rate can be acquired, it is possible to improve the accuracy of the master curve M.
[0086] The present invention is not limited to the embodiments described
above, but includes modifications to the embodiments described above, and
embodiments composed of combinations of those embodiments.
For example, when the super-heater 12 according to the above-described
embodiments includes a primary super-heater and a secondary super-heater
connected to the primary super-heater connected in series, the pressure difference
between the primary super-heater and the secondary super-heater is only a
difference in the degree of pressure loss of the heat-transfer tube, for example, a
difference of about 1 Mpa. In this case, the acting stress of the heat-transfer tube
of the primary super-heater and the acting stress of the heat-transfer tube of the
secondary super-heater can be regarded as the same as described above, and the
difference in degree of damage between the heat-transfer tube of the primary
super-heater and the heat-transfer tube of the secondary super-heater is considered
due to the difference in temperature between the heat-transfer tube of the primary
super-heater and the heat-transfer tube of the secondary super-heater.
In this case, in the damage index acquisition step S10 according to the
above-described embodiments, the damage index may be acquired from each of
the heat-transfer tube of the primary super-heater and the heat-transfer tube of the
secondary super-heater.
Reference Signs List
[0087]
51 Power generation plant
10 Boiler
12 Super-heater
12B Super-heater tube (Heat-transfer tube)
13 Main steam pipe
10 14 Re-heater
15 Re-heated steam pipe
25 Heat exchanger
26 Pipe
27 Bend portion
15 30 Boiler tube
31, 61 First portion
32, 62 Second portion
51 Thermometer
60 Circumferential weld

I/We Claim:
1. A creep life evaluation method, comprising:
a damage index acquisition step of acquiring a damage index of each of a
first portion of a boiler tube used in a boiler and a second 5 portion of the boiler
tube in a different position from the first portion, the second portion being made
of a same material as the first portion;
a life consumption rate evaluation step of evaluating a life consumption rate
of each of the first portion and the second portion;
a correlation acquisition step of acquiring a correlation between the damage
index and the life consumption rate, based on the damage index of each of the first
portion and the second portion and the life consumption rate of each of the first
portion and the second portion;
an evaluation damage index acquisition step of acquiring a damage index of
an evaluation target tube; and
an evaluation step of evaluating a life consumption rate of the evaluation
target tube, based on the correlation and the damage index of the evaluation target
tube.
2. The creep life evaluation method according to claim 1,
wherein an acting stress acting on the second portion during operation of the
boiler can be regarded as the same as an acting stress acting on the first portion,
and
wherein a temperature of the second portion during operation of the boiler is
higher than a temperature of the first portion.
3. The creep life evaluation method according to claim 1 or 2,
wherein a plurality of heat exchangers including the boiler tube is disposed
inside a furnace of the boiler, and
wherein the second portion is included in a same heat exchanger as the first
portion, and the second portion is in 5 a different position from the first portion in a
furnace width direction.
4. The creep life evaluation method according to any one of claims 1 to 3,
further comprising a temperature measurement step of measuring a temperature of
the first portion and a temperature of the second portion during operation of the
boiler from outside a furnace,
wherein the life consumption rate evaluation step includes evaluating the life
consumption rate of each of the first portion and the second portion, using the
temperature of the first portion and the temperature of the second portion obtained
by measurement in the temperature measurement step.
5. The creep life evaluation method according to any one of claims 1 to 4,
wherein the life consumption rate evaluation step includes:
an average particle size acquisition step of obtaining an average
particle size of each of deposits of the first portion and the second portion;
a temperature calculation step of obtaining a temperature of each of
the first portion and the second portion during operation of the boiler, based on a
relationship between an average particle size of a deposit of a structure of a heatresistant
material made of the same material as the first portion and the second
portion and a first parameter related to a temperature and a usage time of the heatresistant
material, the average particle size of each of the deposits of the first
portion and the second portion, and a usage time of the first portion and the
second portion;
a second parameter value acquisition step of obtaining a value of a
second parameter related to a temperature and a rupture time of each of the first
portion and the second portion, based on a relationship between 5 an acting stress of
the heat-resistant material and the second parameter of the heat-resistant material,
and a stress of each of the first portion and the second portion; and
a rupture time acquisition step of obtaining a rapture time of each of
the first portion and the second portion, based on the value of the second
parameter of each of the first portion and the second portion, and the temperature
of each of the first portion and the second portion during operation of the boiler.
6. The creep life evaluation method according to claim 1,
wherein a temperature of the second portion during operation of the boiler
can be regarded as the same as a temperature of the first portion, and
wherein an acting stress acting on the second portion during operation of the
boiler is greater than an acting stress acting on the first portion.
7. The creep life evaluation method according to claim 1 or 6,
wherein the second portion is included in a same circumferential weld of the
boiler tube as the first portion, and the second portion is in a different position
from the first portion in a circumferential direction.
8. The creep life evaluation method according to claim 1, 6, or 7,
wherein the life consumption rate evaluation step includes:
a second parameter value acquisition step of obtaining a value of a
second parameter related to a temperature and a rupture time of each of the first
portion and the second portion, based on a relationship between a stress of a heatresistant
material made of the same material as the first portion and the second
portion and the second parameter of the heat-resistant material, and a stress of
5 each of the first portion and the second portion; and
a rupture time acquisition step of obtaining a rapture time of each of
the first portion and the second portion, based on the value of the second
parameter of each of the first portion and the second portion, and a temperature of
each of the first portion and the second portion during operation of the boiler.
9. The creep life evaluation method according to any one of claims 1 to 8,
wherein the damage index is any of a void number density, a tube
deformation, or a hardness.