JP5086615B2 - Life evaluation method by creep elongation of high strength steel weld and life evaluation method of high strength steel weld - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a life evaluation method by creep elongation of a high strength steel weld and a life evaluation method of a high strength steel weld, and in particular, welding of a joint portion of a high strength ferritic steel used for high temperature and high pressure equipment such as a thermal power plant. It is useful for evaluating creep damage in parts.

  Since, for example, a boiler or the like constituting a thermal power plant is operated in a high temperature and high pressure environment, damage due to creep or the like may be accumulated in the heat-resistant steel that is a material constituting the thermal plant due to long-term operation. Therefore, in the operation of this type of plant, it is important to ensure the stable operation over a long period of time by performing the life evaluation of the heat-resistant steel with high accuracy and maintaining the reliability of the pressure-resistant portion.

  It is known that when a heat resistant steel such as a boiler is subjected to creep damage, a creep void is generated in the heat resistant steel. Since this creep void increases with the progress of creep damage, the remaining life of the heat-resistant steel can be estimated by measuring the number density of creep voids per unit area of the observation surface and the area ratio of creep voids. ing. In addition, it is proposed to obtain a void number density change rate that is an increase of the void number density detected this time relative to the previously detected void number density, and to evaluate the remaining life of the heat resistant steel based on the void number density change rate. (Patent Document 1).

JP 2004-85347 A

  As a method for evaluating the remaining life other than creep voids, it is conceivable to measure elongation associated with creep, but in general, the heat-affected zone (HAZ) of joints such as heat-resistant steels has an absolute elongation before creep rupture. The value was small, and the remaining life of the heat-resistant steel could not be estimated by actually measuring the elongation in the heat-affected zone.

It is known that welds of high-strength ferritic steels such as 9-12Cr steel exhibit a creep fracture mode called type IV damage, but there is no internal cracking until the end of damage, and the damage behavior depends on the shape etc. May change significantly.
Therefore, there are the following problems when performing life evaluation.

1) Conventionally used low alloy steel such as ferritic steel represented by 2Cr steel has a large structural change when damaged, and it was easy to visually confirm the degree of damage. However, high-strength ferritic steels such as 9-12Cr steel have a stable structure and a small structural change due to creep damage. Therefore, it is difficult to visually determine the structural change and to determine the degree of damage. is there.

2) There is also a problem that it is difficult to compare the creep damage on the outer surface and the creep damage inside the plate thickness. This is because even if the creep damage is considered to be small on the surface, the internal creep damage may be large. In chromium-molybdenum steel represented by conventional 2Cr steel, the outer surface of the heat affected zone (HAZ) between the base metal and the weld metal (HAZ) and the amount of creep damage are interrelated, and the distribution of creep voids The modified 9Cr-1Mo high-strength ferritic steel, which has been widely used in recent years, has a large variation in the amount of creep damage between the outer surface and the inner surface, and even if the creep damage is small on the outer surface, it is damaged internally. Has been reported.
In addition, creep voids are usually the most directly beneath the outer surface, but non-destructive inspection may not allow grinding to that depth. Even if grinding is possible, an appropriate grinding amount may not be known on the spot.
In particular, in a bent portion at a long pipe end, the stress distribution in the plate thickness direction is complicated, and it is considered that the above problem is often remarkable.

3) In addition, the microcrack occurs at the end of life, and even if the crack is detected by ultrasonic flaw detection etc., the life after that is very small, and there is a high possibility that appropriate treatment cannot be performed. There is a problem.

  In this way, even if only the outer surface is inspected as in the past, internal damage cannot be judged, and the conventional non-destructive inspection method for low alloy steels has the remaining life of welds of high strength ferritic steels. It could not be used as a judgment evaluation method.

  Therefore, the advent of an evaluation method that can appropriately determine the remaining life of the welded portion of high-strength ferritic steel is desired.

  In view of the above problems, the present invention provides a life evaluation method based on creep elongation of a high-strength steel weld that can appropriately determine the remaining life of a weld of high-strength ferritic steel and a life evaluation method of a high-strength steel weld. This is the issue.

  The first invention of the present invention for solving the above-described problem is characterized in that the heat-affected zone (HAZ) of the joint to be inspected is defined as a predetermined range of the high-strength steel weld including at least one location. The base material and heat affected zone (HAZ) treatment range, or the creep elongation measuring step of the base material portion for measuring the creep elongation of the heat-affected portion of the predetermined range including the high strength steel welded portion, The measurement result obtained in the creep elongation measurement process of the base metal part is compared with the predetermined range of the high-strength steel base part in the initial operation or the length of the predetermined range including the high-strength steel base part. Creep strain measurement step of the base material portion for obtaining a predetermined range of the strength steel base material portion or a predetermined range including the high strength steel base material portion, and the creep strain obtained in the creep strain measurement step of the base material portion Creep strain in a given period from the value of The creep strain rate calculation step of the base material part for calculating the degree, and the result obtained in the creep strain rate calculation step of the base material part, the predetermined range of the high strength steel welded part or the predetermined range including the high strength steel welded part The creep strain rate characteristic curve showing the relationship between the creep strain rate conversion step of the weld to be converted into the creep strain rate and the creep strain rate with respect to the operation time or the creep life consumption rate obtained in advance, and the obtained high strength steel And a fourth life consumption rate measuring step for obtaining a life consumption rate of the inspection object by applying a value of a creep strain rate within a predetermined range of the welded portion or a predetermined range including the high strength steel welded portion. There is a life evaluation method by creep elongation of high strength steel welds.

The second invention is the life evaluation method by creep elongation of the high strength steel weld of the first invention, and the creep of the high strength steel weld of the creep void generated on the outer surface of the high strength steel weld to be inspected. It is in the life evaluation method of the high strength steel welded part characterized by using together with the life evaluation method by void measurement.

According to a third aspect of the present invention, in the second aspect , the void number density is a number per unit area of creep voids generated in the heat resistant steel to be inspected according to the life evaluation method by measuring creep voids of the high strength steel welded portion. A void number density detecting step for detecting the void number density, and a void number density changing step for obtaining a void number density changing rate that is an increase in the detected void number density with respect to the previously detected void number density by the void number density detecting step And applying the value of the obtained void number density change rate to the evaluation curve based on the void number density change rate indicating the relationship between the creep life consumption rate and the void number density change rate obtained in advance, The present invention is a life evaluation method for high-strength steel welds characterized by comprising a life consumption rate measuring step for obtaining a life consumption rate.

According to a fourth aspect of the present invention, in the second aspect , the life evaluation method based on creep void measurement of the high-strength steel weld zone is the void number density or void area ratio of the creep voids on the outer surface of the high-strength steel weld zone to be inspected. In the determination step of the void number density or the void area ratio for determining whether or not a predetermined threshold value or more from the measurement result of the surface void measurement step and the measurement result of the surface void measurement step, and in the determination step, a predetermined threshold value or less In this case, a remaining life measuring step for measuring the remaining life of the welded portion, a flaw detection inspection step for performing an internal ultrasonic flaw inspection (UT inspection) when the determination step is equal to or greater than a predetermined threshold, and the flaw detection In the inspection process, there is a defect evaluation process for determining the presence or absence of internal defects.

According to a fifth invention, in any one of the second to fourth inventions, the predetermined range including the high strength steel welded portion includes at least one heat affected zone (HAZ). It is in the life evaluation method for high strength steel welds.

  According to the life evaluation method based on the creep elongation of the high strength steel weld of the present invention and the life evaluation method of the high strength steel weld, the creep elongation of the location affected by the heat of the high strength steel weld is measured. Accordingly, the remaining life of the heat-resistant steel can be accurately predicted with low cost, and appropriate measures can be taken as necessary.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this reference example and embodiment. In addition, constituent elements in the following reference examples and embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

[Reference Example 1 ]
A life evaluation method based on creep elongation of a high strength steel weld according to Reference Example 1 will be described with reference to the drawings.
FIG. 1 is a flowchart illustrating a determination method of a life evaluation method based on creep elongation of a high-strength steel weld according to Reference Example 1 .
As shown in FIG. 1, the determination method of the life evaluation method by creep elongation of a high-strength steel weld is a weld that measures the creep elongation of a portion of the high-strength steel weld to be inspected that is affected by a predetermined range of heat. The creep elongation measurement step (S101) of the welded portion, the measurement result obtained in the creep elongation measurement step, and the length of the predetermined range of the high-strength steel welded portion in the initial operation are compared to determine the creep strain of the welded portion. By applying the obtained creep strain value to a creep strain characteristic curve showing the relationship between the creep strain measuring step (S102) and the preliminarily obtained operating time or creep life consumption rate and creep strain, the lifetime of the inspection object is applied. A first life consumption rate measuring step (S103) for obtaining a consumption rate, and a remaining life estimation step (S103) for estimating the remaining life of the weld from the life consumption rate obtained in the life consumption rate measurement step. 04) is made from a.

  Here, in the present invention, the high-strength steel welded portion is, for example, a welded portion of a joint portion of high-strength ferritic steel. Further, the predetermined range of the high-strength steel welded portion includes at least one heat affected zone (HAZ) of the joint portion to be inspected.

  Further, in the present invention, the creep elongation means that a predetermined range of distance at the time of measurement of the high-strength steel weld is measured in advance, and the predetermined range of distance of the high-strength steel weld before the start of operation or before measurement. It is the distance of the stretched amount.

Next, the creep elongation of the present invention will be described with reference to FIG. The distance of the predetermined range AB of the high-strength steel weld before the start of operation or before measurement (T ₀ ) of the inspection object is defined as X ₀ . The distance of the predetermined range AB of the high-strength steel welded portion when a predetermined period has elapsed from the start of operation of the inspection object (T ₁ ) is defined as X ₁ . Furthermore, the distance of the predetermined range AB of the high-strength steel welded part when a predetermined period has elapsed from the start of the operation to be inspected (T ₂ ) is X ₂ . At this time, the creep elongation of the predetermined range AB of the high-strength steel weld when a predetermined period has elapsed from the start of operation (T ₁ ) is α ₁ = X ₁ −X ₀ . And the creep elongation of the predetermined range AB of the high-strength steel welded portion when a predetermined period has elapsed from the start of rolling (T ₂ ) is α ₂ = X ₂ −X ₀ . This is repeated sequentially.

  The creep strain (ε) indicates how much the distance in the predetermined range at the time of measurement of the high-strength steel weld is extended with respect to the distance in the predetermined range of the high-strength steel weld before the start of operation. It is.

  For example, FIG. 3 shows an example of measurement of creep elongation using a test piece 14 described later. As shown in FIG. 3, in this test piece 14, the distance of the predetermined range decided beforehand is set to de. The distance measured before the start of the test is 3.97 mm, and the distance measured after a predetermined time has elapsed from the start of the test is 4.02 mm. In this case, the creep strain (ε) is ((4.02-3.97) /3.97) × 100 = 1.26%.

The present invention measures creep elongation in a predetermined time from the start of inspection of the predetermined range of the high-strength steel weld to be inspected. Then, by applying the obtained creep strain value to the creep strain characteristic curve showing the relationship between the time or creep life consumption rate and the creep strain obtained in advance, the lifetime consumption rate of the inspection object is obtained, and the remaining life is calculated. It is to be predicted.
Further, the remaining life means the time required from the creep strain at the time of measurement to the future fracture in consideration of the past use time.

Next, the measurement of creep elongation in the creep elongation measuring step (S101) in the present invention will be described with reference to FIG.
As shown in FIG. 3, the method for measuring the creep elongation of a portion of the high-strength steel welded portion to be inspected that has been affected by heat in a predetermined range is, for example, the base material 10 of the test piece 14 and the heat-affected zone (HAZ) 12. For example, six marks a to f are marked at predetermined positions.
Here, in this test example, the marks a to f are symmetrical with respect to a and f, b and e, and c and d with respect to the weld metal 11 portion.

In Reference Example 1 , as a method of marking a predetermined range of the high-strength steel welded portion, for example, there are a method of making an indentation, a method of oxidizing, a method of marking with non-oxidized ink, a method of providing a protrusion, and the like. .

  In FIG. 3, the distance between the marked ab and ef is the measurement distance of the base material 10. The distance between bc and de is the measurement distance of the heat affected zone (HAZ) 12.

  The measured distance of the base material 10 between ab and ef marked, and the measured distance of the heat affected zone (HAZ) 12 between bc and de is caliper or the like. Can be measured.

  In this test example, the distance between the base material 10 and the heat affected zone (HAZ) 12 is half of the total measurement distance between ab and ef, and between ab and e-. The measurement distance is averaged between f. In addition, the creep elongation of the heat affected zone (HAZ) 12 is half of the total measurement distance between bc and de, and the average of the measurement distance between bc and de Yes.

Further, in Reference Example 1 , a caliper is used to measure the creep elongation due to the thermal influence of the base material 10 and the heat affected zone (HAZ) 12 of the high strength steel welded portion to be inspected. The invention is not limited to this. For example, the distance between the base material 10 and the heat affected zone (HAZ) 12 may be measured using a commercially available high-temperature strain gauge.

  Further, more accurate measurement may be performed using a replica method. The replica method is a method of transferring a structure of a surface of heat-resistant steel subjected to a predetermined treatment, and measuring a distance between predetermined indentations provided in advance by visual observation or image processing based on this, thereby performing creep for a predetermined period. The distance of elongation can be measured.

  Further, the measured creep elongation may be temperature-corrected to the material temperature at the time of each measurement, and the distance of creep elongation for a predetermined period may be measured with high accuracy.

Although the reference example 1 is the treatment range of the base material 10 and the heat-affected zone (HAZ) 12 of the high-strength steel welded portion to be inspected as a range for measuring the length of creep elongation, the high-strength steel welded portion is used as the treatment range. A predetermined range of creep elongation may be measured.

  For example, the distance between be, which sandwiches both sides of the heat affected zone (HAZ) 12 of the test piece 14 shown in FIG. 3, or the distance between a, f, which sandwiches both sides of the heat affected zone (HAZ) 12 and the entire base material 10. The creep elongation for a predetermined period may be measured with half of the measured distance as the distance of the heat affected zone (HAZ) 12.

Moreover, FIG. 4 shows one of the measuring methods of the distance between de which is a heat affected zone (HAZ). As shown in FIG. 4, for example, a distance between De, which is an oblique distance between de, which is the heat affected zone (HAZ) 12, is measured. The distance between de is Y, and the distance between De is Z. At this time, it may be obtained by correcting to the distance between d and e by the following formula (I). As a result, the accuracy error can be reduced.
Y = cosZ (I)

In Reference Example 1 , since the distance between the base material 10 and the heat affected zone (HAZ) 12 can be easily measured using calipers or the like, the base material 10 and the heat affected zone (HAZ) 12 Distance can be measured easily and quickly.

  Here, the correlation between the creep elongation due to the thermal influence of the heat affected zone (HAZ) 12 and the base material 10 and time (t) will be described.

FIG. 5 is a diagram showing the relationship between creep elongation due to the heat effect of the heat affected zone (HAZ) and the base material and the passage of time (0 hours, 1000 hours, 2500 hours).
As shown in FIG. 5, the heat affected zone (HAZ) 12 of the base metal 10 provided with the weld metal 11 was previously marked with a predetermined distance (between de). At the initial stage of operation (0 hour), the predetermined distance X ₀ between de, which is the distance of the heat affected zone (HAZ) 12, was X ₀ = 3.97 mm, for example. In this state, for example, the test was held at 650 ° C. and a load of 66 MPa was applied. For example, at a stage after 1000 hours from the start of the test, the predetermined distance X ₁ between de of the heat affected zone (HAZ) 12 is, for example, X ₁ = 4.00 mm. Further, at a stage after 2500 hours have elapsed since the start of operation, for example, the predetermined distance X ₂ between de of the heat affected zone (HAZ) 12 is, for example, X ₂ = 4.02 mm. At this time, the time during which creep rupture occurred between de was 2678 hours, for example. In addition, creep voids 13 occurred in the heat affected zone (HAZ) 12 as time passed.
Here, creep rupture refers to a phenomenon in which, when a constant stress is kept under a certain temperature environment, the deformation progresses and breaks even with a stress lower than the tensile strength of the material.

As shown in the test results, it was confirmed that the distance of the heat affected zone (HAZ) 12 was increased by the heat effect as time passed. Therefore, by determining in advance the relationship between the creep elongation due to the heat effect and the time using the test piece, it is possible to predict the creep rupture timing of the inspection object.
When conditions such as the material to be inspected, temperature, and specific gravity change, the test may be performed each time.

  Next, in the creep strain measurement step (S102), the measurement result obtained in the creep elongation measurement step (S101) is compared with the length of the predetermined range of the high strength steel weld in the initial stage of operation to determine the creep strain ( ε) is obtained.

  Next, in the lifetime consumption rate measuring step (S103), the first or second creep indicating the relationship between the predetermined operation time (t) or creep lifetime consumption rate (t / tr) and creep strain (ε). By applying the value of the creep strain obtained in the creep strain measuring step (S102) to the strain characteristic curve, the lifetime consumption rate (t / tr) of the inspection object is obtained.

  Here, of the creep strain characteristic curves, the first creep strain characteristic curve is a curve (FIG. 6 described later) showing the relationship between the creep time (t) and the creep strain (ε), and the second creep strain. The characteristic curve is a curve (FIG. 7 described later) showing the relationship between the creep life consumption rate (t / tr) and the creep strain (ε).

  Next, a method for testing the first and second creep strain characteristic curves will be described.

  In FIG. 3, a test piece 14 welded to the above-described weld metal 11 shown in FIG. 3 was used as a large-sized test piece used in this test.

  In this test example, in order to produce a damaged material that simulates the creep damage of an actual boiler weld, “fire SCMV28” (thickness: 32 mm steel plate), which is a commercially available modified 9Cr-1Mo steel, was used. And the joint was manufactured by covering arc welding, and the large-sized creep test piece (32x40mm cross section) including a welding part was extract | collected there.

  Table 1 shows the chemical composition of the test steel. As shown in Table 1, the chemical composition of the test steel is Wt%, C is 0.09%, Si is 0.36%, Mn is 0.46%, P is 0.009%, and S is 0.001%, Cr 8.49%, Mo 0.98%, Ni 0.26%, V 0.2%, Sol. Al was 0.01% and N was 0.005%.

Next, a method for measuring creep elongation will be described.
As shown in FIG. 3, the test piece 14 was marked at six points a to f. The distance between ab and ef was the measurement distance in the base material 10. The distance between bc and de was the measurement distance in the heat affected zone (HAZ) 12.

  First, before starting the test, a predetermined distance between bc and de of the heat affected zone (HAZ) 12 of the test piece 14 and between a and b and ef of the base material 10 are preliminarily determined. A predetermined distance was measured. In this test example, an indentation was previously provided as a mark, and the test was performed. And the predetermined distance between these indentations was measured with a caliper.

  Then, the test piece 14 is held at 650 ° C., a load of 66 MPa is applied to stop the test piece 14 a plurality of times, and a predetermined distance between ab and ef of the base material 10 of the test piece 14 is The predetermined distance between bc and de of the heat affected zone (HAZ) 12 was measured.

  Further, in this test example, the predetermined distance of the base material 10 is the average value of the creep elongation of the base material 10 as half of the total of the predetermined distances between ab and ef. Further, the predetermined distance of the heat affected zone (HAZ) 12 is an average value of the creep elongation of the heat affected zone (HAZ) 12 as a half of the total of the predetermined distance between bc and de.

  The test piece 14 was regarded as an actual machine weld, and life evaluation was performed according to the life evaluation determination flow shown in FIG.

The creep elongation of the heat affected zone (HAZ) 12 of this test, the creep strain (ε) of the heat affected zone (HAZ) 12, and the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 are shown. It is shown in 2.
In this test, since the creep rupture finally occurred at 2678 hours (tr), the creep life consumption rate (t / tr) was set to the value of the measurement time (t) with respect to 2678 hours (tr) after the creep rupture.

Table 3 shows the creep elongation of the base material 10, the creep strain (ε) of the base material 10, and the creep life consumption rate (t / tr) of the base material 10 in this test.
Further, the creep life consumption rate (t / tr) was the value of the measurement time (t) with respect to 2678 hours (tr) when the creep rupture occurred as described above.

(1) When the creep time (t) was 0 hour (before the test), the creep elongation of the heat affected zone (HAZ) 12 and the base material 10 was 0.00 mm.
At this time, the creep strain (ε) of the heat affected zone (HAZ) 12 and the base material 10 was 0.00%.
Further, the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 and the base material 10 was 0.0%.

(2) When the creep time (t) was 1037.0 hours, the creep elongation of the heat affected zone (HAZ) 12 was 0.03 mm, and the creep elongation of the base material 10 was 0.62 mm.
At this time, the creep strain (ε) of the heat affected zone (HAZ) 12 was 0.40%, and the creep strain (ε) of the base material 10 was 0.32%.
Further, the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 and the base material 10 was 37.4%.

(3) When the creep time (t) was 1507.5 hours, the creep elongation of the heat affected zone (HAZ) 12 was 0.05 mm, and the creep elongation of the base material 10 was 0.64 mm.
At this time, the creep strain (ε) of the heat affected zone (HAZ) 12 was 0.66%, and the creep strain (ε) of the base material 10 was 0.33%.
Further, the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 and the base material 10 was 54.3%.

(4) When the creep time (t) was 2004. 4 hours, the creep elongation of the heat affected zone (HAZ) 12 was 0.16 mm, and the creep elongation of the base material 10 was 0.99 mm.
At this time, the creep strain (ε) of the heat affected zone (HAZ) 12 was 2.12%, and the creep strain (ε) of the base material 10 was 0.51%.
Further, the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 and the base material 10 was 72.2%.

(5) When the creep time (t) was 2500.0 hours, the creep elongation of the heat affected zone (HAZ) 12 was 0.16 mm, and the creep elongation of the base material 10 was 1.22 mm.
At this time, the creep strain (ε) of the heat affected zone (HAZ) 12 was 2.12%, and the creep strain (ε) of the base material 10 was 0.63%.
Further, the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 and the base material 10 was 90.0%.

(6) When the creep time (t) is 2678.0 hours (creep rupture), the creep elongation of the heat affected zone (HAZ) 12 is 2.02 mm, and the creep elongation of the base material 10 is 1.91 mm. there were.
At this time, the creep strain (ε) of the heat affected zone (HAZ) 12 was 26.72%, and the creep strain (ε) of the base material 10 was 0.98%.
Moreover, the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 and the base material 10 was 100%.

  Below, the correlation between the creep strain (ε) and the creep time (t) or creep strain rate (ε / t) due to the thermal effect of the heat affected zone (HAZ) 12 and the base material 10 in the test results is shown. The figure is shown.

FIG. 6 is a diagram showing the relationship between the creep time (t) and the creep strain (ε) of the test results.
Further, the curve in the figure is a first creep strain characteristic curve showing the relationship between the creep time (t) and the creep strain (ε).
As shown in FIG. 6, the creep strain (ε) of the heat affected zone (HAZ) 12 was higher than the creep strain (ε) of the base material 10 from the start of operation. The creep strain (ε) of the heat-affected zone (HAZ) 12 increased gently from the start of operation to about 2004. 4 hours. The creep strain (ε) of the heat-affected zone (HAZ) 12 rapidly increased from about 2500.0 hours after the start of operation until 2678.0 hours when creep rupture occurred. On the other hand, the creep strain (ε) of the base material 10 gradually increased from the start of operation to 2678.0 hours.

  Therefore, it is confirmed that the creep strain (ε) of the heat-affected zone (HAZ) 12 due to the thermal effect is gentle and not so changed during the creep time (t) from 0.0 hours to 2004.4 hours. It was done. Then, it was confirmed that the creep strain (ε) of the heat affected zone (HAZ) 12 suddenly increased and creep ruptured from 2500.0 hours close to creep rupture to 2678.0 hours when creep ruptured. It was done.

  Thus, the first creep strain characteristic curve showing the relationship between the creep time (t) and the creep strain (ε) as shown in FIG. 6 is obtained in advance by repeating the heat resistant steel many times until it breaks. The remaining life of the heat-resistant steel heat-affected zone (HAZ) can be predicted by applying the creep strain (ε) detected by the above method to the first creep strain characteristic curve shown in FIG.

FIG. 7 is a graph showing the relationship between the creep life consumption rate (t / tr) and the creep strain (ε) as a test result.
The curve in the figure is a second creep strain characteristic curve showing the relationship between the creep life consumption rate (t / tr) and the creep strain (ε).
The creep life consumption rate (t / tr) was defined as 100% based on 2678.0 hours after creep rupture.

  As shown in FIG. 7, the relationship between the creep life consumption rate (t / tr) and the creep strain (ε) is similar to the relationship between the creep time (t) and the creep strain (ε) shown in FIG. Indicated. From this result, it was confirmed that the relationship between time (t) and creep strain rate (ε / t) can be replaced with the relationship between creep life consumption rate (t / tr) and creep strain (ε). .

  Therefore, it was confirmed that the creep life consumption rate (t / tr) of the heat-affected steel heat-affected zone (HAZ) can be predicted from the creep strain (ε).

  As described above, the second creep strain characteristic curve showing the relationship between the creep life consumption rate (t / tr) and the creep strain (ε) as shown in FIG. Get it. Then, by applying the creep strain (ε) detected by the above method to the second creep strain characteristic curve shown in FIG. 7, the creep life consumption rate (t / tr) of the heat-resistant steel heat-affected zone (HAZ) is obtained. The remaining life of the heat-resistant steel heat-affected zone (HAZ) can be predicted.

Further, in Reference Example 1 , the high-strength steel welded portion to be inspected is not limited to high-strength ferritic steel, particularly improved 9Cr-1Mo steel, and the present invention also applies to other heat-resistant steels. By obtaining the creep life evaluation rate by the method, the remaining life of the welded part of other heat-resistant steel can be predicted.

  In the remaining life estimation step (S104), the remaining life of the welded portion to be inspected is estimated from the creep life consumption rate of the inspection object obtained in the life consumption rate measuring step (S103).

Next, in the remaining life determination step (S105), the remaining life is determined from the remaining life value obtained in the remaining life estimation step (S104).
As a result of the determination of the remaining life, if the remaining life of the inspection object is a predetermined time (for example, 2 years, about 17,000 hours) or more, re-inspection may be performed after the predetermined period has elapsed (S106). ).

  Further, if the remaining life is not more than a predetermined time (for example, about 17,000 hours, for example, 2 years), the possibility of breakage is high until the next inspection, so that a necessary action is taken (S107). ).

  This makes it possible to propose a creep evaluation method for welds of high-strength ferritic steel that has not had an appropriate creep damage evaluation method in the past, and it is possible to ensure the reliability of heat-resistant steel and prevent blasting accidents.

[ Reference Example 2 ]
A life evaluation method by creep elongation of a high strength steel weld according to Reference Example 2 will be described with reference to the drawings.
FIG. 8 is a flowchart showing a determination method of a life evaluation method based on creep elongation of a high-strength steel weld according to this reference example .
As shown in FIG. 8, the determination method of the life evaluation method based on the creep elongation of the high strength steel welded portion is a welding for measuring the creep elongation of a predetermined range of the heat affected portion of the high strength steel welded portion to be inspected. The creep elongation measurement step (S201) of the welded portion, the measurement result obtained in the creep elongation measurement step, and the length of the predetermined range of the high-strength steel welded portion in the initial operation are compared to determine the creep strain of the welded portion. A creep strain measuring step (S202), a weld strain creep strain rate calculating step (S203) for calculating a creep strain rate in a predetermined period from the creep strain value obtained in the creep strain measuring step (S202), The value of the obtained creep strain rate is applied to the creep strain rate characteristic curve showing the relationship between the operating time or creep life consumption rate and the creep strain rate. In addition, a second lifetime consumption rate measuring step (S204) for obtaining the lifetime consumption rate of the inspection object, and a remaining lifetime for estimating the remaining lifetime of the weld from the lifetime consumption rate obtained in the lifetime consumption rate measuring step. It consists of an estimation process (S205).

In the present reference example , the creep elongation measurement step (S201) and the creep strain measurement step (S202) are affected by a predetermined range of heat affected by the high-strength steel weldment to be inspected described in reference example 1. The creep elongation measuring step (S101) of the welded portion for measuring the creep elongation of the steel sheet, the measurement result obtained in the creep elongation measuring step, and the length of the predetermined range of the high strength steel welded portion in the initial operation are compared. Since this is the same step as the creep strain measurement step (S102) for obtaining the creep strain, description thereof will be omitted.

In the creep strain rate calculation step (S203) of the welded portion, the creep strain rate (ε / t) is calculated from the creep strain value obtained in the creep strain measurement step (S202) and a predetermined time (here, the unit is t). ) Is calculated.
The creep strain rate (ε / t) refers to a value obtained by differentiating the creep strain (ε) value over a predetermined time.

  Next, in the second life consumption rate measuring step (S204), the first or second creep strain rate characteristic curve indicating the relationship between the operation time or creep life consumption rate obtained in advance and the creep strain rate is added to the previous curve. By applying the obtained creep strain rate (ε / t), the creep life consumption rate (t / tr) of the inspection object is obtained.

  Here, among the creep strain rate characteristic curves, the first creep strain rate characteristic curve is a curve (FIG. 9 to be described later) showing the relationship between the creep time (t) and the creep strain rate (ε / t). The second creep strain rate characteristic curve is a curve (FIG. 10 described later) showing the relationship between the creep life consumption rate (t / tr) and the creep strain rate (ε / t).

  Next, the correlation between the creep strain rate (ε / t) due to the thermal effect of the heat affected zone (HAZ) 12 and the base material 10 and time (t) or creep life consumption rate (t / tr) is shown. A test method for the first and second creep strain rate characteristic curves will be described.

In this test example, the test example studied in Reference Example 1 was used.
As the creep strain rate (ε / t), a value obtained by differentiating the creep strain (ε) obtained in the test example studied in Reference Example 1 with a predetermined time (t) was used.
Note that the test conditions and the measurement method are the same as those in the test example studied in Reference Example 1 , and thus the description thereof is omitted here.

  Below, the correlation between the creep strain rate (ε / t) and the time (t) or the creep life consumption rate (t / tr) due to the thermal effect of the heat affected zone (HAZ) 12 and the base material 10 in the test results Show the relationship.

FIG. 9 is a diagram showing the relationship between the creep time (t) and the creep strain rate (ε / t).
Further, the curve in the figure is a first creep strain rate characteristic curve showing the relationship between the creep time (t) and the creep strain rate (ε / t).
As shown in FIG. 9, the creep strain rate (ε / t) was higher in the heat affected zone (HAZ) 12 than in the base material 10. The creep strain rate (ε / t) of the heat affected zone (HAZ) 12 and the base material 10 decreased immediately after the start of operation. Then, after the time point at which the creep strain rate (ε / t) becomes the minimum creep strain rate becomes the smallest, the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 and the base material 10 increases. did.

In addition, the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 reached the minimum creep strain rate earlier than the creep strain rate (ε / t) of the base material 10. At this time, the minimum creep strain rate (ε / t) of the heat affected zone (HAZ) 12 was 2.0 × 10 ⁻⁴ % / h at about 800 hours. The minimum creep strain rate (ε / t) of the base material 10 was 4.6 × 10 ⁻⁵ % / h at about 1050 hours.

  In addition, when the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 decreases with time, the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 becomes the smallest. Since it can be determined that the time point at which the minimum creep strain rate is reached has not passed, it can be determined that the test time is about 800 hours before.

  Further, when the creep strain rate (ε / t) of the base material 10 decreases with time, it can be determined that the time point at which the minimum creep strain rate of the base material 10 is reached has not passed, so the test time is It can be determined that about 1050 hours have elapsed.

Therefore, when the measured value is lower than the previous measured value, the portion to be inspected has not yet passed the inflection point of the first creep strain rate characteristic curve. At this time, it can be determined that the endurance time of the portion to be inspected is sufficient, and the life of the portion to be inspected is still sufficient.

  When the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 increases with time, the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 is the smallest. Since it can be determined that the time point at which the minimum creep strain rate is reached has already passed, it can be determined that the test time of the heat affected zone (HAZ) 12 has passed about 800 hours.

  In addition, when the creep strain rate (ε / t) of the base material 10 increases with time, it can be determined that the time point at which the base material 10 reaches the minimum creep strain rate has already passed, so the test time It can be determined that about 1050 hours have passed.

  Therefore, when the measured value becomes larger than the previous measured value, the portion to be inspected has already passed the inflection point of the first creep strain rate characteristic curve. At this time, it can be determined that the endurance time of the portion to be inspected is short and the replacement time of the portion to be inspected is close.

  Thus, the first creep strain rate characteristic curve of the creep time (t) and the creep strain rate (ε / t) as shown in FIG. 9 is obtained in advance by repeating the heat resistant steel many times until it breaks. Then, the creep strain rate (ε / t) detected by the above method is applied to the first creep strain characteristic curve shown in FIG. 9, and whether the value of the creep strain rate (ε / t) increases or decreases with time. By confirming the presence or absence, the remaining life of the inspection object can be predicted.

FIG. 10 is a graph showing the relationship between the creep life consumption rate (t / tr) and the creep strain rate (ε / t).
Further, the curve in the figure is a second creep strain rate characteristic curve showing the relationship between the creep life consumption rate (t / tr) and the creep strain rate (ε / t).

  As shown in FIG. 10, the relationship between the creep life consumption rate (t / tr) and the creep strain rate (ε / t) is the same as the relationship between the creep time (t) and the creep strain (ε) shown in FIG. The behavior was shown.

  From the results of FIG. 10, the relationship between the creep time (t) and the creep strain rate (ε / t) is replaced with the relationship between the creep life consumption rate (t / tr) and the creep strain rate (ε / t). It was confirmed that Therefore, it was confirmed that the creep life consumption rate (t / tr) can be predicted from the creep strain rate (ε / t).

  The creep life consumption rate (t / tr) at the time when the creep strain rate (ε / t) of the heat-affected zone (HAZ) 12 reached the minimum creep strain rate was about 30%.

  Further, the creep life consumption rate (t / tr) was about 38% when the creep strain rate (ε / t) of the base material 10 reached the minimum creep strain rate.

  In addition, when the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 decreases with time, the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 becomes the smallest. Since it can be determined that the time point at which the minimum creep strain rate is reached has not passed, it can be determined that the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 is about 30% or less.

  In addition, when the creep life consumption rate (t / tr) of the base material 10 decreases with the passage of time, it can be determined that the time point at which the base material 10 reaches the minimum creep strain rate has not passed. It can be determined that the creep life consumption rate (t / tr) of the material 10 is about 38 or less.

  Therefore, when the measured value is lower than the previous measured value, the portion to be inspected has not yet passed the inflection point of the second creep strain rate characteristic curve. At this time, it can be determined that the endurance time of the portion to be inspected is sufficient, and the life of the portion to be inspected is still sufficient.

  When the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 increases with time, the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 is the smallest. Since it can be determined that the time point at which the minimum creep strain rate is reached has already passed, it can be determined that the creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 is about 30% or more.

  In addition, when the creep strain rate (ε / t) of the base material 10 increases with time, it can be determined that the time point at which the base material 10 reaches the minimum creep strain rate has already passed. It can be determined that the creep life consumption rate (t / tr) of the material 10 is about 38% or more.

  Therefore, when the measured value becomes larger than the previous measured value, the part to be inspected has already passed the inflection point of the second creep strain rate characteristic curve. At this time, it can be determined that the endurance time of the portion to be inspected is short and the replacement time of the portion to be inspected is close.

  As described above, the second creep strain rate characteristic curve of the creep life consumption rate (t / tr) and the creep strain rate (ε / t) as shown in FIG. Get it. Then, the creep strain rate (ε / t) detected by the above method is applied to the second creep strain rate characteristic curve shown in FIG. 10, and the value of the creep strain rate (ε / t) increases or decreases with time. By confirming whether or not to do so, the remaining life of the inspection object can be predicted.

  Next, in the remaining life estimation step (S205), the remaining life of the welded portion to be inspected is estimated from the creep life consumption rate of the inspection object obtained in the life consumption rate measuring step (S204).

  In the remaining life determination step (S206), the remaining life is determined from the remaining life value obtained in the remaining life estimation step (S205).

Since the subsequent processing method performed based on the result of the remaining life determination in the remaining life determination step (S206) is the same as that of the reference example 1 , description thereof is omitted.

  This makes it possible to propose a creep evaluation method for welds of high-strength ferritic steel that has not had an appropriate creep damage evaluation method in the past, and it is possible to ensure the reliability of heat-resistant steel and prevent blasting accidents.

[ First embodiment]
A life evaluation method for a high strength steel weld according to a first embodiment of the present invention will be described with reference to the drawings.
FIG. 11 is a flowchart showing a determination method of the life evaluation method for the high-strength steel weld according to this embodiment.
As shown in FIG. 11, the thermal life evaluation method for a high strength steel weld according to this embodiment includes a life evaluation method based on creep elongation of the high strength steel weld and an outer surface of the high strength steel weld to be inspected. It is formed by using together with a life evaluation method based on creep void measurement of a high strength steel weld of a creep void generated in the above.

The thermal life evaluation method by the creep elongation of the high strength steel weld zone of the present embodiment uses the life evaluation method by the creep elongation of the high strength steel weld zone of Reference Example 1 shown in FIG.

The creep elongation measurement step (S301), the creep strain measurement step (S302), the life consumption rate measurement step (S303), and the first remaining life estimation step (S304) in the present embodiment are the inspections of Reference Example 1 . The creep elongation measurement step (S101) of the welded portion for measuring the creep elongation of the portion of the target high-strength steel welded portion that has been affected by heat in a predetermined range, the measurement result obtained in the creep elongation measuring step, and the operation The relationship between the creep strain measurement step (S102) of the welded portion for obtaining the creep strain by comparing the length of the predetermined range of the initial high-strength steel welded portion, and the relationship between the operation time or the creep life consumption rate obtained in advance and the creep strain. A first lifetime consumption rate measuring step (S103) for obtaining the lifetime consumption rate of the inspection object by applying the obtained creep strain value to the creep strain characteristic curve indicating Since the remaining lifetime estimation step from the obtained lifetime consumption rate life consumption rate measuring step guess remaining life of the welded portion (S104) and are respectively similar process, explanation is omitted.

Moreover, the thermal life evaluation method by the creep elongation of the high strength steel welding part of this embodiment may use the life evaluation method by the creep elongation of the high strength steel welding part of the reference example 2 shown in FIG.
That is, the thermal life evaluation method based on the creep elongation of the high strength steel weld of the present embodiment is predetermined from the value of the creep strain (ε) obtained as a parameter for examining the threshold for determination for estimating the remaining life of the inspection object. A step of calculating a creep strain rate (ε / t) in the period is added. Then, the remaining life of the inspection object may be determined based on the obtained creep strain rate (ε / t).

  Next, in the remaining life determination step (S305), the remaining life is determined from the remaining life value obtained in the first remaining life estimation step (S304).

  In the result of the determination of the remaining life by the thermal life evaluation method of the high strength steel welded portion, when it is longer than a predetermined time (for example, about 17,000 hours, for example, 2 years), re-inspection is performed after elapse of the predetermined time (S306). .

When the remaining life is determined to be less than a predetermined time (for example, about 17,000 hours, for example, 2 years), a life evaluation method based on creep void measurement is used (S307). Then, in the determination step (S308) by creep void measurement, the remaining life is determined from the remaining life value obtained from the creep void measurement step (S307).
If the remaining life of the inspection object is longer than a predetermined time (for example, 2 years, about 17,000 hours) as a result of the determination of the remaining life, re-inspection may be performed after a predetermined period.
If the remaining life is less than a predetermined time (for example, about 17,000 hours, for example, 2 years), there is a high possibility that it will break before the next inspection, so that a necessary action is taken (S309). ). Thereby, the remaining life of the heat-resistant steel to be inspected is more accurately evaluated.

  Below, the determination method by the creep void measurement of the life evaluation method of the high strength steel welding part which concerns on this embodiment is demonstrated.

FIG. 12 is a flowchart showing an example of a determination method based on creep void measurement in the method for evaluating the life of a high-strength steel weld according to this embodiment.
As shown in FIG. 12, the life evaluation method by creep void measurement of the high-strength steel welded portion is a predetermined time (for example, 2 years) in the determination result of the remaining life in the remaining life determination step (S305) shown in FIG. , Approximately 17,000 hours) or less, a void number density detecting step (S401) for detecting a void number density which is the number per unit area of creep voids generated in the heat-resistant steel to be inspected, A void number density change rate step (S402) for obtaining a void number density change rate that is an increase in the void number density detected this time with respect to the previously detected void number density in the void number density detection step, and a creep life consumption rate obtained in advance An evaluation curve based on the void number density change rate indicating the relationship between the void number density change rate and the void number density change rate is included in the void number density change rate step (S402). By applying the value of the void number density change rate obtained have, those consisting the life consumption rate measuring step of determining the life consumption rate of the test object (S403). From this lifetime consumption rate, the remaining lifetime of the welded portion is estimated (S404).

  In the void number density detecting step (S401), a void number density, which is the number per unit area of creep voids generated in the heat resistant steel to be inspected, is obtained.

  Next, in the void number density change rate step (S402), a void number density change rate that is an increase in the void number density detected this time with respect to the previously detected void number density is obtained.

  Next, in the lifetime consumption rate measurement step (S403), the void number density evaluation curve based on the void number density change rate indicating the relationship between the creep lifetime consumption rate and the void number density change rate obtained in advance is added to the void number density evaluation curve. By applying the void number density change rate value obtained in the change rate step (S402), the creep life consumption rate (t / tr) of the inspection object is obtained.

Next, the remaining life of the heat resistant steel is evaluated based on the creep life consumption rate (t / tr) obtained in the life consumption rate measuring step (S403) (S404).
Then, in the determination step (S405) based on creep void measurement, the remaining life is determined from the remaining life value obtained from the remaining life estimation step (S404).
If the remaining life of the inspection object is longer than a predetermined time (for example, 2 years, about 17,000 hours) as a result of the remaining life determination, re-inspection may be performed after the predetermined period has elapsed (S406). ).
If the remaining life is not longer than a predetermined time (for example, about 17,000 hours, for example, 2 years), the possibility of breakage by the next inspection is high, so that a necessary action is taken (S407). ).

  As described above, the remaining life of the inspection object can be accurately predicted by using the void number density evaluation curve based on the void number density change rate.

  Next, another method showing a determination method based on creep void measurement in the method for evaluating the life of a high-strength steel weld according to this embodiment will be described.

FIG. 13 is a flowchart showing another example of a determination method based on creep void measurement of the method for evaluating the life of a high-strength steel weld according to this embodiment.
As shown in FIG. 13, the determination method of the life evaluation method of the high-strength steel welded portion is a predetermined time (for example, about two years, about the remaining life determination result in the remaining life determination step (S 305) shown in FIG. 11. 17,000 hours) or less, a surface void measuring step (S501) for measuring the void number density (pieces / mm ² ) of the creep voids on the outer surface of the high strength steel weld to be inspected, and the surface void In the void number density determination step (S502) for determining whether or not a predetermined threshold value is exceeded or not based on the measurement result of the measurement step (S501), and when the void number density determination step (S502) is equal to or less than the predetermined threshold value, welding is performed. In the remaining life estimation step (S503) for measuring the remaining life of the part and the void number density determination step (S502), an internal ultrasonic flaw inspection (UT inspection) is performed when a predetermined threshold value is exceeded. Scratches inspection step (S504), in the flaw inspection step (S504), it is made from a determined defect judgment step whether the internal defects (S505).

In the surface void measuring step (S501), an inspection is performed to measure the void number density (pieces / mm ² ), which is the number per unit area of creep voids on the outer surface of the high strength steel weld to be inspected (S501). .

In the void number density determination step (S502), it is determined from the measurement result of the surface void measurement step (S501) whether or not a predetermined threshold value or more. In FIG. 13, the number of voids is determined by setting a predetermined threshold value to 120 / mm ² .

Between the void number density and the void area ratio, because it has a phase function relationship shown in FIG. 14, the void number density of 120 / mm ² is equivalent to 0.047% of the void area ratio, since Can also be converted using the same interphase relationship.

In the void number density determination step (S502), it is assumed that a crack is inherent as shown in FIG. 13 for the remaining life of the weld when the predetermined threshold value (120 pieces / mm ² ) or less is used. The remaining life is estimated (S503).

Note that the threshold value (120 pieces / mm ² ) is the case of the improved 9Cr-1Mo high-strength ferritic steel that has been widely used in recent years. In the case of other materials, the threshold value (120 pieces / mm ² ) is obtained from the creep life consumption rate as described above. do it.

  Further, in this embodiment, the void number density is measured and determined as a parameter for examining the determination threshold. However, the present invention is not limited to this, and the void area ratio is measured and determined. It may be.

  Here, the void number density method for measuring the void number density is to measure the number density of voids in the area in, for example, four fields of view (photo size: 120 mm × 80 mm) of an optical microscope having a magnification of 300 times. . Note that when the magnification is 500 times (for example, SEM), 10 fields of view are used.

  On the other hand, the void area ratio method measures the area ratio of voids in the area in, for example, four visual fields (photo size: 120 mm × 80 mm) of an optical microscope having a magnification of 300 times. In addition, when the magnification is 500 times, 10 visual fields are used.

  In the case of the void area ratio method, the area ratio does not vary by performing the optimum etching process. Further, by using a digital image processing system, the measurement time can be shortened.

FIG. 14 shows an example of a correlation diagram between the void number density and the void area ratio.
In the present embodiment, a determination method using a void number density parameter will be described.

In the void number density determination step (S502), if the value is equal to or greater than a predetermined threshold (120 pieces / mm ² ), an internal ultrasonic inspection (UT inspection) is performed (S504). This is because, when the threshold value is equal to or greater than the predetermined threshold value, it is necessary to perform a UT inspection which is a nondestructive inspection because there is a high probability that a defect exists inside.

In this nondestructive inspection, the presence or absence of an internal defect is determined (S505).
If there is no internal defect, re-inspection is performed after a predetermined time (S506).
As a result of this inspection, if there is an internal result, a necessary action is taken (S507).

Here, the remaining life time is further determined (S508).
If the remaining life is determined to be longer than a predetermined time (for example, 2 years, about 17,000 hours), the inspection may be re-inspected after the predetermined period has elapsed (S506).

  If the remaining life is less than a predetermined time (for example, about 17,000 hours, for example, 2 years), the breakage is likely to occur until the next inspection, and therefore, a necessary action is taken.

Further, if the remaining life determination result is less than a predetermined time (for example, about 17,000 hours for 2 years), an internal ultrasonic inspection (UT inspection) is performed (S504).
This is to confirm the fact that there is a high possibility that an internal crack has occurred.

If a crack is detected, the possibility of a crack caused by creep damage is high, so that a necessary action is taken (S507).
If there is no defect, re-inspection is performed after a predetermined period (S506).

  As a result, the remaining life is determined from the creep voids on the outer surface, ultrasonic inspection is performed, and the presence or absence of defects is determined to determine the presence or absence of internal damage, and appropriate measures are taken as necessary. be able to.

As described above, when the remaining life of the heat-resistant material is predicted by measuring the creep elongation of the welded portion by the method of Reference Example 1 or Reference Example 2 , if the remaining life of the heat-resistant material is short, high strength by creep void measurement is used. By using the method for evaluating the life of steel welds in combination, the remaining life can be accurately predicted.

[ Second Embodiment]
A life evaluation method based on creep elongation of a high-strength steel weld according to a second embodiment of the present invention will be described with reference to the drawings.
FIG. 15 is a flowchart showing a determination method of a life evaluation method based on creep elongation of a high-strength steel weld according to this embodiment.
As shown in FIG. 15, the life evaluation method by creep elongation of the high-strength steel weld according to this embodiment is a predetermined range of the high-strength steel base material to be inspected or a predetermined range including the high-strength steel base material. The creep elongation measurement step (S601) of the base material portion for measuring the creep elongation of the location affected by the heat, the measurement results obtained in the creep elongation measurement step (S601) of the base material portion, and the initial operation The predetermined range of the high-strength steel base material part or the predetermined range including the high-strength steel base material part by comparing the predetermined range of the high-strength steel base material part or the length of the predetermined range including the high-strength steel base material part A base material portion for calculating a creep strain rate in a predetermined period from a creep strain value obtained in a creep strain measurement step (S602) of the base material portion for obtaining a range of creep strain and a creep strain measurement step (S602) of the base material portion. Material creep The results obtained in the creep rate calculation step (S603) and the creep strain rate calculation step (S603) of the base material part are the creep strain of the predetermined range including the high strength steel welded portion or the predetermined range including the high strength steel welded portion. The obtained high strength steel is shown in the creep strain rate characteristic curve showing the relationship between the creep strain rate conversion step (S604) of the welded portion to be converted into speed and the creep strain rate with respect to the operation time or creep life consumption rate obtained in advance. A fourth lifetime consumption rate measuring step (S605) for obtaining a lifetime consumption rate of the inspection object by applying a value of a creep strain rate within a predetermined range of the welded portion or a predetermined range including the high strength steel welded portion; This comprises a remaining life estimation step (S606) for estimating the remaining life of the weld from the life consumption rate obtained in the fourth life consumption rate measurement step (S605).

In the creep elongation measuring step (S601) of the base material portion, the creep strain (ε) of the base material 10 is measured.
In this embodiment, the creep elongation measuring method of the base material 10 in the base material portion creep elongation measuring step (S601) is the thermal effect of the predetermined range of the high-strength steel weld to be inspected described in Reference Example 1. The measurement is performed in the same manner as the creep elongation measuring step (S101) of the welded portion in which the creep elongation of the portion that has undergone the measurement is measured. Therefore, the description in the creep elongation measuring step (S601) of the base material portion is omitted.

  In the present embodiment, the range of measuring the length of creep elongation is the predetermined range of the high strength steel base material to be inspected, but the present invention is not limited to this, for example, the high strength steel welded portion. The length of creep elongation in a predetermined range including the high-strength steel base material portion including both the base material portion and the base material portion may be measured.

  In the creep strain measurement step (S602) of the base material portion, the measurement result obtained in the creep elongation measurement step (S601) of the base material portion and the length of the predetermined range of the high strength steel base material portion in the initial operation are obtained. In comparison, the creep strain (ε) of the base material 10 is obtained.

  In the creep strain rate calculation step (S603) of the base material portion, a predetermined period (here, unit) is determined from the creep strain (ε) value of the base material 10 obtained in the creep strain measurement step (S602) of the base material portion. Is used to calculate the creep strain rate (ε / t) of the base material 10.

  Next, in the creep strain rate conversion step (S604) of the welded portion, from the value of the creep strain rate (ε / t) of the base material 10 obtained in the creep strain rate calculation step (S603) of the base material portion. This is converted into the creep strain rate (ε / t) of the heat affected zone (HAZ) 12.

Here, the step of converting the creep strain rate (ε / t) of the base material 10 into the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 will be specifically described.
First, the creep strain rate (ε / t) of the base material 10 obtained in the creep strain rate calculation step (S603) of the base material portion is the first or second creep strain as shown in FIGS. A value of the minimum creep strain rate (ε / t) of the base material 10 is obtained by fitting to the speed characteristic curve.

  Then, the base material 10 and the thermal effect showing the relationship between the working stress of the base material 10 and the heat affected zone (HAZ) 12 and the minimum creep strain rate (ε / t) obtained in advance as shown in FIG. The value of the minimum creep strain rate (ε / t) of the obtained base material 10 is applied to the minimum creep strain rate characteristic curve of the part (HAZ) 12 to obtain the minimum creep strain rate of the heat affected zone (HAZ) 12 The value of (ε / t) is obtained.

For example, as shown in FIG. 16, when the working stress is 66 MPa and the value of the minimum creep strain rate (ε / t) of the base material 10 is 4.6 × 10 ⁻⁵ % / h, the thermal effect The value of the minimum creep strain rate (ε / t) of the part (HAZ) 12 is 2.2 × 10 ⁻⁴ % / h.

  As shown in FIG. 10, the minimum creep strain rate is a parameter that determines the creep life as known as the relationship of the Monkman-Grant rule. Many methods for estimating the creep strain rate characteristic curve have been proposed. For example, “Iron and Steel” (“Improvement of Ω Method for Estimating Creep Behavior of Improved 9Cr-1Mo Steel”; Park Jun et al., Japan Iron and Steel Institute, 1999, vol. 85, No. 6, p492), See, “Constitutive equation describing creep curve of statically aged modified 9Cr-1Mo steel” (Pak Jiang et al., Japan Institute of Metals, 1999, vol. 63, No. 5, p597-600).

  Based on such knowledge, the base material portion obtained in advance as shown in the corresponding FIGS. 9 and 10 from the value of the minimum creep strain rate (ε / t) of the obtained heat affected zone (HAZ) 12 is obtained. 10 and the first or second creep strain rate indicating the relationship between the operation time (t) or creep life consumption rate (t / tr) of the heat affected zone (HAZ) 12 and the creep strain rate (ε / t). Estimate the characteristic curve.

  Then, the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 from the estimated base material 10 and the first or second creep strain rate characteristic curve of the heat affected zone (HAZ) 12. Is calculated.

  As described above, even when the temperature and the working stress are different depending on the part where the life evaluation of the inspection target is actually performed, the creep strain rate (ε / t) of the base material 10 is set to the first or the first base material 10. A value of the minimum creep strain rate (ε / t) of the base material 10 is obtained by fitting to the second creep strain rate characteristic curve. Then, the value of the minimum creep strain rate (ε / t) of the base material 10 is applied to the minimum creep strain rate characteristic curve of the base material 10 showing the relationship between the acting stress and the minimum creep strain rate (ε / t). The value of the minimum creep strain rate (ε / t) of the heat affected zone (HAZ) 12 is obtained from the minimum creep strain rate characteristic curve of the heat affected zone (HAZ) 12. Then, the first or second creep strain rate characteristic curve of the heat affected zone (HAZ) 12 is specified from the value of the minimum creep strain rate (ε / t) of the heat affected zone (HAZ) 12, and the heat The creep strain rate (ε / t) of the affected part (HAZ) 12 can be calculated.

  In the third life consumption rate measuring step (S605), the first or the relationship between the operation time (t) or the creep life consumption rate (t / tr) obtained in advance and the creep strain rate (ε / t) is shown. By applying the obtained creep strain rate (ε / t) of the heat affected zone (HAZ) 12 to the second creep strain rate characteristic curve, the creep life consumption rate (t / tr) of the inspection object Ask for.

  Next, in the remaining life estimation step (S606), the remaining life of the welded portion to be inspected is estimated from the creep life consumption rate (t / tr) of the inspection object obtained in the life consumption rate measuring step (S605). To do.

  In the remaining life determination step (S607), the remaining life is determined from the remaining life value obtained in the remaining life estimation step (S606).

Since the subsequent processing method performed based on the result of the remaining life determination in the remaining life determination step (S607) is the same as that in Reference Example 1 or Reference Example 2 , description thereof is omitted.

  This makes it possible to propose a creep evaluation method for welds of high-strength ferritic steel that has not had an appropriate creep damage evaluation method in the past, and it is possible to ensure the reliability of heat-resistant steel and prevent blasting accidents.

  In the present embodiment, the creep strain rate (ε / t) of the base material 10 is converted into the creep strain rate (ε / t) of the heat affected zone (HAZ) 12 to calculate the lifetime of the inspection object. Although the consumption rate is obtained, the present invention is not limited to this, and the creep strain (ε) of the heat affected zone (HAZ) 12 is calculated from the value of the creep strain (ε) of the base material 10. It may be converted into a value to obtain the lifetime consumption rate of the inspection object.

  As described above, the life evaluation method based on the creep elongation of the high-strength steel weld and the life evaluation method of the high-strength steel weld according to the present invention are the creep time (t) or creep life consumption rate (t / tr) determined in advance. ) And creep strain characteristic curve showing the relationship between creep strain (ε), or creep strain rate showing the relationship between creep time (t) or creep life consumption rate (t / tr) and creep strain rate (ε / t) By applying the obtained creep strain (ε) value or creep strain rate (ε / t) value to the characteristic curve to the creep strain characteristic curve or creep strain rate characteristic curve, the remainder of the inspection target is obtained. Lifetime can be accurately predicted. It is particularly suitable for the evaluation of creep damage at the welds of joints of high-strength ferritic steel used in high-temperature and high-pressure equipment such as thermal power plants.

It is a flowchart which shows the determination method of the lifetime evaluation method by the creep elongation of the high strength steel welding part which concerns on the reference example 1. FIG. It is explanatory drawing of the relationship between time and creep elongation. It is the figure which showed the test piece used for a preliminary test. It is a figure which shows one of the measuring methods of the distance between de which is a heat affected zone (HAZ). It is a figure which shows the relationship between the creep elongation by heat influence of a heat affected zone (HAZ) and a base material, and time. It is a figure which shows the relationship between the creep time (t) of a test result, and creep distortion ((epsilon)). It is a figure which shows the relationship between the creep life consumption rate (t / tr) of a test result, and creep distortion ((epsilon)). It is a flowchart which shows the determination method of the lifetime evaluation method by the creep elongation of the high strength steel welding part which concerns on the reference example 2. FIG. It is a figure which shows the relationship between creep time (t) and creep strain rate ((epsilon) / t). It is a figure which shows the relationship between creep life consumption rate (t / tr) and creep strain rate ((epsilon) / t). It is a flowchart which shows the determination method of the lifetime evaluation method of the high strength steel welding part which concerns on 1st embodiment of this invention. It is a flowchart which shows an example of the determination method of the lifetime evaluation method by the creep void measurement of the high strength steel welding part which concerns on 1st embodiment of this invention. It is a flowchart which shows the other example of the determination method of the lifetime evaluation method by the creep void measurement of the high strength steel welding part which concerns on 1st embodiment. It is a figure which shows an example of the correlation diagram of a void number density and a void area ratio. It is a flowchart which shows the determination method of the lifetime evaluation method by the creep elongation of the high strength steel welding part which concerns on 2nd embodiment of this invention. It is a figure which shows the relationship between action stress and the minimum creep strain rate ((epsilon) / t).

10 Base material 11 Weld metal 12 Heat affected zone (HAZ)
13 Creep void 14 Specimen

Claims (5)

The heat affected zone (HAZ) of the joint portion to be inspected is a predetermined range of the high strength steel weld zone including at least one location, and the treatment range of the base material and the heat affected zone (HAZ) of the high strength steel weld zone , or the high A creep elongation measuring step of the base material portion for measuring the creep elongation of a portion affected by heat in a predetermined range including the strength steel weld,
The measurement result obtained in the creep elongation measurement step of the base material part is compared with a predetermined range of the high-strength steel base material part in the initial stage of operation or a predetermined range including the high-strength steel base material part. Creep strain measurement step of the base material portion for obtaining a predetermined range of the high strength steel base material portion or a predetermined range including the high strength steel base material portion, and
A creep strain rate calculating step of the base material portion for calculating a creep strain rate in a predetermined period from a value of the creep strain obtained in the creep strain measuring step of the base material portion;
Creep strain rate conversion step of the welded portion that converts the result obtained in the creep strain rate calculation step of the base metal portion into a predetermined range of the high strength steel welded portion or a creep strain rate of a predetermined range including the high strength steel welded portion. When,
A predetermined range of the obtained high strength steel welded portion or a predetermined range including the high strength steel welded portion in the creep strain rate characteristic curve showing the relationship between the creep strain rate and the operation time or the creep life consumption rate obtained in advance. A life evaluation method by creep elongation of a high-strength steel weld, characterized by comprising a fourth life consumption rate measuring step for obtaining a life consumption rate of the inspection object by applying a value of a creep strain rate. Life evaluation method by creep elongation of the high strength steel weld zone according to claim 1,
Life evaluation of high-strength steel welds characterized by the combined use of a creep void measurement on the outer surface of the high-strength steel welds being inspected and a life evaluation method based on creep void measurement of the high-strength steel welds Method. In claim 2 ,
Life evaluation method by creep void measurement of the high strength steel weld,
A void number density detecting step for detecting a void number density which is the number of creep voids generated per unit area of the heat-resistant steel to be inspected;
A void number density change rate step for obtaining a void number density change rate that is an increase in the void number density detected this time with respect to the void number density detected previously by the void number density detection step;
By applying the value of the obtained void number density change rate to the evaluation curve based on the void number density change rate indicating the relationship between the creep life consumption rate and the void number density change rate obtained in advance, the lifetime consumption of the inspection object is applied. A method for evaluating the life of a high strength steel weld, comprising a life consumption rate measuring step for obtaining a rate. In claim 2 ,
Life evaluation method by creep void measurement of the high strength steel weld,
Surface void measurement process for measuring the void number density or void area ratio of creep voids on the outer surface of the high strength steel weld to be inspected;
From the measurement result of the surface void measurement step, a void number density or void area ratio determination step for determining whether or not a predetermined threshold value or more,
In the determination step, if it is equal to or less than a predetermined threshold, a remaining life measuring step of measuring the remaining life of the welded portion;
In the determination step, a flaw detection inspection step of performing an internal ultrasonic flaw inspection (UT inspection) when a predetermined threshold value or more,
The method for evaluating the life of a high-strength steel weld, comprising a defect determination step for determining the presence or absence of an internal defect in the flaw detection inspection step. In any one of Claims 2 thru | or 4 ,
The predetermined range including the high-strength steel weld includes at least one heat-affected zone (HAZ).