JP2000130103A - Gas turbine stationary blade structure and life controlling method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress maximum crack growth of a gas turbine stationary blade and to attain long lives of parts by preliminarily providing cooling holes on paths of cracks for a portion in which growth of the cracks is estimated and making a structure in which stress strength at tips of the cracks is reduced at a point of time when the cracks reach the cooling holes. SOLUTION: When thermal fatigue cracks 3 are detected in a gas turbine stationary blade, development of the cracks 3 is suppressed by working holes 4 in the growth directions of the cracks 3 and reducing specific stress field at tips of the cracks 3 when the cracks 3 reach the holes 4. Because the shapes of the holes 4 reduce stress concentration in the growth directions of the cracks 3, the holes 4 are made elliptical or race track type holes in which the growth directions of the cracks 3 become a minor axis. Because there are many cases where portions generating these thermal fatigue cracks 3 can be estimated from a structural analysis or analysis of trends of past damage data, sometimes these holes 4 are preliminarily worked at a portion where the cracks 3 are estimated to be generated when manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature component for rectifying combustion gas from a combustor in a gas turbine, which is exposed to high-temperature combustion gas and is regularly damaged because it is damaged by thermal fatigue and creep. In addition, the present invention relates to a stationary vane that is inspected and repaired as necessary.

[0002]

2. Description of the Related Art High-temperature components of gas turbines suffer from damages such as repeated thermal strains caused by the start and stop of the plant and creep deformation caused in a high temperature environment during steady operation. The first stage vane is located immediately after the combustor outlet, and is the part of the turbine that is most exposed to high temperatures, and generates high thermal strain during operation of the gas turbine. In recent years, operations with a large number of start / stop times are frequently performed, and thermal fatigue due to repetition of the above-described thermal strain is a main factor of damage to members.
The actual form of damage in the first stage vane is the initiation and propagation of thermal fatigue cracks. Periodic inspections are performed at appropriate intervals to investigate the occurrence of cracks, etc., so that the plant will not be shut down for a long time due to the growth of these damages, or even accidents or breakdowns. FIG. 3 shows an example of a sketch of the crack initiation situation obtained during the inspection. It should be noted that judgments such as repair and parts replacement are also made based on the observed crack length.

As described above, the growth of a crack governs the life of a stationary blade, and it is necessary to suppress the growth of the crack by reducing thermal stress or the like in order to extend the life of a component. Become.
As structures for reducing thermal stress, there are JP-A-8-135402 and JP-A-8-135403. These structures are
In Japanese Patent Application Laid-Open No. 8-135402, the cooling of the blade is ensured and the rigidity of the blade is ensured by reducing the thickness of the blade and providing a reinforcing rib inside. In JP-A-8-135403,
A structure has been proposed in which the end walls are divided to reduce the amount of thermal deformation of each vane segment and to reduce the thermal stress.

However, as shown in FIG. 3, large crack growth is observed from stress concentrated portions such as the end portions of the pea and the blade, and even if the amount of crack generation becomes small due to cooling enhancement, etc. Unless the growth of these maximum cracks can be suppressed, long life cannot be achieved.

Japanese Utility Model Application Laid-Open No. 58-191302, 61-80302
Japanese Patent Laid-Open Publication No. HEI 7-214969 proposes a structure that can process a groove and suppresses crack growth for a rotor blade. The grooves used here are not penetrated and are effective for very shallow cracks. However, when the crack depth exceeds the depth of the grooves, the effect is almost lost. Further, in the actual structure, the stress state is often a multiaxial field, and a stress component other than the direction parallel to the machining groove also acts, so that the strength may be rather reduced.

[0006] In order to suppress the growth of cracks by improving such a structure, the growth of the cracks and stop holes is controlled so that the growth of the cracks is slowed and they do not become the starting points of new cracks. It is necessary to precisely determine the shape, position, etc.

Furthermore, the position of the maximum crack occurrence often differs depending on the individual stator blade segments, and it is necessary to observe the entire surface of the stator blade at the time of inspection, which causes a problem that the inspection time becomes longer.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to suppress the maximum crack growth of a gas turbine stationary blade and achieve a longer life of a component. Another object of the present invention is to provide a structure capable of limiting the crack generation position to several locations in order to shorten the inspection time.

[0009]

The above-mentioned thermal stress, which is the driving force for the thermal fatigue crack growth, is generated by restraining thermal deformation due to temperature fluctuation. Therefore, if the thermal stress is reduced by reducing the structural constraint of the member, crack growth is suppressed. However, once a crack is generated, the constraint at that portion is reduced. Therefore, under a displacement control type load such as thermal stress, the growth of the crack itself leads to a reduction in the structural constraint.

However, the crack tip becomes a singular stress field, and the stress intensity factor and the J integral, which are parameters representing the strength of the singular field, increase as the crack grows. Needs to be smaller. In order to reduce the singular stress field, the structure may be such that the curvature of the crack tip is small.

Therefore, a cooling hole is previously provided on a crack path for a portion where a crack is expected to grow, and when the crack reaches the cooling hole, the stress at the tip of the crack is increased. The structure is such that the strength is reduced.

With such a structure, the thermal deformation caused by the temperature fluctuation is absorbed by the opening / closing opening of the crack, and the thermal stress is reduced. Further, since the strength of the singular stress field at the tip of the crack is also reduced, subsequent crack growth can be suppressed and the life can be extended. Further, by providing in advance a notch serving as a starting point of a crack together with the cooling hole, a site where the crack has occurred is specified, and the amount of work at the time of inspection is reduced.

[0013]

1 and 2 show an example of an embodiment of the present invention. When the thermal fatigue crack 3 is detected, the hole 4 is machined in the growth direction of the crack, and when the crack reaches the hole 4,
By reducing the singular stress field at the crack tip, the crack growth is suppressed. Further, the shape of the hole is an elliptical or race-track type hole in which the growth direction of the crack is a short axis in order to reduce stress concentration in the growth direction of the crack. The locations where these thermal fatigue cracks occur can often be estimated from structural analysis or trend analysis of past damage data. It may be processed.

FIGS. 3 (a) and 3 (b) show examples of sketches of the state of occurrence of cracks in the gas turbine stationary blade observed during the periodic inspection. It can be seen that the cracks grew mainly from the stress concentrated portions such as the corners of the wing and the pea. In order to identify the position where the hole for suppressing the crack growth described above is processed from the past damage data, for example, the following treatment is performed.

As shown in FIGS. 4 (a), 4 (b), 5 (a), 5 (b), the stator vane is divided into several parts, and the crack occurrence status of each part is recorded as data. The data is stored and the data of the damaged vane near the stationary vane is retrieved from the past database using the damage occurrence status of the target vane as an input. Crack growth direction and life are evaluated inversely by the trend analysis.

FIGS. 6 and 7 show examples of crack growth data in the actual machine. These summarize the crack lengths observed during periodic inspections in all the stationary blades of a certain gas turbine, with the horizontal axis representing the number of times of starting and stopping. FIG. 6 shows a crack generated at the end wall portion, which is of the type shown in FIG. FIG. 7 shows a crack from the wing trailing edge, and corresponds to FIG. Such data is used for the trend analysis described above.

FIG. 8 shows an example in which the positions of the above-mentioned holes are determined with respect to the crack from the root of the wing at the end portion.
FIG. 8 shows that the principal stress direction of the same part is indicated by an arrow 7 from the result of the structural analysis.
It is shown by. Since the crack is considered to grow in the direction perpendicular to the principal stress, the direction of crack propagation is expected to be the direction of the solid line shown in FIG. As a result, the hole 9 is processed as a hole for suppressing crack growth.

At the trailing edge of the blade, a plurality of cracks are generated in the same direction. Therefore, as shown in FIG. 9, the cooling hole in this portion is formed into an elliptical hole having a longer diameter in the blade height direction. It has the effect of suppressing crack growth. Here, the reason why the major axis is given in the blade height direction is that, considering the crack growth direction, the stress component in the blade height direction is dominant in this part, and the stress concentration in that direction is reduced. is there.

In the above description, a hole for suppressing the growth of a crack was formed at a site where a crack that has occurred or a site where the growth of a crack is expected is evaluated. FIG. 10 shows a sketch of a crack generation state of a stationary blade different from FIG.
The position of the maximum crack initiation of the outer peripheral side wall is different from that of the stationary blade of FIG. As described above, since the crack occurrence position differs depending on the blade or the segment, at present, the crack occurrence state is investigated at the time of a periodic inspection for all portions of the stationary blade. Simplifying such investigations and shortening inspection time is also important for reducing operating costs.

Therefore, the notch serving as the starting point of the crack is processed in advance so that the crack generation position is the same in each segment, and the above-described crack growth is suppressed in the crack growth direction. By combining the holes, the position where the crack is generated is specified, and the time required for inspection or repair is reduced.

FIGS. 11 and 12 show examples of the structure. When a crack is generated from an end of a member, a structure as shown in FIG. 11 is adopted. When a notch serving as a starting point of a crack is formed in a member, holes serving as stop holes are formed on both sides of the notch as shown in FIG.

FIGS. 13 and 14 show an example of application of the structure to a stationary blade. FIG. 13 shows an example of application to the end wall portion. As a result of stress analysis, the root of the blade and end wall becomes a stress concentration portion and often becomes the starting point of a crack. Therefore, a notch is formed there. Similarly, as shown in FIG. 14, the above-described structure is also introduced to the wing trailing edge.

There are the following two methods for determining the position of a hole for suppressing crack growth. One is
This is a method in which, when an allowable crack length is determined in advance, a position corresponding to the allowable length is set as a hole position. The other is a displacement control type load due to thermal stress, in which the crack growth absorbs thermal deformation and reduces the generated stress. Is used to take advantage of the tendency to decrease.

In general, as shown in FIG. 15, the fatigue crack growth rate da / dN is a fracture mechanics parameter J
It is given by the exponential function of the integration range. This J integral is considered to be the driving force for crack growth. For a Co-base superalloy, which is a stationary blade material, this relationship is expressed by the following equation.

[0025]

Da / dN = 5.63 × 10 ⁻⁵ (ΔJ) ^1.72 (Equation 1) Here, the units of da / dN and ΔJ are mm / dN, respectively.
cycle, kN / m.

In a member such as a gas turbine stationary blade used under conditions where a temperature gradient is generated on the inner and outer surfaces, a large stress gradient is generated in the cross section of the member as shown in FIG. It occurs on the surface on the high temperature side, and the stress decreases rapidly inside the plate thickness. FIG. 17 shows an example in which the relationship between the crack depth and the J-integral range when the crack grows in such a stress field is obtained. This is because the stress distribution in the thickness is 2
It is obtained by approximation using a quadratic curve. It can be seen that the J-integral value increases up to about 1/3 of the plate thickness, but then gradually decreases as the crack grows.

From this and Equation 1, it can be seen that the crack growth rate also tends to decrease when the crack has a depth of 1/3 or more of the plate thickness. Therefore, it is preferable to process the hole at a position where the crack length is such that the crack growth rate decreases. FIG. 17 shows the evaluation in the crack depth direction, but what is actually observed is the crack surface length. FIG. 18 shows an example in which the relationship between the crack surface length and the depth was obtained for the actual machine stationary blade. In the figure, the horizontal axis shows the ratio between the crack depth and the plate thickness, and the vertical axis shows the ratio between the crack surface half length and the depth. This relationship is the same if the member shapes are the same and the stress distribution shapes are similar. Using this relationship, the depth can be estimated from the surface length.

Then, the allowable value of the crack growth rate is obtained from the inspection interval and the number of times of starting and stopping scheduled in the period, and the J-integral value and the crack depth at which the growth rate becomes less than that value are shown in FIG. 17, and the position where the hole is to be machined is determined based on this and FIG.

For example, if the allowable crack growth rate is 4 × 1
When 0 ^-4 mm / cycle, the J integral range is given by
It is necessary to be 3.12 kN / m or less. Assuming that the acting stress range (elasticity analysis value) of the evaluation part is 1120 MPa, FIG.
The value of the vertical axis is 2.5 × 10 ^-6 , and the crack growth rate is 4
The thickness ratio of the cracks of not more than × 10 ⁻⁴ mm / cycle is 0.93. The aspect ratio with respect to the plate thickness ratio of 0.93 is shown in FIG.
Is 0.17. Assuming that the plate thickness of the evaluation portion is 10 mm, the crack surface half length c is 54.7 mm, and a stop hole may be formed at a position further away from the crack initiation point.

The dimensions of the hole to be machined are set so that the portion becomes a stress concentration portion and no crack is generated from the hole. That is, the radius of curvature of the hole and the like are determined so that the life of crack initiation from the notch tip is equal to or longer than the scheduled operation time. When a detailed structural analysis is performed by a finite element method or the like, dimensions are determined based on the results.

For simplicity, for example, as shown in FIG. 19, this portion has a structure in which a notch and a slit are combined, and the stress concentration coefficient of the shape is expressed by the curvature of the notch and the distance connecting both ends. Is considered to be the same as the stress concentration of the ellipse as shown by the broken line in the figure, the shape is determined from the stress concentration coefficient α of the ellipse in the following equation.

[0032]

Α = 1 + 2 (a / ρ) (2) where a is the major axis of the ellipse and ρ is the radius of curvature of the notch tip. The acting stress is generally obtained by a structural analysis of a crack-free member. However, if the crack growth rate can be obtained from actual machine data, the J integral value is calculated back from Equation 1 and then the crack length is calculated from the crack length. The working stress is estimated. The larger the crack length corresponding to a, the larger the radius of curvature ρ. Equation 2 is a stress concentration coefficient when a uniform tensile stress acts. If the stress distribution shapes are different, a value corresponding to the stress distribution shape is used.

From the stress at the notch bottom obtained in this way, the crack initiation life is obtained based on the fatigue life diagram of the smooth material. The crack initiation life is defined as the life when a crack of about one crystal grain size is generated from the notch bottom, and the corresponding data of the smoothing material is used.

Since the stress at the notch bottom is obtained by using the elastic stress concentration coefficient, the stress is generally estimated to be high, which is an evaluation on the safe side. When the curvature of the notch bottom is large, the evaluation on the safe side is excessively performed. Therefore, in order to reduce the margin and perform a rational evaluation, the stress evaluation of the notch bottom is performed according to the Neubar rule.
FIG. 20 shows how to determine the stress according to the Neubar rule. K in the figure
t is the elastic stress concentration factor, and Δσ _n and Δσ are the nominal and the stress range at the notch bottom, respectively.

[0035]

According to the method of the present invention, the maximum crack growth of the gas turbine stationary blade is suppressed, and the life of the component is extended and the reliability of the component during operation is improved. In addition, the location of the maximum crack occurrence, which has been different in the past, can be specified at several locations by individual stator vane segments, and the amount of work required for inspection can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of an outer peripheral end wall of a gas turbine stationary blade according to an embodiment of the present invention.

FIG. 2 is a perspective view of a trailing edge portion of the gas turbine stationary blade of FIG. 1;

FIGS. 3A and 3B are perspective views showing examples of a sketch of a crack occurrence situation of a gas turbine stationary blade.

FIG. 4 is a characteristic diagram showing a distribution state of a maximum crack for each site.

5 (a) and 5 (b) are partial perspective views of the stationary blade in FIG. 4;

FIG. 6 is a characteristic diagram showing a relationship between a crack length and the number of times of starting and stopping in an outer peripheral side wall.

FIG. 7 is a characteristic diagram showing the relationship between the crack length and the number of times of starting and stopping at the trailing edge of the blade.

FIG. 8 is a view showing prediction of a crack propagation direction of pea.

FIG. 9 is a perspective view showing cooling holes at the trailing edge of the blade.

FIG. 10 is a perspective view showing an example of a sketch of a crack occurrence state of a gas turbine stationary blade.

FIG. 11 is a diagram showing an example of a structure in which a notch serving as a starting point of an edge crack and a stop hole are combined.

FIG. 12 is a diagram showing an example of a structure in which a notch serving as a starting point of a surface crack and a stop hole are combined.

FIG. 13 is a plan view showing an example of application to the actual machine stationary blade of FIG. 15;

FIG. 14 is a perspective view showing an application example to an actual machine stationary blade.

FIG. 15 is a characteristic diagram showing a relationship between a crack growth rate and a J integration range.

FIG. 16 is a characteristic diagram showing a stress gradient in a member.

FIG. 17 is a characteristic diagram showing a relationship between a J-integral and a crack depth in the stress field of FIG. 16;

FIG. 18 is a characteristic diagram showing a relationship between a crack aspect ratio and a plate thickness ratio.

FIG. 19 is a diagram showing a stress concentration portion when a crack reaches an elliptical hole.

FIG. 20 is a characteristic diagram showing a relationship between a stress range and a strain range.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Outer end wall, 2 ... Blade part, 3 ... Thermal fatigue crack, 4 ... Hole for suppressing crack growth, 5 ... Blade trailing edge,
Reference numeral 6 denotes an inner peripheral end wall, 7 denotes an arrow indicating a principal stress direction, 8 denotes an arrow indicating a predicted crack growth direction, 9 denotes a cooling hole on a blade ventral side, 10 denotes a notch serving as a crack starting point, and 11 denotes a crack. Stop hole, 12: Notch serving as the starting point of a crack formed in the outer peripheral end wall, 13 ... Notch serving as the starting point of a crack formed in the trailing edge of the blade.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shigeo Sakurai 502 Kandachicho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. (72) Kunihiro Ichikawa 3-1-1 Sachicho, Hitachi-shi, Hitachi, Ibaraki Stock F-term in the Hitachi Plant of Hitachi, Ltd. (reference) 3G002 GA08 GB00 GB01

Claims (9)

[Claims] 1. A gas turbine for driving a generator by adding fuel in a combustor to air compressed by a compressor to generate combustion gas, rotating the turbine by the high-temperature, high-speed combustion gas, and driving a generator. In order to send the combustion gas from the turbine to the rotor blade at an optimal angle, the gas turbine vane located immediately after the combustor and subjected to thermal fatigue damage due to temperature fluctuations caused by the start / stop of the turbine is subjected to structural analysis or actual equipment From the thermal fatigue crack distribution data at the point where high stress is generated and the crack growth is expected, from the point where the crack is expected to be the starting point, to the area estimated to be the crack growth path, A gas turbine vane structure having a cooling hole. 2. A gas turbine stationary blade according to claim 1, wherein the elliptical cooling hole is formed on a line parallel to the turbine axis from the root of the trailing edge of the end blade, and the minor axis direction of the ellipse is the turbine axis direction. A gas turbine vane structure characterized by being provided as described above. 3. The gas turbine stationary blade according to claim 1, wherein an elliptical hole having a major axis in the blade height direction is provided on the blade side near the trailing edge of the blade and on the blade side near the corner of the end wall. Gas turbine stationary blade structure. 4. The gas turbine vane according to claim 1, wherein the shape of the cooling hole in the vicinity of the trailing edge of the blade ventral side is an elliptical hole whose major axis is in the blade height direction. Turbine stationary blade structure. 5. The gas turbine stationary blade according to claim 1, wherein the life of the gas turbine vane is affected by damage due to thermal fatigue, and the generation and growth of a fatigue crack has a notch. 2. The gas turbine vane structure according to claim 1, wherein the gas turbine vane structure has an elliptical cooling hole on a line where crack growth is expected from the notch. 6. The gas turbine vane according to claim 1, wherein a cutout in the turbine axial direction is provided on the end wall side of the root of the blade trailing edge, and an elliptical hole is formed on a line drawn in the turbine axial direction therefrom. Gas turbine vane structure characterized by the following. 7. The gas turbine stationary blade according to claim 1, wherein the blade has a notch near the root end of the blade trailing edge, and further has an elliptical hole from there at an upstream side in the flow direction of the combustion gas. Characteristic gas turbine vane structure. 8. The gas turbine vane structure according to claim 5, wherein the distance from the notch to the elliptical hole is made equal to a predetermined limit crack length, and the crack reaches the elliptical hole during inspection. A method for managing the life of a gas turbine stationary blade, characterized in that repair or replacement is determined based on whether or not it is present. 9. The gas turbine stationary blade structure according to claim 5, wherein a crack propagation speed estimated when a distance from the notch to the elliptical hole is regarded as a crack length is predetermined. Gas turbine vane structure characterized in that the gas turbine vane structure is smaller than the predetermined value.