CA2072029A1 - Turbine blade assessment system - Google Patents
Turbine blade assessment systemInfo
- Publication number
- CA2072029A1 CA2072029A1 CA002072029A CA2072029A CA2072029A1 CA 2072029 A1 CA2072029 A1 CA 2072029A1 CA 002072029 A CA002072029 A CA 002072029A CA 2072029 A CA2072029 A CA 2072029A CA 2072029 A1 CA2072029 A1 CA 2072029A1
- Authority
- CA
- Canada
- Prior art keywords
- eddy current
- assessment
- blade
- condition
- recited
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
- G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
- G01N27/904—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents with two or more sensors
Abstract
56,214 ABSTRACT OF THE DISCLOSURE
The present invention provides a method and apparatus for performing nondestructive material assessment of service exposed combustion turbine blades. According to the invention, the testing is accomplished by inserting eddy current (EC) probes into the blade's cooling holes, and evaluating the eddy current response of the blade. The eddy current probes are preferably coupled together in a differential mode. The measured response is then compared with a previously determined response corresponding with a known material condition. An assessment of the blade is made on the basis of this comparison.
The present invention provides a method and apparatus for performing nondestructive material assessment of service exposed combustion turbine blades. According to the invention, the testing is accomplished by inserting eddy current (EC) probes into the blade's cooling holes, and evaluating the eddy current response of the blade. The eddy current probes are preferably coupled together in a differential mode. The measured response is then compared with a previously determined response corresponding with a known material condition. An assessment of the blade is made on the basis of this comparison.
Description
207~0~
- 1 - 56,214 TURBINE BLADE ASSESSMENT SYSTEM
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatuses for the nondestructive assessment of a metallic material. More particularly, the present invention relates to the nondestructive, in situ, material assessment of service-exposed combustion turbine blades.
Metallic components such as industrial gas turbine blades are used under elevated temperature creep conditions and are designed to withstand the maximum stress which can exist in the structure for the required design life. A safety factor is applied to this stress to allow for material variability and variations in the operating conditions. This design stress, if not exceeded, should preclude failure within the design life. In practice, however, the blade experiences considerable mechanical and thermal stresses which can cause damage such as creep ~cavitation), microstructural embrittlement and cracking. This damage, if undetected, can result in an unexpected failure, costly repairs and severe damage to the turbine unit.
~eriodically, during plant outages, combustion turbine blades that contain no obvious cracks are destructively evaluated in order to monitor and assess the response of blading material to service conditions. During these investigations, stress rupture tests and visual microstructure examinations are performed on selected blades to assess the state of the material and to estimate conditions to which the turbine blades are exposed during service ~ .
- 1 - 56,214 TURBINE BLADE ASSESSMENT SYSTEM
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatuses for the nondestructive assessment of a metallic material. More particularly, the present invention relates to the nondestructive, in situ, material assessment of service-exposed combustion turbine blades.
Metallic components such as industrial gas turbine blades are used under elevated temperature creep conditions and are designed to withstand the maximum stress which can exist in the structure for the required design life. A safety factor is applied to this stress to allow for material variability and variations in the operating conditions. This design stress, if not exceeded, should preclude failure within the design life. In practice, however, the blade experiences considerable mechanical and thermal stresses which can cause damage such as creep ~cavitation), microstructural embrittlement and cracking. This damage, if undetected, can result in an unexpected failure, costly repairs and severe damage to the turbine unit.
~eriodically, during plant outages, combustion turbine blades that contain no obvious cracks are destructively evaluated in order to monitor and assess the response of blading material to service conditions. During these investigations, stress rupture tests and visual microstructure examinations are performed on selected blades to assess the state of the material and to estimate conditions to which the turbine blades are exposed during service ~ .
2~72~2~
- 2 - 56,214 operation. These destructive examinations consist of comparing pre-service and post-service material properties and microst~uctures. Material specifications serve as a guide in assessing remaining life and the comparison is used to determine whether remaining blades can be put back into service. The advantages of an accurate material assessment method include the avoidance of costly unscheduled outages and the ability to extend the useful life of the blade.
Although analyses of properties from post-service turbine blades provide useful information on life extension, the evaluation process is both time consuming and costly. In addition, the frequent removal of blades for destructive analysis is costly. In the case of combustion turbines, the operation cycle, type of fuel and environmental conditions can vary significantly from machine to machine. For instance, for a given turbine model, some blades may experience higher temperatures than others. As a result, blades can have different microstructures even though they have accumulated the same service exposure time.
Some combustion components operate at very high temperatures (metal temperature between 1500F to 1800F
(815-C to 982C)) and are subjected to different loading and environmental conditions. Figure 1 depicts a cross section of a typical combustion turbine blade airfoil 10. Such blades are produced from a high temperature creep resistant non magnetic nickel base superalloy.
The blade comprises a root (not shown) and the airfoil 10. The blade root is used to attach the blade to the turbine disc, and operates at relatively low temperatures, while the airfoil experiences much higher temperatures as it passes through the hot gases created by the combustion process. To keep the airfoil cool during operation, small radial cooling holes lOA, lOB, lOC, etc., are drilled along the length of the airfoil during the manufacturing process.
During operation, air passes through these holes, cooling the blade from the interior to the exterior. As a result, large %~72~2~
- 2 - 56,214 operation. These destructive examinations consist of comparing pre-service and post-service material properties and microst~uctures. Material specifications serve as a guide in assessing remaining life and the comparison is used to determine whether remaining blades can be put back into service. The advantages of an accurate material assessment method include the avoidance of costly unscheduled outages and the ability to extend the useful life of the blade.
Although analyses of properties from post-service turbine blades provide useful information on life extension, the evaluation process is both time consuming and costly. In addition, the frequent removal of blades for destructive analysis is costly. In the case of combustion turbines, the operation cycle, type of fuel and environmental conditions can vary significantly from machine to machine. For instance, for a given turbine model, some blades may experience higher temperatures than others. As a result, blades can have different microstructures even though they have accumulated the same service exposure time.
Some combustion components operate at very high temperatures (metal temperature between 1500F to 1800F
(815-C to 982C)) and are subjected to different loading and environmental conditions. Figure 1 depicts a cross section of a typical combustion turbine blade airfoil 10. Such blades are produced from a high temperature creep resistant non magnetic nickel base superalloy.
The blade comprises a root (not shown) and the airfoil 10. The blade root is used to attach the blade to the turbine disc, and operates at relatively low temperatures, while the airfoil experiences much higher temperatures as it passes through the hot gases created by the combustion process. To keep the airfoil cool during operation, small radial cooling holes lOA, lOB, lOC, etc., are drilled along the length of the airfoil during the manufacturing process.
During operation, air passes through these holes, cooling the blade from the interior to the exterior. As a result, large %~72~2~
- 3 - 56,214 thermal gradients and stresses are created which can significantly degrade the blade material with time.
When service exposed blades are removed and inspected, significant microstructural and material property differences are observed. These differences can be directly related to the blade's metal temperature and exposure time.
In general, service blades which have experienced lower operating temperatures for shorter times have better material properties than those exposed to higher temperatures for longer times.
Figure 2 depicts the cross-section of a blade's airfoil 10, including a temperature profile from a blade that was in service for 10,000 hours. As shown, the highest metal temperature occurs at the leading and trailing edges and at the concave surface (pressure side) of the blade. Near the centermost cooling holes 10D, 10E, 10F, 10G, lower metal temperatures occur, with the coldest area located in the center of the thick part of the airfoil. The microstructure in th~ latter area i8 similar to those of a pre-service blade, l.e., unaffected by service temperature.
Westinghouse Electric Corporation, the assignee of the instant application, has demonstrated that special nondestructive sensors can detect and characterize time-temperature dependent degradation such as creep (U.S. Patent No. 4,746,858) and temper embrittlement (U.S. Patent No.
When service exposed blades are removed and inspected, significant microstructural and material property differences are observed. These differences can be directly related to the blade's metal temperature and exposure time.
In general, service blades which have experienced lower operating temperatures for shorter times have better material properties than those exposed to higher temperatures for longer times.
Figure 2 depicts the cross-section of a blade's airfoil 10, including a temperature profile from a blade that was in service for 10,000 hours. As shown, the highest metal temperature occurs at the leading and trailing edges and at the concave surface (pressure side) of the blade. Near the centermost cooling holes 10D, 10E, 10F, 10G, lower metal temperatures occur, with the coldest area located in the center of the thick part of the airfoil. The microstructure in th~ latter area i8 similar to those of a pre-service blade, l.e., unaffected by service temperature.
Westinghouse Electric Corporation, the assignee of the instant application, has demonstrated that special nondestructive sensors can detect and characterize time-temperature dependent degradation such as creep (U.S. Patent No. 4,746,858) and temper embrittlement (U.S. Patent No.
4,528,856) in some materials. These Patents may be referred to for further background on the present invention.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and apparatus which, in conjunction with commercially available eddy current instrumentation, can be used to detect, characterize and monitor the extent of time-temperature related damage in metallic materials, such as combustion turbine blades. A further object of the present invention is to eliminate the need for the costly destructive testing typically used to characterize material properties of service exposed turbine blades. A still further object of the present 207~29 - 4 - 56,214 invention is to provide a method and apparatus that can sort the damaged from the undamaged service blades. For sorting by eddy current to be successful, an eddy current "signature"
for the blade is preferably acquired immediately after manufacture and periodically during service. (A si~nature is the measured current through oir impedance of an eddy current probe in the vicinity of induced eddy currents, or the difference between the currents through or impedances of two different probes or one probe at two different points along the blade.) For blades already in service, eddy current signatures are not generally available. A second approach is to use a new blade as a reference standard and compare its eddy current response with those from used blades. This may yield erroneous results, however, because manufacturing practices and blades' chemical compositions may have changed over time. This will cause differences in initial properties which may render comparison between old and new blades invalid. The present invention achieves the above objectives by providing a method and apparatus for performing nondestructive material assessment of, e.g., a turbine blade.
The method according to the invention employs the detection of eddy current signatures induced in the material being assessed, and correlating the detected signature to a known standard. In addition, the present invention overcomes the aforementioned problems with sorting damaged from undamaged blades through a unique self-calibration scheme.
According to the invention, a pair of eddy current probes are inserted into separate holes in the material (e.g., cooling holes in a turbine blade airfoil). One of the probes is designated the "reference probe," and is inserted into a hole in the thickest region of the blade. This region is apt to be the least affected by heating of the blade. The other probe, designated the "assessment probe," is sequentially inserted into the other cooling holes. At each of the assessment probe positions, an eddy current difference signature (hereinafter eddy current signature) is computed by taking the difference between the current in the assessment 2072~
_ 5 _ 56,214 probe and the current in the reference probe, e.g., by coupling the two probes to operate in a differential mode.
The eddy current signatures are compared with one or more standard signature(s) corresponding to a known condition(s) of the blade material. For example, a standard signature is preferably obtained from the thickest region of the blade, where heating effects are minimal. An estimation of the material condition at each of the assessment probe locations is then made by manually or automatically correlating the measured signatures with one or more signatures corresponding to known conditions of the material.
In its broadest sense, the invention encompasses apparatuses comprising first means for inducing an eddy current in a first region of the material and for detecting a first eddy current signature within the vicinity of the first region, second means for inducing an eddy current in a second region of the material and for detecting a second eddy current signature within the vicinity of the second region, and third means for computing the difference between the first and second eddy current signatures.
A more specific apparatus embodying the invention comprises means for detecting an eddy current signature within the vicinity of a first hole, the first hole defining a reference hole; means for detecting an eddy current signature within the vicinity of a second hole, the second hole defining an assessment hole; and means for computing the difference between the eddy current signatures detected in the vicinity of the reference and assessment holes. The condition of the material is determinable by correlating the difference to a known condition of the material. A preferred embodiment of the invention further includes means for measuring an eddy current signature of a material having a known condition, which signature is indicative of the known condition.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 depicts a cross section of a known turbine blade airfoil.
2072~29 - 6 - 56,214 Figure 2 depicts a typical temperature profile of the airfoil of Figure 1.
Figure 3 depicts exemplary eddy current signatures of service exposed turbine blades.
5Figure 4(A) is a side view of a pair of eddy current probes in accordance with the present invention.
Figure 4(B) is a cross sectional view of the eddy current probes of Figure 4(A).
Figure 5 depicts the placement of the eddy current probes into cooling holes of a turbine blade.
Figure 6 is a block diagram of a turbine blade assessment system according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments will now be described with reference to the drawings, wherein like numerals designate like elements.
Figure 3 depicts eddy current signatures generated from the surfaces of sections of service blades. The uppermost curve in the figure, i.e., curve 16, is an exemplary eddy current signature of a new turbine blade. Curves 18 and 20 represent eddy current signatures of turbine blades with service histories of 13,000 and 14,000 hours, respectively.
According to the invention, these signatures are detected with specially designed eddy current probes 12, 14 (shown in Fig.
4) coupled to a current measurement and display device 22 (see Fig. 6). The eddy current signatures enable one to distinguish between blades with no service history and blades with thousands of hours of service exposure.
According to one embodiment of the invention, a set of eddy current coils 12, 14 are inserted into the cooling holes 10A, 10B, 10C, etc. of a service blade airfoil 10.
Since the cooling holes have a very small diameter (e.g., typically .050-.090 in. (1.27-2.29 mm)), the invention comprises a unique eddy current probe design (shown in Figure 4), which employs small eddy current coils 26, 28. Coil 26 is part of probe 12, hereinafter referred to as the "reference probe." Coil 28 is part of probe 14, hereinafter referred to 207202~
- 7 - S6,214 as the "assessment probe." (The reason for these labels will become apparent from the remaining detailed description.) Referring now to Figure 4, the eddy current coils 26, 28 are wound on individual air-core shafts 30, 32, forming a pa:Lr of bobbin-like probes. The probes 12, 14 are wired differentially via subtractor 13 and connected to commercially available eddy current test equipment 22, as shown in Figure 6. The reference probe (probe 12) is inserted into a cooling hole located in the thickest portion of the airfoil 10, e.g., one of holes lOD, lOE, lOF or lOG. As discussed above, this region of the blade operates at relatively low temperatures and will have a microstructure similar to when it was manufactured, and therefore serves as a unique reference point. The assessment probe (probe 14) is then inserted into a neighboring cooling hole. The two probes are then excited, which induces eddy currents in the airfoil 10 in the respective vicinities of the reference and assessment probes, and the current through the assessment coil is subtracted from the current through the reference coil, producing a reference signature. The reference signature is recorded and displayed by the eddy current measurement device 22, and optionally stored in storage device 24. The assessment probe 14 is moved to another cooling hole and the eddy current signature measured at this hole is compared to the reference signature.
As the thermal damage, if any, moves from the blade surface inward toward the cooling holes, the eddy current signatures will be affected. Therefore, the measured eddy current signature, corresponding to a given pair of cooling holes in a given blade, can be correlated with a known condition of a similar blade. The correlation may be carried out by visually or automatically comparing measured eddy current signatures with signatures for corresponding holes in a known standard (e.g., an airfoil in a known or reference condition), and interpolating the results to determine the airfoil's condition. The automatic correlation may be carried out by a microprocessor in, e.g., the storeage device 24. This procedure is repeated until the eddy current response from all 2~a2~
- ~ - 56,214 cooling holes lOA, lOB, lOC, etc. has been compared to the signatures of the known standard.
Referring now to Figure 5, the probes 12, 14 can be positioned to different depths within the cooling holes lOA, lOB, lOC, etc., as shown. This permits an assessment oP the blade's degradation from the tip of the blade to the root. ln addition, the probes 12, 14 can be pulled or pushed simultaneously along the length of the cooling hole. This allows for automated scanning and computer aided inspection, if so desired. Using computer acquisition and display software, the dynamic scans can be differentially compared and reconstructed to provide a detailed enhanced map of the blade's condition.
In an alternative embodiment of the present invention, the two probes 12, 14 can be connected in a driver/pickup mode. According to this embodiment, the reference probe 12 is pulsed and operated at low frequencies (100 Hz to 10 kHz). The assessment probe 14, is used to receive the electromagnetic signal as it passes through the blade 10.
In a further variation of the invention, the eddy current probes 12, 14 are positioned on the surface of the blade 10. Both the strength of the signal and changes in frequency are monitored and evaluated for changes as a result 2S of material degradation. The principle of the invention, however, remains unchanged. The eddy current probes are employed to detect an eddy current signature, or set of signatures, and these signatures are correlated with a known condition of the material, e.g., corresponding to a known service life and known operating conditions.
It will be apparent to those skilled in the art that many modifications can be made to the above-described preferred embodiments. For example, the invention is not limited to the the specific embodiment of the eddy current probes described above. Accordingly, the scope of the present invention is not intended to be limited by the preferred embodiments, but by the following claims.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and apparatus which, in conjunction with commercially available eddy current instrumentation, can be used to detect, characterize and monitor the extent of time-temperature related damage in metallic materials, such as combustion turbine blades. A further object of the present invention is to eliminate the need for the costly destructive testing typically used to characterize material properties of service exposed turbine blades. A still further object of the present 207~29 - 4 - 56,214 invention is to provide a method and apparatus that can sort the damaged from the undamaged service blades. For sorting by eddy current to be successful, an eddy current "signature"
for the blade is preferably acquired immediately after manufacture and periodically during service. (A si~nature is the measured current through oir impedance of an eddy current probe in the vicinity of induced eddy currents, or the difference between the currents through or impedances of two different probes or one probe at two different points along the blade.) For blades already in service, eddy current signatures are not generally available. A second approach is to use a new blade as a reference standard and compare its eddy current response with those from used blades. This may yield erroneous results, however, because manufacturing practices and blades' chemical compositions may have changed over time. This will cause differences in initial properties which may render comparison between old and new blades invalid. The present invention achieves the above objectives by providing a method and apparatus for performing nondestructive material assessment of, e.g., a turbine blade.
The method according to the invention employs the detection of eddy current signatures induced in the material being assessed, and correlating the detected signature to a known standard. In addition, the present invention overcomes the aforementioned problems with sorting damaged from undamaged blades through a unique self-calibration scheme.
According to the invention, a pair of eddy current probes are inserted into separate holes in the material (e.g., cooling holes in a turbine blade airfoil). One of the probes is designated the "reference probe," and is inserted into a hole in the thickest region of the blade. This region is apt to be the least affected by heating of the blade. The other probe, designated the "assessment probe," is sequentially inserted into the other cooling holes. At each of the assessment probe positions, an eddy current difference signature (hereinafter eddy current signature) is computed by taking the difference between the current in the assessment 2072~
_ 5 _ 56,214 probe and the current in the reference probe, e.g., by coupling the two probes to operate in a differential mode.
The eddy current signatures are compared with one or more standard signature(s) corresponding to a known condition(s) of the blade material. For example, a standard signature is preferably obtained from the thickest region of the blade, where heating effects are minimal. An estimation of the material condition at each of the assessment probe locations is then made by manually or automatically correlating the measured signatures with one or more signatures corresponding to known conditions of the material.
In its broadest sense, the invention encompasses apparatuses comprising first means for inducing an eddy current in a first region of the material and for detecting a first eddy current signature within the vicinity of the first region, second means for inducing an eddy current in a second region of the material and for detecting a second eddy current signature within the vicinity of the second region, and third means for computing the difference between the first and second eddy current signatures.
A more specific apparatus embodying the invention comprises means for detecting an eddy current signature within the vicinity of a first hole, the first hole defining a reference hole; means for detecting an eddy current signature within the vicinity of a second hole, the second hole defining an assessment hole; and means for computing the difference between the eddy current signatures detected in the vicinity of the reference and assessment holes. The condition of the material is determinable by correlating the difference to a known condition of the material. A preferred embodiment of the invention further includes means for measuring an eddy current signature of a material having a known condition, which signature is indicative of the known condition.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 depicts a cross section of a known turbine blade airfoil.
2072~29 - 6 - 56,214 Figure 2 depicts a typical temperature profile of the airfoil of Figure 1.
Figure 3 depicts exemplary eddy current signatures of service exposed turbine blades.
5Figure 4(A) is a side view of a pair of eddy current probes in accordance with the present invention.
Figure 4(B) is a cross sectional view of the eddy current probes of Figure 4(A).
Figure 5 depicts the placement of the eddy current probes into cooling holes of a turbine blade.
Figure 6 is a block diagram of a turbine blade assessment system according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments will now be described with reference to the drawings, wherein like numerals designate like elements.
Figure 3 depicts eddy current signatures generated from the surfaces of sections of service blades. The uppermost curve in the figure, i.e., curve 16, is an exemplary eddy current signature of a new turbine blade. Curves 18 and 20 represent eddy current signatures of turbine blades with service histories of 13,000 and 14,000 hours, respectively.
According to the invention, these signatures are detected with specially designed eddy current probes 12, 14 (shown in Fig.
4) coupled to a current measurement and display device 22 (see Fig. 6). The eddy current signatures enable one to distinguish between blades with no service history and blades with thousands of hours of service exposure.
According to one embodiment of the invention, a set of eddy current coils 12, 14 are inserted into the cooling holes 10A, 10B, 10C, etc. of a service blade airfoil 10.
Since the cooling holes have a very small diameter (e.g., typically .050-.090 in. (1.27-2.29 mm)), the invention comprises a unique eddy current probe design (shown in Figure 4), which employs small eddy current coils 26, 28. Coil 26 is part of probe 12, hereinafter referred to as the "reference probe." Coil 28 is part of probe 14, hereinafter referred to 207202~
- 7 - S6,214 as the "assessment probe." (The reason for these labels will become apparent from the remaining detailed description.) Referring now to Figure 4, the eddy current coils 26, 28 are wound on individual air-core shafts 30, 32, forming a pa:Lr of bobbin-like probes. The probes 12, 14 are wired differentially via subtractor 13 and connected to commercially available eddy current test equipment 22, as shown in Figure 6. The reference probe (probe 12) is inserted into a cooling hole located in the thickest portion of the airfoil 10, e.g., one of holes lOD, lOE, lOF or lOG. As discussed above, this region of the blade operates at relatively low temperatures and will have a microstructure similar to when it was manufactured, and therefore serves as a unique reference point. The assessment probe (probe 14) is then inserted into a neighboring cooling hole. The two probes are then excited, which induces eddy currents in the airfoil 10 in the respective vicinities of the reference and assessment probes, and the current through the assessment coil is subtracted from the current through the reference coil, producing a reference signature. The reference signature is recorded and displayed by the eddy current measurement device 22, and optionally stored in storage device 24. The assessment probe 14 is moved to another cooling hole and the eddy current signature measured at this hole is compared to the reference signature.
As the thermal damage, if any, moves from the blade surface inward toward the cooling holes, the eddy current signatures will be affected. Therefore, the measured eddy current signature, corresponding to a given pair of cooling holes in a given blade, can be correlated with a known condition of a similar blade. The correlation may be carried out by visually or automatically comparing measured eddy current signatures with signatures for corresponding holes in a known standard (e.g., an airfoil in a known or reference condition), and interpolating the results to determine the airfoil's condition. The automatic correlation may be carried out by a microprocessor in, e.g., the storeage device 24. This procedure is repeated until the eddy current response from all 2~a2~
- ~ - 56,214 cooling holes lOA, lOB, lOC, etc. has been compared to the signatures of the known standard.
Referring now to Figure 5, the probes 12, 14 can be positioned to different depths within the cooling holes lOA, lOB, lOC, etc., as shown. This permits an assessment oP the blade's degradation from the tip of the blade to the root. ln addition, the probes 12, 14 can be pulled or pushed simultaneously along the length of the cooling hole. This allows for automated scanning and computer aided inspection, if so desired. Using computer acquisition and display software, the dynamic scans can be differentially compared and reconstructed to provide a detailed enhanced map of the blade's condition.
In an alternative embodiment of the present invention, the two probes 12, 14 can be connected in a driver/pickup mode. According to this embodiment, the reference probe 12 is pulsed and operated at low frequencies (100 Hz to 10 kHz). The assessment probe 14, is used to receive the electromagnetic signal as it passes through the blade 10.
In a further variation of the invention, the eddy current probes 12, 14 are positioned on the surface of the blade 10. Both the strength of the signal and changes in frequency are monitored and evaluated for changes as a result 2S of material degradation. The principle of the invention, however, remains unchanged. The eddy current probes are employed to detect an eddy current signature, or set of signatures, and these signatures are correlated with a known condition of the material, e.g., corresponding to a known service life and known operating conditions.
It will be apparent to those skilled in the art that many modifications can be made to the above-described preferred embodiments. For example, the invention is not limited to the the specific embodiment of the eddy current probes described above. Accordingly, the scope of the present invention is not intended to be limited by the preferred embodiments, but by the following claims.
Claims (25)
1. A nondestructive method of assessing the condition of a metallic material having at least two holes, the method comprising:
(a) defining at least one of said holes as a reference hole, and at least one other of said holes as an assessment hole;
(b) detecting an eddy current signature within the vicinity of the reference hole;
(c) detecting an eddy current signature within the vicinity of the assessment hole; and (d) assessing the material by computing the difference between the eddy current signatures detected in steps (b) and (c), and correlating said difference to a known condition of the material.
(a) defining at least one of said holes as a reference hole, and at least one other of said holes as an assessment hole;
(b) detecting an eddy current signature within the vicinity of the reference hole;
(c) detecting an eddy current signature within the vicinity of the assessment hole; and (d) assessing the material by computing the difference between the eddy current signatures detected in steps (b) and (c), and correlating said difference to a known condition of the material.
2. A nondestructive method of assessing the condition of a metallic material as recited in claim 1, further comprising the step of measuring an eddy current signature of a material having said known condition, said condition being determined by visual inspection of the material.
3. A nondestructive method of assessing the condition of a metallic material as recited in claim 1, wherein steps (b) and (c) comprise the steps of inserting an eddy current probe into the reference and assessment holes, respectively, and measuring the respective currents through the eddy current probes as influenced by the material.
- 10 - 56,214
- 10 - 56,214
4. A nondestructive method of assessing the condition of a metallic material as recited in claim 1, further comprising repeating steps (b), (c) and (d) with the eddy current probes inserted to different depths within the reference and assessment holes, thereby providing an assessment of the material at multiple depths throughout its cross section.
5. A nondestructive method of assessing the condition of a metallic material as recited in claim 1, wherein the step (d) of comparing the eddy currents detected in the vicinity of the reference and assessment holes and making an assessment of the material comprises:
(i) computing the difference between the current in the reference probe and the current in the assessment probe;
(ii) comparing the difference computed in step (i) with a predefined current corresponding to a known condition of the material; and (iii) assessing the material's condition in accordance with the results of step (ii).
(i) computing the difference between the current in the reference probe and the current in the assessment probe;
(ii) comparing the difference computed in step (i) with a predefined current corresponding to a known condition of the material; and (iii) assessing the material's condition in accordance with the results of step (ii).
6. A nondestructive method of assessing the condition of a metallic material as recited in claim 1, further comprising the step of, prior to step (b), exposing the material to a substantially changing magnetic field.
7. A nondestructive method of assessing the condition of a metallic material as recited in claim 1, further comprising the step of, prior to step (b), applying an ac signal to at least one of the eddy current probes to induce eddy currents in the material.
8. A nondestructive method of assessing the condition of a turbine blade having at least two cooling holes, the method comprising:
- 11 - 56,214 (a) defining at least one of said cooling holes as a reference hole, and at least one other of said cooling holes as an assessment hole;
(b) detecting eddy currents within the vicinity of the reference hole;
(c) detecting eddy currents within the vicinity of the assessment hole; and (d) assessing the blade material by computing the difference between the current in the reference probe and the current in the assessment probe, comparing the difference with a predefined current corresponding to a known condition of the blade material, and correlating the difference to a known condition of the blade material.
- 11 - 56,214 (a) defining at least one of said cooling holes as a reference hole, and at least one other of said cooling holes as an assessment hole;
(b) detecting eddy currents within the vicinity of the reference hole;
(c) detecting eddy currents within the vicinity of the assessment hole; and (d) assessing the blade material by computing the difference between the current in the reference probe and the current in the assessment probe, comparing the difference with a predefined current corresponding to a known condition of the blade material, and correlating the difference to a known condition of the blade material.
9. A nondestructive turbine blade assessment method as recited in claim 8, wherein steps (b) and (c) comprise the steps of inserting an eddy current probe into the reference and assessment holes, respectively, and detecting eddy current signatures through the eddy current probes, as influenced by the blade.
10. Method of claim 9 further comprising repeating steps (b), (c) and (d) with the eddy current probes inserted to different depths within the reference and assessment holes, thereby providing an assessment of the blade at multiple locations radially along the blade.
11. A nondestructive turbine blade assessment method as recited in claim 9, further comprising: repeating steps (c) and (d) over substantially all of the blade's cooling holes, and thereafter constructing a map of the blade's condition over a cross section of the blade.
12. A nondestructive turbine blade assessment method as recited in claim 8, wherein steps (a)-(d) are performed with the blade in its operating environment.
- 12 - 56,214
- 12 - 56,214
13. A nondestructive turbine blade assessment method as recited in claim 8, further comprising the step of, prior to step (b), exposing the turbine blade to a substantially changing magnetic field.
14. A nondestructive turbine blade assessment method as recited in claim 8, further comprising the step of, prior to step (b), applying an ac signal to at least one of the eddy current probes to induce eddy currents in the blade.
15. A nondestructive turbine blade assessment method as recited in claim 8, wherein the reference holes are defined within an area of the blade where heating effects on the blade are minimal as compared with other areas of the blade.
16. A nondestructive turbine blade assessment method as recited in claim 3, wherein the eddy current probe comprises an eddy current coil wound around a cylindrical shaft, and when the eddy current probe is employed to detect eddy currents, having leads coupling opposite ends of the coil to means for measuring currents induced therein.
17. Method of claim 16 wherein the eddy current coil is wound around an air-core shaft.
18. An apparatus for nondestructivly assessing the condition of a metallic material having at least two holes, comprising:
(a) first detecting means for detecting an eddy current signature within the vicinity of a first hole, said first hole defining a reference hole;
(b) second detecting means for detecting an eddy current signature within the vicinity of a second hole, said second hole defining an assessment hole; and (c) computing means coupled to said first and second detecting means for computing the difference between - 13 - 56,214 the eddy current signatures detected in the vicinity of the reference and assessment holes, the condition of the material being determinable by correlating said difference to a known condition of the material.
(a) first detecting means for detecting an eddy current signature within the vicinity of a first hole, said first hole defining a reference hole;
(b) second detecting means for detecting an eddy current signature within the vicinity of a second hole, said second hole defining an assessment hole; and (c) computing means coupled to said first and second detecting means for computing the difference between - 13 - 56,214 the eddy current signatures detected in the vicinity of the reference and assessment holes, the condition of the material being determinable by correlating said difference to a known condition of the material.
19. The apparatus recited in claim 18, further comprising means for measuring an eddy current signature of a material having a known condition, said signature being indicative of said known condition.
20. The apparatus recited in claim 19, wherein said first amd second detecting means comprise an eddy current probe coupled to means for measuring the respective currents through the eddy current probe as influenced by the material.
21. The apparatus recited in claim 20, further comprising means for inserting said eddy current probe to different depths within the reference and assessment holes, thereby providing means for assessing the material at multiple depths throughout its cross section.
22. The apparatus recited in claim 21, wherein said computing means comprises:
(i) means for computing the difference between the current in the reference probe and the current in the assessment probe;
(ii) means for comparing the difference between the current in the reference probe and the current in the assessment probe with a predefined current corresponding to a known condition of the material; and (iii) means for assessing the material's condition in accordance with the result of said comparison.
(i) means for computing the difference between the current in the reference probe and the current in the assessment probe;
(ii) means for comparing the difference between the current in the reference probe and the current in the assessment probe with a predefined current corresponding to a known condition of the material; and (iii) means for assessing the material's condition in accordance with the result of said comparison.
23. The apparatus recited in claim 22, further comprising means for exposing the material to a changing magnetic field.
- 14 - 56,214
- 14 - 56,214
24. The apparatus recited in claim 22, further comprising means for applying an ac signal to at least one of said eddy current probes to induce eddy currents in the material.
25. An apparatus for nondestructivly assessing the condition of a metallic material, comprising:
(a) first means for inducing an eddy current in a first region of the material and for detecting a first eddy current signature within the vicinity of the first region;
(b) second means for inducing an eddy current in a second region of the material and for detecting a second eddy current signature within the vicinity of the second region; and (c) third means coupled to said first and second means for computing the difference between the first and second eddy current signatures, the condition of the material being determinable by correlating said difference to a known condition of the material.
(a) first means for inducing an eddy current in a first region of the material and for detecting a first eddy current signature within the vicinity of the first region;
(b) second means for inducing an eddy current in a second region of the material and for detecting a second eddy current signature within the vicinity of the second region; and (c) third means coupled to said first and second means for computing the difference between the first and second eddy current signatures, the condition of the material being determinable by correlating said difference to a known condition of the material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US720,038 | 1991-06-24 | ||
| US07/720,038 US5140264A (en) | 1991-06-24 | 1991-06-24 | Method for non-destructively assessing the condition of a turbine blade using eddy current probes inserted within cooling holes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2072029A1 true CA2072029A1 (en) | 1992-12-25 |
Family
ID=24892398
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002072029A Abandoned CA2072029A1 (en) | 1991-06-24 | 1992-06-23 | Turbine blade assessment system |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US5140264A (en) |
| CA (1) | CA2072029A1 (en) |
| IT (1) | IT1258962B (en) |
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| US5371462A (en) * | 1993-03-19 | 1994-12-06 | General Electric Company | Eddy current inspection method employing a probe array with test and reference data acquisition and signal processing |
| US5670879A (en) * | 1993-12-13 | 1997-09-23 | Westinghouse Electric Corporation | Nondestructive inspection device and method for monitoring defects inside a turbine engine |
| DE4342602A1 (en) * | 1993-12-14 | 1995-06-22 | Busch Dieter & Co Prueftech | Electronic component, in particular coil unit |
| US5442285A (en) * | 1994-02-28 | 1995-08-15 | Westinghouse Electric Corporation | NDE eddy current sensor for very high scan rate applications in an operating combustion turbine |
| DE4410987A1 (en) * | 1994-03-30 | 1995-10-05 | Foerster Inst Dr Friedrich | Eddy current probe for measuring conductor surface irregularities |
| US5659248A (en) * | 1994-10-17 | 1997-08-19 | General Electric Company | Multilayer eddy current probe array for complete coverage of an inspection surface without mechanical scanning |
| US5617025A (en) * | 1994-10-19 | 1997-04-01 | Syron Engineering & Manufacturing Corporation | Side part sensor for determining the presence or absence of a nut and a hole disposed adjacent the nut |
| US5602474A (en) * | 1995-06-06 | 1997-02-11 | United Technologies Corporation | Detecting cracks in non-uniform areas of metal parts including position correlation |
| US5811970A (en) * | 1996-05-10 | 1998-09-22 | Northrop Grumman Corporation | Electromagnetic test for microstructure anomalies such as alpha-case, and for carbide precipitates and untempered and overtempered martensite |
| US5821747A (en) * | 1997-01-08 | 1998-10-13 | Queen's University At Kingston | Method and apparatus for scanning a plurality of parallel pipes for flaws using tube-to-tube through transmissions |
| US5744952A (en) * | 1997-02-25 | 1998-04-28 | Mcdermott Technology, Inc. | Eddy current measurement of tube element spacing |
| ES2191504B1 (en) * | 1999-12-28 | 2005-02-16 | Universidad De Oviedo. | EXPERIMENTAL COMBUSTER FOR THE TEST OF GAS TURBINE ALABES MATERIALS. |
| FR2811076B1 (en) * | 2000-06-29 | 2002-09-20 | Snecma Moteurs | METHOD FOR MEASURING THE WALL THICKNESS OF A HOLLOW BLADE |
| US7023205B1 (en) | 2000-08-01 | 2006-04-04 | General Dynamics Advanced Information Systems, Inc. | Eddy current sensor capable of sensing through a conductive barrier |
| US6487922B1 (en) | 2000-09-25 | 2002-12-03 | Siemens Westinghouse Power Corporation | Steam turbine inlet sleeve inspection apparatus and method |
| US6619109B1 (en) | 2000-09-25 | 2003-09-16 | Siemens Westinghouse Power Corporation | Steam turbine inlet bell seal inspection apparatus and method |
| US6707297B2 (en) * | 2002-04-15 | 2004-03-16 | General Electric Company | Method for in-situ eddy current inspection of coated components in turbine engines |
| EP1394360A1 (en) * | 2002-08-23 | 2004-03-03 | Siemens Aktiengesellschaft | Nondestructive method for testing a component as well as method to produce a gas turbine blade |
| DE10335657B4 (en) * | 2003-08-04 | 2015-04-30 | Alstom Technology Ltd. | Parametric production of cooling holes |
| US6943570B2 (en) * | 2003-09-26 | 2005-09-13 | Honeywell International, Inc. | Device for detecting a crack on a turbine blade of an aircraft engine |
| JP4062232B2 (en) * | 2003-10-20 | 2008-03-19 | 株式会社日立製作所 | X-ray CT apparatus and imaging method using X-ray CT apparatus |
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| US11710489B2 (en) | 2004-06-14 | 2023-07-25 | Wanda Papadimitriou | Autonomous material evaluation system and method |
| US11680867B2 (en) | 2004-06-14 | 2023-06-20 | Wanda Papadimitriou | Stress engineering assessment of risers and riser strings |
| US7075296B2 (en) * | 2004-11-09 | 2006-07-11 | Siemens Power Generation, Inc. | Inspection carriage for turbine blades |
| US7323868B2 (en) | 2005-09-21 | 2008-01-29 | General Dynamics Advanced Information Systems, Inc. | System and method for temperature independent measurement of standoff distance using an eddy current sensor |
| US7162384B1 (en) * | 2005-09-21 | 2007-01-09 | General Dynamics Advanced Information | System and method for temperature compensation of eddy current sensor waveform parameters |
| US8486545B2 (en) * | 2005-09-28 | 2013-07-16 | Southwest Research Institute | Systems and methods for flaw detection and monitoring at elevated temperatures with wireless communication using surface embedded, monolithically integrated, thin-film, magnetically actuated sensors, and methods for fabricating the sensors |
| JP2008089328A (en) * | 2006-09-29 | 2008-04-17 | Hitachi Ltd | Eddy current flaw detector and eddy current flaw detection method |
| US9551689B2 (en) | 2010-02-26 | 2017-01-24 | United Technologies Corporation | Inspection device utilizing eddy currents |
| US11156585B2 (en) | 2019-02-08 | 2021-10-26 | Raytheon Technologies Corporation | Method of nondestructive turbine airfoil inspection and repair |
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| US3407352A (en) * | 1965-06-07 | 1968-10-22 | Western Electric Co | Method of and apparatus for monitoring the thickness of a non-conductive coating on a conductive base |
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| US4095181A (en) * | 1976-12-17 | 1978-06-13 | The Boeing Company | Rotating pot shaped eddy current probe in which only a small fraction of the lip forming the outer core portion is retained |
| CH625619A5 (en) * | 1977-12-07 | 1981-09-30 | Bbc Brown Boveri & Cie | |
| US4194149A (en) * | 1977-12-15 | 1980-03-18 | The Babcock & Wilcox Company | Method for generating the eddy current signature of a flaw in a tube proximate a contiguous member which obscures the flaw signal |
| JPS55141653A (en) * | 1979-04-20 | 1980-11-05 | Mitsubishi Heavy Ind Ltd | Deterioration state deciding method of strong precipitation hardness type iron base alloy |
| US4418315A (en) * | 1981-05-22 | 1983-11-29 | Combustion Engineering, Inc. | Method for effecting a surface examination of coated components |
| US4578643A (en) * | 1983-11-18 | 1986-03-25 | Westinghouse Electric Corp. | Simulation apparatus for eddy current inspection techniques |
| US4528856A (en) * | 1984-01-17 | 1985-07-16 | Westinghouse Electric Corp. | Eddy current stress-strain gauge |
| US4746858A (en) * | 1987-01-12 | 1988-05-24 | Westinghouse Electric Corp. | Non destructive testing for creep damage of a ferromagnetic workpiece |
| US5028100A (en) * | 1989-06-15 | 1991-07-02 | Trustees Of The Thomas A. D. Gross 1988 Revocable Trust | Methods for nondestructive eddy-current testing of structural members with automatic characterization of faults |
-
1991
- 1991-06-24 US US07/720,038 patent/US5140264A/en not_active Expired - Lifetime
-
1992
- 1992-06-10 IT ITMI921420A patent/IT1258962B/en active IP Right Grant
- 1992-06-23 CA CA002072029A patent/CA2072029A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| IT1258962B (en) | 1996-03-11 |
| ITMI921420A1 (en) | 1993-12-10 |
| ITMI921420A0 (en) | 1992-06-09 |
| US5140264A (en) | 1992-08-18 |
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| FZDE | Discontinued |