Details
| Original language | English |
|---|---|
| Title of host publication | Electromagnetic Nondestructive Evaluation (XVII) |
| Publisher | IOS Press |
| Pages | 226-233 |
| Number of pages | 8 |
| ISBN (print) | 9781614994060 |
| Publication status | Published - 2014 |
Publication series
| Name | Studies in Applied Electromagnetics and Mechanics |
|---|---|
| Volume | 39 |
| ISSN (Print) | 1383-7281 |
| ISSN (electronic) | 1879-8322 |
Abstract
Conventional non-destructive eddy-current testing and induction-based thermographic techniques do not allow for the characterization and evaluation of a turbine blade's substrate material and the thin corrosion protective layer (20⋯50 μm) separately, because of the low electrical conductivity of 0.5-1.5 MS/m and the relatively large eddy-current penetration depth at standard testing frequencies. Using testing frequencies in the megahertz range limits the inductively excited volume to the near-subsurface region and enables the layer and substrate materials to be individually studied. Within the Collaborative Research Centre 871, novel high frequency, non-destructive eddy-current and induction thermography inspection techniques are being developed and used for material characterization and damage detection in turbine blades [1], [2]. Experiments were carried out using high-pressure turbine blades of the first and second stage made of René 142 and PWA 1426 with metallic PtAl-, MCrAlY-, and ceramic (YSZ) thermal barrier coatings. The high-frequency eddy-current inspection technology with test frequencies in the megahertz range up to 100 MHz reduces the standard penetration depth to less than 50 μm. This allows for the detection of local damages and defects, as well as the characterization of the materials' condition separately from the substrate material with emphasis on the condition of the thin PtAl- and MCrAlY-coatings. Delamination and chemical changes in the coating such as oxidation or sulfidation lead to altered local electrical conductivities and magnetic properties and can be identified by using high frequency, eddy-current testing techniques while the lift-off effect is simultaneously used to measure the thermal barrier's coating thickness. The high frequency induction thermography inspection technology with pulsed excitation up to 3 MHz focuses on fast and sensitive detection of the surface and near subsurface damages in the turbine blade's coating and the substrate material. The relevant surface defects are distinguished from other microstructural imperfections as well as from changes of infrared spectral emissivity due to surface impurities and geometric effects by using a series of sequential excitation pulses followed by a pixel-wise analysis of the thermal response in the component with respect to the excitation. With this multiscale approach the inspection time and resolution can be varied by using exchangeable infrared optics with various focal lengths. Global component inspection can be achieved with a wide angle lens, which is suitable for fast detection of larger damages (>1 mm2) such as cracks, chipping, spalling and delamination of the coating. The evaluation of micro-damage occurs subsequently on a local scale with a higher resolution macro lens scan and a resolution of up to 15 μm/px, but longer measurement time per surface area.
Keywords
- Coating, Eddy-Current, High Frequency, Induction Thermography, Pulsed Excitation, Substrate Material, Turbine Blades
ASJC Scopus subject areas
- Engineering(all)
- Mechanical Engineering
- Engineering(all)
- Electrical and Electronic Engineering
Cite this
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Electromagnetic Nondestructive Evaluation (XVII). IOS Press, 2014. p. 226-233 (Studies in Applied Electromagnetics and Mechanics; Vol. 39).
Research output: Chapter in book/report/conference proceeding › Contribution to book/anthology › Research › peer review
}
TY - CHAP
T1 - High frequency eddy-current and induction thermography inspection techniques for turbine components
AU - Fra̧ckowiak, Wojciech
AU - Bruchwald, Oliver
AU - Reimche, Wilfried
AU - Bach, Friedrich Wilhelm
AU - Maier, Hans Jürgen
PY - 2014
Y1 - 2014
N2 - Conventional non-destructive eddy-current testing and induction-based thermographic techniques do not allow for the characterization and evaluation of a turbine blade's substrate material and the thin corrosion protective layer (20⋯50 μm) separately, because of the low electrical conductivity of 0.5-1.5 MS/m and the relatively large eddy-current penetration depth at standard testing frequencies. Using testing frequencies in the megahertz range limits the inductively excited volume to the near-subsurface region and enables the layer and substrate materials to be individually studied. Within the Collaborative Research Centre 871, novel high frequency, non-destructive eddy-current and induction thermography inspection techniques are being developed and used for material characterization and damage detection in turbine blades [1], [2]. Experiments were carried out using high-pressure turbine blades of the first and second stage made of René 142 and PWA 1426 with metallic PtAl-, MCrAlY-, and ceramic (YSZ) thermal barrier coatings. The high-frequency eddy-current inspection technology with test frequencies in the megahertz range up to 100 MHz reduces the standard penetration depth to less than 50 μm. This allows for the detection of local damages and defects, as well as the characterization of the materials' condition separately from the substrate material with emphasis on the condition of the thin PtAl- and MCrAlY-coatings. Delamination and chemical changes in the coating such as oxidation or sulfidation lead to altered local electrical conductivities and magnetic properties and can be identified by using high frequency, eddy-current testing techniques while the lift-off effect is simultaneously used to measure the thermal barrier's coating thickness. The high frequency induction thermography inspection technology with pulsed excitation up to 3 MHz focuses on fast and sensitive detection of the surface and near subsurface damages in the turbine blade's coating and the substrate material. The relevant surface defects are distinguished from other microstructural imperfections as well as from changes of infrared spectral emissivity due to surface impurities and geometric effects by using a series of sequential excitation pulses followed by a pixel-wise analysis of the thermal response in the component with respect to the excitation. With this multiscale approach the inspection time and resolution can be varied by using exchangeable infrared optics with various focal lengths. Global component inspection can be achieved with a wide angle lens, which is suitable for fast detection of larger damages (>1 mm2) such as cracks, chipping, spalling and delamination of the coating. The evaluation of micro-damage occurs subsequently on a local scale with a higher resolution macro lens scan and a resolution of up to 15 μm/px, but longer measurement time per surface area.
AB - Conventional non-destructive eddy-current testing and induction-based thermographic techniques do not allow for the characterization and evaluation of a turbine blade's substrate material and the thin corrosion protective layer (20⋯50 μm) separately, because of the low electrical conductivity of 0.5-1.5 MS/m and the relatively large eddy-current penetration depth at standard testing frequencies. Using testing frequencies in the megahertz range limits the inductively excited volume to the near-subsurface region and enables the layer and substrate materials to be individually studied. Within the Collaborative Research Centre 871, novel high frequency, non-destructive eddy-current and induction thermography inspection techniques are being developed and used for material characterization and damage detection in turbine blades [1], [2]. Experiments were carried out using high-pressure turbine blades of the first and second stage made of René 142 and PWA 1426 with metallic PtAl-, MCrAlY-, and ceramic (YSZ) thermal barrier coatings. The high-frequency eddy-current inspection technology with test frequencies in the megahertz range up to 100 MHz reduces the standard penetration depth to less than 50 μm. This allows for the detection of local damages and defects, as well as the characterization of the materials' condition separately from the substrate material with emphasis on the condition of the thin PtAl- and MCrAlY-coatings. Delamination and chemical changes in the coating such as oxidation or sulfidation lead to altered local electrical conductivities and magnetic properties and can be identified by using high frequency, eddy-current testing techniques while the lift-off effect is simultaneously used to measure the thermal barrier's coating thickness. The high frequency induction thermography inspection technology with pulsed excitation up to 3 MHz focuses on fast and sensitive detection of the surface and near subsurface damages in the turbine blade's coating and the substrate material. The relevant surface defects are distinguished from other microstructural imperfections as well as from changes of infrared spectral emissivity due to surface impurities and geometric effects by using a series of sequential excitation pulses followed by a pixel-wise analysis of the thermal response in the component with respect to the excitation. With this multiscale approach the inspection time and resolution can be varied by using exchangeable infrared optics with various focal lengths. Global component inspection can be achieved with a wide angle lens, which is suitable for fast detection of larger damages (>1 mm2) such as cracks, chipping, spalling and delamination of the coating. The evaluation of micro-damage occurs subsequently on a local scale with a higher resolution macro lens scan and a resolution of up to 15 μm/px, but longer measurement time per surface area.
KW - Coating
KW - Eddy-Current
KW - High Frequency
KW - Induction Thermography
KW - Pulsed Excitation
KW - Substrate Material
KW - Turbine Blades
UR - http://www.scopus.com/inward/record.url?scp=84904023103&partnerID=8YFLogxK
U2 - 10.3233/978-1-61499-407-7-226
DO - 10.3233/978-1-61499-407-7-226
M3 - Contribution to book/anthology
AN - SCOPUS:84904023103
SN - 9781614994060
T3 - Studies in Applied Electromagnetics and Mechanics
SP - 226
EP - 233
BT - Electromagnetic Nondestructive Evaluation (XVII)
PB - IOS Press
ER -