Transient thermography testing of unpainted thermal barrier coating (TBC) systems

Grzegorz Ptaszek, Peter Cawley, Darryl Almond, Simon Pickering

Research output: Contribution to journalArticle

  • 12 Citations

Abstract

Test piece surfaces are sometimes coated with a black, energy absorbing paint before transient thermography is applied. This practice is not acceptable to some thermal barrier coating (TBC) manufacturers and servicers of these systems since thermal barrier coatings are porous so the paint contaminates the coating and it is very difficult and costly to remove. Unfortunately, unpainted TBC surfaces have low emissivity, and after service their colour is usually uneven. The low emissivity gives low signal levels and also problems with reflections of the incident heat pulse, while the variation in emissivity over the surface gives strong variation in the contrast obtained even in the absence of defects. Additionally, the TBC is translucent to mid-wavelength IR radiation which negatively affects the location of disbonds based on the thermal responses. This paper investigates the effects of uneven discolouration of the surface and of IR translucency on the thermal responses. It has been shown that unpainted TBC systems can be inspected reliably by using higher power flash heating equipment assembled with an IR glass filter and a long wavelength IR camera. The paper also shows that the problem with uneven surface emissivity can be overcome by applying 2nd time derivative processing of the log-log surface cooling curves.
LanguageEnglish
Pages48-56
JournalNDT and E International
Volume59
DOIs
StatusPublished - Oct 2013

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Thermal barrier coatings
coating
emissivity
Testing
paints
coatings
Paint
heating equipment
discoloration
surface cooling
Heating equipment
Discoloration
Wavelength
wavelengths
flash
cameras
color
filters
heat
Cameras

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Transient thermography testing of unpainted thermal barrier coating (TBC) systems. / Ptaszek, Grzegorz; Cawley, Peter; Almond, Darryl; Pickering, Simon.

In: NDT and E International, Vol. 59, 10.2013, p. 48-56.

Research output: Contribution to journalArticle

Ptaszek, Grzegorz ; Cawley, Peter ; Almond, Darryl ; Pickering, Simon. / Transient thermography testing of unpainted thermal barrier coating (TBC) systems. In: NDT and E International. 2013 ; Vol. 59. pp. 48-56
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