THE POSSIBILITY OF THERMOGRAPHIC CONTROL METHOD APPLICATION FOR DETECTION OF CRACKS IN STEEL STRUCTURES

Abstract

The paper discusses a possibility of using thermographic non-destructive testing to 
search for cracks in steel structures. The basis of non-destructive thermal control is the registration 
of changes in the thermal field that occurs when the thermodynamic balance of the object with the 
environment  is  disturbed,  which  appears  on  the  surface  and  whose  nature  allows  to  obtain  the 
necessary  information.  The  method  of  thermal  control  is  based  on  the  interaction  of  the  thermal 
field  of  the  object  with  thermodynamic  sensitive  elements  (thermocouple,  photodetector,  liquid 
crystal  element,  bolometer),  which  convert  the  field  parameters  (intensity,  temperature  gradient, 
contrast, radiance) into electrical signal of the recording device. As a result of the experiment, it 
was  confirmed  that  the  thermographic  control  method  can  be  used  in  the  examination  of  steel 
structures for a qualitative assessment of latent defects and damage. As measuring instruments for 
the  experiment,  thermal  cameras  with  different  resolutions  of  the  IR  image  sensor,  infrared 
thermohygrometer,  and  luxmeter  were  used.  During  the  experiment,  there  was  no  fundamental 
difference  of  the  use  thermal  cameras  with  different  types  of  IR  matrices.  When  using  a  more 
accurate Flir E8 thermal camera, the thermogram  had  a clearer definition of  surface temperature 
compared  to  Flir  C2.  This  feature  can  be  used  for the  quantitative  determination  of  defects,  for 
example, the depth and size of a crack under a paint layer, but fundamentally, for the qualitative 
detection  of  defects  and  damage,  the  use  of  more  accurate  equipment  is  not  a  prerequisite.  The 
problems arising when using the method of thermal non-destructive testing and possible methods 
for solving them are indicated. The authors conclude that the method of thermographic control can 
be used in the examination of steel structures for a qualitative assessment of the presence of cracks. 
To a large extent, the quality of thermograms is influenced by gloss degree of the surface of studied 
object, a high gloss degree does not allow reliable data to be obtained, to reduce the gloss degree, 
the  surface  of  the  examined  object  requires  the  application  of  a  special  coating  with  a  high 
emissivity.