Active Infrared Thermography for Non Destructive Evaluation of Defects in Wear Resistance and Thermal Barrier Coatings

In fossil fuel power generation plants, steam generation tubes and turbine blades are critical for overall performance of plant. The materials are subjected to bear heavy wear and temperature during operation. The manufacturer has an option of using high wear resistant and high temperature materials which are costlier or using cheaper materials with ceramic coatings over it. The coatings exposed to harsh conditions will withstand mechanical and thermal stresses, hence coating needs to be adhered properly on the material. Coatings of 300-500 micron thickness serve the purpose and the techniques available for spray are High Velocity Oxy Fuel (HVOF), Plasma, Twin wire arc, etc. The evaluation of coatings w.r.t quality is required to be done for required life of components. Comparing to the traditional Non-Destructive Tests such as Acoustic Emission, Ultrasonic, and Eddy Current, Magnetic Particle and Radiography Tests where experimental equipment is non-portable, tedious and time consuming and difficulties during interpretation of results. A new approach Infrared Thermography Testing (IRT) has been introduced for qualitative evaluation of coatings. In this technique, high energy optical source along with Pulse phase thermography system has been used for detection of surface and sub surface coating defects in Wear resistant and thermal barrier coatings. Pulse phase thermography is helpful in finding defects in high reflecting and thermal conductive materials like steel. The IRT methodology and IR results are discussed in this paper.