Pulsed infrared imaging (PII) has become a prominent technique for large area, non-contact inspection for many types of advanced materials and structures. This paper discusses applications relating to the evaluation of repaired composite materials.
This paper discusses a new technique for locating and detecting wall thickness reduction in boiler tubes caused by erosion/corrosion. Traditional means for this type of defect detection utilizes ultrasonics (UT) to perform a point by point measurement at given intervals of the tube length, which requires extensive and costly shutdown or `outage' time to complete the inspection, and has led to thin areas going undetected simply because they were located in between the sampling points. Pulsed infrared imaging (PII) can provide nearly 100% inspection of the tubes in a fraction of the time needed for UT. The IR system and heat source used in this study do not require any special access or fixed scaffolding, and can be remotely operated from a distance of up to 100 feet. This technique has been tried experimentally in a laboratory environment and verified in an actual field application. Since PII is a non-contact technique, considerable time and cost savings should be realized as well as the ability to predict failures rather than repairing them once they have occurred.
Historically, steel has been a material that has been shunned by the thermal imaging community because of its thermal characteristics and because in most applications it is relatively thick. A new approach to evaluate this material for thickness changes caused by corrosion/erosion is discussed within this presentation. Some of the structures that have been evaluated are above ground storage tank floors, boiler tubes used in power plant facilities, pipes, and 55 gallon drums. Thermal imaging techniques have been developed to locate areas of material thickness loss within these examples using a high resolution thermal imager and a `pulsed' or `stepped' heat source. The thermal energy from the heat source is directed toward the inspection surface and begins to conduct through the material thickness. Areas that have been reduced in thickness will form a thermal gradient on the inspection surface which is detected by the thermal imager.
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