Internal corrosion and joint failure detection for the inspection of vertical geothermal heat exchangers by infrared thermography

The need for greater efficiency in the field of shallow closed-loop geothermal systems has led to the proposal for groutless coaxial geothermal heat exchangers made of steel. In terms of heat transfer performance, they are superior to traditional grouted U-shaped or double-U plastic ones, but they are still not well accepted by the market because there are doubts about their safety in terms of reliability. This work aims to explore the detectability of defects that can lead to external pipe failures such as corrosion or leakages, using active infrared thermography, in order to contribute to the proposal of possible on-site inspection procedures. The experimental work was carried out in the laboratory on a pipe sample that was made of threaded-jointed sections of steel. Defects of various entities have been artificially introduced to simulate internal corrosion, generally related to the presence of chemicals in the heat transfer fluid. Different failures in threaded joints were also simulated and detected after the processing of thermal data.