What type of non-destructive testing methods are used to assess the condition of a TBM's cutterhead?

Several non-destructive testing (NDT) methods are employed to assess the condition of a TBM cutterhead without causing damage. These methods help identify wear, cracks, and other defects that can affect its performance. Ultrasonic testing (UT) is used to detect internal flaws and measure the thickness of the cutterhead components. It works by transmitting high-frequency sound waves through the material and analyzing the reflected waves. Changes in the wave pattern indicate the presence of flaws or variations in thickness. Magnetic particle testing (MT) is used to detect surface and near-surface cracks in ferromagnetic materials, such as steel. It involves applying a magnetic field to the component and then dusting it with magnetic particles. The particles accumulate at cracks, making them visible. Dye penetrant testing (PT) is used to detect surface cracks and other discontinuities. It involves applying a liquid dye to the surface, allowing it to penetrate into any cracks, and then removing the excess dye. A developer is then applied, which draws the dye out of the cracks, making them visible. Visual inspection is a basic but important NDT method. Trained inspectors visually examine the cutterhead for signs of wear, cracks, and other damage. Borescope inspection allows for the inspection of internal surfaces and hard-to-reach areas. A borescope is a flexible tube with a camera and light source that can be inserted into small openings. Thermography (infrared testing) can detect areas of increased temperature, which might indicate friction or stress concentrations, hinting at underlying damage. 'Non-destructive testing (NDT)' refers to testing methods that do not damage or destroy the component being tested. The 'cutterhead' is the rotating front part of the TBM fitted with disc cutters.