Non-Destructive Testing
Material Integrity Assessment in Milazzo
Cracks and defects of various types can affect the performance of components and structures to such an extent that their detection becomes an essential part of quality control in all fields of engineering. The set of techniques and procedures aimed at evaluating the integrity of materials or manufactured products is generally classified under the name "Non-Destructive Testing" (NDT). Among the various non-destructive testing techniques are radiographic methods, ultrasonic methods, liquid penetrant inspection, magnetic particle testing, thermography, techniques based on electromagnetic fields, and visual inspection. These methods share the characteristic of not altering the physical-mechanical properties of the tested component while operating within a quality system that complies with the applicable standard requirements.
Applications of NDT
Non-invasive testing is essential for achieving objectives of often critical importance. These operations are employed to:
- Ensure the integrity and reliability of products (longer service life, lower probability of failures and operational interruptions)
- Prevent accidents and safeguard human lives
- Improve the design process (detecting recurring failures or fractures in specific regions)
- Control the production process and maintain a consistently high-quality standard
- Reduce production costs (e.g., by inspecting semi-finished products before they are used to manufacture final products)
Most Commonly Used Techniques
Non-destructive testing can be performed in different ways, depending on the context and the machinery involved. Some of the most common techniques include:
- Volumetric Testing (Radiography or Ultrasound), These methods allow the detection of internal defects within a component and are divided into:
- Radiography (RT): Uses X-rays or gamma rays, with results visible on film.
- Ultrasound (UT): Analyses ultrasonic waves reflected or transmitted within the component.
- Surface Testing (Magnetic Particle, Liquid Penetrant, Eddy Current, Visual Inspection), these methods provide information on surface or near-surface defects. They include:
- Magnetic Particle Testing (MT): Application of a magnetic field to ferromagnetic materials. Defects cause variations in the magnetic flux, visible using special powders or fluorescence (viewed under a Wood’s lamp in the absence of light).
- Liquid Penetrant Testing (PT): Application of a liquid that penetrates defects by capillary action, with defect visibility enhanced by colour contrast or fluorescence (viewed under a Wood’s lamp in the absence of light).
- Infrared Thermography (IT): Analysis of thermal emission in the infrared spectrum. Defects cause disturbances in the thermal field.
- Eddy Current Testing (ET): Analysis of induced currents in a conductive material when exposed to an alternating magnetic field. Defects appear as "disturbances" in current propagation.
- Visual Inspection (VT): Conducted with the naked eye by an expert operator trained in defectology.
