Final answer:
Visual Testing is the most commonly used NDE technique for surface examination due to its ease and cost-effectiveness, followed by Liquid Penetrant Testing and Magnetic Particle Testing for more in-depth inspection.
Step-by-step explanation:
The Non-Destructive Evaluation (NDE) techniques used for surface examination include Visual Testing (VT), Liquid Penetrant Testing (LPT), Magnetic Particle Testing (MPT), Eddy Current Testing (ECT), Radiographic Testing (RT), and Ultrasonic Testing (UT). Among these, Visual Testing is often the most commonly used method due to its simplicity and cost-effectiveness. It is the basis of any initial inspection. However, for a more in-depth surface and subsurface examination, techniques like Liquid Penetrant Testing and Magnetic Particle Testing are frequently employed.
Liquid Penetrant Testing is widely used due to its effectiveness in detecting surface-breaking flaws on non-porous materials. It involves applying a visible or fluorescent dye solution to the clean surface of a component. After a dwell time to allow the penetrant to seep into any surface defects, a developer is applied, which draws the penetrant out of the flaws, revealing their presence under appropriate lighting conditions.
Magnetic Particle Testing is another common technique, especially for detecting surface and near-surface discontinuities in ferromagnetic materials. This technique uses magnetic fields and ferrous particles to identify surface flaws. The area to be inspected is magnetized, and magnetic particles are applied; if defects are present, the particles will form visible indications as they are drawn into the flaws by magnetic flux leakage.