Which of the following is NOT a common non-destructive testing method used for turbine blades and disks?

• A. Penetrant Testing
• B. Magnetic Particle Inspection
• C. Eddy Current
• D. Ultrasonic Testing

Answer: (D)

The main idea is about which NDT methods are most practical for turbine blades and disks. For these components, inspections focus on surface and near-surface defects, since those are where fatigue cracks often initiate. Penetrant testing is ideal for revealing surface-breaking cracks on clean metal surfaces. Magnetic particle inspection works well on ferromagnetic materials to show surface indications, and eddy current testing provides fast screening of surface and near-surface flaws on conductive materials.

Ultrasonic testing, while excellent for locating internal flaws and measuring thickness, is less common for blades and disks because of their complex geometry (thin, curved airfoil sections and tight bore areas), the need for a coupling medium, and the extensive scanning setup required. These practical considerations make UT less routinely employed than the other three methods, though it can be used in specific cases.