What is non-destructive testing (NDT) and give two common methods used on turbine components?

• A. Testing that destroys the part to measure breaking point.
• B. Testing that alters the part after use.
• C. Testing that preserves the part while evaluating integrity; penetrant testing and magnetic particle inspection.
• D. Testing that only uses thermal imaging.

Answer: (C)

Non-destructive testing means evaluating a component’s condition without damaging it, so the turbine part can stay in service while inspectors look for cracks, porosity, or other defects. On turbine components, two widely used non-destructive methods are penetrant testing and magnetic particle inspection. Penetrant testing applies a liquid dye to the surface; after excess is removed, a developer draws out the penetrant from any surface-breaking defect, producing a visible indication. This works well for tight cracks, seams, and porosity on accessible surfaces and leaves the part intact. Magnetic particle inspection magnetizes the part; surface and near-surface defects disrupt the magnetic field, causing magnetic particles to gather at the flaw and form a visible indication under appropriate lighting. It’s especially effective for ferromagnetic turbine alloys and is also non-destructive. Other options either describe destructive testing, which damages the part, or focus on a single method like thermal imaging, which is another NDT technique but not the two common methods named here.