When performing nondestructive inspection, which method is best suited for detecting surface and slightly subsurface cracks in ferromagnetic steel parts?
ACS code: AM.I.K
Correct answer: magnetic particle inspection
Rationale: Magnetic particle inspection relies on magnetizing a ferromagnetic part so that a crack distorts the magnetic field and creates leakage fields that attract iron particles, revealing the flaw. Because it works only on materials that can be magnetized, it is the preferred method for steel parts and can show surface and slightly subsurface defects. Liquid penetrant detects only flaws open to the surface, and ultrasonic gauging is primarily used to measure thickness rather than reveal small cracks visually.
Liquid penetrant inspection is capable of detecting defects only when those defects are:
ACS code: AM.I.K
Correct answer: open to the surface of the part
Rationale: Liquid penetrant inspection works by drawing dye into a discontinuity by capillary action, then drawing it back out with a developer to form a visible indication. The dye can only enter a flaw that breaks the surface, so the method finds only surface-connected defects. Subsurface flaws and any defect hidden under paint or primer cannot trap or release penetrant and so go undetected.
Which inspection method uses high-frequency sound waves to locate internal flaws and measure the thickness of a part?
ACS code: AM.I.K
Correct answer: ultrasonic inspection
Rationale: Ultrasonic inspection introduces high-frequency sound waves into a part and analyzes the energy that reflects from the back surface or from an internal discontinuity, allowing both flaw detection and thickness measurement. Eddy current uses induced electrical currents rather than sound, and radiographic inspection uses X-rays or gamma rays passing through the part to expose film.
Eddy current inspection detects discontinuities in a part by sensing changes in:
ACS code: AM.I.K
Correct answer: an induced electromagnetic field in the part
Rationale: Eddy current inspection passes alternating current through a coil to induce circulating eddy currents in a conductive part. A crack or change in conductivity alters those currents, changing the coil's electromagnetic field, which the instrument senses. Reflected sound is the basis of ultrasonic inspection, and drawing dye from cracks describes penetrant inspection.
When inspecting an engine cylinder for internal cracks and other defects without disassembly, a mechanic would most likely use a:
ACS code: AM.I.K
Correct answer: borescope
Rationale: A borescope is an optical instrument that allows a mechanic to view internal areas of an engine, such as cylinder walls and valves, through small access openings without disassembly, making it ideal for finding cracks, pitting, or other internal damage. A dial indicator measures small linear movement or runout, and a micrometer measures external or internal dimensions, neither of which provides a visual view inside the cylinder.
Radiographic (X-ray) inspection is particularly useful because it can reveal defects that are:
ACS code: AM.I.K
Correct answer: located internally within the part
Rationale: Radiographic inspection passes penetrating radiation through a part onto film or a sensor, where internal voids, cracks, and inclusions show as density changes. This makes it valuable for finding flaws buried inside a part that surface methods cannot reach. Surface-only flaws are the realm of penetrant inspection, and the method is not restricted to magnetic materials the way magnetic particle inspection is.
When tapping a bonded honeycomb structure during a coin-tap inspection, a dull or dead sound generally indicates:
ACS code: AM.I.K
Correct answer: a separation or void within the bonded area
Rationale: In the coin-tap (ring) test, a coin or light tapping tool is moved across a bonded or honeycomb structure while the inspector listens. A clear, sharp ring indicates sound bonding, while a dull or dead thud signals a disbond, delamination, or void beneath the surface. A dull sound does not indicate a good bond, and surface corrosion is detected by visual rather than tapping methods.